Numerical Simulation Of Fluid Mud Formation And Movement On Muddy Coast

Fluid mud is a commonly observed form of fine-grained sediment with specialrheological behavior and high fluidity in muddy coasts and estuaries. The formationand movement of fluid mud have great influence on siltation problems in harbors andnavigation channels. Therefore, the formation and movement of fluid mud have beenstudied in the present dissertation. Firstly a three-dimensional hydrodynamic-cohesivesediment coupling model was developed based on the finite volume method toreproduce the formation of fluid mud. A one-dimensional fluid mud model wasdeveloped to simulate the movement of fluid mud and then on the basis of it atwo-layer model of three-dimensional hydrodynamics and two-dimensionalvertically-averaged fluid mud movement was established. Then combining theatmosphere model, the wave model and the model coupling toolkit, awind-wave-current-cohesive sediment-fluid mud integrated model was proposed andapplied to investigate the formation and movement of fluid mud and channel siltationunder different wind and wave conditions in typical muddy coast Lianyungang Harbor.The specific research contents and main results are summarized as follows:(1) Based on the finite volume method, a three-dimensionalhydrodynamic-cohesive sediment coupling model under combined wave and currentcondition was developed with the inclusion of processes of cohesive sediment and theinteraction between current and sediment. The model was validated by relatedexperimental data. The results demonstrated that the model was capable ofreproducing the dynamics of current and cohesive sediment, which contributed to thesimulation of formation of the fluid mud.(2) The friction factor between the non-Newtonian fluid and the bed was derivedand introduced to a one-dimensional, shallow water, finite difference fluid mud modelto calculate the resistance at fluid mud-bed interface. The model was validated byexperimental data and a good agreement was achieved.(3) Based on the above models, an unstructured grid, two-layer model ofthree-dimensional hydrodynamics and two-dimensional fluid mud was developed tosimulate the formation and movement of fluid mud, taking account of the interactionbetween the fluid mud and the water column. Its capability of simulating both thedynamics of water column and the underlying fluid mud was validated by experimental data.(4) At estuarine and coastal areas, serious siltation in harbor and navigationchannel always occurred under extreme weather conditions such as Typhoon. With thecombination of two-layer model, atmosphere model, wave model and model couplingtoolkit, a three-dimensional integrated model of wind-wave-current-cohesivesediment-fluid mud was developed and applied to investigate the hydrodynamics,sediment and fluid mud transport, and channel siltation during Typhoon and storm.(5) The integrated model was applied to investigate the fluid mud movement andchannel siltation of typical muddy coast Lianyungang Harbor under differentconditions of wind and wave. It was concluded that the cohesive sediment wassuspended to a high concentration by the strong wind wave and subsequentlydeposited in the channel to form fluid mud and cause siltation.