A Fundamental Study on Sedimentation (Part 1)- On Critical Current Velocity to Transport Particles

Abstract

An experimental study of the critical current velocity necessary to transport particles is described in this report., The study has clarified the following points: (1) A problem of special importance with regard to the traction of sedimentary particles is the velocity distribution near the part of the particle in relation to its size., Velocity distribution on the upper part of the particle has no direct influence on the traction., (2) The critical current velocity required to start motion of a sedimentary particle can be accurately shown by the mean current velocity from the bottom to the top of this particle at the very instant motion begins., The writer named this mean velocity the "proper critical velocity"., (3) In order to learn the relation between current velocity and particle size, the "proper critical velocity" must be used, because the current velocity varies vertically., The proper critical velocity, "Vp", on a smooth flat bottom is given by the following empirical formula: Vp=kdn where k is a constant, d is the diameter of the particle, n≒1., 5 (corresponds to d≒0., 1∼0., 75mm) 1., 0 (corresponds to d≒0., 75∼3., 5mm)(4) If many particles of the same size exist on the bottom, the Vp of these particles increases owing to the friction between the particles.,