Numerical Investigation of Wave-Current Loads on a Submerged Plate by HOBEM

ABSTRACT

The potential numerical wave flume is applied in this study to estimate the forces and the moment on a submerged plate in the combined wave-current flow by solving the Laplacian equation based on the higher order boundary element method (HOBEM). The free surface motion is tracked by solving the free surface boundary conditions and is advanced in time using the fourth-order Runge-Kutta scheme. The performance of the potential numerical wave flume is assessed by comparing with the published theoretical results and the experimental measurements. The forces and the moment on the submerged plate alternatively increase to the peak value and then decrease to zero with increasing plate breadth, and they are found to increase with increasing water depth. Additionally, it is found that the use of Doppler shifted solutions is not sufficient for considering the effect of depth-uniform current on waves. The generation of higher harmonics due to a sudden change in water depth and the current-induced form drag are found to make significant contributions to the wave loading.

INTRODUCTION

The submerged plate, used as a breakwater device, is less dependent on the bottom topography, more economical and can assure open scenic views. It allows seawater to exchange freely between the sheltered region and the open sea to prevent stagnation, pollution, transport of sediment to maintain the general partition of the natural seabed. It has been applied as an efficient breakwater in coastal and offshore zones Thus, investigations on submerged plate have been focused on their reflection and transmission characteristics (Stamos and Hajj, 2001.), or the generation of higher order bound and free harmonic waves that affects the sailing conditions (Brossard and Chagdali, 2001; Lin et al., 2014). However, the effects of wave-induced forces and moment on submerged structures are of practical importance as well to assure the strength and stability of the structure over the design life. Extensive researches have shown that the mutual influence of waves and currents is intensified in shallow waters/coastal areas (Isaacson and Cheung, 1993; Chen et al. 1999). Methods that can provide accurate predictions of forces and moment on submerged structures in combined waves and currents are required for the safe and cost efficient design of submerged structures in coastal areas.