Development Of A Numerical Wave Tank Based On The Lattice Boltzmann Method

The numerical wave tank to study the interaction between waves and structures is of great significance for ensuring the safety of offshore facilities.However,there are bottlenecks in the parallel efficiency of the existing numerical wave tanks in complex situations.So,it is important to seek new methods and develop numerical wave tanks and programs with higher parallel efficiency.To this end,this paper develops a threedimensional numerical wave tank based on the lattice Boltzmann method,and make an efficient parallel computing program to verify the model.The research contents and conclusions of this paper are as follows.(1)Based on the incompressible multi-relaxation LB free-surface model,with improved numerical algorithm and stability,a three-dimensional free surface flow model is established.The comparison between ideal examples,numerical simulations and experimental measurements shows that the model has the ability to simulate the complex motion of free-surface with gravity.(2)Based on the free surface flow model,a two-dimensional non-reflective numerical wave tank(LBM-NWT2D)is established by combining the momentum source wave generation and the sponge layer wave damping method.The comparison between ideal examples,numerical simulations and experimental measurements shows that LBM-NWT2 D has the ability to generate waves without re-reflection,simulate wave interaction with structures,and wave breaking process.Numerical simulations also found the phenomenon of spurious current on the free surface of the model.(3)By analyzing the lattice Boltzmann equation with forcing term,the numerical errors induced by the boundary schemes are obtained.Two modified methods of modified pressure and forcing term correction method are proposed to solve the problem of energy dissipation and spurious current.The comparison between ideal examples,numerical simulations and experimental measurements shows that both improved models can solve the problem of energy dissipation,the modified pressure method is simpler and more practical,and the forcing term correction method is more applicable.(4)Based on the improved numerical model of three-dimensional free surface flow,a three-dimensional non-reflective numerical wave tank(LBM-NWT3D)is established using active absorption method of wave making and wave-eliminating method.The effects of velocity boundary scheme,Mach number,lattice constant,multi-relaxation collision model and relaxation parameters on the simulation results are discussed by numerical experiments,and the model is optimized and improved.The comparison between numerical experiments and analytical solutions shows that LBM-NWT3 D has the ability to generate waves without re-reflection and simulate the wave force on the structure.The comparison between numerical experiments and experimental measurements shows that LBM-NWT3 D has the ability to simulate the reflection,diffraction,transformation and breaking of waves caused by structures or topography.(5)Based on the C++ language,a parallel numerical wave tank program was programmed to optimize the computational efficiency of the program on the “Tianhe-1A” supercomputer.Numerical experiments show that the LBM-NWT has a speedup ratio of 127.2 when using 128 nodes on “Tianhe-1A”,which has higher computational efficiency and parallel scalability.When using 16 nodes,compared to Open FOAMbased numerical wave tank(OF-NWT),the computational efficiency of the LBM-NWT is 5.3 times that of the OF-NWT,which is more suitable for solving engineering problems on the supercomputer.