Author(s): Yarko Nino; Alonso Atala
Linked Author(s): Yarko Niño
Keywords: No Keywords
Abstract: A discrete two-dimensional model based on simple rules to simulate the motion of individual particles over a bed formed by similar particles is used to study the emergence and evolution of wind ripples. The rules for particle motion consider both the process of particle saltation and particle creeping, and assume that the bed is formed by identical spheres. Results of the simulation show that the basic instability mechanism of the initially flat bed is related to the low probability of a grain located immediately downstream from a high point of the bed to be removed by the collision with a saltating particle. The simulated ripples emerge naturally from the flat bed and evolve in time by increasing their height and wavelength. It is found that the ripple celerity decreases with ripple height, such that a wave coalescence process, in which faster, smaller ripples merge with slower, larger ripples, provide the mechanism for ripple growth. An exponentially decreasing growth rate is found for the ripples, which implies that equilibrium is reached asymptotically. Although the wavelength to height ratio of the simulated ripples tend to be much lower than observed values in nature, and also the longitudinal profiles of the simulated ripples tend to be much more triangular in shape than real ones, the richness of the strongly non-linear processes that this simple model is able to simulate makes this type of approach worth of being pursued further.
Year: 1997