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MARITIME RESEARCH NEWS 1 Vol. 17/ISSN 0784-6010 2003 Maritime Institute of Finland 1 List of Contents: Editor’s corner......................................................3 Jerzy Matusiak Ice load monitoring system for ice going ships....4 Mikko Lensu Viscous-flow computations at full-scale ship Reynolds numbers................................................5 Jerzy Matusiak Juha Schweighofer page 3 Morison’s equation in statistical fatigue Mikko Lensu analysis of floating offshore structure.................6 page 4 Jani Leskinen Ultimate strength analysis for new passenger vessels concepts...................................7 Hendrik Naar Local impact strength of all steel sandwich panels...................................................8 Juha Kristjan Tabri Schweighofer page 5 The Nordic Boat Standard and the Blue Shield have made their job.........................10 Jani Leskinen Gunnar Holm page 6 New type of dynamometers for pod-propulsor model tests............................ ......11 Ilkka Saisto, Ahti Ajo Recent Publications............................................12 Hendrik Naar Cover Photo: Samuli Hänninen page 7 MARITIME INSTITUTE OF FINLAND Kristjan Tabri page 8 VTT Industrial Systems P.O.Box 1705, FIN-02044VTT, Espoo, Finland Phone +358-4561 Telefax +358-9-455-0619 HUT Ship Laboratory Otakaari 4, FIN-02150, Espoo, Finland Phone +358-9-451-3501 Telefax +358-9-451-3419 Gunnar Holm page 10 Editors: Saara Hänninen & Pentti Tuononen, VTT Industrial Systems Ilkka Saisto Maritime news home page: page 11 http://www.vtt.fi/tuo/institute/ 2 EDITOR’S CORNER COMPUTATION FLUID DYNAMICS (CFD) AND MODEL TESTING Computational methods have already established a firm The development of Finflo-ship would not be possible position as a tool of a preliminary hydrodynamic hull without the experimental research in the field of ship design. In Finland the industry uses on a routine basis, hydrodynamics. Even with a CFD-tool being developed the potential flow models when ranking hull versions in to a certain level we need hydrodynamic model tests. respect to the wave-making. The problems with the Tests are necessary at present and will be needed in the inviscid models are that firstly they are unable to give future for the final evaluation of the power requirement ship resistance and secondly they do not yield enough of a design. Model tests are also required in the process detailed flow information (ship’s wake, separation etc.). of validating the computational methods. Development These limitations are absent when using the flow models of the numerical methods and broadening the scope of which incorporate both the wave-making and the vis- their application is impossible without a thorough vali- cous flow modelling. These are usually tailor-made com- dation. puter programs dedicated to the needs of ships’ hydro- dynamic design. This kind of method, called Finflo-ship, Especially for a novel ship design power prediction has been developed at Otaniemi. This method is in a based solely on the model tests and on the experience- stage of becoming a commercial software to be used by gained extrapolation may yield erroneous results. A com- the industry. bination of CFD and model tests seems to be the most promising mean of making reliable power prediction of The experiences associated with the recent applications a ship. Although this new approach is in the early stage of Finflo-ship are very good. The method does not only of development, it is becoming a serious alternative to predict accurately the resistance of a ship model but also the traditional approach. it is capable to handle the full-scale ship flows. Recently held seminar on the ‘Uncertainties of ship hull resist- Prof. Jerzy Matusiak ance prediction’ (http://www.hut.fi/Yksikot/Laiva/ HUT Ship laboratory Tutkimus/Seminar2003/index.html) gives the detailed in- formation on this topic. Also, the article of Mr. Juha Schweighofer in this issue of MRN elaborates on the same subject. 3 ICE-LOAD MONITORING SYSTEM FOR ICE-GOING SHIPS Mikko Lensu HUT Ship Laboratory The past ice season has been a good re- tures and the ship hull is also a statistical selected structural members are minder of the hazards of ice navigation. process. Only a part of the encountered instrumented for load measurements. The Tankers navigating without a proper ice thick ice features damage the ice navi- second component, monitoring software, class in the Gulf of Finland, which has gating ship. The damage probability de- analyses the measured data using statis- not had as difficult ice conditions in fif- pends also on the ship’s operation, espe- tical models. Finally, a user interface dis- teen years, have hit the headlines, and the cially its speed. plays the load level and other relevant ships’ progress has been followed by a information to the ship officers. The main concerned public. The need to reduce the With the help of statistical models for