应用基于GPU的离散单元法模拟研究立管颗粒流动

发布时间：2018-01-04 15:22

本文关键词：应用基于GPU的离散单元法模拟研究立管颗粒流动　出处：《中国科学院大学(中国科学院过程工程研究所)》2017年博士论文　论文类型：学位论文

【摘要】：立管系统凭借其构造简单、造价低廉等优点,广泛应用于颗粒物料的输送。但实际工业应用立管仍然面临着不稳定排料这一挑战,不稳定排料不仅降低了颗粒的输送效率,而且影响着生产运行的稳定性和安全性。已有研究工作虽然对立管不稳定排料有一定研究,但其本质原因仍不清楚。本论文从立管内颗粒流动入手,在阐述清楚颗粒流动机理的基础上,揭示了立管排料稳定性问题的本质;同时,构建了立管稳定运行的约束性方程;并拓展了当量重力理论模型用于模拟负压差下的立管排料。理解立管排料稳定性的关键是明确立管内颗粒流动特征及机理。传统的立管排料模拟研究中,料面高度普遍偏低,不足以摆脱孔口对其上部颗粒的影响,导致立管内过渡区的流动特征及机理不明确。基于此,本论文通过优化的离散单元法(DEM),通过提高模拟料面高度,完全摆脱了孔口的影响,明确了过渡区的流动特征及机理。结果表明,在立管排料状态改变过程中,过渡区内存在关键转变区域。当关键转变区域出现不稳定流动后,加速颗粒传递到孔口处需要一定时间,在这段时间,孔口处颗粒速度并无变化,立管依然维持稳定排料。这也揭示了立管排料稳定性问题的本质其实是立管内颗粒流动稳定性发生了变化,维持颗粒分布平衡的借以克服重力的颗粒与管壁面之间稳定摩擦作用消失,排料量的波动只是颗粒流动变化的作用结果,也是立管内不稳定流动的宏观表现。在此基础上,将关键转变区域空隙率初始变化时所对应的立管料面高度定义为避免不稳定流动的临界料柱高度。在深入研究了颗粒性质(如颗粒密度、颗粒内摩擦系数)以及设备设计参数(孔口尺寸)对立管临界料柱高度的基础上,构建了立管稳定运行的约束性方程,为相关工业设计及操控提供了理论指导。另外,传统负压差立管排料模拟采用CFD-DEM耦合的方法,计算过程复杂。针对该问题,本文结合散料力学和DEM模型,提出了当量重力理论模型,用以计算负压差情况下的立管排料。该模型通过散料力学理论优化DEM模型中的重力加速度项,无需DEM和其它流体软件进行耦合,达到了简化模型和提升效率的效果,为后续展开立管研究奠定了基础。
[Abstract]:Riser system with its simple structure, low cost and other advantages, is widely used in conveying granular materials. But the actual industrial application of riser is still faced with unstable discharge this challenge, unstable discharge not only reduces the transmission efficiency of the particles, but also affects the stability and safety of the operation. The existing research work although the riser unstable discharge has some research, but its essence is still not clear. In this thesis, the vertical pipe flow of particles, in this clear basic particle flow mechanism, reveals the essence of riser discharge stability; at the same time, the construction of the riser constraint equation and stable operation; expand the equivalent theory of gravity model for the simulation of the standpipe discharge. The discharge stability of vertical pipe understanding key is clear vertical flow characteristics and mechanism of tube particles. The traditional riser discharge simulation study, the burden The height is generally low, not enough to get rid of the upper orifice particles, the flow characteristics and mechanism of vertical transition zone inside the tube is not clear. Based on this, this paper through the optimization of the discrete element method (DEM), by increasing the simulation burden height, completely out of the hole influence, clear flow characteristics and mechanism the transition zone. The results showed that in the riser discharge state change process, there is the key transition region of the transition zone. When the key transition region of unstable flow, accelerate the particles transfer to the orifice will take some time, during this time, the orifice particle velocity does not change, still maintain a stable discharge tube. It also reveals the riser nature of discharging stability problem is in fact a vertical pipe flow stability of particles changed, maintain a balance in order to overcome the particle distribution of gravity and particle wall steady friction dissipation Yet, the discharge quantity of particle flow volatility is the change of the results, the macro performance is vertical unstable flow tube. On this basis, the riser material height is defined as the critical to avoid the unstable flow column height corresponding to the key transition region when the change of initial void ratio. In depth study of the particles properties (such as particle density, particle friction coefficient) and design parameters of equipment (Kong Kou size) riser critical material column height on the basis of the construction of the riser constraint equation of stable operation, providing theoretical guidance for industrial design and control. In addition, the traditional standpipe method is used to simulate the discharge CFD-DEM coupling, complex calculation process. Aiming at this problem, the bulk material mechanics and the DEM model this paper proposed equivalent theory of gravity model, calculating the standpipe discharge conditions for the model. Through the material mechanics The optimization of gravity acceleration in DEM model does not require coupling of DEM and other fluid software. It achieves the effect of simplifying model and improving efficiency, and lays the foundation for further research on riser.

【学位授予单位】：中国科学院大学(中国科学院过程工程研究所)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TQ022

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