Experimental And Numerical Study On Hydrodynamic Characteristics Of Coral Reef

Pacific and Atlantic Oceans are widely distributed with coral reefs,so is South China Sea.Topography of a coral reef is characterized by a steep front slope and a shallow reef flat,which is quite different from a sandy beach.Special topography of a coral reef produces distinctive hydrodynamic conditions in nearshore area.With the acceleration of marine exploitation and the steady progress of South China Sea construction,research on the hydrodynamic characteristics of coral reefs and the overtopping of vertical structures on reef flats will be of great significance.Physical model experiments are carried out on a simplified coral reef topography with a 1:5 front and a horizontal reef flat.The characteristics of wave breaking,wave energy transferring and the law of set-up of irregular waves on coral reefs are explored,and the average overtopping law of the vertical dike on the reef flat is studied.Wave conditions are designed as combination of three reef flat depths,four incident wave periods and four incident wave heights.The experimental results show that for irregular waves,the hydrodynamic conditions on coral reefs need about 200 wave periods to reach steady.After wave breaking,the wave energy begins to spread to higher and lower frequencies in the process of propagation to shoreline,and the low frequency energy dominates when it reaches the end of reef flat.The maximum set-up on reef flat increases with the increase of incident wave period,decreases with the increase of water depth on reef flat,and has a positive linear relationship with incident wave height.The existing formulas for overtopping vertical structures are validated by using the data obtained in this experiment.On the basis of summing up the previous results,the formulas for overtopping of vertical dikes on coral reef flats are proposed.A numerical model is established in OpenFOAM to simulate the process of overtopping with the same scale of the experiment.The numerical simulation results show that OpenFOAM can reproduce the incident wave train well.The simulated values of wave height and water level at each measuring point in the flume are very close to the experimental values,and the simulated values of overtopping discharge are in good agreement with the experimental values.