China
Africa
Explore chapters and articles related to this topic
Fundamentals of Plasma
Published in Eiichi Kondoh, Micro- and Nanofabrication for Beginners, 2021
When two particles collide, the momentum must be conserved along the directions of the action of force. On the other hand, the kinetic energy is not always conserved. The collision that satisfies the conservation of energy is called elastic collision, and the collision that does not satisfy the conservation law is called inelastic collision. The energy lost during an inelastic collision transfers to the colliding particles. This energy is spent for ionization or other activation processes. The term collision here can be imaged as a usual impact motion of rigid bodies, whereas, in fact, it is the interaction that occurs when two bodies move very close together.
Engineering Mechanics
Published in P.K. Jayasree, K Balan, V Rani, Practical Civil Engineering, 2021
P.K. Jayasree, K Balan, V Rani
The line of impact of the two colliding bodies is the line joining the centers of these bodies and passes through the point of contact or point of collision. Before the impact, if the two bodies are moving along the line of impact, the collision is called as direct impact. Now consider the two bodies A and B having a direct impact as shown in Figure 4.49b. Let m1 = mass of the first body, u1 = initial velocity of the first body, v1 = final velocity of the first body, and m2, u2, v2 = corresponding values for the second body. According to the law of conservation of momentum, m1u1+m2u2=m1v1+m2v2
Inverse grading in granular flows
Published in G.N. Pande, S. Pietruszczak, H.F. Schweiger, Numerical Models in Geomechanics, 2020
M. A. Kern, W. J. Ammann, L. Vulliet
The model of granular flow presented here is a 3D extension of a 2D “hard disc model” of a granular flow of discs with bimodal size distribution , see (Nakagawa & Imaizumi 1992) or (Herrmann & Luding 1998). A box with length lx, width ly and infinite height contains spherical particles with a random radius distribution ri ∈ [rmin,rmax]. The particles can move freely subject only to gravitation until they collide with another particle or with the bottom of the box (see Fig. 1). The box is inclined by an angle ψ with respect to the horizontal and its bottom is “roughened” by a periodic function. Furthermore, the box has periodic boundary conditions in the sense that particles leaving the box through a wall enter the box through the opposite wall again. Particles in the vicinity of a wall can also interact with particles in the vicinity of the opposite wall. The individual particles’ mechanical properties are described by the longitudinal and transversal restitution coefficients e and b representing the inelastic behaviour of one single particle under collision and by the transversal Coulomb friction coefficient μ. The coefficient of restitution is defined as the ratio of longitudinal or tangential relative velocity after and before the collision of two particles. The interaction between the particles happens by instantaneous, binary collisions. This means that the interaction of two particles by exchange of momentum and spin is supposed to take place at one distinct time point.
Exploring the effects of gravel shapes on vibration compaction behaviours of coarse-grained mixtures via DEM simulations
Published in International Journal of Pavement Engineering, 2023
Rengui Lai, Feng Xu, Qun Qi, Zhihong Nie
The restitution coefficient is defined as the ratio between the separation velocities of two objects after the collision and the approaching velocities of two objects before the collision. Given the difficulty of measuring the instantaneous velocities before and after the collision, the restitution coefficient can be expressed by the initial height and maximum rebound height of particles, provided that the potential energy and kinetic energy of the collided particles can be completely converted. To ensure that the instantaneous kinetic energy after the collision is fully converted into the potential energy at the maximum rebound height (Combarros et al., 2014, Qi et al., 2023a), spherical particles were used to calibrate the restitution coefficients.
Experimental study on the rebound characteristics of oblique collision of ash particles and the influence of ammonium bisulfate
Published in Aerosol Science and Technology, 2022
Shihao Hu, Qi Yin, Yize Zhang, Kefa Cen, Hao Zhou
The process of ash particles depositing on the heat exchange surface can be simplified to the rebound process of the ash particles colliding with the target surface. When the particle is in contact with the impact plane, the forces on the particle include friction, thermophoresis, and surface forces. The surface forces are caused by adhesion and the van der Waals force (Abd-Elhady and Malayeri 2013). In collision dynamics, the restitution coefficient is a common parameter that reflects the energy consumption during impact. The definition of restitution coefficient e is the percentage of rebound velocity to incident velocity (Zhou et al. 2016): where and are the impact and rebound velocities of ash particles, respectively, is the kinetic energy of the incident particles (angular momentum is ignored), and is the energy dissipation during impact. According to Liu, Li, and Yao (2011), energy dissipation can be divided into two parts, first-contact energy loss and energy dissipation through damping effects (friction and adhesion) or plastic deformation. The first-contact energy loss is independent of the impact velocity. The energy loss caused by plastic deformation and damping effects is closely related to the impact velocity. When the collision is a perfect elastic collision, the coefficient of restitution is 1. When the ash particle dissipates all the kinetic energy and attaches to the target surface, the coefficient of restitution is 0.