Annual Report 2011

ForWindCenter for Wind Energy Research ForWindCenter for Wind Energy Research

Annual Report 2011

[email protected] - www.forwind.de - phone: +49(0)441 798 5090

UmschlagAnnaul report 2010.indd 1 20.12.2012 14:21:40 Annual Report 2011 1

ForWindCenter for Wind Energy Research

Annual Report 2011 2

GREETING

In 2011 the German government decided to gradually phase-out nuclear power by 2022 and to implement a policy for greater energy efficiency and an accelerated switch to renewable energy. The tragic accident in Fukushima, where some nuclear reactors were destroyed by a heavy tsunami, was the catalyser for this significant change of energy policy. With these decisions, the government expedited the plans of the Energy Concept, which was adopted in September 2010. The Energy Concept is a roadmap towards an environmentally sound, reliable and affordable future energy system which is completely based on sustainable principles. According to the scenarios developed in preparation of the Energy Concept, wind energy will play a key role in electricity production in 2050 with a share of about 50%. This requires a massive expansion of wind power capacity, both on- and offshore, to around 45 GW by 2020 and 85 GW by 2050 (compared with 30 GW today).

This is a tremendous opportunity – and at the same time a huge challenge – for the German wind energy sector, including the R&D community. Reading the summaries of ForWind’s research activities carried out in 2011, it seems to me, that ForWind has developed a keen eye for the specific needs of the European wind energy industry and is obviously willing to face the new challenges. Since its establishment in 2003 ForWind has enhanced its profile and output rapidly. ForWind now covers a wide range of wind energy competences including the energy conversion process, wind resource, rotor, gear, generator, power electronics, electrical grid, support structures, offshore and onshore operation and last but not least environmental impacts.

The offshore wind energy technology is one of the fastest growing sectors in the wind energy industry and the motor for innovation and research needs. ForWind’s research is on the leading edge of these developments. Virtually all research projects contribute to improve the offshore wind energy systems and thus strengthening the offshore wind energy industry. ForWind is the only German wind energy research centre, that is involved in research projects on all three German offshore wind parks (Alpha Ventus, EnBW Baltic 1, BARD Offshore 1) which are currently being installed. ForWind is not only conducting exemplary research but also excels in education. The fast growing offshore wind industry needs a steady supply of highly qualified personnel. At the moment, there is a severe lack of experienced experts, engineers and managers with knowledge of the offshore wind energy technology and management. ForWind has anticipated these shortcomings by establishing the first worldwide Continuing Studies Program Offshore Wind Energy. This part-time study program is geared towards engineers and managers engaged in the offshore wind industry as well as in other maritime industries. Its objective is to give insight into the technical and engineering aspects of offshore wind energy projects, and to teach management principles for these projects, their risks, and interfaces.

ForWind competence in education is recognised by its participation in the ERASMUS MUNDUS Master Course “European Wind Energy Master (EWEM)”, which was selected for support by the ERASMUS MUNDUS program of the European Commission in July 2011. The joint master program starts in the academic year of 2012 and is organised by a consortium of four universities renowned for their endeavours in wind energy and offshore technology: Delft University of Technology (coordinating university), Technical University of Denmark, Norwegian University of Science and Technology and the Carl von Ossietzky Universität Oldenburg.

With the Annual Report 2011 ForWind underlined his reputation as an industrious, creative and vital research center once again and strengthened its position as an excellent research institute for wind energy, not only in Germany but also on a wordwide scale.

Dr. h.c. Ir. Jos Beurskens Chairman of the ForWind Scientific Advisory Board Chairman of the ForWind Advisory Board Annual Report 2011 3

PREFACE

2011 was a highly enterprising year for ForWind: Membership numbers once again increased and now stand at an all-time high of 21. This enabled ForWind to diversify its fields of research in the area of wind energy even further. But 2011 was also a year of entering into prolific and rewarding co-operations in order to strengthen wind energy in Germany and Europe. Two of these deserve special mention – because they have been influencing ForWind’s work and research to a very high degree:

In May 2011 ForWind and the Fraunhofer Institute for Wind Energy and Energy System Technology (IWES) joined forces to form the “Wind Energy Research Association”. More than 430 employees at 35 institutions and research institutes work together in the new association, creating a joint research infrastructure, which allows them to conduct basic and application-oriented groundwork on hitherto unprecedented scale. The association congregates its members research competencies and enables the optimal implementation of synergies as well as effective and efficient development of solutions for difficult problems in the wind energy sector.

ForWind and IWES take on a leading role in another project as well: The WindPowerCluster. In cooperation with the Wind Energy Association WAB, ForWind and IWES masterminded the entry of the WindPowerCluster into the Leading-Edge Cluster competition by the Federal Ministry of Education and Research. The WindPowerCluster is a complex business and research network comprising of more than 200 research institutes and wind energy enterprises. Its aim is to develop the northwest region of Germany as a worldwide leading region for the wind energy sector by creating process chains and an industrial infrastructure for the offshore wind energy sector. The arduous and elabo- rate work did not go without reward: The WindPowerCluster was the only competitor from the federal states Bremen and Lower Saxony reaching the final of the Leading-Edge Cluster competition. Work on the WindPowerCluster lead to a growing and beneficent collaboration among the wind energy actors in Germany’s northwest region, leaving the research landscape in a formidable position for future challenges.

We are very grateful to the State of Lower Saxony for its continued support. This forms the basis from which we develop new research aspects leading to further applied projects and developments with our partners from the industry. The successive developments of joint research projects with industrial partners are mainly financed by the Bundesministerium für Umwelt, Naturschutz und Reaktorsicherheit (BMU) or directly through industrial co- operations as has been documented in this report.

We would like to thank all ForWind personnel for their commitment to the center and their outstanding contributions to its success, our business and research partners for many fruitful joint efforts, and the members of ForWind‘s advisory board for their always stimulating work.

Prof. Dr.-Ing. Bernd Orlik Prof. Dr.-Ing. habil. Raimund Rolfes Academic Speaker Deputy Speaker 4

CONTENT

Greeting Preface

The Organization • Executive Board ______6 • Advisory Board ______7 • Research Institutes ______7 • Associated Members of ForWind ______7

Projects

WIND AS A RESOURCE • WAUDIT – Wind Resource Assessment Audit and Standardization ______8 • Analysis of the Shadowing Effects and Wake Turbulence Characteristics of Big Offshore Wind Farms by Comparison of »alpha ventus« and »BARD Offshore 1« (GW Wakes) ______10 • Parallel Computing Cluster for CFD and Wind Turbine Modelling ______12 • Active Grid and Turbulence Research Facility ______16 • Development of New Anemometers for Atmospheric Flow Measurements ______18 • Particle Image Velocimetry – Research and Development ______20

SUPPORT STRUCTURES • RAVE: GIGAWIND alpha ventus – Holistic Design Concept for Offshore Wind Energy Turbine Support Structures on the Base of Measurements at the Offshore Test Site Alpha Ventus ______22 • GROWup – Grouted Joints for Offshore Wind Energy Converters under Reversal Axial Loading and Upscaled Thicknesses ______28 • Cyclic Performance of Horizontally Loaded Piles for Offshore Wind Energy Converters in Layered Subsoil______30 • OPTIWELD – Ecological and Economical High Performance Joining Techniques for Tubular Steel Towers of Wind Energy Converters ______32 • NaStafEE – Sustainability of Steel Structures of Renewable Power Plants ______34 • Design, Testing, Realisation and Verification of Low Noise Construction Methods and Noise Reduction Techniques During Construction of Offshore Wind Turbines ("Schall 3") ______36 • HyproWind: Realistic Underwater Sound Scenarios Based on Forecast Modeling and Monitoring R egarding Piling Noise During Wind Farm Construction in the German North Sea ______38

WIND POWER SYSTEMS • »Baltic I«: Control of Offshore Wind Farms by Local Wind Power Prediction as Well as by Power and Load Monitoring ______40 • RAVE-OWEA "Verification of Offshore Wind Turbines" ______42 • RAVE-LIDAR II – Development of Nacelle-based Lidar Technology for Performance Measurement and Control of Wind Energy Converters ______46 • Mapretec – Automated Preforming Process to Transform a Flat Textile Lay up into a 3D Outline for Large Fibre-Composites as Rotorblades ______48 • Optical Free Field Measurements of Rotor Blade Deformations ______50 • Laboratory for Inside-Sensoring ______52 • Laboratory for Large-Scale Gear-Measurements ______54 • Fatigue Life of Rolling Element Bearings in Wind Power Drive Trains ______56 • Cyclo Converters for Low-Speed Wind Generators ______58 • Stochastic Methods and Modeling ______60 Annual Report 2011 5

WIND POWER SYSTEMS • Probabilistic Safety Assessment of Offshore Wind Turbines ______62 • The Influence of Wind Turbines on Air Traffic Control Radar and Navigation Signals ______64 • Investigation of Sonar Transponders for Offshore Wind Energy Converters and Technical Integration to an Overall Concept ______66 • Maintenance Planning and Control of Wind Energy Turbines ______68

WIND ENERGY INTEGRATION • Safewind – Multi-scale Data Assimilation, Advanced Wind Modelling and Forecasting with Emphasis to Extreme Weather Situations for a Safe Large-scale Wind Power Integration ______70 • RAVE – Grid Integration of Offshore Wind Farms ______73 • The OffshoreGrid-Project: An Offshore Transmission Grid for Wind Power Integration ______74 • Integration of Fluctuating Energy Resources through a Self-Organized Supply-Demand-Matching ______76

Qualification

• MSc Programme "European Wind Energy Master (EWEM) – Erasmus Mundus" ______78 • Continuing Studies Programme Wind Energy Technology and Management ______80 • Continuing Studies Programme Offshore Wind Energy ______82 • ForWind Academy: Partner for Qualification in the Wind Energy Sector ______84 • Job and Education Fair “zukunftsenergien nordwest 2011” ______86

ForWind – Events

• ForWind Course of Lectures ______88 • Hannover Messe 2011 ______90 • Wind Energy Research Alliance (Association) – ForWind and Fraunhofer IWES form a Nationwide Unique Research Cooperation ______92 • Wind Energy Cluster in northwest Germany – WindPowerCluster ______93 • Global Wind Day with ForWind ______94 • Innovationcampaign for Study Possibilities in Lower Saxony ______95 • International Delegations and Visitors at ForWind – Selection of 2011 ______96 • ForWind Office has Moved around the Corner ______97

Documentation

PUBLICATION LIST ______98 1. Peer Reviewed Articles ______98 2. Articles ______99 3. Conference Contributions ______101 4. Other Publications ______105 5. Lectures ______106 6. Project Reports ______107 7. PhD Theses ______108 8. Diploma, Master and Bachelor Theses ______108

LIST OF FORWIND STAFF MEMBERS ______112

IMPRINT ______116 6 FORWIND – CENTER FOR WIND ENERGY RESEARCH

The Organization

ForWind, the Center for Wind Energy Re- ForWind was founded in 2003 through the Bremen joined in 2009. What continues to search of the Universities of Oldenburg, support of the Ministry for Science and make ForWind unique in Germany is that Hannover, and Bremen combines scientific Culture of Lower Saxony. it is a university research center serving to know-how with research geared towards pass along its broad spectrum of exper- the industry. ForWind bundles the compe- Since 2006, a formal agreement of the tise to the industry by way of cooperating tencies of the three universities and is an Universities of Oldenburg and Hannover projects. Within the industry, ForWind has adept industry contact. The administrative exists to form a corporate research center established itself as a competent research office of ForWind is located in Oldenburg. as a joint institution. The University of partner.

Prof. Dr.-Ing. Bernd Orlik Prof. Dr.-Ing. habil. Raimund Rolfes Prof. Dr.-Ing. Gert Goch

Prof. Dr. Martin Kühn Prof. Dr. Joachim Peinke Prof. Dr.-Ing. Peter Schaumann

Executive Board

ForWind is led by a six member executive The current executive board is made up of board consisting of two members of the Carl von Ossietzky Universität Oldenburg, Prof. Dr.-Ing. Bernd Orlik Prof. Dr.-Ing. Gert Goch, the Leibniz Universität Hannover and the (Academic Speaker), Prof. Dr. Martin Kühn, Universität Bremen respectively. All mem- Prof. Dr.-Ing. habil. Raimund Rolfes Prof. Dr. Joachim Peinke, bers have equal authority. (Deputy Speaker), Prof. Dr.-Ing. Peter Schaumann. Annual Report 2011 7

Advisory Board Research Institutes - Institute of Machine Elements and Engineering Design, Leibniz Universität Hannover, Chairman: The following institutes and research Prof. Dr.-Ing. Gerhard Poll groups belonging to the Universities of - Institute of Physics, Beurskens, Jos, Dr. h.c. Oldenburg, Hannover and Bremen are ac- AG Energy Meteorology, Energy research Centre of the Netherlands tive in ForWind: University of Oldenburg, (ECN) - Bremen Institute for Metrology, Dr. Detlev Heinemann Automation and Quality Science - Institute of Physics, (BIMAQ), University of Bremen, AG Marine Physics, Members: Prof. Dr.-Ing. Gert Goch University of Oldenburg,

- Department of Computing Science, Dr. Rainer Reuter Hermsmeier, Jörg, Dr.-Ing. Environmental Informatics, - Institute of Physics, AG Turbulence, EWE Aktiengesellschaft University of Oldenburg, Wind Energy and Stochastics – TWIST, Meier, Klaus, Dr. Prof. Dr. Michael Sonnenschein University of Oldenburg, wpd AG - Franzius Institute of Hydraulics, Prof. Dr. Joachim Peinke Waterways and Coastal Engineering, - Institute of Physics, Nachbaur, Karin, Dr. Leibniz Universität Hannover, AG Wind Energy Systems – WE-Sys, The Senator for Education and Science of Prof. Dr.-Ing. habil. Torsten Schlurmann University of Oldenburg, Bremen - Institute of Building Materials Science, Prof. Dr. Martin Kühn Schroeder, Hans, Dr.-Ing. Leibniz Universität Hannover, - Institute for Steel Construction, Ministry for Science and Culture of Lower Prof. Dr.-Ing. Ludger Lohaus Leibniz Universität Hannover, Saxony - Institute of Concrete Construction, Prof. Dr.-Ing. Peter Schaumann Leibniz Universität Hannover, - Institute of Soil Mechanics, Foundation Schubert, Matthias Prof. Dr.-Ing. Jürgen Grünberg Engineering and Waterpower REpower Systems AG - Institute for Drive Systems and Power Engineering, Ritterbach, Benedikt, Dr.-Ing. Electronics, Leibniz Universität Hannover, Salzgitter Mannesmann Forschung GmbH Leibniz Universität Hannover, Prof. Dr.-Ing. Martin Achmus Prof. Dr.-Ing. Axel Mertens and - Institute for Structural Analysis, Tworuschka, Hartmut, Dr.-Ing. Prof. Dr.-Ing. Bernd Ponick Leibniz Universität Hannover, HOCHTIEF Construction AG - Institute for Electrical Drives, Power Prof. Dr.-Ing. habil. Raimund Rolfes Weigel, Lars Electronics and Devices (IALB), - Institute of Turbomachinery and Fluid SGL Rotec GmbH & Co. KG University of Bremen, Dynamics-TFD, Prof. Dr.-Ing. Bernd Orlik and Leibniz Universität Hannover, Prof. Dr.-Ing. Nando Kaminski Prof. Dr.-Ing. Jörg Seume Guests: - Institute of Electric Power Systems, Leibniz Universität Hannover, Drechsler, Rolf, Prof. Dr. Prof. Dr.-Ing. Lutz Hofmann Associated Members of ForWind: University of Bremen - Institute of Fluid Mechanics and Environmental Physics in Civil Institute of Machine Elements and Hulek, Klaus, Prof. Dr. Engineering, Machine Design, Leibniz Universität Hannover Leibniz Universität Hannover, Prof. Dr.-Ing. Berthold Schlecht Simon, Babette, Prof. Dr. Prof. Dr. Insa Neuweiler Carl von Ossietzky Universität - Institute for Integrated Product Oldenburg Development, University of Bremen. Prof. Dr.-Ing. Klaus-Dieter Thoben 2011 Korr 1

8 WIND AS A RESOURCE

WAUDIT – Wind Resource Assessment Audit and Standardization

Carl von Ossietzky Universität Oldenburg, aspects of wind energy. The third school, masts measurement campaign GROWIAN Institute of Physics, held in October at Delft University of Tech- is being used in order to characterize it. Erika Dautz, Fatima Keshtova, nology, was dedicated to the presentation Detlev Heinemann, Joachim Peinke skills of the fellows. Additionally, the first Once the spatial correlations are known, Standardization Workshop of WAUDIT the next step is the simulation of stochastic took place in May 2011, hosted by the Uni- intermittent 3-dimensional wind fields with Introduction versity of Hamburg. The objective was to advanced characterisation of turbulence on develop a consensus for the collection of scales ranging from a few meters to some WAUDIT is a Marie-Curie project funded high-quality data and for model validation hundred meters. As a starting point a model under the FP7-People program. The project procedures for wind resource assessment based on Continuous Time Random Walk consortium is composed of 13 members and tools. (CTRW) theory is used. A description of 17 associated partners. ForWind Oldenburg this model is given in [4]. is involved in the work packages “Simula- tion of stochastic wind field” and “Offshore Project Description The model enables to adapt parameters in Meteorology”. The goal of WAUDIT is the order to reproduce time dependent statisti- generation of a pool of researchers in the Work package “Simulation of cal features of wind turbulence [4,5]. After field of wind resource assessment. The sci- stochastic wind fields” tuning the parameters of the CTRW model, entific motivation of the project is based on The IEC standard 61400-1 [1] specifies dif- the analysis (Fig.2) shows an adequate re- TPWind’s 3% vision which aims at reduc- ferent wind field models to simulate inflow production of the intermittent statistics on ing uncertainties in wind resource assess- conditions for wind turbines. These models small time scales. Current challenges in- ment and forecasting below 3% by 2030, re- are generating purely Gaussian statistics clude the proper implementation of the spa- gardless of site conditions. At training level, for the speed wind variations, which is in tial structure of gusts into the simulation. WAUDIT aims at providing the best work- contrast to experimental data [2,3]. Actual ing environment for early stage researchers. measured data reveals statistics of velocity increments that are not Gaussian, but In 2011, two out of three WAUDIT schools highly intermittent in space and time. Ad- took place. The second school took place in ditionally, the spatial structure of gusts is Brussels in February and covered various important and here data from the multi met

Figure 2: Comparison of probability density functions (PDFs) of wind speed increments for wind fields measured during the GROWIAN campaign (triangles) and for wind fields generated with the CTRW model (circles). The increments are normalized. Scales from bottom to top are time lag = 1.2, 2.4, 4.8, 10, 30s. Additi- onally, PDFs are modeled by using the Castaing [7] equation. For clarity of pre- Figure 1: The participants of the WAUDIT Standardization Workshop that took place on sentation, the individual PDFs are shifted the KlimaCampus in Hamburg. vertically. Annual Report 2011 9

In WAUDIT, ForWind cooperates with other international research institutions partners such as École des Ponts ParisTech (ENPC), where a multi-fractal analysis of wind fields is done as well as with industrial partners such as WINDRAD.

Work package “Offshore Meteorology” In this study the ability of a numerical model to capture the dynamics at off- and near-shore areas is evaluated. Due to the heterogeneity of surface conditions dynamical processes are more complex in coastal areas than over the open sea. The mesoscale Weather Research and Forecasting Model (WRF) [6] is applied in a configuration of three nested grids centered at the German North Sea coast. The input for WRF is provided by the 6-hourly global analysis data of the European Centre for Medium-Range Weather Forecasts (ECMWF) which pro- Figure 3: Cross-section of a sea-breeze in the WRF simulations. Wind speed vides data on a horizontal grid of 0.25° x (coloured and arrows), potential temperature (black lines). 0.25°. WRF dynamically downscales this data to the innermost domain with a grid point distance of 3 km and 52 vertical levels. The boundary layer in the model is parameterized by the Mellor-Yamada-Janjic scheme and the Eta similarity theory is applied near to the surface. The simulations To analyse the atmospheric boundary layer have been conducted for May 6-10, 2008, under these conditions the simulations when the field campaign Helipod4Wind, have been compared with the Helipod data. References organized by ForWind, took place in the The Helipod probe is carried by a helicop- [1] IEC 61400-12-1, 1st Ed. 2005-12 target area. The model results are compared ter and developed for the measurement of [2] Böttcher, F.; Barth, S.; Peinke, J.: with data from 46 weather stations, the Heli- atmospheric turbulence. Within the field Small and large scale fluctuations in pod data set, the offshore met-mast FINO1 campaign Helipod4Wind 12 flights have atmospheric wind speeds. Stochastic and soundings. been conducted from 6 to 10 May over the Environmental Research and Risk islands and the coast of the North Sea and Assessment; 21: pp. 299–308 (2007) Statistic error measures (ME, RMSE) reveal around FINO1 in order to obtain a high- [3] Morales, A.; Wächter, M.; that wind speed and temperature are simu- resolution meteorological dataset. The Peinke, J.: Characterization of wind lated worst over coastal areas. To improve investigations are not completed yet, but turbulence by higher-order statistics. the simulations in coastal areas several tests first results from the analysis show that Wind Energy (2011) with different sea surface temperature (SST) the quality of the WRF simulations differs [4] Kleinhans D.; Friedrich R.: data sets as an additional input for the WRF from day to day depending on the meteoro- Simulation of intermittent wind model have been conducted. First results logical situation. fields: A new approach. DEWEK show that the quality of the simulation de- 2006 Proceedings, Bremen,Germany, pends on the resolution of the SST data, but (2006) further analysis has still to be done in future. Summary [5] Mücke,T.; David Kleinhans, D.; Peinke, J.: The development of a sea breeze was first ForWind Oldenburg is involved in two of Atmospheric turbulence and its recognized in the measurements and simu- the work packages of the initial training influence on the alternating lated successfully with WRF. It evolves network project WAUDIT. While in one loads on wind turbines. Wind Ener- during daytime and penetrates inland ad- of the work packages a stochastic model gy Volume 14,Issue 2, pp. 301–316, vecting cold air from the sea. The simu- March 2011 for the description of an atmospheric tur- lated sea breeze shows common character- [6] Skamarock, W. C. et al.: bulent wind field is further developed, the istics of a density current like an elevated A Description of the Advanced head, a lifted nose, a weaker back-flow at performance of the mesoscale model WRF Research WRF Version 3, NCAR higher levels and a strong rear-to-front in- applied for the purpose of wind resource Technical Note, p. 113 (2008) flow which exceeds the propagation speed. assessment is evaluated. 10 WIND AS A RESOURCE

Analysis of the Shadowing Effects and Wake Turbulence Characteristics of Big Offshore Wind Farms by Comparison 2011 Korr3 of »alpha ventus« and »BARD Offshore 1« (GW Wakes)

Carl von Ossietzky Universität Oldenburg, tiple overlapped wind turbine wakes in big This work package is already running. Cur- Institute of Physics, Wind Energy Systems offshore wind farms and on the wake of the rently the first two lidar systems and other (project-coordination), whole wind farm itself. electronic components are currently tested Turbulence Wind Energy and Stochastic in an onshore measurement campaign be- TWiSt, Energy Meteorology, GW Wakes aims to understand these com- fore they will be installed in “alpha ventus” Marine Physics plex flow situations better and to develop in summer 2012. Partners: BARD Engineering GmbH, computational models that can be used for Fraunhofer IWES project group an optimized planning of big offshore wind Turbulence characterization Computational Fluid and System farms in the future. For this goal innovative The measurements performed in the off- Dynamics laser remote wind measurements will be shore wind farms are going to end up in a This project is funded by the German performed in “alpha ventus” and “BARD- large pool of data suitable to validate mod- Federal Ministry for the Environment, Offshore 1”, two offshore wind farms in- els used to evaluate turbulence properties Nature Conservation and Nuclear Safety stalled in the North Sea. such as turbulence intensity, integral length (BMU) on the basis of a resolution of scale and turbulence spectra at different the German Bundestag under the code positions in the wind farm. number 0325397A. Project description Duration: 08.2011 – 10.2014 Besides, the data collected by the multi- The main activities included in GW Wakes lidar system is planned to be used to vali- are as the following: date engineering models simulating stati- Introduction cally and dynamically the effects of wakes. Measuring technique The increasing demand of energy as well To measure the flow within and around the Modelling and validation of as the increasing political interest in re- offshore wind farms, a so called multi-lidar meteorological stream-flows newable energy production occurring in system will be used. It consists of two re- The wind farm “BARD Offshore 1” is be- the last years, pushed wind energy to ex- spectively three scanning long range lidar ing modeled and different flow conditions plore offshore sites where wind turbines units that are synchronized and controlled are being simulated with a Large-Eddy- (WT) can profit of generally higher wind remotely. The units will be placed on dis- Simulation code upgraded in order to in- speeds than those available on land at the tant platforms available in the wind farms clude the effect of the WTs. The results of same altitudes. To exploit the most of this to measure in the same volume of the at- the simulations will be compared with the advantage, the number of WTs installed in mosphere from different directions. This multi lidar measurements delivered by the offshore wind farms, as well as their rotor allows measuring the 2D respectively 3D experimental campaign. diameter is getting larger. wind speed since each lidar is able to measure the component of the wind vector that Besides, meso-scale meteorological simu- The major goal of the project GW Wakes is is aligned to the line of sight of the lidars lations of the region including “Bard Off- to study the interactions of the increasing laser beam. The first deployment will be shore 1” will be performed and compared population of wind farms in the North Sea. in “alpha-ventus” with two lidars and af- with the multi lidar data as well. It is known that a WT placed in the wake terwards in “BARD Offshore 1” with three of another one has less energy available to lidars. The technique permits measure- Technology transfer convert and at the same time experiences ments in a range up to approx. 8 km. The The results achieved in the other work more turbulence than a wind turbine in free planned set up of the multi lidar system packages will be be used in the upgrade of flow. This leads to a decreased power out- gives several scan possibilities, e.g. the in- wind farm modeling software in order to put and increased loads compared to a WT flow and the wake of the whole wind farms improve the accuracy in the evaluation of in free flow. The focus of the project lies will be measured as well as the interaction loads acting on WTs operating in single as on the studies of the flow situation of mul- of wakes inside the wind farm. well as multiple or partial wake conditions Annual Report 2011 11

and to include the influence of neighbour wind farms on the energy production prog- nosis.

Summary

Multi-lidar technology is planned to be used to investigate the air stream around and within large offshore wind farms. In this framework, two offshore experimental campaigns are planned in order to deliver valuable data suitable for validation of theoretical models used to characterize turbulence and wakes inside a wind farm. The data are also being used in comparison with wind field simulation generated with LES codes or meteorological mesoscale softwares. The results arising from the research activities are to be included in wind farm modeling software in order to Figure 1: Artists view of the measurement range of three long-range lidars improve their overall accuracy. placed inside “BARD Offshore 1”

Figure 2: 3D visualization of the concept of multi-lidar measurements planned in “alpha ventus” including the representation of a wind turbine wake flow generated by LES simulations 12 WIND AS A RESOURCE 2011 Korr 2 Parallel Computing Cluster for CFD and Wind Turbine Modelling

Carl von Ossietzky Universität Oldenburg, for performing computationally intensive OpenFOAM Institute of Physics, tasks as those mentioned above. The For- Open Field Operation And Manipulation Detlev Heinemann, Wind/Fraunhofer alliance has now a power- is a C++ toolbox for the development of Iván Herráez Hernández, ful infrastructure at its disposal which sets customized numerical solvers, and pre-/ Hannes Hochstein, Wided Medjroubi, the stage for performing larger simulations post-processing utilities for the solution of Joachim Peinke, Matthias Schramm, with higher resolution, for optimizing exist- continuum mechanics problems, including Gerald Steinfeld, Björn Witha ing models and developing new methods to computational fluid dynamics (CFD). Sev- obtain more realistic results. eral versions of OpenFOAM are installed on FLOW and it is mainly used in simu- Introduction lating flows over airfoil sections and entire Project Description wind turbines.Moreover mesoscale moduls In the present-day wind energy research UlF and COSMO. the application of Computational Fluid Dy- Technical specifications namics (CFD) plays a key role. It is widely The Flow cluster is composed of: Moreover, the mesoscale models WRF used for calculating the flow around rotor • 122 "low-memory" compute nodes of and COSMO have been installed. They are blades and entire wind turbines as well as type IBM dx360 M3. Each node has 12 mainly applied for wind resource assess- for simulating turbine wakes and the flow cores (2 sockets with 6 Westmere-EP ment studies. within and behind wind farms. Moreover, 2.66 GHz cores), with 24 GB RAM per CFD is an essential tool when turbulence is node. Other Projects using FLOW: involved as for most engineering applica- • 64 "high-memory" compute nodes of "Baltic 1" (page 40), "RAVE-OWEA" tions. Recent high-resolution CFD codes, type IBM dx360 M3. Each node has 12 (page 42), "SafeWind" (page 70), "WAU- possessing more capabilities and offering cores (2 sockets with 6 Westmere-EP DIT" (page 8). higher spatial and temporal resolution, 2.66 GHz cores), with 48 GB RAM per need powerful computing systems and in- node. Evaluation of the performance of FLOW frastructure. The single nodes are interconnected via Extensive performance studies have been blocking-free QDR Infiniband. They are done with the LES model PALM on For example, to simulate wind turbine diskless and linked with an ISILON Stor- FLOW. For comparison the same stud- wakes in a complete wind farm with a large- age System. The queueing system em- ies have also been performed on the SGI- eddy simulation (LES) model, a model do- ployed to manage user jobs for FLOW is Clusters of the North-German Supercom- main of about 4 km x 4 km x 4 km and a Sun Grid Engine (SGE). puting Alliance (HLRN), which is one of spatial resolution of 2 m is required which the most powerful computers in Germany results in 8 x 109 grid points. Only a mas- Models running on FLOW and worldwide. Each of the two clusters in sively parallel supercomputer is capable of The following models have been installed Hannover and Berlin has about 5 to 6 times dealing with such simulations. on FLOW: as much CPUs as FLOW.

For this purpose, a new supercomputer with PALM – A Parallelized LES Model Fig. 1 shows the results of two scaling stud- 186 nodes (2232 CPUs) has been installed. PALM is a large-eddy simulation (LES) ies, one with a rather small run with „only“ The hardware of the „High-Performance model for atmospheric and oceanic flows 4 x 106 grid points, the other one with a Computing Cluster“ (HPC Cluster) is fund- which is especially adapted to perform on larger run comprising 1 x 109 grid points ed by the Federal Ministry for the Environ- massively parallel computer architectures. similar to typical wind farm simulations. ment, Nature Conservation and Nuclear It can be freely used for scientific research Ideally, a simulation would need half the Safety (Bundesministerium für Umwelt, and has been applied for numerous investi- time, when doubling the number of CPUs. Naturschutz und Reaktorsicherheit (BMU) gations of the atmospheric boundary layer. PALM comes very close to the ideal per- with about 1.2 million €. The HPC Clus- Since 2009, it has been used by members formance. Only for very large numbers of ter, called FLOW (Facility for Large-Scale of the Energy Meteorology group and CPUs the performance decreases slightly. Computations in Wind Energy Research), is adapted to simulate wind turbine wakes. available for all ForWind and IWES/Fraun- Whereas the scalability of PALM on hofer scientists since May 2011 and allows FLOW is as good as on the HLRN cluster, Annual Report 2011 13

Figure 1: Scalability of the LES model PALM on FLOW and HLRN clusters.

the computations need generally less time on FLOW. For the small run, CPU times were 10 to 30% lower, for the large run still about 5 %.

Originally, the cluster was operated in a shared node mode. This means, that if a job occupies only some but not all of the CPUs on one node, another job can use the remaining CPUs on that node. However, this policy led to highly variable computing times for one and the same job. Differ- ences of up to 50% were observed, which resulted in a reduced overall performance of the cluster. Additionally, the planning of jobs is difficult. After a switch to a non- shared node policy (only one job per node), Figure 2: Schematic of the different horizontal boundary conditions applicable in the LES model PALM. Top: cyclic boundary conditions, center: non-cyclic boundary con- the computing times were steady within ditions with laminar inflow, bottom: non-cyclic boundary conditions with turbulent 1-2 %, so that a reliable planning of jobs inflow. is possible. The disadvantage is that some CPUs may remain idle and not usable. Though, the overall performance will be significantly higher as with the shared node smaller than the actual investigation area, ary conditions in direction of the mean flow, policy leading to an increase in efficiency. saving a lot of computing time. For homo- which is possible in PALM. In this case, the geneous situations as a simple convective model domain is fixed and equivalent to Scientific results boundary layer without wind turbines this the investigation area. The upstream flow Inflow boundary conditions for wake simu- is still a reasonable technique. For a wake reaching the turbine is constant throughout lations with PALM: simulation, however, cyclic boundary con- the whole simulation time. However, a very So far, all known LES studies of wind ditions have a major drawback: The tur- long model domain is required to generate a turbine wakes have applied cyclic bound- bulence generated in the wake of a turbine turbulent flow. With cyclic boundary condi- ary conditions in both horizontal direc- would enter the domain again and modify tions the turbulence develops gradually in tions. This is equivalent to the model do- the flow upstream of the turbine. This is time. The turbine is not switched on until a main being shifted with the mean flow in schematically shown in Fig. 2. An alterna- quasi-stationary state is reached. In the non- time. Thus, the model domain can be much tive is the application of non-cyclic bound- cyclic case, the inflow is always laminar and 14

turbulence has to develop spatially between The numerical simulations were done using measurements are believed to be unreliable the inflow and the turbine. Tests showed that OpenFOAM. The results of these simula- at these locations because of possible mal- a very large model domain (at least 20-30 tions are compared with the experimental functions of the pressure transducers, what km) is required which increases the compu- data available from the Mexico project. This can also be seen by the large scatter of the tational costs immensely. should constitute the base of “best practice experimental data. In general, the simula- recommendations” for future numerical tions were able to predict the pressure dis- To overcome this waste of resources but at simulations. The numerical simulations tribution satisfyingly. This trend is further the same time keep the advantages of non- were carried out with a steady-state solver confirmed when plotting the axial depend- cyclic boundary conditions, a turbulent in- called MRFSimpleFoam. It is a Reynolds ence of axial wind speed at different radial flow can be realized in PALM by perform- Averaged Navier Stokes solver (RANS) positions along the blades. To improve the ing a separate prerun with cyclic boundary which deals with multiple systems of refer- simulations further, a finer mesh will be conditions and much smaller domain size ence. The turbulence model used is the k- used in future and 3-dimensional effects of than in the main run. When the flow in the omega SST. Three different wind speeds of the flow will be investigated in more detail. prerun is fully turbulent, the flow field is 10, 15 and 24 m/s are performed. The ro- repeatedly mapped to the domain of the tational speed is kept constant at 424 rpm, 3D turbulent flow around a modified main run. Starting the main run, the turbu- and the pitch angle is -2.3 degrees and no wind turbine blade lent fluctuations are continuously recycled yaw is considered. The optimization of the design of a wind at some distance downstream of the inflow. turbine blade is considered here, in par- Hence, the flow in the main run is already The analysis of the results is based on the ticular the root region of the blade. In this turbulent at the inflow and only a small pressure distributions along the blade sec- region secondary flows occur due to the distance between inflow and turbine is re- tions and on the PIV measurements. Fig. 3 Coriolis and centripetal forces. These sec- quired. As several tests have been success- represents the pressure distributions along ondary flows reduce the efficiency of the ful, it is intended to perform planned wind 5 sections of the blade for a wind speed of wind turbines and therefore need to be in- park simulations with this method. u = 10 m/s (in blue our numerical, in red vestigated. the experimental results). A fairly good Validating different numerical models agreement exists between the experimental The simulations were performed with with the Mexico experiment dataset and the numerical data (this is also the case OpenFOAM. A given profile together with In order to validate numerical models, for u = 15 m/s and u = 24 m/s). its modified version is simulated. The blade numerical simulations of wind turbines investigated belongs to a 2MW wind tur- aerodynamics are compared to experi- However, a mismatch exists in the in- bine. A grid of 3.8 millions of cells is used. mental results obtained from the Mexico ner blade sections (small r/R values). The The solver MRFSimpleFoam is used and a Project. This project stands for Model Experiments in Controlled Conditions. It involved extensive measuring of loads and flow characteristics from a 3-bladed wind turbine placed in the large low-speed Facil- ity (LLF) in Marknesse, NL, of the DNW (German Dutch Wind Tunnels). The first phase of the Mexico project is part of the International Energy Agency (IEA) task29. It is a joint project in which 20 partners from 11 countries cooperate together. The focus of IEA Task29, is to improve and understand aerodynamic models by means of dedicated wind tunnel measurements.

The wind turbine on which the experiments- were conducted has a rotor diameter of 4.5 m, and the blades are twisted with their design being based on 3 different profiles (namely DU91-W2-250 in the root region, RISO A1-21 in the mid region, and NACA 64-418 in the tip region). Figure 3: Pressure distribution along the blade at u = 10 m/s. Annual Report 2011 15

Reynolds number of 2.2 x 10-6 is simulated. strong fluctuations in the wind speed occur compared to the experimental results at the We plot the pressure coefficients (Cp) for more frequently. For proper CFD investi- centerline of the fractal grid and at a vertical both blades (original and modified) as a gations of the aerodynamical features of a distance z = 0.95. The same comparison is function of radial positions. When we are wind turbine it is a challenge to generate done for the skewness. close to the modified region of the blade, the such intermittent inflow conditions. One Cp values of the original and the modified possibility to produce and to characterize The numerical results are in a very good blade are totally different. It is found that such inflow conditions is to use fractal grids. agreement with the experimental data. This the normal forces produced by the modi- shows that the simulations are able to pre- fied blade are higher than the one produced The fractal grids make it possible to ob- dict the complex flow in the wake of the by the original blade, also the stagnation tain, after a quite short distance behind the fractal grid in a satisfactory manner. The point is shifted further downstream of the grid, more realistic inflow wind fields than same results were obtained when comput- blade. The differences in the Cp diminish the commonly used laminar or simplified ing the flatness. as the radial position is increased towards turbulent inflow. The faster such an inter- the unmodified region. Finally, as expected, mittent wind field can be generated, the no difference is seen when one leaves the less power of the computer is needed and Summary modified region. thus, the more possibilities for other flow calculations remain. The fractal nature of A new supercomputer (HPC cluster From this analysis the gain in power can the grid causes a multiscale excitation of „FLOW“) with more than 2000 cores has be estimated, and we obtained values of the wake flow. Therefore, the turbulence been installed and is available for all sci- about 1.25% gain for the modified blade. obtained from fractal grids is closer to the entists of the ForWind/Fraunhofer alliance This result is to be taken with caution as “real” turbulence. At ForWind, numerical since May 2011. It allows for performing the meshes used in both simulations are not simulations of the unsteady flow behind a computationally intensive tasks in wind exactly the same. Possible consequences fractal grid are conducted using the Delayed energy research, so that essential progress of this aspect are currently under investi- Detached Eddy Simulation (DDES) solver can be expected in the development and gation. More extensive simulations are to of OpenFOAM. The grid used possesses 5 improvement of wind turbines. It has been be conducted to assert these encouraging iterations, the inflow speed considered is 5.2 shown that FLOW has a similar scalability preliminary findings. m/s and the results are compared with ex- than the HLRN supercomputer and compu- perimental data obtained in the wind tunnel. tations on FLOW need generally less time. Fractal Grid Several scientific results in different projects Wind turbines encounter a turbulent inflow Fig. 4 illustrates the turbulence intensity have been already obtained using FLOW which is intermittent, which means that obtained from the numerical simulation for high-peformance numerical simulations.

