This study presents a numerical investigation on the mechanism of nonlinear wave-induced porous seabed response. The fully dynamic equations based on Biot's theory are solved for the poro-elastic seabed behavior. The nonlinear wave pressure on seabed surface is calculated by an empirical formula available, which is able to consider effects of both wave skewness and wave asymmetry. A parametric study is performed to analyze seabed behavior with respect to various degrees of wave nonlinearity. It is shown that wave skewness and asymmetry considerably modify the spatial and temporal distribution pattern of pore pressure by changing the wave shapes.
Wave-induced porous seabed response plays an important role in the mechanism of seabed instability around marine structures. Distribution of pore pressure in the seabed is mostly concerned as it may cause destruction of surface soil layer under extreme conditions. A large amount of physical understanding and empirical formulations on wave-induced seabed response have been obtained under the assumption of linear waves (Jeng, 2003). In reality, however, waves always exhibit nonlinear characteristics. In general, nonlinear waves could be classified into two types with respect to wave shapes, including the skewed waves and asymmetric waves (Abreu, Silva, Sancho and Temperville, 2010). The skewed waves represent the waves in shoaling zone (e.g., second-order Stokes waves), which have a relatively high crest and a flat trough. The asymmetric waves represent the waves in surf zone (e.g., saw-tooth waves with forward leaning shapes), which have a steep wave front and a gentle rear. As indicated by a few previous studies (Jeng and Lin, 1997; Chen, Huang and Cong, 1996), seabed response under nonlinear waves is significantly different from that under linear waves. However, most of previous studies on this topic focused on the second-order Stokes waves, i.e., skewed waves, which only represents the nonlinear waves in a limited region. Our understanding on the seabed response under asymmetric waves or combined skewed-asymmetric waves is still incomplete.