颗粒物质的混合是化学工业生产的重要单元操作,由于颗粒物质运动行为的复杂性,工业混合器中的颗粒运动规律及物理机制至今仍未被全面认识。作为一种精细的数值方法,离散单元法(discrete element method,DEM)在单颗粒尺度上描述颗粒物质...颗粒物质的混合是化学工业生产的重要单元操作,由于颗粒物质运动行为的复杂性,工业混合器中的颗粒运动规律及物理机制至今仍未被全面认识。作为一种精细的数值方法,离散单元法(discrete element method,DEM)在单颗粒尺度上描述颗粒物质的受力与运动行为,因此在研究混合机理方面具有独特优势。随着DEM模型与计算技术的快速发展,DEM已被广泛应用于各种混合过程的研究。通过DEM可以全面考察不同的颗粒性质、混合器类型以及操作条件等因素对混合机理的影响,从而对于指导粉体工业的生产操作及设备优化改进具有重要意义。本文重点阐述了DEM在无黏颗粒、黏结性颗粒、非球形颗粒混合过程模拟以及大规模计算等方面的最新进展,并对未来发展进行了展望。展开更多
为实现占据多个流体网格的大颗粒在流场中运动的仿真,基于计算流体力学和离散单元法耦合(computational fluid dy namics-discrete element mothod,CFD-DEM),提出了一种新的数值方法。使用黏结颗粒模型将大颗粒近似表示为多个小球形颗...为实现占据多个流体网格的大颗粒在流场中运动的仿真,基于计算流体力学和离散单元法耦合(computational fluid dy namics-discrete element mothod,CFD-DEM),提出了一种新的数值方法。使用黏结颗粒模型将大颗粒近似表示为多个小球形颗粒黏结而成,基于非解析CFD-DEM方法计算流体对每个小球颗粒的作用力,将所有小球颗粒运动参数的平均值用于描述整个黏结颗粒的运动状态。通过黏性流体中球形大颗粒的沉降运动模拟,比较仿真结果与相关实验数据,结果表明:该方法不仅能准确模拟球形大颗粒的沉降运动,而且与浸没边界法相比计算效率更高。与传统的解析CFD-DEM方法相比,此方法还可以方便且准确地模拟三维情况下非球形大颗粒在流场中的运动。展开更多
We explore the effect of particle shape on the angle of repose (AoR) in granular packing using a three-dimensional discrete element method.Non-spherical particles were modeled using super-ellipsoids characterized by a...We explore the effect of particle shape on the angle of repose (AoR) in granular packing using a three-dimensional discrete element method.Non-spherical particles were modeled using super-ellipsoids characterized by aspect ratio and blockiness.The relationship between AoR and particle shape was examined,followed by a series of analyses on the origin of AoR from a microscopic perspective.Results show that,with blockiness deviating from unity,AoR has an approximate "M" shape that exhibits a strong to weak trend with aspect ratio,matching results of previous reports.Another finding suggests a parabolic relationship between normalized AoR and normalized coordination number,AoR increases with anisotropy related more with the anisotropy of particle orientation than with the anisotropy of contact normal.Particle shape is more likely to affect AoR by affecting the tangential force than the normal contact force.An analysis based on traction indicates that dips in stress associated with the tangential force (compared with the normal force) and non-spherical particles (compared with spheres) are more significant.For various particle shapes,AoR is positively correlated with friction mobilization but is negatively correlated with friction mobilization for various coefficient of friction.展开更多
Particle mixing and segregation are common phenomena in rotary drums,which are challenging to be controlled and driven artificially in powder technology.In this work,the discrete element method(DEM)was applied to cons...Particle mixing and segregation are common phenomena in rotary drums,which are challenging to be controlled and driven artificially in powder technology.In this work,the discrete element method(DEM)was applied to construct the novel rotary drum composed of different shaped curved sidewalls.By varying the operation