水平摆振下谷物偏析效果的离散元模拟研究
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摘要
为了强化厚料层谷物颗粒的分层效果,利用三维离散单元法,结合颗粒空隙填充及动能、动量理论,分析了水平摆振条件下谷粒与短茎秆的分层机理及薄厚料层的分层效果,并采用颗粒体积分数法评价了摆振槽结构改进对厚料层谷物分层的影响。结果表明,在周期性水平摆振作用下,颗粒之间的碰撞使颗粒间缝隙不断变化,同时由于在碰撞时短茎秆的动量远小于谷粒动量,使得短茎秆被排挤到上部空间,而谷粒则渗透至料层下部空隙,最终形成偏析分层。而厚料层谷物因料层密实,底部颗粒间的压力和阻尼较大,使得谷物的动能和垂直方向的动量较薄料层小,导致分层效果较差。在同等参数下,圆柱突起结构振动体的颗粒体积分数相较于光槽振动体颗粒体积分数提高了10%。
For strengthening layering effect of thick-layer grain particles,a simulation study for segregation process of grains and short stalks when plain trough cylinder vibration body is under horizontal pendulum oscillations was carried out using the three-dimensional discrete element method. And the grain segregation mechanism was analyzed in detail based on the theory of gap filling,kinetic energy and momentum of the grain particles. By comparing different contacting times,kinetic energy and momentum of the particles in the segregation process of thin and thick material layer,we analyzed the reason of the poor layered effect of the thick material layer. The analysis results show that:under the action of periodic horizontal pendulum oscillations,the collision between particles change the gap of grain particles,which provides precondition for layering,and the collision and friction between particles and vibration body provide energy for layering. Because the energy and momentum of the short stalks is far less than the grains during the collision of the grains and short stalks,the short stalks are crowded to the upper space,and the grains are permeated to the gap of the lower part of the material layer,and then the layering is formed. Meanwhile,thick material layer is dense,and pressure and damping are bigger between bottom grains,which makes kinetic energy and momentum of vertical direction of the grains less than thin material layer,causing a poor layering effect. The particle volume fraction of the vibration body of adding cylindrical bump structurere is improved by 10% compared to that of the lightslot vibration body after improvement.
For strengthening layering effect of thick-layer grain particles,a simulation study for segregation process of grains and short stalks when plain trough cylinder vibration body is under horizontal pendulum oscillations was carried out using the three-dimensional discrete element method. And the grain segregation mechanism was analyzed in detail based on the theory of gap filling,kinetic energy and momentum of the grain particles. By comparing different contacting times,kinetic energy and momentum of the particles in the segregation process of thin and thick material layer,we analyzed the reason of the poor layered effect of the thick material layer. The analysis results show that:under the action of periodic horizontal pendulum oscillations,the collision between particles change the gap of grain particles,which provides precondition for layering,and the collision and friction between particles and vibration body provide energy for layering. Because the energy and momentum of the short stalks is far less than the grains during the collision of the grains and short stalks,the short stalks are crowded to the upper space,and the grains are permeated to the gap of the lower part of the material layer,and then the layering is formed. Meanwhile,thick material layer is dense,and pressure and damping are bigger between bottom grains,which makes kinetic energy and momentum of vertical direction of the grains less than thin material layer,causing a poor layering effect. The particle volume fraction of the vibration body of adding cylindrical bump structurere is improved by 10% compared to that of the lightslot vibration body after improvement.
引文
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[21]贾富国,韩燕龙,刘扬,等.稻谷颗粒物料堆积角模拟预测方法[J].农业工程学报,2014,30(11):254-260.
[22]李菊,赵德安,沈惠平,等.基于DEM的谷物三维并联振动筛筛分效果研究[J].中国机械工程,2013,24(8):1018-1022
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[24]DAS H.Separation of paddy and rice on an oscillating tray type separator[J].Journal of Agricultural Engineering Research,1986,34(2):85-95.
[2]KNIGHT J B,JAEGER H M,NAGEL S R.Vibrationinduced size separation in granular media:the convection connection[J].Physical Review E,1993,70:3728-3731.
[3]ROSATO A,STRANDBURG K J,PRINZ F,et al.Why the Brazil nuts are on top:Size segregation of particulate matter by shaking[J].Physics Review Letters,1987,58(10):1038-1040.
[4]姜泽辉,荆亚芳,赵海发,等.振动颗粒物质中倍周期运动对尺寸分离的影响[J].物理学报,2009,58(9):5923-5929.
[5]OSAMU S.Dilatancy,buckling,and undulations on a vertically vibrating granular layer[J].Physical Review Letters,2005,72(5):1-7.
[6]GARCIMARTIN A,MAZA D,ILQUIMICHE J L,et al.Convective motion in a vibrated granular layer[J].Physical Review E,2002,65(2):1-5.
[7]赵永志,江茂强,郑津洋.巴西果效应分离过程的计算颗粒力学模拟研究[J].物理学报,2009,58(3):1812-1818.
[8]BURTALLY N,KING P J,SWIFT M R.Spontaneous air-driven separation in vertically vibrated fine granular mixtures[J].Science,2002,295:1877-1879.
[9]MULLIN T.Mixing and demixing[J].Science,2002,295:1851-1860.
[10]KENNEDY D,NORMAN C.What don’t we know[J].Science,2005,309:75-79.
[11]梁宣文,李粮生,侯兆国,等.垂直振动作用下二元混合颗粒分层的动态循环反转[J].物理学报,2008,57(4):2300-2305.
[12]史庆藩,阎学群,厚美瑛,等.振动混合颗粒形成的反巴西果分层及其相图的实验观测[J].科学通报,2003,48(4):328-330.
[13]DURAN J.Sand,powder,grains[M].New York:Springer,2000.
[14]AUMA TRE S,KRUELLE C A,REHBERG I.Segregation in granular matter under horizontal swirling excitation[J].Physics Review E,2001,64(4):1-4.
[15]ODA M,IWASHITA K,KAKIUCHI T.Importance of particle rotation in the mechanics of granular materials[M].Rotterdam:Balkema,1997
[16]ZHU H P,ZHOU Z Y,YANG R Y,et al.Discrete particle simulation of particulate systems:Theoretical developments[J].Chemical Engineering Science,2007,62(13):3378-3396.
[17]ZEILSTRA C,HOEF M A,KUIPERS J A M.Simulation of density segregation in vibrated beds[J].Physics Review E,2008,77(3):1-13.
[18]赵永志,江茂强,徐平,等.颗粒堆内微观力学结构的离散元模拟研究[J].物理学报,2009,58(3):1819-1825.
[19]赵永志,程易.水平滚筒内二元颗粒体系径向分离模式的数值模拟研究[J].物理学报,2008,57(1):322-328.
[20]李洪昌,李耀明,唐忠,等.基于EDEM的振动筛分数值模拟分析[J].农业工程学报,2011,27(5):117-121.
[21]贾富国,韩燕龙,刘扬,等.稻谷颗粒物料堆积角模拟预测方法[J].农业工程学报,2014,30(11):254-260.
[22]李菊,赵德安,沈惠平,等.基于DEM的谷物三维并联振动筛筛分效果研究[J].中国机械工程,2013,24(8):1018-1022
[23]SAKAGUCHI E,SUZUKI M,FAVIER J F,et al.Numerical simulation of the shaking separation of paddy and brown rice using the discrete element method[J].Journal of Agricultural Engineering Research,2001,79(3):307-315.
[24]DAS H.Separation of paddy and rice on an oscillating tray type separator[J].Journal of Agricultural Engineering Research,1986,34(2):85-95.