浮式海上风力发电机组结构的先进高效时域分析方法

Frode Bratbak, Arne Christian Damhaug,Jens Eftang, Torstein Skår - DNV Contents 1Introduction2Methodology2.1Sesam time-domain methods for FOWT substructures2.1.1The Direct Load Generation method2.1.2TheLoadReconstruction2.1.3TheResponseReconstruction2.2Dynamicsensitivity2.3Pythonworkflowforcomparisonofresults3Results3.1TheEMULFDelta3.2Inputtocomparison3.3Assessment of transient response for turbine fault cases3.4Assessment of structural dynamic sensitivity3.5Comparison of methods for calculation of structural response143.5.1Fatiguedamage3.5.2Elementprincipal4ConclusionReferencesAppendixAPythonscriptsAppendix BLoad and Response ReconstructionB.1Unit load, wave, and motion responsesB.2ReconstructionB.2.1NodalresponseB.2.2Wave-inducedresponse Executive summary For the rapidly developing Floating OffshoreWind Turbine (FOWT) industry, computersimulations are essential tools for design andstrengthassessment.Computationalefficiency,robustness and accuracy are paramount. Thiswhitepaper presents three advanced time-domain methods implemented in the DNVSesamsoftwaresuite,specificallydesignedto Duetoitshighcomputationalefficiencyandaccuracywhenpredicting quasi-static structural responses, the ResponseReconstruction method is recommended for structuressubjected to loads where the structural dynamic effects are AnaddedbenefitoftheResponseReconstructionmethodis that it primarily uses tools and methods which are familiarto engineers used to frequency-domain analyses, such as For structures and loads where structural dynamic effectsaresignificant,LoadReconstructionisthepreferredmethod. It provides in this case nearly identical results totheDirectLoadGenerationmethod,butwithasignificantly The baseline method, Direct Load Generation, is a time-stepping method that computes the hydrodynamic pressure Load Reconstruction uses precalculated transfer functionstoreconstructthehydrodynamicpressurefieldonthestructure from the rigid-body motions and wave data The Direct Load Generation method must be used wheneffects from non-linear hydrodynamic pressures are Insummary,thechoiceofmethoddependsonthespecificcharacteristics of the structure and the loading conditions.For quasi-static analyses, Response Reconstruction is the Response Reconstruction goes a step further byreconstructing the quasistatic structural response directly 1.Introduction Thefloatingoffshorewindturbine(FOWT)industry is rapidly evolving, with a large numberof different substructure design conceptsgoing through various phases of design anddevelopment. While frequency- domain (FD)methods are often used for the more classicalfloatingoffshore(oilandgas)substructures, are used as the basis for comparison, and FLS damage iscomputed. The model was developed as part the EMULF(EfficientMethodsforUltraLargeFloatingWindStructures) For the obtained results, linear hydrodynamics isconsidered. Certain non-linear extensions are availablefor the different methods, as discussed in the respectivefollowing sections. All methods support the inclusion ofnon-linear Morison loads, however such loads are not This whitepaper is concerned with three time-domain Although the Load Reconstruction and ResponseReconstruction methods rely on unitary responsescalculated in the frequency domain, the reconstructedpressures and responses are in the time domain and thus The Direct Load Generation method, which is a time-stepping method that computes the hydrodynamicpressurefieldonthestructureandthenperformsadynamicor quasistatic time-domain structural analysis.The Load Reconstruction method, which reconstructs the The following limitations should however be noted: (i)forcaseswherestructuraldynamiceffectsaresignificant,the Response Reconstruction method is not applicable asit considers quasistatic response only;(ii) for cases where large variation in draught, trim or heel An integrated load analysis (ILA) is performed as anecessarypreceedingworkflowstep.FromtheILAtheresulting structural rigid-body motions, the mooring lineand tower interface loads (forces and moments), and thewave elevation (or wave components) time histories are The paper is structured as follows. In Section 2 the threemethods are described in detail, including the underlyingtheory and implementation. In Section 3 the methods are Appendices provide additional technical details on theimplementation of the methods in the Sesam software In this paper the three methods are discussed in detail.Results are presented for a FOWT substructure model, theEMULFDeltafloater,whichisatriangularsemisubmersiblesteelfloaterwithawindturbinetowerlocatedontopofthe 2.Methodology TheSesamsoftwaresuite[14]offersthreetime-domainstructuralanalysisworkflows:theDirectLoadGenerationmethod,the Following the generation or reconstruction of the time-domain structural response, a postprocessing such as fatigue limit state(FLS) or ultimate limit state (ULS) is typically performed. In this paper FLS is considered, but the methods are equally a