Figure 4: The turbulence intensity distribution in the wake of the fractal grid. Experimental data is represented by the red-dotted line and simulations by the blue dotted-line. 16 WIND AS A RESOURCE

Active Grid and Turbulence Research Facility

Carl von Ossietzky Universität Oldenburg, Project description not only statistically but also chronologi- Institute of Physics, cally. Analyses also indicate that the flap Nico Reinke, Joachim Peinke, Characterization of flow structures size represents the lower limit of directly Michael Hölling The active grid allows for the generation manipulable flow structures. This repro- of turbulent wind fields, whose proper- ducibility of turbulent flow situations al- ties can be adjusted by different excitation lows for a new approach to study the Introduction protocols for the stepper motors. Based on impact of turbulence on the wind energy these protocols, flow structures of various conversion process. For example differ- The dynamical response of wind energy sizes can be created and defined characteris- ent control strategies can now be compared converters (WEC) to turbulent wind fields tics can be impressed onto the wind field. for repeated turbulent flow conditions. is still a challenging issue. In addition to Nevertheless, the resulting flow is always a These first results are so promising that numerical simulations, ForWind addresses superposition of defined, controlled struc- several groups are interested to use this this problem with specially designed ex- tures and the natural decay of turbulence. experimental approach. As a consequence periments in the wind tunnel at the Uni- Therefore, characterization measurements a new Turbulence Research Facility is versity of Oldenburg, e.g. on wind turbine have been performed to investigate the under construction for the use of active models and rotor blade profiles, respec- impact of this natural decay on the gener- grid generated turbulence only. The outlet tively. For realistic inflow conditions it is ated wind fields. Excitation protocols ac- cross-section of this facility will be 1.0 m crucial to create turbulent wind fields that cording to figure 1(a) have been used to in width and 0.8 m in height, the measuring show characteristics comparable to those generate increasing velocity pulses. In this section (open as well as in closed) will be ambient in the atmospheric boundary layer sequence a flap position of 0° corresponds about 4 m in length behind the active grid (ABL). At ForWind such wind conditions to a minimum blockage of the flap and and wind velocities up to 20 m/s should be are generated by means of an active grid, therefore results in the highest velocity. reached. In 2011 the basic design was com- consisting of sixteen axes with square flaps Hot-wire measurements have been carried pleted, the foundation was built and the fan mounted to them. Each of these axes is out at different positions on the centerline was ordered and delivered. Ongoing work connected to a stepper motor, which can downstream of the active grid. Figure 1(b) deals with the characterization of the fan, be controlled individually using different shows the evolution of the resulting wind where the finishing of the complete facility excitation protocols. This active grid enables velocity pulses behind the active grid. It is scheduled for summer 2012. the generation of vertical velocity profiles can clearly be seen that the velocity pulses and turbulent wind fields with highly gusty smear out with increasing distance to the Re-design of active grid (intermittent) behavior (see [1] and ref- grid and the natural decaying process due One design aspect is the minimum achiev- erences). Even though first experiments to internal friction and boundary effects able solidity of the grid, which is currently show promising results, the active grid is becomes more and more dominant [2]. about 23%, and is mainly given by the sup- still subject to further developments re- This has to be accounted for in future ex- porting structures (axes) of the mounted garding excitations protocols as well as citation protocols especially when down- flaps. In addition, the minimum and ba- grid design. stream homogeneity is crucial, for exam- sic turbulence intensity, respectively, is ple for measurements with wind turbines in strongly influenced by the wakes created wind park configuration. by the axes and the flaps of the active grid. In order to be more flexible in adjusting the Based on the study of these well-defined solidity and turbulence intensity the axes pulses the reproducibility of the turbulent have been re-designed. In the current de- flow conditions has been investigated. One sign each axis is a solid rod with the flaps excitation protocol for randomized move- screwed to it (figure 2(a)). These solid rods ments of the axes has been repeated several have been replaced by a modular design, times and velocity measurements of the where each flap is attached to their neigh- flow at different locations have been per- bors by small connectors (figure 2(b)). formed. First results show that in fact even This will reduce the minimum solidity of turbulent wind fields can be reproduced, the whole grid to 5%, which is about five Annual Report 2011 17

(a) (b)

40 flap position [°] 20

0 0 0.5 1 1.5 2 time [s]

Figure 1: (a) Sequence of realized protocol for the generation of increasing velocity pulses. Each pulse has a duration time of 0.2 seconds. (b) Resulting velocity of the implemented sequence with increasing distance to the grid. The colors correspond to wind velocities as shown in the calibration column on the right, all expressed in m/sec.

(a) (b)

Figure 2: (a) Original solid axis and (b) re-designed axis with connectors between the fl aps.

times smaller than the original design. The Summary References lack of solid axes shall reduce the wake effects caused by these cylindrical structures, Velocity measurements behind the active [1] Knebel, P.; Kittel, A.; which results in a smaller basic turbulence grid with respect to the stability of fl ow Peinke, J.;: Atmospheric Wind Field intensity and thus in an increase of the re- structures show an increasing effect of Conditions Generated by Active producibility. natural decaying turbulence with increas- Grids, Experiments in Fluids, ing distance to the grid. In order to gain a Volume 51, Number 2, 471-481, DOI: 10.1007/s00348-011-1056-8 (2011) better understanding of the interaction of [2] Wächter, M.; Hölling, M.: excitation protocols of the active grid and Milan, P.; Morales, A.; Mücke, T.; the decaying process further downstream, Reinke, N.; H. Heißelmann, H.; a new “turbulence research facility” was Peinke, J.: Wind Energy and the designed. In addition, the axes of the grid Turbulent Nature of the have been re-designed in order to mini- Atmospheric Boundary Layer, mize the solidity and the wake effects of Journal of Turbulence, the axes, respectively. to be published 18 WIND AS A RESOURCE

Development of New Anemometers for Atmospheric Flow Measurements

Carl von Ossietzky Universität Oldenburg, Project description within a sector of about ± 35°. Latest im- Institute of Physics, provements of the 2d-ALCA focused on Hendrik Heißelmann, 1. 2d Atmospheric Laser-Cantilever- the manufacturing of the cantilever. The Jaroslaw Puczylowski, Joachim Peinke, Anemometer application of the laser pointer principle Michael Hölling The limitations in temporal and spatial requires a highly reflective surface of the resolution of the standard anemometers tip of the cantilever, which could not have led to the development of the 2d Atmos- been realized using polishing processes Introduction pheric Laser-Cantilever-Anemometer (2d- due to its fragility. Instead a small 0.3 x ALCA), see figure 1. It was realized in the 0.3 mm2 mirror was attached to the canti- Standard anemometers for measurements framework of a research program of the lever (figure 1). First measuring tests with under atmospheric conditions provide a Forschungsplattform in Nord- und Ost- the 2d-ALCA on a met mast near shore low spatial resolution of about 20 cm and see Nr. 3 (FINO3) in collaboration with showed heavy wear and damages due to suffer from systematic measurement errors the Fachhochschule Kiel. The programme the aggressive environment consisting of due to their design. Besides a low sampling includes highly resolved measurements salty and humid air. As a result some sen- frequency of 1 Hz, cup anemometers tend within the turbulent atmospheric boundary sitive parts of the sensor were sealed with to overestimate the wind speed under tur- layer in offshore environment. Therefore latex for better protection. Furthermore the bulent inflow due to an asymmetry in the the 2d-ALCA is equipped with a canti- cantilever was coated with a thin layer of dynamic response to increasing and de- lever, which experiences a deformation gold using a galvanic process. Currently creasing wind caused by the sensor’s mo- due to the drag force caused by the mov- the 2d-ALCA is undergoing tests regarding ment of inertia. Ultrasonic anemometers, ing air. The cantilever is made of stainless the signal quality and reliability. on the other side, have supporting struc- steel and measures only 2 mm in length, tures for the build-in transducers whose 0.4 mm in width and is about 25 µm thick. 2. Sphere Anemometer wakes affect the velocity and direction It is mounted to the front of the sensor and Goal of the project “Kugelanemometer” is measurement within the measurement vol- faces the main flow direction. By using the improvement of the sphere anemom- ume. ForWind is working on the develop- the light-pointer principle in combination eter towards the application in harsh off- ment of two new sensors, namely the 2d with a two-dimensional position sensitive shore environments. The joint project of Atmospheric Laser-Cantilever-Anemom- detector (2D-PSD) the complete deforma- ForWind in cooperation with the BARD eter (2d-ALCA) and the sphere anemom- tion, including bending and twisting, can Group started in September 2010 and is eter, to improve the quality of atmospheric be detected [1]. This allows for simultane- funded by the German Federal Ministry for flow measurements in terms of reliability ous measurements of the longitudinal and the Environment, Nature Conservation and and temporal and spatial resolution. transversal velocity component of the flow Nuclear Safety (BMU).

Figure 1: Picture of 2d Atmospheric Laser-Cantilever-Anemometer. The zoom shows the cantilever with mirror. Annual Report 2011 19

The sphere anemometer consists of a light to allow for the longer signal transmis- sphere mounted atop of a flexible support- sion cables needed. After installation, the ing tube, which is fixed to the anemom- sphere anemometer’s performance will be eter casing. Once the setup is exposed to compared to those of cup anemometers and the flow, the acting drag forces cause the a 3D ultrasonic anemometer, since those sphere-tube-combination to bend. The dis- are standard anemometers in wind energy. placement of the sphere can be measured Hence, both reference sensors were char- by means of the light-pointer principle, acterized in wind tunnel experiments. For which is adopted from atomic force micro- the Gill WindMaster Pro 3D ultrasonic scopy and works in analogy to the 2d-AL- anemometer experiments under different CA. Here, a laser diode is mounted on the inflow angles revealed an angle-dependent tip of the tube and aimed onto a 2D-PSD. deviation from the reference wind speed. The displacement of the laser spot on the As expected, the strongest deviations were 2D-PSD is linked to the wind speed and found for angles where support structures direction via a two-dimensional calibration of the anemometer itself caused flow dis- function. In contrast to ultrasonic anemom- turbances in the measurement volume (see eters, no correction of wake effects from also [3]). The severity of these effects is transducers and mounts is necessary for the clearly depending on the inflow velocity. sphere anemometer. Figure 2: Picture of latest prototype of sphere anemometer with increased dis- The sphere anemometer setup as of 2010 tance between laser diode and optical sen- [2] was replaced by a new design with in- sor. creased distance between laser diode on top and the 2D-PSD at the bottom of the In cooperation with the project partner anemometer housing. The increased light BARD Group, a data acquisition system path serves as an optical amplifier of the with PC, data loggers, amplifiers, lightning sphere displacement. It allows for the use protection etc. was composed and prepared of stiffer tube materials and enables the for the installation in the wind turbine na- substitution of the previously used glass celle. The anemometers and the data ac- Figure 2: Picture of latest prototype fiber tubes by more isotropic stainless steel quisition system will be installed on the of sphere anemometer with increased tubes. Thus, the resonant frequency of the BARD 5.0 test wind turbine in Hooksiel in distance between laser diode and optical sphere-tube-combination was increased early 2012. sensor. (from ~40 Hz to ~80 Hz) while at the same time the oscillation amplitudes of the system were reduced. This significantly im- Summary References proved the quality of the sphere anemom- [1] Puczylowski, J.; Peinke, J.; eter’s 2D calibration characteristics and With the sphere anemometer and the 2d Hölling, M.: High resolved yield higher accuracy and reliability of the Atmospheric LCA, ForWind has continued measurements performed with the measured data. the development of two sensors for wind 2d-Atmospheric-Laser Cantilever measurements in offshore environments. Anemometer, Proceedings of 7th As part of the project, the sphere anemom- While the sphere anemometer is supposed EAWE PhD Seminar on Wind Energy eter will be installed on an offshore wind to be an alternative to standard sensors in in Europe (2011) turbine. Therefore, a streamlined and wind energy, the 2d-ALCA was designed [2] Heißelmann, H.; Peinke, J.; more robust sphere anemometer setup for turbulence investigations on very small Hölling, M.: Comparing the sphere was constructed based on the new design spatial and temporal scales. For the im- anemometer to standard used in successful laboratory tests (figure provement of the 2d-ALCA some effort was anemometers for wind energy, th 2). Besides the general geometric proper- made regarding the optimization of its can- Proceeding of the 7 EAWE PhD Seminar on Wind Energy in Europe ties from the previous experiments, the tilever and the sensor’s resistivity towards (2011) water-tightness was emphasized in these corrosion. Additionally, a new sphere an- [3] A. Wiesner, et. al.: The Influence considerations. Additionally, the sensor emometer setup with optimized geometry, of the Sensor Design on Wind Meas- electronics was modified to achieve a tran- watertight housing and modified electron- urements with Sonic Anemometer sition from voltage outputs (as used in the ics was constructed to achieve an improved Systems, J. of Atmos. and Oceanic laboratory) to standardized current outputs performance. Offshore installation of both Technol., 18, 1585-1608 (2001) of 4…20 mA. This was necessary in order anemometers will be in early 2012. 20 WIND AS A RESOURCE

2011 Korr 2 Particle Image Velocimetry – Research and Development

Carl von Ossietzky Universität Oldenburg, Project Description recorded in side-view. In Figure 1 two ve- Institute of Physics, locity plots show the evaluated time-aver- Tim Homeyer, Lars Kröger, PIV in Aeroacoustics aged flow for inflow wind speeds of 35 m/s Bernhard Stoevesandt, A cylinder made of plastic with a small and 36 m/s respectively. It is observable Christoph Hindriksen, Christina Heßeling, rectangular cavity in the surface milled at that for wind speeds of about 35 m/s and Joachim Peinke, Gerd Gülker 102.5° measured from the stagnation point below the flow separates from the surface has been investigated in our acoustic wind in front of the cavity. At 36 m/s and above tunnel [1]. An interesting aeroacoustic ef- the boundary layer reattaches to the sur- Introduction fect can be observed: When a certain wind face before separating behind the cavity. speed is reached, the cavity suddenly be- Thus, the transition causes that the cavity Optical flow measurement techniques are gins to whistle in a loud tonal noise. The is blown with high local wind speeds. This powerful tools in fluid dynamics investi- noise disappears just as abruptly when effect is known as ‘drag crisis’, in which gations. The main advantage compared to the wind speed is decreased again. It has the drag is reduced abruptly and the wake other standard methods like e.g. Hot Wire turned out, that the standard cavity noise is narrowed. The known critical Reynolds Anemometry is its non-invasive character, theory by Rossiter is not applicable for this number of the transition on a cylinder (with which allows the measurement of com- special flow situation. Neither the occur- intrinsic hysteresis) is around Re = 350.000. pletely undisturbed velocity fields. One ring frequencies match the predicted ones, For our setup this corresponds to a wind well-suited optical technique is Particle nor the sudden onset and stop of the noise speed of about 37 m/s, which is in good Image Velocimetry (PIV) which is a full- is properly predicted. To get more insight agreement with the observed transition and field method and thus delivers an entire in the flow structure PIV has been used to the stop of the radiated sound. Thus, with two dimensional velocity field. This yields visualize the global flow situation around the help of PIV measurements the reason a complete overview of the flow situation this probe. A Nd:YAG double pulse laser is for the sudden onset and stop of the noise by only one single measurement. The tech- used to illuminate the cylinder with a light could be revealed. The occurring frequen- nique can be applied for essential investi- sheet perpendicular to the cylinder and to cies can be explained by Kelvin-Helmholtz gations and optimizations of e.g. blade ele- the mean flow direction. 50 double images instabilities which are formed in the sepa- ments in a wind tunnel. The main principle for different wind speeds respectively are rated boundary layer. of PIV is the registration of light scattered from tracer particles which are added to the flow and which follow the flow smoothly. In air DEHS particles with diameters between 0.3 and 1µm are widely-used. A high power pulse laser and cylindrical lenses are used to form a two dimensional light sheet which illuminates the flow. The light scattered by the particles is recorded with a digital camera from the side. Consecu- tive recordings were taken with a certain time difference and evaluated resulting in a complete 2D-vector field of the flow velocity within the illuminated regime (2D-2C).

Figure 1: PIV measurements of the averaged circulating flow around a cylinder with a small cavity at 102.5° measured from the stagnation point. Colored velocity magnitudes at 35m/s (left) and 36m/s inflow wind speed (right). The clearly visible onset of the drag crisis (narrower wake) was leading to a loud aeroacoustic noise generation at the cavity. Annual Report 2011 21

PIV for Validation of Simulations In CFD (Computational Fluid Dynamics) a great demand for measurement data exists in order to validate codes that compute velocity fields around flow bodies. The state- of-the-art method to deliver such velocity fields of real flow situations is PIV. Thus, measurements were performed on a Wort- mann FX 79-W-151 airfoil to validate simulations carried out by the ForWind CFD group [2]. To this end the wing with 9.5 cm chord length has been fixed at an angle of attack of 12° in a small wind tunnel with an inflow wind speed of 3 m/s. The PIV Figure 2: Averaged streamwise component of the velocity Vx of the measurement (left) setup is similar to the one described above. and of the simulation (right) of a Wortmann FX 79-W-151 airfoil normalized with the The same flow situation with exactly the inflow wind speed V = 3 m/s. same Re-number has been simulated with 0 the Nektar CFD code [3], which is a Na- vier-Stokes solver that performs direct numerical simulation. Figure 2 shows the averaged streamwise component of the velocity resulting from the PIV measurement and from the simulation. It can be observed that the simulation reproduces the real flow

Digital Holographic PIV Standard PIV measurements can only re- in a water filled glass cuvette have been veal two velocity components in a two di- performed in order to get highly time re- References mensional plane (2D-2C). ForWind carries solved Lagrange particle trajectories [4]. out research in a method named Digital Lagrange trajectories are not only of inter- [1] Homeyer, T.; Kirrkamm, N.; Haut, C.; Schultz-von Glahn, M.; Holographic PIV where the whole velocity est to gain insight into the flow, but also to Kampers, G.; Peinke, J.; Mellert, field in a three dimensional volume can be answer open questions in highly turbulent V.; Gülker, G.: Untersuchungen flows e.g. the Heisenberg-Yaglom predic- resolved. The main advantage compared to geräuscherzeugender Kavitäten auf other 3D-3C methods is the compact setup, tion of fluid particle accelerations. einem Zylinder, Proceedings der since only one camera and a low power 19. GALA-Fachtagung, (2011) laser are necessary. The three dimensional [2] Kröger, L.: Charakterisierung information of the velocity field is gained Summary eines Wortmann Flügelprofils im by a holographic recording of an illumi- Windkanal mittels PIV und Vergleich nated particle field with a CCD or CMOS The optical flow measurement technique mit CFD-Simulationen, Bachelor The- camera. In an inline setup the scattered PIV is a frequently used tool to visualize sis, University of Oldenburg, (2011) light of the particles (object wave) and the flows around airfoils or other flow bod- [3] Sherwin, SJ.: Nektar solver web page, http://www3.imperial.ac.uk/ unscattered light (reference wave) interfere ies. It has been used to analyze the sudden spectralhp, (2009) on the camera chip, forming a digital holo- occurring drag crisis on a cylinder with a [4] Gülker, G.; Hindriksen, C.; Home- cavity that shows interesting aeroacoustic gram. The reconstruction of the particle yer, T.; Peinke, J.: Optimization of a positions is completely performed in the effects. The technique has also been used digital in-line holography setup used computer by solving the diffraction equa- to validate CFD calculations by comparing with a high-speed camera, Progress tions. When a sequence of holograms is simulations and measurements on the same in Turbulence IV: Proceedings of the recorded and the particle positions in the airfoil, which results in a very good agree- iTi Conference in Turbulence 2010, investigated flow are reconstructed, the ment of the flow fields. Besides standard Springer Proceedings in Physics, in particles can be tracked throughout the PIV measurements, ForWind conducts re- press volume. This gives an insight into the com- search on a promising technique that uses plete velocity field in the volume. Lately, digital holography to gain information recordings with a high speed camera with about the complete three dimensional ve- up to 625fps of 10µm polystyrene particles locity field in a volume. 22 SUPPORT STRUCTURES

RAVE: GIGAWIND alpha ventus – Holistic Design Concept for Offshore Wind Energy Turbine Support Structures on the Base of Measurements at the Offshore Test Site Alpha Ventus

Project partners: and GIGAWINDplus. The methods created Load modelling for waves and its Leibniz Universität Hannover and validated on offshore structures like correlation effects to wind Institute of Structural Analysis the FINO1 research platform will now be This sub-project is focused on three tasks, Prof. Raimund Rolfes (coordinator); transferred to real OWT. Additionally, one primarily on the estimation of load coef- Institute of Steel Construction focus is the integration of these methods ficients for the calculation of wave loads Prof. Peter Schaumann (vice coordinator); into one modular simulation- and design on OWT structures, secondarily on the cor- Franzius-Institute of Hydraulic, Water- package. relation of wind and wave action at the always and Coastal Engineering pha ventus test site, and finally on extreme Prof. Torsten Schlurmann; load estimations due to breaking waves. Institute of Building Materials Science Prof. Ludger Lohaus; Project Description The coefficients for the wave load calcu- Institute for Geotechnical Engineering lation, using the Morison approach, scatter Prof. Martin Achmus; Priority objective of this project is the in literature. Therefore model tests on the Fraunhofer-Gesellschaft reduction of the cost for OWT support tripod structure with non-breaking waves Institute for Wind Energy and Energy structures. The project can be divided into have been performed in the large wave System Technology sub topics like loads, durability and foun- flume since 2010. The tested cases with Dr. Holger Huhn; dations. Since mid of 2010 first data from various sea state parameters are currently REpower Systems AG (cooperation the test field is available and used within investigated to reveal more specific Cd and partner) CM coefficients for load calculations on AREVA Wind GmbH (cooperation partner) the work packages. In total, eight packages were formed within GIGAWIND alpha offshore foundation tripod structures. The Funded by the Federal Ministry for the ventus: evaluated data from water pressure sen- Environment, Nature Conservation and sors, installed on a tripod structure (Fig. 1, Nuclear Safety (BMU) Duration: 03.2008 – 04.2012

Introduction

When planning and erecting an offshore wind turbine (OWT) one of the biggest cost factors, compared to onshore WT, is the support structure. These higher costs may be reduced by increasing the knowledge of several key factors as there are for example soil conditions and behaviour or dynamic loads from waves. In particular this aspect becomes more important due to the fact that thousands of OWTs are planned in the North and Baltic Sea.

Since 2001 the research group GIGAWIND is engaged in optimizing support structures for planned offshore wind turbines. The Figure 1: Tripod structure at test site alpha ventus with water pressure sensors (left), research project GIGAWIND alpha ventus evaluated circumferential pressure distributions (top right) and derived time dependent ties in with its parent projects GIGAWIND loads (bottom right) Annual Report 2011 23

left) of test site alpha ventus, has delivered circumferential pressure distributions (Fig. 1, top right), from which time dependent loads can be derived (Fig. 1, bottom right). The experimentally identified load distributions will be compared to calculated values.

For the second task the collected data at the FINO 1 platform is used to correlate the wind and wave load development at the test field. The wave direction and characteristic sea state parameters are investigated in regard to the changing wind direction and intensity.

The third task focuses on breaking waves and their local pressure development on the foundation structure. Model tests and numerical simulations are used to further increase knowledge about the intensity and location of peak pressures and thus total forces on offshore foundation structures. „Results from laboratory experiments show local peak pressures up to 10 times in regard to the stagnation pressure in the area Figure 2: Development, production and assembly of the measurement of the hitting wave crest.“

Lifetime, fatigue analysis and joining techniques have been adopted for numerical models. hand, in the underwater-zone intense ma- The currently applied structural and fatigue A monitoring system (prototype), meas- rine fouling was identified. Furthermore, assessment of support structures for OWT uring the relative displacements between production techniques for the mortar layer is based on common design rules, which pile and sleeve in grouted joints under have been developed and the filling pro- treat structures as unique. This means realistic load conditions, has been devel- cedure has been tested on small-scaled that varying aspects of material qualities, oped (Fig. 2). A rigid, magnetically to components.. First results from laboratory manufacturing and loading are considered both pile and sleeve connected measur- tests show good characteristics concern- by high safety factors which may result in ing construction transfers the relative dis- ing stability against sedimentation (2.8 m conservatively designed, heavy and expen- placements into the measuring box (Fig. 2, at diameter of 7.0 cm) and self-leveling sive structures. Focussing on the influence top). First measurements gained at test site (1.0 m at diameter of 70.0 cm). Moreover, of manufacturing aspects, parameters like alpha ventus have been evaluated in 2011. laboratory tests with the aim of optimizing geometry tolerances and aspects of weld- Measured loads, wind and strain data were the mortar composition are in process. It is ing like distortions were measured during compared with relative displacements in already proved that the resistance against the manufacturing in order to get more in- order to examine and evaluate the plausi- water and chloride penetration can be information about their development during bility and feasibility of this measurement creased by addition of polymer disper- the production process and their influence system. sions. on fatigue critical stress concentration at welded nodes. After analysing different Corrosion protection for offshore steel Health monitoring systems measurement techniques, terrestrial laser structures During the design process of an OWT sup- scanning and tachymetry were favoured Installed test coupons (tripod, test site “al- port structure numerous assumptions on as fast and most practicable. Both tech- pha ventus”) have been visually inspected the resistance and impact side are made. niques were applied during two separate in April 2011. After a strong winter, no Hence, exact influences on the load bear- field campaigns. The results successfully damage was observed on the mortar sur- ing behaviour are unknown. As a result it detected by laser scanning and tachymetry face in the “splash zone”. On the other is very important to monitor the structures 24 SUPPORT STRUCTURES

state. If the actual state of the structure can damaged structures are needed. To estimate monopile foundations, but also in the near- be predicted by measured data, the time be- the different states for an OWEA in alpha field and esp. beneath the main column of tween maintenance intervals could be cus- ventus, acceleration data from two dozen the tripod, in the latter case reaching much tomized and damages could be detected at sensors is evaluated over a time span of higher scour depths than around the single an early state to reduce the service costs. For more than one year. Modal parameters and foundation piles. This influence of the lo- damage detection, the Multiparameter-Ei- residues are extracted to build a base line for cal and global changing bed surface on the genvalue Problem (MEP) is used in GWav the classification and later damage detec- soil-mechanical bed characteristics has to (Cottin 2001). It is based on a mathematical tion. After damage detection the remaining be considered when regarding the stability model in combination with modal proper- bearing strength has to be determined from of the soil and the foundation structure. A ties from measured data. In a first step, the these parameters. Additional numerical sim- comparison between large-scale model tests mathematical model is updated with the ex- ulations will support the damage detection and in-situ measurements of scours in the tracted modal properties. Changes in modal by measured data. alpha ventus test site has shown that the properties can be traced back to structural scour pattern could qualitatively be well damage. The MEP calculates changes in Scour around complex foundation reproduced in the experiments. Neverthe- stiffness from changes in the modal param- structures less, scour depths in the experiments were eters. It is necessarily required to evaluate Within the work package investigations on lower due to restrictions in the wave flume data over a long time span, since modal scour and scour protection systems around model setups. Therefore, direct influences properties do not only change due to dam- complex foundation structures and esp. the of the load parameters, i.e. multi-directional age but also due to surrounding conditions. tripod foundation have been carried out by waves, tide-induced current flow and a com- The huge amount of data necessitates an means of 1:40 and 1:12 small- and large- bination of both as well as structural param- automated selection by global parameters as scale physical model tests in wave flumes eters leading to enhanced scour are further wind or rotor speed. Modal properties cal- as well as further investigations by means investigated during the current period by culated from these data sets build the basis of numerical simulations using CFD code. means of numerical simulations using CFD for damage detection. The basic functional Regarding the scour process itself it can code. Locations of enhanced scour threat at capability and its extension to an automatic be stated that the characteristics of the lo- the structures can for example be identified identification of changes in local stiffnesses cal and global scour development around regarding bed shear stress amplification fac- have been proved for two onshore WTC the tripod, described by depths and extent, tors, exemplarily given in Fig. 2. Further- so far. Artifical damage could be detected, are directly influenced by the load param- more, a sediment transport formulation is localized and quantified. Further, in order eters and the orientation of the structure, implemented in the numerical code, which to show the applicability of the MEP for i.e. turning angle in reference to the main is used to directly calculate time-dependent damages of different sizes and for different load direction. Scour does not only occur scour depths and extends influenced by locations, additional laboratory tests with directly at the piles as it is well known for above mentioned factors.

Figure 3 – (left): Large-scale 1:12 model structure of the tripod foundation and scour pattern. in the wave flume; - (right): bed shear stress amplification factors for combined wave and (tidal) current load

Annual Report 2011 25

Behaviour of piles for offshore wind The main reason for that is a compaction of to the numerical model. The result is capa energy foundation structures under the soil beneath the pile shaft due to cyclic city degradation dependent on the magni- static and cyclic axial loading shearing, which leads to a reduction of the tude of the applied load and the number of Tripod and jacket foundation structures are normal contact stresses acting between pile cycles (Fig. 4). fixed to the seabed by three or four long and soil. In a model proposed by Richter & steel pipe piles located at the corners of the Kirsch (2010), compaction occurs up to a Automated Validation of Parametric Struc- foundation structure’s footprint. The design distance at which a threshold value of cy- tural Model comprises pile driving analyses, analysis clic shear stress in the soil is reached. The A well-adjusted, parametric structural of bending stresses with respect to extreme calculation bases on the results of cyclic model is an important basis for numerous load and fatigue limit states, proof of suffi- simple shear tests, in which the volume applications throughout the whole design cient horizontal and axial pile capacity and compactions due to cyclic shearing are process of an OWT. Such a model is a consideration of horizontal and axial pile measured. requirement for precise numerical simula- displacements. Cyclic behaviour of axially tions and optimization of the design of a loaded piles is an important issue, since This analytical approach was implemented support structure for OWTs. Measured in- the capability of transferring skin friction in a newly developed calculation method situ data support the process of modelling. into the ground is highly dependent on the based on numerical simulations. In a first Algorithms for both, automated system level and the number of load cycles. Under calculation stage, the cyclic shear strains in identification with auto-regressive (AR) cyclic axial loads, degradation of ultimate the soil are determined. Dependent on the models (ARSYS) and for the automated skin friction and with that a decrease of the number of cycles, the volume contractions validation of numerical models (Vali-Tool) pile capacity is to be expected. for each element are calculated and applied have been developed and implemented in

Fig. 4 – (left): Reduction of skin friction under tensile loads for a test pile (D=2.50m, L=25.0m); - (right):Decrease of horizontal stress in the numerical model (N=10000) 26 SUPPORT STRUCTURES

Matlab. Measured data from an OWT with- Holistic Design Concept NREL 5MW Baseline Turbine was applied in the test site alpha ventus was used for For dimensioning and optimizing OWT a for the turbine model. The first part of the system identification. An advantage of the design framework called DeSiO (Design verification consisted of a modal analysis of identification method (AR-method) is the and Simulation Framework for Offshore the OWT. Secondly, several load cases were fact that frequencies can be taken directly Wind Turbines) is being developed within analyzed taking into account a rigid or flex- from analytical formulas rather than from GIGAWIND alpha ventus. Hereby, the re- ible rotor-nacelle-assembly (RNA) in com- discrete spectra (peak picking). Further- sults of the research done in the fields of bination with several wind and wave con- more only a smaller number of data points the design aspects like hydrodynamics, ditions [1]. Moreover, the environmental is needed. Here, the first four modes could wave loads, lifetime analysis, corrosion aspects like marine growth, buoyancy, and be identified using ARSYS. Consecutively protection, structural health monitoring, hydrodynamic added mass were considered. a numerical model was updated with these scour protection, soil modelling as well as identified values. One can choose between model validation using measurement data In 2011 it was achieved to link the single six different optimization algorithms are considered. Hence, DeSiO provides the tools, developed in the aforementioned within ValiToo, the behaviour of these al- user with a collection of interfaces in order work packages, to the holistic simulation en- gorithms has been analyzed during the last to control and to link different commercial vironment. This applies for the MBS-based year (Haake 2010). In 2011 identification and non-commercial simulation tools. software Adams (combined with FAST and and model validation with data from al- Aerodyn), and for the coupled simulation, pha ventus test site has continued, taking For a successful deployment of the structur- the FE-based program Poseidon with the construction data into account. Within this al finite element (FE) code within DeSiO, Flex5 (Version REpower), too. Thus holistic scope soil stiffnesses as well as dynamic the programs Poseidon and Waveload have simulations can be performed. Fig. 5 gives relevant water masses have turned out to been verified within the project Offshore an overview of DeSiO’s structure and the be suitable validation parameters. Code Comparison Collaboration Continu- coupling of its’ elements. To ensure an easy ation (OC4). During this project a refer- handling while evaluating or validating nu- ence support structure (tower and UpWind- merical results a validation module is being Jacket) was used. As a reference turbine the developed.

Fig. 5: Design and Simulation Framework for Offshore Wind Turbines (DeSiO) – overview of structure and implemented tools Annual Report 2011 27

References Patel, R., Achmus, M. Singh, B., Abdel-Rahman, K.: Abdel-Rahman, K.; Achmus, M.: DEM Simulations of Soil-Pile Inter- Behaviour of Foundation Piles for face under Static and Cyclic Loading, Offshore Wind Energy Plants under Particles 2011 – II Axial Cyclic Loading, International Conference on Simulia Customer Conference, Particle-based Methods – Barcelona/Spain, May 16th-19th (2011) Fundamentals and Applications, Abdel-Rahman, K.; Achmus, M.: Barcelona, October 26-28 (2011) Numerical Modeling of Tension Piles Rolfes, R., Häckell, M.W. & Haake, G.: under Axial Cyclic Loading, Automated System Identification and International Symposium on Validation of Numerical Models of Computational Geomechanics Offshore Wind Turbines as Basis for (ComGeo II), Dubrovnik/Croatia, SHM-Analysis, in Proceedings of the April 27th-29th (2011) 8th International Workshop on Cottin, N.: Structural Health Monitoring, Dynamic Model Updating – Stanford, CA, USA, pp. 2149–2156 A Multiparameter Eigenvalue (2011) Problem, Mechanical Systems and Stahlmann, A., Schlurmann, T.: Inves- Signal Processing, vol. 15, no. 4, pp. tigations on Scour at Tripod Founda- 649–665 (2001) tion Structures in the Haake, G.: German Offshore Test Site alpha ven- Systemidentifikation mit tus, Proceedings of the EWEA Autoregressiven Modellen und Offshore 2011 Conference, Amster- Validierung numerischer Struktur- dam, December30th (2011) modelle bei Offshore-Windenergie- Stahlmann, A., Schlurmann, T.: anlagen, Dissertation, Mitteilungen Erfassung und Analyse der Wechsel- des Instituts für Statik und Dynamik wirkungen von Strömungsprozessen der Leibniz Universität Hannover, ISSN und Kolkphänomenen an Offshore 1862-4650, Nr. 11/2010 (2010) Windenergieanlagen, Messen in der Hildebrandt, A.; Schlurmann, T.: Geotechnik 2010, Braunschweig, Pressure distribution of a breaking February (2010) wave on a circular cylinder surface Stahlmann, A., Schlurmann, T.: from laboratory experiments, Physical Modeling of Scours around Chinese-German Joint Symposium Tripod Foundation Structures for on Hydraulic and Ocean Engineering, Offshore Wind Energy Converters, Tianjin (2010) International Conference on Coastal Hildebrandt, A.: Engineering, Shanghai, July 5th (2010) Physical Modeling and CFD Simulation of Wave Slamming on Offshore Wind Turbine Structures, ANSYS Conference & 28. CADFEM user‘s meeting, Aachen, November 3rd-5th (2010) Hildebrandt, A; Stahlmann, A.; Schlur- mann, T. (2010): Dreibeinige Riesen – Wellenlast und Kolkuntersuchungen an Offshore Windanlagen, Maga- zinbeitrag in „eta green“, Ausgabe Februar Mai, T.; Wilms, M.; Hildebrandt, A.; Schlurmann, T. (2010): Comparison of Drag and Inertia Coefficients for a Circular Cylinder in Random Waves Project homepage: www.gigawind.de Derived from Different Methods, International Conference on Coastal Engineering, Shanghai, July 28 SUPPORT STRUCTURES

2011 GROWup – Grouted Joints for Offshore Wind Energy Converters under Reversal Axial Loadings and Upscaled Thicknesses

Leibniz University Hannover or eccentricities from the installation proc- structures. Within GROWup, the fatigue Institute for Steel Construction ess of the foundation piles can be compen- behaviour of large scaled tube-to-tube con- (project management) sated. Due to large water depths, different nections with large grout wall thicknesses Peter Schaumann, installation techniques for the foundation as well as influences of different grout-ma- Stephan Lochte-Holtgreven, Anne Bechtel piles have been developed (pre- or post- terials and early-age-cycling movements Institute of Building Materials Science piled), leading to an increased required will be investigated. Furthermore, pump- Ludger Lohaus, Nick Lindschulte, grout gap of the hybrid joint. Considering ing techniques of different grout materials Michael Werner an estimated life-time of 20 to 25 years, all under harsh offshore conditions will be components including the grouted joints examined. The combination of all aspects Industrial Partners: Fraunhofer IWES, have to be designed for high dynamic load- will lead to a holistic design. Project-Group Substructures, Hannover ings from wind and wave actions. Due Germanischer Lloyd Industrial Services to missing design guidelines for grouted Fatigue tests on axially loaded small- GmbH, Hamburg joints with large grout wall thicknesses, a and large scaled grouted joints RWE OLC, Hamburg reliable and economic design is difficult. Available design approaches for the ulti- REpower Systems, Osnabrück Influences of material specific installation mate limit state of axially loaded grouted Strabag Offshore GmbH, Stuttgart requirements are currently not considered joints are based on experimental results SIAG Engineering, Emden in current offshore guidelines. from the 1970’s and 80’s. Compared to Project funding: connections with grout wall thicknesses Federal Ministry for the Environment, up to 500 mm, background tests of the Nature Conservation and Nuclear Safety Project Description technical guidelines concentrated on (BMU) comparable small wall thickness and sig- The research project GROWup, which is nificantly smaller slenderness ratios. Ad- Project duration: funded by the German Federal Ministry ditionally, only a few number of fatigue 2011/06/01 – 2014/05/31 of the Environment, Nature Conservation tests on axially loaded grouted joints have and Nuclear Safety (BMU) (funding code: been performed in the past. Fig. 1 shows 0325290), focuses on the design and instal- the available fatigue test data for axially Introduction lation of grouted joints in lattice support loaded grouted joints. It can be seen that

Most of the German offshore wind farms (OWFs) in the North and Baltic Sea are located in water depths between 25 and 50 m. Compared to different European OWFs the water depth is quite high. Support structure solutions like Monopiles are mainly used for shallow waters. With increasing water depths lattice steel support structures like Tripod, Tripile or Jackets are favoured due to a reduced amount of steel, less installation weights, and also optimized loading conditions for deep waters.

