Numerical Investigation Of Solitary Wave Over Permeable Fringing Reef

A tsunami is a natural disaster,which is caused by earthquakes,volcanic eruptions,submarine landslides,strong storms,etc.When it spreads from the far sea to the near shore,the water depth becomes shallower and the wave height increases rapidly due to the effect of shallowing.In recent years,tsunami events have occurred frequently around the world.As a major maritime country,China has a coastline of 18,000 kilometers on the mainland,14,000 kilometers of island coastlines,and the total length of coastline is 32,000 kilometers.The sea area is affected by the geological activity of the Eurasian plate,the Pacific plate and the Indian Ocean plate,and many coastal areas are susceptible to tsunamis.Coral reefs are widely distributed along the coastlines in the tropical and sub-tropical regions,which can be used as a buffer to reduce the destructiveness of tsunamis.When the tsunami spread from the open sea areas to the shores,because of the wave breaking and friction at the bottom of coral reefs,its energy dissipate gradually and destruction decreased continuously.The protective capability of coral reefs against tsunami hazards has been proved in this paper.In this paper,the non-hydrostatic model NHWAVE is used to simulate the propagation and deformation of solitary wave on permeable fringing reef.The tsunami wave is simplified to a solitary wave,and wave propagation,deformation and elevation on fringing reef has been studied in this task,which can provide necessary reference for the parameter design of the coral reef engineering This study firstly established models to verify the propagation ability of solitary wave on fringing reef and the ability to flow in porous media,and then established a numerical model of fringing reef with permeable layer on reef flat and reef crest to compare permeable fringing reef and impermeable fringing reef.The differences in the hydrodynamic characteristics of solitary wave propagation on permeable fringing reef and impermeable fringing reef are compared.The hydrodynamic characteristics(such as free surface,maximum wave height,wave energy dissipation,maximum wave runup,wave reflection coefficient and transmission coefficient,and flow field)of fringing reef are systematically investigated by considering the effects of eight prominent factors,i.e.different median diameters,permeable layer thicknesses,permeable layer porosity,different incident wave heights,reef flat water depth,fore reef slope,back reef slope and relative width of reef crest.The main conclusions include:(1)The existence of the permeable layer makes the wave energy attenuate more rapidly,and effectively reduces the wave velocity along the reef flat after the wave broken,which increases with the thickness of the permeable layer When it is increased to d/h=0.2,more water flow infiltrates and produces strong vortices,which intensifies the oscillation of the free liquid surface,increases the wave height of each measuring point,and effectively reduces the wave height.The maximum difference is 0.525m,a decrease of about 82.5%;(2)With the change of porosity and median particle size in the porous media parameters,the wave height and flow velocity do not change significantly,but the resistance term in the porous media is reduced to a certain extent,reducing The seepage resistance of waves propagating along the reef flat is reduced,which increases the wave height;(3)For the fringing reef flat with permeable layer,the incident wave height is in the range of H/h=0.1～0.3 compared with the case where the permeable layer is not considered.(4)The increase of reef flat water depth increases the base water depth at each measuring point and the overall water volume on the reef flat,which reduces the friction loss of waves during the propagation of the reef flat to a certain extent.(5)For different fringing reef terrains,the wave climb decreases with the slowing of the rear reef,which is basically independent of the slope slope of the front reef and the relative width of the reef cap.(6)The existence of the permeable layer reduces the wave reflection and increases the wave transmission,and with the increase of the relative width of the reef cap,the water blocking effect gradually increases,and the transmission coefficient gradually decreases.