Study On The Arch Test And Simulation Of Silo Unloading

As the leaders of grain warehousing in China at present,silos stand out for a wealth of advantages of small flour area,good airtight condition,convenient mechanized and automatic operation,low circulation and construction cost,etc.At present,most of the silos still adopt gravity dependent discharge method,while the problem is that arching effect always works,which restrains the food from discharging by itself and brings difficulties to the processing and transit.More seriously,the arching will arouse a sharp increase in the pressure exerted on the silo wall,and that will be a threat to the warehouse itself and the facilities in it,as well as the safety of the food staff.Therefore,enough attention must be paid to the arching problem in the silos.This topic is based on the national natural fund's project(51708182)“Study on the dynamic evolution mechanism of silo unloading and overpressure of silo wall” and a basic research project in Henan province department of education “Study on the mechanism of grain arching and subsidence in granaries under multi-factor coupling(16 b560002)".Selecting wheat as the main grain variety,I studied the physical parameters related to food arching and the main influence factors based on indoor experimental research,and the mechanism of silo's unloading grain arching via PFC numerical simulation,theoretical calculation and mechanical analysis of silo's unloading grain arching mechanics mechanism.The main research contents and conclusions cover the following several aspects:(1)For the quantitative analysis of the main factors that influence the food into the arch,the three different arc plate static arching tests were carried out.Combined with relevant food regulations and direct shear test,the conclusions are: A.The increase of physical properties such as moisture content and impurities lead to the increase of the Angle of internal friction of wheat,which further increases the arching chance.B.With the augment of the grain loading height,the density of the wheat granule in the cambered region increased,and it is more liable for the loading height of 80 cm to form arches than that of the 30 cm.C.The most cambered wheat grain moisture content range is 13% ~ 15%,impurity rate 0.7% ~ 0.8%,the scope of internal friction Angle 30 ° ~ 36 °,and the friction coefficient range between the wheat grain and the silo wall is 0.44 ~ 0.46.(2)For the study of the pressure exerted by food arching,three different static arc plate stress was tested on stress on the wall of granaries,the maximum of warehouse wall's stress all occurred at the measuring point depth of 0.8 m,the minimum value appears at the strain gauge installation location of 0.1 m.The maximum differential pressure in the three cases was 1.68 times and the minimum 1.29 times.PFC software was used to simulate the distribution of bulk material in the wall pressure distribution when grain unload into arch,and the simulation results showed that the Angle of bottom funnel has less influence on the pressure distribution.The comparison with the calculation results of Janssen formula reveals that the pressure distribution of the three is basically in line with the variation within the error range.(3)Based on the indoor test,I've used PFC bulk particle simulation software to simulate the dynamic process of the grain's unloading into arch.The intergranular force chain diagram and the velocity distribution diagram display the shift of the discharging process of instantaneous arch.When the grain form into arch completely,the height of unloading grain of models with bottom funnel angel of 55 °,45 °,and 65 °accounted for(not calculate funnel)third,1/5,1/10 of warehouse capacity respectively,the corresponding zero pressure areas are 0 to 0.1 m,0-0.2 m,and 0-0.3 m.Simulation results show that the loading will pass the force arch to arch foot through the particles,and thus the arch foot has bigger pressure,with overpressure radio between 1.796 and 3.458,the value 3.458 appearing on the right side of the warehouse wall of the model with the bottom funnel angle of 65° and the value 1.796 appearing on the left side with the angle of 55°.(4)I derived the dynamic distribution equation of the horizontal pressure of the arch wall via the systematic analysis of the equation of dynamic mechanical mechanism of arch based on the arch face,which shows: the horizontal force is in direct proportion to ? the distribution pressure in the whole flow area of the loading and the radius of silos,inversely proportional to the friction coefficient between the storage and wall,and negatively correlated to ? the angle of internal friction between the granules.Thereinto,the silo's vector height of arching is in direct proportion to the radius of the silos and positively related to the external friction angle.