Similar to Monopiles, the connection between foundation pile and lattice substructure is realized by the grouted joint. With Figure 1: Fatigue test results on axially loaded grouted joints this tube-to-tube connection, inclinations (Picture: Copyright GROW 0327585) Annual Report 2011 29

preliminary S-N-curves are based on ap- Furthermore existing small-scale test Due to the possibility of visual inspection proximately 30 tests at different loading methods and their limited ranges will be during the filling process, a transparent As a consequence of checked, refined or added to ensure the ap- shuttering skin will be realized on one side .(-1 ׃ regimes (R = 0 the rare number of test data, shown S-N- plication safety for this kind of grout plac- of the formwork by using acryl based ma- curves are actually not included in offshore ing technology. The reliable feasibility un- terials. Hereby a direct visible access to the guidelines for grouted joints. Furthermore, der offshore conditions will be of primary filling process in such geometries is given, no harmonised concept for the fatigue de- importance. In this research project the test contrary to real offshore projects. The ex- sign of axially loaded grouted joints exists. methods as a parallel control facility dur- pected fresh concrete pressure during the ing the grouting process can be checked pumping process and the lower load bear- Based on the results of the BMU-re- and calibrated at the large-scale filling tests ing capacity of acryl based materials in search projects GROWup (funding code: for the first time. comparison to wood have to be taken into 0327585) the BMU-research project account for the formwork construction. GROWup will investigate the axial fatigue The large-scale test facility (Fig. 2) for The transparent fields for visual access performance of grouted joints, as they can filling processes is based on a formwork should be as large as possible. In addition be found in jacket or tripod substructures. similar to wall casting procedures which is the “classic” formwork construction will The influence of different grout wall thick- able to represent significant geometries of be modified to include significant influenc- nesses and grout materials will be exam- grouted joints for Offshore Wind Energy es due to the offshore grouting process like ined in large scaled tests. Due to the fact Converters (OWEC) from today. The safe- variability of gap sizes, consideration of that offshore installation companies try to ty of application is mainly influenced by geometric imperfections, and contact be- reduce the grouting and curing time, the the flowability and setting behaviour of the haviour in the area of shear keys. After fill- influence of early age cycling movements material in critical areas like filling inlet ing process the whole formwork is able to and ongoing construction after a short cur- and possible discontinuities like shear keys be placed in a horizontal direction allowing ing time in the axial performance of the or constrictions in relation to the geometry an easy and safe demolding process. Dis- grouted joints will be investigated in small of the annular gap. tributed over the hardened grout wall body scale test specimen. Besides different grout an adequate number of specimens will be materials and grout ages, a self-developed Therefore a straight formwork without extracted and investigated. test-setup using an eccentric shaft will any circumferential curvature will be used simulate early age cycling movements. representing a segment of a whole grouted During the project the influences of the The ‘pre-damaged’ test specimen will be joint including typical load bearing ele- material properties like flowability, sta- loaded subsequently. ments like shear keys. Hereby the essential bility against segregation as well as time- influences for the filling procedure could dependant stiffening behaviour will be en- Pumping tests be engaged with a cost-efficient version in gaged, investigated and taken into account The manufacturing and casting procedure comparison to a real structure. as recommendations for grouting opera- for grouted joints offshore is also part of tions in OWEC. the research project GROWup and will be investigated in a separate working package (WP). Within this WP adapted procedures Summary as test methods will be developed to prove the usability of different grout materials. The BMU-research project GROWup fo- Later on the usability of grout materials cuses on the design and installation of should be established by involved certi- grouted joints with large grout wall thick- fier. A key aspect of the investigations is to ness in lattice support structures. The fi- visualize the filling process because there nancial support by the Federal Ministry for are practically no useable possibilities of the Environment, Nature Conservation as control or inspection on-site. A consistent well as the support by Fraunhofer IWES, basis to appraise the offshore-suitability Germanischer Lloyd, REpower Systems, of planned materials will be provided by RWE-OLC, SIAG, and Strabag Offshore this test program including realistic fill- are kindly acknowledged. ing tests. In a large-scale level of approx. 1:1 the essential parameters as e.g. mixing technique, placing technology, construction, compression, time, flowability, and Figure 2: Large-scale pump-test facility stability against segregation will be con- for realistic filling processes sidered. 30 SUPPORT STRUCTURES

Cyclic Performance of Horizontally Loaded Piles for 2011 korr 2 Offshore Wind Energy Converters in Layered Subsoil

Leibniz Universität Hannover, For cyclic one-way loading and drained In the present studies different combina- Institute for Geotechnical Engineering, conditions the SDM allows the evaluation tions of non-cohesive subsoil of two lay- Martin Achmus, Johannes Albiker of the pile deformation behavior under ers were regarded, one layer composed consideration of the site specific soil condi- of very dense and the other one of loose tions as well as the loading conditions and sand with friction angles of 42° and 32.5°, Introduction the number of cycles. In the present study, respectively. The transition between the the method is applied to numerically iden- two layers was chosen firstly at the upper The monopile is an often used foundation tify the effects of subsoil conditions on the third and secondly in the middle of the type for offshore wind energy converters, performance. In this context, pile deforma- embedded pile length. For both cases two which are planned to be built in a vast tion accumulation curves are examined and simulations were driven, one with the very number in the coming years. A monopile compared to each other quantitatively and dense sand overlaying the loose sand and consists of a single open steel pipe pile of qualitatively, and values for the empirical the other one in the reverse collocation. In large diameter up to several meters which is parameters mentioned above are firstly all simulations the same absolute load of driven into the seabed. The loading condi- derived. H = 760 kN was applied. tions for these structures differ from usual offshore structures. Due to that, a consid- In Fig. 1 the results are shown, in terms of eration of cyclic load effects is extremely Project Description the deflection accumulation lines. In the important. Up to now, the possibilities to graphs additionally the envelope lines are address these problems for monopiles are The generated model has been used in a first integrated, which represent the pile behav- limited. Some approaches exist for apply- step for an investigation of the pile deforma- ior in loose and very dense homogeneous ing numerical schemes or alternatively for tion behavior in homogeneous non cohesive subsoil under the same load. The curves using empirical equations to predict the soils of different stiffnesses. The friction representing the simulations with a layer accumulation of pile deflections with the angles were chosen to φ = 42°, 37.5°, 35° division at the upper third of the embed- number of load cycles. and 32.5°, respectively, and the stiffness ded pile length lie approximately centrally parameters were adjusted accordingly by between the two envelopes. This observa- A numerical scheme termed Stiffness comparative static calculations with the p- tion first of all plausibilizes the results in Degradation Method (SDM) has been de- y-method described in API (2000). κ was a certain manner, as a curve progression veloped at the authors’ institute. Here, a assigned values between 675 for φ = 42° outside the envelopes would be somewhat numerical simulation is combined with the and 475 for φ = 32.5°, and λ between 0.5 illogical. From the resemblance of the ac- results of cyclic triaxial tests. A 3-D finite and 0.6, respectively. The calibration pro- cumulation lines it can be derived that nei- element model is used to calculate the pile cedure was carried out with flexible small ther the thinner upper layer nor the thicker deformation behavior. The soil behavior diameter piles, for which the p-y-method is lower layer per se has a predominant in- is modeled by an elastoplastic material generally believed to give reliable results. fluence on the deformation accumulation law with Mohr-Coulomb failure criterion. behavior. When making a layer division The stiffness modulus of the soil is defined Regarding the application field of offshore in the middle of the embedded pile length, stress dependent after Ohde (1939), intro- wind energy converters in Germany, the however, the curves in both cases lie close ducing two stiffness parameters κ and λ. southern part of the North Sea is the prin- to that envelope curve that represents the For describing the cyclic deformation be- cipal area to be considered. Here the sub- subsoil conditions of the respective upper havior of the soil in element tests (cyclic soil is generally composed of non cohesive layer. It appears obvious that when making triaxial tests) an exponential approach after layers of different density characteristics. the layer division at 1/2L, the characteris- Huurman (1996) is used, which describes Hence, it is an interesting task to investi- tics of the upper layer have a predominant the increase of plastic strain in dependency gate how the cyclic performance of piles influence on the pile deformation behavior. of two soil density dependent parameters in layered non cohesive subsoil correlates In the above area the stiffness degradation is more pronounced, as here the cyclic (b1 and b2) and the load level. For a more or disagrees with the performance of piles detailed description of the method refer to embedded in homogeneous subsoil. stress is higher with respect to the stress at Achmus et al. (2008) & Kuo (2008). failure and thus the cyclic loading of the soil elements is higher. Annual Report 2011 31

Summary

The cyclic deflection accumulation behavior of a stiff pile embedded in sand, which is exposed different loading and soil density conditions, has been evaluated. Firstly, based on the results of a series of model tests and under the application of a scaling law, a numerical model was developed and validated. In the following, simulations in homogeneous and in layered subsoil were carried out.

Different cases of subsoil composed of two non cohesive layers of differing soil stiffness were evaluated. It was found that the stiffness properties of the above laying soil in the vicinity to the mudline have a predominant influence on the pile deformation and accumulation behavior due to the higher cyclic loading and thus a higher stiffness degradation of the soil elements. For flexible piles this should be even more obvious, because in this case in the lower section only very low stresses are acting on the pile. Investigating the behavior of cyclic horizontally loaded flexible piles, among others, will be a task for future research on the considered topic.

Figure 1: Accumulation of the pile head deflections for simulations with layered subsoil, layer division at the upper third (above) and at the middle (below) of the embedded pile length

References API. Recommended Practice for Planning, Kuo, Y.S.: On the behavior of large- Designing and Constructing Fixed Off- diameter piles under cyclic lateral Achmus, M.; Albiker, J. (2012). Cyclic shore Platforms-Working Stress Design. load. Mitteilungen des Instituts für performance of horizontally loaded American Petroleum Institute, RP 2A-WSD Grundbau, Bodenmechanik und piles in layered subsoil. (2000) Energiewasserbau, 12th Baltic Sea Geotechnical Huurman M.: Development of traffic Universität Hannover, Heft 65 (2008) Conference, 31.05.-02.06.2012 (paper induced permanent strain in concrete Ohde, J.: Zur Theorie der Druckvertei- submitted & accepted). block pavements, Heron, Vol. 41, No. 1, lung im Baugrund. Der Bauingenieur, Achmus, M.; Kuo, Y.-S.; pp.29-52 (1996) Vol. 20, S. 451-459 (1939) Abdel-Rahman, K: Zur Bemessung von Monopiles für zyklische Lasten. Bauingenieur, Bd. 83, Heft 7-8 (2008) 32 SUPPORT STRUCTURES

2011 OPTIWELD – Ecological and Economical High Performance Joining Techniques for Tubular Steel Towers of Wind Energy Converters

Leibniz University Hannover Introduction Project Description Institute for Steel Construction Peter Schaumann, Mareike Collmann Rated power and dimensions of wind ener- In particular, submerged arc welding Partners: gy converters have increased significantly (SAW) is suited very well to manufacture Leibniz University Hannover, Institute of during the last few years. In consequence, large components with large cross sections Materials Science the requirements on tower constructions and long welds. Thus, SAW has been es- SIAG Tube & Tower GmbH also grow following the development of tablished to weld longitudinal and circum- Kjellberg Finsterwalde Schweißtechnik larger and heavier turbines. Beside pre- ferential welds of wind towers. This proc- und Verschleißschutzsysteme GmbH stressed concrete towers, tubular steel tow- ess is characterised by an invisible burning Funded by the German Federal Ministry ers are usually chosen as support structures electric arc which is covered by a layer of of the Environment, Nature Conservation for onshore wind turbines. For this type granular flux. During the process some of and Nuclear Safety (BMU) of tower, the structural design is mainly the granular flux melts. This slag cover provides a protection from attack by the atmos- Duration: 07.2009 – 06.2012 driven by the ultimate and fatigue limit state and leads to large dimensions and phere and forms smooth weld transitions at thicknesses. In addition, the transport limi- the same time. Single or multiple electrode tation of 4.30 m in diameter for towers of wire variations exist for further increasing onshore wind turbines creates the need for the efficiency of the process. When manu- higher plate thicknesses in the lower steel facturing a wind turbine tower, the first step sections. For manufacturers the capacity is to form the sheets into a circular cross sec- of welding efficiently and economically is tion by the way of rolling. Afterwards, the reached. Therefore, developing alternative endings are joined by longitudinal welds. welding technologies are of growing inter- These separate sections are then connected est and objective of current research work. by circumferential welds to form a single tower segment which can reach a length of 12 up to 35 m. With increasing dimensions and plate thicknesses each stage takes more time and quality assurance is made increasingly difficult.

Figure 1: Stages of the manufacturing process at the tower manufacturer SIAG Tube & Tower GmbH Annual Report 2011 33

Figure 2: Comparison of weld form, welding sequence and number of passes

By combining arc welding and beam weld- arc welding is the prevailing welding tech- Summary ing procedures the performance of welding nique for tubular steel towers and was de- can be increased significantly. Within the fined and documented as base for the final The increasing demand of large compo- here described project the first time combi- comparison. The second part of investiga- nents in the steel working industry, espe- nation of submerged arc and plasma beam tions concentrates on the evaluation of the cially the offshore industry, shows the need welding carried out as keyhole process is weld seams. Because after all, the connec- for high performance and faster welding investigated. Like laser beams, plasma tions, which are carried out with the newly techniques. This is also true for the here- beams provide the deep-weld effect. High developed procedures, must fulfill the in described tower manufacturing where quality and fast welding is possible when normative regulations in terms of ultimate plate thicknesses increase with increasing combining the positive attributes of SAW and fatigue strength. To support this evalu- wind turbine height and power output. At and plasma beam welding: Plasma beam ation process metallurgical investigations, first, the requirements for newly developed welding offers the possibility for fast weld- tensile and fatigue tests are done. Further- welding procedures have been emphasized ing of high thicknesses within one pass, more, the potential of numerical welding on by using the example of wind tower whereas SAW protected the weld seam simulation can be shown to enhance the production. For now, the development and against atmospheric influences, adds filler significance of welding tests especially modification of the welding techniques material and provides a smooth seam ap- concerning the heat management during NVEBW and plasma beam welding in pearance for a good fatigue performance. welding. combination with SAW has been finished Until now, the performance of the newly and reproducible welding results are pos- installed combined welding technique is sible. The investigations of the mechanical reliable for plate thicknesses up to 20 mm. qualities are not finished completely. Thus, this combination delivers a com- petitive solution for heavy and large steel structures. Furthermore, the potential of Non Vacuum Electron Beam Welding References [3]Deißer, T. A.; Priebe, S.; (NVEBW) as another beam welding tech- Schaumann, P.; Mickley, M.; [1] Hinneberg, D.; Eisenstein, B.; Hassel, T.; Konya, R.; Bach, F.-W.: nique has been investigated for the appli- Panoch, A.: Verfahrenstechnische Herausforde- cation on large steel structures with high European patent application rungen beim Fügen dicker Bleche mit plate thicknesses. At the moment the maxi- EP 1 570 939 A1 – Unterpulver- dem Elektronenstrahl an Atmosphäre mum reachable plate thickness is 30 mm Schweißverfahren. Applicant: und einem Plasma-UP-Hybridverfahren, in combination with SAW. In the course Howaldtswerke-Deutsche Werft, Schweißen im Schiff- und Ingenieurbau of investigations, preheating emerged as (2005) 2011, DVS-Berichte 277, to be suitable to avoid welding defects like [2] Schaumann, P.; Mickley, M.; ISBN 3-87155-269-0, pp. 13-18, cracking and pores. Priebe, S.; Deißer, T. A.; Hassel, T.; Hamburg (2011) Bach, F.-W.: The research activities are divided into Challenges in joining thick metal two parts: First of all, the development and sheets for tubular steel towers of wind energy converters, Proceedings modification of the welding techniques of the Eurosteel 2011, ISBN 978-92- NVEBW and plasma beam welding were 9147-103-4, pp. 531-536, Budapest, in the focus of research to get reproducible (2011) welded joints of high quality. Submerged 34 SUPPORT STRUCTURES

NaStafEE – Sustainability of Steel Structures of Renewable Power Plants

Leibniz Universität Hannover Method (BREEAM) facilitate to evaluate Existing rating systems for buildings as the Institute for Steel Construction and to certify buildings according to sus- German Assessment System for Sustainable (project management) tainable quality. Building (BNB 2010) and the rating system Peter Schaumann, Anne Bechtel of the German Sustainable Building Coun- Ruhr-Universität Bochum In the past cost effectiveness and construc- cil (DGNB) built the starting point estab- Energy Systems and Energy Economics tional aspects of the structure have been lishing a sustainable rating system for steel Hermann-Josef Wagner, the design drivers for new constructions. constructions of renewable. Christoph Baack, Jessica Lohmann Increasing importance of environmental Universität Duisburg-Essen friendly products and the reduction of CO2- The rating system of the BNB consists Department for Steel Construction emissions have an impact to the develop- of the six categories of sustainability: en- Natalie Stranghöner, Jörn Berg ment of holistic design concepts in all in- vironment, economy, sociocultural and dustries. Especially the renewable section functional criteria, technical aspect, proc- Project Funding: producing ‘green’ energy is presupposed to ess criteria, and local effects. Each of these Federal Ministry of Economics and Technology (BMWI), follow sustainable concepts. categories is defined by a certain number of German Federation of Industrial Research criteria and indicators reflecting the impact Associations (AIF), Owing to missing systems for constructions of the building and the used materials. The The Research Association for Steel apart from buildings, the research project final rating results from weighted catego- Application (FOSTA), ‘Sustainability of steel structures of renewa- ries and additionally weighted criteria and German Comittee for Steel Constructions ble power plants’ (NaStafEE) contributes to indicators. To reach a holistic rating the (DASt) establish a rating system for steel construc- whole life cycle of the building including Project duration: tions for renewable energy systems. the building products, has to be taken into 2010/05/01 – 2012/10/31 account, driven by the idea “from cradle- to-grave”. The rating systems by BNB and Project Description DGNB provide the basis for the new rating Introduction system for steel constructions of renewa- Motivated by recent market forecasts and bles which additionally includes indicators Sustainability, the concept of fulfilling the the potential for development for renewable reflecting the special impact of steel struc- need of present people without compro- energy, carefully selected renewable con- ture of renewables. mising the ability of future generations to structions are analyzed within the research satisfy their needs, was defined in the late project NaStafEE, funded by the German Based on a detailed research, indicators 80’s by the Brundtland report. During that federal ministry of economics via the AIF describing the sustainability for steel con- time the goal was to enable poor people (funding code: 16599). Recent forecast e.g. structions of renewables were composed meeting their basic needs for life and cre- the German Reference Scenario 2009 raised and analysed regarding their applicability ate an intergenerational justice. Due to the by the German Federal Ministry for the En- to steel structures. The impact to the envi- ongoing change of the world climate, the vironment, Nature Conservation and Nu- ronment is commonly reflected by the life task of fulfilling sustainable criteria gains clear Safety shows the expected growth of cycle assessment (LCA) method conform- importance regarding effects of products to single renewables and the resulting essential able to DIN EN ISO 14040. This method environment and society. Beside the general expansion. Especially the wind energy mar- was used in studies to show the environ- consumption industry the building industry, ket and the energy biomass utilisation will mental impact of Offshore Wind Turbine displaying a great sector, has to be on the mainly contribute to the regenerative elec- (OWT) substructures. pursuit of sustainable goals. tric power within the future. A first analysis of these data compared with the steel mass As shown by Wagner et al. [2] one of the With regard to the design of buildings in Eu- needed for each steel structure lead to a decisive components of OWT regarding rope sustainability aspects are already taken significant market and growth potential for ecological sustainability criteria is the into account. Established rating systems steel products regarding renewable sector substructure consisting of driven piles and such as the German Sustainable Building for Germany [1]. connecting structure e.g. Jacket or Tripod. Council (DGNB) or the British Research Depending on the type of substructure and Establishment Environmental Assessment the pile length this substructure requires Annual Report 2011 35

up to five-times more steel than the tower. flecting the company costs that arise dur- Summary Hence, for a first comparison of results ing development and manufacturing the the focus was set to the substructure of structures. Complementary to the eco- Within the research project NaStafEE a rat- OWT. Lattice substructures like Jacket and nomical and ecological aspects the social ing system for evaluating the sustainable Tripod (Fig. 1) were analyzed by a LCA, effect reflects the third decisive parameter of steel structures for renewable is under including the common indicators as e.g. regarding sustainability. The social impact development. First analysis of the market the global warming potential and the cu- encompasses the effect of the manufacture growth and future potential was conducted mulative energy demand [3]. The results of and work environment to the worker. Re- reflecting the increasing steel demand. Be- these investigations showed that the con- garding the mounting and erection of steel sides first generated criteria and indicators struction phase is decisive for the environ- structures the occupational safety plays for the five sustainability categories a life mental impact. Comparison of the results an important factor. This category evalu- cycle assessment of the substructure types for Jacket and Tripod revealed that the ates the safety precaution including safety Tripod and Jacket showed the environ- ecological values for the Tripod are higher training of the staff. Beside the social in- mental impact of these structures. Further than for the Jacket. This results from the dicators reflecting the effect to the worker, investigations will concentrate on the de- higher amount of steel needed for the Tri- the general social orientation of the com- velopment of additional criteria and trans- pod structure. pany can be taken into account. The unit to ferring the rating system to steel structure measure the social impact is presented by of renewable to verify the applicability. The economical effect of steel structures qualitative statements. Further indicators for renewable is commonly presented by in the category process and technique were the financial costs originating from mate- developed. Future investigations concen- rial and production costs including erec- trate on complementing the assessment by tion and maintenance. Beside the life cycle additional quantified indicators for sustain- costs additional indicators representing able elements. economical effects were developed re-

References

[1] Schaumann, P.; Bechtel, A.; Wagner, H.-J.; Baack, C.; Lohmann, J.; Stranghöner, N.; Berg, J.: Sustainability of steel constructions for renewables. Stahlbau. 10/2011: p.711-719, Ernst & Sohn Verlag, Berlin, Germany (in German). [2] Wagner, H.-J. et al.: Life Cycle Assessment of the offshore wind farm alpha ventus, Münster LIT-Verlag 2010 (in German) [3] Schaumann, P.; Bechtel, A.; Wagner, H.-J.; Baack, C.; Lohmann, J.; Stranghöner, N.; Berg, J.: Indicators for Environmental and Social Assessment of Steel Support Structures for Offshore Wind Turbines, Proceedings of the EWEA Offshore 2011, 29th November – 1st December 2011, Amsterdam, The Netherlands. Figure 1: Offshore Wind Turbine with Jacket (left) and Tripod (right) substructure 36 SUPPORT STRUCTURES

2011 Design, Testing, Realisation and Verification of Low Noise Construction Methods and Noise Reduction Techniques During Construction of Offshore Wind Turbines ("Schall 3")

Leibniz Universität Hannover, underwater sound measurements, as well ples are the optimisation of the impulse Institute of Structural Analysis, as for standardisation and evaluation of pile driving parameters by lengthening Raimund Rolfes, Malgorzata Neuber, measurements, e.g. [1] and [2]. Moreover the stroke or the use of vibration pile driv- Jörg Rustemeier, Tanja Grießmann two different types of the noise mitigation ers. Secondary concepts reduce the noise Partners: concept “bubble curtain” could be tested during sound propagation. Here acoustic German Wind Energy Institute (DEWI), successfully. Especially a large bubble enclosures and air bubble curtains are the Wilhelmshaven, curtain applied under the construction of main research objectives. Institute of Technical and Applied Physics the FINO3-monopile reduced underwater (itap), Oldenburg sound immission considerably in all direc- Within the project Schall 3 noise reduction tions [3]. techniques have being investigated by the Funded by the Federal Ministry for the use of computational simulations, small Environment, Nature Conservation and Nuclear Safety (BMU) scale experimental tests in laboratory and Project description tests in different facilities. Duration: 12.2007 – 08.2011 Noise mitigation concepts can be divided In order to gain deeper understanding of into two main groups: primary and second- the physical processes in bubble curtains Introduction ary concepts. Primary concepts influence experiments in a tank and in a lake have or reduce the noise at the source. Exam- successfully been conducted. Furthermore The installation of wind turbines is accompanied by the emission of underwater noise into the marine environment. Especially during pile driving activities, which are in most cases necessary to fix offshore foundations to the seabed, the maximum toler- able sound pressure levels defined by the German Umweltbundesamt (UBA) are potentially exceeded. Due to possible stress reactions, impacts on hearing capabilities, communication and orientation, sound levels from pile driving represent a potential danger to marine life. At present there are no noise mitigation concepts which are at the same time physically efficient, easy to handle during offshore activities on the construction site and where the process will be cost-efficient. For this reason the research in the field of hydro sound reduction is a vital challenge, and providing that the development of offshore wind energy is compatible with the protection of nature. Since 2000 a straight line of research projects of the partners ISD/DEWI/itap has improved knowledge in the field of Figure 1: Small Towing Tank of the Hamburg Ship Model Basin (Source: ISD) Annual Report 2011 37

underwater sound measurements at test site alpha ventus due to vibration piling have been evaluated.

Within the scope of low noise construction methods a new drilling method “Her- renknecht Vertical Shaft Machine” has been successfully tested in the city of Neapel.

Summary

The Institute of Structural Analysis has performed calculations based on a numerical model to simulate the interaction of piling hammer, pile and both the adjacent soil and the water body during pile driving procedure. Based on that coupled model the sound propagation in the water can be calculated. As a second step the optimisation of the impulse pile driving parameters can Figure 2: Test location of Atlas Elektronik in Bremen (Source: ISD) be performed. Main focus is on the identification of suitable middle sections with ideal stiffness and damping parameters leading to an extension of the pulse duration and thus to reduced noise emissions. The results Hamburg Ship Model Basin (Fig. 1). More fully extrapolating the results from the lake show a possible reduction of 5 to 7 dB in experiments with different tube systems to offshore applications like FINO3 a re- the near range for middle sections with a filled with compressed air of varying pres- duction of more than 5 dB for the Sound low elasticity modulus at high compression sures and subjected to CW-signals have Exposure Level (SEL) might be possible. strength. been conducted in a test location of Atlas Elektronik in Bremen (Fig. 2). The tests All results – including a detailed discus- Tests with bubble curtains have been per- have shown promising results for nozzle sion – will be published in 2012. formed in the small towing tank of the tubes coated with a diaphragm. By care-

References [2]Elmer, K.-H.; Betke, K.; Neumann, T.: [3] Grießmann, T.; Rustemeier, J.; Standardverfahren zur Betke, K.; Gabriel, J.; Neumann, T.; [1] CRI/DEWI/ITAP: Ermittlung und Bewertung der Belastung Nehls, G.; Brandt, M.; Diederichs, A.; Standardverfahren zur Ermittlung und der Meeresumwelt durch die Schallimmis- Bachmann, J.: Bewertung der Belastung der sion von Offshore-Windenergieanlagen. Erforschung und Anwendung von Meeresumwelt durch die Abschlussbericht zum BMU-Projekt Schallminimierungsmaßnahmen beim Schallimmission von Offshore- „Schall II“ (FKZ 0329947). Rammen des FINO3- Monopiles. Windenergieanlagen (Schall-1). Final Bundesministerium für Umwelt, Natur- Final report of the research project report for project No. 0327528A, schutz und Reaktorsicherheit, "Erforschung und Anwendung von funded by the Federal Ministry for the Berlin (2007) Schallminimierungsmaßnahmen beim Environment, Nature Conservation and Rammen des FINO3-Monopiles – Schall Nuclear Safety (2004) FINO3", No. 0325023A and 0325077, funded by the Federal Ministry for the Environ-ment, Nature Conservation and Nuclear Safety (2010) 38 SUPPORT STRUCTURES 2011 HyproWind: Realistic Underwater Sound Scenarios Based on Forecast Modeling and Monitoring Regarding Piling Noise During Wind Farm Construction in the German North Sea

Leibniz Universität Hannover; reliable forecast model available to give an terize the pile while driven into the sea Institute of Structural Analysis, answer to the questions mentioned above. bed. As pile and sea bed properties vary Raimund Rolfes, Moritz Fricke, Furthermore there is the need for a uniform depending on the construction project, Tanja Grießmann mapping of the expected underwater noise the finite elements model is developed as immissions to allow for the ecological a multi-dimensional parametric sweep as Partners: evaluation during the approval procedure shown in fig. 1. In addition, the parametric German Wind Energy Institute, of construction activities. approach will give a better understanding Wilhemshaven German Federal Maritime and of sound radiation from the pile and the Hydrographic Agency, Hamburg To this end a cooperation project between role of the penetrated soil. the Institute of Structural Analysis (ISD), Duration the German Wind Energy Institute (DEWI) Having a look to the spatial coverage of 09/2010 - 08/2013 as well as the German Federal Maritime piling noise of up to 100 km, it becomes and Hydrographic Agency (BSH) was es- clear that the finite element method reach- tablished. The project deals with the imple- es its functional limit. On this account the Introduction mentation of a forecast tool for underwater dimension of the finite elements model noise immissions due to pile driving in the is limited to a range of about 100 m. The The construction of offshore wind energy German North Sea and the preparation of calculation of long-range sound propaga- converters and voltage transformer plat- uniform noise maps. tion is accomplished using the MMPE- forms often requires the operation of high- Algorithm (Monterey-Miami Parabolic energy pile driving equipment to mount the Equations) which is capable for range-de- support structure at the sea bed. Today it is Project Description pendent transmission loss calculations in well known that underwater sound caused shallow water [5]. by piling activities can seriously affect the Hydro-acoustic Modelling behaviour and physical health of marine As a central part of the project a hydro- Considering the coupling between FEM mammals. In order to minimize negative acoustic model is implemented using a hy- and PE calculation two different approach- effects on the marine environment due to brid approach based on the finite elements es will be investigated. The first approach construction noise of projected offshore method (FEM) and parabolic equations matches the accumulated acoustic energy wind energy converters it is necessary to (PE). Finite elements are used to charac- which propagates through a convex hull have a realistic forecast of the expected underwater sound exposures.

There have been several research projects attending to underwater piling noise in the past ([1], [2]). During these projects single offshore construction projects like the erection of alpha ventus were investigated with respect to underwater noise. The main attention was paid to acoustic measurements and their consistent evaluation using the values Leq, SEL and Lpeak. Considering the large number of expected piling activities in the German North Sea it will be indispensible to look at cumula- tive effects as well as occasionally over-

lapping noise emissions to evaluate the ecological relevance. Currently there is no Figure 1: Parametric model for the pile and penetrated soil Annual Report 2011 39

surrounding the construction site during a single hammer blow (see fig. 2). Therefore the hull is located in the overlap region between FE and PE model. As a second approach the acoustic pressure and particle velocity fields in the overlap region are considered to coincide between the two models. Thus, the second approach even implies the energy match as a mandatory condition.

Noise-Mapping The results of the calculations explained Figure 2: Coupling between FE and PE calculations based on energy matching above are of the so called Nx2D-type, i.e. a calculation for a single construction site generates a set of N vertical slices in radial direction. In order to give a better under- standability of the results, a uniform representation is developed during the project. Therefore the calculation results are re-ar- ranged from the vertical slices to horizontal layers for different water depths. As can be seen from fig. 3 the values Leq and SEL are then displayed in so called noise maps which are already established in the context of noise evaluation in urban planning.

Long-Term Measurements The third part of the project is formed by the installation and operation of long-term measurement stations in the North Sea. One system located at the research platform FINO1 is already running, a second system will be installed at FINO3. These systems are used for a permanent recording of the acoustic pressure level. A third, self- sustaining system based on a moored buoy will be used for measurements at tempo- rary hot spots of piling noise.

Figure 3: Exemplary representation of forecast results for a single construction site

References [3] Elmer, K.-H.; Betke, K.; Neumann, T. [5] K. B. Smith, Convergence, stability, (2007). Standardverfahren zur Ermittlung and variability of shallow water acoustic [1] DEWI/CRI/itap (2004). und Bewertung der Belastung der predictions using a split-step Fourier Standardverfahren zur Ermittlung und Meeresumwelt durch die Schallimmission parabolic equation model, Journal of Bewertung der Belastung der Meeres- von Offshore-Windenergieanlagen Computational Acoustics, Bd. 9, Nr. 1, umwelt durch die Schallimmission [4]– „Schall II“. Abschlussbericht zum pp. 243–286 (2001) von Offshore-Windenergieanlagen Forschungsvorhaben FKZ 0327528A des [2]– „Schall I“. Abschlussbericht zum Bundesministeriums für Umwelt, Natur- Forschungsvorhaben FKZ 0327528 A schutz und Reaktorsicherheit. Mitteilungen des Bundesministeriums für Umwelt, des Instituts für Statik und Dynamik der Naturschutz und Reaktorsicherheit Leibniz Universität Hannover, Nr. 08/2007 Figure 1: Parametric model for the pile and penetrated soil 40 WIND POWER SYSTEMS

»Baltic I«: Control of Offshore Wind Farms by Local Wind Power Prediction as Well as by Power and Load Monitoring

Carl von Ossietzky Universität Oldenburg, gration and operational management. Fur- One focus is the flow around the wind tur- Institute of Physics, Wind Energy Systems thermore it is planned to prepare the main bines and the interaction of the atmospheric (project-coordination), research results for integration in commer- boundary layer with the turbulence created Energy Meteorology, TWiSt cial wind farm management systems. by the wind turbines within the wind farm. Lüder von Bremen, Actuator discs or an actuator line approach Martin Dörenkämper, Constantin Junk, describe the wind turbines in the model. Martin Kühn, Jan Riepe, Philip Rinn, Project description Different thermal stratifications and their Gerald Steinfeld, Jens Tambke, Juan José Trujillo, Matthias Wächter influence on the wind turbine wakes will Power output monitoring be investigated. Data from a measurement Partners: The evaluation of wind farm performance campaign within the wind farm will serve EnBW Erneuerbare Energien, relies on measurements and simulations of as realistic inflow conditions to model the Endowed Chair of Wind Energy the wind characteristics. A VAD-Lidar is thermal stratification of the boundary layer This project is funded by the German used for vertical wind profile investigations with high accuracy. In this way, a deep in- Federal Ministry for the Environment, close to the wind farm. This is supplement- sight into the structure of the marine bound- Nature Conservation and Nuclear Safety ed by a Long-Range-Lidar which allows for ary layer at the wind farm and its influence (BMU) on the basis of a resolution of studying any desired measurement plane on wind turbine wakes is given. the German Bundestag under the code and wakes inside the wind farm. Both meas- number 0325215A. The BMU and Project urement-devices are set up on the substation The dynamic power characteristic of the Management Jülich are thanked for pro- in the north-west of the wind farm. turbines is derived by stochastic response viding data from the FINO project. analysis of wind and power measurement Duration: 03.2011 – 05.2014 The heterogeneous marine atmospheric data. In this task one challenge is to derive boundary layer above the Baltic Sea is in- the dynamic power characteristics from fluenced by a combination of the special nacelle anemometer wind measurements, Introduction meteorological marine effects and – due to which unavoidably are disturbed by the ro- the near shoreline – the onshore wind condi- tor. Also, as the wind passes the rotor be- In May 2011 the first commercial off- tions blowing towards the wind farm. This fore it is recognized by the anemometer, shore wind farm in the German Baltic Sea, marine boundary layer will be analyzed with the temporal connection between driving “EnBW Baltic 1”, started operation. Its 21 the Large Eddy Simulation model PALM. and response is affected. Both properties wind turbines are situated about 13 km off the coast as shown in figure 1 and are capable of supplying up to 50,000 homes with electricity at a maximum power of 48.3 Megawatts. The operator and owner of the wind farm, EnBW Erneuerbare Energien, the Endowed Chair of Wind Energy Stutt- gart and ForWind – University of Old- enburg conduct the joint research project »Baltic I« to expand experience in offshore wind farms of commercial dimensions. At ForWind the research groups Energy Mete- orology, TWiSt and Wind Energy Systems are involved in the project. Major research findings shall highlight opportunities for improvement in energy yield, operational costs and revenues due to energy feed-in regarding aspects of power and load monitoring, wind power prediction, grid inte- Figure 1: Location and layout of the wind farm “EnBW Baltic 1” Annual Report 2011 41

of nacelle wind measurements have turned Wind power prediction and grid Decision model for operational out to implicate non-trivial effects. Using integration management data from other wind farms, a procedure Figure 2 shows a time series of 102 m wind A decision model which permits to operate has been developed to handle this type of speed measured at FINO 2 which is near the a commercial wind farm under economic data. As soon as measurements are avail- location of the wind farm. This example il- and safety aspects will be developed. The able inside the project, the new procedure lustrates the very high wind energy potential model shall assess costs and revenues from will be evaluated and adapted to the wind in the Baltic Sea and that daily wind power the forecasted wind power for different feed- farm “EnBW Baltic 1”. The power output fluctuations are very high. To integrate large in conditions like allowance, electricity stock of the single turbines will be systematically amounts of wind energy into the power sys- exchange or direct marketing. Furthermore it compared and a monitoring strategy will be tem, it is necessary to predict wind power shall consider the demand for balance energy developed. for the intra-day and day-ahead forecast ho- and examine whether an involved reduction rizon as accurate as possible and to estimate of farm power and allowance could still be Load monitoring the uncertainties for each wind power pre- a profitable technique under certain weather Commonly, load monitoring is based on diction (WPP). conditions. As conditions and loading of sin- expensive measurements applying sensitive gle wind turbines play an important role for instruments to wind turbine components. During the last years weather services such operating and maintenance costs, these might Thus, in most cases this method is only de- as the European Center for Medium-Range become relevant factors for operational man- ployed to validate design loads during tem- Weather (ECMWF) established Ensemble agement strategies, too. The decision model poral measurement campaigns at prototype Prediction Systems (EPS) that allow for can potentially integrate findings from the wind turbines. probabilistic wind power forecasts. The us- research project »Baltic I« directly. age of ECMWF’s EPS wind speeds in dif- Knowledge of occurring loads on wind tur- ferent model heights at the offshore wind bines in commercial operation is enormous- farm will not only decrease forecast errors Summary ly valuable as it allows to estimate wearing compared to forecasts based on determin- and the detection of potential sources of istic model output, but will also improve The joint research project »Baltic I« aims defects. This information helps to improve the prediction of forecast uncertainties (e.g. at an economically optimized operation strategies in operation and maintenance, confidence intervals for different forecast of large offshore wind farms by enhance- which play a significant role in offshore horizons). Moreover probabilistic wind ment of local power prediction and moni- projects subjected to difficult accessibility power forecast systems developed and toring of power and loads. By these means and high costs for logistics. evaluated within this work package will be of monitoring, a more economic and safe very important for the prediction of extreme operation of individual wind turbines shall One approach for a continuous load moni- weather events which can lead to wind farm be achieved. The main research results are toring system without additional sensor cut-offs. Another task will be the optimi- going to be prepared for integration in com- technology is to access signals determined zation of the WPP either by the combina- mercial wind farm management systems. In routinely by the wind turbine system for tion of ECMWF’s ensemble forecast with particular the project »Baltic I« accounts for control purposes although these standard ECMWF’s deterministic forecast or by the minimizing the risks in revenue for offshore signals are not directly related to loads. It combination of forecasts from different farms operating in the specific meteorologi- has been demonstrated for single onshore weather prediction services. cal conditions of the Baltic Sea. wind turbines that loads on wind turbine components can be correlated to a combination of standard signals such as power production, rotational speed, pitch angle, tower top acceleration and others via methods applying neural networks. These methods use statistical parameters of standard signals during operation to estimate damage equivalent loads and load spectra. The task will enhance the methods for turbines inside offshore wind farms and hence will contribute to an optimization of operation and maintenance management.

Figure 2: 102 m wind speed measurement at FINO 2 in the Baltic Sea in 2011 42 WIND POWER SYSTEMS

RAVE-OWEA "Verification of Offshore Wind Turbines"

Carl von Ossietzky Universität Oldenburg, non-intensive engineering models that de- fluxes, which are key properties for the de- Institute of Physics, scribe the vertical structure of the atmos- scription of the environmental conditions Martin Kühn, Joachim Peinke, pheric boundary layer have been developed in that a WT has to operate. Detlev Heinemann, Nadja Busch-Saleck, and their results have been verified by data Martin Dörenkämper, Bernd Kuhnle, from the FINO1 offshore met mast. Moreo- Therefore, USAs have also been installed Patrick Milan, Allan Morales, ver, solutions of the averaged Navier-Stokes at three heights at the FINO1 met mast. Kathleen Poland, Michael Schmidt, equations by mesoscale models were However, the signals of these USAs are Jörge Schneemann, Elisabeth Stütz, Davide Trabucchi, Juan José Trujillo, checked for their accuracy at offshore sites. considerably affected by AV, the mast and Gerald Steinfeld, Jens Tambke the mounting structures of the three USAs WP2, led by ForWind Oldenburg, focuses [1] (fig. 1). Using the raw data without ap- on the flow conditions in offshore wind plying any corrections will lead to large farms as well as the interaction between errors in the further analysis. The distur- neighbouring wind farms. The turbulent bances of the measurements have to be Introduction atmospheric flow in an offshore environ- quantified, and, if possible, to be corrected, ment as well as the intra wind farm flow is in particular to gain reliable information on “Alpha ventus” (AV), Germany’s offshore studied with a large-eddy simulation (LES) vertical fluxes and therefore atmospheric wind farm test site is considered to be the model with integrated wind turbine models. stability. Preliminary work, done by other starting point of a large-scale utilization of The numerical results are compared with institutions, is appreciated, but ForWind German offshore wind resources. Scien- results from the measurement campaign at pays special attention to the correction tific concomitant research at AV is funded AV. The LES data sets will be used in order of vertical wind speed and temperature by the German government. Since April to improve engineering wake models for measurements. The correction of the data 2010 AV has been in operation, delivering an application to offshore wind farms with obtained from the ultrasonic anemometers unique data from an operational offshore multi-megawatt WTs. Interactions between was therefore a focus of the work of For- wind farm to the research community. adjacent wind farms are studied by apply- Wind in WP1 in 2011. ing mesoscale models. ForWind has also All research projects dealing with AV are started to develop a multi-LIDAR-system Another focus was to study the dependence bundled in the “Research at alpha ven- consisting of long-range lidars in order to of the power performance of offshore wind tus” (RAVE) initiative. One of the largest be able to get full 3D information on the turbines on atmospheric stratification. RAVE projects is called “Verification of atmospheric flow. Moreover, in WP2 For- One-year meteorological data measured Offshore Wind Turbines” (OWEA). The Wind has developed a stochastic model, at the FINO1 met mast and time series of OWEA project that started in 2007 and that with which wind speeds and power pro- power generated by the wind turbines of will end in 2012, is led by ForWind Olden- duction by a wind turbine can be simulated one of the manufacturers involved in the burg. The OWEA consortium comprises with a high temporal resolution of 1 Hz. OWEA project have been analyzed in this universities, research centers, wind turbine This model can be used to study extreme study. As an initial step, the impact of at- (WT) manufacturers and certification insti- wind situations including events of ex- mospheric stratification on the power pro- tutions and verifies the essential aspects in treme changes of the wind speed within a duction of a single wind turbine in free the design and operation of offshore WTs. very short period of time. These are events flow (i.e. non-wake flow) was studied. For causing large loads on a WT. AV, the availability of data with high reso- Besides coordinating OWEA, ForWind lution in time and (vertical) space from the Oldenburg is involved in the research in FINO1 met mast allows to investigate, e.g. two of OWEA's five work packages (WP). Project Description the atmospheric stratification at this site. In WP1, ForWind aims at reducing uncer- Parameters related to stratification such as tainties in the evaluation of power curves Atmospheric influences on the power shear and turbulence intensity have been and associated risks in the estimation of production of an offshore wind turbine analysed together with power data from energy yields. E.g., the impact of the at- The application of ultrasonic anemometers nearby wind turbines. According to the mospheric stratification on the power pro- (USAs) is a direct, widely recommended preliminary results obtained in this study, duced by a wind turbine is studied in detail. and potentially the most reliable way to the power output of a WT in undisturbed Moreover, easy-to-use and computationally obtain information on vertical turbulent flow at AV shows a strong dependence on Annual Report 2011 43

roughness length depends on the distance between the wind turbines in the wind farm, the rotor diameter, the hub height and aerodynamic properties of the rotor blades.