parameters of particle and sidewall shapes as well as the length-to-diameter(L/D)ratio of drums,the axial mixing and segregation processes of binary size-induced particles were investigated.The results show that the axial flow velocity of the particle mixtures is noticeably weakened once the particle angularity increases,making the non-spherical particles to mix better in rotary drums compared to the spherical particles.Besides,in the short drums with size-induced spherical particles,the axial segregation characteristics are significantly enhanced by the convex sidewalls while suppressed by the concave sidewalls.However,for size-induced non-spherical particles,the axial segregation structure can be present in rotary drums with plane and concave sidewalls while not in drums with convex sidewalls.Moreover,the axial segregation band structure of spherical particles eventually increases proportionally with the increased drum L/D ratios.In contrast,the non-spherical particles cannot form obvious multi-proportional segregation bands.展开更多
针对具有初始各向异性的间断级配砂土细粒潜蚀问题,引入可以考虑颗粒投影面积影响的Ganser拖曳力计算模型,实现非球形颗粒的计算流体动力学(computational fluid dynamics,简称CFD)和离散元(discrete element method,简称DEM)的双相耦...针对具有初始各向异性的间断级配砂土细粒潜蚀问题,引入可以考虑颗粒投影面积影响的Ganser拖曳力计算模型,实现非球形颗粒的计算流体动力学(computational fluid dynamics,简称CFD)和离散元(discrete element method,简称DEM)的双相耦合。通过与单颗粒下沉试验的对比,验证了该数值方法在解决异形颗粒与流体相互作用时的适用性。在此基础上,生成具有不同沉积方向和不同细粒含量的初始各向异性试样,模拟向上渗流潜蚀试验,并在试验中监测细粒流失量、强弱力链组成以及颗粒组构变化等宏微观特性,研究不同充填状态下(欠填充和过填充)不同组构各向异性土体渗流潜蚀特征。之后,对受潜蚀前后的试样进行了排水三轴试验,探究渗流对土体强度弱化的影响。结果表明,过填充试样质量损失随着颗粒沉积角度的增大而增大,而欠填充试样质量损失随沉积角度先增大后减小;欠填充试样细粒损失主要来源于低连通性细颗粒,而对于过填充试样,潜蚀则会导致低连通性和高连通性细颗粒数量同时减小。此外,三轴试验表明,潜蚀致土体峰值强度发生显著弱化,且峰值强度随沉积角度的变化也会受到土体充填状态的影响。展开更多
文摘颗粒物质的混合是化学工业生产的重要单元操作,由于颗粒物质运动行为的复杂性,工业混合器中的颗粒运动规律及物理机制至今仍未被全面认识。作为一种精细的数值方法,离散单元法(discrete element method,DEM)在单颗粒尺度上描述颗粒物质的受力与运动行为,因此在研究混合机理方面具有独特优势。随着DEM模型与计算技术的快速发展,DEM已被广泛应用于各种混合过程的研究。通过DEM可以全面考察不同的颗粒性质、混合器类型以及操作条件等因素对混合机理的影响,从而对于指导粉体工业的生产操作及设备优化改进具有重要意义。本文重点阐述了DEM在无黏颗粒、黏结性颗粒、非球形颗粒混合过程模拟以及大规模计算等方面的最新进展,并对未来发展进行了展望。
文摘为实现占据多个流体网格的大颗粒在流场中运动的仿真,基于计算流体力学和离散单元法耦合(computational fluid dy namics-discrete element mothod,CFD-DEM),提出了一种新的数值方法。使用黏结颗粒模型将大颗粒近似表示为多个小球形颗粒黏结而成,基于非解析CFD-DEM方法计算流体对每个小球颗粒的作用力,将所有小球颗粒运动参数的平均值用于描述整个黏结颗粒的运动状态。通过黏性流体中球形大颗粒的沉降运动模拟,比较仿真结果与相关实验数据,结果表明:该方法不仅能准确模拟球形大颗粒的沉降运动,而且与浸没边界法相比计算效率更高。与传统的解析CFD-DEM方法相比,此方法还可以方便且准确地模拟三维情况下非球形大颗粒在流场中的运动。
基金the Fundamental Research Funds for Central Universities,State Key Laboratory of Subtrop-ical Building Science(2017KA04)partially by Science and Technology Program of Guangzhou(201707020047)。
