Numerical Wave Flume And Its Application In Calculation Of Wave Forces On Semi-circular Breakwater

As one of the most common phenomena in the ocean, wave is the dominant dynamic load exerting on the structures in the sea, which is hence the key factor needed to be considered in designing of coastal structures. One of the problems concerned most in designing breakwater is the maximum force acting on the breakwater at given wave conditions. The wave pressure calculation of the new type of breakwater, the semi-circular breakwater, is rather complex because of its special shape. The present wave force formulas are all based on empirical or semi-empirical theories, which have limitation in some degree in the application, especially in the submerged case, where their predicted results of total force are quite doubtable.A 2-D numerical wave flume is established based on the N-S equations, in which the k ?εtwo-equation turbulence model is adopted to close the governing equations and the VOF method is used for the reconstruction of the free surface. Interaction process of regular waves with a semi-circular breakwater is simulated by the numerical wave flume. Comparison between modeled processes of wave pressure on the surface of the semi-circular breakwater and the measured ones shows good agreement. It is found from the numerical results that accumulation of water quantity and thus setup of the mean water level behind the dike will occur if the computational domain behind the breakwater is not long enough. This may result in underestimation of the total horizontal forces exerted on the breakwater by 16-20%. Two solutions are proposed to solve the problem, one is by extending the length of the computational domain behind the breakwater to 4-5 times the wave length, the other is by adding numerical absorber in the end of the computational domain behind the breakwater.Computational results indicate that both the uprising tendency of the wave pressure on the rear of the breakwater and the descending tendency of the total horizontal wave forces can be avoided.By adopting more efficient matrix solver in the computational codes, i.e. the Bi-CGSTAB method, the computating time is saved by 30%.