Numerical Simulation Of Turbidity Currents Based On FLOW3D

Turbidity currents is an important carrier to transport the continental sediment to the deep-sea.It's also an important research object of sediment "source to sink".Due to the lack of turbidity current actual observation data,the understanding of flow characteristics and sedimentary characteristics of turbidity current also is still not well understood,laboratory scale turbidity current research takes cost,and also has certain limitations.So by means of numerical simulation of turbidity current theory research has important scientific significance and economic value.In this study,CFD(Computational Fluid Dynamics)software FLOW3 D was used to explore the flow characteristics and deposition characteristics of turbidity flow under different particle sizes,slopes and inflow mechanisms(sudden-release flow,sustained-inflow).The model results of turbidity currents and deposition under different particle sizes show that particle sizes and contents have important influences on the morphological evolution and sedimentary characteristics of sudden-release turbidity currents.In terms of dynamics,due to the different settling velocity of sediment particles,the change of mixing particle size will greatly affect the hydrodynamic characteristics of turbidity flow.In terms of deposition,with the increase of time,the total mass of sediments in the bottom bed increases,and the sediments near the release of turbidity current accumulate the most,and the sediment mass decreases gradually with the increase of distance,until all the sediments are deposited,the sediment quality will not change any more.Due to the different proportion of coarse and fine particles in turbidity currents,the final position of the complete deposition of the turbidity current will also be different.At the early stage of turbidity current release,the elevation of the topography will be carried forward by the entrapment of the turbidity current with a large velocity at the head of the turbidity current,and the sediment that should have been deposited at this position will form "?" type on the terrain,and the coarser particles,the more obvious this phenomenon is,which has an important impact on the topography shaping.The model results of turbidity currents and deposition under different slope conditions show that,in terms of dynamics,there is a positive correlation between the experimental gradient and the maximum velocity of turbidity current.The turbidity current with higher velocity decays faster in the subsequent motion when it reaches the flat slope.In terms of sedimentation,the change trend of the elevation of the flat slope after the turbidity currents of the three slopes flows through is consistent,and the elevation of the topography gradually decreases with the increase of the distance.At the slope break,the sediment amount with a small slope is more.The model results of turbidity currents and deposition under different inflow mechanisms(sudden-release flow,sustained-inflow)show that,in terms of dynamics,the advance distance of sudden-release turbidity currents at the same time is always greater than that of sustained-inflow turbidity currents.The maximum density of sustainedinflow turbidity currents is concentrated not far from the entrance and presents a stable and uniform state on the slope.The maximum of the bottom shear velocity of the suddenrelease turbidity currents appears in the front of head,while the maximum of the bottom shear velocity of the sustained-inflow turbidity currents appears not far from the entrance.In terms of deposition,both of them are consistent in the change trend of horizontal topographic elevation.As the distance increases,the topographic elevation gradually decreases.Finally,the sudden-release turbidity currents deposition distance is longer than the sustained-inflow turbidity currents deposition distance.