challenge is the monitoring software, es- risk of oil spills that may follow from se- ice thickness variation and the ice-hull pecially the prediction function. In a typi- rious ice damage has been generally rec- interaction process, it is in principle pos- cal situation of tactical ice navigation, the ognised. sible to calculate the probability with ship enters a more difficult ice type. In which hull damage is suffered when the order to forewarn the crew of the dam- However, penetration of the ship hull by ship navigates in a certain ice type at a age risk, the statistics of the loading proc- ice features and the resulting environmen- certain speed. The models have two ba- ess should be generated for the new ice tal or human catastrophe is an extreme sic applications. Long-term statistics can type within a short period of time during scenario. Less serious hull damage – de- be used to develop ice rules for ice navi- which the damage risk is small. flections of plating or local collapse of gating ships, while short-term statistics some structural member – can also occur can be used to assist navigation. This is The usual method – fitting a statistical in ships that navigate following the ice best realised in terms of a monitoring sys- distribution to a histogram – cannot be rules. This does not necessarily mean that tem that follows the ice load level. If the applied to short periods. A simple and the ship is not suited to the ice conditions. level is too high, speed may be reduced straightforward method is based on the The pack ice cover has a large variation or another route taken. magnitude of maximum load occurring and very thick ice features are encoun- during a period. As the period lengthens, tered also when the average ice thickness A short-term load monitoring system has the expected maximum load also in- appears to be well below the risk limit. been developed by the HUT Ship Labo- creases following a certain rule. In most Such features are encountered with a ratory in a project funded by TEKES and cases the rule is a simple power law that probability that depends on the ice type. by NEMARC, which is a shipping com- appears as a straight line in a logarithmic The ice type can be described by statisti- pany owned by Fortum and Kvaerner plot. The line has two parameters, level- cal properties related to thickness varia- Masa-Yards (Lensu 2002). Any such sys- ness and steepness, and these parameters tion. The interaction between the ice fea- tem has three main components. First, determine the statistics that are required for the risk estimation. The line can be generated during short periods and the prediction is done simply by extending the line to longer periods in the future. This simple approach also provides a method for studying how the load level depends on ice conditions and speed to the load. The steepness of the line is typi- cal to the ice type, and the level of the line depends on ice thickness. The more variation in thickness, the steeper the line. Fig. 1 compares level and ridged ice, and it is seen that during longer periods larger loads occur in ridged ice even though it would be less thick. A decrease in speed then reduces the level of the line without changing the steepness. REFERENCE: Lensu, M. 2002. Ice navigation assisted by short-term ice-load monitoring. Hel- sinki University of Technology, Ship Figure 1. The lines in the plot can be understood as ‘ice loading states’. It is seen Laboratory report M-275. that not only thickness but also thickness variation changes the loading state. 4 VISCOUS-FLOW COMPUTATIONS AT FULL-SCALE SHIP REYNOLDS NUMBERS Juha Schweighofer HUT Ship Laboratory Numerical investigations of turbulent bulent flows at full-scale ship Reynolds ues based on measurements and tradi- free-surface flows are usually carried out numbers using the RaNS solver, FINFLO, tional extrapolation methods are less than at the Reynolds number of a model-scale were started in 1996. In recent years, at five percent, and the free surface can be ship. The results obtained must be scaled the Ship Laboratory, these skills have evaluated qualitatively correctly. This to full scale, which might cause errors in been improved, allowing the evaluation work is being continued in the EU project the case of new vessel types where the of turbulent flows around ships, includ- EFFORT (European Full-Scale Flow Re- scaling mechanisms are not known. Com- ing the evaluation of the free surface at search and Technology), where additional putations of full-scale ships are attractive full-scale ship Reynolds numbers. The ships are being computed, and respective as no scaling is necessary, and the allow- boundary layer is entirely resolved, the measurements are being carried out at ances may be reduced. The shape of the RaNS equations are solved without the model- and full-scale ship Reynolds num- hull, and the propeller may be optimised application of wall functions, and the free bers, Verkuyl and Raven (2003).