Numerical Simulation Of Nonlinear Ship Waves In Deep Waters

The main research work of this thesis are as follows:(1)A numerical simulation model of three-dimensional nonlinear ship waves in deep water is established.Based on the potential flow theory and Kelvin theory,the Kelvin source and Rankine source are used to form waves like ship waves on the free liquid surface.The boundary element method is used to reduce the space dimension of the problem solution and construct the boundary integral equation.Combined with the nonlinear free surface boundary conditions,the nonlinear equations for solving the three-dimensional nonlinear ship waves are formed by numerical discretization.(2)A banded preconditioner Jacobian-free Newton-Krylov(JFNK)algorithm for solving nonlinear ship waves numerical model is proposed.The JFNK method is used to compute the large-scale nonlinear equations.The core content of the method is to use the preconditioned generalized minimum residual(GMRES)method to solve the correction value of each iteration in the Krylov subspace.In this thesis,according to the characteristics of nonlinear ship waves problem,a strip preconditioning method is proposed to further improve the computational efficiency of nonlinear equations and save a lot of running memory.(3)A parallel solution framework for nonlinear ship waves is proposed.Firstly,the nonlinear ship waves solving program is mainly divided into four parts: constructing the nonlinear equations,constructing the preconditioned matrix,inverting the preconditioned matrix,and to solving the linear equations by using the GMRES algorithm.Then,based on Compute Unified Architecture(CUDA)programming,the parallel calculation of the four parts was implemented on GPU in sequence by writing the kernel function and utilizing the GPU acceleration library.The calculation efficiency of nonlinear ship waves is improved obviously.(4)The simulation results of polymorphic ship waves are generated,and the observation characteristics of nonlinear ship waves are investigated.By adjusting the Froude number,source strength,and source type of the simulation model,the ship wave simulation mechanism related to this simulation model was explored,and the numerical simulation of ship waves at different speeds and sizes was realized,and the validity of the simulation model was also verified.Then the simulation model is used to further explore the wake angle of the ship waves,and the change law of the wake angle of the ship waves is summarized.The results show that the simulation results produced in this thesis are consistent with the actual ship waves.It is found that the wake angle of ship waves decreases gradually with the increase of Froude number,and steadily increases with the increase of source point intensity.Thus,the observation characteristics of ship waves are accurately described.The banded preconditioner method proposed in this thesis can save two thirds of the running memory,and the proposed parallel solution framework can obtain 20 times of the acceleration ratio,which effectively reduces the space complexity and time complexity of the nonlinear ship waves algorithm.The research work of this thesis improves the theoretical research system of nonlinear ship waves and optimizes numerical solution of mathematical model for nonlinear ship wave,which has important theoretical significance and engineering value for the research and application of ship waves.