The Coupled Numerical Model For Wave Actions On Structures In The Nearshore Zone And Its Applications In Engineering

Abstract As the depth-averaged simplification of the three-dimensional potential flow model, the horizontal two-dimensional Boussinesq equations are suitable for solving efficiently nonlinear wave propagation and transformation in large shallow water regions (for example, harbor or coastal region with similar size). On the other hand, because of depth-averaged simplification, the Boussinesq equations can not be applied in solving such problems as wave actions on submerged breakwaters, floating bodies etc., in which flow variations with depth must be considered. For these problems, one must solve potential flow models or viscous flow models, which are usually applied to a relatively small computational region around the structure and not suitable for large fluid domains, this is because both the 3D potential model and the 3D viscous model are far more CPU time-consuming. Besides, all the flow features attached to viscosity (vorticity, boundary layer) are disregarded in the modelling by potential flow theory. One must solve viscous flow models to access these details of flow. In order to obtain simultaneously and efficiently nonlinear wave transformations in a harbor or coastal region, details of three dimensional flow around structures and hydrodynamic loads of wave on marine structures, combining advantages of Boussinesq model and NS-VOF model, we unfolded the study of establishing Boussinesq / NS coupled numerical models. The entire research work includes the following parts: 1) The Boussinesq equations numerical model with implicit differential method is setup. Numerical experiments reveal that the implicit method is accurate and unconditional stable. The Sommerfeld radiation condition (SRC) combined with sponge layer technique is applied at open boundaries, and numerical tests verify the performance of SRC assisted by the sponge layer technique. Computational results of regular waves propagating on a circular shoal are in good agreement with the experimental data, showing that the Boussinesq equation numerical model with implicit differential method can give a satisfactory description of wave transformation over the topography and can be applied in practical engineering. 2) The three dimensional numerical wave basin (NWB)based on 3D Navier- Stokes equations and the VOF method is setup. The wave maker boundary condition for the VOF method is proposed. On other boundaries, in addition to reflection boundary conditions, the open boundaries are treated by the technique of velocity reduction zone(VRZ) at first, in which vertical velocity is reduced exponentially inside the VRZ. Then Sommerfeld radiation condition is applied at the open boundary. The performance of the present open boundary treatment is verified by numerical experiments. 3) The 1D Boussinesq/2D NS-VOF coupled model is set up. Matching boundary conditions for pressure, velocity and wave surface elevation on the common matching boundary are proposed, and the I D/2D coupled numerical model is setup, which is combination of the 2D NS-VOF model applied in the inner region (that is, the near-field surrounding a marine structure), and the ID Boussinesq model applied in the outer region. Numerical experiment shows that the present matching boundary cond...