Bursting-Layer Modeling Based on the Assumption of the Averaged Sea Surface for Strong Wind-Driven Currents

Abstract

Abstract In the sea, which is affected by strong winds that cover the water surface with wind-wave breakers, the sea surface layer, called the bursting layer by authors, is generated immediately below the mean water level. For treatment of strong wind-driven currents, it is necessary to model the bursting layer correctly based on observed data. However, an essential difficulty occurs in that, because of large water surface displacement caused by developed wind waves, water particle velocities above the wave trough level cannot be measured continuously in the Eulerian coordinates when measuring the velocity of strong wind-driven currents. Consequently, it is impossible to apply the Reynolds average rule to the velocity field above the wave trough level. In this study, an experiment that uses a wind-wave tank with a double bottom is performed to measure the horizontal velocity of currents driven only by the wind stress. The vertical distribution up to the mean water level is determined to make its vertically integrated value agree with the total mass flux of the wind-driven currents. Furthermore, the vertical distribution of the Reynolds stress is derived by solving a Reynolds equation; its solution agrees with the given velocity distribution. Numerical simulation was performed to reproduce the strong wind-driven currents. Results showed that the bursting-layer model can correctly calculate the steep vertical distribution of the current velocity in the bursting layer.