The third model implemented in COSMO has been developed by Blahak et al. (2010). This model uses a different approach, as the wind farm effects are modeled by adding an additional sink term to the momentum equation and an additional source term in the prognostic equation for the turbulent kinetic energy.

All parameterizations have been applied in idealistic mesoscale simulations as well as for realistic simulations (fig. 2), in that the simulations were driven by data from DWD’s global model GME.

Figure 1: Direction depending, bin-averaged turbulence intensities (TI) in 10min- A much larger wind farm than AV had to be time series, measured by FINO 1 USAs (10Hz sampling rate) from 01 to 09/2011. The assumed in the simulations, as the grid spac- positions of the seven nearest turbines and the mast are indicated by cyan-coloured, ing in the mesoscale model is comparable vertical lines and the gray area, resp. Easterly winds are strongly disturbed by the to the extension of AV. A direct comparison mast and alpha ventus. Anemometer mounting structures, located between 170° and of wind farm wake effects simulated by the 310°, do not show an influence on the TI of atmospheric winds mesoscale model with data measured at AV is not possible. Therefore, the LES model developed earlier in this project will be applied for a verification and further development of the wind farm parameterizations in the remaining time of the OWEA project. the wind shear. Based on the wind speed Recently several research groups have Simulation of lidar based wake tracking quotient between 103 m and a height close started to use meteorological mesoscale In big offshore wind farms many WTs op- to the lower tip of the wind turbine (41.5 m), models to characterize wind farm interac- erate in the wake of other WTs. Several shear classes were defined for different wind tions. At ForWind, the mesoscale model models try to describe the wind field in the speed ranges. It turned out that the power COSMO is used for that purpose. wake. Some of them concern only about the curves for different shear classes deviate static wind profile of the wake, while oth- by more than 10% from each other in the To be applicable to the study of wind farm ers deal also with its dynamical aspects. The intermediate wind speed range (8-12 ms- interactions, a wind farm model had to be discrete particle model (DPM) [2] describes 1), with lower outputs shears occurring with added to the mesoscale model. In order to the flow in the wake by the means of several larger power. In a next step the analysis will assess the performance of currently avail- wind field volumes which behave as passive be extended to WTs in the wake of other able wind farm parameterizations, differ- tracers driven by the large scale structures wind turbines. ent wind farm models have been added of turbulence. According to this model, the to COSMO at ForWind. One of the mod- wake deficit meanders both in vertical and Simulations of intra- and inter wind els added is a parameterization following horizontal direction. farm flows Lettau (1969), in which the wind farm is While so far the focus of the work of For- described as a locally increased surface In preparation of the long-range LiDAR Wind in WP2 had been the development roughness. Moreover, the parameterization measurement campaign planned in WP2 of of an LES model with included WT model developed by Calaf et al. (2010) has been the OWEA project, the Lidar Scanner Simu- that can be used to study the intra wind added to COSMO. As in the Lettau param- lator (LiXim) [3] is used along with a wind farm flow, the work was recently also ex- eterization, the wind farm is parameterized field generated by LES with actuator line tended towards the development of tools by locally increasing the roughness length. model in order to evaluate the possibility of for the simulation of intra wind farm flows. In Calaf’s model the enhancement of the the detection of the center of the wake defi- 44 WIND POWER SYSTEMS

The research concentrates on the differences in performance with respect to wake tracking between a nacelle and a ground based measurement approach. Single lidar devices measure the wind along the so called line-of-sight, i.e. along the laser beam, therefore a good alignment with the wind is desired to achieve reliable measurements. Assuming minimal errors in the yaw control of the WT, a nacelle mounted lidar should reduce the uncertainty of the wake tracking [4]. However, ground based lidars are the most common solution nowadays and misalignment between the laser beam and the wind direction must be considered. Figure 2: Horizontal component of the wind speed at 86 m after 12 h of simulation Simulations are performed with a virtual (start of the simulation: December 21st, 12 UTC). The blue rectangle indicates the nacelle mounted and a ground based lidar boundaries of the imaginary wind farm. system. Initially, the latter is aligned with the mean wind direction and positioned 450 m in front of the WT. Afterwards, misalignments of 20°, 40°, 50° and 60° are simulated by moving the lidar along a line perpendicular to the wind turbine axis (figure 3). Eventually, the error in the wake tracking is determined for the nacelle based and the ground based system with respect to the reference wake field.

Fig. 2 and 3 show that both setups are able to track the wake position directly using the line-of-sight wind component. Concerning the misalignment of a ground based lidar Figure 3: Left: Experimental setup with positions of lidar systems Lxx (ground based), with respect to wind direction, the wake LN (nacelle lidar) and downstream distance of target plane. Right: Scanning trajectory tracking method seems to be robust. How- as suggested by [4]. ever, the results suggest that errors may increase with increasing misalignment angles up to 1% at 60°. A quantification of the absolute error needs more simulations in order to perform statistics of different operational conditions.

Stochastic modeling of wind power generation. A stochastic approach is proposed to model the power output of a WT. The model generates a time series of power output P(t) using a time series of wind speed u(t) as in- Figure 4: Horizontal wake meandering. Left: comparison of the position of the wake put, ergo the conversion process u(t)→P(t) center evaluated from the wind field (WF), the nacelle mounted lidar (LN) and the is modelled. The procedure solves the sto- ground based lidar without misalignment (L0). Right: detail showing the filter effect of chastic differential equation of Langevin the trajectory averaging. The ground based lidar performs better thanks to the highest trajectory repetition rate given by the smaller angles movements required to reach the target from a further distance. Annual Report 2011 45

a large offshore wind farm might extend over several tens of kilometers, which is in agreement with results from satellite- based wind speed estimates downstream of Horns Rev wind farm. In preparation of a Lidar measurement campaign nacelle and ground based Lidar measurements have been simulated in order to check their ability to track the wake position. Moreover, a stochastic model has been developed that is able to generate accurate time series of the power production of WTs with high temporal resolution.

References

[1] Tautz, S.; B. Lange, Heinemann,D.: Correction of the heat and momentum flux measurements with the ultrasonic anemometers at the FINO I offshore meteorological mast for flow distortion and mounting effects. Figure 5: Excerpt of the initially given power signal PWEC (black) and the modeled signal Proceedings of the German Wind Pstoch (red) for 30 minutes at frequency 2.5 Hz. The 10-minute mean values (horizontal full lines) and 10-minute standard deviations (horizontal dashed lines) are plotted with Energy Conference DEWEK 2004, corresponding colors. Wilhelmshaven, Germany (2004) [2] Trujillo, J.J.; Kühn, M.: Adaptation of a lagrangian dispersion model for wind turbine where Γ(t) is a set of random, normal- good agreement with the initially given wake meandering simulation, distributed numbers with mean value 0 power signal [6]. Two typical signals are European Wind Energy Conference, and variance 2. The matrices D(1) and D(2) compared in figure 5. A new method is be- Marseille (2009) are called drift and diffusion fields. The ing implemented to adapt such a stochastic [3] Trabucchi, D. ; Trujillo, J.J.; drift field (1) D characterizes the response model to the fatigue loads experienced by Steinfeld, G.; Schneemann, J. dynamics of the WT, while the diffusion wind turbines. Machta, M.; Cariou J.P. ; Kühn, M.: matrix D(2) quantifies random turbulent Numerical assessment of fluctuations. The innovative concept of the performance of lidar windscanners Langevin power curve [5] originates from Summary for wake measurements, EWEA annual event, Brussels (2011) the drift field (1)D , as it represents the sta- [4] Trujillo, J.J.; F. Bingöl,F.; ble fixed points of the conversion process In the OWEA project ForWind aims at de- Larsen, G.C.; Mann, J.; Kühn, M.: u(t)→ P(t). veloping methods to mitigate the risk in off- Light detection and ranging shore energy yields. Extensive analysis of measurements of wake dynamics, The drift and diffusion matrices can be both meteorological data and wind turbine part II: two-dimensional scanning, estimated directly from some initial meas- data obtained from the German offshore Wind Energy, 14, 61-75 (2011) urement signals {u(t) ; P(t)} on a wind tur- test site has been carried out in order to [5] Gottschall, J.; Peinke, J: bine following [5]. These signals should be study the impact of atmospheric stratifica- How to improve the estimation of sampled at a frequency in the order of 1Hz. tion on power curves. It turned out that the power curves for wind turbines. The use of high-frequency data is neces- atmospheric stratification should be taken Environmental Research Letters, Vol. 3, No. 1, pp. 015005 (7pp) sary to describe the fluctuating, intermit- into account in order to get more reliable (2008) tent behavior of wind power generation. As estimates of the energy yield. Mesoscale [6] Milan, P.; Wächter, M.; Peinke, a result, the reconstructed signal displays models with different wind farm param- J.: Stochastic modeling of wind appropriate statistics. Ten-minutes aver- eterizations have been applied to study the power production, Proceedings of age, variance, spectrum and gust statistics interactions between adjacent wind farms. EWEA 2011, Brussels (2011) of the modeled power signal are in very First simulations reveal that the wake of 46 WIND POWER SYSTEMS

RAVE-LIDAR II – Development of Nacelle-based Lidar Technology for Performance Measurement and Control of Wind Energy Converters

Carl von Ossietzky Universität Oldenburg, Project Description fluctuations which have already caused Institute of Physics, changes in rotational speed or loads. When Christoph Bollig, Martin Kühn, Up to now the implementation of these vi- evaluating the averaged or instantaneous Martin Kunze, Rainer Reuter, sions suffers from fundamental obstacles, power production, it is unclear from which Matthias Wächter despite the progress in many fields of wind exact wind conditions they have been ob- Partners: energy technology. Large uncertainties tained. Thus, a precise performance analy- ForWind – Center for Wind Energy due to the complex inflow within the rotor sis is impossible. Research, University of Oldenburg area influence the control and operation of (Coordinator) wind energy converters. This problem be- The emphasis of the completed RAVE Endowed Chair of Wind Energy (SWE), comes even more serious with growing ro- project LIDAR (development of lidar wind University of Stuttgart tor diameters beyond 120 m. Current con- measurement for the offshore test field) trol concepts can only react to wind field and its extension LIDAR+ was the appli- Introduction

For future multi-megawatt wind energy converters (WEC) in large-scale offshore wind farms new and advanced control strategies are required. Dynamic wind loads have to be reduced efficiently and with minimal controller operation, in order to deliver electricity to the grid in an optimized way. Already small deviations from normal operation have to be detected using new instruments - namely lidar - and adapted control strategies.

From these general considerations, the following main research topics of the RAVE- LIDAR II project have been developed:

• How can a robust and cost-efficient nacelle-based lidar system be demonstrated for power performance measurement and control of wind turbines? • How can the power performance of wind turbines inside wind farms be assessed and monitored using nacelle- based lidar wind measurements? • How can nacelle-based wind measurements be utilised for predictive turbine control facilitating gust compensation Figure 1: Lidar scanner developed at SWE Stuttgart whithin the LIDAR project, deployed at the WEC AREVA Wind M5000 and optimization of energy yield? Annual Report 2011 47

cation of existing lidar technology and the The new robust lidar takes advantage of Summary development of methods and measurement using the spinner for a scanning operation. procedures using largely available technol- The configuration avoids the use of a dedi- The project RAVE-LIDAR II continues the ogy. The current project LIDAR II focuses cated scanner or other moving mechanical successful work of the completed LIDAR on the following topics, which are consid- parts when measuring wind vector data. project and aims at results which can di- ered crucial for the vision of a future "intel- Based on ruggedized embedded technolo- rectly be utilised for the development of ligent offshore wind turbine": gy it will provide reliable long-term meas- cost-efficient large-scale wind energy con- 1. Prototype of a robust and cost-efficient urements of wind profiles. verters. The offshore test field alpha ven- lidar for nacelle-mounted application on tus serves as an ideal testing opportunity WEC, which is suitable for industrialisa- These components shall be developed and for lidar development as well as for new tion. tested with the help of diagnostic equip- control and monitoring strategies. The 2. Methods to determine the power perform- ment which is already installed in the off- co-operation with turbine manufacturers ance of a WEC using a nacelle-based lidar shore test field alpha ventus. ensures the relevance for future industrial for inhomogeneous inflow in wind farms, utilisation. which are common operating conditions Furthermore, the results concerning na- in contrast to the idealized conditions ac- celle-based lidar technology and power cording to IEC 61400-12-1. performance evaluation shall be standard- 3. Procedures for monitoring the Langevin ized and distributed to the wind energy power characteristic using the robust sector through the FGW committee "power lidar. curve". In addition to nacelle-based meas- 4. Control strategies for optimization of urements, uncertainties in standardized power performance and reduction of power curve measurements due to the loads, using nacelle-based lidar measure- blockage effect shall be investigated. ments.

● ● ● ● ● ● ● ● ●

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● r ●

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Figure 2: Drift field for the determination of a WEC's dynamic power characteristic 48 WIND POWER SYSTEMS

Mapretec – Automated Preforming Process to Transform a Flat Textile Lay up into a 3D Outline for Large Fibre-Composites as Rotorblades

Universität Bremen, Introduction Project Description Institute for Integrated Product Development, Increase the percentage of automation in In the mapretec project, the technical tex- Jan-Hendrik Ohlendorf, Martin Rolbiecki, the rotor blade manufacturing process is tiles are laid automatically on special car- Tim Schmohl, Dieter H. Müller, the topic of the research project mapretec. riers by building a flat preform and then fi- Klaus-Dieter Thoben Rotor blades for wind turbines are normal- nalised in contour mould of the rotor blade ly made of long-fibre reinforced polymer by using the Compact Moulding Technol- composites due to their beneficial strength- ogy (CMT). Special fixing technologies to-mass relationship und extraordinary are used to avoid the uncontrolled moving stiffness. Because of the high number of effects of each layer. technical textile plies, the employment time of the manual process and the pro- Additionally innovative sensor technology duction quality is highly influenced by the is used to identify the parameter to control experience, knowledge and intuition of the the automation process. engaged employees. The combination of the automation, the With regard to the background of employ- preform technology and the liquid com- ment at sea, an increase of quality require- posite moulding (LCM) is used for a new ments of the manufacturing in combina- process chain with advantages of accuracy tion with the increasing blade length, the in positioning and repeatability as well as manual production process is less effec- an increasing production speed. tive. Faults in quality may lead to failure, repair or even replacement meaning great Summary expenses. This process chain for the automated man- With textile draping different effects can ufacturing of rotor blades is realized by a occur such as incorrect positions of rovings production cell concept with an innovative or the entire layer. This may cause nega- control and quality system. This project is tive effects on the strength or mechanical funded by the German Federal Environ- characteristics of the construction unit. In ment Ministry (BMU) and is realized in order to keep these effects as small as pos- cooperation with the SAERTEX GmbH sible, the automation of draping and cut- & Co. KG and support of the rotor blade ting processes is a solution. manufacturer AREVA Blades GmbH. Annual Report 2011 49

Figure 1: Initial startup of continuous cutting-system for rotorblade preforms (picture: BIK / M. Postera) 2011 korr 2 50 WIND POWER SYSTEMS

Optical Free Field Measurements of Rotor Blade Deformations

Leibniz Universität Hannover, the design process for larger scale wind Project Description Institute of Turbomachinery and Fluid turbines it is crucial to further investigate Dynamics, the complex deformations and deflections The project is subdivided into two major Jan Winstroth, Florian Herbst, of rotor blades under working conditions. parts. The first project phase consists of Benedikt Ernst, Jörg Seume In order to determe the dynamic motion preliminary tests to demonstrate feasibility. Carl von Ossietzky Universität Oldenburg, of a rotor blade of an actual wind turbine In detail, a model test bench of a wind tur- Institute of Physics, without mounting additional sensors inside bine will be designed, implemented and fit- Jörge Schneemann, Bernd Kuhnle, or on top of the blade, an optical method ted with the necessary optical equipment for Martin Kühn called Image Pattern Correlation Tech- IPCT. The test bench features a two-bladed nique (IPCT) will be applied and qualified. rotor without profiling which will be pro- Partner: REpower Systems SE, pelled by an electric servodrive. A concept Osterrönfeld With the recent advances in digital image photography and digital image processing, study of the test bench is shown in Fig. (1). Funding: Ministry for Science and Culture IPCT has seen a lot of attention from re- Deflection of the blades will be achieved by of Lower Saxony searchers around the world for non-contact external actuators. The focus is on the flap- wise and torsion mode of the rotor blades. Duration: 12.2011 - 05.2013 (Phase 1) measurements of vibration and deformation [1]. Application of IPCT is mostly Each blade will be instrumented with resist- limited to small measurement volumes and ance strain gauges to validate the results ob- the measurements are usually performed tained by IPCT measurements. Both, results Introduction in laboratories or similar controllable en- from the strain gauges and the IPCT meas- vironments. Nevertheless, several authors urements will be validated against numeri- The output of a wind turbine scales with have successfully applied optical correla- cal results from finite element simulations. its dimensions. Larger turbines mean larger tion and tracking techniques similar to The key elements for the first stage of the rotors which results in an increased stress IPCT on wind turbines [i.e. 2, 3, 4]. Based project are: on each blade during operation. To assure on those prior achievements, the objective operational safety and to further improve of this project is to improve the measure- • dynamic deformation measurement in a ment accuracy of IPCT to a degree where rotating system small torsion angles of the rotor blade can • modal analysis and system identification be detected. with IPCT on a wind turbine model test bench. Another crucial part during the first phase of the project is the selection of proper optical equipment. Wind turbines reach tip speeds up to 80 m/s. For IPCT, both cameras must be able to capture sharp images without motion blur in this section. In addition, IPCT requires a minimum resolution of 10 pixels square per target marker on the blade. For modern wind turbines, reaching rotor diameters of up to Figure 1: Concept study for the 126 meters, this translates into high resolu- wind turbine model test bench tion cameras or big target markers.

Based on the knowledge and experience gained during the first project period, in the second period IPCT will be further developed with regards to wind turbine applications. In order to demonstrate feasibility, the IPCT will be applied to a full scale Annual Report 2011 51

wind turbine. The objective is to measure Summary the dynamic deformation and deflection of a rotor blade from a ground fixed position. The project is a proof of principle study to In this project, the cameras will be focused show that IPCT has a lot of potential for ap- only on the outer part of the blade and a plication on wind turbines. As soon as fea- fixed azimuth range. A sketch of a possible sibility has been demonstrated and results measurement setup is shown in Fig. (2). are validated, the technique can provide Since IPCT measurements have never been better insight on the interaction of incom- validated for wind turbine application, the ing turbulent wind and blade deflection/ blade root moments will also be measured deformation. The results obtained from by means of strain gauges. Furthermore, all IPCT can provide a basis for validation and operational parameters of the wind turbine improvement of numerical models. Other will be recorded and syncronised with the scenarios of application are also imagina- IPCT measurements. In order to measure ble. For example, health monitoring during the incoming turbulent wind field in front operation can save a lot of money when of the rotor, a LiDAR system (Light De- failures caused by material fatigue will be tecting and Ranging) will be used. By cor- detected in an early stage. The project has relating the data from IPCT and LiDAR it started just recently, however a first con- is possible to gain a deep insight into the cept for the wind turbine model test bench interation between rotor and wind. In ad- is already worked out and will be manu- dition the results of this study can be used factured as soon as all internal concept and to validate numerical software tools for design reviews are passed. aerodynamic and aeroelastic simulations References of wind turbines. [1] Niezrecki, C.; Avitabile, P.; Warren, C.; Pingle, P.; Helfrick, M: Review of Digital Image Correlation Applied to Structural Dynamics, 9th International Conference on Vibration Measurements by Laser and Non- Contact Techniques and Short Course. AIP Conference Proceedings, Volume 1253, pp. 219-232 (2010) [2] Corten, G.P.; Sabel, J.C: Optical motion analysis of wind turbines, SV Research Group. Delft University of Technology, ISBN 90-75638-01-9 (1995) [3] Corten, G.P: Optical motion analysis of wind turbines, In: European Union wind energy conference. Bedford UK (1996) [4] Ozbek, M.; Rixen, D.J.; Erne, 0.; Sanowb, G: Feasibility of monitoring large wind turbines using photogrammetry, Energy 35 (12), S. 4802 - 4811 (2010) [5] Paulsen, U.S.; Erne,O.; Moeller,T.; Schmidt, T.E: Wind Turbine Operational and Emergency Stop Measurements Using Point Tracking Videogrammetry, Conference: SEM 2009 Annual Conference & Exposition on Experimental & Applied Mechanics (2009) Figure 2: Propossed setup for infield measurements with IPCT and LiDAR 52 WIND POWER SYSTEMS 2011 K1

Laboratory for Inside-Sensoring

Universität Bremen, ing operation depending on ambient condi- sors that can support the construction and Bremen Institute for Metrology, tions such as temperature, wind speed and maintenance crews by automating certain Automation and Quality Science direction as well as internal conditions, for tasks, improving measurements and thus Jan F. Westerkamp, Michael Sorg, example temperature distribution, wear objectifying the results, and introducing Gert Goch and oil level. new inspection tasks. Most of these sen- Duration: 2009 - 2012 sors are currently not commercially avail-

Funded by the Federal Ministry for the To detect early initial damages, before any able. However, there are functional models Environment, Nature Conservation, and major damages with subsequent total fail- for some of the essential material proper- Nuclear Safety (BMU) ure, service providers observe the vibration ties (mechanical stress, force, torque, dis- characteristics of the drive train with con- tortion, surface roughness, wear, fatigue). dition monitoring systems. They prima- These have to be optimized for the long Introduction rily measure and record the structure-borne term application inside of wind turbines noise of the main drive train components and their components. A disproportionately high gear failure rate main bearing, gear box and generator. To- of approximately 26 % leads to unaccept- day, the usual sensor of choice is an ac- An example for one of the new sensors is an able long downtimes of wind turbines. celerometer attached to the outside of the incremental rotary encoder and contactless The actual loads at the turbine shafts, the monitored component. vibration sensor based on an optical navi- machine bed and inside the gear box have gation sensor [1]. An intended application long been underestimated. The predominantly applied preventive are measurements on both rotor and gen- maintenance strategy with fixed periods erator shaft of a wind turbine. With its high Only few states can be observed and meas- between inspections generally leads to angular resolution and measuring speed the ured from the outside, i.e. deformations a replacement of components that is too sensor can improve the resolution of the vi- and changes in temperature on frames or early or too late, after the initial damage bration analysis of other gearbox measure- acoustic noise and oscillations. However, has significantly progressed. This mainte- ments. Furthermore, it can combine these most of the problems (e.g. gear deforma- nance strategy results in more and longer measurements with the axial displacement tion, corrosion on tooth flanks) occur in- machine downtimes and additional main- of the shaft with micrometer resolution. side the gearbox where they currently defy tenance and replacement part costs. There- the direct observation by sensors. fore, the continuous acquisition and analy- With the new research wind turbine the sis of the states and condition of a wind University of Bremen has an excellent The aim of the project is to develop a labo- turbine is of growing importance and an testing facility for the newly developed ratory for research in new sensor technolo- important step towards a condition-based sensors and further research projects. The gies and sensor applications for wind tur- maintenance. This in turn will enable the REpower 3.4M104 (figure 1) with a hub bines. service providers to reduce the number of height of 128 m, build and operated by maintenance trips while still maintaining a WindGuard WEA Uni Bremen GmbH & high level of operational availability espe- Co. KG will be fully operational in Febru- Project Description cially for offshore wind turbines. However, ary 2012. the condition-based maintenance requires Further promising solutions are sensors Gear boxes of wind turbines have to be measurements with sensors inside the for contactless measurement like optical, designed for substantial dynamic loads. process, i.e. the gear box, because many capacitive, magnetic, thermal or resistive At the same time the demand for lighter changes or initial damages cannot be reli- principles. They allow a dynamic detec- as well as cost-effective drive trains in- ably detected by vibration analysis or other tion of the gear condition under load with creases. In order to design gear boxes to common sensors. respect to the local distribution of forces, meet these requirements the manufactur- moments, vibrations and temperatures, ers require more and more realistic data of Integrating sensors inside a gear box is a thermographic contact pattern analysis as the actual performance of the drive train. very demanding task. As an intermediate well as monitoring of corrosion and fatigue Every gear box for example has its own step towards this goal, the Inside-Sensor- conditions on materials. New in-process- vibration characteristics which varies during Laboratory will look into new sen- Annual Report 2011 53

measuring methods permit to take meas- Summary The target-oriented development of spe- urements with a measurement uncertainty cially adapted sensors will use the results up to sub-micrometer range both during The Inside-Sensoring Laboratory offers of root cause analyses of damages to gears the production and while working process. a design and test environment for manu- and bearings. Correlating measurements One of the targets is a permanent detection facturers and research institutions for the with the progression of real life damages of the converters condition from a distance development of new sensors for the drive will allow improved forecasting of com- so that defects and corrosions can be iden- train of wind turbines. ponent failures. The detailed knowledge tified and repaired, before any failures can of undesired geometric deviations and occur. surface properties of gear components will enable service providers to determine the operating characteristics and the cause for operation anomalies. This will reduce maintenance costs by assisting the maintenance teams and minimizing the number of maintenance trips.

Ultimately, the goal is to support the mi- gration from a preventive to a condition- based maintenance [2] by new and improved sensors.

References

[1] Westerkamp, J. F.; Sorg, M.; Bredemeier, C.; Goch, G.: Berührungslose Messung des Dreh- winkels und der Axialbewegung an Rotorwellen von Windenergiean- lagen. In: Puente León, F.; Beyerer, J. (Hrsg.): XXV. Messtechnischen Symposiums des Arbeitskreises der Hochschullehrer für Messtechnik e.V. (AHMT), Karlsruhe. Shaker Verlag, Aachen, ISBN 978-3-8440- 0388-8. (2011)Engineering 23, Nr. 1, pp. 9-33, (1999). [2] Schuh, P.; Tracht, K.; Wester- kamp, J. F.; Sorg, M.; Bredemeier, C.; Goch, G.: Zustandsorientierte Instandhaltung von Windenergieanlagen. In: VDI Wissensforum GmbH (Hrsg.): VDI- Berichte, Band 2151, 6. VDI-Fachta- gung Schwingungsüberwachung, Leonberg bei Stuttgart. VDI-Verlag, Düsseldorf, ISBN 978-3-18-092151-8, pp. 33-34. (2011) Figure 1: Research Wind turbine REpower 3.4M104 of the University of Bremen 54 WIND POWER SYSTEMS

2011 K1 Laboratory for Large-Scale Gear-Measurements

Universität Bremen, Introduction gears and also with larger gears of ships, Bremen Institute for Metrology, milling plants and lifting stations proved Automation and Quality Science, Wind energy systems (WES) have been to be not directly transferable to large- Axel von Freyberg, Karsten Lübke, built for a few decades now. They were scale gears of wind energy converters. At Martina Fuhrmann, Jan F. Westerkamp, supposed to operate for a period of 20 considerably less weight relating to power Gert Goch years. But, especially for the large-scale they have to meet significantly different Duration 2009 – 2011 converters, this goal is often not achieved. load and ambient conditions. The research Funded by the Federal Ministry for the Damaged gears cause a percentage of 20 activities at the BIMAQ are aimed at en- Environment, Nature Conservation, and – 25 % of the overall failure rate of wind hancing the understanding of the interre- Nuclear Safety (BMU) energy converters [1]. Other sources relate lations between the design, the manufac- the “lion’s share … of the annual liability turing, the geometrical quality inspection cases” to the failure of the gear unit [2]. and the future functional characteristics of WES-gears concerning contact pattern, The comprehensive experience gained wear, life cycle, type of damages occur- with small automobile and industrial ring and noise emission.

Figure 1: Gear measurement on BIMAQ’s coordinate-measuring machine Leitz PMM-F 30.20.7 Annual Report 2011 55

Project Description of optical measuring methods is scheduled satisfy the functional or manufacturing for the future progress of the project since principles of gears. This projects aims at A new Coordinate Measuring Machine optical sensors may be easier to implement developing standards to meet the require- (CMM) of type Leitz PMM-F 30.20.7 in the manufacturing process due to a rela- ments of uncertainty determination for figure 1 has been started up at the Bremen tively short measuring time. The previous- large-scale gears. The standards should be Institute for Metrology, Automation and ly examined optical measuring principles, similar to the device under test with respect Quality Science at the University of for example light-section method or fringe to shape and size. Bremen. Situated in an air-conditioned lab, pattern projection technology, show larger which is planned to be certified by the Ger- measurement uncertainties than tactile man Institute of Accreditation (DAkkS), CMM-measurements. Besides, they rely Summary the very flexible portal-type CMM is capa- on optically cooperative and accessible ble to measure any workpiece up to a size surfaces. However, these constraints are The research in the project “Laboratory of 3000 mm x 2000 mm x 700 mm fea- less serious due to the scale and the manu- for large-scale gear-measurements” will turing a volumetric measuring error of E ≤ facturing tolerance of large-scale gears. help to enhance the extent and precision of (1.3 + L/400) µm. It is the heart of a new Therefore, optical measuring can be a cost- the measurement of large-scale gears and centre for measurement of large gears e.g. saving and effective alternative solution to thus improves the reliability of the trans- manufactured for WES. tactile CMM. mission. The comprehensive approach of this research comprises an analysis of the The BIMAQ primarily develops enhanced New measuring strategies and evaluation manufacturing effects on the gear geom- methods and algorithms for geometrical algorithms will deliver information that al- etry as well as an analysis of the correla- quality inspection of large-scale gears with lows for a better analysis, control and opti- tion between geometry deviation and op- this measuring device. Building on that, mization of gear manufacturing processes. erational characteristics or damages. The cause-effect relations between damages With the help of separation algorithms, development of efficient measuring strat- observed and the gear-manufacturing can individual geometrical deviations on the egies for coordinate-measuring machines be identified and analyzed. final large-scale gear can be attributed to and the use of laminar optical sensors are certain effects in the manufacturing. Meas- necessary means in order to improve the Damages caused by problems with materi- urements in various stages result in a com- measuring process. al characteristics such as elasticity, tensile- prehensive understanding of the separate and compression strength, voids and so on manufacturing steps. Profile side milling, are steadily decreasing, whereas the dam- for example, which is used in the manufac- ages caused by geometrical deviations are turing of large-scale internal toothings, fa- still an important issue. These deviations cilitates an increased probability for pitch from the desired condition (form errors, errors and distortion as a result of thermal distortion) cannot be avoided in the differ- stress. ent stages of gear manufacturing and represent causes for damages. The influences The models, which will be developed in the of the manufacturing processes, the type of context of this project, are used to forecast process chain and the separate manufactur- integral operational characteristics such as ing parameters on the emergence of dam- the contact pattern and, as a long-term ob- ages and life cycle of gears are subject of jective, the noise emission from the actual the current research. gear geometry. Knowledge about the correlation between these characteristics and New measuring strategies, particularly de- the gear geometry allows for adjustments signed for large-scale gear-measurements, that lead to optimized operational charac- have to be developed in order to analyze teristics (contact pattern, noise and energy cause-and-effect of geometrical deviations. efficiency) without premature failure. References While reasonably reducing the measuring [1] Bauer, E.; Wikidal, F.: Verfrühte time, the information content has to be Measuring large-scale gears requires a Ausfälle von Verzahnungen und increased. Adapted evaluation algorithms suitable calibration and a periodical un- Wälzlagerungen, Allianz Report, allow for an improved judgment of large- certainty determination of the CMM. Step pp. 2–6, (2004). scale gears in order to provide correlations gauges and sphere standards available for [2] Weber, T., Schreiber, G.: with the observed damages. Nowadays, measuring volumes of up to 1 m³ are not Bewegtes Innenleben, In: neue measuring data is still recorded almost ex- well-suited to determine the uncertainty Energie, Nr.2, pp. 56–60, (2009). clusively by tactile CMM. The application for this measuring task since they do not 56 WIND POWER SYSTEMS

2011 Fatigue Life of Rolling Element Bearings in Wind Power Drive Trains

Leibniz Universität Hannover, Project Description neglected due to the small number of revo- Institute for Machine Design and lutions during which they act, as long as the Tribology, The current fatigue life theory for rolling static safety limit is not exceeded. Janina Brencher, Roman Böttcher, element bearings relies on Palmgren’s ap- Gerhard Poll proach with an exponential relationship be- Influences on the bearing life time such as tween a stationary equivalent bearing load slip and preload due to unfavourable but and expected life with a failure probability often unavoidable operation conditions are Introduction of 10%. In the course of time, this method not investigated properly and are therefore has been refined and now accounts also not even taken into account in the fatigue The project focuses on basic investigations for contamination, lubricant film thickness life calculation. This applies for the sto- into the fatigue life of rolling element bear- and the existence of a fatigue limit below chastic loads introduced by the air flow via ings when subject to varying load levels, which bearing life is not limited by fatigue, the rotor as well as the reactions from the slip or preload. The approach is a combina- provided lubrication conditions and clean- electrical power transmission via generator tion of fatigue tests on various bearing test liness are favourable. and frequency converter from the other side. rigs including metallographical and X-ray Both those external inputs interact with the examination of the bearings, and theoreti- However, the prediction of fatigue life for mechanical transmission characteristics of cal considerations including FE-analysis changing load levels is still based on the as- the powertrain which finally determine the of the stresses within the material close to sumption that the so called Palmgren-Miner loads encountered by each single element the contact zone. In parallel, a method is theorem is valid. An influence of the load such as bearings. developed to more accurately predict the history and, especially, the order in time in loads and stresses in rolling element bear- which the load levels occur, are regarded It is known that macroscopic tensile stress- ings in the real application for existing and as irrelevant. Also, short time events, even es superimposed to the contact stresses future wind power plants. though possibly entailing high stresses, are promote rolling contact fatigue, while

Thereby, the manufacturers of large size transmissions and wind power plants shall be enabled to design their systems based on more realistic life predictions of vital components such as bearings. This would help to enhance reliability and reduce uncertainties and risks accompanying major technological steps and innovations such as large size offshore wind power plants involving high capital investments.

Figure 1: Plakativer Lagerschaden Annual Report 2011 57

macroscopic compressive stresses, e.g. effect to the fatigue life during subsequent dissipated into the lubricant, a rotating in- residual stresses as a consequence of heat operation with lower loads. X-Ray diffrac- ner ring will get warmer around its circum- treatment, are beneficial. tion analyses of run bearing parts showed ference whereas the outer ring will heat considerably higher compressive residual up partially. The radial bearing clearance High shear stresses at the surface due to stresses underneath the rolling contact ar- shrinks due to different expansions. Once imperfect separation by a hydrodynamic eas after application of those extraordinary the bearing clearance is used up due to the lubricant film in combination with sliding loads when compared with bearings oper- excessive expansion of the inner ring, the motions locally encompass tensile stress ating continuously at ordinary loads. bearing will be preloaded with a pressure components and local deformations, simi- distribution around the entire circumfer- lar to the deformations and stress fields As a consequence, as short-period extraor- ence of the bearing surface additional to generated by overrolled hard particles. dinarily high loads tend to increase fatigue the pressure due to operation load. This That happens e.g. when there are small life rather than having a detrimental effect, leads to high stresses that not only have a rotational oscillations during or nearly at these load peaks cannot be responsible negative affect on fatigue life on its own standstill, an effect which is closely re- for the majority of so far unexplainable merit, but also cause higher temperatures lated to “false brinelling”. It also occurs defects in gearboxes of large size trans- in the contact area and therefore further that rollers slip in quickly rotating bearings missions and wind power plants. Instead, stresses due to expansion. In addition, high when the load is too low, resulting in scuff- based on practical experience gained in the oil temperatures can lead to inadequate ing failures in extreme cases. Finally, there recent past, operation at low loads with in- lubricant separation of the bearing compo- are also axial sliding motions e.g. due to stationary conditions may cause slip in the nents and therefore to wear. varying rotor thrust which may negatively bearings resulting in stresses which subse- influence bearing fatigue life when hap- quently shorten bearing life. Preload situations as described in the previ- pening during a state of mixed lubrication ous paragraph and other unfavorable oper- due to low speeds. All mentioned effects Due to losses e.g. generated by friction, the ation conditions can be tested on a bearing can occur at wind power plants while op- temperature increases in the contact area test rig for large size bearings at the IMKT. erating with part load. of rotating bearings. Depending on rota- The test rig enables investigations with one tion speed, loads, lubrication, bearing size, single test bearing of various types with an A project for investigation of short time bearing type etc., the increase in tempera- outer diameter up to 800 mm that can be special loads was successfully finalized at ture will vary between different parts of the tilted dynamically. The maximum rotation- the turn of the year 2011. By means of the specific bearing. The temperature gradient al speed is up to 1200 min-1. experimental investigations it was found between inner and outer ring is thereby that a small number of revolutions with particularly crucial. As soon as the gen- The axial and radial load on the test bear- high normal loads indeed have a positive erated heat is higher than the heat that is ing can be applied dynamically by means of hydraulic cylinders both in tension as well as in compression.

Summary

In the past, large enough safety factors helped to ensure that in despite of uncertainties regarding life prediction and load assumption bearings regularly exceeded or at least reached their rated lives. Since then, also due to refined calculation methods, bearing systems have been designed closer to their limits and, at the same time, the fast development of wind power in general and offshore wind turbines in particular has made it more difficult and risky to rely on existing design. Therefore, it is necessary to investigate the basic behaviour of large size bearings to acquire a fatigue life model that can be applied at the Figure 2: GLWP design of wind power plants. 58 WIND POWER SYSTEMS

Cyclo Converters for Low-Speed Wind Generators

Leibniz Universität Hannover, Using one or more spare modules per However, these advantages hold only true Institute for Drive Systems and Power branch allows these modules to take over for operating points with largely different Electronics, operation of failing modules. This gives frequencies on the two three-phase sys- Lennart Baruschka, Axel Mertens an inherent redundancy for the converter tems. For example, assuming an output fre- system. quency of 50 Hz, best results are achieved for an input frequency between 10 Hz and 30 Hz[4]. This makes the converter very Comparison to Existing Topologies well suited for large-scale direct driven Introduction wind generators giving an output frequency Compared to existing modular multilevel of about 20 Hz. The ongoing project aims Large-scale wind generators are reaching topologies such as the Modular Multi- at a more detailed identification of advan- a size where the use of traditional two- or level Converter (M²LC, [2]) or the Direct tageous and disadvantageous modes of three-level converters for feeding into a Modular Multilevel Converter [3], the operation for the Hexverter. Examples for low voltage supply grid becomes disad- Hexverter’s main advantage is the fact that parameters under research are the reactive vantageous due to large currents and large it requires a considerably lower number powers, the frequencies of the connected harmonic filters. This makes multi-level of modules. Also, less energy storage is systems and the difference of voltages. An- topologies with more than three output required in the modules. Both facts com- other very challenging part of the research voltage levels a promising alternative for bined lead to lower manufacturing costs. is the control system. It does not only need future developments. They offer the option to control the input and output currents of directly feeding into medium-voltage Numerical simulations show the efficiency but also the energy stored in the modules grids. Especially modular topologies show of the Hexverter topology to be compara- as this corresponds to the module capaci- advantages like very low harmonic content tively high, lowering the requirements for tors’ voltages. For accomplishing this, the of their output voltages, low switching fre- the converter’s cooling system. current circulating in the hexagon and the quency, small harmonic filters and inherent redundancy. Motivated by the examination of different modular topologies [1], the novel modular cyclo converter topology „Hexverter“ was developed at the IAL (Fig. 1). This article gives a short overview on the new Hexverter topology.

