Multi-disciplinary Optimization of Rotor Nacelle Assemblies for Offshore Wind Farms An Agile Systems Engineering Approach Tanuj Tanmay Multi-disciplinary Optimization of Rotor Nacelle Assemblies for Offshore Wind Farms An Agile Systems Engineering Approach by Tanuj Tanmay in partial fulfillment of the requirements for the degree of Master of Science in Sustainable Energy Technology at Delft University of Technology Student number: 4614844 Project duration: Nov 13, 2017 - Aug 13, 2018 Thesis committee: Prof.dr. Simon Watson TU Delft, Chairman Dr.ir. Michiel Zaaijer TU Delft, Supervisor Dr. Julie Teuwen TU Delft Sebastian Sanchez Perez- TU Delft Moreno Keywords: systems engineering, multi-disciplinary optimization, offshore wind farms, rotor nacelle assembly Cover photo: Siemens An electronic version of this thesis is available at http://repository.tudelft.nl/. Whatever you do will be insignificant, but it is very important that you do it. Mahatma Gandhi CONTENTS Summary 5 Preface 7 Glossary 9 1 Introduction1 1.1 Overview..................................1 1.2 Problem statement.............................2 1.3 Scope....................................3 1.4 Research theme...............................3 1.4.1 Main objective............................3 1.4.2 Research objective #1........................4 1.4.3 Research objective #2........................5 1.4.4 Research objective #3........................5 1.5 Report organization.............................6 2 Systems Engineering of Offshore Wind Farms7 2.1 Background.................................7 2.1.1 Systems engineering.........................7 2.1.2 MDAO................................8 2.1.3 Agility................................8 2.2 System ontology..............................9 2.2.1 WINDOW..............................9 2.2.2 Coupling of RNA with WINDOW................... 12 3 Design Iteration #1 13 3.1 Use case................................... 14 3.2 Literature survey.............................. 15 3.3 Development................................ 16 3.3.1 Model assessment.......................... 16 3.3.2 Blade................................. 17 3.3.3 Hub & Nacelle............................ 24 3.3.4 Cost................................. 30 3.3.5 Coupling the disciplines....................... 31 3.4 Validation.................................. 33 3.5 Analysis................................... 36 3 4 CONTENTS 4 Design Iteration #2 43 4.1 Use case................................... 44 4.2 Literature survey.............................. 46 4.3 Development................................ 48 4.3.1 Design scaling............................ 48 4.3.2 Aerodynamic design......................... 48 4.4 Validation.................................. 49 4.4.1 Response variables.......................... 49 4.4.2 Energy yield............................. 50 4.4.3 Cost................................. 53 4.4.4 Levelized cost............................ 55 4.4.5 Error analysis............................ 55 4.5 Analysis................................... 58 4.5.1 Square farm layout.......................... 58 4.5.2 Rectangular farm layout....................... 61 5 Design Iteration #3 65 5.1 Use case................................... 66 5.2 Literature survey.............................. 68 5.3 Development................................ 69 5.3.1 Model assessment.......................... 69 5.3.2 Model update............................ 70 5.4 Validation.................................. 73 5.4.1 Error identification.......................... 73 5.4.2 Error analysis............................ 74 5.5 Analysis................................... 75 5.5.1 RNA Scaling with different configurations.............. 75 5.5.2 Reliability study of different configurations............. 78 6 Concluding Remarks 81 6.1 Conclusion................................. 81 6.2 Retrospection................................ 84 6.3 Recommendation.............................. 84 Epilogue 85 A Appendix 87 A.1 Chapter 3.................................. 87 A.2 Chapter 4.................................. 91 A.3 Chapter 5.................................. 