| The theoretical formula of the dynamic side pressure increase mechanism and the effective prediction of dynamic side pressure during the discharge process of the clear silo will help the production of silos to be safe and stable,the difference of the ratio of height to diameter is the important reason for the increase of dynamic lateral pressure.Therefore,based on the NSFC project(51578216),this paper uses model tests,numerical simulations and theoretical analysis,take the ratio of height to diameter as the entry point.To study the effects of different high diameter ratios on the discharge pressure and discharge flow state.The reasons for the increase of dynamic side pressure are expounded from the two different aspects of macro flow state and fine view of power arch,the shallow silo with high diameter ratio greater than 1.0 and less than 1.5 is discussed emphatically,and whether it is economical and reasonable to select the maximum value as the design value for the two calculation methods given in the silo specification.And further proposed a new and applicable theoretical calculation method.The main research content and conclusions were as follows:(1)Based on the experimental verification of deep silo model with a height to diameter ratio of 2.9,six silo models with different high diameter ratios were established by PFC,of which three were deep silos(H/D.>1.5)with high diameter ratios: 2.9(model silo a),2.2(model silo b)and 1.76(model silo c),and 3 shallow silos(H/D<1.5)the high diameter ratio was: 1.47(model warehouse d),1.28(model warehouse e)and 1.1(model warehouse f).Discrete element simulation results can be analyzed,the maximum dynamic side pressure was occurred in the lower position of the silo,the same height of the silo,the larger the diameter of the silo,the maximum dynamic side pressure is the overall upward trend,but non-linear.(2)On the based of research(1),a detailed study of the model silos was carried out,and the flow of storage particles in different operating conditions during the discharge process,the velocity field at different moments and the evolution of the force chain network were extracted,and it was available from the macro discharge flow state,as the diameter of the silogradually increases,the moment of the mixing flow appears more and more early,when the silo diameter is large enough,the mass flow state will no longer appear.And it can be concluded that the change of axial force was the main reason that leads to the change of the micro-flow characteristics of the storage particles and the change of the flow pattern and the influence of discharge pressure.From the point of view of the power arch,the time required for the knot arch was related to the size of the silo,for the silo,the larger the diameter of the silo,the more difficult the knot arch to occur.(3)The model test of silo unloading was carried out.Then,proposes a side pressure calculation method suitable for the shallow and circular silo and considering the side wall and storage material elasticity.The calculation methods of the shallow and circular silo,deep silo and the methods in this paper were compared and analysed.The design of circular shallow silo based on Rankine theory was not safe enough,and the dynamic lateral pressure calculated by deep silo based on Janssen theory was conservative.The results show that the relative error of each corresponding depth measuring point(the difference between dynamic theoretical value and the test value and the ratio of the test value)was between 31% and 69%,and the error was large.However,the side pressure calculation method suitable for the shallow and circular silo and considering the side wall and storage material elasticity.The results of the calculation were in good agreement with the measured value of the test... |
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