Application of GPU-based Discrete Simulation to Flow and Mixing Mechanisms of Granular Materials

离散单元法（Discrete Element Method）是颗粒流模拟研究的主流方法，且发展迅速、应用广泛，能有效的揭示出实验难以获取的流动信息。然而，其计算量大、计算时间长、模拟规模小等缺陷严重制约了其应用和发展。针对此问题，本论文在前期及合作工作基础上设计并实现了面向多尺度异构超级计算系统的高效大规模离散单元模拟程序。应用该方法及程序定量研究了三维水平滚筒中颗粒流动速度场的相似性问题以及工业尺度的螺旋输送器中物料的混合问题，从机理和应用研究两方面阐明了该方法及模拟程序的有效性。 所开发的耦合使用中央处理器(Central Processing Unit, CPU)和图形处理器(Graphics Processing Unit, GPU)的高效大规模DEM模拟程序，在单节点测试中较单纯使用CPU快达25倍，并在多节点CPU/GPU并行时具备良好的可扩展性，为随后的实例研究奠定了基础。 论文以此研究了处于Rolling流型的三维水平滚筒，重点考察了颗粒的几何参数及各种物理属性对其稳态速度场的影响。研究表明：这些参数的影响程度不同，而粒径比具有一定的支配作用。同时，颗粒的滑动摩擦系数和杨氏模量对速度场的影响较大。对不同的滚筒直径，只要保证模拟系统的粒径比一致，稳态速度场将基本保持不变。由于颗粒物质的离散属性以及其相互作用的复杂性，即使在相对简单的Rolling流型中，滚筒的稳态速度场也呈现丰富的内部结构。 本文还对工业尺度螺旋输送器中物料的流动状态进行了大规模模拟。通过统计物料的混合指标和停留时间分布考察了其几何结构和操作条件对物料混合效果的影响。研究表明，螺旋输送器的混合性能强烈地依赖于操作条件和结构尺寸，转速和物料的添加速率对物料的整体混合和轴向混合效果影响最大，其次是混合段螺距和混合区域的长度。该结论对在螺旋输送器的工业设计中根据生产的具体要求合理地选择技术参数、降低能耗具有指导意义。 论文最后总结了所获得的主要成果，展望了离散单元模拟在研究颗粒流动的内在机理和工业应用方面的前景

螺旋输送器中颗粒混合过程的模拟

采用离散单元法(discrete element method,DEM)模拟了工业尺度螺旋输送器中两种不同密度与粒径的颗粒的流动状态与混合过程。采用Lacey混合指标的定量分析表明,该输送器的混合性能强烈地依赖于操作条件和结构尺寸,转速和物料的添加速率对混合效果影响最大,其次是混合段螺距和物料粒径。根据工业生产的具体要求,可参考上述发现合理地选择技术参数、提高混合效率、降低能耗。</p

GPU加速的并行粒子模拟在线可视化

粒子模拟是研究离散粒子和连续介质运动规律的常用方法。而大规模的粒子模拟通常借助高性能计算系统。近年来,得益于其众核架构,图形处理器(GPU)已成为高性能计算的重要设备,并被广泛用于大规模粒子模拟过程的加速。本文讨论了一种对GPU加速的分布式粒子模拟进行在线可视化的方法。在该方法中,GPU除了被用于加速粒子模拟过程外,也被用于数据到图像的快速转换。同时,并行绘制技术被用于分布式数据的可视化。通过本文所述的方法,用户可在并行计算运行过程中,通过显示于拼接显示墙的高分辨率图像,实时地观察到粒子模拟中发生的现象,并对计算过程进行跟踪和调整

GPU加速的并行粒子模拟在线可视化

粒子模拟是研究离散粒子和连续介质运动规律的常用方法。而大规模的粒子模拟通常借助高性能计算系统。近年来，得益于其众核架构，图形处理器（GPU）已成为高性能计算的重要设备，并被广泛用于大规模粒子模拟过程的加速。本文讨论了一种对GPU加速的分布式粒子模拟进行在线可视化的方法。在该方法中，GPU除了被用于加速粒子模拟过程外，也被用于数据到图像的快速转换。同时，并行绘制技术被用于分布式数据的可视化。通过本文所述的方法，用户可在并行计算运行过程中，通过显示于拼接显示墙的高分辨率图像，实时地观察到粒子模拟中发生的现象，并对计算过程进行跟踪和调整

颗粒物质混合行为的离散单元法研究

The mixing of granular materials is an important unit operation in many industries. Due to the complex behaviors of granular flows, general laws and fundamental mechanisms of granular flows in industrial mixers are not completely understood yet. As a detailed numerical approach, the discrete element method (DEM) describes the forces and motions of granular materials at the particle scale, and thus has notable advantages over experimental approaches in the research of mixing mechanisms. With the rapid developments of its models and the computational technologies, this method becomes more and more popular in the simulations of various mixing processes. The effects of particle properties, mixer types, and operating parameters on mixing rate and mixing mechanisms could be investigated comprehensively through DEM, which would be quite valuable for the design and optimization of mixers as well as their optimal operations. Moreover, the high computational cost of industrial-scale simulations could be greatly alleviated by the fast developments of computer hardware, such as the advent of graphics processing unit (GPU). This review summarizes the recent progresses of DEM simulations on mixing, with emphasis on the treatments for non-cohesive particles in different kinds of mixers (rotary and fixed), cohesive particles (fine and wet), non-spherical particles (direct description of shape and multi-sphere method), and large-scale implementations. Finally, future development of the DEM method in mixing simulations is prospected

颗粒物质混合行为的离散单元法研究

The mixing of granular materials is an important unit operation in many industries. Due to the complex behaviors of granular flows, general laws and fundamental mechanisms of granular flows in industrial mixers are not completely understood yet. As a detailed numerical approach, the discrete element method (DEM) describes the forces and motions of granular materials at the particle scale, and thus has notable advantages over experimental approaches in the research of mixing mechanisms. With the rapid developments of its models and the computational technologies, this method becomes more and more popular in the simulations of various mixing processes. The effects of particle properties, mixer types, and operating parameters on mixing rate and mixing mechanisms could be investigated comprehensively through DEM, which would be quite valuable for the design and optimization of mixers as well as their optimal operations. Moreover, the high computational cost of industrial-scale simulations could be greatly alleviated by the fast developments of computer hardware, such as the advent of graphics processing unit (GPU). This review summarizes the recent progresses of DEM simulations on mixing, with emphasis on the treatments for non-cohesive particles in different kinds of mixers (rotary and fixed), cohesive particles (fine and wet), non-spherical particles (direct description of shape and multi-sphere method), and large-scale implementations. Finally, future development of the DEM method in mixing simulations is prospected