Fluid Mud Transportation Under Waves And Currents Based On Bingham-Plastic Model

In estuary and coastal areas, fluid mud is often observed. Fluid mud transport isimportant to the evolution of the estuarine and costal line and the maintenance ofwater way. Bingham-Plastic model is employed to describe the stress and strainrelation of fluid mud in this paper. The simplified equations of fluid mud motionunder waves and currents are presented by order analysis.Based on the simplified equations, the profile of the fluid mud layer wasobtained by theoretical analysis. As no waves exist, the thickness of the fluid mudlayer on the flat bottom can be larger than1m for long navigation channel. On theslope of1/500, the thickness of the fluid mud layer is less than0.2m. The flumeexperiments were carried out. The thickness of the fluid mud layer under still waterwas measured. The results of experiment agree well with the theoretical ones.The effect of waves on the fluid mud layer thickness was studied theoretically. Itis found that waves can decrease the fluid mud layer thickness greatly. Thetransportation of fluid mud under the interaction of waves and currents is alsoinvestigated by a simplified mathematical model. It is found that the fluid mudtransportation can occur even as the bed shear stress is much smaller than the yieldstress of fluid mud. The fluid mud transport rate increases with the wave amplitude,wave-length, and the bed shear stress. When the thickness of fluid mud layer is small,the fluid mud transport rate increases with the thickness of fluid mud layer. And themean velocity of fluid mud approaches a constant as the fluid mud thickness is largeenough.The experiments of fluid mud transport under currents with fluctuation watersurface were carried out in this paper. The instantaneous flow velocity field wasmeasured by the technique of particle image velocimetry (PIV) and the velocity offluid mud was measured by recording the displacement of a fluid mud sheet dyed withred color. The velocity of the fluid mud on the surface for different current velocityand bulk density of fluid mud was obtained by experiments. The data of experimentand the theoretical one have the same order.