Cyclical pulsation properties of particles in cone silo

Abstract

Intense particle pulsation during discharging may lead to the vibration of silo, even the failure of silo structure. To date, the studies related to particle pulsation have mainly concentrated in the following aspects: the noise caused by vibration of silo, the minimum decisive height to produce silo music and the factors affecting particle pulsation. However, the above studies cannot in depth analyze the motion state nor the flow law of all particles in silo. To explore the pulsation characteristics of particles, in this paper we simulate the discharging tests of ellipsoidal particles in deep silo with different half-cone angles based on the discrete element method, in order to reveal the mechanisms of particle pulsation and variation of contact force among the particles in the silo. In each simulation discharging test, the cylinder section of silo is divided into 4 fixed areas where flow behavior and the motion characteristics of particles are analyzed. The simulation results show that the velocity fluctuation of particles exists in the whole discharging process. At the early stage of discharging, the cyclical pulsation with large amplitude appears while irregular fluctuation with small amplitude occurs in the later stages. The study also finds that the dynamic characteristics of the axial force among particles are the same as those of velocity pulsation in the corresponding areas. Besides, the amplitude of particle pulsation shows an increase trend and the contact force of particles presents more periodic pulsation along the negative direction of outlet. The pulsation characteristics(velocity pulsation and force pulsation) of adjacent particle layers are similar, including similar waveform and identical cycle. During the intense pulsation stage, each minimum of the axial force of particles in the top layer is close to the gravity, indicating that the contact force among these particles disappears. Furthermore, the periodic pulsation of particles causes the contact force among particles to periodically disappear. It is noted that the stability of discharging, frequency, amplitude and duration of the intense pulsation increase with the decrease of the half-cone angle. In order to evaluate the fluctuation degree of the velocity pulsation, the standard deviation of particle velocities is used. Note that the particle velocities are no longer subjected to the influence of rising trend, which result is obtained by the finite difference method. The results show that the standard deviation gradually increases with the decrease of half-cone angle. This is because the increase of half-cone angle causes the time and amplitude of stable fluctuation to decrease. This numerical study of particle pulsation will provide the reference for safety design of discharging devices.