Preliminary Study on the Development of a Platform for the Optimization of Beach Stabilization Measures against Beach Erosion II - Centering on the Development of Physics-Based Morphology Model for the Estimation of an Erosion Rate of Nourished Beach

摘要

In this study,a physics-based 3D morphology model for the estimation of an erosion rate of nourished beach is newly proposed.As a hydrodynamic module,IHFOAM toolbox having its roots on the OpenFoam is used.On the other hand,the morphology model comprised a transport equation for suspended sediment,and Exner type equation derived from the viewpoint of sediment budget with the bed load being taken to accounted.In doing so,the incipient motion of sediment is determined based on the Shields Diagram,while the bottom suspended sediment concentration,the bed load transport rate is figured out using the bottom shearing stress directly calculated from the numerically simulated flow field rather than the conventional quadratic law and frictional coefficient.In order to verify the proposed morphology model,we numerically simulate the nonlinear shoaling,breaking over the uniform beach of 1/m slope,and its ensuing morphology change.Numerical results show that the partially skewed,and asymmetric bottom shearing stresses can be successfully simulated.It was shown that sediments suspended and eroded at the foreshore by wave breaking are gradually drifted toward a shore and accumulated in the process of up-rush,which eventually leads to the formation of swash bar.It is also worth mentioning that the breaker bar formed by the sediments dragged by the back-wash flow which commences at the pinnacle of up-rush as the back-wash flow gets weakened due to the increased depth was successfully duplicated in the numerical simulation.