Numerical Study On Wave Dissipation Of Submerged Breakwater Under The Action Of Long-period Swell

The study of long-period swell has always been a complex problem.Although its wave height is small,its wavelength is long so that it has very strong transmission ability and is easy to penetrate wave-permeable breakwater.And the speed of long-period swell is great and it carries huge energy,so it has a great impact on the rolling characteristics of moored ships.Accidents caused by long-period swell are common,which bring great troubles to the port construction and operation.However,from the current research,the protective effect of all kinds of permeable breakwaters on long-period swell is still not satisfactory.The crest of submerged breakwater is mostly near the average water level.When wave crosses the submerged breakwater,it breaks or deforms violently,and the dissipation of wave energy results in the weakening of the wave motion behind the breakwater,which is exactly the wave dissipation mechanism of submerged breakwater.Submerged breakwater is widely used in coastal engineering because of its unique advantages in wave prevention,beach protection,siltation promotion and ecological landscape.Previous studies focused on the propagation process of short wave over submerged breakwater and the change of wave height,and there was no study on the change of wave height of long-period swell over submerged breakwater.And meanwhile the type of submerged breakwater used in numerical experiments was relatively single,and the type of submerged breakwater crest was not improved and explored.In this paper,a two-dimensional numerical wave flume is built by OpenFOAM,an open source CFD software,to simulate the propagation process and wave height variation of long-period swell over the submerged breakwater,and analyze the wave dissipation effect of the submerged breakwater under different conditions,so as to provide a basis for the protection engineering of the sea area affected by long-period swell.Firstly,by comparing the results of physical experiment and numerical simulation,the accuracy and applicability of the two-dimensional numerical wave flume for submerged breakwater are verified by choosing the dachronic curve of wave surface in stable wave band.Then,the numerical model is used to simulate the propagation process of long-period swell over the submerged breakwater and the change of wave height.The effects of relative depth,relative width,slope and period on the transmission wave height of submerged breakwater are discussed respectively.The relationship between transmission coefficient of submerged breakwater and various influencing factors under long-period swell is studied.Next,combined with the previous research on the structure of submerged breakwater,the crest is changed from flat to sawtooth.The wave transmission height behind the toothed submerged breakwater under long-period swell is calculated by the established numerical model,and compared with the flat-top submerged breakwater under the same conditions,the wave dissipation effect of the toothed submerged breakwater is analyzed.Finally,the research contents and main research results are summarized to provide reference for the design of breakwater structure under the action of long-period swell,and the future research of the type of submerged breakwater structure is prospected.