【作者】 牛小静；

【导师】 余锡平；

【作者基本信息】 清华大学 ， 水利工程， 2008， 博士

【摘要】 泥质海岸的动力特性及其与海洋动力环境的相互作用是海岸及近海工程中有着重要理论意义和广泛应用价值的研究课题。本论文将海床上可运动、可变形的底泥作为单相非牛顿流体,从不可压缩流体运动的基本方程出发,建立了波浪作用下底泥运动的数值模型以及水体与底泥耦合运动的数值模型,并以此为基础分析了波浪与泥质底床的相互作用过程,相比于以往基于理论解析的研究方法具有更为广泛的应用前景。底泥运动以不可压缩流体运动的连续方程和动量方程为基本方程,同时针对底泥复杂的非牛顿流变特性,引入了一个高度综合的粘弹塑性模型。该模型对应的流变方程能简化为常见的粘性模型、粘弹性模型、粘弹塑性模型。基本方程的数值求解由SMAC方法拓展而成,并针对大粘度底泥运动问题需要提高计算稳定性的事实,对动量方程的时间离散进行了改进。数值模型在平板起动流计算中的应用证明了其有效性。论文还通过对二维槽道进口段流动进行计算,分析了不同格式的稳定性和计算效率。波浪作用下底泥运动的数值模型是将波浪作用简化为作用于泥层顶部的周期性波压,忽略了底泥动力相应对波浪的影响。论文采用不同的底泥流变模型,系统分析了底泥粘性、弹性、塑性在波浪作用下的底泥运动中对底泥运动速度的幅值、物质输移速度、能量耗散等的影响,还探讨了波高与底泥运动特征量之间的关系。水体与底泥耦合运动模型中考虑了底泥对波浪的影响,以及水体紊动和域内存在多个运动界面的情况。模型中采用k-ε模型处理紊流,自由水面利用VOF方法追踪。泥层界面用泥沙物质守恒方程描述,并针对底泥分层的情况,利用ENO的思路结合Youngs界面重构技术特别构建了数值处理方法。耦合模型能很好地反映波浪与底泥的相互作用。模型应用于计算波浪在不同性质的泥床上的传播和变形过程,并与实验比较,在一定程度上明确了底泥流变模型的适用范围。论文还初步探讨了底泥呈层特性对波浪衰减的影响,以及复杂地形条件下底泥对波浪传播和变形的影响。更多还原

【Abstract】 The dynamic interaction between waves and muddy seabed is studied. The mud is considered as a non-Newtonian fluid with complex rheological property including viscosity, elasticity, and plasticity. An extraordinarily generalized constitutive equation is proposed, which includes various existing models as special cases. The numerical method is based on the well-known SMAC method in modern CFD, but the discretization of the momentum equations is replaced by a weighted implicit scheme to achieve a better stability, which is definitely necessary when mud with very large viscosity is involved.The response of muddy seabed to surface water waves is investigated based on the non-Newtonian fluid flow model established. The wave action is represented by periodic pressure acting on the surface of the seabed. The effects of the viscosity, the elasticity, and the plasticity of the mud on the motion of the seabed and its resulting mud transport are discussed. The relationship between wave height and the amplitude of the velocity, the rate of mass transport and energy dissipation is also clarified.A fully coupled model is also developed to deal with the dynamic interaction between waves and the muddy seabed. The k-εturbulence model is used. The free water surface is treated by the VOF method, while the numerical method for tracing the moving water-mud interfaces and the interfaces between different mud layers is specially developed, which combines the essence of ENO and Youngs’reconstruction scheme. The coupled model is applied to the study of wave propagation over a mud layer under various conditions. It is demonstrated that the viscous model is fairly satisfactory for mud with low density, but the plastic feature of the mud plays an important role when the density of the mud is relatively large. The model is also employed to study the effects of the seabed stratification on wave motion. It is also shown to be applicable to problems with practical background.更多还原