Experimental and numerical study on energy dissipation in freely cooling granular gases under microgravity

Energy dissipation is one of the most important properties of granular gas, which makes Its behavior dltterent trom that of molecular gas. In this work we report our investigations on the freely-cooling evolution of granular gas under microgravity in a drop tower experiment, and also conduct the molecular dynamics （MD） simulation for comparison. While our experimental and simulation results support Haff＇s law that the kinetic energy dissipates with time t as E（t） （1 ＋ t/v） 2, we modify ~＂ by taking into account the friction dissipation during collisions, and study the effects of number density and particle size on the collision frequency. From the standard deviation of the measured velocity distributions we also verify the energy dissipation law, which is in agreement with Haff＇s kinetic energy dissipation.

Parametric study of the clustering transition in vibration driven granular gas system

A parametric study of the clustering transition of a vibration-driven granular gas system is performed by simulation.The parameters studied include the global volume fraction of the system,the size of the system,the friction coefficient,and the restitution coefficient among particles and among particle-walls.The periodic boundary and fixed boundary of sidewalls are also checked in the simulation.The simulation results provide us the necessary“heating”time for the system to reach steady state,and the friction term needed to be included in the“cooling”time.A gas-cluster phase diagram obtained through Kolmogorov-Smirnov(K-S)test analysis using similar experimental parameters is given.The influence of the parameters to the transition is then investigated in simulations.This simulation investigation helps us gain understanding which otherwise cannot be obtained by experiment alone,and makes suggestions on the determination of parameters to be chosen in experiments.

DEM simulation of granular segregation in two-compartment system under zero gravity

In this paper,granular segregation in a two-compartment cell in zero gravity is studied numerically by DEM simulation.In the simulation using a virtual window method we find a non-monotonic flux,a function which governs the segregation.A parameter is used to quantify the segregation.The effect of three parameters：the total number of particles N,the excitation strength F,and the position of the window coupling the two compartments,on the segregation and the waiting time%are investigated.It is found that the segregation observed in zero gravity exists and does not depend on the excitation strength F.The waiting time T,however,depends strongly on F：the higher the F,the lower the waiting time V,The simulation results are important in guiding the SJ-10 satellite microgravity experiments.

A Quadrature-Based Kinetic Model for Dilute Non-Isothermal Granular Flows

A moment method with closures based on Gaussian quadrature formulas is proposed to solve the Boltzmann kinetic equation with a hard-sphere collision kernel for mono-dispersed particles.Different orders of accuracy in terms of the moments of the velocity distribution function are considered,accounting for moments up to seventh order.Quadrature-based closures for four different models for inelastic collisionthe Bhatnagar-Gross-Krook,ES-BGK,the Maxwell model for hard-sphere collisions,and the full Boltzmann hard-sphere collision integral-are derived and compared.The approach is validated studying a dilute non-isothermal granular flow of inelastic particles between two stationary Maxwellian walls.Results obtained from the kinetic models are compared with the predictions of molecular dynamics(MD)simulations of a nearly equivalent system with finite-size particles.The influence of the number of quadrature nodes used to approximate the velocity distribution function on the accuracy of the predictions is assessed.Results for constitutive quantities such as the stress tensor and the heat flux are provided,and show the capability of the quadrature-based approach to predict them in agreement with the MD simulations under dilute conditions.