(139c) Determining Collisional Dissipation Rate for Elongated Rods with Friction Using Homogeneous Cooling System Simulations

Authors: 
Buettner, K. E., University of Florida
Guo, Y., Zhejiang University
Curtis, J. S., UC Davis
Discrete element method (DEM) simulations of homogeneous cooling systems (HCS) are performed to study the effect of interparticle friction on the collisional dissipation rate for elongated rods. The Coulombic friction model is implemented to consider the tangential force between two contacting cylinders. In the simulations, three parameters are varied: coefficient of friction (μ), coefficient of normal restitution (e), and the particle aspect ratio (AR). The translational and rotational degrees of freedom are examined separately and it is found that there is equipartition between the translational, but not for the rotational degrees of freedom. This non-equipartition is expressed through the transition from two effective rotational degrees of freedom for smooth cylinders, to three for frictional. It is found that the collisional dissipation rate initially increases as μ increases and reaches a plateau when μ is approximately 0.3 for e = 1.0. Also, the effect of friction is gradually shadowed by normal contact damping as e decreases from unity. The total collisional dissipation rate can be decomposed into a component due to friction and a component due to normal contact damping. The model describing the energy loss due to normal contact damping for frictionless elongated rods was previously developed using a simple modification of the spherical model. In the present work, a new model for energy loss due to friction is also developed from the spherical model, in which the coefficient of normal restitution, e, is replaced using an effective value, eeff, that is a function of μ.

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