基于离散元的砌块振动成型密实过程的模拟与实验研究
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摘要
砌块成型机工作时,主要是采用振动成型。目前砌块成型机散粒物料振动研究和设计的方法主要有两种,一种是基于连续介质力学而建立的设计理论和设计方法,但该理论和方法把散粒群体作为整体来考虑,所以不能很好地解决振动成型的设计问题。另一种是依靠经验或试验的方法,但该方法既费时费力又很难达到理想的设计效果。本研究首次利用离散元方法对振动成型工艺中粒群密实过程进行了计算机模拟。
20世纪70年代,Cundall等提出离散元法,其基本思想是把散粒群体简化成具有一定形状和质量颗粒的集合,赋予接触颗粒间及颗粒与接触边界间某种接触力学模型和模型中的参数,以考虑颗粒之间及颗粒与边界间的接触作用和颗粒与边界的不同物理机械性质。离散元法采用动态松弛法、牛顿第二定律和时步迭代求解每个颗粒的运动和位移,因而特别适合于求解非线性问题。正是由于诸多优点,使得离散元法已成为研究散粒群体动力学问题的一种通用方法,并在岩土工程与风沙流动,散粒物料的输送、混合、分级,颗粒的结块与碰撞,土壤与机械的相互作用,化工过程装备和矿山装备等研究领域得到广泛应用。
本文介绍了离散单元法的基本原理,着重讨论了球颗粒体接触时的接触力的计算,分别讨论无粘连力时两颗粒体法向和切向接触力的计算。对于离散元法计算中参数的选择及其对计算的影响也作了探讨。文中较详细地介绍了所引入的干颗粒离散元程序总体结构、编程思想,及数据存储、迭代计算、时步的确定等,以使读者对离散元法的实现过程有进一步的了解。
利用并开发PFC2D离散元软件对振动过程中粒群孔隙度的变化情况进行了试验研究,揭示了振动条件下孔隙度变化的规律,探讨了颗粒摩擦系数、颗粒粒径、振动源频率和振幅对孔隙度变化的影响。结果表明孔隙度与摩擦系数成正比,与颗粒粒径成反比;振幅与孔隙度变化呈二次曲线关系;采用高频振动有助于减小孔隙度变化的波动。研究结果对于合理设计振动参数,对提高机制砌块生产质量有一定参考价值。
Vibration is the main production mode used in this block forming progress.The research and design of block-making machine mainly has two kinds of methods. One is the design method and theory based on the continuum mechanics method, but it considers granular particles as a continuous whole, as a result it can not analyze the movement process of every particle and interactions between particles, so it can not solve problems existing during designing seed-metering device well. Another method is according to the experience and trial, whereas usually it is not only time-consuming but also strenuous without ideal results. A computer simulation of compacting process in vibration molding has been performed through distinct element method (DEM) for the first time.
In seventies of the 20th century, Cundall et al. put forward the DEM primarily. The basic thought is to simplify granular colony as a set of particles with a certain kind of shape and mass, and endues the particle-particle and particle-boundary relationship with a certain kind of contact mechanics model and some parameters. The DEM is applied to research the contact effects, which influence the particle-particle and particle-boundary relationship, and the different physical and mechanical characteristics between particle and contacted boundary. The dynamic laxity method, the Newton's Second Law and time step iteration are introduced in DEM to calculate the movement and displacement of each particle, and thus it is especially compatible to resolve the nonlinear problem. Because of these virtues mentioned above, DEM has become a popular method on studying the kinetic problem of granular colony, and it is widely applied in the field of rock engineering and sands flowing; the transportation, mixing, classification of granular materials; the agglomeration and collision of granular materials; the interaction between granular materials and related mechanical parts; the equipment of chemical industry and mine engineering.
The fundamental principle of DEM is introduced in this paper, and the calculation of normal or tangential contact force without adhesion between sphere particles is discussed. The reasonable parameters in DEM and its affection to calculation precision are discussed at the same time. For readers to understand the realization of DEM more clearly, the DEM program which will be adapted in the paper is introduced in detail in aspect of general structure, programming thinking, data restoring, iterated calculation, and the calculation of time step.
The simulation of the vibrating process is done by the discrete element method analysis software- PFC2D. The change of porosity in the process of vibration of granule groups is studied and the change law is revealed. The effect of four aspects is also discussed, which are friction coefficient of granular, particle size, vibration frequency and amplitude. The porosity is positively related to friction coefficient of granular and negatively correlated to particle size. Quadric curve can be used to model the relationship between vibration amplitude and porosity. The fluctuation of change of porosity can be decreased by choosing higher vibration frequency. These research results possess a certain reference value to the design of vibration parameters and improve the quality of building block.
