Current effects on nonlinear wave scattering by a submerged plate

On the basis of a time-domain higher-order boundary element method, a two-dimensional fully nonlinear numerical wave flume is developed to investigate the nonlinear interactions between a regular wave and a submerged horizontal plate in the presence of uniform currents. A two-point method is used to discriminate bound (i.e., nonlinearly forced by and coupled to free waves) and free harmonic waves propagating upstream and downstream from the structure. The proposed model is verified against experimental and other numerical data for wave-current interaction without obstacles and nonlinear wave scattering by a submerged plate in the absence of currents. A first-order analysis shows that the reflection coefficient increases in the following current (i.e., current in the same direction as the incident wave) and decreases in the opposing current (i.e., current in the opposite direction to the incident wave). Moreover, the plate length for the maximum reflection to occur is not sensitive to the current. A second-order analysis indicates that downstream from the plate, the current has a stronger influence on the secondary free mode than on the first free mode. The energy transfer between the fundamental wave and the higher harmonics is intensified by a following current but weakened by an opposing current. The second free harmonic wave amplitude is affected more by the opposing current than it is by the following current.