Computer Simulation Of Aeolian Sand Ripples And Its Stability Analysis

On the basis of previous investigations of the sand aeolian ripples, cellular automata theory and recent studies on dynamics of two-phase wind-sand fluid flow, this paper presents some improvements and modifications on the existing numerical simulation of sand aeolian ripples, and discusses its stability as well. The main achievements are made in the following four aspects:1. According to the cellular automata theory and N-0 model and Miao-Mu-Wu model, the rules of saltation and creep in two dimensional and three dimensional cases are improved respectively and the evolution processes of sand aeolian ripples are simulated successfully. With the reasonable change of control parameters, the simulated results reproduce the actual sand aeolian ripples in nature, such as Y shape joint. The results of the modified numerical simulation are much closer to the real sand aeolian ripples in nature than those of the existing simulations.2. Based on two dimensional model, the influence of the four control parameters l₀,q,band d in numerical simulation rules is analyzed and their physical meanings are also discussed. The results show that: l₀ is in direct proportion to the wind stress force andrelevant to the friction velocity; the sand ripple length decreases with parameter b; the value of q is equivalent to the diameter of the sand grain, and controls the stability ofaeolian ripples to some extent; and with the increasing of the value of parameter d, the boundary effect diminishes gradually.3. In the perspective of fluid mechanics, an analytical solution of sand aeolian ripples is obtained and the geometric characteristics of sand aeolian ripples are described by discussing approximate solutions to Stokes wave equation under different conditions. When Stokes wave is in its limit situation, its shape is in accordance with the surface stability of the grass checkboard. The conclusions provide theoretical background for the practical projects.4. Corresponding to the stability theory of incompressible fluid flow, the stability of the sand aeolian ripples is analyzed. By discussing the stability of the two-dimensional and three-dimensional models before and after the improvement, the critical value and/or the stability criterion are obtained. This will provide some theoretical background for further research work.