SPH modeling of caisson stability on rubble-mound foundation under wave action

Abstract

<p indent="0mm">The caisson breakwater is the representative protective structure in coastal and offshore zones, which is mainly composed of the reinforced concrete caisson and the rubble-mound foundation. The displacement and inclination of caisson structures are generally considered to be the typical features of the failure of the composite breakwaters. Therefore, understanding the motion response characteristics of caisson structures under wave action is of great importance for the design and the safe operation of caisson breakwaters. The dynamic response of caisson breakwaters under wave action is very complex, due to the interaction between wave-porous media-solid structures. In order to predict the stability of caisson breakwaters numerically, the complex free surface flow and the porous flow in the permeable foundation, as well as the contact interaction between the permeable foundation and the caisson structure should be accurately described. The existing numerical research for wave interaction with caisson breakwaters is usually assumed that the caisson structure is fixed in space, and the main interests focus on the wave deformation, the wave load acting on the caisson structure as well as the velocity and pressure fields in the vicinity of the composite breakwater. Few studies pay attention to the motion response and the instability of caisson structures. In addition, the traditional grid-based numerical models are commonly introduced to model wave interaction with the composite caisson breakwaters. These models, although powerful, may have difficulty dealing with extremely large deformation problems and usually also require an explicit surface capturing scheme. In comparison, the mesh-free smoothed particle hydrodynamics(SPH) method does not require the explicit surface capturing scheme in treating strong nonlinear flows with large free surface deformation and enables the easy modeling of coastal structures with complex geometrical boundaries. In this paper, based on the previously established SPH porous flow model, a contact interface boundary condition is developed between the permeable foundation and the upper caisson structure by modeling the supporting force and the sliding friction force at the interface boundary, and a new SPH model is established to study the caisson stability on the permeable foundation under wave action. Compared with the corresponding experimental data, it is found that the developed SPH model can reasonably predict the horizontal wave load, the vertical lift force acting on the caisson structure, and the motion response of the caisson structure. Compared with the other numerical model, it is found that the motion responses of the caisson structure predicted by the present SPH model have a better agreement with the experimental data. All the results indicate that the developed SPH model can be used as a robust tool to predict the stability of caisson breakwaters. However, it is undeniable that the predicted motion response of the caisson structure still deviates from the corresponding experimental data slightly. The main reason is that the contact interface boundary condition between the caisson structure and the permeable foundation ignores the deformation of the contact surface and the adjustment of the stress distribution, which is caused by the embedded effect of the caisson toe and the stone dislocation of the rubble-mound foundation.