Influence of Porous Seabed Characteristics on Wave Forces Acting on Monopile

This study investigated the wave attenuation and wave forces acting on the monopile due to porosity characteristics of the seabed. A three-dimensional numerical analysis model of wave-porous seabed-monopile-interactions is established, in which the modified Reynolds-averaged Navier-Stokes (RANS) equation and Forchheimer saturation drag model are used to control porous flow, while the fluid volume method (VOF) is used to track free surface. Based on the proposed model, wave attenuation induced by porous seabed is first studied, taking into consideration the interaction between waves and porous seabed. Second, the numerical variation of the wave forces acting on the monopile under the same wave action with porous seabed or rigid seabed is analysed, highlighting the necessity of considering the porous characteristics of the seabed. Finally, the influence of the seabed porous characteristics on the numerical variation of the wave forces is further studied using the single variable control method. The numerical results show that the porous characteristics of the seabed have obvious attenuation effect on wave propagation. Additionally, under the given wave parameters and the characteristics of the porous seabed, the maximum wave forces acting on the monopile is about 35% higher than that of the rigid seabed. This suggests that ignoring the porous characteristics of seabed will result in an underestimation of the wave forces and could cause security risks. In addition, the wave forces acting on the structure are closely related to the porous characteristics of the seabed. The results show that the maximum wave forces decrease as the particle size increases, while increasing first and then decreasing with an increase of porosity. One thing to note is that porosity affects the variation trend of wave forces acting on monopile changing with seabed thickness.