Hydrodynamic Performance Study Of Bottom-Supported Wind Turbine Installation Platform

China’s sea area is vast and has abundant wind resources.Especially in the offshore intertidal zone,the wind resources are more abundant,but the offshore intertidal zone is affected by the tidal ebb and flow and the short time of high water level,so it will be more difficult to operate and construct in the offshore intertidal zone.At present,most of the construction operations in the intertidal zone use the bottom-supported platform,which sits on the seabed through ballast water,but according to the geological exploration data,it is found that the intertidal zone area has a cover layer,mainly consisting of silty clay,powdery clay,medium and coarse sand and granite and other soils,which has a restrictive effect on the bottom-supported platform bottom-supported operation.In this thesis,we take a bottomsupported platform as the object of study,and investigate the process of lifting operation under shallow seabed after migrating to the operating sea under towing draft.The main research contents of this thesis are as follows:(1)Referring to the test results of a semi-submersible marine platform in a pool,the test results of a typical working condition in the frequency and time domains are selected and compared with the results of a typical working condition under numerical simulation.The results show that the results obtained from the simulation are slightly smaller than the experimental results,and the error between the two is less,which verifies the accuracy of the hydrodynamic numerical simulation method.(2)To address the hydrodynamic performance of the descent process of the bottomsupported platform,a hydrodynamic model of the bottom-supported platform is established to study the additional mass,radiation damping,amplitude response operator and first-order wave force from different draft depths.At the same time,the stochastic dynamic response of the platform under three different sea conditions is analyzed by spectral analysis method,and short-term statistics of the reference points at the bottom of the platform are carried out to analyze the maximum displacement of the platform as well as the bottom touching height calculation.The results show that the motion response amplitude operator in the direction of transverse rocking and bow rocking changes significantly when the bottom-supported platform dives,while the motion response amplitude operator in the rest directions is not affected by the draft,and the first-order wave force characteristics are consistent with the motion response amplitude operator.The motion response of the seated platform increases with the increase of the sea state level,and the bottoming occurs when the dive reaches a certain height.(3)In order to study the influence of different soils on the hydrodynamic performance of the seabed,the bearing capacity of the seabed platform on clay and sand are studied to obtain the constraint stiffness of clay and sand on the seabed platform,and then the influence of different wind and wave incidence angles and different water depths on the motion response of the seabed platform is analyzed.The results show that the kinematic response of the seated platform is greater when it is restrained by clay than by sand;the kinematic response of the platform under head-on waves is more obvious than under cross waves and oblique waves,and the mooring cable tension is greater;the deeper the water depth is,the smaller the amplitude of the kinematic response of the platform is and the smaller the mooring cable tension is.(4)The motion response of the platform and the turbine impeller when the seabed platform is lifted on different seabed soils is considered.A model of the 5MW wind turbine impeller is established and coupled with the transport barge and the seabed platform,and the effects of different lifting conditions and the presence or absence of the transport barge on the motion response of the seabed platform and the wind turbine impeller under different sea conditions are considered.The results show that the motion response amplitude of the seated platform and the impeller of the wind turbine is larger than that of the sandy soil when the soil of the seated bottom is clay.In the absence of a barge,the motion response of the seated platform and the impeller of the fan is larger than that of the barge,and the operation of cross wave and wave period should be avoided.