潮滩水流加减速阶段边界层流速剖面的比较

COMPARISON OF VELOCITY PROFILES ASSOCIATED WITH TIDAL ACCELERATION AND DECELERATION OVER INTERTIDAL FLATS

江苏大丰地区潮滩由于水深较浅,潮流、波浪等动力较强,整个水层可视为边界层,其主体部分是对数层,即水流流速在垂向上呈对数分布。在潮流的加减速阶段,流速剖面将可能偏离对数分布,从而使对数剖面法计算出来的边界层参数造成误差。使用MIDAS-400用户化数据采集系统,在大丰潮滩获得了多层流速、浊度等同步高频观测数据,基于修正后的von Karman-Prandtl模型对u-lnz进行回归分析、数据内部一致性分析来定义流速对数剖面并与未修正前经典理论得到的边界层参数进行比较。分析结果表明,修正后的流速剖面更符合实际情况,边界层参数除了受水流加速度的影响外,还和沙纹等因素有关。另外,边界层参数的变化量与特征加速度负相关。

Since the intertidal flats at Dafeng, Jiangsu Province are characterized by shallow water, strong tidal currents and waves, the whole depth of flow can be regarded as the boundary layer, i.e. the velocity profile is logarithmic structure. However, it may depart from the usual logarithmic form in an accelerating or deceleration tidal flow and will result in tremendous error if the logarithmic von Karmen-Prandtl equation is used to calculate the parameters. Current speeds and turbidities have been measured by using MIDAS-400 at various heights over the tidal fiats. The u-lnz regression analysis and the internal consistency analysis were adopted and a realistic logarithmic velocity profile was established by modifying yon KarmanPrandtl equation. The analysis indicates that the parameters are associated not only with the acceleration or deceleration of currents but also with sand ripples. The changes of boundary layer parameters are in negative correlation with the characteristic acceleration.