【作者】 郝嘉凌；

【导师】 严以新； 宋志尧；

【作者基本信息】 河海大学 ， 港口、海岸及近海工程， 2006， 博士

【摘要】 本文从流体动力学原理出发，利用Prandtl混合长度和von Karman自相似理论建立了河口海岸近底层水流结构的对数线性模式及其扩展模式，籍此，从理论上进一步研究潮流运动的摩阻特性。 底部剪切应力可由τ=ρu_*²来确定，其中ρ是密度，u_*是底部摩阻流速，是底部边界层研究的重要参数。本文叙述了u_*计算的三类方法：1) 紊动动能耗散率法；2) 流速剖面法；3)经验阻力系数法。针对使用较常见的流速剖面法，本文介绍了四种方法 1) 近底两层流速时间系列估计粗糙长度；2) 最小二乘法；3) 霍夫变换法：4) 枚举法结合最小二乘法。其中，尝试引入霍夫变换法确定流速剖面参数，因此对于该方法的有效性进行了验证，并应用于ADCP实测数据，与传统最小二乘法进行比较。同时探讨采用枚举法结合最小二乘法确定流速剖面参数，详细叙述求解过程并用于实测流速资料的拟合分析。 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）。通过对英国大陆南部西Solent水道和德国白令海南部的Eckerforde海湾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，表明本文建立的对数线性模式有以下优点：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。 但从理论上得到的近底流速分布的对数线性模式对近底层的数据要求较高，一般近底1m之内至少需要四层测量数据，而这些数据在实际应用时很难得到。因此，本文根据潮流运动特征，增加表面梯度为零的约束条件将该模式进行扩展研究，使其能适用于传统的六点法测量数据。该扩展模式为对数抛物模式，适用于全水深，是潮流速分布模式。通过长江口和江苏岸外西洋海域两个实例计算分析，并与对数扩展模式比较，结果表明该潮流速分布模式在各层数据上都与实测数据具有良好的相关性且物理量z₀与u_*之间具有更好的一致性和相关性，可应用于河口海岸流速分析研究。 鉴于实际河口海岸近岸水流由于受风浪等作用不满足表面流速梯度为0的条件，水浅时表层的流速梯度可能对底部水流结构产生作用，因此，考虑引入实际的表面流速梯度，得到更多还原

【Abstract】 On the basis of fluid dynamic principle, the log-linear model of the near-bed tidal velocity and its extending model in estuarine and coastal waters were established by introducing Prandtl’s mixing length theory and von Karman self-similarity theory. Furthermore, the friction characteristics of tidal current were studied.The bottom shear stress could be determined by τ = pu_*~2, where ρ is density of water, u_* isfriction velocity, both are important parameters for studying bottom boundary layer. Three types of method solving u_* are described: 1) Turbulent kinetic dissipation method; 2) Velocity profile method; 3) Experiential drag coefficient method. For the usual velocity profile method, four kinds of method are given: 1) Estimating roughness length from velocity time series of two near-bottom layers; 2) The least square method; 3)Hough transform method; 4) Enumerating combined with the least square method. The Hough transform method is adopted to determine the parameters of velocity profile, and the validation of the method and the application to ADCP field date were carried and compared with the least square method. Meanwhile, the enumerating zO combined with the least square method was used to determine the parameters of velocity profile, the detailed process was given and the fitting and analysis to field data were carried out.Many observed data show that the near-bed tidal velocity profile deviates from the usual logarithmic law. The amount of deviation may not be large, but it results in large errors when the logarithmic velocity profile is used to calculate the bed roughness height and friction velocity and bottom shear stress. Based on their investigation, Kuo et al,(1996) indicated that the deviation amplitude may exceed 100%. By the analysises of the velocity profile data observed at the west Solent south mainland of England, and Eckerforde Bay southern Baltic Sea, using the least square fit combing with enumerating roughness height Zo, the following conclusions can be obtained from the comparison of the log-linear velocity profile with the usual logarithmic law: 1) The log-linear velocity profile is closer to measured value than the logarithmic velocity profile and has higher precision. 2) The roughness height and the friction velocity determined by the log-linear velocity profile are more correlative than that of logarithmic velocity profile, and the former is more consistency in phase.更多还原