Research On Dynamic Fine Macro Mechanism Of Overloading Of Silo Wall By Grain Unloading

China will plan and implement the grain storage construction of 50 million tons,which requires the expansion of a large number of grain silos.However,the overpressure calculation theory of silos is not perfect and there is a lack of quantitative description of particle mechanical behavior at the micro level,which leads to frequent silo accidents.Previous studies mainly focused on the calculation of lateral pressure of silo wall during grain unloading and arch formation,but the overpressure problem of silo wall did not refine the process of grain unloading,and the study of its microscopic evolutionary mechanism was not well done.At the same time,the calculation of overpressure coefficient of silo wall during grain unloading and arch formation is single and fuzzy,and there is no detailed and in-depth study on the dynamic mechanical process of secondary overpressure,so the dynamic mechanical mechanism of overpressure during grain unloading and arch formation cannot be better reflected.This paper conducts an in-depth study on the fine macro mechanism of silo wall overpressure based on the national natural science foundation of China(51708182)project "research on silo grain arch formation and its dynamic evolution mechanism on silo wall overpressure" and the basic research project of henan provincial department of education(16B560002)"research on the mechanism of silo grain arch formation and collapse under multi-factor coupling effect".The author uses physical model and discrete element software to simulate the process of unloading grain into arch,detailed analyzes the dynamic changes of the warehouse wall overpressure process and unloading grain into a fine under the arch of the macro dynamic mechanics,the silo discharging mouth size or unloading speed the influence of the lateral pressure coefficient of overpressure on the silo wall,eventually correction coefficient of the warehouse wall overpressure K calculation formula.The main work consists of the following parts:(1)we set high precision pressure sensor in the silo model,through dynamic strain gauge two phases of the process of unloading grain into arch warehouse wall stress monitoring analysis,refinement of unloading grain into arch pressure data,draw the conclusion: the unloading grains into arch is closely related to the silo discharging mouth size,test the most easy to form arch of silo discharging mouth size is 100 mm,the arching number23 times.In this part,a discrete element model is established based on the scale reduction of the physical model to quantitatively analyze the lateral pressure data in two stages of the overpressure process.It is concluded that: compared with the mean value,the lateral pressure data at each point of different outlet sizes in the conventional overpressure stage have little change,and the error range is basically kept within 10%.In the stage of arch overpressure,the maximum error is up to 200%.(2)This part of the refinement of the overpressure formation process,it is divided into two stages and introduce the conventional overpressure coefficient(C1)and into the concept of overpressure coefficient(C2),contrast analysis of the test and simulation of the lateral pressure data,draw the conclusion: conventional overpressure stage,50 mm,75 mm and 100 mm of discharging mouth size model of conventional overpressure coefficient(C1),fluctuations in the value of 1 is only remain the same.In the arch overpressure stage,the maximum arch overpressure coefficient(C2)of 50 mm,75mm and 100 mm outlet is 3.35 times,2.35 times and 2.17 times of the overpressure coefficient(C1)in the conventional stage.According to the preliminary judgment,the unloading speed has little influence on the conventional overpressure coefficient(C1)and a great influence on the overpressure coefficient(C2)in the arch forming stage.This part more mesoscopic analysis into the arch during starting and completion of food particles between the chain,the distribution of velocity field,the arch when the change of porosity,the shear displacement and shear force and other factors,the discharge rate on the influence of overpressure process,two conclusions:conventional overpressure stage,food overpressure formed particles,leading to the faulting and constantly in the process of discharging increases gradually in the direction of the drag along the grain flow,discharge outlet near the upper chain comparatively more strong,more stress,mainly related to the friction between particles at this time of change,has nothing to do with the particle flow speed.In the process of arch overpressure formation,the sharp decrease of grain unloading speed leads to the rapid increase of stress in the force chain,the increase of cohesion between particles,and the sharp decrease of porosity,which is reflected in the increase of the arch overpressure coefficient(C2).In the microscopic aspect,it is further explained that the influence of discharging speed is the overpressure coefficient of archformation(C2).(3)Based on the insufficient formula for calculating the overpressure coefficient K found in the research process,the article regards grain particles as ideal elastomers and modifies the formula for calculating the overpressure coefficient K of the wall of the silo discharged into the vault.This article using the physical model test for unloading grain into arch two overpressure process parameters,control discrete element simulation and experimental results,it detailed the silo unloading grain into a fine under the arch of the macro dynamic mechanics mechanism,study the discharge rate on the silo wall lateral pressure coefficient of overpressure,the influence of the final correction calculation formula of the warehouse wall overpressure coefficient K,the results can help prevent silo unloading grain intooverpressure accident provide certain basis.