Experimental And Simulation Study Of Silo Unloading Flow State And Side Pressure

During the unloading process of the silo,the pressure of the silo wall will also show different changing rules when the flow pattern of the unloading changes.To this end,this paper uses a combination of physical model test and discrete element numerical simulation to study the pressure distribution law of the silo wall under different discharge flow conditions.There are many factors influencing the increase of the dynamic silo wall pressure.In this paper,the discrete element models with different height-diameter ratios are established to study the mechanism of the position of the peak action point of the silo wall pressure at different storage heights from a micro perspective.as follows:?1?Self-designed and customized semi-circular plexiglass test silo through physical model tests,using calcined ceramic balls with physical and mechanical parameters similar to grain particles as bulk materials,and measuring the storage and unloading conditions through pressure sensors The bin wall pressure value adopts different charging methods to ensure different material density,observe the different discharge flow state changes,and analyze the volatility and overpressure of the bin wall pressure under different discharge flow states.?2?Establish the silo model with the same height to diameter ratio as the model test in?1?through the discrete element program,adopt the central charging method?that is,loose charging?,observe different discharge flow patterns,and compare the model test results comparing.The discharge flow pattern,particle velocity and force chain network distribution in the simulation results are jointly analyzed to explore the mesoscopic mechanism of pressure changes in the silo wall under storage and discharge conditions.?3?Use the PFC program to establish a numerical simulation silo model,keep the silo diameter as an invariant D,change the storage height H of the storage materials to be 2D,2.5D and 3D,taking into account the peak discharge pressure peak,particle velocity distribution The evolution law of the coordination number difference,through the sensitivity of the peak pressure distribution of the silo wall to the initial state,study the influence of the storage height of the storage material on the force of the silo structure.Draw a critical curve with the relative particle velocity"V_ri=0.001"as the critical value,divide the material area when the pressure peak occurs into flowing and static areas,and compare the difference of the coordination number of different material areas.Study the mechanism of the peak action point of the silo wall pressure at the level of view.?4?Through the physical model test in?1?,the following conclusions are drawn:when the initial compaction of the storage material is large,the discharge flow state appears as a tubular flow;when the initial compaction of the storage material is small,the discharge flow state appears as a whole Flow?Coexistence of overall flow and funnel flow?Continuous conversion of funnel flow,and the pressure of the silo wall has the most obvious sudden change at the moment of discharge.Due to the dynamic arching mechanism under unloading conditions,the bin wall pressure will fluctuate to varying degrees,and the bin wall pressure volatility changes in different discharge flow regimes,among which the overall volatility is the largest.At the same time,the point of maximum volatility in the overall flow region has the largest overpressure coefficient of 1.85.Comparing the numerical simulation results in?2?with the results of the model test,it is found that the discharge flow patterns of the two are consistent,and when the particle surface velocity of the storage surface is consistent with the particle velocity of the central channel,it can be completed as a whole to the funnel Logo.By comparing and analyzing the PFC model simulation results of different storage heights in?3?,it was found that the particle arrangement and distribution under storage conditions affect the peak discharge pressure distribution,and the peak wall pressure distribution of the bottom half of the silo has an initial state Has a higher sensitivity.Under the unloading condition,as the height of the storage material increases,the position depth of the peak pressure point of the silo wall increases,and it is all about 0.3m from the silo bottom.The reason why the peak pressure action point appears at a height of about 0.3m from the bottom of the silo is that it is located at the junction of the material flow area and the static area,and the dilatation effect is most obvious near this position.