波浪场中物质输移离散系数的理论分析

THEORETICAL ANALYSIS ON DISPERSION COEFFICIENT IN WAVE FIELD

海岸水域波浪引起的物质输移扩散存在着不同于水流引起的物质输移扩散的特征.通过解析的方法对垂向扩散方程进行求解,推导出波浪和潮流共同作用下的海岸水域物质输移离散系数的理论公式.分析中将总的离散系数分为潮流、质量输移流、纯波浪波动作用以及潮流与质量输移流、潮流与波浪波动、质量输移流与波浪波动的相互作用6部分,通过分析各组成部分特征,得出海岸水域物质输移中波浪所产生的离散效应主要是质量输移流贡献,波浪水质点运动及波流相互作用对时间平均离散系数的贡献较小的结论.仅波浪的作用(不包括潮流)的有关结果与他人数值模拟和实验结果的吻合良好,证明了该理论推导的正确性.给出了时间平均离散系数及离散系数波动幅值随波浪周期和波高的变化特征,同时将结果应用于垂向环流,给出了垂向环流对应于质量输移流所产生的离散系数的特征.

Transportation and diffusion caused by coastal waves had the different characteristics due to the flow conditions. Through solving the vertical diffusion equations by analytic methods, this paper inferred a theoretical formula for the dispersion coefficient under the combined action of the wave and the tidal current. It divided the general dispersion coefficient into six sections, which included coefficients caused by tidal current, Stokes drift, wave oscillation and interaction among them. Meanwhile, it drew a conclusion that the contribution of dispersion effect caused by coastal waves was mainly produced by Stokes drift, while the contributions on time-averaged dispersion coefficient by the motion of water points and the wave-current interaction were much smaller. Furthermore, the results without the tidal current were in agreement with those of numerical simulation and experiments, which proved the correctness of theoretical derivation. This paper introduced the variation characteristics that the time-averaged dispersion coefficient and the amplitude of dispersion coefficient changed with the variation of wave period and wave height. Meanwhile, we applied the results to vertical circulation and obtained the characteristics of dispersion coefficient compared to stokes drift.