Numerical Simulation Of The Effect Of Freak Wave On High-rise Cap With Multiple Piles Foundation And Submarine Cable Laying In Offshore Wind Farm

In order to adapt to the seabed conditions of some sea areas in the southeast coast,offshore wind turbine foundations often use high-rise cap with multiple piles foundation,which have a composite structure of large-scale cap and small-scale piles.The accurate calculation of the wave load on the small-scale foundation piles needs to consider both the effect of the incident wave and the diffraction effect generated by the large-scale cap.The paper carries out computational research on this aspect.In addition,because the wave load caused by extreme waves is a great threat to the wind power foundation,the calculation also considers the role of the freak wave.At the same time,the hydrodynamic calculation and analysis of the submarine cable laying ship and the submarine cable itself under actual sea conditions are also carried out.The relevant research results have certain theoretical research significance,and will promote the construction of offshore wind farms.First,in order to accurately calculate the wave load on the small-scale piles in the composite structure,and figure out the influence of the incident wave wave number,pile diameter and pile position on the small-scale pile wave load.In this paper,a three-dimensional wave numerical model of a composite structure composed of a large-scale pile and a small-scale pile is constructed in Fluent based on the VOF method.Through numerical calculation,the incident wave force,diffracted wave force and total wave force acting on the small-scale piles of the composite structure are obtained.The Morison formula results are compared,and the characteristics of the wave load on the small-scale piles are discussed.The results show that under certain wave conditions,the wave diffraction caused by the large-scale piles has a greater influence on the wave load on the small-scale piles.Secondly,the numerical simulation of the interaction between different types of waves and high-rise cap with multiple piles foundation is carried out.Compared with the physical model test of wave flume,the reliability of the model for calculating wave load on high-rise cap with multiple piles foundation is verified.The difference of wave load between freak wave and regular wave on foundation is compared and analyzed.The results show that the maximum value of the wave force is equal to the incident wave force,but the total force issmaller than the incident wave force due to the phase difference determined by the diffraction potential distribution.Finally,in order to consider the impact of the harsh marine environment on the laying of submarine cables,this paper also uses the annual marine dynamic environmental data measured in the sea area where the Guishan Offshore Wind Farm is located,based on Orcaflex to establish a numerical model for the connection of the submarine cable to the main platform.The initial laying process of the submarine cable to the offshore booster station was analyzed by numerical simulation.For different wave current conditions,we focus on the ship's motion response and cable hydrodynamic analysis under the influence of waves,ocean currents and other environmental factors,and consider the possible presence of freak wave.The research results show that the freak wave has a great influence on the swaying motion and cable tension of the submarine cable ship,and the wave flow direction along the longitudinal direction of the ship is a relatively bad working condition.