Simulation of 3D nonlinear wave-structure interactions in a numerical wave basin

An efficient computer method has been developed for simulation of 3D nonlinear free-surface flows in a so-called 'numerical wave basin'. The numerical method is mainly based on the Rankine-source formulation combined with a time-stepping scheme. Linear triangular elements are used to discretize the governing equation and the problem boundary. At geometrical singularities, the continuity of the velocity potential and the discontinuity of its normal derivative are enforced to meet different Neumann conditions. In the computation of the coefficient matrix, the analytic solutions are used in the local-field: multiple expansions are applied for intermediate-field computations; and the source/normal-dipole approximations are adopted in the farfield. The GMRES(m) iterative method with diagonal preconditioning has been used for solving the derived linear system with a large number of unknowns at each time step. A practical and efficient 'open' boundary condition has been presented for stable and long-term simulations. The parallel computing approach has been exploited for speeding up the current large-size computing process and achieving high resolutions. It is found that two major computing processes: calculating the coefficient matrix and solving the derived linear system by the GMRES(m) method at each time step, are both parallel-oriented.; The developed numerical method has successfully been used for studies: (1) 3D wave basin flow simulation; (2) nonlinear wave generation and radiation; (3) 3D second-order wave radiation and (4) 3D second-order wave diffaction. Compared with the linear frequency domain solutions, the current time domain simulations of the 3D wave basin flows manifest more detailed information for the time interval as model tests in the wave basin. The capability and the efficiency of the current approach for studying fully-nonlinear wave-structure interactions have been demonstrated through simulations of the nonlinear waves generated by two moving boundaries. Furthermore, a numerical scheme has been presented in this work to compute the inhomogeneous terms in the second-order free-surface conditions, for studying the second-order wave radiation and diffaction problems. Good agreements have been obtained between the computed results and the published experimental and numerical data.; The current numerical method can be readily applied to many marine hydrodynamic problems such as ship motion in wave, current-wave-ship interactions, irregular-wave generation and body interactions.