圆锥料仓内颗粒周期性脉动特征研究

料仓卸料过程中的颗粒脉动会引起料仓振动甚至导致结构失效.为了明晰颗粒脉动特征,本文进行了椭球颗粒在不同半锥角深仓的模拟卸料实验,将料仓圆筒部划分为4个固定区域以研究区域内颗粒的运动信息,分析了料仓圆筒部颗粒系统的运动特征.研究结果表明:整个卸料过程颗粒速度始终处于波动变化中,卸料前期表现为大振幅、周期性的剧烈脉动,卸料后期平均速度的变化则是小振幅无规律的波动;剧烈脉动时段各区域的颗粒层平均受力的变化规律与颗粒速度脉动特征相似,越接近储料顶端颗粒脉动振幅越大,表现出更规律的周期性脉动,相邻颗粒层间的脉动波形相似且周期相同,剧烈脉动过程中顶面颗粒呈周期性的自由落体运动,该时段内顶层颗粒每一次的自由落体运动都会引起该范围内颗粒间接触力消失;料仓半锥角越小时剧烈脉动频率越高、振幅越大且脉动持续时间也越长,卸料速度越稳定,且颗粒速度不会出现带有上升趋势的波动.研究结果可为卸料设备的安全设计提供参考.

Cyclical pulsation properties of particles in cone silo

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.