Incorporation of the effects of accelerating flow in the design of granular bed protections

For the design of granular bed protections often a stability parameter is used. The stability parameter represents the forces that are acting on the stones and is used to predict the response of the bed to these forces. Existing parameters are often derived for a limited range of application. When the parameter is used outside this range, the bed response is not predicted sufficiently accurate. Some of the existing stability parameters are derived to incorporate the effects of turbulence properly. Other researches investigated the influence of the acceleration on the stone stability and derived a parameter from that. But none of the existing stability parameters incorporate both effects together. In this thesis the complex interaction between velocities, turbulence and acceleration is incorporated into one stability parameter. The stability parameter is designed such that it incorporates the effect of turbulence correctly, incorporates the effect of advective acceleration and that can be applied to non-uniform flows. A relation between the proposed stability parameter and the dimensionless entrainment rate is derived. This is done for a wide range of flows and geometries to make the stability parameter as general as possible. There are three unknown constants in the stability parameter. One for the value of the turbulence relative to the velocity, one for value of the acceleration force relative to the quasi-steady forces, and one for the method of determining the acceleration force. These constants are determined with a correlation analysis. The constants that result in the highest correlation between the stability parameter and the dimensionless entrainment rate are chosen. The proposed stability parameter leads to a considerable higher correlation with the bed response than the existing parameters for the data sets used in this report. A power law is used to formulate a relation between the proposed stability parameter and the dimensionless entrainment rate. The
Environmental Fluid Dynamics
Hydraulic Engineering
Civil Engineering and Geosciences