Project Description

The Hexverter consists of six modular branches made up of n identical power modules each. By combining the modules' switching states in different ways, it is possible to synthesize 2*n+1 different branch voltages. Thus, a large number of modules leads to a very close approximation of the desired voltage waveform. In addition, the switching frequencies of the single modules add up to a high effective switching frequency. Both effects combined make for a comparatively very small harmonic filter to be sufficient. Figure 1 Annual Report 2011 59

Figure 2 voltage difference between the star-points personal computer running a real-time op- a wind generator to maintain a certain set- of the connected systems can be used. Dif- erating system. This makes it possible to point output power regardless of the wind ferent approaches to achieve the desired simultaneously control all modules with speed for a couple of minutes. It also makes capacitor voltages and ensure stable opera- a frequency of 10 kHz. First results from fault ride-through a lot more performant. tion are being compared [5]. this setup show that stable operation of the Hexverter can be achieved. Measurements comply well with the analytic results. Summary Laboratory Setup Next steps In this project, a novel modular multi- For verification of the analytic results, a level cyclo converter is being examined. laboratory setup has been built at the IAL A next step is to look at fault ride-through It shows promising advantages for use in (Fig. 2). It is rated at 50 kW and consists capabilities. Also, it is possible to include large-scale wind generators. However, of a total of 42 power modules and six batteries into each module. This not only more research is required to completely measurement modules. The control system makes converter control a lot easier by sim- reveal all the topology’s advantages and has been realized based on a custom-built plifying the energy control, but it also allows disadvantages.

[2] Hiller,M.; Krug,D.; Sommer,R.; [4] Baruschka, L.; Mertens, A.: References Rohner, S.: A New 3-Phase Direct Modular A New Highly Modular Medium Voltage Multilevel Converter, Proceedings of [1] Baruschka, L.; Mertens, A.: Converter Topology for Industrial Drive the 14th European Conference on Po- th Comparison of Cascaded H-Bridge Applications, 13 European Conference wer Electronics and Applications, and Modular Multilevel Converters for on Power Electronics and Applications, EPE 2011, pp. 1-10 (2011) BESS Application, Energy Conversion 2009. EPE ’09, pp. 1-10 (2009) [5] Baruschka, L.; Mertens, A.: Congress and Exposition, 2011. ECCE [3] Korn, A. J.; Winkelnkemper, M.; A New 3-Phase AC/AC Modular 2011, pp. 909-916 (2011) Steimer, P.; Kolar, J. W.: Direct Modular Multilevel Converter with Six Branches Multil-Level Converter for Gearless in Hexagonal Configuration, Energy Low-Speed Drives, Proceedings of the 14th Conversion Congress and Exposition, European Conference on Power Electronics ECCE 2011, pp. 4005-4012 (2011) and Applications, EPE 2011, pp. 1-7 (2011) 60 WIND POWER SYSTEMS

2011 korr1 Stochastic Methods and Modeling

Carl von Ossietzky Universität Oldenburg, Project Description Synthetic generation of intermittent Institute of Physics, wind fields Ali Hadjihosseini, Fatima Keshtova, Advanced characterization of Reliable wind measurements are non- M. Ramzan Luhur, Patrick Milan, Allan atmospheric turbulence trivial and costly, especially if a grid Morales, Philip Rinn, Matthias Wächter The proper description of wind turbulence of measurement points is required. at a site is crucial for the proper and safe Algorithms for synthetic generation of design as well as for the efficient operation wind fields, on the other hand, are still Introduction of wind energy converters (WEC). unable to reproduce all statistical aspects Turbulence is a complex challenge and of real wind. Especially the typical Stochastic methods and stochastic therefore a stochastic approach appears temporal intermittency, i.e., the strikingly modeling offer an efficient approach to adequate. However, most of the progress high probability of extreme wind speed the dynamics of complex systems. The in this field has been achieved considering changes, is not reproduced by common - generally few - crucial variables of the ideal laboratory turbulent data. For wind approaches based on spectral models. A system under investigation are separated energy, the challenge is to transfer these model based on stochastic processes has from the larger number of less important ideal laboratory results to atmospheric been developed [2] which models this ones, which are represented by simplified cases. Namely offshore wind data from temporal intermittency in good quality. noise terms. This leads to compact models FINO I has been investigated and modeled In 2011 this model has been adapted to which are computationally highly efficient, on the basis of the cascade model of match additionally the spectral properties nevertheless covering the essential turbulence (following Kolmogorov’s work of measured wind situations. Further dynamics. Moreover, noisy components of 1962 [1]) with an extension considering steps will include ensuring the absence of are neither neglected nor averaged out, but the turbulent kinetic energy (TKE) as divergence which is an important feature their contribution to the dynamcs can be a random variable. Our model gives of incompressible turbulent flows, such as precisely analyzed by advanced methods. impressive qualitative and quantitative atmospheric wind. Especially in atmospheric flows the level results. It has also the advantage of of complexity is generally very high. The incorporating the well known turbulence Lift and drag dynamics of airfoils in application of stochastic methods leads to intensity. Operationally this enables the turbulent inflow practical approaches in many cases. statistical estimation of high-frequency Of special interest for wind turbine design wind speed fluctuations, even if the high- and operation are the dynamic loads frequency data is not available. contributed by aerodynamic forces acting on the rotor blades. These forces have direct effect on the power output as well as on the wind turbine life. Continuing the work of 2010, a stochastic model of lift and drag coefficient dynamics is being further developed with the perspective to be integrated into a numerical WEC model. Based on measurement data, a stochastic differential equation, namely the Langevin equation, is applied to the high frequency dynamics of the lift and drag coefficients of an airfoil. Extending the investigations of last year, the conditional probability functions (PDFs) p(x(t+t)|x(t)) have been considered, where unsatisfactory results have been observed specially for higher time lags. In order to investigate and overcome this limitation, the model was Figure 1: Synthetic wind field generated by stochastic processes extended to a two-dimensional and four- Annual Report 2011 61

dimensional embedding of the process. signals and their corresponding statistics. even occur on the surface of a calm sea and Both approaches contributed good A new application is being implemented not reach extreme amplitudes, but still be results as the one-dimensional model. so as to model the power output of entire fatal for ships due to their unexpectedness Furthermore the reproduction of phase wind farms using a similar procedure. an abnormal features. These phenomena space trajectories was improved compared Encouraging results were obtained, as the are investigated in the research project to the one-dimensional case. The quality wind farm model also reproduces power “Extreme Ocean Gravity Waves” in of reproduced conditional PDFs for higher gusts and intermittency. Such tool will cooperation with the Technical Unversity time lags was substantially increased. become increasingly relevant to estimate of Hamburg-Harburg. As a first step a Nevertheless some characteristics of power fluctuations in future, largely wind- stochastic analysis of measured wave the measurements remain which are not powered networks. data was performed. The time series of reflected in the model. The results obtained the surface elevation x(t) was examined so far show good progress towards the Efficiency and energy yield by means of n-point (or time) statistics optimization of operating wind farms goal, and encourage further improvements p(x1, t1, ..., xn, tn), which denotes the joint of the models. Investigating operational characteristics of probability density function of x at n wind turbines within one wind farm shows different times. The presence of Markov Modeling of electrical power output of that large differences in performance properties could be shown, opening the wind turbines between individual turbines can occur. possibility of a three-point closure. Further Wind turbines permanently work in This can be only partly explained by wake steps will include extracting a Fokker- turbulent inflow conditions, converting effects. The aim of this project, coordinated Planck equation from the experimental wind fluctuations into power fluctuations. by Deutsche WindGuard GmbH, is to data which grasps the evolution of the scale As a result, wind turbines transform wind analyze causes for different performances dependent dynamics of rougue waves. gusts into larger power gusts, that are and to obtain adequate optimizations to frequently fed into the electric grid. This increase efficiency. From high frequency intermittent nature of wind power remains measurements of the operational Summary at the scale of wind farms and larger wind characteristics as well as meteorological clusters. The ongoing development of data and additional ground-based lidar Stochastic methods and modeling are wind energy calls for a proper modeling measurements detailed analysis of the continuously developed at ForWind. of such effects to ensure grid stability. This overall performance is performed and in The high degree of complexity in justifies the need for models that integrate particular the Langevin Power Curve of atmospheric flows and their interaction the effects on wind gusts onto electrical each turbine is derived. Additionally the with wind energy converters makes these power fluctuations. A stochastic model was pitch angles of each turbine are measured methods practical alternatives to large- developed at ForWind during the previous and analyzed to investigate their influence scale, fully deterministic approaches. years. This model is based on the stochastic on the turbine performance. The developed Moreover, through advanced analysis of Langevin equation, and generates a optimizations shall be implemented on the noisy features, valuable information can power output signal from any given input turbines and the effects shall be evaluated. be extracted which is complementary wind speed signal. Satisfying results are to results of more traditional methods. observed on operating wind turbines as Dynamics of rougue waves Depending on the state of development, the modeled power signals reproduce the Rogue waves seem to appear from nowhere methods are applied in research projects turbulent-like behavior of measured and disappear without a trace. They may and cooperation with industry partners.

References

[1] Kolmogorov, A. N.: A refinement of previous hypotheses concerning the local structure of turbulence in a viscous incompressible fluid at high Reynolds number, J. Fluid Mech. 13, pp. 82-85 (1962) [2] Kleinhans, D.: Stochastische Modellierung komplexer Systeme, PhD Thesis, University of Münster, Germany (2008) Figure 2: Ocean wave elevation time series (excerpt) 62 WIND POWER SYSTEMS

Probabilistic Safety Assessment of Offshore Wind Turbines

Leibniz Universität Hannover Introduction Summary Franzius Institute of Hydraulics, Waterways and Coastal Engineering, Within this project safety assessments of Performing networked investigations, the Torsten Schlurmann, Arndt Hildebrandt, Offshore Wind Turbine structures and the project partners get parameters for proba- Mayumi Wilms grid-connection are carried out. Uncertainty bilistic approximations. Numerical and is recognized by conventional deterministic other simulation models are implemented Institute for Drive Systems and Power design methods only implicitly and une- and first probabilistic analyses are carried Electronics, Axel Mertens, Bernd Ponick, qually. Thus, probabilistic methods are used out. The results of current work are listed Jörn Steinbrink, Felix Fuchs, Meike Wehner to determine and consider statistical spreads in the annual report 2011. within numerical analysis. Institute of Electric power Systems / Electric Power Engineering Section, Lutz Hofmann, Stefan Brenner Project Description Institute of Building Materials Science, Ludger Lohaus, Thomas Steinborn, Linked by probabilistic methods as well as Michael Werner common used measurement data the project Institute of Concrete Construction, partners investigate the support structure, Steffen Marx, Michael Hansen, the mechanical-electrical energy conver- Boso Schmidt sion and the electronic transformation up to Institute for Steel Construction, the network supply. In the structural part, a Peter Schaumann, Alexander Raba numerical model of the OWT support struc- Institute of Soil Mechanics, ture is implemented and validated. Based Foundation Engineering and Waterpower on measurement data relevant values and Engineering, statistical distributions of extreme action ef- Martin Achmus, Khalid Abdel-Rahman, fects are determined. Further, the safety and Kirill Schmoor serviceability of laterally loaded piles are Institute of Machine Elements and investigated. The mechanical part detects Engineering Design, fatigue damages on rolling element bearing Gerhard Poll, Roman Böttcher, with condition monitoring systems. In the Ulrich Wischhöfer, Janina Brencher electrical part a search coil system to detect faults in the generator is dimensioned. Institute of Structural Analysis, Raimund Rolfes, Jan Goretzka, Furthermore, the reliability of different grid Tanja Grießmann connection topologies is examined and the lifetime of the power modules of the rotor Institute of Turbomachinery and Fluid side converter of a doubly fed induction Dynamics generator system is analyzed. Jörg Seume, Benedikt Ernst Annual Report 2011 63

For further information see

www.psb.uni-hannover.de 64 WIND POWER SYSTEMS 2011 The Influence of Wind Turbines on Air Traffic Control Radar and Navigation Signals

Leibniz Universität Hannover, Project Description capture windows at a specific position. For Institute of Principles in Electrical the initial tests, a “BO 105” helicopter op- Egineering and Metrology, Flight inspection of radar or navigation erated by the German Aerospace Research Heyno Garbe aids, as it is regularly performed, does Agency (DLR) was used to carry a refer- Partner: FCS Flight Calibration Services not clearly reveal the properties of the ence antenna and a dedicated mesurement GmbH, Braunschweig, transmission channel in terms of precise receiver with additional signal recording Jochen Bredemeyer electromagnetic field measurements. An capability. Figure 1 shows the assembly of extreme example, to illustrate the case, is the helicopter, the antenna (white disc) and radar flight testing, where flight inspection the receiver (orange box) during this test. is reduced to a mere target representation. The intended original purpose of this Introduction A binary decision is made by radar signal system was to measure the absolute field processing if the aircraft can be detected, strength of terrestrial navigation aids, us- The operational performance of radar for or if a loss of track occurs. ing antennas traceable to national calibra- air space surveillance or navigation aids tion standards. The signal-in-space record- may be degraded by wind turbine instal- This project focusses on modelling the ed for this project was the raw bandpass lations in the vicinitiy of these systems. It transmission channel with appropriate signal containing all unprocessed informa- has been reported several times that air- electromagnetic solvers. A validation by tion of the transmission channel. craft flying overhead a wind turbine farm real world measurements is mandantory. are not detected by Air Traffic Control This requires dedicated measurement sys- The same measurement principle includ- (ATC). This is in a wider sense a problem tems that provide results suitable for a ing the raw bandpass signal can how- of electromagnetic compatibility. simplified direct comparison with numeri- ever be used to derive the electromag- cal solutions. The key question to answer netic field measurements of the new Numerous studies investigating such ef- is how far the complexity of a numerical wind turbine / radar (or navigation aid) fects have provided differing results, very simulation can be reduced so that the re- interaction project, and the subsequent likely caused by inconsistent physical sults are still close enough to reality. Cer- comparison against simulation results. models of the transmission channel. How- tain objects known to contribute to signal All numerical results of the transmission ever, correct modeling is a prerequisite to degradation of various navigation or radar channel will undergo a steady validation correctly predict the impact of a planned facilites define the model cases to be in- process. This requires to continuously wind turbine installation on a radar or nav- vestigated in this project. obtain measurement results from various igation aid for ATC. In Germany, the Air systems at different frequencies ranging Traffic Act (Luftverkehrsgesetz, LuftVG), Initial tests were performed in the 108- from 108 MHz to 4 GHz. Article 18a, must be applied. According to 112 MHz band to measure the Instru- this, all planned objects or constructions ment Landing System (ILS) signal-in- close to an ATC facility must obtain prior space. An ILS is the main navigation aid approval by the responsible Air Navigation at airports allowing automatic landing Service Provider (ANSP). For more com- under bad weather conditions. In con- plex cases, an expertise or study is required ventional flight inspection, a turboprop to answer the question if the object is likely or jet aircraft is employed which too to interfere with the facility or not. quickly penetrates the area of interest, e.g. in the vicinity of a scattering object. In mid-2011 a joint working group of the For this project, an increased observa- German Federal Ministry for the Envi- tion time at a specific position within the ronment, Nature Protection and Nuclear air space is required, in order to obtain a Safety, the Ministry of Defense and ex- continuous data stream of the same trans- ternal experts came to the conclusion that mission channel under the given envi- there are major issues to be resolved with ronmental conditions. Consequently, the respect to the forecast of interoperablity measurement system is based on a hover- between radar and wind turbines. ing platform permitting much longer data Annual Report 2011 65

Summary

The project first started in 2011, as a result of the detecion of a significant gap between the recent linear field simulation of complex systems and the non-linear behavior of a navigation systems signal transmission channel. A measurement system, originally designed for field strength measurements, was adapted to validate numerical simulations. First in-flight tests have shown the viability of this concept. The ever-increasing installation of wind turbine generator and wind park capacity in many regions of the world potentially puts at risk the safe operation of vital civil and military Air Traffic Control surveillance and navigation facilites. Therefore, there is a strong need for simulation expertise to assist the industry in reliably, precisely and cost-effectively forecasting any potential influences.

Figure 1: Helicopter carrying reference antenna and receiver to measure the impact of wind turbines on transmission channels.

Further Informations:

http://www.wind-energie.de/verband/fachgremien/arbeitskreise/radar 66 WIND POWER SYSTEMS 2011 Investigation of Sonar Transponders for Offshore Wind Energy Converters and Technical Integration to an Overall Concept

Leibniz Universität Hannover; To this end a cooperation project between Hydro-acoustic measurements and Institute of Structural Analysis the Institute of Structural Analysis (ISD), simulation Raimund Rolfes, Moritz Fricke, the company THALES Instruments GmbH, As underwater sound propagation depends Tanja Grießmann the Institute of Technical and Applied Phys- on several influences like seabed properties, Partners: ics (itap), the German Wind Energy Institute sound speed profile and swell [3], extensive Thales Instruments GmbH, Oldenburg (DEWI) as well as the company BioConsult measurements and simulations are carried German Wind Energy Institute, SH GmbH & Co. KG was established. out to achieve a range-dependent estima- Wilhelmshaven tion of detectability of the response signal Institute of Technical and Applied Physics generated by the sonar transponder. The so- Oldenburg Project Description nar transponder system consists of a control BioConsultSH GmbH & Co. KG, Husum unit that is located inside the OWEC and an Duration: Motivation electro-acoustic transducer mounted at the 03/2009-03/2011 The large number of OWECs that are in- support structure at half the water depth. tended to be installed in the North Sea and Within the project two transponder systems Baltic Sea implicates an increasing risk for have been installed at the foundations of Introduction collisions between submarine vehicles and AV10 and AV12 for test purposes. As the wind energy converters. Contrary to their emitted warning signal has a frequency in The operating license of Offshore Wind En- application in vessels above the water sur- the range of 7-8 kHz, the acoustic wave ergy Converters (OWEC) normally requires face, navigation systems based on radar length is approximately 20 cm. Therefore, the installation and operation of sonar trans- techniques are not suitable for submarines both the directivity of the transducer itself ponder units in order to achieve an acous- due to the high damping of electromagnetic and shadowing effects caused by the sup- tical warning of submarines. The installed waves in water. On that account the navi- port structure have to be taken into account sonar transponders are intended to be ac- gation of submarine vehicles is performed to understand the dependency of radiated tivated by a signal that is transmitted from on the basis of acoustic systems known as sound intensity on the horizontal direction. a submarine in emergency. In this case the SONAR (Sound Navigation and Ranging). In terms of long-range propagation, refrac- transponder is supposed to transmit a rec- These systems can be operated in passive tion due to the layered sound speed, scatter- ognition signal that allows the submarine a or active mode. In active mode the sonar ing at the sea surface and attenuation due to localization of the OWEC where the trans- system is emitting an acoustic signal that wind-generated air bubbles near the water ponder is mounted at. The exact specifica- is reflected by an obstacle so that a delayed surface are the most relevant physical ef- tion of this kind of warning was worked out signal can be received. When operated in fects in mid- and high-frequency underwater by the German navy in cooperation with the passive mode, the sonar system is an ex- sound propagation. Research Branch of Waterborne Sound and clusively receiving device using sound that Geophysics (FWG). In order to assure a suf- is generated by an obstacle or target itself. To this end, a hybrid model is used for the ficient signal-to-noise ratio and a certain op- In case of a damaged sonar system neither acoustic simulation. The characterization of eration distance even under bad conditions active nor passive navigation can be per- the source is done using the boundary ele- the source level of the sonar transponder formed. In this case the on-board underwa- ments method. The transmission loss is cal- has to be high enough. On the other hand ter telephone is used to emit an acoustical culated by a three-dimensional ray-tracing the influence on marine mammals has to be emergency signal that triggers the sonar procedure. The main advantage of this hy- taken into account both in the far and the transponder system at the OWEC to gener- brid approach is the capability to take a di- near field. ate a response signal. For a reliable detec- rectivity pattern of the source into account. tion of the response signal at a distance of Fig. 1 shows the comparison between simu- The project aims at the development of a 2sm from the OWEC the transponder has to lated and measured data concerning the di- technically matured transponder system, the provide a source level of at least 200dB re rectivity. Note that measured and simulated simulation and testing of the system under 1µPa @1m ([2]). values are normalized to the direction of 0°. realistic conditions as well as the ecological These measurements were carried out at a evaluation with respect to marine mammals. radius of 900m and in the angles of 0°, 45°, Annual Report 2011 67

180°, 135° and 180° relative to the transducer at AV12 under good weather conditions. It becomes visible that there is a distinct directivity in the horizontal plane as well as a high correlation between simulated and measured data. Fig. 2 shows the simulated transmission loss both in the vertical plane (main direction) and in the horizontal plane (half water depth, i.e. 15 m) assuming good weather conditions. The two diagrams on the lower left of fig. 2 show the dependency of attenu- Figure 1: (a) Mounting of the transducer at the Tripod; (b) BEM-model containing the ation due to near-surface air bubbles and at- transducer and a section of the monopile using a symmetry plane to reduce tenuation of depth ([5]). It becomes obvious computationals costs (green); (c) Comparison of the simulated and measured directivity (measured at a distance of 900m from the transducer) that the directivity even affects the far sound field because of the negligible roughness of the sea surface.

During the project, two measurement campaigns were carried out at alpha ventus in 2010 under good weather conditions and in 2011 under bad weather conditions ( fig. 3: “10/2010” and “02/2011”). In order to determine both the range- and angle-dependence of the sound field, the measurements were performed at 25 positions in horizontal angles of 0 to 180° and distances of 450 to Figure 2: Simulated propagation loss and environmental conditions (wind speed: approx. 7200 m. 5m/s; sea state: 1-2)

Summary

Simulations and measurement results con- sistently show a significant correlation between rough weather conditions and the limitation of the operating distance of the sonar transponder (see Figure 3). Nevertheless it is likely that the developed transponder system will allow the localization of offshore wind farms by submarines at a distance of 2 nauti- Figure 3: Predicted and measured transmission losses vs. range for different weather

cal miles even under bad conditions. scenarios

References [3] Hampel, S.; Langer; S. Cisilino, A.P.: [5] Ainslie, M.A.: Coupling boundary elements to a raytra- Effect of wind-generated bubbles on [1] Jensen, F.B.; Kuperman, W.A.; cing procedure. International Journal for fixed range acoustic attenuation in Porter, M.B.; Schmidt, H: Numerical Methods in Engineering. shallow water at 1-4 kHz. Journal of the Computational Ocean Acoustics, Vol. 73, pp. 427-445 (2008) Acoustical Society of America, Vol. 118, Springer-Verlag, New York (2000) [4] Etter, P. C.: Underwater Acoustic pp. 3513-2523 (2005) [2] Nissen, I.: Modeling and Simulation. 3rd Edition. [6] Trevorrow, M.V.: Measurements of Akustische Kenntlichmachung von Spon Press. Oxon, UK near-surface bubble plumes in the open künstlichen Unterwassergefahrenquellen (ISBN: 0-419-26220-2) (2003) ocean with implications for high- – Modellierung und Leistungsdaten, frequency sonar performance. Journal Kurzbericht des Forschungsbereiches of the Acoustical Society of America, des Bundeswehr für Wasserschall und Vol. 114, pp. 2672-2684 (2003) Geophysik KB-2004-1, Kiel (2004) 68 WIND POWER SYSTEMS

2011 Maintenance Planning and Control of Wind Energy Turbines

Universität Bremen, Bremen Institute for maintenance personnel checks components mination of external influences was con- Mechanical Engineering, as specified in the maintenance instruc- ducted using the example of rotor blades. Kirsten Tracht, Peter Schuh tions, such as gear boxes, blades, bearings Maintenance activities, such as repair and or the condition of oil. overhaul tasks are evaluated in close collaboration with factors influencing the Introduction The most expensive and most complex maintainability. For example, the repair of strategy is the condition based maintenance surface damages and cracks within the ro- A key task to support broadening of wind strategy. By means of sensors and remote tor blade are directly related to the follow- energy is to increase energy and cost effi- monitoring methods, service providers try ing influences: ciency of wind energy turbines by means to prevent unplanned part failures. The ad- • wind speed of customized maintenance activities. To- vantage of a constant monitoring leads to • temperature day, insufficient experience in series op- knowledge about wear and tear, which is • availability of resources erations of multi mega watt wind energy used for spare parts demand planning and Considering a maximum wind speed is turbines, stochastic disturbances and high resource allocation. Herewith, downtimes essential for the safety of maintenance load cycles are a challenge for service pro- can be shortened or prevented. personnel. Therefore, the maximum wind viders. In combination with unplanned part speed should not exceed 8m/s. In case of failures, missing maintenance resources lamination works on the rotor blade, the and a lack of methods for resource plan- Project Descritpion temperature values during maintenance ning and control, existing challenges result should be between 16°C and 30°C. Fur- in prolonged machine downtimes. Maintenance of wind energy turbines thermore, absolute humidity has to be strongly depends on external influences. taken into account. If the temperature and To reduce downtimes, service opera- If external influences arise, feasibility of the humidity are out of the limits, mainte- tors use different maintenance strategies. maintenance tasks can be delayed or pre- nance processes are delayed and machine There are different maintenance strategies vented. Therefore, minimizing machine downtime is prolonged. Besides relevant to ensure availability. Besides the major downtimes is hindered. external parameter, resource availability criterion timing of maintenance activities, has to be planned to perform planned and planning horizon and abrasion of machine To optimize maintenance tasks of wind unplanned maintenance tasks efficiently. components are other criteria for the strat- energy turbines, external influences have Maintenance influences are shown in the egies. They are defined in DIN 31051, to be determined and quantified. Deter- following figure: which separates corrective, preventive and condition based maintenance [1].

As soon as a machine component is defect, causing a breakdown of the whole wind energy turbine, corrective maintenance tasks are necessary. Service providers cannot predict part failures by means of da- tabase analysis and stochastic methods or condition monitoring. They have to react in a very short term horizon, repairing the defective machine as soon as possible and controlling available resources to prevent long machine downtimes.

Preventive and periodic maintenance tasks have to be conducted regarding the type of turbine as well as construction permits and operation licenses. During periodic tasks Figure 1: Influences on the feasibility of Onshore-wind energy turbines [2] Annual Report 2011 69

An approach is to consider the parameters shown in figure 1 by means of linear pro- gramming. Therefore an entity-relationship model (ERM) has been developed. It includes all relevant information, coming from the wind energy turbine (Onshore), the resource availability and the logistical model. An extract of the ERM is shown in figure 2.

Considering the capacity of maintenance personnel it is the aim of the approach to reduce maintenance costs by means of a hierarchical, revolving planning method. Controlled releases of maintenance orders avoid stocks and process delays. Orders are not released until all necessary resources and personnel are available and until the predicted maintenance parameters reach a tolerated value [3]. Figure 2: ERM Model of planning method [3]

For that purpose, there are five main functions that are run iteratively. • scheduling By means of a prototype, the planning ap- Summary • planning of capacity proach has been tested and evaluated with- • evaluation of weather conditions in a maintenance company. Testing crite- Today, maintenance of wind energy tur- • itinerary planning rions were the proportion of value added bines is mostly performed by means of cor- • operation control time. Value added time means the time that rective activities. Due to the fact that fea- Within the first iteration a schedule of is used to repair or overhaul a component sibility of maintenance activities strongly orders is produced on the basis of order for example. In contrast to that, waiting depends on resource availability, qualifica- approval dates. Those dates are used to time due to insufficient weather parameters tion profile of maintenance personnel and estimate spare parts demand. The second isn’t value added time. Evaluation and us- stochastic parameters, such as weather function generates operation plans for age of the prototype showed that waiting conditions or unplanned defects, a novel maintenance personnel. The function fo- and machine setup time could be reduced approach for maintenance planning is nec- cuses on the qualification profile of em- and repair time has been raised. Taking essary. bime developed a planning tool ployees. Within the third function weather into account that more orders can be proc- prototype to consider relevant parameter conditions are regarded. Therefore, weath- essed, the profit of a maintenance company in maintenance planning for wind energy er clusters are introduced. The require- can be increased. [3] turbines. Herewith value added time has ments, arising from maintenance activities been increased. are considered in the clusters. To predict feasibility of maintenance tasks, the weather forecast is used when clustering and a References [3] Tracht, K.; Kouamo, S. T.: time span for the start date of maintenance Optimierung der Instandhaltungs- tasks is determined. By means of iterative [1]n.n.: DIN 31051: planung von Onshore-Windenergie- optimizations, an operation schedule ac- Grundlagen der Instandhaltung. anlagen, crues. The schedules are used to estimate Beuth Verlag GmbH, Berlin (2003) ZWF Zeitschrift für wirtschaftlichen the shortest tour for maintenance teams, [2]Tracht, K.; Goch, G.; Schuh, P.; Fabrikbetrieb 106, 01/02, pp. 75–79 considering cost, dates and resource avail- Westerkamp F. J.; Sorg, M.; (2011) ability. In case of orders of highest priority, Bredemeier, C.: Zustandsorientierte Instandhaltung such as unplanned machine downtime, the von Windenergieanlagen, 6. VDI-Fach- operation control takes place. It is used to tagung Schwingungsüberwachung, allocate maintenance personnel to the wind VDI Berichte 2151, Leonberg, pp. 33–45 energy turbines concerned. (2011) 70 WIND ENERGY INTEGRATION

2011 korr 1 Safewind – Multi-scale Data Assimilation, Advanced Wind Modelling and Forecasting with Emphasis to Extreme Weather Situations for a Safe Large-scale Wind Power Integration

Carl von Ossietzky Universität Oldenburg, University of Denmark), energy & meteo At 26 January 2010 ECMWF introduced Institute of Physics, Lueder von Bremen, systems GmbH (Germany), Overspeed winds in 100 m height of the EPS. Before Thomas Petroliagis, Nicole Stoffels GmbH & Co. KG (Germany), Energinet. that date only Ensemble winds in 10 m dk (Denmark), ECMWF (European Centre height were available to compute probabil- for Medium-Range Weather Forecasts), istic wind power forecasts. It is well known EDF (Electricity de France), EirGrid (Ire- that the extrapolation of 10 m winds to hub Introduction land), CSIRO (Australia), University of height introduces high uncertainties as no Oxford (U.K.), University Compultense of data to describe the atmospheric stabil- The integration of wind generation into Madrid, Universidad Carlos III de Madrid, ity is available from the EPS. The use of power systems is affected by uncertainties Public Power Corporation (Greece), Me- 100 m EPS winds improves deterministic in forecasting the expected power output teo France, TERI (India), Acciona Eolica and probabilistic scores compared to 10 m of wind farms. False estimating of mete- CESA (Spain), SONI (System Operator winds. The root mean square forecast er- orological conditions or large forecasting for Northern Ireland, U.K.), RTE (France), ror (RMSE) of the ensemble mean (solid errors (phase errors, near cut-off speeds etc), Institute of Communication & Computer line) and of the control forecast (dashed are very costly for infrastructures (i.e. un- Systems – National Technical University line) is shown in Fig.1 for four German expected loads on turbines) and reduce the of Athens. control zones. The RMSE with 100 m EPS value of wind energy for end-users. The aim of Safewind is to substantially improve wind power predictability in challenging or ex- Summary treme situations and at different temporal and spatial scales. Going beyond this, wind pre- ForWind is involved in four workpackages dictability is considered as a system design to improve wind power forecasts. In work- parameter linked to the resource assessment package 4 (Alerting&Data Assimilation phase, where the aim is to take optimal deci- Techniques for Improved Short-term Wind sions for the installation of a new wind farm. Power Predictability) ForWind elaborates methods to adequately monitor and assess Project Description the weather situation over Europe in order to detect severe deviations in the wind pow- Safewind is a Small of Medium-scale fo- er forecast due to extreme events. ForWind cused research project funded by European cooperates with other partners that develop Commission under the 7th Framework Pro- the alerting framework to issue warnings in gram. The project has started 1.9.2008 and case of severe deviation between forecast will terminate at 31.8.2012. The project is and observed wind power feed-in. coordinated by ARMINES (Association pour la Recherche et le Développement The goal of Workpackage 5 (Optimized des Méthodes et Processus Industriels, Ensemble Forecast Systems applied to France). Among the partners are end-users, Wind Power Prediction) is to deliver the Figure 1: RMSE of wind power forecast for weather services, companies and several meteorological component of skillful EnBW (black), 50 Hertz (red), Tennet (olive) probabilistic wind power predictions based research institutes and universities. The and Amprion (yellow) control zone with on ECMWF's Ensemble Prediction Sys- partners are: CENER (Centro Nacional de 10 m (top) and 100 m (bottom) EPS winds. Energías Renovables, Spain), IMM (Insti- tem (EPS). In a second step the benefit The ensemble mean (solid) and the control tute of Mathematical Modelling) and RI- for probabilistic wind power forecasts is forecast (dashed) are displayed for the SOE National Laboratory at the Technical demonstrated. period February 2010 to April 2011. Annual Report 2011 71

winds (Fig.1, top) is for lead times up to The spatial distribution of the poor 96 h 60 h and for all regions about 2% (rela- wind power forecast of Xynthia can be tive to installed capacity) lower than with seen in Figure 4. Large absolute forecast 10m winds (Fig.1, bottom). For longer errors of more than 90 MW per grid point lead-times the improvement is still 1%. At occur (Fig. 4, bottom). However, the 70% forecast day D+3 the scores for the ensem- uncertainty interval (Fig. 4, middle) in ble mean and the (single) control forecast those grid points is very large. Conclu- start to diverge, i.e. the superiority of the sively, a high uncertainty was indicated ensemble mean compared to the control and enough time was given to take actions forecast is about 1% at Day+5. like, for instance, to increase the amount of regulating reserves to balance deviations from the day-ahead forecast.

Figure 2: The CRPSS demonstrates the superiority in probabilistic sense of 100 m EPS winds over 10m for all lead times up to Day+5 for Germany (solid) and the 50 Hertz control zone (dashed).

Probabilistic scores are improved considerably when using 100m EPS winds compared to 10m winds (Figure 2). It was found that the ensemble spread with 10m winds is far too small and that the spread is clearly improved utilizing 100m winds. Figure 3: Powergram of probabilistic Figure 4: 96 h wind power forecast of wind power forecast of storm Xynthia storm Xynthia for the 50Hertz control In combination with ForWind’s involve- at 1 March 2010 (0UTC) in the 50Hertz zone valid for 01. March 2010, 0UTC. ment in Workpackage 6 (Novel Methods control zone. The forecast uncertainty is Ensemble-Mean (top), forecast uncer- for Wind Power Forecasting and Extremes), extremely reduced in the newer forecast tainty expressed as width of the 70% new ways to visualize ensemble wind run (bottom) issued at 27 Februar (0UTC) confidence interval (middle) and absolute power forecasts have been developed. As compared to the medium-term forecast forecast error (bottom) in MegaWatt. (top). Measused wind power in red, an example storm Xynthia that hit Germa- ensemble mean in blue, control (deter- ny February 29th and March 1st 2010 was ministic) forecast in green and simulated chosen. The powergrams in Figure 3 show wind power in orange. The vertical bars that there are clear indications of Xynthia represent the 50%, 90% inner quantils four days in advance for the 50Hertz con- and the minimal and maximal value of trol zone. The 48h wind power forecast of the distribution. Xynthia is very good in every sense, i.e. the amplitude and the timing is correct for the deterministic and the ensemble forecast. Furthermore the uncertainty is very low as indicated by the short vertical bars. 72 WIND ENERGY INTEGRATION

Figure 5: Average temporal (1h) gradient of simulated wind power in the year 2007 relative to installed wind power capacity (top left) and relative to produced wind energy (top right) on grid point level. Extreme temporal gradients (99% quantil) are shown in the bottom figures with (right) and without (left) spatial smoothing in an area of 50km radius (see circle).

Workpackage 7 (Wind Resource Assess- zation of the gradients with energy yield ment vs Predictability) investigates which per grid point becomes relevant (Fig. 5, top References relevant aspects should be considered in right) and shows that the average temporal [1] von Bremen, L.: high penetration scenarios to facilitate wind gradients is lower for offshore sites. How- Assessment of ECMWF’s 100m EPS power integration into the power system. ever, grid regulators are more interested in Winds in probabilistic Wind Power Predictability of wind power plays an im- the maximal temporal gradient. In order Forecasting. 16th International portant role here, but also spatial smoothing to avoid arbitrary and sampling effects the Conference on Intelligent System of wind power fluctuations. In Figure 5 wind 99% quantil is shown in Figure 5 (bottom). Application on Power power fluctuations are analysed as temporal The highest gradients in the German Bight Systems (ISAP), Sept. 2011, Crete, (1h) gradients of wind power generation. are only half of the highest gradients in Greece (http://www.isap-power.org/ Wind speeds in 68m height of the COSMO- South Germany (Fig. 5, bottom left). The Sessions.html) EU analysis of the German Weather Service spatial smoothing of temporal gradients [2] von Bremen, L.: (DWD) are transformed into wind power at within an area of 50km radius reduces the Assessment of ECMWF’s 100 m EPS each grid point. The average (absolute) gra- gradient by a factor of 2 for most parts of Winds in Probabilistic Wind Power dient is offshore considerably higher than Germany (Fig. 5, bottom right). Forecasting. Poster at the Meeting of the European Meteorological Society onshore when assuming the same installed (EMS), September 2011, Berlin. wind power per grid point (Fig. 5, top left). (http://presentations.copernicus.org/ Since the energy yield offshore is almost EMS2011-779_presentation.pdf) doubled (compared to onshore) a normali- Annual Report 2011 73

RAVE – Grid Integration of Offshore Wind Farms

Carl von Ossietzky Universität Oldenburg, Project Description Summary Institute of Physics, Nadja Busch-Saleck, Lueder von Bremen The project RAVE – Grid Integration is During the project ForWind has developed a funded by the German Federal Ministry for simple metric (totalfluc) to characterize wind the Environment, Nature Conservation and and wind power fluctuations [1]. This index Introduction Nuclear Savety with about 1.45 Mill. €. The summarizes the absolute values of the tem- project is coordinated by Fraunhofer IWES poral gradient over 6h. The time resolution The goal of the project RAVE – Grid In- in Kassel and has started in July 2008 and used is five minutes. An example of strong tegration is to develop strategies and tools will terminate in June 2012. The project fluctuations is shown in Figure 1 and has a to integrate offshore wind power into the partners are: University Kassel, WEPROG value of totalfluc for wind power of 4.2. It electricity supply system. Integration strat- GmbH, Areva Multibrid, REpower Sys- was found that the wind speed and the at- egies are necessary for the future expan- tems AG, Hochschule Magdeburg-Stendal, mospheric stability can be used to character- sion of offshore wind energy in Germany German Weather Service (DWD), Uni- ize and forecast totalfluc. The deterministic otherwise very high shares of fluctuating versity Magdeburg. ForWind finalized its forecast of totalfluc is not possible. However, wind power can not be integrated without contribution in June 2011 and delivered the it is useful and possible to forecast the risk compromising the stability of the supply final project report at 1. September 2011. to exceed a certain threshold of totalfluc. The system. The project focuses on reducing Since aggregated wind power data of alpha usage of Pool man's Ensemble data (PEPS) the need for balancing energy and reserve ventus are very delayed and were not avail- for wind speed in the algorithm enables to power with an advanced wind power fore- able to the researchers, it was necessary to include the uncertainty of forecasted wind casting system that ensures save grid inte- estimate/simulate the wind power of alpha speed into the prediction of fluctuations. The gration. The results of the project shall give ventus from 100 m FINO1 winds. Brier Skill Score (BSS) shows that predic- an outlook which challenges have to be tions of fluctuations less than 4 utilizing the tackled in an offshore wind power scenario proposed forecasting algorithm have im- that is envisaged by the German Govern- proved skill compared to the climatological ment (25GW in 2030). reference of the occurrence of wind power fluctuations. The skill in autumn and winter Precise wind power forecasts are needed is best, while the skill is least in spring. It is to minimize the need of balancing and re- suggested that in future studies the under- serve power for the integration of offshore standing of the development of strong wind wind power in the German power system. fluctuations utilizing more advanced meas- ForWind has developed a new wind pow- urement data, e.g. sea surface temperature er forecasting method to alert for strong and atmospheric stability is intensified. fluctuating wind conditions utilizing Poor Man’s Ensemble (PEPS) by several Euro- pean Weather Services.

