EFFECT OF BED SURFACE-STRUCTURE ON SPHERICAL-PARTICLE STABILITY

This paper describes the effect of bed surface structure on the rolling stability of a cohesionless spherical particle. The bed surface structure was investigated in terms of the vertical and horizontal orientation. The former is defined by the relative protrusion, whereas the latter is defined by the angle of attack of the undisturbed approach flow. Experiments showed that both these parameters have an important influence on rolling particle stability. The study also presents a theoretical analysis based on the balance of driving and resisting moments about a pivot point. Comparisons between the experimental data and theoretical results show that the pivotal analysis is inadequate to fully describe the mechanism of sediment entrainment, especially at low relative protrusions. The tendency for a particle to saltate in relatively high flows reduces the effect of the angle of attack or the pivotal position on the threshold of sediment motion.