Research Of Calculation Methods For The Super Element Of Offshore Wind Turbine Substructure

Due to the limited resources for the exploiting of onshore wind energy,the developing of offshore wind energy is prosperously in the worldwide.It should be noted that the complex geological and environmental load conditions may become the potential challenges for the construction of offshore wind farms,such as how to stimulate the structural responses of offshore wind turbines(OWTs)under such conditions accurately.The fully coupled analysis method is applied to the research of OWTs,especially for the floating offshore wind turbines(FOWTs).The integrated rotor-nacelle-servo-tower-support system analysis model is established based on the fully coupled analysis method.While different for the assumption of the rigid body for the substructure of the FOWT,the meshing of the finite element model of the substructure influence the accuracy of the fully coupled analysis model of the bottom fixed OWT significantly.Meanwhile,the complexity of the FE model also increase the simulation time significantly,especially for the substructures with substantial degree of freedoms(DOFs),such as the elevated pile platform.So the semi-integrated analysis method which can guarantee the accuracy of the numerical model,is extensively applied to the design and research of bottom fixed OWT,in order to improve the simulation efficiency.The aero-elastic analysis model of the rotornacelle-servo-tower-super element system and the FE model of the substructure is established based on the semi-integrated analysis method.It should be noted that,the super element(SE)is the equivalent stiffness and mass matrix of the substructure,and the accuracy of the SE can influence the analysis results of the semi-integrated analysis method significantly.Based on the above introduction,the following investigations are performed for the calculation of the super elements of the bottomed fixed OWT.(1)The software for the calculation of super elements is developed based on the theories of Guyan,SEREP and C-B condensation methods.(2)The super elements of the substructures are derived based on the above condensation methods,and the relevant finite element and aero-elastic analysis models are established for the validation of the reduced stiffness and mass matrix.(3)Influence of the parameters of the condensation methods on the accuracy of the super elements is investigated with the consideration of the variation of the substructures and load cases,and the principles for the selections of such parameters are suggested.(4)The applicability of the SEREP and C-B methods is validated by comparing with the fully coupled analysis model.The mechanisms of the influence of the condensation method’s parameters on the modelling accuracy of the reduced stiffness and mass matrix shall be revealed,also the discrepancies between the semi-integrated and the fully coupled model shall be investigated during the study.Furthermore,the proper condensation methods for the calculation of the super elements of OWT substructures,and the relevant principles for the selection of the parameters shall be summarized based on the above research.