Study On Hydrodynamic Performance Of Large-scale Monopile Offshore Wind Turbine Under Highly Nonlinear Wave

With the continuous development of offshore wind energy technology,the application prospects of offshore wind turbine monopile foundation are more and more attractive.However,the offshore turbine capacity and the diameter of the monopile are also increasing.The influence of the nonlinear wave load on the large-scale wind turbine with large monopile on the structural safety of the system cannot be ignored.Therefore,this paper uses CFD method to investigative the effect of highly nonlinear wave loads on the monopile foundation for 10 MW large offshore wind turbine combining complex Eastern Seas in order to provide certain reference for the structural reliability and long-term safety operation of the wind turbine system.In this paper,the numerical wave tank is firstly established,and Fifth-Order Stokes wave theory is used to generate wave field by using wave generation and wave absorption program.After comprehensive consideration of calculation time and accuracy,a suitable and uniform mesh division scheme is determined.In addition,in order to verify the applicability of the numerical water tank for studying the hydrodynamic load problem of the monopile foundation,the experimental data from OC5 OWT monopile model test is used to validate our numerical model.Secondly,the effects of nonlinear wave loads based on Fifth-Order Stokes wave on 10 MW OWT monopile foundation is investigated.The influence of different wave steepness parameter kA and water depth parameter kd on the run-up height,pressure and horizontal wave force around monopile foundation is discussed in detail.The wave load calculated by CFD is compared with the Morison equation and the potential flow theory based on the High-Order Boundary Element method(HOBEM).For cold region areas such as the Bohai Sea in China,the breaking cone is used to reduce the ice load.This paper studies the effect of ice-breaking cones of the monopile on hydrodynamic loads.By comparing the hydrodynamic response of the monopile foundation with different ice-breaking cone,the advantages and disadvantages of each structure are analyzed.Then,based on the Fifth-Order Stokes wave theory,the numerical water tanks for breaking wave with different slopes are established.The paper focuses on the effects of different forms of breaking waves such as spilling breaking wave and plunging breaking wave on the run-up height,pressure and wave force around the monpile foundation.The differences between the breaking wave and the traveling wave on the hydrodynamic performance of the monopile foundation are analyzed and discussed.Several different methods to calculate breaking force are compared and analyzed,and their respective scopes of application is discussed.With the increase of wave height,the variation of hydrodynamic performance after the wave breaking changes from the plunging breaking wave to the spilling breaking wave is explored.Finally,the freak wave function is programmed based on C language and JONSWAP spectrum,and the hydrodynamic load of 10 MW monopile foundation under the action of freak wave is analyzed.The research focuses on the influence of freak wave on the run-up height,pressure and wave force,and then explores the interaction mechanism between strong nonlinear wave and large diameter monopile foundation,in order to provide a reference for the design of extra larger-diameter monopole in the future.