DEM study to determine the relationship between particle velocity fluctuations and contact force disappearance

Abstract

Particle pulsation, which includes velocity and force fluctuations, has already widely existed during the discharge from a silo or hopper. To clarify the characteristics of particle pulsation, in this work, discharge from a 3D conical silo was simulated using the platform with the discrete element method (DEM). The velocity and total force fluctuations were quantitatively analyzed during the initial duration of the discharge and the relationship between velocity fluctuation and contact force disappearance was investigated. Furthermore, the effects of hopper half angle and static friction coefficient (between particle and wall) on velocity fluctuation and contact force disappearance were discussed. The results indicate that both the velocity and total force fluctuations can be divided into three stages and there is a one-to-one corresponding relationship in the violent fluctuation stage. The crest time of velocity fluctuation is the same as the time of contact force disappearance (i.e., particle motion is freely falling body) which only occurs in the violent fluctuation stage. Compared to the larger hopper half angle, the velocity fluctuation exhibits a larger amplitude and higher frequency and the contact force disappearance frequently occurs at the smaller hopper half angle. The velocity fluctuation presents an irregular small amplitude, with no occurrences of contact force disappearance below the critical value of the static friction coefficient, while the velocity fluctuation shows a regular large amplitude, with occurrences of contact force disappearance beyond the critical value. The results are useful for understanding the dynamic behavior of a rice particle during discharge from the conical silo.