Study On Rolling Friction Effect Under Typical Grain Particles And Evolution Mechanism Of Grain Unloading Velocity Field

As an important structure,silo is widely used in the filling and discharging of bulk materials in agriculture and industry.As a typical granular particle,the friction characteristics of grain are much more complicated than those between engineering materials or solids.In particular,the irregularity of grain particle has a great influence on the friction characteristics during the dynamic process of silo unloading.The friction characteristics of granules can directly or indirectly affect the flow state of granules,thereby affecting the safety of grain storage and unloading.Therefore,it is of great practical and theoretical significance to systematically study the frictional coupling effect of different typical grain particles in the unloading state for studying the meso-dynamic mechanism of grain particles.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",the rolling friction coupling effect of three typical grain particles(soybean,wheat and corn)in silo unloading process was studied in this paper.Using laboratory physical model test and discrete element simulation,the effects of the friction characteristics of grain particles on the evolution of grain velocity field in the unloading process were systematically investigated.The main contents and conclusions are as follows:(1)In this paper,the rolling friction coefficients of soybean,wheat and corn grains were measured by the inclined tripod method,and the rolling friction coefficients among grain grains and between grain grains and silo materials were measured respectively,which provided the data evolution basis for simulating dynamic grain unloading.At the same time,the laboratory grain unloading test was carried out to monitor the flow state of grain unloading and the rate of discharge port,which provided the experimental verification basis for the establishment of the simulation model.(2)The soybean,wheat and corn granules were fitted by the multi-sphere combined particle model in the discrete element software,and the silo unloading simulation scene was established.The simulation results were compared with the test results to verify the rationality and accuracy of silo grain unloading simulation.It is proved that the grain unloading simulation based on the multi-sphere combined particle model can objectively and accurately reveal the macro and micro mechanical mechanism in the grain unloading process of silo,which provides a new research method for revealing the macro and micro dynamic characteristics of grain unloading in silo.(3)Based on three typical grain multi-sphere composite particle models,mesh division and data processing of silos under discrete element simulation were carried out.The spatial distribution and evolution mechanism of velocity field were quantitatively analyzed from three aspects of vertical velocity,horizontal velocity and angular velocity,and the influence mechanism of internal and external rolling friction on grain flow of soybean,wheat and corn grains in silo unloading process was clarified.(4)By comparing the velocity field evolution of three kinds of grain in the unloading process under the effect of internal and external rolling friction,the similarities and differences of the evolution law of velocity field based on grain particles with typical shape were explored,and the influence mechanism of internal and external rolling friction on the velocity field of different grain seeds was also explored.In this paper,based on the latest research results of granular mechanics in recent years,a multi-sphere composite particle model was established for three typical grain particles of soybean,wheat and corn,and the unloading conditions were simulated respectively.The influence mechanism of internal and external rolling friction on the evolution of grain velocity field under different grain shapes was explored,and the shape effect and rolling friction effect of grain grains were related.The research results have important reference value for silo safety design and research and development.