References

[1] von Bremen, L., N. Busch-Saleck: Estimate Severe Offshore Wind Power Fluctuations for Better Grid Integration. Proc. of 10th German Wind Energy Figure 1: Example for strong wind (dotted) Figure 2: Seasonal dependent Brier Skill Conference (DEWEK), Bremen (2010) and (simulated) wind power (solid) Score for several levels of the fluctuations

fluctuations at FINO1 (4. June 2009). index totalfluc0.0-1.0. 74 WIND ENERGY INTEGRATION

The OffshoreGrid-Project: An Offshore Transmission Grid for Wind Power Integration

Carl von Ossietzky Universität Oldenburg, Project Description • Feedback from & acceptance by stake- Institute of Physics, holders Jens Tambke, OffshoreGrid is a policy consulting project Michael Schmidt, Lueder von Bremen, for the European Commission within the Offshore wind power scenarios Gerald Steinfeld Intelligent Energy Europe Programme Initially a realistic scenario of installed (IEE). The project has developed a scien- offshore wind power capacity in Northern tific view on an offshore grid along with Europe was developed for 2020 and 2030. Introduction a suited regulatory framework regarding The scenario is adjusted towards the Eu- technical, economic and policy aspects. ropean Wind Energy Association (EWEA) An offshore power transmission grid in The project is targeted towards European targets, which foresee an installed offshore Northern Europe has become a serious and policy makers, industry, transmission sys- wind capacity of 40 GW by 2020 and 150 important topic among the power industry, tem operators and regulators. In the first GW by 2030 in the EU-27. The final sce- the power transmission sector, national part, the geographical scope has been nario consists of 326 locations with an ex- governments and the European Commis- Northern Europe (the regions around the pected total capacity of 43 GW in 2020 and sion. The ambitious targets and plans for Baltic Sea and the North Sea, the English 127 GW in 2030. offshore wind power development in Euro- Channel and the Irish Sea). The study is a pean seas, in particular the North Sea, have supporting document for the preparation of Onshore wind power scenarios created several questions on how to con- further legislative measures. In particular, The scenario for the installed onshore wind nect the future wind power capacity and the outcomes serve as a major input for the power capacity in 2020 and 2030 were de- how to integrate it into the national power current work on infrastructure plans by the veloped per region. For this purpose, Eu- systems in an efficient and secure way. An European Commission. rope was divided into 46 regions. EWEA’s offshore power transmission grid in North- new targets for onshore wind energy used ern Europe in order to interconnect power This is outlined in the Second Strategic En- in this study are 190 GW in 2020 and 270 systems and offshore wind farms is also ergy Review, namely the Baltic Intercon- GW in 2030 for EU-27. discussed as an element of a unified Euro- nector Plan, the Blueprint for a North Sea pean “SuperGrid”. Offshore Grid and the completion of the Wind power generation time series Mediterranean ring. ForWind calculated synchronous hourly However, several barriers – technical, mar- time series of historical wind speed and ket, legal, regulatory – inhibit its develop- Strategic objectives of the project: power with a high-resolution weather ment. Moreover, an objective view on the • Recommendations on electricity grid model for all offshore wind farm loca- optimal layout, the associated costs and the topology and capacity choices tions and for the onshore wind capacity in necessary requirements to proceed has not • Guidelines for investment decisions & the defined regions. The simulated period existed so far. The OffshoreGrid project project execution comprises three years (2006-2008), with has provided policy recommendations for • Starting point of an coordinated ap- the focus on the year 2007. The calcula- the political process towards such a grid in proachfor a Mediterranean ring tions were performed with the Weather pursuing the efficient integration of renew- Research and Forecasting Model called ables, the integration of market regions, se- As specific objectives, the project pro- WRF [3], which is a meso-scale numeri- curity of supply and the competitiveness of vides: cal weather prediction model with the abil- the European economy. • A selection of blueprints for an off- ity to simulate the atmospheric conditions shore grid over a wide range of horizontal resolutions • Business figures for investments and from 100 km to 1 km. The input for WRF return is provided by the 6-hourly global analysis • Insight in interaction of design drivers data (Final Analysis, FNL) from the United and techno-economic parameters States’ National Centers for Environmental • Representative wind power time series Prediction (NCEP). Annual Report 2011 75

The WRF-simulations dynamically down- tive’ power curves have to anticipate pos- Summary scale the FNL data from six-hourly reso- sible future improvements in wind turbine lution on a horizontal grid of 1° by 1° to efficiency and increased hub heights. The OffshoreGrid project delivers a scien- one-hourly data on a 9x9 km² grid (in geo- tific, technic and economic assessment of graphical coordinates, 1° corresponds ap- different design options for the future of Eu- proximately to 50-111 km.). Acknowledgement rope’s electricity grid. This study has served as a basis for the “Blueprint for a North Sea The conversion of wind speed to wind pow- ForWind is grateful for the contribution Offshore Grid” by the European Commis- er depends on the wind turbine characteris- of the project partners in the OffshoreGrid sion. ForWind in Oldenburg has computed tics represented by the power curve. Stand- consortium and the funding from the Eu- realistic, synchronous wind power time se- ard power curves are given for a single wind ropean Commission (EACI) within the In- ries for 400 future offshore wind farms and turbine. In order to model the output of large telligent Energy Europe (IEE) programme. 16000 onshore wind power locations. The wind farms distributed over a region, new- We would also like to thank our national analysis of this data has shown that large est available results in the wind energy com- partners, ABB, Nexans Deutschland, RWE fluctuations in national grids can be strong- munity on real-life offshore power curves, Innogy, Siemens, Vattenfall Europe Trans- ly reduced by a trans-European electricity array losses due to wake effects, electrical mission and the Ministry for Science and grid. Future studies have to analyze how so- losses and turbine availabilities were used Culture of Lower Saxony in Germany. (See lar energy can further optimize a renewable in this project. Moreover, the applied ‘effec- also www.offshoregrid.eu) energy mix in Europe.

Figure 1: OffshoreGrid Design Case "Direct Design". For details, Figure 2: OffshoreGrid Design Case "Split Design". For details, please check the full report on www.offshoregrid.eu please check the full report on www.offshoregrid.eu

References [2] IEE Project Tradewind, Wind Power [3] The Weather Research and Integration and Exchange in the Forecasting Model (WRF), [1] IEE Project OffshoreGrid, Trans-European Power Market, Project website: www.wrf-model.org, Project website: www.offshoregrid.eu, Project website www.trade-wind.eu, accessed 31/01/2012 accessed 31/01/2012 accessed 31/01/2011 76 WIND ENERGY INTEGRATION

Integration of Fluctuating Energy Resources through a Self-Organized Supply-Demand-Matching

Carl von Ossietzky Universität Oldenburg, this context the term emergence describes in this system corresponds to a preferably Department of Computing Science a phenomenon that becomes visible at perfect matching of device schedules and Christian Hinrichs, Michael Sonnenschein the global level of a system but is based target load curve. There are no other types only on local interactions between units. of agents in this system. This phenomenon is super-additive, i. e. Introduction it cannot be deduced by simply observing Interaction description individual behaviours [1]. This part determines both the self- The present power grid is designed as a organization mechanism and the relatively static, hierachical system. In emergence of a global system property. such a system, the feed-in is proactively Project Description It has to be defined which type of controlled through the scheduling of communication to use. The entities can generators to match a predicted future The project at hand exploits self- either communicate directly by sending demand in electrical power. However, feed- organization mechanisms in order to design each other messages, or indirectly through in of dispersed renewable energy resources an adaptive coordination strategy for modifications of the environment which (DER) like wind energy converters intelligently scheduling individual actions are sensed by other entities. Furthermore, depends on weather conditions and cannot of controllable loads. The study is carried an organizational structure has to be be freely scheduled. Therefore, alternative out via individual-based discrete-event chosen which relates entities to each other supply-demand-matching strategies have simulation, so each load is represented by in terms of communication and interaction to be explored in order to retain a stable a software agent in a simulated multi-agent capabilities [3]. Here, locality is a crucial future energy supply. system. The following system has been property: In general, an entity in a self- proposed [4]: organizing system has only a local view In addition to scheduling the power and therefore partial knowledge about the generation to follow a predicted demand, System description system. Finally, behavioural rules for the it is feasible to incorporate controllable The goal of the system is to find a entities must be designed which operate loads into the supply-demand-matching combination of schedules for a set of on the sensory inputs of the entities and process. For large industrial loads this controllable loads. The chosen schedules induce a reaction to these. The rules may method has already been used for several should produce a summed load curve that also be dependent on the state of the entity decades. To cope with the increasing matches an externally given target load (i. e. its current goals and beliefs) or its operation of fluctuating energy resources, curve as close as possible. This target curve situation in the system (spatial as well as this principle will have to be applied to a consists of one or more equally spaced organizational). Rules can also be bound to much larger number of units. However, an intervals of constant load. probabilistic decisions. intelligent scheduling of individual actions (e.g. load shifts) for many units poses a Entity description In the proposed system, agents communicate combinatorial optimization problem which Participating entities are modelled as in a stigmergy-like fashion [2]. Each cannot be solved centrally in an efficient software agents representing controllable agent has a limited set of neighbouring way. loads, which are able to operate in different agents that it can observe. That means an modes. So for each considered interval in agent is able to sense which schedules its The complex task of efficiently the target load curve, each agent may have neighbours currently have chosen. There coordinating a large number of units can be a set of several varying operational modes is no organizational pattern besides this faced by means of self-organization, which from which it has to choose exactly one. neighbourhood relation. The agents act closely relates to the class of distributed The set of chosen operational modes per upon a single simple rule: Build a schedule artificial intelligence. Systems exhibiting agent for the considered time span forms from the set of available operational modes self-organization are able to (re-)organize a schedule for the underlying appliance. that, summed with the currently chosen themselves without external guidance, Agents are selfless; therefore the main schedules of all visible neighbours, match and are highly adaptive and scalable. In goal of the agents is social welfare, which the globally known target load curve as Annual Report 2011 77

close as possible. This rule is triggered 100 simulation runs, 1000 agents, 20 operational modes per agent whenever any neighbouring agent changes 500 its local schedule. System equilibrium is reached when no agent is possible to 1.0 improve its schedule selection with respect 0.9 boxplot of simulation lengths 400 to its neighbourhood and therefore no more activity is triggered. 0.8

0.7 300 solution quality (lowersolutionquality better) is Summary 0.6 mean quality of 20000 random solutions 0.5 Fig. 1 shows exemplary results of 200 100 runs with each 1000 agents and 0.4 random operational modes. Two random 0.3 minimum/maximum/mean solution quality communication amountof (sensory per inputsagent) proposed by the agents over time neighbours were assigned to each agent. 100 On the vertical axis (left), solution quality 0.2 is shown (lower is better). The horizontal 0.1 mean amount of communication axis represents simulation time – agents 0.0 0 require exactly one time step to choose 0 10 20 30 40 50 60 simulation time a new schedule. However, any two agents which are not directly neighbours may change their schedule selections in Figure 1 parallel. Because system equilibrium may be reached in an arbitrary number of steps, a boxplot has been included in the fi gure which represents the points in time where the several simulation runs stopped. The dashed green line marks the mean quality of 20000 randomly chosen solutions. The solid red curve shows the mean solution quality produced by the system over time. The lower and upper blue curves depict the minimum and maximum solution qualities in each time step, respectively. In addition, the grey curve below shows the mean amount of communication used in each simulation time step. It is scaled to “amount of sensory inputs per agent” (see vertical axis on the right hand side). References [3] Horling, B.; Lesser, V.: A survey of multi-agent It is easy to see that the solutions proposed [1] Di Marzo Serugendo, G.; Gleizes, organizational paradigms. The by the agents rapidly converge to a quality M.-P.; Karageorgos, A.: Knowledge Engineering Review. 19, value of 0.2, which is twice as good as the Self-organization in multi-agent 281 (2005). mean random solution quality of 0.48. This systems. The Knowledge Engineering [4] Hinrichs, C.; Vogel, U.; result, as well as further simulations under Review. 20, 165 (2006). Sonnenschein, M.: several parameter sets (i.e. population [2] Grassé, P.-P.: La reconstruction du Approaching Decentralized size, network topology), reveal that nid et les coordinations Demand Side Management via Self- interindividuelles chez self-organizing agents with only partial Organizing Agents. In: Yolum, Tumer, Bellicositermes natalensis et Stone, and Sonenberg (eds.) ATES knowledge are able to fi nd near-optimum Cubitermes sp. La théorie de la Workshop, solutions of the stated combinatorial stigmergie: Essai d’interprétation Proc. of 10th Int. Conf. on optimization problem in a short amount du comportement des termites Autonomous Agents and Multiagent of time and with a limited amount of constructeurs. Insectes sociaux. 6, Systems (AAMAS 2011). Taipei, communication. pp. 41–80 (1959). Taiwan (2011). 78 QUALIFICATION

MSc Programme "European Wind Energy Master (EWEM) – Erasmus Mundus"

Partners: And over 40 other leading universities, re- Wind Physics Delft University of Technology (TU Delft), search institutions, and companies world- • Atmospheric aerodynamics and Technical University of Denmark (DTU), wide participate as associated partners. In turbulence Norwegian University of Science and July 2011 EWEM was selected for support Wind farm aerodynamics Technology (NTNU), • through the Erasmus Mundus programme Carl von Ossietzky Universität Oldenburg (UniOL). by the European Commission. Rotor Design • Aerodynamics • Structure and design Description Activities • Composite Design Material Production and Manufacturing Starting in the academic year 2012-2013 The EWEM degree programme offers four ForWind / University of Oldenburg of- specialisations: Wind Physics, Rotor De- Electrical Power systems fers a new Erasmus Mundus Master sign, Electric Power Systems and Offshore • Power Systems Course: “European Wind Energy Master Engineering. The first semester contains a • Power Electronics and Drives (EWEM)”. The joint master programme is common programme. The multidiscipli- offered by a consortium of four renowned nary and project-oriented teaching is in- Offshore Engineering universities in wind energy and offshore tended to teach students to transfer knowl- • Installation, Accessibility & technology: Delft University of Technol- edge beyond their specialised field and to Maintenance ogy (TU Delft, coordinating university), place design choices in their social con- • Design of Offshore Support Structures Technical University of Denmark (DTU), text. The four specialisations are orientated • Modelling & Optimization of Soil Norwegian University of Science and along the energy conversion chain, each Mechanics & Mooring Systems Technology (NTNU) and the Carl von with two or three areas of focus: Ossietzky Universität Oldenburg (UniOL). Annual Report 2011 79

Lecture in Wind Physics: Prof. Dr. Martin Kühn, scientific head of the Erasmus Mundus Master Course in Oldenburg, discusses with students and postgraduates.

The consortium hopes to provide 120 to Erasmus Mundus Next Steps 150 graduates each year for the fast-growing wind energy sector. During the course The European Commissions‘s Erasmus First intake of students is in fall 2012. of the programme the selected participants Mundus programme is a cooperation and must study at least at two of the institu- mobility programme and aims to enhance tions in the consortium. Candidates must the quality in higher education between have earned an excellent BSc diploma Europe and the rest of the world. Erasmus equivalent to 180 ECTS by completing at Mundus is a prestigious quality label and least 3 years of studies at university. De- provides support to higher education insti- pending on the specialisation, candidates tutions, individual students, researchers and should have a BSc in one of the following: university staff and any organisation active Mechanical Engineering, Aerospace Engi- in the field of higher education. Selected neering, Physics, Mathematics, Electrical master courses receive funding for scholar- engineering, Civil Engineering, Structural ships and fellowships for students and aca- engineering, Marine Engineering or a de- demics. Competition is fierce: in July 2011 gree with equivalent core content. 30 proposals, including EWEM, were se- Link lected from a total of 177 applications. Further information: www.windenergymaster.eu 80 QUALIFICATION

2011 Continuing Studies Programme Wind Energy Technology and Management

ForWind; The Continuing Studies Programme Wind experience in their academic and oc- Moses Kärn, Christoph Schwarzer Energy Technology and Management is cupational areas, be it technological, especially designed to support companies planning management, administration, Partner: Wind Energy Agency WAB, and professionals in the wind energy sec- or law. Thus the student group’s line-up City of Oldenburg tor in their development. The programme will reflect the heterogeneous profiles, is directed equally to specialists and execu- which are often found within a compa- tive staff in the wind energy sector, as well ny’s typical departmental work group. Description as to recent graduates and those who wish to enter this field. It offers comprehensive - Project Work: For the duration of the In its sixth year of existence the Continu- systematic understanding of wind energy program an eight-person team will ing Studies Programme Wind Energy Tech- projects from scientific grounds to techni- work on a complex wind energy project. nology and Management (“Windstudium”) cal, legal and economic realization, as well During this process, questions will arise is still a unique offer for professionals with as skills in planning and project manage- relevant to all areas of the curriculum academic background to obtain part-time ment. and the students will collectively re- professional education. The programme solve these issues and the project’s has been developed in close cooperation The programme is especially designed to tasks. The project work will provide a between ForWind and WAB. Numerous fit the requirements of professionals. It of- lot of practical experience, which will partners from research, education, indus- fers a mix of learning methods: self-study reflect what the students have been try, and businesses in the field of wind of reading materials, a two-day seminar learning, and ‘real’ experience in com- energy supported the realization of this once every month, and project work in munication with experts from a variety continuing academic education for profes- teams. The total duration of the programme of disciplines. sionals. The programme is sponsored by is eleven months. It is intended to be short GE Energy, Bremer Landesbank, and WSB but intensive. A certificate is issued by the - Teaching Material: The course pack is Service GmbH. University of Oldenburg upon successfully divided into basic and speciality areas. passing the examinations. The basic areas are obligatory for all of the students and within the specialized Approach/Activities The realization of wind energy projects areas half will be examinable. The stu- requires that experts from a variety of dif- dents will choose the speciality areas The rapid growth of the wind energy sec- ferently disciplines work closely together. they wish to be examined upon, there- tor is making an important area for future This innovative program of study is one fore allowing them to focus on their development and offering manufacturers, that addresses exactly such challenges, and personal areas of expertise and interest. subcontractors and service providers sig- furthermore fosters a ‘know-how-transfer’ nificant potential. At the same time, the from acknowledged experts in the field and The programme is constantly evaluated wind energy sector is suffering from a lack from Universities thus, providing current and further developed in close consultation of highly skilled workers, and the compe- and expert knowledge. The program’s study with a wind energy advisory board that tition with the automobile and aircraft in- materials were developed in partnership meets annually to advise the programme’s dustry. The successful development of the with the University of Oldenburg’s continu- administrators, and to arrange the co- wind energy sector will be closely tied to ing education experts and satisfy the highest instructors and guest speakers. The co- the availability of training and professional of academic didactic standards. instructors are experienced representatives certification opportunities. Since there are from the industry who present concrete still are not enough full-time programmes The interdisciplinary approach is the central aspects and expert knowledge, which com- at universities the increasing demand for theme that the program is based upon and plements the main instructors’ teachings. experts with high-level qualifications re- is represented by the following special char- quires immediate action to qualify profes- acteristics. The administrators of the Continuing Stud- sionals. ies Programme in Wind Energy Technol- - Group Dynamics: The selection pro- ogy and Management operate an active cess will be based on bringing together network of alumni in order for the students a group of people with a wide range of to continue to stay in touch with each other, Annual Report 2011 81

Field trips, here to the construction site of a wind farm in Holle near Oldenburg, enrich the practical experience of students in the Continuing Studies Programme in Wind Energy Technology and Management.

to assist them in the exchange of profes- Results Next Steps sional information, and to support further Start of the seventh class: September 2012 continuing education possibilities. The With six fully booked course cycles and (application deadline June 1st, 2012) fifth alumni event takes place in Oldenburg a rising demand for the sevenths class the rd th on March 23 and 24 , 2012, and activities programme has reached a strong position will be continued. in the market. From the beginning the demand was greater than the available student places, so competition for one of the Link 24 student places is high. The drop-out rate is extremely low: only one out of 120 par- Further information: www.windstudium.de ticipants did not finish the programme. 82 QUALIFICATION

Continuing Studies Programme Offshore Wind Energy

ForWind – Center for Wind Energy Offshore wind has a need for highly skilled ticipants systematically to the technology Research of the Universities Oldenburg, specialists with multi-disciplinary know- and the management of offshore wind en- Hanover, and Bremen how and experience. It offers new job op- ergy projects. The programme will cover all Moses Kärn, Dr. Juliane Reichel, portunities to personnel from onshore wind specific offshore wind energy topics from Christoph Schwarzer and maritime industries, oil & gas and ship- technical, legal and economic points of Partners: ping sectors, but also to classically trained view. Special attention is given to the whole Wind Energy Agency WAB, engineers, e.g. mechanical, civil or electri- life cycle of an offshore wind farm and the City of Oldenburg cal. However, structured and specialized ac- complex management challenges. The cur- ademic study programmes with onshore or riculum will be divided into five modules: Duration: 06/2011 – 12/2012 (development phase) offshore wind energy focus are only slowly Offshore Conditions and Wind Farm Design, emerging and will still not be able to meet Project Development, Offshore Wind Farm Funded by: the market‘s growing demand. Components and Procurement, Offshore Metropolitan Region Bremen-Oldenburg Wind Farm Installation and Offshore Wind e.V., Ministry for Environment and Cli- Farm Operation. These modules correspond mate Protection Niedersachsen, Project Description to five classroom instruction periods that and the Senator of Economics, Labour and Harbours of the Free Hanseatic City will be organised on a bi-monthly schedule of Bremen, ForWind, the Wind Energy Agency WAB, and located in Bremerhaven and Oldenburg, Oldenburger Energiecluster OLEC e.V., and the City of Oldenburg have a long- Germany. Bremerhaven Economic Development standing cooperation: they were the first Company Ltd. ones world-wide to establish a part-time The Continuing Studies Programme Off- study programme for professionals in shore Wind Energy will be built on a well- Sponsored by: Bremer Landesbank, nkt cables GmbH, wind energy on academic level: known as established portfolio of teaching and learn- and wpd offshore solutions GmbH. the Continuing Studies Programme Wind ing methods as a “blended learning mix”: Energy Technology and Management or Participants will be enabled to learn in dif- short: “Windstudium”. Based on the suc- ferent ways while they stay in their jobs, for The Continuing Studies Programme cess of this programme the three partners example by private study (distance educa- Offshore Wind Energy is currently in its have again joined forces and are now de- tion), classroom instruction or e-learning. development phase. veloping a new programme in English, the Lecturers will be known experts from re- Continuing Studies Programme Offshore search and practice. Field trips supplement Wind Energy. This will be adapted to the the programme with hands-on experience. Introduction specific needs of the offshore industry Between the classroom instruction periods, and will be putting special emphasis on a newly developed web-based learning plat- A successful development of the offshore interface management during the entire form allows for an interactive exchange. wind sector is closely tied to the availabil- course of studies. It will cover all relevant Case study work in project groups will be ity of qualified personnel. Offshore wind offshore wind topics and present them an essential element of the Continuing Stud- energy is developing into a full-size indus- along with corresponding technological, ies Programme Offshore Wind Energy. The try sector bringing together two formerly financial and legal expert knowledge. The case studies follow the contents of the mod- separate worlds: the maritime and the wind new programme will be open to specialists ules and will be accompanied by known industry. Companies and their staff are fac- and executive staff from the wind energy experts in the field. The students will be ing a lot of new challenges in basically all industry, offshore industry or maritime in- grouped in interdisciplinary teams and work aspects of their activities: technically, le- dustry and start in October 2012. Places in out the different offshore wind energy topics gally, economically, logistically, and on the the programme are limited to 24, and the from different stakeholders’ perspectives. management level. The complexity and size students will be selected by the directors of offshore wind farm projects, the speed of of studies out of all applications received The participants will receive a graded uni- innovations, and the dynamic change proc- until the deadline of 30 June 2012. versity certificate of the Carl von Ossietzky esses, along with the high risks involved are University of Oldenburg after passing the factors that put the jobs of experts and man- The Continuing Studies Programme Off- nine month programme successfully. After agers on a very high level of responsibility. shore Wind Energy will introduce the par- completion all students become part of the Annual Report 2011 83

exclusive alumni network which offers a The curriculum / Der Studienablauf web-based alumni forum, annual seminars for exchange of experiences, and meeting Case Study Case Study Case Study Project Project Case Study Operation & points at trade fairs and conferences. Development I Development II Installation Maintenance

Seminar I Seminar II Seminar III Seminar IV Seminar V Case Studies Case Summary Oshore Project Project Installation Operation Wind Farm Development I Development II & Design Maintenance Supported by numerous partners, For- Wind, the Center of Wind Energy Research, and the Wind Energy Agency WAB have

Seminars teamed up in a project to develop the Con-

1 Offshore Wind 3 Approval 6 Offshore Wind 9 Grid Connection 12 Operation and tinuing Studies Programme Offshore Wind Farm Design Procedures and Legal Turbine and Submarine Maintenance Energy. This part-time study programme Conditions Cable 2 Economic 7 Support on academic level is especially designed Conditions Structure 4 Project Design 10 Logistics and to meet the needs of the growing offshore and Management Installation 8 Transformer wind energy industry. The start of the nine Substation Platform month programme is scheduled for Octo- Units 5 Financing and 11 HSE Insurance (Health, Safety, ber 2012. It will teach experts and manag- Environment) ers in the different fields all the necessary know-how to improve the management of complex offshore wind farm projects. The Continuing Studies Programme Offshore Wind Energy is a part-time programme using a “blended learning mix” of distance education, e-learning, classroom instruction, and case study work and focuses on the development of professional skills such as management skills, knowledge exchanges and international qualification.

Celebrating the inauguration of the Continuing Studies Programme Offshore Wind Energy with 60 guests from science, industry, commerce, and politics on November 3rd 2011 in Bremerhaven. In the picture (from left to right): Contact Hon.-Prof. Matthias Stauch (Senator of Economics, Labour and Harbours of the Free Hanseatic City of Bremen), For further information regarding Nils Schnorrenberger (Bremerhaven Economic Development Company Ltd.), the programme visit the website Ronny Meyer (Wind Energy Agency WAB), Roland Hentschel (Business Development http://www.offshore-wind-studies.com Department Oldenburg), or contact Ulla Ihnen (Ministry for Enviroment and Climate Protection Niedersachsen), Dr. Juliane Reichel, Dr. Joachim Peters (Metropolitan Region Bremen-Oldenburg e.V.), ForWind, Prof. Dr. Bernd Siebenhühner (University of Oldenburg), telephone: ++49 441 798 5085, Dr. Juliane Reichel (ForWind), email: [email protected]. Dr. Stephan Barth (ForWind).

84 QUALIFICATION 2011 korr1 ForWind Academy: Partner for Qualification in the Wind Energy Sector

ForWind: Seminars on offer take up current issues Approach/Activities Dr. Stephan Barth, Nicole Kadagies, occurring in the real-world and present Moses Kärn, Christoph Schwarzer interfaces to scientific knowledge gained A total of 24 one-, two- and three-day Partner: Overspeed GmbH & Co. KG from research and development. ForWind seminars were offered in 2011 with round Academy is particularly adept when it about 225 participants. With an increased comes to a high level of expertise and the marketing and a continued co-operation didactic preparation of seminar topics and with “Haus der Technik” (Essen), the Description content. ForWind Academy follows high number of participants is expected to rise ambitions and is not merely offering in- considerably in 2012. ForWind Academy provides comprehen- troductory knowledge in a rush. Seminars sive qualification on academic level for conveye fundamental knowledge, give In the last 25 years the wind energy sector the wind energy sector through seminars, insight into research questions, and offer has been experiencing rapid growth, mak- in-house courses, and individual coaching. practice oriented know-how. ing it an important area for future develop- ForWind Academy is a joint project of For- ment. In Germany the wind energy sector Wind and Overspeed GmbH & Co. KG and ForWind Academy offers a platform for employes about 100,000 persons. At the was launched in June 2008. This co-opera- intensive advanced education and the ex- same time, the wind energy business is suf- tion opens up a possibility to provide high- change of ideas among experts in the field. fering from a lack of highly skilled person- quality seminars and advanced training on It brings together people with different oc- nel, a situation aggravated because there topics ranging from research to applica- cupations, experience, and careers. Target are not enough structured and specialized tions in industry. Through ForWind’s wide groups are young professionals as well as academic training programmes or courses. network it is possible to provide expert experts and decision makers in the wind However, the demands on experts have speakers from universities national and energy sector. Also, those who wish to en- reached a level which make special wind international. Dr. Hans-Peter (Igor) Waldl ter this field find seminars that suit their energy qualifications essential. Predic- himself, managing director of Overspeed need for introduction into wind energy. tions tell that by 2020, the number of em- GmbH & Co. KG, possesses expertise as Apart from advanced training, ForWind ployed persons in wind energy could rise to a consultant and course instructor with 20 Academy also aims at creating and sup- 330,000 in the EU. In the coming 20 years years of wind energy experience. porting an alumni network of experts. offshore wind energy employment will

Figure 1: Demonstration of a LiDAR- System at the one-day seminar „LiDAR – Wind measurement for onshore and offshore Windfarms“ on November 11th, 2011, Bremen, Germany. Main speakers were Prof. Dr. Dipl.-Ing. Martin Kühn, Juan José Trujillo M.Sc., both ForWind – Center for Wind Energy Research, Oldenburg, Germany Annual Report 2011 85

exceed onshore employment. According to the study Wind at Work (EWEA 2009) more than 375,000 people will be employed in the European wind energy sector in 2030 – 160,000 onshore and 215,000 offshore. A successful development of the on- and offshore wind energy sector will be increasingly tied to the availability of highly skilled professionals. In the light of this trend, the partners ForWind and Overspeed GmbH & Co. KG began to offer a range of topics in the areas of management, planing and engineering which are highly relevant to the wind energy sector on- and offshore.

Results

ForWind Academy has established its reputation as one of the places to look when it comes to high-level seminars dealing with current topics on an academic level and with a high degree of relevance to practical applications. The growing number of seminars and participants shows that ForWind Academy is on a successful way.

Furthermore, ForWind Academy will continue the co-operation with “Haus der Technik e.V.” in Essen, Germany.

ForWind Academy is also active in organ- ising workshops about qualification needs and career possibilities in the wind energy sector. For example, ForWind in cooperation with the network Wind Energy Agency WAB and Overspeed GmbH & Co. KG organise the successful workshop „Qualification in the Wind Energy Indus- try“ at HUSUM WindEnergy 2012 at the windcareer job fair in Husum, Germany. The host is expecting more than 100 visi- Figure 2: LiDAR-System tors for the one-day workshop which offers information on further training opportunities and ForWind Academy.

Next Steps Link: Execution of the current seminars and con- Further information about the For- ception of the new 2012 programme. Wind Academy, the seminar offers and its partners are provided at: www.forwind-academy.com 86 QUALIFICATION

2011 Job and Education Fair “zukunftsenergien nordwest 2011”

ForWind – Center for Wind Energy Introduction Project Description Research of the Universities Oldenburg, Hanover, and Bremen The renewable energies are an important The job and education fair for renew- Corinna Wermke, Christoph Schwarzer economic factor in Germany and especially able energies and energy efficiency, the Partners: in the northwest region. Their potenial for „zukunftsenergien nordwest“, openend Windenergie-Agentur Bremerhaven/ growth is high, and they offer an important its gates for the second time on the 11th Bremen e.V. (WAB), perspective for future employment. With and 12th of March 2011 in Bremen. Bremerhavener Gesellschaft für more than 370.000 employees nationwide 87 companies, Universities, institutes for Investitionsförderung und the renewable energies are a job-motor further training and research instituts in- Stadtentwicklung mbH (BIS), already. Experts predict a further develop- volved in renewable energies and energy Stadt Oldenburg, Wirtschaftsförderung, ment of more than 500.000 jobs until 2030. efficiency were presenting themselves on Oldenburger Energiecluster (OLEC) e.v., But at the same time, the renewable ener- the jobfair. The more than 5000 visitors of Hochschule Bremerhaven gies sector, like many others, suffers from the fair met attractive employers with open Sponosored by: a lack of specialists. And there still are not job opportunities, traineeships, informed EWE AG, Deutsche Biogas AG, enough adequately specialized training and themselves on prospects for further educa- GE Wind Energy GmbH further education programmes. The renew- tion, and received insight into the branch able energies are a relatively new occupa- by taking part in 5 technical workshops. tional area and always in competition to The „zukunftsenergien nordwest“ offered Under the patronage of the other well established career paths in tra- exhibitors a high-profile public platform Federal Ministry for the Environment, ditional industries. Therefore the job and where companies and service providers Nature Conservation and Nuclear Safety, education fair in the Northwest, the „zuku- meet together with an audience interested Minister Dr. Norbert Röttgen. nftsenergien nordwest“, is still an impor- in their sector along with potential young Job and Education Fair tant event for the region demonstrating its applicants and those looking to enter from “zukunftsenergien nordwest 2011” rich job and qualification opportunities in other fields of expertise. This programme renewable energies. was complemented by excursions to well- known companies and regional facilities as well as application trainings.

The „zukunftsenergien nordwest“ is supposed to take place once a year alternat- ingly in Oldenburg and Bremen. It started 2010 in Oldenburg.

Outlook

The „zukunftsenergien nordwest 2012“ is set to grow in 2012. Sponsors have changed and will be Bremer Landesbank and Enercon GmbH. The Partners will stay the same just as the patronage of the Fed- eral Ministry for the Environment, Nature Conservation and Nuclear Safety, Minister Dr. Norbert Röttgen. By 2012 public funding by the Metropolregion Bremen-Olden- burg e.V. will be ceased. Annual Report 2011 87 88 EVENTS

ForWind – Events

ForWind Competence Center Elke Seidel ForWind Course of Lectures

Since 2006, ForWind has offered a unique public course of lectures concerning various, predominantly technical aspects of ForWind Vortragsreihe energy research and supply – mainly Sommersemester 2011 focused on wind energy. Serving as a Neuer Veranstaltungsort: connecting link among research institu- Ammerländer Heerstr. 136, 26129 Oldenburg tions, universities and the industry, in- Seminarraum 114, 1. Stock vited national and international speakers discuss their area of expertise. Donnerstag, 01.09.2011, 16:15 Uhr

Rotorblattfertigung: Donnerstag, 15.09.2011, 16:15 Uhr Was kann die Windenergie Industrialisierung der von der Luftfahrt lernen? Summer Term 2011 Windbranche Dr. Hilmar Apmann, Premium AEROTEC GmbH, Ronny Meyer, Rotorblattfertigung: Was kann die Leiter der Abteilung Konzept- & Technologie-Entwicklung WAB e.V., Geschäftsführer, Windenergie von der Luftfahrt lernen? Clustermanager des WindPowerClusters Dr. Hilmar Apmann,

Premium AEROTEC GmbH, Leiter der Donnerstag, 29.09.2011, 16:15 Uhr Abteilung Konzept- & Technologie- Das EEG und politische Entwicklung Rahmenbedingungen Industrialisierung der Windbranche aus Sicht eines Anlagenherstellers Ronny Meyer, Dr. Ruth Brand-Schock, ENERCON GmbH, WAB e.V., Geschäftsführer, Leiterin Büro Berlin Clustermanager des WindPowerClusters Das EEG und politische Rahmen- Die Vortragsreihe wird unterstützt von:

Weitere Informationen zu den Veranstaltungen finden Sie bedingungen aus Sicht eines unter www.forwind.de/vortragsreihe Die Veranstaltungen stehen allen Interessierten offen. Informationen zur Vortragsreihe und zum Eintrag in den Anlagenherstellers Verteiler erhalten Sie bei Elke Seidel, [email protected]. Dr. Ruth Brand-Schock, ENERCON GmbH, Leiterin Büro Berlin Annual Report 2011 89 90 EVENTS

Hannover Messe 2011, April 4th - 8th

As in previous years, ForWind partici- sion measurements of wind speeds and and Culture Prof. Dr. Johanna Wanka, pated in the Hannover Messe 2011 at the directions was introduced. ForWind also the Minister for Economics, Labour and joint stand of Lower Saxony “Energie aus developed a new stochastic method to de- Transport Jörg Bode, the Minister for En- Niedersachsen”, introducing ForWind termine the power characteristic of a wind vironment, Energy and Climate Protec- and its services in research, consultancy, turbine which is far more efficient than tion Hans-Heinrich Sander as well as his education, further education and events. the IEC-standard. Parliamentary State Secretary Dr. Stefan Birkner. In 2011 ForWind presented three exhibits In addition, ForWind presented an exhibit in Hanover: explaining the formula of how electrical In addition to the presentation of ForWind The measurement facility Multi-LiDAR power is generated out of wind speed and at the booth, ForWind was also asked to which is under development at ForWind also at what speed and why wind power participate in the “Branchen- und Export- (based on LIDAR (Light Detection And turbines have to cut out – a schooling forum Erneuerbare Energien“, providing Ranging )) allows for velocity measure- exhibit where people can turn the crank two talks within the industry forum RE- ments in complex atmospheric flows in themselves. SEARCH MEETS INDUSTRY. three dimensions with a high temporal and spatial resolution. Amongst many other visitors, ForWind could welcome several political guests For laboratory wind flows, the 2D-Laser- from Lower Saxony: the Prime Minister Cantilever-Anemometer for high-preci- David McAllister, the Minister of Science Annual Report 2011 91 92 EVENTS

Wind Energy Research Alliance – ForWind and Fraunhofer IWES Form a Nationwide Unique Research Cooperation

ForWind and the Fraunhofer Institute for research facilities available allow both at Alpha Ventus), the “Joint Programme Wind Energy and Energy System Technol- basic and application-oriented research. on Wind Energy” of the “European Ener- ogy IWES joined forces to form the Wind gy Research Alliance (EERA)” as well as Energy Research Alliance, announced on The close cooperation between ForWind the European “Wind Energy Technology the occasion of the “Leibniz Dialog on the and Fraunhofer IWES is strengthened by Platform”. Future” at the University of Hanover by Fraunhofer project groups for wind en- ForWind Managing Director Dr. Stephan ergy in Oldenburg and Hanover as well as Also both ForWind and Fraunhofer IWES Barth and Prof. Dr.-Ing. Andreas Reuter, a research group for offshore site investi- are project managers and the representa- head of the Fraunhofer IWES. gations at the University of Bremen. Fur- tives of Germany in the “Implementing ther cooperation between ForWind and Agreement for Cooperation in the Re- More than 430 employees at 35 institu- Fraunhofer IWES takes place on a na- search, Development and Deployment of tions and research institutes work to- tional and international level at the Ger- Wind Energy Systems” of the Internation- gether in this new alliance. The numerous man research initiative RAVE (Research al Energy Agency (IEA).

ForWindCenter for Wind Energy Research Annual Report 2011 93

Wind Energy Cluster in Northwest Germany – WindPowerCluster

For the second time ForWind partici- ergy enterprises in the northwest region During the dinner debate on November pated in the competition "Deutschlands- of Germany into a complex business and 22nd in the Fraunhofer Forum Berlin, Spitzencluster - Mehr Innovation. Mehr research network. organized by ForWind, more than 200 Wachstum. Mehr Beschäftigung" (More representatives of economy, politics and Innovation, More Growth, More Jobs) At the annual summer party of Lower administration informed themselves on ob- to find Germany`s leading edge business Saxony on June 27th in Berlin, the Wind- jectives and potential for the future. clusters, initiated by the Federal Minis- PowerCluster was presented and, among try of Education and Research (Bunde- others, promoted by Dr. Oliver Liersch, Speakers were the Minister for Science sministerium für Bildung und Forschung (Parliamentary State Secretary of Lower and Culture of Lower Saxony, Prof. Dr. Jo- (BMBF)) as part of its high-tech strategy Saxony`s Ministry for Economics, Labour hanna Wanka, Dr. Joachim Lohse, Senator for Germany. and Transport), Dr. Philipp Rösler (Federal für Umwelt, Bau und Verkehr des Landes Minister of Economics and Technology), Bremen, Dr. Heiner Heseler, Staatsrat beim The partners Windenergie Agentur WAB Dr. Stefan Birkner (Parliamentary State Senator für Wirtschaft, Arbeit und Häfen e.V., the Fraunhofer Institute for Wind Secretary of Lower Saxony`s Ministry for des Landes Bremen, Ronny Meyer, Man- Energy and Energy System Technology Environment, Energy and Climate Protec- aging Director WAB e.V. and Prof. Dr.- IWES and ForWind have combined over tion) and Jürgen Trittin (Chairman of the Ing. Andreas Reuter, Director Fraunhofer 300 research institutions and wind en- parliamentary group the Green Party). IWES.

