Numerical Simulation Of XBeach Model With Diffraction

Shore protection structures and shoreface nourishment projects may cause wave diffraction and refraction,and change the hydrodynamic condition of coastal areas.The possible impacts of these projects need to be predicted and analyzed before implementation.And numerical simulation is one of the comparatively economical and feasible methods.The classification and research progress of the numerical model for sandy coast according to the development history of the model is reviewed,and the development status and problems of the process-based open source regional model XBeach is introduced with emphasis.And on this basis,an extended version of XBeach model is presented in this paper to improve the accuracy of predicted wave and current fields and sandy beach evolution in scenarios where wave diffraction takes effect.Following the approach successfully implemented in spectral wave model SWAN,a diffraction parameter is introduced into wave action balance equation in XBeach to take wave diffraction into account.Alternative wave breaking index and the formula for the critical velocity are also tested in the extended model to achieve better model-data agreement.The extended model is validated by comparing the simulation results with the physical tests for fixed and movable sea bed.The computed wave height,wave-induced current filed and beach evolution are found in satisfactory agreement with the measurements,the numerical modeling capacity of the extended model to represent wave diffraction effect is thus demonstrated.Based on the model performance evaluation method of relative mean absolute error,new evaluation indexes were established to analyze the influence of computational grid precision and angular resolution on the calculation accuracy of diffraction wave height.It is pointed out that the mesh accuracy should not be less than 1/8 wavelength in the numerical simulation with diffraction effect,and the appropriate angle resolution setting under some mesh precision conditions is given,which lays a foundation for the application of the model.At the same time,the explicit method is used to replace the implicit dispersion relation to solve the wave wavelength for reducing computation time,and simulation results show the effectiveness of the method.Finally,based on the modified XBeach model,the evaluation system of the protection effect of offshore breakwaters considering the engineering quantity is established.In the meantime,the influence of the width of the gap and the height of the offshore breakwaters on the plane sandy beach is simulated and analyzed under certain conditions.The optimal scheme under this condition is given.