Dejie Guo

Study on Mean Field by Numerical Analysis of Nearshore Current

Tokuzo Hosoyamada

 The rip current is a kind of the beach nearshore current, it’s caused by the strong mass transportation from offshore to onshore, which caused by nonlinearity of the wave motion. The rip current is basically an offshore flow, which compensates for mass transport by waves from offshore to the onshore. The flow becomes strong and weak in the coastal direction and becomes a partially strong flow. In general, nearshore current studies are often aimed at investigating the causes of beach erosion. Among them, the rip current is mysterious, and a high-speed flow in coastal direction is generated with a beautiful cusp topography, even though no incident wave in the coastal direction. This phenomenon is difficult to observe. So, the purpose of this study is observing the differences of rip current with the wave’s basic equation on the virtual coastal topography. With the nonlinear long wave equation, 9 kinds of wave incidents conditions, 9 kinds of shore conditions , total 81 cases had been calculated. Through the many cases, considering the details of the nearshore current on different wave condition and shore condition. We also use diffusive calculation and particle method as the method to recognize the nearshore current visually.
 With the numerical analysis result, we found out that when wave height is low, rip current had been occurred easily in the long-period waves incident and gentle slope of shore cases. When high wave coming, with the sudden slope of shore, there is a shore slope make the rip current’s flow velocity be maximum. And the longshore current also act same characteristics. In the uniform slope of shore cases, rip current will be occurred easily long-period waves incident and gentle slope of shore cases, the span of rip current been longer in the long-period waves incident than the short-period waves.