Wave induced forces and scour on seabed structures

A beta version of the Delft3D hydrodynamic model system has been developed that incorporates a non-hydrostatic solution which allows for the simulation of surface waves. The model is forced with a water level boundary condition derived from the solution of Fenton's wave theory for highly non-linear waves in shallow water. The modelled velocity and pressure fields for the case of a flat seabed are compared to the Fenton solution. The modelled velocity and pressure fields agree well with the theoretical solution, particularly for the section of the water column between the seabed and the mean water level. Cases with simple seabed structures are implemented in the model domain and potential impact and differential (uplift) pressures are assessed. In addition, the modelled bed shear stress is compared to empirical results induced by the wave motion is assessed which indicates that with sufficient model resolution the model system is capable of being applied to assess sediment stability and scour characteristics under operational and design conditions. This paper presents a description of the model system and theoretical validation. Estimates of the forces induced by design waves on a seabed structures are detailed and in particular the potential variation between instantaneous and phase-average force magnitudes are highlighted.