Study on Three-Dimensional Beach Deformation Model for Nonlinear Multi-Directional Random Waves

本研究的目的是建立一个精确实用的非线性多向随机波浪作用下三维海滩演变的数值模型。采用Isobe（1994）提出的非线性缓坡方程作为波流模型，并对破波进行了修正，提出了一个可自动确定破波点的破波能量耗散项。针对多向随机波的破断准则，通过引入多向不规则性和频率不规则性的具体参数，提出了破断指标的原型。改进了近岸边界条件，使其包含了多向随机波作用下的冲刷带动力学。对Nwogu（1993）导出的扩展的boussinesq型方程进行了修正，以适用于包括冲浪带和冲荡带在内的近岸波和流。在输沙模型中，以Dibajnia和Watanabe（1997）提出的片流输沙速率公式为基础，利用一组不对称振荡流速确定净输沙速率。这个公式被推广到波浪和水流方向不同的一般水平面问题。在预测净输沙量后，求解泥沙质量守恒方程，确定地形变化。通过与多向不规则波浪作用下海岸结构周围波浪、水流和海滩变形的实验室数据对比，验证了模型的有效性。

The objective of the present study is to develop an accurate and practical numerical model for three-dimensional beach evolution under nonlinear multi-directional random waves. Nonlinear mild slope equations proposed by Isobe (1994) were adopted as a wave-current model and modified with respect to wave breaking by formulating a breaker-induced energy dissipation term, in which the breaking point can be automatically determined. For the breaking criterion on multi-directional random waves, a prototype of breaking index was proposed by introducing specific parameters for multi-directionality and frequency-wise irregularity. The nearshore boundary condition was also improved to include swash zone dynamics under multi-directional random waves.The extended Boussinesq-type equations derived by Nwogu (1993) were modified for applications to nearshore waves and currents including surf and swash zones. For a sand transport model, the sheet flow transport rate formula proposed by Dibajnia and Watanabe (1997) was used as a basis, which can determine the net sand transport rate using a set of asymmetric oscillatory flow velocities. The formula was extended to general horizontal plane problems where waves and currents were in the different directions. After predicting the net sand transport rate, the conservation equation of sediment mass was solved to determine the topographic change. The validity of the model was confirmed through comparisons with laboratory data on waves, currents and beach deformation around coastal structures under multi-directional irregular waves.