基于XBeach模型的离岸堤群防护效果评价指标

离岸堤等海岸防护工程会引起波浪的绕射和折射，改变海岸区域的水动力情况。针对XBeach模型进行扩展以提高波浪绕射作用下波浪场、流场和岸滩演变的预测精度，并利用双突堤绕射试验对模型进行验证，数值计算结果与实测结果吻合较好。同时开展了坡度为1∶50的理想平直海滩（含离岸堤）的演化数值试验，试验结果表明改进后岸滩演变更加合理。基于拓展的XBeach模型建立了考虑工程量的离岸堤群防护效果评价体系，同时在特定条件下对口门宽度及离岸堤高度对平直沙质海岸可能产生的影响进行了模拟和分析，并给出了该条件下的最优方案。所提出的指标区别于以往学者对离岸堤后沙质海滩的形态演变研究，具有较高的实际工程应用价值。

Evaluation index of protection effect of breakwaters based on XBeach model

Shore protection structures such as detached breakwaters may cause wave diffraction and refraction, and change the hydrodynamics in coastal region. An extended version of XBeach model is presented in this paper to improve the accuracy of prediction on wave, current fields and sandy beach evolution when wave diffraction takes effect. The extended model is validated by comparing the simulation results with the physical test of wave propagation through a breakwater gap, with satisfactory agreement. Numerical simulation test was carried out for an ideal flat beach with a slope of 1∶50 behind a breakwater and results show that the extended model generates more reasonable results. Based on the extended XBeach model, the evaluation system of the protection effect is established for the offshore breakwater group considering the engineering quantity. The possible effects of width and height of breakwaters on the evolution of plane sandy coast are analyzed under certain wave condition based on numerical tests leading to the optimal scheme finally presented. The proposed index is different from previous researches on the morphological evolution of sandy beaches behind the breakwaters, and has high practical engineering value.