Current Effect on Nonlinear Wave Height

Abstract

Abstract Interaction of uniform and shear currents with nonlinear waves is studied by use of the computational fluid dynamics approach. A range of nonlinear waves are considered including shallow- and deep-water waves, and the effect of currents of variable speed and direction on the wave height is investigated. Uniform current consists of a fixed horizontal velocity across the water depth, while shear current imposes a linearly varying velocity from the seafloor to the still-water level. The current speeds are selected such that they remain comparable with the horizontal particle velocity under the wave crest and wave trough. A computational wave-current tank is developed for this purpose and the combined wave-current condition is obtained by developing a new wave-current maker in an open-source computational fluid dynamics package, namely OpenFOAM. The model is tested against laboratory measurements of various types of wave and currents and very good agreement is observed. The model is then used to investigate how currents of different profile, speed and direction modify the wave field. While the focus of the study is on the effect of these currents on the change of wave height, the surface elevation of the waves is also assessed in some cases. Discussion is provided on the differences between current effect on the wave height of shallow-water waves vs deep-water waves. The wave nonlinearity is found to play a remarkable role on how the wave changes under the ambient current. Shear currents are observed to have a stronger influence on the change of wave height than uniform currents.