Author(s): Xin Chen; Xiping Yu
Linked Author(s):
Keywords: Erosion depth; Oscillatory sheet flow; Sediment transport; Sheet flow layer thickness; Two-phase model
Abstract: Erosion depth and sheet flow layer thickness are two important parameters that characterize the thickness of mobile bed under sheet flow conditions. Both instantaneous and maximum values of the two parameters are studied by comparing experimental data and empirical models. The experimental data are collected from cases falling into the sheet flow regime covering a wide range of oscillatory flow conditions with and without net current, and surface gravity waves. The sediment diameters are 0. 13mm~1. 6mm with conventional density of 2650kg/m3, while wave periods are 3. 8s~9. 1s and maximum free stream velocity are 0. 44m/s~2. 2m/s. Typical empirical formulas based on Shields parameters are compared with each other, which include the typical homogeneous and nonhomogeneous relations derived from the bedload transport theory, and the nonlinear relations derived from the suspendedload transport theory. Effects of unsteadiness, sediment diameters and mass conservation, which play important roles but are usually not considered in the two parameters, are also included in some formulas and discussed. Two-phase model is also applied for further evaluation of empirical models’ accuracy. With much higher accuracy than typical bedload empirical formulas, the new prediction based on suspendedload transport theory is also simple and easy to be used for mobile bed thickness under sheet flow conditions in coastal engineering.
Year: 2013