Study On The Evolution Of The Wave Propagation Over The Submerged Sill

As the wave propagating to the offshore, wave will become deformed because of the influence of the topography and the buildings which case the shoaling, refraction, diffraction, inflection or breaking etc. Besides, the current is relatively strong in the entrance of title inlet and estuaries, which makes the nearshore wave field more complex. The submerged breakwaters are the buildings which are commonly used on the coastal protection engineering, whose functions including beach protection, accretion promotion, enclosing tideland for cultivation, diversion, and so on.By keeping the higher order term, using different velocity term and adding some "deep water terms", the resulting set of equations have significantly improved linear dispersion properties in the water of intermediate depth and extended the range of its applicability. Based on Nwogu's extended Boussinesq equations, the finite difference scheme is applied. In order to increase the numerical stability and decrease the wave energy in larger frequency and in more direction, internal generation of wave is applied, and the sponge layers are set for absorbing the wave energy. The cnoidal wave is made by this way of which numerical results agree well with the analytical solutions so this model can be used to make nonlinear wave. Then the evolution of the wave propagation over the submerged sill is imitated using this model, which results agree well with the experimental data in the aspect of wave surface and the harmonic. Considering a range of modulation rates, group frequencies, and difference frequencies, the primary frequencies, super harmonics and the sub-harmonics induced by bichromatic wave groups are examined in DULT's laboratory. It is also found that the following current and the opposing current have evidently impact on wave evolution. Not only the low frequency waves induced by bichromatic waves are analyzed, but also the evolution of free long waves over the submerged sill is simulated. The results show that they have super harmonics in its own internal structure. At last the free long waves combined the short waves are simulated in the constant depth water, and compared with theoretical values which have a good agreement. So the Boussinesq equations have great advantages in modulation of long wave and short wave.