Numerical prediction for the performance of a floating-type breakwater by using a two-dimensional particle method †

Abstract The nonlinear free-surface motions interacting with a floating body were investigated using the Moving Particle Semi-implicit (MPS) method proposed by Koshizuka and Oka [6] for incompressible flow. In the numerical me-thod, more realistic Lagrangian moving particles were used for solving the flow field instead of the Eulerian ap-proach with a grid system. Therefore, the convection terms and time derivatives in the Navier-Stokes equation can be calculated more directly, without any numerical diffusion, instabilities, or topological failure. The MPS method was applied to a numerical simulation of predicting the efficiency of floating-type breakwater interacting with waves. Keywords: Floating-type breakwater, Wave transmission rate, Particle method, Navier-Stokes equation, Waves interacting with a floating body 1. Introduction In order to efficiently utilize the coastal area, vari-ous kinds of breakwater should be studied and devel-oped. Although fixed breakwaters have excellent per-formance onshore, they are associated with economi-cal and technical problems in their construction off-shore, as well as environmental by restricting the cir-culation of seawater. However, floating-type breakwa-ters have many advantages compared to fixed ones, i.e. flexibility of future extensions, mobility, preservation of environments and economical efficiency, etc. As a result, a few investigations have proposed to improve the performance of floating breakwaters [1, 2, 3, 5, 8, 11, 12, 14]. Of these, most numerical approaches relat-ing to floating breakwaters have focused on develop-ing numerical techniques that capture the fully nonli-near free-surface motion based on a grid system. However, there are many different approaches that do not employ a grid system; for example, the so-called particle methods with a fully Lagrangian treatment [6, 10]. The particle methods seem to be more feasible and effective than conventional grid methods for solv-ing the flow fields associated with complicated boun-dary shapes or coupling effects between a fluid and structure. In the present study, the efficiency of a floating-type breakwater interacting with waves was investigated numerically, using the Moving Particle Simulation (MPS) method supposed by Koshizuka and Oka [6] for an incompressible flow. In this method, more realistic Lagrangian moving particles were used for solving the flow field rather than an Eulerian approach with a grid system. Therefore, the convection terms and time derivatives in the Navier-Stokes equation can directly be calculated, without any numerical diffusion, instability or topological failure. The method consisted of particle interaction models to represent the gradient, diffusion, incompressibility and free-surface boundary conditions.