长江口盐水入侵三维数值模拟

A 3 D Numerical Model for Saltwater Intrusion in the Changjiang Estuary

建立了河口区盐水入侵计算的三维数学模型．该模型将整个计算水域通过简单的坐标变换转换成单位方体，三个坐标方向的空间网格均可采用非均匀网格，对变换后的基本方程进行差分离散，水平方向的空间导数采用显式中心差分，垂直方向的空间导数采用隐式中心差分，三角方程用ＴＤＭＡ法求解．水位采用回代计算以提高精度．该模型运用长江口水域的盐水入侵计算，结果表明，算出的含盐度时空分布与实测一致．模型的主要特点是：变换简单，显隐式结合，稳定性尚好。

A 3 D numerical model is developed to compute saltwater intrusion in estuaries. The irreqular water body is considered as a unit cube with simple transformation of coordinates . The basic equations are transformed to a transformed coordinate system. Because of simple transformation of coordinates, the form of basic equations in the new coordinate system is similar with that in the old one. The variable grids in three coordinate directions are used to simulate the local topograph. The transformed set of equations are solved by finite difference techniques. In finite difference approximations explicit central difference scheme is used for horizontal direction space derivatives, and implicit central difference scheme for vertical direction space derivatives. All tridiagonal equations are solved by TDMA method. The second order accuracy of water level can be retained by returning computation. The model has been tested by computing the saltwater intrusion at the mouth bar in the Changjiang estuary and the results show that the salinity time space distribution of computation is in agreement with measured data. The model is characterized by simple transformation of coordinates, combination of explicit implicit difference scheme, good computation stability and fast computation speed.