Macro And Micro Mechanism Simulation Of Silo Discharge Based On Multi-sphere Combined Particle Model

Silos are widely used for filling and discharging bulk materials in many industries.grain particle is a typical bulk material,the macro-micro bridge of grain particles are established by the mean of discrete element numerical simulation,and the meso-dynamic characteristics of grain particle in silo are studied,it is the main method to quantitatively study the grain particle flow characteristics in silos.However,the simplified model of single round grain can not accurately reflect the irregular shape of grain,and it is difficult to simulate the macro-micro dynamic mechanism of grain in silo unloading process.Therefore,it is of great theoretical and practical significance to establish a discrete element model which is more consistent with the real shape of grain.Based on the National Natural Fund Project(51708182)"research on the dynamic evolution mechanism of grain arching during discharge and its overpressure effect on the silo wall",a multi-sphere combined particle model was established by using the discrete element software,and the physical model tests of silo discharge were carried out in the laboratory,the accuracy of the simulation model is verified,and based on the model,the flow characteristics and arch collapse of silo during grain unloading process are studied in detail.The main findings and conclusions are as follows:1.In this paper,the simulation silo model is established by using EDEM discrete element software,and the wheat grain is fitted by multi-ball combined grain model.The particle contact detection Algorithm and the calculation of 3D grain contact force are described in detail,the unique mode of contact force calculation of multi-sphere particles,and the update mode of particle mechanics behavior and movement characteristics based on Newton's second law.2.The grain discharge tests were carried out in laboratory,and the grain discharge rate,flow pattern and porosity were monitored.The simulation results were compared with the experimental results to verify the rationality and simulation accuracy of the multi-sphere combined particle model.The results show that the multi-sphere combined particle model can reveal the macro-and micro-mechanical mechanism of grain discharge process objectively and accurately,and which can provide a new research means for further revealing themacro-and meso-characteristics of grain unloading in silos.3.Based on the multi-sphere combined particle model,the spatial distribution and evolution mechanism of the flow characteristics are analyzed from two aspects of velocity and angular velocity by slice observation and data processing of simulation silo.It is proved that the flow characteristic parameters are greatly affected by the flow pattern and the wall shear boundary,and the flow characteristic parameters are important representations of the flow pattern partition.4.Based on the multi-sphere composite particle model,the mechanical behavior of granular materials during discharge is studied from the meso-scale by selecting three moments of “before stable arching”“stable arching” and “arch collapse”.The paper not only confirmed the existence of the arching effect during discharge,but also carried out a comprehensive quantitative study on the evolution mechanism of grain force in the process of silo arching.In this paper,combined with the latest research results of granular mechanics in recent years,a multi-sphere combined particle model is established for grain with irregular shape,which provides a new analytical model for grain discrete element simulation.The model is used to study the evolution mechanism of grain flow characteristics and the arching stress evolution mechanism of grain discharge.