The effect of linear shear current on head-on collision of solitons

Head-on collision of two solitary waves in the presence of linear shear currents is studied by the use of the High-Level Green-Naghdi (HLGN) theory. The finite difference method is used to solve the HLGN model in the time-domain simulation. The initial values are obtained by the steady solution of solitary waves in the presence of linear shear currents. Shear currents with different velocities are considered to assess their effect on the solitary-wave collision. Three aspects of the head-on collision process in the presence of shear current are studied, namely, the wave elevation, velocity field, and particle trajectory. Results show that the background linear shear current significantly affects the wave elevation, velocity field, and particle trajectory during the head-on collision. It is observed that in the presence of the current, the wave elevation is narrower near the maximum surface displacement and is wider near the still-water level. It is also shown that near the seafloor, the horizontal velocity is opposite of the current direction, while it is following the current direction near the free surface. The opposite shear current results in the formation of a vortex in the fluid field. At the point of the collision, the vortex appears at a lower vertical position and shifts upstream of the current direction. Following the particle trajectories in the presence of the shear current, it is observed that the particles do not return to their initial positions after the head-on collisions, and the loop motions of the particles become smaller with larger current velocities.