Simulation Study On Wave Attenuation Through Flexible Vegetation With Following Currents

Nature-based Solutions(Nb S)and the Construction of Ecological Civilization put forward higher requirements for coastal disaster prevention and mitigation in China.Wave dissipation by vegetation has become a frontier topic of coastal engineering because of its revetment function and ecological benefits.The existing numerical simulation of wave dissipation by vegetation mostly focus on linear wave and rigid vegetation.However,waves and currents coexist in the actual coast,and the motion of flexible vegetation is more complicated than that of rigid vegetation.In order to improve the capability of disaster prevention and mitigation and coastal ecological environment restoration and management in China,it is necessary to deeply understand the mechanism of wave and current on the dynamic characteristics of flexible vegetation and the wave attenuation mechanism by flexible vegetation in combined wavecurrent conditions.Then,the quantitative analysis method based on numerical simulation is explored.The simulation study on wave attenuation through flexible vegetation with following currents is carried out from microscopic and macroscopic aspects.The simulation method of wave attenuation by submerged flexible vegetation under combined waves and currents is proposed.On that basis,the reliability of the simulation method of wave attenuation by submerged flexible vegetation under combined waves and currents is demonstrated.Then,the dynamic characteristics and the law of wave attenuation of flexible vegetation under the effect of waves and currents are illuminated.The research results can demonstrate the importance of current to wave attenuation by flexible vegetation under combined wave and current flows,optimize the simulation theory and method of wave attenuation by vegetation,broaden the application scope of the numerical model of wave attenuation by vegetation,and improve the understanding of wave damping by flexible vegetation.The main contents and conclusions of this study are as follows:(1)The existing numerical model of submerged flexible vegetation dynamics and wave attenuation is introduced,and the simulation method of submerged flexible vegetation movement and wave attenuation vegetation under combined waves and currents is proposed.The driving conditions of the model are modified to expand the application scope of the numerical model of wave attenuation by vegetation.Subsequently,the wave dissipation simulation by flexible vegetation in combined waves and currents is realized.(2)The dynamic and wave attenuation numerical models of submerged flexible vegetation in the environment of regular waves with the following current are established,and the ability of the models to reproduce the rocking motion of single vegetation,the wave height distribution along the water area of group vegetation and the wave attenuation coefficient is verified.On that basis,the reliability of the numerical simulation method of submerged flexible vegetation movement and attenuation under combined waves and currents is demonstrated.Finally,the calculation formula of the drag coefficient of flexible vegetation in wave-current conditions is fitted.(3)The dynamic characteristics of single flexible vegetation in the environment of regular waves with the following current are revealed.Within the range of the simulation parameters,for the cases where the maximum oscillatory wave velocity is small,the maximum horizontal force of the vegetation and the maximum horizontal displacement of the vegetation top are negatively correlated with Keulegan-Carpenter number,velocity ratio,Cauchy number,Reynolds number and Ca L at first,and then positively correlated.With the increase of the maximum oscillatory wave velocity,the maximum horizontal force of vegetation and the maximum horizontal displacement of the vegetation top have a significant positive correlation with the above dimensionless constants.There is a negative correlation between the swing of vegetation top and the seleced dimensionless constants.Within the range of constant current velocity,the variation range of the swing and the maximum horizontal displacement of vegetation top are also negatively correlated with the blade length ratio.The influence mechanism of each dimensionless constant is also discussed.(4)The law of wave propagation and attenuation through flexible vegetation in the environment of regular waves with the following current is discussed.Within the range of the simulation parameters,when the constant current velocity is small,there is a certain rule for the wave elimination through flexible vegetation.The attenuation of the wave in the flexible vegetation area decreases slightly and then increases with the increase of current velocity,which is negatively correlated with water depth and positively correlated with wave height.With the continuous increase of the current velocity,there is no obvious rule for wave attenuation of the flexible vegetation.At the same time,the influence mechanism of each factor is discussed combined with the dynamic characteristics of vegetation.