INITIATION OF SHELL MOTION ON SAND BEDS: AN EXPERIMENTAL STUDY
摘要
Experimental study on initiation of bivalve shell motion on a horizontal sand bed, under a unidirectional flow of water, is presented. Experiments were carried out in a flume with three types of bivalve shells,namely Coquina Clam, Cross-barred Chione and Ponderous Ark, to test the condition for initiation of motion. The shape parameters of bivalve shells are defined appropriately. Experiments were conducted in a flume with a horizontal bed, and the critical shear stresses were estimated using Vanoni's side-wall correction. The characteristic parameters affecting the initiation of shell motion on a horizontal bed in rough-turbulent regime identified based on the physical reasoning and dimensional analysis are the Shields parameter (nondimensional critical shear stress), nondimensional competent mean velocity,nondimensional sand roughness, nondimensional flow depth and shape parameter. Equations of Shields parameter and nondimensional competent mean velocity for the initial movement of shells on a horizontal sand bed with convex upward and downward conditions are obtained using experimental data.