砕波帯内における戻り流れの鉛直分布の理論的表示法

抄録

The purpose of the present paper is to establish the theoretical predictions for the vertical distribution of undertow inside a surf zone. The basic equation is based on an eddy-viscosity model and on an assumption that the average shear stress over a wave motion could be described in terms of the different linear function of the vertical distance from the sloping bottom at the two separate regions, which are the upper side and the lower one of the level of the wave trough. The coefficient of eddy-viscosity ν_t could be described in terms of an function of the vertical distance from the sloping bottom, just because the created vortices and turbulence in wave breaking will be spreading downwards from the water surface while decaying instantly. As a result in comparison of the results of our numerical analyses with Okayasu et al.'s flume tests, it is found that the change of ν_t has much effect on the characteristics of vertical distribution of undertow, especially near the bottom and surface, and is also shown that the surface vorticity has greater effects on characteristics of the vertical distribution of the undertow than any other factor.