河口海岸近底层潮流速分布模式初步研究

Preliminary study on the tidal velocity profile in the near-bottom layer in the estuary and coast waters

许多现场实测资料表明,潮流近底流速剖面偏离传统的对数分布。虽然偏离值可能不大,但利用对数剖面去计算河底粗糙长度和剪切应力时会引起较大的误差。有研究者的数值试验表明,如果通过流速是对数分布来估计粗糙长度和底部切应力,偏差可能超过100%(Kuo等,1996)。本文从流体动力学原理出发,利用Prandtl混合长度和Von Karman自相似理论,建立河口海岸近底层潮流速分布的对数线性模式。通过对英国大陆南部西Solent水道实测水流垂向分布进行枚举粗糙长度z0结合最小二乘法拟合,并将计算结果与传统的对数模式的结果比较,表明本文模式有以下优点:①精度高,计算值更接近实测值;②所确定的粗糙长度z0和摩阻流速u*的相关系数更高,且两者在相位上更趋一致。

Many observed data show that the near-bottom tidal flow velocity profile departed from the usual logarithmic law. The amount of the departure may not necessarily be large, but it results in the larger errors when the profiles are used to calculate the bed roughness length and shear stress. Based on numerical test, some investigators （Kuo et al., 1996） present that deviation amplitude of calculated roughness length and bottom shear stress may exceed 100% if applying the logarithmic velocity profile. Based on fluid dynamic principle, the tidal velocity profile in the near-bottom layer in estuary and coast is established by introducing Prandtl mixing length theory and Von Karman self-similar theory. By the analysis of the velocity profile data observed at the west Solent south mainland of England, using the least square fit combining with enumerating roughness length z0, the following conclusions can be obtained from the comparison of the logarithmic-linear velocity profile with the conventional logarithmic velocity profile： 1. The logarithmic-linear velocity profile is closer to measured value than the logarithmic velocity profile and has higher precision. 2. The roughness length and the friction velocity determined by the logarithmic-linear velocity profile is more correlative than that of logarithmic velocity profile, and the former is more consistency in phase.