三维粒-床碰撞过程数值模拟研究 Alternative Title Numerical Simulation of Three Dimensional Grain/bed Collision Process 张瑞 Thesis Advisor 薄天利 2014-05-28 Degree Grantor 兰州大学 Place of Conferral 兰州 Degree Name 硕士 Keyword 粒-床碰撞 混合粒径 击溅函数 侧向速度 侧向角度 DEM方法 Abstract 本论文采用DEM和软球模型相结合的方法对风沙流中三维粒-床碰撞过程开展研究。首先针对研究者所关心的二维粒-床碰撞实验及理论模拟所造成的误差问题，详细的给出了三维与二维在定性和定量上的差异。而后，给出了三维单一粒径粒-床碰撞过程的起跳特征，重点给出了反弹和溅起沙粒的侧向速度和角度，最后，重点关注了侧向冲击对三维混合粒径粒-床碰撞过程的影响，给出了击溅函数及相关起跳特征。主要工作如下： 1. 在定性和定量上比较了三维和二维的粒-床碰撞过程。研究发现，三维模拟的结果与真实情况更为接近，将粒-床碰撞过程简化成二维圆盘碰撞的理论存在问题。 2. 考虑了床面粒径、冲击速度、冲击角度、冲击粒径等因素对三维单一粒径粒-床碰撞过程的影响，得出了三维情况下的击溅函数，以及溅起速度的分布函数，并讨论了反弹和溅起沙粒的侧向速度和角度，给出了溅起侧向速度的分布。 3. 采用更接近自然沙的粒径分布形式，得到了三维混合粒径情况下的击溅函数，并研究了侧向冲击以及冲击速度、角度、粒径、旋转因素对反弹溅起沙粒的侧向速度和侧向角度的影响。发现溅起侧向速度在侧向冲击情况下不再符合高斯分布，而是偏峰分布。 Other Abstract 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 of 2D and 3D experiments and simulations of grain/bed collision process, we study the both collision cases. And we find that the results of 3D simulation are much closer to the actual situation, the theory of simplifying the grain/bed collision process to 2D 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 t... URL 查看原文 Language 中文 Document Type 学位论文 Identifier https://ir.lzu.edu.cn/handle/262010/226012 Collection 土木工程与力学学院 Recommended CitationGB/T 7714 张瑞. 三维粒-床碰撞过程数值模拟研究[D]. 兰州. 兰州大学,2014.
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