Study on submerged plate type breakwater very close to free surface

A device system,composed of a submerged horizontal plate is proposed to be one type of breakwater.The plate is supposed to be thin,rigid and close to the free surface.Based on fully nonlinear theory,a numerical wave tank technique is utilized to investigate the wave elimination mechanism of the device.The shallow water effect,return flow and higher order high harmonic wave components behind plate,are three contributions to wave elimination.From the viewpoint of engineering application,the ratio of plate submergence to wave height and the ratio of plate length to wavelength are two decisive coupling factors to wave transmitted coefficients.Carefully regulating these two factors,transmitted wave coefficient will be controlled under 0.2 to 0.5.From numerical simulation,for plate very close to free surface,at least third order wave elevation and hydrodynamic force should be considered which reveals the limitation of linear theory.