91 References 93 SUMMARY The models with different fidelities for the siloed application of niche wind farm dis- ciplines - rotor aerodynamics, aeroelasticity or wake aerodynamics - are prevalent in literature. These models are often used sequentially while designing a wind farm that may lead to a sub-optimal design due to their agnosticism towards the inter-disciplinary influences. This paper demonstrates the multi-disciplinary optimization of rotor nacelle assemblies for offshore wind farms. The designs of three aspects of rotor nacelle assembly are addressed - rotor blade, power density and drive train configuration - that support the development of an open-source agile systems engineering framework and allow flex- ibility in their utility to various stakeholders of offshore wind farms. The first research objective is to develop insight into the benefits of systems engineer- ing by studying the effect of system scope on the rotor design. The dissemination of knowl- edge on the utility of the tool in painting a bigger picture of an offshore wind farm among the wind energy researchers is intended. It is found that the siloed application or the op- timization of blade design in a limited system scope leads to a sub-optimal design at the wind farm level because they fail to capture the inter-disciplinary influences with the support structure, wake effect and cable topology. The LCOE of the wind farm is mini- mum when the system scope for the blade design is at the wind farm level. The second research objective is to study the effect of the rotor radius and its rated power on the LCOE of the wind farm. The dissemination of knowledge on the utility of the tool in designing a wind turbine specific to a particular offshore site among the wind tur- bine/farm developers is intended. The disciplines outside the RNA respond non-linearly to the changes in the RNA size, which necessitates a systems engineering framework that captures such inter-disciplinary dynamics to find an optimal rotor size. It is found that a turbine with lower power density is optimal for a site with lower wind resource, and vice-versa. The position of the substation has a large influence on the cable topology and the farm layout. The third research objective is to compare various drive train configurations and the effect of their reliability on the LCOE of the wind farm. The dissemination of knowledge on the utility of the tool to select an optimal drive train configuration for a given rotor among the wind turbine manufacturers is intended. The coupling of cost, efficiency and reliability of the drive train configurations to the offshore wind farm enables detailed comparison of such configurations at the wind farm level. The analysis leads Permanent Magnet Synchronous Generator with 1-stage gearbox to be the most favorable configu- ration. A higher reliability from Permanent Magnet Synchronous Generator with direct- drive is expected so that its levelized cost of energy breaks-even with that of the geared configurations. 5 PREFACE The opportunity for research in form of a thesis in the masters programme was the pri- mary factor that lured me to TU Delft. The remarkable journey of this thesis was marked by the test of perseverance, the sense of gratification and the realization of the passion for wind energy. This journey would not have been possible without the help and sup- port of the people around me. My utmost gratitude goes to Dr. Michiel Zaaijer and Sebastian Sanchez. Dr Zaaijer’s nimble remarks, words of wisdom, easy accessibility and meticulous feedback gave the necessary shape and direction to the thesis. Without the elegant framework built by our Chief Software Architect, Sebastian, and his help, it would not have been possible to ac- complish the goals of this project. My gratitude extends to my friends and family whose support never let the stress of the thesis to creep into me. I would specially like to thank Steyn Verschoof for orientating me to the Dutch lifestyle. The final credit goes to Ayn Rand’s The Fountainhead for being the fountainhead of my motivation and courage for the disruptive idea of pursuing this masters. Tanuj Tanmay Delft, August 2018 7 GLOSSARY Abbreviations AEP Annual Energy Production BEM Blade Element Momentum CARB Compact-Aligning toroidal Roller Bearing CFD Computational Fluid Dynamics DFIG Doubly Fed Induction Generator DTU Danmarks Tekniske Universitet FEM Finite Element Method FUSED Framework for Unified Systems Engineering and Design of Wind Plants IEC International Electrotechnical Commission IO Input-Output LCOE Levelised Cost of Electricity MDAO Multi-Disciplinary Analysis & Optimization N5RT NREL 5 MW Offshore Reference Turbine NREL National Renewable Energy Laboratory O&M Operations and Maintenance OWF Offshore Wind Farm PMSG Permanent Magnet Synchronous Generator RNA Rotor Nacelle Assembly SE Systems Engineering SRB Spherical Roller Bearing TI Turbulence Intensity UTS Ultimate Tensile Strength WINDOW Windfarm Integrated Design and Optimization Workflow 9 10 PREFACE WISDEM Wind-Plant Integrated System Design and Engineering Model XDSM Extended Design Structure Matrix Subscripts aer o aerodynamic bed bedplate cc cable cost conv converter decom decommissioning des design dt drive train edge edgewise elec electrical ew east to west direction f l ap flapwise gb gearbox gen generator gr av gravity hss high speed shaft l ss low speed shaft mb main bearing