基于离散单元法的稻米-茎秆分离机理研究

Mechanism Research on Separation of Paddy-Stalks Based on Discrete Element Method

为了在簸箕中实现稻米与茎秆的分离并揭示其分离机理,对稻米-茎秆二元混合体系在水平振动下的运动行为进行了研究。运用软件SolidWorks建立几何模型,在离散元软件EDEM中进行仿真计算,设定生成稻米总质量为240g,茎秆总质量为6g,振动频率为6Hz,振幅为20mm,仿真总时长为20s。结果表明:簸箕中的稻米和茎秆在垂直方向上出现明显的分层现象,且茎秆位于稻米上方。运用动能定理,并结合理论力学与流体力学相关理论,可以对分离机理作出合理解释。在整个运动过程中,茎秆平均动能为稻米的8.3%,而茎秆在Z方向平均受力为稻米的5442.3倍,是导致稻米-茎秆分离的主要原因。引入稻米体积浓度来量化分层程度,在运动初始时刻,稻米的体积浓度为0.56。研究过程中发现系统中存在局部能量较低的问题,而且正、反向对流卷的存在导致稻米-茎秆没有完全分离,得到稻米体积浓度为0.87。通过在容器底面加横筋的方式,增加簸箕圆弧壁与底部颗粒之间的碰撞,提高系统能量,消除对流卷,最终得到稻米体积浓度接近1。而且添加横筋后,簸箕中的谷物和茎秆分离速度加快,分离效率提高,在10s时即可完成分离。最后对比了二者的分离构型,发现簸箕加横筋之后,稻米-茎秆在水平方向也出现了分离,分界线为一条倾斜的直线。通过对谷物分离的研究可以为农业生产提供新的工艺与设备。

In order to separate paddy and stalks in dustpan and reveal the separation mechanism,we conducted the research on the behavior of rice-stalk binary mixed system under horizontal vibration.The geometrical model was established by Solid Works software and the simulation calculation was conducted by EDEM software.The total mass of generated paddy was 240g,the total mass of generated stalks was 6g,the vibration frequency was 6Hz,the amplitude was 20mm,and the total simulation time was 20s.The results show that paddy and stalks in dustpan obviously showed two layers in the vertical direction and stalks were above paddy.The separation mechanism can be reasonable explained by using the Kinetic Energy Theorem and the theories from Theoretical Mechanics and Fluid Mechanics.The average kinetic energy of stalks are 8.3% of paddyduring the whole movement,,and the average force of stalks in the Z direction was 5442.3 times of paddy,which was the main reason for the separation of paddy-stalk.The volume concentration of paddy was lead into quantify the degree of stratification,and the volume concentration of paddy is 0.56 at the initial stage of simulation.During the research,It was found that there was a problem of low local energy in the system during the research,and the existence of positive and negative convective rolls result in paddy-stalks not being completely separated,and the volume concentration of paddy was 0.87.By adding transverse bulges on the bottom plate and arc wall of the container,the collision between arc wall and bottom particles was increased,the system energy was increased,and the convective rolls were eliminated,and finally the volume concentration of paddy was close to 1.Moreover,the separation speed of paddy and stalks in dustpan was accelerated,the separation efficiency was improved,and the separation can be completed at 10s after the addition of transverse bulges.Finally,two separation configurations were compared and new phenomenon can be found that paddy-stalks also separate in the horizontal direction and the boundary was a slant line.It was vitally important to study on grain separation,which could provide new technologies and equipment for agricultural production.