Dr. Stephan Barth, Managing Director of ForWind, moderated the forum. 94 EVENTS

Global Wind Day with ForWind

“Global Wind Day” is a worldwide event Council – GWEC – coordinate Global ForWind supported Global Wind Day in that occurs annually on 15 June. It is a Wind Day through a network of partners. 2011 with several activities informing on day for discovering wind and the power The day started as a European one in wind energy and promoting the project and the possibilities it holds in changing 2007 and went global in 2009. Last year, WindPowerCluster in the northern region our world. more than 230 events were organized in in a “tour bus“ as well as via an informa- 40 countries around the globe.* tion booth when the touring exhibition

The European Wind Energy Association *Source: ship “Faszination Offshore” anchored in – EWEA – and the Global Wind Energy (http://www.globalwindday.org/about-wind-day/) the harbor of Oldenburg. Annual Report 2011 95

Innovationcampaign for Study Possibilities in Lower Saxony

180 seconds was the allotted time limit for Together with six professors of different Kühn pointed out how long it takes to Prof. Dr. Martin Kühn, endowed professor backgrounds from Lower Saxony, he took produce the energy contained in 100ml of Wind Energy Systems at the University part in the internet campaign “Bannervor- raw oil by the use of offshore wind and of Oldenburg and member of ForWind`s lesung“ initiated by “Innovatives Nied- explained the difference between conven- Executive Board, to give a lecture on his ersachsen” to promote Lower Saxony`s tional power and power gained by off- area of expertise to inspire his audience – study possibilities. Themed “Harvesting shore wind energy. while standing in a box. Wind Energy“ (“Wind ernten”) Martin

BANNERVORLESUNG WIND ERNTEN VON PROFESSOR MARTIN KÜHN

Der Wind, der Wind, das himmlische Kind. Oder sollte man besser sagen: das strombringende Kind? Der Atom- ausstieg ist beschlossen und erneuerbare Energien sind die Zukunft. Wenn du aktiv an der Energieversorgung der Zukunft mitarbeiten möchtest, dann musst du nach Oldenburg! Hier kannst du dich im Studiengang „Engineering Physics“ auf erneuerbare Energien speziali- sieren. Diesen und über 1.000 andere spannende und vielfäl- tige Studiengänge gibt es bei uns in Niedersachsen. Mehr Infos zum Fach „Windenergie“ und alle anderen Bannervorlesungen findest du auf: www.innovatives.niedersachsen.de/bannervorlesung 96 EVENTS

International Delegations and Visitors – a Selection of 2011

High-Level Visit from China Offshore-Potential in Japan EAWE-President Tavner in Oldenburg

A delegation of twelve Chinese University During a short visit for scientific exchange, Prof. Dr. Peter Tavner, Professor of the Presidents as well as a representative of the Dr. Atsushi Yamaguchi, Assistant Professor School of Engineering and Computing State Administration of Foreign Experts Af- at the Tokyo University (Workgroup Prof. Sciences at Durham University and acting fairs (SAFEA) visited the University of Old- Ishihara) visited ForWind in Oldenburg, president of the EAWE – European Acad- enburg to inform themselves on wind ener- presenting recent research projects and emy of Wind Energy came to Oldenburg gy research and scientific marine research, holding a talk about “The offshore wind en- to give a talk about “Wind Turbine Condi- welcomed by the president of the University ergy potential and the pilot research project tion Monitoring – Can we see the Effects of of Oldenburg, Prof. Dr. Babette Simon. in Japan” including the current state of re- Turbulence“ and to meet Prof. Dr. Joachim alisation of a Japanese offshore wind energy Peinke, acting Vice President of EAWE to test field. exchange plans of the future development of EAWE.

Delegation from Taiwan Business Visit from China German-Dutch Dialogue

In September Dr. Lung-Sheng Steven Lee, Sun Lixiang, “Vice General Manager” of A delegation of politicians and scientists President and Professor of the National the windturbine manufacturer Guodian met in Oldenburg at a conference for ag- United University (NUU) in Maoli (Tai- United Power Cooperation (GDUPC) and ricultural research. Members of the Dutch wan) accompanied by his colleagues Dr. Qiying Zhang, Director of GDUPC`s de- Ministry for Economics, Agriculture and Jiunn-Chi Wu (National Central University) velopment department gave an insight into Innovation (Ministerie van Economische and Mrs. Lui Wen-Huei (Ministry of Educa- the fast growing wind energy industry sec- Zaken, Landbouw en Innovatie) and of the tion Taiwan) visited the Unversity of Olden- tor in China. GDUPC is planning to open a Federal Ministry of Food, Agr i cul ture and burg to recieve information on educational German office inter alia to cooperate with Consumer Protection (Bundesministerium concepts in the field of energy. research institutions. für Ernährung, Ladwirtschaft und Ver- braucherschutz (BMELV)) discussed new ways of research and informed themselves on wind energy research. Annual Report 2011 97

ForWind Head Office has Moved around the Corner

A great change in 2011 implying lots of the majority of ForWind’s Oldenburg sci- The new location is not far away from the new possibilities, but also including much entists and the newly set up Fraunhofer former one but with the great advantage work and preparation, was the relocation IWES project group Aerodynamics and of bringing people together and shorten- of the ForWind head office together with CFD (computational fluid dynamics). ing ways.

As of April 26th 2011, the new address of ForWind – Center for Wind Energy Research ForWind`s head office is: Ammerländer Heerstrasse 136 26129 Oldenburg 98 DOCUMENTATION

Documentation

Publication List Knebel, P.; Kittel, A.; Peinke, J.: Schmoor, K.; Achmus, M.: Atmospheric Wind Field Conditions On the Influence of the Variability of Generated by Active Grids Soil Parameters on the Behaviour of Experiments in Fluid, 51, pp. 471-481 Laterally Loaded Piles in Sand, 1. Peer Reviewed Articels (2011) Proceedings of the 9th International Probabilistic Workshop, Braunschweig, Achmus, M. : Lipinsky, D.; Brüning, C.; Mayer, C.; (2011) Bemessung von Monopiles für die Arlinghaus, H. F.; Skubacz, T.; Poll, G.: Gründung von Offshore-Windenergie- Oberflächenanalyse der aus Additiven Shayeganfar, F.; Hölling, M.; Peinke, J.; anlagen – Konzepte und offene Fragen gebildeten tribologischen Schichten Reza Rahimi Tabar, M.: Bautechnik, Jg. 88, Heft 9, pp. 602-616, mit der Flugzeit-Sekundärionen- The Level Crossing Analysis of German (2011) massen-spektrometrie Stock Market Index (DAX) and Daily Oil Tribologie und Schmierungstechnik, Price Time Series Baruschka L.; Mertens, A.: 58(2011)2, pp. 29-35 Physics A online A New 3-Phase AC/AC Modular Multi- doi: 10.1016/j.physa.2011.07.037, (2011) level Converter with Six Branches in Lohaus, L.; Wefer, M.; Oneschkow, N.: Hexagonal Configuration Ermüdungsbemessungsmodell für Stresing, R.; Kleinhans, D.; Friedrich, R.; Energy Conversion Congress and Exposi- normal-, hoch- und ultra-hochfeste Peinke; J.: tion, ECCE 2011, pp. 4005-4012; (2011) Betone Different Methods to Estimate the Beton- und Stahlbetonbau, Jahrgang Einstein-Markov Coherence Length in Baruschka,L.; Mertens, A.: 106, Heft 12, pp. 836-846, Ernst & Sohn, Turbulence A New 3-Phase Direct Modular Multile- (2011) Phys. Rev E 83, 046319 (2011) vel Converter Proceedings of the 14th European Confe- Medjroubi, W.; Stoevesandt, B.; Tracht, K.; Goch, G.; Schuh, P.; rence on Power Electronics and Applica- Carmo, B.; Peinke, J.: Westerkamp F. J.; Sorg, M.; tions, EPE 2011, pp. 1-10, (2011) High-Order Numerical Simulations of Bredemeier, C.: the Ow around a Heaving Airfoil Zustandsorientierte Instandhaltung Friedrich, R.; Peinke, J.; Sahimi, M.; Computers and Fluids, 51-1, 68{84 (2011) von Windenergieanlagen Reza Rahimi Tabar, M: 6. VDI-Fachtagung Schwingungsüber- Approaching Complexity by Stochastic Medjroubi, W.; Stoevesandt, B.; wachung, VDI Berichte 2151, Leonberg, Processes: From Biological Systems to Peinke, J.: pp. 33-45, (2011) Turbulence Wake Classfication of Heaving Airfoils Phys. Report, 506, pp. 87-162 (2011) Using the Spectral /hp Element Tracht, K.; Kouamo, S. T.: Method Optimierung der Instandhaltungs Gatzen, M.; Poll, G.: Journal of Computational and Applied planung von Onshore-Windenergie- Polymerzusätze in Wälzlagerfetten, Mathematics, in print (2011) anlagen Tribologie und Schmierungstechnik ZWF Zeitschrift für wirtschaftlichen 58(2011)2, pp. 42-46, (2011) Morales, A.; Wächter; M.; Peinke, J.: Fabrikbetrieb 106, 01/02, pp, 75-79, Characterization of Wind Turbulence (2011) Hinrichs, C.: by Higher-Order Statistics Selbstorganisierte Koordinationsver- Wind Energy, online (2011) Trujillo, J.J.; Bingöl, F.; Larsen, G.; Mann, fahren für ein dezentrales Supply- DOI: 10.1002/we.478, (2011) J.; Kühn, M.: Demand Matching im elektrischen LiDAR Measurements of Wake Dyna- Verteilnetz Mücke, T.; Kleinhans, D.; Peinke, J.: mics Part II: Two Dimensional Scanning Energieinformatik 2011 – Tagungsband Atmospheric Turbulence and its Wind Energy 14(1), pp. 61-75, zum 2. Doktorandenworkshop des GI Influence on the Alternating Loads on doi:10.1002/we.402, (2011) Arbeitskreises Energieinformations- Wind Turbines systeme (GI AK EINS), Appelrath, H.-J.; Wind Energy 14, 301 (2011) Vasconcelos, V.; Raischel, F.; Haase, van Dinter, C.; Filipova-Neumann, L.; M.; Peinke, J.; Wächter, M.; Lind, P.G.; Nieße, A.; Sonnenschein, M.; Kleinhans, D.: Weinhardt, C. (Hrsg.), Karlsruhe, (2011) Principal Axes for Stochastic Dynamics Phys. Rev. E 84, 031103, (2011) Annual Report 2011 99

von Hollen, J.; Leis, A.; Poll, G.; 2. Articles Herraez, I.: Reithmeier, E.: Validating OpenFoam with the MEXICO Einfluss von Beschädigungen der Baruschka, L.; Mertens, A.: Dataset Gegenlauffläche auf das tribologische A New 3-Phase Direct Modular Multi- Proceeding of the 7th EAWE PhD Meeting Verhalten von Radialwellendichtringen level Converter on Wind Energy in Europe Delft, th th und Verfahren zur messtechnischen Proceedings of the 14th European Confer- Octobre 27 -28 2011, (2011) Detektion und Charakterisierung ence on Power Electronics and Tribologie und Schmierungstechnik, Applications, 2011, EPE 2011, pp. 1-10. Hinrichs, C.; Vogel, U.; Sonnenschein, M.: 58(2011)2, pp. 16-22 (2011) Approaching Decentralized Demand Side Management via Self-Organizing Wächter, M.; Milan, P.; Mücke, T.; Baruschka, L.; Mertens, A.: Agents Peinke, J.: A New 3-Phase AC/AC Modular Multi- ATES Workshop, Proc. of 10th Int. Conf. Power performance of wind energy level Converter with Six Branches in on Autonomous Agents and Multiagent converters characterized as stochastic Hexagonal Configuration Systems (AAMAS 2011), Yolum, Tumer, process applications of the Langevin Energy Conversion Congress and Exposi- Stone and Sonenberg (eds.), Taipei, power curve tion, 2011. ECCE 2011, pp. 4005-4012, Taiwan 2011 Wind Energy 14, pp. 711-717, (2011) 2011 Homeyer, T.; Kirrkamm, N.; Haut, C.; Gafsi, H.; Goch, G.: Schultz-von Glahn, M.; Kampers, G.; Calibration Routine for In-Process Peinke, J.; Mellert, V.; Gülker, G.: Roundness Measurements of Steel Untersuchungen geräuscherzeugender Rings During Heat Treatment Kavitäten auf einem Zylinder Proceedings of SPIE, Band 8082, Optical GALA 2011, Proceedings, (2011) Measurement Systems for Industrial Inspection, Optical Metrology 2011, Knebel, P.; Hölling, M.; Wächter, M.; München. SPIE, Bellingham, WA, 2011. Peinke, J.: ISBN 978-08194-8682-0, pp. 808231- Active Grid Generated Turbulence 808231-808231-808238. EWEA 2011 Proceedings, Brüssel, 14. , 18.03.2011 (2011) Gafsi, H.; Goch, G.: In-Process Roundness Measurements Lohaus, L., Lindschulte, N.: of Steel Rings During Gas Quenching Ductile Tube Constructions with Ultra VDI-Berichte, Band 2156, Laser Metrology High Performance for Precision Measurement and Inspec- Proceedings of the fib Symposium tion in Industry (LMPMI) 2011, 6th IMEKO Prague, June 2011 Symposium, Braunschweig. VDI-Verlag, Düsseldorf, 2011. Lohaus, L., Wefer, M., Oneschkow, N.: ISBN 978-3-18-092156-3, pp. 155-160. High Performance Concrete – How Do Deal with Fatigue? Gafsi, H.; Goch, G.: Proceedings of the fib Symposium Semi-Optical In-Process-Metrology to Prague, June 2011 Determine the Roundnes Deviation of Bearing Rings During Heat Treatment Lohaus, L.: Zoch, H. W.; Lübben, T. (Hrsg.): 3rd Spezialbetone im Kraftwerksbau International Conference on Distortion 21. Kassel-Darmstädter Baubetriebs- Engineering 2011, Bremen. 2011. seminar Schalungstechnik, Tagungsband, ISBN 978-3-88722-724-1, pp. 583-590. November 2011

Heißelmann, D.; Peinke, J.; Hölling, M.: Lübke, K.; von Freyberg, A.; Stöbener, D.; Comparing The Sphere Anemometer Ghebreyesus, B.; Goch, G.: to Standard Anemometers for Wind Comparison of Different Strategies For Energy Multi-Axes Milling of Involute Gears Proceeding of the 7th EAWE PhD Meeting The proceedings of MTTRF 2011 Meeting, on Wind Energy in Europe Delft, Chicago, Illinois, USA. 2011, pp. 107-112. Octobre 27th-28th 2011, (2011) 100 DOCUMENTATION

Milan, P.; Wächter, M.; Peinke, J.: Stöbener, D.; von Freyberg, A.; Zhang, P.; Renken, V.; Goch, G.: Stochastic Modeling of Wind Power Fuhrmann, M.; Goch, G.: Cross-Plane Quality Control Concept of Production Characterisation of Gear Distortions the Bearing Ring Production EWEA 2011 Proceedings, Brüssel, with Areal Parameters Lübben, T.; Zoch, H. W. (Hrsg.): March 14th-18th 2011, (2011) Zoch, H. W.; Lübben, T. (Hrsg.): 3rd 3rd International Conference on International Conference on Distortion Distortion Engineering 2011, Ohlendorf, J.-H.; Rolbiecki, M.; Schmohl, Engineering, Bremen. 2011, pp. 147-154. 3rd International Conference on T.; Müller, D. H.; Thoben, K.-D.: Distortion Engineering 2011 Bremen. Entwicklung von Handhabungseinrich- Wächter, M.; Hölling, M.; Milan, P.; Bremen, 2011 tungen für biegeschlaffe Materialien Peinke, J.: ISBN 978-3-88722-724-1, pp. 45-52 – Automatisierter preform-Aufbau für Turbulence and the Nature of the Rotorblätter von Windenergieanlagen Atmospheric Boundary Layer Brökel, K.; Stelzer, R.; Feldhusen, J.; Rieg, Proceedings of the 6th AIAA Theoretical F.; Grote, K.-H. (Hrsg.): 9. Gemeinsames Fluid Mechanics Conference, Hawaii, Kolloquium Konstruktionstechnik, Ros- June 27th-30th 2011, (2011) tock, Shaker Verlag, pp. 141-146, October 7th-8th 2011, (2011) Westerkamp, J. F.; Sorg, M.; Bredemeier, C.; Goch, G.: Reinke, N.; Renken, E.; Knebel, P.; Berührungslose Messung des Dreh- Peinke, J.; Hölling, M.: winkels und der Axialbewegung an Atmospheric Boundary Layer Velocity Rotorwellen von Windenergieanlagen Profiles Generated by an Active Grid Puente León, F.; Beyerer, J. (Hrsg.): Proceeding of the 7th EAWE PhD Meeting XXV. Messtechnischen Symposiums des on Wind Energy in Europe Delft, Arbeitskreises der Hochschullehrer für Octobre 27th-28th 2011, (2011) Messtechnik e.V. (AHMT), Karlsruhe. Shaker Verlag, Aachen, 2011 Rockel, S.; Peinke, J.; Hölling, M.: ISBN 978-3-8440-0388-8 Dynamics Of A Floating Wind Turbine Model Westerkamp, J. F.; Stöbener, D.; Proceeding of the 7th EAWE PhD Meeting von Freyberg, A.; Furhmann, M.; on Wind Energy in Europe Delft, Goch, G.: Octobre 27th-28th 2011, (2011) Auswertung flächenhafter Messungen an Großverzahnungen Rolfes, R.; Häckell, M. W.; Haake, G.: Puente León, F.; Beyerer, J. (Hrsg.): Automated System Identification and XXV. Messtechnisches Symposium des Validation of Numerical Models of Arbeitskreises der Hochschullehrer für Offshore Wind Turbines as Basis for Messtechnik e.V. (AHMT), Karlsruhe. SHM-Analysis Shaker Verlag, Aachen, 2011 Proceedings of the 8th International ISBN 978-3-8440-0388-8 Workshop on Structural Health Monitor- ing, Stanford, CA, USA. pp. 2149-2156 Zerbst, S., Haase, K.-H., Rolfes, R., Knops, M. : Schmoor, K.; Achmus, M.: Novel Sensor Concept for Monitoring On The Influence of the Variability of of Wind Turbine Blades Soil Parameters on the Behaviour of Proceedings of the 8th International Laterally Loaded Piles in Sand Workshop on Structural Health Proceedings of the 9th International Monitoring 2011, Volume 2, Probabilistic Workshop, Braunschweig, pp. 2157-2166, San Francisco, November 17th-18th 2011 Sept. 13th-15th, 2011 ISBN: 978-1-60595-053-2 Schuh, P.; Tracht, K.; Westerkamp, J. F.; Sorg, M.; Bredemeier, C.; Goch, G.: Zustandsorientierte Instandhaltung von Windenergieanlagen VDI Wissensforum GmbH (Hrsg.): VDI- Berichte, Band 2151, 6. VDI-Fachtagung Schwingungsüberwachung, Leonberg bei Stuttgart. VDI-Verlag, Düsseldorf, 2011. ISBN 978-3-18-092151-8, pp. 33-34. Annual Report 2011 101

3. Conference Contributions Barth, S.: Greve, T.: Wind as a Fuel Hydrothermale Karbonisierung, Abdel-Rahma K.; Achmus, M. : SIEMENS-Forum, Hannover, Germany, Dialog Zukunftsenergie des Energie Numerical Modeling of Tension Piles April 4th 2011 Kompetenz Zentrum e.V., Region Braun- under Axial Cyclic Loading schweig Ostfalia HAW, Wolfenbüttel, International Symposium on Computatio- Barth, S.: November 8th 2011 nal Geomechanics (ComGeo II), Windphysik und deren Ansprüche an Dubrovnik/Croatia, April 27th-29th, (2011) Geodaten Grießmann, T.; Rustemeier, J.; Rolfes, R.: 25th Anniversary of the Academy of Einsatz von Blasenschleiern zur Fischer, T.; de Vries, W.; Rainey, P.; Geosciences and Geotechnologies, Reduktion des Rammschalls im Wasser Schmid, B.; Argyriadis, K.; Kühn, M.: Hannover, Germany, November18th 2011 Forum Geotechnik und Baubetrieb, Integration of Support Structure and Institut für Geotechnik und Baubetrieb. Turbine Design – Final Results of WP4 Barth, S.: Technische Universität Hamburg-Harburg, Task 4.1 on Offshore Support Windphysik und deren Ansprüche an April 21th 2011 Structures of the EU UpWind Project Geodaten ISOPE, Maui, 2011 (peer reviewed), (2011) 4th German Geo Forum, Berlin, Germany, Grießmann, T.; Rustemeier, J.; Neuber, April 11th 2011 M.; Rolfes, R.: Abdel-Rahman, K.; Achmus, M.: Unterwasserschall bei der Errichtung Behavior of Foundation Piles for Off- Bredemeyer, J.; Schrader, T.; von Offshore-Windenergieanlagen shore Wind Energy Plants under Axial Kleine-Ostmann, T.; Münter, K.: VDI-Fachkonferenz: Schall und Cyclic Loading Quasi-Stationary Measurements of Atc Schallemissionen von Windenergie- Simulia Customer Conference, Barcelona/ Radar Signals-In-Space anlagen, Hamburg, November 29th– Spain, May 16th-19th 2011 International Radar Symposium (IRS) December 1st 2011 2011, Leipzig, September 7th–9th 2011, Achmus, M.: (2011) Gülker, G.: Geotechnical Design of Horizontally Laser-optische Untersuchungen an and Axially Loaded Offshore Piles Dobschinski, J.; Wessel, A.; Lange, B.; Kunst- und Kulturobjekten Offshore Foundations for Wind Turbines, von Bremen, L.: Abschlusskolloquium des Projektes Bremen, July 4th 2011 Visualizing And Optimizing The Relia- TERAART, Fraunhofer Institut IWS, bility Of Ensemble Prediction Systems Dresden , November 23rd 2011 Achmus, M.; Albiker, J.; Peralta, P.; tom EWEA 2011, March 2011, Brussels, (2011) Wörden, F.: Drechsler, S.; Mach, J.-N.: Hadjihosseini, A.; Wächter, M.; Peinke, J.: Scale effects in the Design of Large Verbesserter Kraftschluss im Umschlin- Stochastic Analysis of Rogue Waves Diameter Monopiles gungs-CVT durch optimierte Oberflächen- International Workshop on Rogue Wave, EWEA Annual Conference, Brussels, mikrostrukturierung, Dresden, Germany, March 14th-17th 2011, (2011) Informationstagung 2011 der Forschungs- November 7th- 11th 2011 vereinigung Antriebstechnik e. V., Heißelmann, H.; Peinke, J.; Hölling, M.: Achmus, M. : November 23th-24th 2011, Würzburg, FVA Comparing The Sphere Anemometer to Zur Mindesteinbindetiefe von horizontal Forschungsreport 2011 Standard Sensors for 2D Wind Mea- belasteten Offshorepfählen surements 8. Kolloquium des Forschungszentrums Fricke, M; Ehrt, O.; Krieger, J.; Hayek, W.; 64th Annual Meeting of the American Küste (FZK), Maritimer Wasserbau und Rolfes, R.: Physical Society – Devision of Fluid Dyna- Küsteningenieurwesen, Hannover, Development and Simulation of Sonar mics (APS-DFD) Baltimore, USA, March 10th 2011 Transponders to Prevent Submarines November 20th-22nd 2011 from Collisions with Offshore Wind Farms Barth, S.: EWEA Offshore 2011. Amsterdam, Nether- Heißelmann, H.; Peinke, J.; Hölling, M.: Innovations in Wind Energy – From lands (2011) Comparing the Sphere Anemometer Research To Wind Power Plants To Standard Anemometers for Wind dena Forum, Hannover, Germany, Fuchs, F.: Energy April 5th 2011 Steady State Lifetime Estimation 7th EAWE PhD Meeting on Wind Energy of Power Semiconductors in Rotor in Europe, Delft, Netherlands, Barth, S.: Side Converter of a 2 MW DFIG Wind October 27th- 28th 2011 Innovations in Wind Energy Turbine via Power Cycling Capability 3rd German American Wind Energy Analysis Herraez, I.: Conference, Houston, Texas, USA, EPE’11 ECCE 4th European Conference Flow over a Wind Turbine: Simulation June 28th 2011 on Power Electronics and Applications, And Validation Birmingham (UK), 30. August 30th – 5th European Postgraduate Fluid September 1st 2011 Dynamics Conference, Göttingen, August 9th- 12th 2011 102 DOCUMENTATION

Herraez, I.: Keshtova, F.: Luhur, M.R.; Milan, P.; Schneemann, J.; Simulation and validation of the Characterization of Turbulence by Wächter; Peinke, J.: MEXICO-Wind Turbine with OpenFOAM Higher-Order Statistics Stochastic Modeling of Lift Dynamics 6th OpenFoam Workshop, PennState Third EAWE-WAUDIT PhD School on Wind Under Turbulent Conditions University, USA, June 13th-16th 2011 Energy, Delft, Netherlands, DPG 75th Annual Meeting and Spring October 24th-26th 2011 Meeting 2011, Dresden, Herraez, I.: March 13th-18th 2011 Validating OpenFoam with the MEXICO Keshtova, F.; Peinke, J.: Dataset Intermittent Spatial and Temporal Matha, D.; Fechter, U.; Kühn, M.: 7th EAWE PhD Seminar on Wind Energy Structure of Wind Fields Non-linear Multi-Body Mooring System in Europe, Delft, Netherlands, 7th EAWE PhD Seminar on Wind Energy Model for Floating Offshore Wind October 27th-28th 2011 in Europe, Delft, Netherlands, Turbines October 24th-26th 2011 EWEA OFFSHORE2011, Amsterdam, (2011) Hölling, M.; Morales, A.; Wächter, M.; Peinke, J.: Kühn, M.: Medjroubi, W.: Atmospheric Turbulence and its Is Windpower Innovative Anymore? Frequency Selection in Heaving Airfoil Relevance for Wind Energy Related RETC Innovationsforum, Hamburg, June Wakes Using a High-order Numerical Research 15th 2011 Method,Numerical Method in Details 64th Annual Meeting of the American 24th Chemnitz Finite Element Method Physical Society – Devision of Fluid Dyna- Kühn, M.: Symposium, Holzhau, mics, (APS-DFD) Baltimore, USA, Lessons Learned aus 20 Jahren September 28th- 30th2011 November 20th- 22th2011 Offshore Leibniz Zukunftsdialog, Hannover, Medjroubi, W.: Homeyer, T.; Kirrkamm, N.; Haut, C.; May 19th 2011 Frequency Selection in Heaving Airfoil Schultz-von Glahn, M.; Kampers, G.; Wakes Using a High-order Numerical Peinke, J.; Mellert, V.; Gülker, G.: Kühn, M.; Steinfeld, G.; Dubois, J.; Method Investigations of Cavity Noise Emeis, S.; Foreman, R.; Kruse, J.; Lutz, T.; Summer School Complex Motion in Flu- Generation on a Cylinder Meister, K.; Neumann, T.; Quappen, J.; ids, Krogerup Hojskole, Denmark, XXXI. Dynamics Days Europe, Oldenburg, Rettenmeier, A.; Siegmeier, B.; Tambke, August 7th- 13th 2011 September 12th-16th 2011 J.; Trujillo, J.J.; Wächter, M.: Verification of Offshore Wind Turbines Morales, A.: Homeyer, T.; Kirrkamm, N.; Haut, C.; at Alpha Ventus – Overview on First Adaptive De-Trending and Stochastic Schultz-von Glahn, M.; Kampers, G.; Measurement Analyses Analysis of Wind Time Series Peinke, J.; Mellert, V.; Gülker, G.: EWEA Offshore 2011, Amsterdam, (2011) DPG 75th Annual Meeting and Spring Untersuchungen geräuscherzeugender Meeting 2011, Dresden, Kavitäten auf einem Zylinder Kuhnle, B.; Trujillo, J.J.; Kühn, M.: March 13th-18th 2011 DGLR, DEGA, X-Noise Workshop Analysis of Aero-Elastic Simulations in Strömungsschall, Berlin, Wind Farms With Measurements at the Morales, A.: November 17th-18th 2011 Offshore Test Field Alpha Ventus Characterization of Wind Turbulence 7th EAWE PhD Seminar 2011 Seminar on With Higher-Order Statistics, Boundary Homeyer, T.; Kirrkamm, N.; Haut, C.; Wind Energy in Europe, Delft, (2011) Layer Turbulence (Blt-Bbos) Schultz-von Glahn, M.; Kampers, G.; KNMI (Royal Netherlands Peinke, J.; Mellert, V.; Gülker, G.: Langner, M.: Meteorological Institute), Untersuchungen geräuscherzeugender Investigation of Driver Behavior Based De Bilt Netherlands, May 26th 2011 Kavitäten auf einem Zylinder on Langevin Analysis 19. GALA-Fachtagung Lasermethoden in XXXI. Dynamics Days Europe, Oldenburg, Morales, A.; Peinke, J.; Millan, P.: der Störmungsmesstechnik,Ilmenau, September 12th- 16th 2011 Statistical Unfolding of Atmospheric September 6th-8th 2011 Turbulence Lünsdorf, O.; Sonnenschein, M.; Mohr- 64th Annual Meeting of the American Keshtova, F.: mann, M.; Hofmann, L.; Gronstedt, Ph.; Physical Society – Devision of Fluid Dyna- Characterization and Modeling of Kurrat, M.: mics (APS-DFD) Baltimore, USA, Turbulent Wind Profile Möglichkeiten einer netzorientierten November 20th-22th2011 Standardization Workshop, Hamburg, Betriebsweise zur weiteren Integration University of Hamburg, Germany, dezentraler Energieumwandlung auf May 19th- 20th 2011 Verteilnetzebene ETG-Kongress 2011 Annual Report 2011 103

Neubauer, T.: Peinke, J.: Peinke, J.: Quantifizierung von Leistungsdichte- Analysis of Extreme Weather/Stock Windenergie eine turbulente Energie- grenzen von Wälzlagern zur Vermei- Market Events quelle für das Netz dung von Drehzahlschäden Summer Modern Computational Science: II. Innovationsworkshop: Informationstagung 2011 der Forschungs- Simulation of Extreme Events Energiespeicherung und deren vereinigung Antriebstechnik e. V., FVA (MCSextreme), University of Oldenburg, zukünftige Applikationen, Halle, Salle, Forschungsreport 2011, Würzburg, August 15th-26th 2011 May 23rd- 24th 2011 November 23th-24th 2011, FVA Forschungsreport 2011 Peinke, J.: Peinke, J.: A New Class Of Turbulence – Insights Wind Farm Projects in Europe Ohlendorf, J.-H.; Rolbiecki, M.; From The Perspective Of N-Point NSF Workshop on Wind Energy & Schmohl, T.; Müller, D. H.; Thoben, K.-D.: Statistics Turbulence, Universidad del Turabo, Entwicklung von Handhabungseinrich- 1st UK-Japan bilateral workshop: Caguas, Puerto Rico, tungen für biegeschlaffe Materialien Turbulent fl ows generated / designed in February 24th-26th 2011 - Automatisierter preform-Aufbau für multiscale / fractal ways: fundamentals Rotorblätter von Windenergieanlagen and application Departmend of Poll, G.: 9. Gemeinsames Kolloquium Aeronautics, Imperial College London, Fluid Rheology, Traction/Creep Re- Konstruktionstechnik, March 28th-29th 2011 lationships and Friction in Machine Oktober 7th-8th 2011 Elements with Rolling Contacts Peinke, J.: 38. Leeds-Lyon Symposium on Tribology, Ohlendorf, J.-H.; Rolbiecki, M.; Stochastic Modelling and Extreme Lyon, France, Schmohl, T.: Winds September 6th-9th 2011 MAPRETEC - Automatisierte Herstel- EAWE 2nd Ph.D. School von Karman lung von Rotorblättern für WEA Institute for Fluid Dynamics, Brussels, Poll, G.: Arbeitskreis XXL-Produkte, Bremerhaven, Belgium, November 7th-11th 2011 Rheologie von Schmierstoffen in kon- November 23th 2011 zentrierten Wälzkontakten Peinke, J.: 7. Arnold-Tross-Kolloquium, Hamburg, Ottink, K.; Poll, G.: Struktur des Windes: Das Umfeld für die June 17th 2011 Analysis of The Lubricant Film Thick- Regelung und Steuerung der Windener- ness on Rod Seals By Application of gieanlage, Fachveranstaltung MSR-Tech- Poll, G.; Wang, D.; Neubauer, T.: The Fluorescence Method nik an Windenergieanlagen Wälzlager-Reibmomente unter Berück- 21st International Conference on Fluid Haus der Technik, Essen, sichtigung der Schmierstoff-Rheologie Sealing, Buckinghamshire (UK), August 17th-18th 2011 und –versorgung November 30th-December 1th 2011 VDI-Tagung Gleit und Wälzlagerungen, Peinke, J.: Schweinfurt, Ottink, K.; Wennehorst, B.; Poll, G.: Turbulence and Wind Energy May 24th-25th 2011 Analysis of the Lubricant Film Thick- Festkolloquium Prof Schöll – Order and ness on Rod Seals by Application of Chaos in Physical Systems: Analysis and Puczylowski, J.; Hölling, M.; Peinke, J.: the Fluorescence Method Control, TU Berlin, New Measurement Technique for 66th Annual Meeting and Exhibition, Institut für Theoretische Physik, Berlin, Turbulent Flow as a Replacement for Society of Tribologists and Lubrication February 2nd 2011 Hot-Wire Anemometry Engineers (STLE), Atlanta (GA USA), 64th Annual Meeting of the American May 15th-19th 2011 Peinke, J.: Physical Society - Devision of Fluid Dyna- Turbulenzen als unbekannte Größen mics (APS-DFD) Baltimore, USA, Patel, R.; Achmus, M.; Singh, B.; von Offshore-Winden November 20th- 22th 2011 Abdel-Rahman, K. : 2. VDI-Fachkonferenz Offshore-Windener- DEM Simulations of Soil-Pile Interface gieanlagen, Bremerhaven, Puczylowski, J.; Peinke, J.; Hölling, M.: under Static and Cyclic Loading September 27th-28th 2011 New Anemometers for Particles 2011 – II International Characterization of Atmospheric Conference on Particle-based Methods Peinke, J.: Turbulent Ows on Small Scales – Fundamentals and Applications, Barce- Turbulenz und Windenergie ETC13, 13th European Turbulence lona, October 26th-28th 2011 Institutskolloquium, Conference, Warschau, 12. - 15.09.2011 Humboldt-Universität Berlin, Berlin, January 11th 2011 Reinke, N.; Stoevesandt; B.: Experimental Contribution to MexNext II IEA/EERA Meeting, Amsterdam, December 7th- 9th 2011 104 DOCUMENTATION

Reinke, N.; Renken, E.; Knebel, P.; Stoevesandt, B.; Herraez, I.; Plischka, H.; Trabucchi, D.; Trujillo, J.J.; Steinfeld, G.; Peinke, J.; Hölling, M.: Peinke, J.: Schneemann, J.; Kühn, M.: Atmospheric Boundary Layer Velocity Short Report on MexNEXT Subtask 4.6: Simulation of measurements of wake Profiles Generated by an Active Grid 3D-Ows dynamics with nacelle and ground 7th EAWE PhD Meeting on Wind Energy IEA-Wind Task 29 Meeting, Jeju, Korea, based lidar wind scanners in Europe, Delft, Netherlands, Juune 14th-16th 2011 Wake Conference Visby, Visby, (2011) October 27th-28th 2011 Stoevesandt, B.; Hochstedt, H.; von Bremen, L.: Renken, E.; Knebel, P.; Hölling, M.: Weitemeyer, S.; Peinke, J.: Assessment of ECMWF’s 100m EPS Generation Of Homogeneous Shear Generating Turbulent in Flow For Cfd Winds in Probabilistic Wind Power Turbulence by Using an Active Grid EERA-Aerodynamics/IEA-Aerodynamics Forecasting DPG 75th Annual Meeting and Spring experts meeting, Amsterdam, 16th International Conference on Meeting 2011, Dresden, December 8th-9th 2011 Intelligent System Application on Power March 13th-18th 2011 Systems (ISAP), Stoevesandt, B.; Reinke, N.; Crete, (Greece), September 2011 Rinn, P.; Milan, P.; Wächter, M.; Peinke, J.: Fanzhong Meng: Stochastic Modeling of Wind Turbine Contribution to the IEA-Task MexNEXT von Bremen, L.: Characteristics Phase II Assessment of ECMWF’s 100m EPS Workshop, Selbstorganisation und IEA Wind Task 29 Meeting, Amsterdam, Winds in Probabilistic Wind Power Komplexität, December 7th 2011 Forecasting Zaferna-Hütte, August 7th-12th 2011 Meeting of the European Meteorological Stoffels, N.; von Bremen, L.: Society (EMS), September, Berlin, (2011) Rinn, P.; Milan, P.; Wächter, M.; Peinke, J.: Improving the Cosmo-Eu Model for Stochastic Modeling of Wind Turbine Better Wind Power Predictions in the von Bremen, L.: Characteristics European Transmission System Characterizing Wind Power Variability 7th EAWE PhD Seminar on Wind Energy Operator Zones Reduction through Spatial Smoothing in Europe, Delft, Netherlands, 7th PhD Seminar on Wind Energy in Euro- Effects October 27th-28th 2011 pe, October 2011, Delft, The Netherlands, Energy and Climate Workshop at IC3, (2011) Barcelona, May 27th 2011 Rinn, P.; Milan, P.; Wächter, M.; Peinke, J.: Wind Energy Conversion – a Stochastic Thieken, K.; Achmus, M.: von Bremen, L.; Tambke, J.; Response Problem Zum Einfluss der kombinierten Be- Heinemann, D.: XXXI. Dynamics Days Europe, Oldenburg, lastung auf das Tragverhalten von Studying Wind Power Forecast Errors September 12th-16th 2011 Pfählen in nichtbindigen Böden on the European Scale Pfahlsymposium 2011, Braunschweig, EWEA 2011, Brussels, March 2011 Rockel, S.; Peinke, J.; Hölling, M.: February 17th-18th 2011 Dynamics of A Floating Wind Turbine von Bremen, L., Tambke, J.; Stoffels, N.; : Model Tischmacher, H.; Gattermann, S.; Simulation einer europäischen Wind- 7th EAWE PhD Seminar on Wind Energy Kriese, M.; Wittek, E. C. ; Ponick, B.; leistungsprognose in Europe, Delft, Netherlands, Poll, G.: 2. Fachtagung Energiemeteorologie, October 27th- 28th 2011 Lagerströme bei umrichtergespeisten Bremerhaven, April 2011 Elektromotoren Rustemeier, J.; Grießmann, T.; Rolfes, R.: VDI-Tagung Gleit- und Wälzlagerungen, von Bremen, L.; Stoffels, N.; Tambke, J.: Use of Bubble Curtains to Mitigate Schweinfurt, Smoothing of Variability and Forecast Hydro Sound Levels at Offshore May 24th-25th 2011 Error in Europe’s Wind Power Construction Sites Production 4th International Conference and Trabucchi, D.; Trujillo, J.J.; Steinfeld, G.; Meeting of the European Meteorological Exhibition on Underwater Acoustic Schneemann J.; Machta, M.; Cariou, J.P.; Society (EMS), Berlin, September 2011 Measurements: Technologies & Results, Kühn, M.: Kos, Greece, Numerical assessment of performance von Gallera, D.; Trujillo, J.J.; Nicklas D.: June 20th-24th 2011 of lidar WindScanner for wake Leistungskennlinienberechnung von measurements Windenergieanlagen unter Einsatz Schaumann, P.; Dubois, J.; Achmus, M.; Bruxelles, EWEA 2011 eines Datenstrommanagementsystems Abdel-Rahman, K.; Seidel, M.: DSEP 2011: Workshop on data and event Local Dynamics of Jacket Support processing (2011) Structures for Offshore Wind Turbines, European Offshore Wind 2011 Amsterdam, Netherlands, November 29th-December 1st 2011 Annual Report 2011 105

