| The silo was a kind of structure widely used for storing bulk materials in agriculture and industry. The normal pressure on the wall which influenced by the flow pattern of the material was the main reason that leaded to the strength failure of the wall. Discharge from a wall outlet was a new discharging method during which the flow pattern of the bulk material was quite different from that stated in EN 1991-4 or GB50884-2013. So making clear the flow pattern and the distribution of normal pressure during discharge was important to the design of the silo discharged by a wall outlet.Test method and DEM simulations were used to simulate the process of discharge from the wall outlet in this article. The flow pattern of the surface and internal buck material, the change of the flow channel, discharge ratio, discharge rate, the distribution of the normal pressure on the wall, discharge overpressure factor were discussed as well as the effects of aspect ratios, dimensions of outlets and the types of buck material. The comparisons between the simulating results and those obtained by the design codes were also carried out.A series of experiment studies on silos which were filled with glass beads were carried out to study the flow pattern, normal wall pressure and the effects of dimensions of outlets during the wall outlet discharge. Results showed that the flow region and the static region existed during the whole discharge process. The normal wall pressures in the static region and in the pressure ears during discharge were much greater than that in the static storage state and were less in the flow channel. The discharge overpressure factors were between 1.5 and 2.0 in the static region; and it was bigger than 2.0 in the pressure ears.Discrete Element Method (DEM) simulations were carried out to study the flow pattern, normal pressure and effects of aspect ratio during discharge in wall outlet silos with glass beads. The DEM model was verified by the tests from discharge time, distribution of normal pressure, discharge ratio and flow pattern. The verified model was used to simulate the discharge from the outlet wall in silos with different aspect ratios. Simulation results showed that funnel flow happened in silos with low aspect ratios while the flow channel expanded to the whole section in the silo with the high aspect ratios. In the simulations, the distributions of normal pressure on wall in the flow zone showed parabolic shape along the height and the level of normal pressure was less than that in static region. To silos with the same volume, the discharge rate rose with the aspect ratio.A series of test studies on silos filled with fine sand and soybeans discharged from the wall outlet were carried out to study the effects of types of materials on the flow pattern and normal wall pressure during the wall outlet discharge. The results showed that the flow region and the static region existed during the discharge process. The pipe flow happened in fine sand test while mixed flow happened in soybean test. Eccentric normal pressure occurred in fine test. The normal pressures in the flow channel were just between 22.0% and 67.7% of those in the static storage state while between 1.03 and 1.79 times in the static region. In soybean test, symmetrical normal pressures acted on the upper wall whose overpressure factors were less than 1.5. Because of the change of flow channel, the peak of overpressure factor in the middle of the wall could reach 3.10.The comparisons of the large eccentric discharge stated in EN 1991-4 and the wall outlet discharge were carried out. The limitations of large eccentric discharge model in the standard were analysed when the flow pattern model and normal pressure model of funnel flow and mixed flow in wall outlet discharge were presented. Attentions in the design of silo discharged by wall outlets were also given. |
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