Numerical Simulation Of Wave Motions In A Reef-Lagoon-Channel System Based On A Boussinesq-type Model

Coral reefs act as natural barriers to protect the coastline,can reduce storm surge,erosion of the coastline.Therefore,the study of wave transformation on the reef-lagoon-channel systems is of certain guiding significance for coastal protection and offshore engineering construction.In this paper,the Funwave-TVD wave model based on the completely nonlinear Boussinesq equation is used to simulate the transformation of irregular waves in a 2-DH reeflagoon-channel systems.Firstly,the established model was verified via the comparison of spectrum,total wave height,short wave height,infragravity wave height,water set-up and the wave run-up on the back-reef beach were compared at the same time after the wave-current field was stabilized in the experiment.Furthermore,the wave transformation in the reef-lagoonchannel systems were simulated and analyzed under the effect of various factors,such as different incident wave heights,reef-fat water levels,spectral peak period,fore-reef slope,reef width,beach slope,friction coefficient of coral reef bottom and width of channel.Finally,the generation of infragravity wave in the system and the resonance mechanism of infragravity wave on the reef flat are analyzed.The results show:On the reef flat and lagoon,short wave increases with the increase of the incident wave heights,spectral peak period and water depth of the reef flat,and decreases with the increase of the friction coefficient of coral reef bottom and reef flat width,but because the channel width change brings the change of the influence of various,so short wave has no obvious regularity,and it not sensitive to the change of other influencing factors;infragravity wave increase with the increase of the incident wave heights,spectral peak periods,fore-reef slope steepness and channel width,and decreases with the increase of friction coefficient,the reef flat width influence on low frequency long wave is mainly composed of waves in the process of spreading to move and the reef flat to low frequency resonance mutual influence,and it not sensitive to the change of other influencing factors;set-up increases with the increase of the incident wave height and the width of the reef flat,but decreases with the increase of the water depth of the reef flat and the channel width,and it showing insensitivity to the change of other influencing factors;In the channel,short waves increase with the increase of incident wave height,reef flat water depth,fore-reef slope steepness and width of reef flat,but decreases with the increase of friction coefficient and spectral peak period,has no obvious regularity for the change of rift width,and it insensitive to the influence of other factors;infragravity wave increase with the increase of the incident wave heights,water depth of the reef flat and fore-reef slope steepness,but decreases with the increase of the width of reef flat,and it not sensitive to the change of other influencing factors;set-up increases with the increase of the width of reef flat,but decreases with the increase of the channel width,and it showing insensitivity to the change of other influencing factors.The wave runup on the beach behand the reef flat increases with the increase of incident wave heights,spectral peak period,water depth of the reef flat and forereef slope steepness,but decreases with the increase of the width of reef flat and friction coefficient,and it showing insensitivity to the change of other influencing factors;The wave runup on the beach behand the channel increases with the increase of incident wave heights,spectral peak period,fore-reef slope steepness,beach slope steepness and channel width,but decreases with the increase of the width of reef flat and friction coefficient,and it showing insensitivity to the change of other influencing factors.The mechanism of infragravity wave generate is analyzed,the result shows that the infragravity wave is mainly generated by the movement of the breaking point.By analyzing the mechanism and resonance mode of the infragravity wave on the reef flat,we have found that the resonance is close to the expectation.For more analysis of the effect of the channel on the resonance shows that the existence of channel enhances the resonance of the semi-open reef flat,but weaken the resonance of other modes.