Wächter, M.: 4. Other Publications Barth, S.: Stochastic Modeling of Wind Power Windenergie Production Achmus, M.: Luncheon of the Oldenburg University EWEA 2011, Brüssel, Baugrunduntersuchungen und President, Oldenburg, Germany, th th th March 14 -18 2011 Gründungen für Windenergieanlagen, May 4 2011 Fachseminar Türme und Gründungen bei Wächter, M.; Hölling, M.; Milan, P.; Windenergieanlagen im Haus der Technik Greve, T.: Peinke, J.: e.V., Essen, March 22th/23th 2011 Hydrothermal Carbonization Turbulence and The Nature of the Delegation from Universidade Federal do Atmospheric Boundary Layer Achmus, M.: Amazonas (UFAM) in Manaus, rd 6th AIAA Theoretical Fluid Mechanics Bodenmechanische Laborversuche zur Oldenburg, February 23 2011 th th Conference,Hawaii, June 27 -30 2011 Untersuchung des Bodenverhaltens unter zyklischer Belastung Hölling, M.; Milan, P.: Wächter, M.; Milan, P.; Mücke, T.; Fachseminar, Baugrunderkundung, Wind Energy I Peinke, J.: Gründungsinstallation und -monitoring Universidade Tecnologica Federal do Stochastic Modeling of Turbulent Wind für Offshore-Windenergieanlagen, Parana (UTFPR), Curitiba, Brasilien, th rd Fields Haus der Technik e.V. in Essen, February 21 - 23 2011 EERA-Aerodynamics/IEA-Aerodynamics December 8th/9th 2011 experts meeting, Amsterdam, Kühn, M.; Gasch, R.; Sundermann, S.: th th December 8 -9 2011 Achmus, M.: Chap. 8 Structural Dynamic Offshore-Windenergieanlagen – Gasch, R.; Twele, J.: Wind Power Plants - Weber, N.: Baugrunduntersuchung und Tragver- Fundamentals, Design, Construction and Optimierte Beölung von halten der Gründung Operation, 2nd ed., Springer (2011) Synchronisierungen Fachseminar der FORWIND-Academy Informationstagung 2011 der Forschungs- und dem Haus der Technik e.V. Offshore- M. Kühn, vereinigung Antriebstechnik e. V., Windenergie – Design und Installation Chap. 16 Offshore Wind Farms Würzburg, FVA Forschungsreport 2011 von Tragstrukturen in der Nordsee, Gasch, R.; Twele, J.: Wind Power Plants - rd th November 23 -24 2011 Bremerhaven, September 7th/8th 2011 Fundamentals, Design, Construction and Operation, 2nd ed., Springer (2011) Wennehorst, B.; Engelke, E.; Poll, G.: Achmus, M. : Modelling Radial Lip Seal Friction – a Offshore Wind Energy Converters – Kühn, M.: Multi-Scale Mixed Lubrication Soil Investigations and Foundation Darth Vader und die Windenergie – Approach Design Wie man mit Laserschwertern den 21st International Conference on Fluid National Cheng Kung University, Tainan, Wind verstehen lernt Sealing, Buckinghamshire (UK), Taiwan, Oktober 27th 2011 Tag der Physik, Universität Oldenburg, 9. November 30th- December 1st 2011 November 9th 2011 Barth, S.: Wennehorst, B.; Poll, G.: ForWind – Wind Energy Research Kühn, M.; Trujillo, J.J.; Schneemann, J.; Fundamental Studies on the Delegation from Thailand, Bremerhaven, Harris, M.; Cariou, J.P.: Tribological Characteristics of Radial Germany, October 24th 2011 LiDAR - Windmessung für On- und Lip Seals Offshore-Windparks – Theorie, Erfah- 66th Annual Meeting and Exhibition, Barth, S.: rungen und Praxisempfehlungen th Society of Tribologists and Lubrication ForWind – Wind Energy Research Bremen, November 10 2011 Engineers (STLE), Atlanta (GA USA), Delegation from The Netherlands, th th May 15 -19 2011 Oldenburg, Germany, October 13th 2011 Kühn, M.; Trujillo, J.J.; Mikkelsen, T.; Rettenmeier, A.: Barth, S.: Proposal for a New Iea Wind Task: Hightech aus Nordwest – Forschung Wind Lidar Systems for Wind Energy und Innovationen in der Windenergie Deployment (LIDAR) VDI, Emden, Germany, 67th Meeting of the Executive Commit- November 8th 2011 tee of the IEA Implementing Agreement on Co-operation in the Research and Barth, S.: Development of Wind Energy Systems, th Wind Energy Deployment in Germany Amsterdam, April 13 2011 IEA Wind ExCo, Dublin, Ireland, Oktober 19th 2011 106 DOCUMENTATION

Kühn, M.; Klaus, T.: 5. Lectures Gülker, G.: Windenergie – Rückenwind für eine Kohärente Optik zukunftsfähige Technik Achmus, M. : Carl von Ossietzky Universität Oldenburg, Bührke, Th.; Wengenmayr, R. (Hrsg.), Grundbaukonstruktionen Institute of Physics, Erneuerbare Energie. Alternative Energie- Leibniz Universität Hannover, Institute Winter term 2010/2011 konzepte für die Zukunft, Wiley-VCH, for Geotechnical Engineering. 3. Aufl., Weinheim (2011) Summer term 2011 Gülker, G.: Kohärente Optik Kühn, M.: Bredemeyer, J.: Carl von Ossietzky Universität Oldenburg, Wind Energy Research at ForWind – Funkmesstechnik in der Luftfahrt Institute of Physics, University Oldenburg Leibniz Universität Hannover, Winter term 2011/2012 Delegation from China, Oldenburg, Summer term 2011 June 23th 2011 Heinemann, D.; Kühn, M.; et al.: Bredemeyer, J.: Introduction to Engineering Physics Lohaus L.; Lindschulte N.: Radaranwendungen in der Luftfahrt Carl von Ossietzky Universität Oldenburg, Offshore Windenergie Anlagen – Leibniz Universität Hannover, Institute of Physics, Grouted Joints (Verarbeitung, Winter term 2011/2012 Winter term 2010/2011 Ausführung, Überwachung) Fachseminar ForWind, Bremerhaven, Chernukha, P.; Gardner, A. D.; Heinemann, D.; Kühn, M.: September 2011 Mulleners, K.; Richter, K.; Raffel, M.: Introduction to Renewable Energies Rotoraerodynamik Carl von Ossietzky Universität Oldenburg, Peinke, J.: Leibniz Universität Hannover, Institute Institute of Physics, Summer term 2011 Erneuerbare Energien of Turbomachinery and Fluid Dynamics, Max-Eyth-Schule, Berufsbildende Schulen Winter term (2011/2012) Hölling, M.; Peinke, J.: Schiffdorf, February 16th 2011 Wind Energy Garbe, H.: Carl von Ossietzky Universität Oldenburg, Peinke, J.: Messverfahren für Signale und Institute of Physics, Windenergie Systeme (Measurement Techniques for Winter term 2011/2012 Impulsreferat 41. Sitzung des Signals and Systems) Auswahlgremiums, Leibniz Universität Hannover, Hölling, M.; Peinke, J.: Deutsche Bundesstiftung Umwelt, Summer term 2011/2012 Wind Energy Osnabrück, October 11th-12th 2011 Carl von Ossietzky Universität Oldenburg, Garbe, H.: Institute of Physics, Elektromagnetische Verträglichkeit Winter term 2010/2011 (Electromagnetic Compatibility) Leibniz Universität Hannover, Kühn, M.: Winter term 2011/2012 Advanced Wind Energy Technology Carl von Ossietzky Universität Oldenburg, Goch, G.: Institute of Physics, Summer term 2011 Verzahnungsmesstechnik Bremen Institute for Metrology, Kühn, M.: Automation and Quality Science, Finite Element Analysis Universität Bremen, Carl von Ossietzky Universität Oldenburg, Winter term 2010/2011 Institute of Physics, Winter term 2010/2011 Goch, G.: Geometrische Messtechnik mit Labor Kühn, M.; Peinke, J.; Heinemann, D.: Bremen Institute for Metrology, Wind Energy – Topics of Ongoing Automation and Quality Science, Research (Colloquium) Universität Bremen, Carl von Ossietzky Universität Oldenburg, Sommer Term 2011 Institute of Physics, Winter term 2010/2011 and Grießmann, T.; Häckell, M.: summer term 2011 Schwingungsprobleme bei Bau- werken Kuhnle, B.: Gottfried Wilhelm Leibniz Universität Modelling of Wind Turbine Dynamics Hannover, Institute of Structural Analy- (Bladed Software Seminar) sis, Winter term Carl von Ossietzky Universität Oldenburg, Institute of Physics, Summer term 2011 Annual Report 2011 107

Kurrat, M.; Sonnenschein, M.: Thoben, K.-D.: 6. Project Reports Dezentrale Energiesystem Anwendung von Konstruktions- eLearning-course, University of Braunsch- methoden Bandmann, J., Jansen, F., Rieser, S., weig and University of Oldenburg, Universität Bremen, Institut für Wottrich, J.: Winter term 2011/2012 integrierte Produktentwicklung (BIK), Fertigungsentwicklung einer Sommer term 2011 automatisierten, dreidimensionalen Lohaus, L.: Handhabungstechnologie mit integri- Innovatives mit Beton (Betontechnolo- Thoben, K.-D.: erter bildoptischen Überwachung gie der Sonderbetone) CAD – Management und virtuelle Projektarbeit, Leibniz-Universität Hannover, Institute of Produktentwicklung BIK, Universität Bremen (2011) Building Materials Science, Winter term Universität Bremen, Institut für 2010/2011 integrierte Produktentwicklung (BIK), Devechi G., Thraen M.: Sommer term 2011 Untersuchung der Verbundbedingun- Peinke, J.: gen dünnwandiger UHPC-Rohre mittels Fluidynamik Thoben, K.-D.: Ultraschallmessung Carl von Ossietzky Universität Oldenburg, Definition und Evaluierung von Projektarbeit, Institute of Physics, Produkteigenschaften Leibniz Universität Hannover (2011) Winter term 2010/2011 Universität Bremen, Institut für integrierte Produktentwicklung (BIK), Diekmann, H.; Meister, S.: Peinke, J.: Sommerterm 2011 Auswirkungen von Wassergehalts- Mechanik schwankungen auf die Frisch- und Carl von Ossietzky Universität Oldenburg, Thoben, K.-D.: Festmörteleigenschaften von Verguss- Institute of Physics, Einführung in die Konstruktions- mörteln für Grouted Joints Winter term 2010/2011 methodik Studienarbeit, Universität Bremen, Institut für Leibniz Universität Hannover (2011) Rolfes, R.; Jansen, E.; Jacob, H.-G.; integrierte Produktentwicklung (BIK), Scheffler, S.: Sommer term 2011 Duus, O., Kunkel L.: Faserverbund-Leichtbaustrukturen Untersuchungen des Spannungs- und Gottfried Wilhelm Leibniz Universität Thoben, K.-D.: Dehnungsverhaltens dünnwandiger, Hannover, Institute of Structural Analysis, K-Lehre 1 ummantelter UHPC-Rohre mit ver- Winter term Universität Bremen, Institut für schiedener Lasteinleitung integrierte Produktentwicklung (BIK), Projektarbeit, Rolfes, R.; Jansen, E.; Nasdala, L.: Winter term 2010/2011 Leibniz Universität Hannover (2011) Finite Elemente Anwendungen in der Statik und Dynamik Thoben, K.-D.: Gajewski K.: Gottfried Wilhelm Leibniz Universität K-Lehre 2 & 3 Einfluss von chloridhaltigen Lösungen Hannover, Institute of Structural Analysis, Universität Bremen, Institut für auf die Dauerhaftigkeit von dyna- Summer term integrierte Produktentwicklung (BIK), misch belasteten Bauteilen aus UHPC Seume, J.; Scheuren, J.; Rockendorf, G.; Sommer term 2011 Studienarbeit, Goméz, A.: Leibniz Universität Hannover (2011) Erneuerbare Energien Thoben, K.-D.: Leibniz Universität Hannover, Institute Produktionssystematik Gossmann, A.: of Turbomachinery and Fluid Dynamics, Universität Bremen, Institut für Konstruktive Anpassung und Summer term 2011 integrierte Produktentwicklung (BIK), Erweiterung eines Prüfstands- Sommer term 2011 konzeptes für Wälzlager eines Thoben, K.-D.: Windkraftanlagenbetriebes Anwendung eines 3D-CAD-Systems Weber, F.: Projektarbeit, Universität Bremen, Institut für Concurrent Engineering Leibniz Universität Hannover (2011) integrierte Produktentwicklung (BIK), Universität Bremen, Institut für Winter term 2010/11 integrierte Produktentwicklung (BIK), Gütz, P.: Sommerterm 2011 Zur Abschätzung des Tragverhaltens Thoben, K.-D.: von Offshore-Rammverpresspfählen Anwendung und Vergleich von Westerkamp, J. F.; Sorg, M.: Studienarbeit, Kreativitätstechniken Optische Messverfahren für den Leibniz Universität Hannover (2011) Universität Bremen, Institut für Antriebsstrang in Windenergieanlagen integrierte Produktentwicklung (BIK), Bremen Institute for Metrology, Sommer term 2011 Automation and Quality Science, Universität Bremen, Winter Term 2010/2011 108 DOCUMENTATION

Kröger, L.: 7. PhD Theses 8. Diploma, Master and Bachelor Untersuchungen zum Sandeinbau mit Theses der Rieselmethode Engelke, T.: Projektarbeit, Einfluss der Elastomer-Schmierstoff- Arroyo-Klein, S.: Leibniz Universität Hannover (2011) Kombination auf das Betriebsverhalten Technical and Economic Assessment of von Radialwellendichtringen Utilizing Vanadium Redox flow Batter- Kruse, S.: PhD Thesis, ies for Grid Integration of Wind Power Analyse und rechnerische Prognose Leibniz Universität Hannover (2011) Carl von Ossietzky Universität Oldenburg des Installationsvorgangs von Suction- (2011) Bucket-Gründungen Hacke, B.: Seminararbeit, Früherkennung von Wälzlagerschäden Asproulakis, K.: Leibniz Universität Hannover (2011) in drehzahlvariablen Windgetrieben Correlation Between Predicted Behav- PhD Thesis, iors and Real Time Data Kühnel, A.,; Reiffer, L.: Leibniz Universität Hannover (2011) Carl von Ossietzky Universität Oldenburg Vergleich der Nachweisführung von (2011) verschiedenen Grenzzuständen der Käsler, Y.: Tragfähigkeit für horizontal belasteter Doppler-Windlidar-Messungen der Assaminew, W. T.: Pfähle Umströmung einer Windenergieanlage Investigation of horizontal bearing Projektarbeit, PhD Thesis, capacity of driven open steel tube Leibniz Universität Hannover (2011) Carl von Ossietzky Universität Oldenburg piles for offshore-wind energy turbines (2011) Master Thesis, Löhr, F.; Lemke, K. : Leibniz Universität Hannover (2011) Untersuchungen zur Anwendbarkeit Knebel, P.: der p-y-Methode Aktives Gitter zur Simulation atmos- Bani, H.: Studienarbeit, phärischer Windfelder im Windkanal Krümmungsbasierte automatische Tren- Leibniz Universität Hannover (2011) PhD Thesis, nung zweidimensionaler Messpunkt- Carl von Ossietzky Universität Oldenburg wolken in Kreise und Geraden - Cur- Pleger, F.: (2011) vature based automatic separation of Untersuchungen der Festbetoneigen- two-dimensional measuring point sets schaften von UHPC in dünnwandigen Medjroubi, W.: into circles und straight lines Rohrprofilen Numerical Simulation of Dynamic Stall Bachelor Thesis, Projektarbeit, for Heaving Airfoils Using Adaptive Fachbereich Produktionstechnik, Univer- Leibniz Universität Hannover (2011) Mesh Techniques sität Bremen, (2011) PhD Thesis, Schmidt, M.: Carl von Ossietzky Universität Oldenburg Beck, H.: Kombinierte Prüfungen eines min- (2011) Umsetzung eines dynamischen Nach- eralischen Korrosionsschutzes zur laufbelastungsmodells für Freifeldmes- Offshore-Anwendung Schmidt, T.: suingen von alpha ventus Projektarbeit, Mischreibung und Verschleiß in Hy- Carl von Ossietzky Universität Oldenburg Leibniz Universität Hannover (2011) draulikdichtsystemen – Modellbildung, (2011) Simulation und experimentelle Analyse Schultenkämper, M.: PhD Thesis, Bezrodnaya, S.: Probabilistische Voruntersuchung einer Leibniz Universität Hannover (2011) Untersuchung des Tragverhaltens Gründungskonstruktion für Offshore- dünnwandiger UHPC-Rohre unter sta- Windenergieanlagen Xu, Qi: tischer Beanspruchung Studienarbeit, Analyse der inneren Lastverteilung Diploma Thesis, Leibniz Universität Hannover (2011) eines Kugelgleichlauffestgelenks Leibniz Universität Hannover (2011) PhD Thesis, Sved, D., Reinhard, B.: Leibniz Universität Hannover (2011) Bloh, M.: Konzeptgestaltung einer automatisi- Optimization of the design of wind erten Vorrichtung für den Aufbau von Zerbst, S.: turbine rotor blades using the “Cuckoo textilen Preforms für Rotorblätter von Global Approach for Early Damage Search“ algorithm Windkraftanlagen Detection on Rotor Blades of Wind Diploma Thesis, Projektarbeit, BIK, Energy Converters Leibniz Universität Hannover (2011) Universität Bremen (2011) Veröffentlichung der Dissertation in den Mitteilungen des Instituts für Statik und Dynamik der Leibniz Universität Hannover, Nr. 13/2011, November 2011, ISSN 1862-4650, (2011)

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Boithling, F.: Gehrs, J.: Koch, M.: Untersuchungen zur horizontalen Konstruktion einer kontinuierlichen Analyse von Netzfehlern bei Winden- Tragfähigkeit von Stahlrohrrammpfäh- Zuschnittvorrichtung für textile ergieanlagen mit permanenterregter len für Offshore-Windenergieanlagen Bahnware Synchronmaschine und Mittelspan- Diploma Thesis, Diploma Thesis, nungsumrichter in der Simulation Leibniz Universität Hannover (2011) BIK, Universität Bremen (2011) Master Thesis, Leibniz Universität Hannover (2011) Brown, N.: Hahn, S.: Modelling of Wind Turbine Wake Me- Untersuchung von Ansätzen für ein Kotsonis, T.: andering for the Use in Energy Yield System zur Planung energieautonomer Offshore Wind Parks Availability and and Load Calculations Regionen Maintenance Model (OWPAM) Carl von Ossietzky Universität Oldenburg Bachelor Thesis, Carl von Ossietzky Universität Oldenburg (2011) Carl von Ossietzky Universität Oldenburg (2011) (2011) Bussières, F.: Kouamo, T.: Multivariate Analysis of a Wind Hindriksen, C.: Verbesserung der Planungs- und Turbine Rotor Blade Root Connection Analyse von dreidimensionalen Strö- Entscheidungssicherheit in der In- Using the Finite Element Method mungen mit Hilfe digitaler In-Line- standhaltung von Onshore-Windkraf- Carl von Ossietzky Universität Oldenburg Holographie unter Verwendung einer tanlagen (2011) Hochgeschwindigkeitskamera Master Thesis, Master Thesis, bime, University of Bremen (2011) De Vecchi, R.: Carl von Ossietzky Universität Oldenburg Analysis and Blending Wind Resources (2011) Kröger, L.: from Multiple Masts for Energy Charakterisierung eines Wortmann Assessment Höflich, S.; Kreitlow, R.; Kublanck, D.; Flügelprofils im Windkanal mittels PIV Carl von Ossietzky Universität Oldenburg Salvasohn, D.; Wilbrandt, M.; Wuttke, M.: und Vergleich mit CFD-Simulationen (2011) Logistikgerechte Konstruktion und Bachelor Thesis, Handhabung von Rotorblättern für Carl von Ossietzky Universität Oldenburg Donath, B.: Windenergiesysteme – Von der (2011) Validierung von Berechnungsverfahren Fertigung bis zur Montage zur zyklischen Mantelreibungs-degra- Master Project, bime, University of Lecerf, B.: dation von axial belasteten Pfählen Bremen (2011) Entwicklung und Optimierung eines Diploma Thesis, Flügelprofils für Windkraftanlagen bei Leibniz Universität Hannover (2011) Hoffmann, T. J.: niedriger Reynoldszahl Wirtschaftlichkeit von Diploma Thesis, Ebrahimi, M.: Automatisierungssystemen in der Carl von Ossietzky Universität Oldenburg Investigation of the Thermal Load of Rotorblattfertigung (2011) Power Semiconductors Used in Wind Bachelor Thesis, Turbines with Doubly Fed Induction BIK, Universität Bremen (2011) Maier, J.: Generator The analyses of planning processes to Master Thesis, Jimmy, M: maintain rotor blades of wind Leibniz Universität Hannover (2011) Einfluss weicher Schichten unterhalb generators in reference to stochastic eines Pfahls auf das Tragverhalten parameters Espinosa, O. P.: unter axialer Druckbelastung Bachelor Thesis, Prepreg Technology in the Production Master Thesis, bime, University of Bremen (2011) of Rotor Blades for Windturbines Leibniz Universität Hannover (2011) Bachelor Thesis, Montealegre, F.: BIK, Universität Bremen (2011) Kichungo Ngoma, D.: HVDC Transmission Links in Large Accuracy of Different Wind Power Scale Offshore Wind Farms Fuchs, A.; Strüwing, C.: Prediction Approaches and Recommen- Carl von Ossietzky Universität Oldenburg Umbau und anschließende Charakteri- dations for Particular Applications (2011) sierung eines Windkanals mittels Par Carl von Ossietzky Universität Oldenburg ticle-Image-Velocimetry, Hitzdraht- und (2011) Mrukwa, A.: Laser-Cantilever-Anemometer, sowie Optimierung und Weiterentwicklung der Vergleich dieser Messverfahren eines adaptiven Aufnahme- und Be- Master Thesis, leuchtungssystems für die Erkennung Carl von Ossietzky Universität Oldenburg von textilen Oberflächenstrukturen (2011) Bachelor Thesis, BIK, Universität Bremen (2011) 110 DOCUMENTATION

Rockel, S.: Tesfay, Y.: Dynamische Eigenschaften einer Investigation of the Prediction Cut-Off schwimmenden Modell- Events in Wind Farms at Extreme Wind Windenergieanlage Conditions Diploma Thesis, Carl von Ossietzky Universität Oldenburg Carl von Ossietzky Universität Oldenburg (2011) (2011) Thomsen, M.: Sanchez, R. G.: Variantenuntersuchung und Bemes- Material Flow Assessment of Rotor sung eines Offshore-Messmastes Blade Production for Windturbines Master Thesis, Master Thesis, Leibniz Universität Hannover (2011) BIK, Universität Bremen (2011) Tschierschke, M.: Schramm, M.: Einflussgrößen auf die Faserorien- Berechnung einer turbulenten drei- tierung trockener Textilien dimensionalen Strömung an einer Bachelor Thesis, Windkraftanlage BIK, Universität Bremen (2011) Diploma Thesis, Carl von Ossietzky Universität Oldenburg Useche, G.: (2011) Untersuchungen zum Tragverhalten zyklisch horizontal belasteter Pfähle Schweer, N. : Master Thesis, Numerische Untersuchungen des Leibniz Universität Hannover (2011) Einflusses der Kolkbildung auf das Pfahlverhalten unter horizontaler Vöge, M.: Belastung Konstruktion einer Vorrichtung für die Bachelor Thesis, Handhabung textiler Faserhalbzeuge Leibniz Universität Hannover (2011) Bachelor Thesis, BIK, Universität Bremen (2011) Seethapathy, P. K.: Extrapolation of Wind Turbine design Weitemeyer, S.: for far offshore environments in the Experimental Study of Turbulence period 2017-2020 Generated by Fractal Grids Master Thesis, Diploma Thesis, Carl von Ossietzky Universität Oldenburg Carl von Ossietzky Universität Oldenburg (2011) (2011)

Segelke, M.: Wendland, J.: Konzeptentwicklung einer Applikation Modellversuche zur Analyse baustof- für den Einsatz von Textilbindern flicher und herstellungsbedingter Diploma Thesis, Einflüsse auf Grouted Joints BIK, Universität Bremen (2011) Diploma Thesis, Leibniz Universität Hannover (2011) Smirnov, A.: Simulation eines rauen Wälzkontaktes Wentland, H.: unter Berücksichtigung von Reibung Aufbau und Inbetriebnahme eines Diploma Thesis, Drehmomentprüfstandes Leibniz Universität Hannover (2011) Bachelor Thesis, Fachbereich Produktionstechnik, Sun, Z.: Universität Bremen, (2011) Approximation von modifizierten Profilen evolventischer Zylinderrad- flanken mit automatischer Trennung der zugehörigen Messpunkte Bachelor Thesis, Fachbereich Produktionstechnik, Universität Bremen, (2011) Annual Report 2011 111 112 DOCUMENTATION

List of ForWind Staff Brencher, Janina Goch, Gert, Prof. Dr.-Ing. Institute of Machine Design and Tribology Bremen Institute for Metrology, Members +49 511 762-2267 Automation and Quality Science (BIMAQ) [email protected] University of Bremen +49 421 218 64600 Abdel-Rahman, Khalid, Dr.-Ing. M.Sc. Busch-Saleck, Nadja, Dr. [email protected] Institute for Geotechnical Engineering, Institute of Physics, +49 511 762 2273 AG Energy Meteorology Goretzka, Jan, M.Sc. [email protected] +49 441 798 5077 Institute of Structural Analysis [email protected] +49 511 762 4273 Achmus, Martin, Univ.-Prof. Dr.-Ing. [email protected] Institute for Geotechnical Engineering, Dapperheld, Jörg +49 511 762 4155 Institute of Physics, Greve, Thomas, Dipl.-Phys. [email protected] AG Turbulence, Wind Energy and Institute of Physics, AG Turbulence, Wind Stochastics – TWIST Energy and Stochastics – TWIST Albiker, Johannes, Dipl.-Ing. +49 441 798 3535 +49 441 798 5057 Institute for Geotechnical Engineering, [email protected] [email protected] +49 511 762 3529 [email protected] Dautz, Erika, Mag. Grießmann, Tanja, Dr.-Ing. Institute of Physics, Institute of Structural Analysis Ambroise, Hugues, M.Sc. AG Energy Meteorology +49 511 762 2247 Institute of Physics, +49 441 798 5079 [email protected] AG Wind Energy Systems – WE-SYS [email protected] +49 441 798 5078 Grundmeier, Nico [email protected] Dörenkämper. Martin, M.Sc. ForWind Competence Center Institute of Physics, +49 441 798 5087 Barth, Stephan, Dr. AG Wind Energy Systems – WE-SYS [email protected] ForWind Competence Center +49 441 798 5077 +49 441 798 50913 martin.doerenkä[email protected] Gülker, Gerd, Dr. [email protected] Institute of Physics, AG Turbulence, Wind Engel, Franca Energy and Stochastics – TWIST Battermann, Dagmar ForWind Competence Center +49 441 798 3511 ForWind Competence Center +49 441 798 5087 [email protected] +49 441 798 5060 [email protected] [email protected] Hadjihosseini, Ali, M.-Sc. Ernst, Benedikt, Dipl.-Wirtsch.-Ing. Institute of Physics, AG Turbulence, Wind Beck, Hauke, M.Sc. Institute of Turbomachinery and Fluid Energy and Stochastics – TWIST Institute of Physics, Dynamics +49 441 798 5043 AG Wind Energy Systems – WE-SYS +49 511 762 2734 [email protected] +49 441 798 5064 [email protected] [email protected] Häckell, Moritz,Dipl.-Ing. Fricke, Moritz, Dipl.-Ing. Institute of Structural Analysis, Betcke, Jethro, M.Sc. Institute of Structural Analysis +49 511 762 4393 Institute of Physics, +49 511 762 4393 [email protected] AG Energy Meteorology [email protected] +49 441 798 3927 Haunhorst, Frauke [email protected] Frings, Kirstin ForWind Competence Center Institute of Physics, +49 441 798 5090 Böttcher, Roman AG Wind Energy Systems – WE-SYS [email protected] Institute of Machine Design and Tribology +49 441 798 5060 +49 511 762 3691 [email protected] Heinemann, Detlev, Dr. [email protected] Institute of Physics, Fuhrmann, Martina, M.Sc. AG Energy Meteorology Bredemeier, Carsten, Dipl.-Ing. Bremen Institute for Metrology, +49 441 798 3543 Bremen Institute for Metrology, Automation and Quality Science (BIMAQ) [email protected] Automation and Quality Science (BIMAQ) University of Bremen University of Bremen +49 421 218 64612 +49 421 218 64608 [email protected] [email protected] Annual Report 2011 113

Heißelmann, Hendrik, Dipl.-Phys. Kirrkamm, Nils, M.Phy. Lünsdorf, Ontje Institute of Physics, AG Turbulence, Wind Institute of Physics, AG Turbulence, Wind OFFIS, Oldenburg Energy and Stochastics – TWIST Energy and Stochastics – TWIST +49 441 798 2751 +49 441 798 3643 +49 441 798 5056 [email protected] [email protected] [email protected] Mainz, Thomas Henking, Rainer, Dr. Kohlmeier, Martin, Dr.-Ing. ForWind Competence Center ForWind Competence Center Institute of Structural Analysis +49 441 798 5089 +49 441 798 5096 +49 511 762 4208 [email protected] [email protected] [email protected] Medjroubi, Wided, Dr. Herraez Hernandez, Ivan, M.-Sc. Kolb, Tobias, M.A. Institute of Physics, AG Turbulence, Wind Institute of Physics, AG Turbulence, Wind ForWind Competence Center Energy and Stochastics – TWIST Energy and Stochastics – TWIST +49 441 798 5093 +49 441 798 5055 +49 441 798 5055 [email protected] [email protected] [email protected] Kouamo, Theorine, M.Sc. Milan, Patrick, M.Sc. Hesseling, Christina, Dipl.-Phys. Bremen Institute for Mechanical Institute of Physics, AG Turbulence, Wind Institute of Physics, AG Turbulence, Wind Engineering Energy and Stochastics – TWIST Energy and Stochastics – TWIST + 49 421 218 64834 +49 441 798 5054 +49 441 798 3514 [email protected] [email protected] [email protected] Kruse, Dennis, M.Sc. Morales, Allan, M.Sc. Hölling, Michael, Dr. Bremen Institute for Metrology, Institute of Physics, AG Turbulence, Wind Institute of Physics, AG Turbulence, Wind Automation and Quality Science Energy and Stochastics – TWIST Energy and Stochastics – TWIST (BIMAQ), +49 441 798 5054 +49 441 798 3951 University of Bremen [email protected] [email protected] +49 421 218 64631 [email protected] Müller, Dieter H., Prof. Dr.-Ing. Homeyer, Tim, Dipl.-Phys. BIK – Institut für integrierte Produktent- Institute of Physics, AG Turbulence, Wind Kühn, Martin, Prof. Dr. Dipl.-Ing. wicklung, Bremen Energy and Stochastics – TWIST Institute of Physics, +49 421-218- 50129 +49 441 798 3514 AG Wind Energy Systems – WE-SYS [email protected] [email protected] +49 441 798 5061 [email protected] Neuber, Malgorzata Junk, Constantin, MSc Institute of Structural Analysis Institute of Physics, AG Wind Energy Kuhnle, Bernd , Dipl.-Ing. +49 511 762 2885 Systems – WE-SYS Institute of Physics, AG Wind Energy [email protected] +49 441 798 5079 Systems – WE-SYS [email protected] +49 441 798 5064 Ohlendorf, Jan-Hendrik, Dipl.-Wirtsch.-Ing. [email protected] BIK – Institut für integrierte Kadagies, Nicole, Dipl-Geol. Produktentwicklung, Bremen ForWind Competence Center Langner, Michael, Dipl.-Phys. +49 421-218- 64876 +49 441 798 5088 Institute of Physics, AG Turbulence, Wind [email protected] [email protected] Energy and Stochastics – TWIST +49 441 798 5052 Pahn, Thomas, Dipl.-Ing. Kärn, Moses [email protected] Institute of Structural Analysis ForWind Competence Center +49 0511 762 4208 +49 441 798 5082 Laupichler, Anne, Dipl.-Phys. [email protected] [email protected] Institute of Physics, AG Turbulence, Wind Energy and Stochastics – TWIST Parniak, Agnieszka, Dipl.-Ing. Keshtova, Fatima, Dipl.-Phys. +49 441 798 5055 Institute of Physics, AG Turbulence, Wind Institute of Physics, AG Turbulence, Wind [email protected] Energy and Stochastics – TWIST Energy and Stochastics – TWIST +49 441 798 3535 +49 441 798 5059 Lindschulte, Nick, Dipl.-Ing. [email protected] [email protected] Institute of Building Materials Science +49 511 762 3258 [email protected] 114 DOCUMENTATION

Pawletta, Peter Reil, Benjamin, M.Sc. Schmoor, Kirill, Dipl.-Ing. ForWind Competence Center Institute of Structural Analysis Institute for Geotechnical Engineering, +49 441 798 5087 +49 511 762 17213 +49 511 762 5106 [email protected] [email protected] [email protected]

Pehlken, Alexandra, Dr.-Ing. Reinke, Nico, Dipl.-Phys. Schneemann, Jörge, Dipl.-Phys. BIK – Institut für integrierte Institute of Physics, AG Turbulence, Wind Institute of Physics, Produktentwicklung, Bremen Energy and Stochastics – TWIST AG Wind Energy Systems – WE-SYS +49 421-218- 64876 +49 441 798 3455 +49 441 798 5062 [email protected] [email protected] [email protected]

Peinke, Joachim, Prof. Dr. Riepe Jan, Dipl.-Ing. Scholle, Niklaas, Dipl.-Ing. Institute of Physics, AG Turbulence, Wind Institute of Physics, AG Wind Energy Institute of Building Materials Science Energy and Stochastics – TWIST Systems – WE-SYS +49 511 762 3258 +49 441 798 3536 +49 441 798 5063 [email protected] [email protected] [email protected] Schröder, Christian, Dipl.-Ing. Plump, Vanessa Rinn, Philip, Dipl.-Phys. Institute for Geotechnical Engineering, ForWind Competence Center Institute of Physics, AG Turbulence, Wind +49 511 762 4152 +49 441 798 5087 Energy and Stochastics – TWIST [email protected] [email protected] +49 441 798 5052 [email protected] Schuh, Peter, M.Sc. Pohland, Kathleen, Dipl.-Ing. Bremen Institute for Mechanical Institute of Physics, Rockel, Stanislav, Dipl.-Phys. Engineering AG Wind Energy Systems – WE-SYS Institute of Physics, AG Turbulence, Wind +49 421 218 64832 +49 441 798 5065 Energy and Stochastics – TWIST [email protected] [email protected] +49 441 798 3455 [email protected] Schwarzer, Christoph, Dipl.-Oek. Poll, Gerhard, Prof. Dr.-Ing. ForWind Competence Center Institute of Machine Design and Tribology Rolbiecki, Martin, Dipl.-Wi.-Ing. +49 441 798 5084 +49 511 762-2416 BIK – Institut für integrierte Produktent- [email protected] [email protected] wicklung, Bremen +49 421-218 64875 Seidel, Elke Puczylowski, Jaroslaw, M.Sc. [email protected] ForWind Competence Center Institute of Physics, AG Turbulence, Wind +49 441 798 5092 Energy and Stochastics – TWIST Rolfes, Raimund, Prof. Dr.-Ing. habil. [email protected] +49 441 798 3643 Institute of Structural Analysis [email protected] +49 511 762 3867 Segelken, M.A. [email protected] ForWind Competence Center Ramzan, Muhammad, M.Sc. +49 441 798 5093 Institute of Physics, AG Turbulence, Wind Rustemeier, Jörg, M. Sc. [email protected] Energy and Stochastics – TWIST Institute of Structural Analysis +49 441 798 5053 +49 511 762 2885 Seume, Jörg, Prof. Dr.-Ing. [email protected] [email protected] Institute of Turbomachinery and Fluid Dynamics Reck, Martin, M.Sc. Schmidt, Michael, Dipl.-Phys. +49 511 762 2733 Institute of Physics, Institute of Physics, [email protected] AG Wind Energy Systems – WE-SYS AG Energy Meteorology +49 441-798-3560 +49 441 798 5074 Sonnenschein, Michael, Prof. Dr. [email protected] [email protected] Departement for Informatik, Abteilung Umweltinformatik, Oldenburg Reichel, Juliane, Dr. Schmohl, Tim, Dipl.-Ing. +49 441 798 2750 ForWind Competence Center BIK – Institut für integrierte Produktent- [email protected] +49 441 798 5085 wicklung, Bremen oldenburg.de [email protected] +49 421 218 64872 [email protected] Annual Report 2011 115

Sorg, Michael, Dipl.-Ing. Tracht, Kirsten, Prof. Dr.Ing. Witha, Björn, Dipl.-Met. Bremen Institute for Metrology, Bremen Institute for Mechanical Engi- Institute of Physics, Automation and Quality Science (BIMAQ) neering AG Energy Meteorology University of Bremen +49 421 218 64841 +49 441 798 5075 +49 421 218 64620 [email protected] [email protected] [email protected] Trujillo, Juan José, M.Sc. Wolff, Miriam, Dipl.-Inf. Steinborn, Thomas, Dr.-Ing. Institute of Physics, ForWind Competence Center Institute of Building Materials Science AG Wind Energy Systems – WE-SYS: +49 441 798 5092 +49 511 762 3105 +49 441 798 5062 [email protected] [email protected] [email protected] Zerbst, Stephan, Dipl.-Ing. Steinfeld, Gerald, Dr. Ungurán, Robert. Dipl.-Ing. Institute of Structural Analysis Institute of Physcis, Institute of Physics, +49 511 762 8674 AG Energy Meteorology AG Wind Energy Systems – WE-SYS [email protected] Institute of Physics, AG Turbulence, Wind [email protected] Energy and Stochastics – TWIST +49 441 798 5073 von Bremen, Lueder, Dr. [email protected] Institute of Physics, AG Energy Meteorology Stoffels, Nicole, Dipl. Met. +49 441 798 5071 Institute of Physics, AG Energy [email protected] Meteorology +49 441 798 5079 Wächter, Matthias, Dr. [email protected] Institute of Physics, AG Turbulence, Wind Energy and Stochastics – TWIST Stütz, Elisabeth, Mag. +49 441 798 5051 Institute of Physics, AG Energy [email protected] Meteorology +49 441 798 5077 Weicken, Hannes, Dipl.-Ing. [email protected] Institute of Building Materials Science +49 511 762 8966 Tambke, Jens, Dipl.-Phys. [email protected] Institute of Physics, AG Energy Meteorology Wermke, Corinna, Dipl.-Sozialwiss. +49 441 798 5072 ForWind Competence Center [email protected] +49 441 798 5086 [email protected] Thoben, Klaus-Dieter, Prof. Dr.-Ing. habil. BIK – Institut für integrierte Produktent- Werner, Michael, Dipl.-Ing. wicklung, Bremen Institute of Building Materials Science +49 421-218- 50005 +49 511 762 3477 [email protected] [email protected]

Tipping, Melanie Westerkamp, Jan F., Dipl.-Ing. ForWind Competence Center Bremen Institute for Metrology, Automa- +49 441 798 5083 tion and Quality Science (BIMAQ) [email protected] University of Bremen +49 421 218 64609 Trabucchi, Davide, M.Sc. [email protected] Institute of Physics, AG Wind Energy Systems – WE-SYS Winstroth, Jan, Dipl.-Ing. +49 441 798 5062 Institute of Turbomachinery and Fluid [email protected] Dynamics +49 511 762 8925 [email protected] 116 DOCUMENTATION

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Publisher ForWind – Center for Wind Energy Research of the Universities of Oldenburg, Hannover and Bremen

Executive Board Prof. Dr.-Ing. Bernd Orlik Prof. Dr.-Ing. habil. Raimund Rolfes Prof. Dr.-Ing. Gert Goch, Prof. Dr. Martin Kühn, Prof. Dr. Joachim Peinke, Prof. Dr.-Ing. Peter Schaumann.

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Annual Report 2011

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