Research On Characteristic And Mass Transport Of Cohesive Mud Under Surface Waves

Not only the rheological and kinetic characteristic of the cohesive mud,but also its interaction with waves in the coastal and estuarine areas plays an important role in predicting and solving the erosion and deposition problems of the beach.As a result,it makes the research on the cohesive mud have vast of applied foreground and research values.Therefore,the cohesive sediment from Tianjin Dagang is studied systematically on its rheological property,settling character as well as the incipient motion.Moreover,the mass transport velocity of power law mud under surface waves in a two-layer system is examined theoretically.The static rheological experiments of the cohesive sediment with different density are carried out in Chapter 2.As a result,the relationship between the shear stress and the shear rate is analyzed,and the relationship between densities and the rheological parameters which are fitted by both Bingham plastic model and power law model is also discussed.Then,the settling tests of the cohesive sediment with different density are performed,which analyzes the effects of the cohesive sediment concentration on the settling velocity,and the relationship of them is fitted as well.The incipient motion of the cohesive sediment with different density due to surface waves is investigated experimentally in Chapter 3.Firstly,both the critical incipient velocity and stress are calculated from the critical incipient wave height,which takes the “the movement of small amounts of cohesive sediment” as the standard in the experiments.As a result,the variations of critical incipient velocity and stress with the increasing of the cohesive sediment density are presented,and the fitting relations between either of them and density are represented,respectively.It turns out that the incipient law of cohesive mud satisfies the extended Shields diagram.Then,combined with the results from the static rheological tests,the relationship between the critical incipient stress and the Bingham yield stress is listed.Furthermore,the experiments verification is also given by comparing with experimental results in the literature,which shows a good agreement.The mass transport velocity of power-law mud under surface waves in a two layer system is examined theoretically in Chapter 4.The wave motion is driven by the periodic pressure on the free water surface,and the mud is descried by a power-law model.According to the key assumptions of shallowness and small deformations,a perturbation analysis is carried out to the second order to find the mean Eulerian velocity in an Eulerian coordinate system.The numerical iteration method is adopted to solve these non-linear equations at the leading order,and an improved cinque-diagonal chasing method is used to solve the second-order linear problem.As a result,the effects of flow index on the flow field,wave height and the mass transport in both layers are examined.