文摘We explore the effect of particle shape on the angle of repose (AoR) in granular packing using a three-dimensional discrete element method.Non-spherical particles were modeled using super-ellipsoids characterized by aspect ratio and blockiness.The relationship between AoR and particle shape was examined,followed by a series of analyses on the origin of AoR from a microscopic perspective.Results show that,with blockiness deviating from unity,AoR has an approximate "M" shape that exhibits a strong to weak trend with aspect ratio,matching results of previous reports.Another finding suggests a parabolic relationship between normalized AoR and normalized coordination number,AoR increases with anisotropy related more with the anisotropy of particle orientation than with the anisotropy of contact normal.Particle shape is more likely to affect AoR by affecting the tangential force than the normal contact force.An analysis based on traction indicates that dips in stress associated with the tangential force (compared with the normal force) and non-spherical particles (compared with spheres) are more significant.For various particle shapes,AoR is positively correlated with friction mobilization but is negatively correlated with friction mobilization for various coefficient of friction.
基金support from the National Natural Science Foundation of China (grant No.51775109)Natural Science Foundation of Jiangsu Province (grant No.BK20221465)the Jiangsu Province Elevator Intelligent Safety Key Construction Laboratory Open Project (grant No.JSKLESS202105).
文摘Particle mixing and segregation are common phenomena in rotary drums,which are challenging to be controlled and driven artificially in powder technology.In this work,the discrete element method(DEM)was applied to construct the novel rotary drum composed of different shaped curved sidewalls.By varying the operation parameters of particle and sidewall shapes as well as the length-to-diameter(L/D)ratio of drums,the axial mixing and segregation processes of binary size-induced particles were investigated.The results show that the axial flow velocity of the particle mixtures is noticeably weakened once the particle angularity increases,making the non-spherical particles to mix better in rotary drums compared to the spherical particles.Besides,in the short drums with size-induced spherical particles,the axial segregation characteristics are significantly enhanced by the convex sidewalls while suppressed by the concave sidewalls.However,for size-induced non-spherical particles,the axial segregation structure can be present in rotary drums with plane and concave sidewalls while not in drums with convex sidewalls.Moreover,the axial segregation band structure of spherical particles eventually increases proportionally with the increased drum L/D ratios.In contrast,the non-spherical particles cannot form obvious multi-proportional segregation bands.
文摘针对具有初始各向异性的间断级配砂土细粒潜蚀问题,引入可以考虑颗粒投影面积影响的Ganser拖曳力计算模型,实现非球形颗粒的计算流体动力学(computational fluid dynamics,简称CFD)和离散元(discrete element method,简称DEM)的双相耦合。通过与单颗粒下沉试验的对比,验证了该数值方法在解决异形颗粒与流体相互作用时的适用性。在此基础上,生成具有不同沉积方向和不同细粒含量的初始各向异性试样,模拟向上渗流潜蚀试验,并在试验中监测细粒流失量、强弱力链组成以及颗粒组构变化等宏微观特性,研究不同充填状态下(欠填充和过填充)不同组构各向异性土体渗流潜蚀特征。之后,对受潜蚀前后的试样进行了排水三轴试验,探究渗流对土体强度弱化的影响。结果表明,过填充试样质量损失随着颗粒沉积角度的增大而增大,而欠填充试样质量损失随沉积角度先增大后减小;欠填充试样细粒损失主要来源于低连通性细颗粒,而对于过填充试样,潜蚀则会导致低连通性和高连通性细颗粒数量同时减小。此外,三轴试验表明,潜蚀致土体峰值强度发生显著弱化,且峰值强度随沉积角度的变化也会受到土体充填状态的影响。
