Numerical Simulation Of Three Dimensional Grain/Bed Collision Process

As the basis for understanding the macro wind-blown sand, grain/bed collision process is one of the key topics in physics research. Combined with DEM and soft-model approach, this thesis focuses on the significant three dimensional grain/bed collision process in the wind-blown sand. First, aiming at the problems concerned by researchers that the errors caused by the two-dimensional grain/bed collision experiments and simulations are indistinct, we compare the results of three-dimensional and two-dimensional collision cases, and detailedly obtain the difference in qualitative and quantitative. Secondly, three-dimensional mono-sized grain/bed collision process is studied, and the main points are the lateral velocities and angles of rebound and ejection grains. Finally, we extent to three-dimensional mixed-sized grain/bed collision process, and focus on the effect of the lateral impact, and we obtain the splash function and the lift-off characteristics. The main works are as follows:1. Considering that most researchers don’t know the differences of2D and3D experiments and simulations of grain/bed collision process, we study the both collision cases. And we find that the results of3D simulation are much closer to the actual situation, the theory of simplifying the grain/bed collision process to2D collisions has defects. It’s significant to carry out grain/bed collision research in three-dimensional space. These make a full preparation for the next research.2. The effect of the size of the grain bed, impact velocity, impact angle and impact size on the three-dimensional mono-sized grain/bed collision process are discussed. We obtain the splash function of this situation, and the probability distribution function (PDF) of ejection velocity. Besides, we discuss the lateral velocities and angles of rebound and ejection grains, and the PDF of the lateral ejection velocity is obtained. Relatively comprehensive lateral information of three-dimensional mono-sized grain/bed collision is given.3. Based on the three-dimensional mono-sized research, we adopt the distribution of natural sand grains to study the three dimensional mixed-sized grain/bed collision process. The splash function of three dimensional mixed-sized grain/bed collision is obtained, and we argue the variation of lateral velocity and angle of rebound and ejection grains with lateral impact angle, impact velocity, impact angle, impact size and angular velocity. The results demonstrate that the mean lateral rebound and ejection angle increase with the lateral impact angle, and in lateral impact cases, the probability distributions of the lateral ejection velocity are single-peaked and skewed, rather than a symmetrical Gaussian distribution function.