Author(s)

S.-J. Choi & O. T. Gudmestad

Abstract

Several studies have shown that the occurrence of a breaking wave over a submerged shoal can induce a jet-like strong current on the lee side of the submerged shoal, and the forces on structures following breaking waves can be perceived as wave forces being superimposed on strong current forces. In the present paper, the strong current was assumed to be induced by a breaking wave, a so-called breaking wave induced current. Firstly, a MIKE 21 BW model was established to quantify wave heights and current velocities at structural positions over a submerged shoal. Secondly, the wave plus current forces and moments, the wave forces and moments without the current, and the wave forces and moments on a flat bottom (no breaking) are calculated and compared, using the wave heights and current velocities at the structural positions which were calculated above. Finally, the design wave forces and moments on a structure in waves and current coexisting fields are determined. The results of threedimensional numerical analysis did show that in spite of the fact that the wave heights on the lee side of the submerged shoal appeared to be very small (0.027– 0.067 m) compared with the wave heights on the flat bottom (0.14 m), a strong current (0.246–0.391 m/s) surely occurred on the lee side of the submerged shoal due to radiation stress differentials given by the breaking of the incident waves. The comparison of the total forces on the structure without the current and with the current showed that the wave plus current forces in this area increased by an average of 200% to 250% compared with the wave forces without current. Moreover, the wave plus current forces rather exceeded the wave forces which were calculated for waves on a flat bottom prior to breaking. Keywords: breaking wave induced current, submerged shoal, MIKE 21 BW, radiation stress, wave plus current force, waves and current coexisting fields.

Keywords

breaking wave induced current, submerged shoal, MIKE 21 BW,radiation stress, wave plus current force, waves and current coexisting fields