Motion Law of a Sphere in Bingham Fluid with Thixotropy

The thixotropy properties and the motion law of a sphere in the Bingham fluid have been studied. Through observation of the settling motion of a single sphere in the Bingham fluid on the X-ray screen, it has been discovered that the mud in estuaries and along sea bay, and the hyperconcentrated flow all behave as the Bingham fl fluid with thixotropy properties as the large sediment concentration. Through derivation, the theoretical relationship between the yield stress and non-settling maximum sphere supported by the stress for the Bingham fluid has been developed, the equations for calculating the increasing yield stress and the non-settling maximum sphere diameter with the duration at rest of the slurry have been obtained. In consideration of the effect of thixotropy on fluid motion, the Navier-Stokes equation group for the Bingham thixotropy fluid has been developed. Through further study of the flow boundary condition of settling motion of ii single sphere in the Bingham thixotropy fluid, and the solving of the Navier-Stokes equation group, under the small Reynolds number, the theoretical equation of the drag force of the Bingham thixotropy fluid flowing around a sphere has been deduced. The theoretical relationship between drag coefficient and Reynolds number has been derived. By use of the experimental data of rheological test of various slurries measured with viscometer and those of single sphere motion observed on the X-ray screeen, the above equations have been verified. The equations are in good agreement with the experimental data for various slurries.

Evolution of a confined gravelly river to a braided-meandering river in the Late Cretaceous Khasi group,southern Shillong plateau,NE India

This paper intends to unravel the depositional condition of the Basal Conglomerate/Jadukata Formation and the Lower Mahadek Formation in southern Shillong Plateau,NE India deposited during the Late Cretaceous period.The studied succession is entirely siliciclastics in composition and was built up on the Precambrian basement rocks.State-of-art facies analysis and palaeocurrent evidence helped us to reconstruct the palaeogeography and palaeoenvironment.The facies tracts reveal that frequent hyperconcentrated mass flow deposits dominated the proximal part of the river channels.Gradually,the river evolved to a sandy braided and finally mud-dominated,meandering system.The river channel changed its pattern through onlapping and progressive elimination of the accommodation space created by the tectonic subsidence/upliftment.Major shifts in palaeocurrent direction at different stages of the river evolution confirm the role of tectonics on the river channel evolution.QFL detrital modes of the sandstones reflecting lithic wacke composition and the recycled orogeny corroborate the interpretation.Rapid lateral and vertical facies transition suggests a pull-apart type basin due to ongoing rifting.Geochemical analyses also show signatures of the overlapping tectonic conditions supporting the pull-apart basin model.

ON THE STRUCTURE AND MOVEMENT MECHANISM OF FLOW WITH HYPERCONCENTRATION OF SEDIMENT

This paper, based on the information obtained from flume experiments and field observations, concerns with the analyses of the flow with hyperconcentration of sediment containing a certain amount of fine particles. Attention is focused on the classification of flow with hyperconcentration of sediment, the properties of the Bingham shear stress τB and rigidity coefficient η, the movement mechanism of fluid within flow-core and non-flow-core regions, the shear stress distribution and so on. Several formulae have been proposed to indicate vertical velocity distribution of 2-dimensional steady and uniform turbulent flow with hyperconcentration of fluid. The formulae can be applied either to the flow of the Bingham fluid or to that of the Newtonian fluid.