Masashige Yamasaka

Three-dimensional fully developed shallow-water flow in mildly curved bends

A mathematical model which describes three-dimensional fully developed flow in mildly curved open channel is developed. The side-wall boundary layers are included in the analysis, and the normal component of the secondary current is constrained to be zero at the side walls. It is found that the advective transport of fluid momentum due to the secondary current induces accumulation of primary-flow (streamwise) fluid momentum near the outer bank. The analysis makes it possible to analyze the curvature-induced excess of shear stress at the outer bank. The model is well supported by available laboratory data.

Fall velocity of single spheres in vertically oscillating fluids

The settling or rising velocity of a single spherical particle in a vertically oscillating fluid is analysed in terms of the nonlinear perturbation technique. It is demonstrated that the retardation of the particle in an oscillating fluid is caused essentially by the nonlinear nature of the drag force, and the retardation is found to be governed by three independent variables, the Reynolds number of the settling sphere in still fluid, the dimensionless velocity amplitude of the fluid oscillation and the dimensionless frequency of fluid oscillation. It is shown that the existing theories are special cases of the present analysis. The model is tested with Hos data which cover wide ranges of the three independent parameters, and it supports the current theory.