Numerical Study on Seepage-induced Failure of Caisson Type Breakwaters Using a Stabilized ISPH

Abstract: This paper presents a stabilized incompressible smoothed particle hydrodynamics (ISPH) method to simultaneously simulate surface and seepage flow. The Navier-Stokes type equation, which manipulates the linear and nonlinear resistance effects caused from porous materials, are employed for tracking fluid motions in porous medium. The SPH method is one of the mesh-less particle methods and its Lagrangian nature is considered to be fit to express the large deformation of free surfaces. Some research on fluid flows in porous medium have been done by using the particle methods. In particular, Akbari introduced the apparent density which is numerically calculated by multiplying the original fluid density with the porosity. By means of his technique, fluid volume in porous medium is successfully conserved. However, fluid pressure around solid boundaries can be overestimated because of the density gap between the fluid and fixed solid boundary particles. With the aim of obtaining the smooth and quantitatively accurate pressure distribution, we proposed a new SPH approximation called as the mass and density correction. Through some fundamental numerical tests, the accuracy of the proposed method was sufficiently confirmed. This paper also presents a hydraulic experiment on caisson type breakwaters solely focusing on seepage flow through the rubble mound without considering any other factors such as wave force and scour. Two cases of the experiments were implemented with different hydraulic models; a breakwater model without reinforcement and that reinforced with sheet piles. As for the latter one, the sheet piles are set to be quite thin against the whole model structure. This issue can lead to considerably-high particle resolution in the particle methods because a certain number of solid particles need to be placed on the thin structure. In order to overcome this problem, a new boundary treatment using the reversible boundary particles is suggested. We conducted a numerical analysis on this experiment and confirmed that the analysis results show good agreement with the experiments.