Analysis of nonphysical attraction force and new coefficient of restitution based on a nonlinear viscoelastic contact model in cohesionless granular system

This investigation implements systematical research on the coefficient of restitution (CoR) and nonphysical attraction force. Firstly, a characteristic length is redefined based on energy conservation. On this basis, a new general CoR model is derived through characteristic length. Subsequently, a new constraint equation of the power exponents is proposed from the new CoR model. The new CoR model is validated by experimental data regardless of whether the initial impact velocity is very low or high speed. Secondly, we systematically analyze the real reason for the nonphysical attraction force in the viscous damping loop. The simulation shows the nonphysical attraction force cannot be removed from the viscous damping loop. The real reason for the nonphysical attraction force lies in the natural property of the viscous damping factor. Finally, to eliminate the effect of the attraction force on the motion status of colliding particles after impact, a balance coefficient is introduced to compensate for the deficiency of nonphysical attraction force and original damping factor. The simulation proves that the post-impact velocity of colliding particles can be precisely captured using a viscous contact force model with a balance coefficient.