| In the unloading process of silos,the dynamic pressure of silos on silo walls is the main reason for the circular damage of silos walls.However,there is no accurate theory for predicting the dynamic pressure of silo wall in the world.For dynamic pressure,there are many influencing factors and its formation mechanism is so complex.Among these,the kind of storage material is a more important factor.The dynamic pressure of different storage materials is big disparity.So,in order to ensure the safety of silo design and use,It is urgent to study the dynamic pressure and the causes of dynamic overpressure of soybean and wheat under deep and shallow bins.Therefore,this paper relies on the National Natural Science Foundation of China’s surface project "Research on lateral pressure mechanism of silos based on energy conversion"(Approval No: 51578216),using the height-diameter ratio of 2.2 and 1.4 of silo,using soybean and wheat storage materials for the experiment.On this basis,two kinds of physical parameters were used to simulate the unloading of deep bin by PFC.The size and distribution law of dynamic pressure of silo unloading are obtained.Through comparetive study,the influence of two kinds storage materials on dynamic pressure is explored.the contact force chain network and velocity field of particles are obtained by PFC,the reasons of dynamic overpressure and different dynamic pressure of the two kinds of storage materials were studied.Compared between the experiment and simulation,the pressure correlation between the flow pattern and the dynamic was studied by method of combined force chain network and velocity profile.And using 0.1m and 0.05 m diameter unloading outlet for testing under the deep bin,explore the contact between outlet size and dynamic pressure.Specific research contents are as follows:(1)Model silos with height-diameter ratio of 2.2 and 1.4 were manufactured and designed,soybean and wheat were used for unloading test.Static and dynamic pressure were obtained.Overpressure coefficients were calculated.The size and regularity of dynamic pressure during unloading of silos were analyzed,and the effects of two kinds of storage materials on dynamic pressure were also analyzed.It was found that the dynamic pressure increased first and then decreased,and the oscillation occurs during the increase and decrease,the maximum dynamic pressure occurred at the beginning of unloading,and the overpressure coefficient was the largest at the height of 1/3 silo.Under deep bin test,The maximum overpressure coefficient of soybean is 2.27,which is 1.49 times that of wheat.Under shallow bin test,the maximum overpressure coefficient of soybean is 2.22,which is 1.72 times that of wheat.(2)In order to study the influence of unloading outlet size on dynamic pressure,0.1m and 0.05 m diameter discharge port was used in deep bin of soybean.It is found that the dynamic pressure of the silo wall is proportional to the size of the discharge port.(3)Two kinds of physical parameters were used to simulate the unloading of deep bin by PFC.The validity of the simulation method was verified by comparing the experimental and simulated pressure data.The relationship between the dynamic pressure and flow state is studied by compare the simulated flow pattern and the experimented flow pattern.It was found that the flow pattern changed from whole flow to tubular flow,and the dynamic pressure of the whole flow was higher.(4)Particle contact force chain network and velocity field are obtained by PFC.The causes of dynamic pressure difference of two kinds of storage materials and dynamic overpressure from force chain network and velocity field,and the maximum position of overpressure is analyzed from the shape of force chain network.It is found that the dense force chain network can inhibit the flow of storage materials,and the force chain arch results in the increase of dynamic pressure. |
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