20世纪70年代,Cundall等提出离散元法,其基本思想是把散粒群体简化成具有一定形状和质量颗粒的集合,赋予接触颗粒间及颗粒与接触边界间某种接触力学模型和模型中的参数,以考虑颗粒之间及颗粒与边界间的接触作用和颗粒与边界的不同物理机械性质。离散元法采用动态松弛法、牛顿第二定律和时步迭代求解每个颗粒的运动和位移,因而特别适合于求解非线性问题。正是由于诸多优点,使得离散元法已成为研究散粒群体动力学问题的一种通用方法,并在岩土工程与风沙流动,散粒物料的输送、混合、分级,颗粒的结块与碰撞,土壤与机械的相互作用,化工过程装备和矿山装备等研究领域得到广泛应用。
本文介绍了离散单元法的基本原理,着重讨论了球颗粒体接触时的接触力的计算,分别讨论无粘连力时两颗粒体法向和切向接触力的计算。对于离散元法计算中参数的选择及其对计算的影响也作了探讨。文中较详细地介绍了所引入的干颗粒离散元程序总体结构、编程思想,及数据存储、迭代计算、时步的确定等,以使读者对离散元法的实现过程有进一步的了解。
利用并开发PFC2D离散元软件对振动过程中粒群孔隙度的变化情况进行了试验研究,揭示了振动条件下孔隙度变化的规律,探讨了颗粒摩擦系数、颗粒粒径、振动源频率和振幅对孔隙度变化的影响。结果表明孔隙度与摩擦系数成正比,与颗粒粒径成反比;振幅与孔隙度变化呈二次曲线关系;采用高频振动有助于减小孔隙度变化的波动。研究结果对于合理设计振动参数,对提高机制砌块生产质量有一定参考价值。
Vibration is the main production mode used in this block forming progress.The research and design of block-making machine mainly has two kinds of methods. One is the design method and theory based on the continuum mechanics method, but it considers granular particles as a continuous whole, as a result it can not analyze the movement process of every particle and interactions between particles, so it can not solve problems existing during designing seed-metering device well. Another method is according to the experience and trial, whereas usually it is not only time-consuming but also strenuous without ideal results. A computer simulation of compacting process in vibration molding has been performed through distinct element method (DEM) for the first time.
In seventies of the 20th century, Cundall et al. put forward the DEM primarily. The basic thought is to simplify granular colony as a set of particles with a certain kind of shape and mass, and endues the particle-particle and particle-boundary relationship with a certain kind of contact mechanics model and some parameters. The DEM is applied to research the contact effects, which influence the particle-particle and particle-boundary relationship, and the different physical and mechanical characteristics between particle and contacted boundary. The dynamic laxity method, the Newton's Second Law and time step iteration are introduced in DEM to calculate the movement and displacement of each particle, and thus it is especially compatible to resolve the nonlinear problem. Because of these virtues mentioned above, DEM has become a popular method on studying the kinetic problem of granular colony, and it is widely applied in the field of rock engineering and sands flowing; the transportation, mixing, classification of granular materials; the agglomeration and collision of granular materials; the interaction between granular materials and related mechanical parts; the equipment of chemical industry and mine engineering.
The fundamental principle of DEM is introduced in this paper, and the calculation of normal or tangential contact force without adhesion between sphere particles is discussed. The reasonable parameters in DEM and its affection to calculation precision are discussed at the same time. For readers to understand the realization of DEM more clearly, the DEM program which will be adapted in the paper is introduced in detail in aspect of general structure, programming thinking, data restoring, iterated calculation, and the calculation of time step.
The simulation of the vibrating process is done by the discrete element method analysis software- PFC2D. The change of porosity in the process of vibration of granule groups is studied and the change law is revealed. The effect of four aspects is also discussed, which are friction coefficient of granular, particle size, vibration frequency and amplitude. The porosity is positively related to friction coefficient of granular and negatively correlated to particle size. Quadric curve can be used to model the relationship between vibration amplitude and porosity. The fluctuation of change of porosity can be decreased by choosing higher vibration frequency. These research results possess a certain reference value to the design of vibration parameters and improve the quality of building block.
引文
[1]张明莉.振动技术在砌块成型机中的应用,建筑机械,2005(1):102-103.
[2]Cundall P A,Strack O L.A discrete numerical model for granular assembles.Geotechnique,1979,29(1):47-65.
[3]Thornton C.A direct approach to micromechanically based continuum models for granular material.In Satake M,eds.Mechanics of Granular Material.Japanese SMFE society,1989:145-150.
[4]魏群.散体单元法的基本原理数值方法及程序,科学出版社,1991:8-16.
[5]李艳洁,徐泳.用离散元模拟颗粒堆积问题,农机化研究,2005(2):57-59.
[6]付宏,董劲男,于建群.基于CAD模型的离散元法边界建模方法,吉林大学学报(工学版),2005(6):626-631.
[7]赵跃民,张曙光,焦红光.振动平面上粒群运动的离散元模拟,中国矿业大学学报,2006(9):586-590.
[8]Cundall P A,Hart R D.Development of generalized 2-D and 3-D discrete element programs for modeling jointed rock.ITASCA Consulting Group,Misc.Paper SL 28521,U.S.Army Corps of Engineers,1985.
[9]UDEC news and world report,Official Publication of the UDEC Users Group,ITASCA Consulting Group,Inc.,1985.
[10]User' s Manual of FLAC,ITA SCA Consulting Group,Inc.,1987.
[11]Coetzee M J,etc.FLAC BASICS,ITASCA Consulting Group,Inc.,1993.
[12]Cundall P A,Strack O L.Particle flow code in dimensions.Itasca Consulting Group,Inc.,1999.
[13]Mishra B K,Murty C V R.On the determination of contact parameters for realistic DEM simulation of ball mills.Powder Technol.,2001,115:290-297.
[14]Tsuji Y,Tanaka T,Ishida T.Lagrangian simulation of plug flow of cohesionless particles ina horizontal pipe.Powder Technol.,1992,71: 239-250.
[15]王泳嘉,宋文洲,赵艳娟.离散单元法软件系统 2D-Block的现代化特点.岩石力学与工程学报.2000,19(增):1057-1060.
[16]吴爱祥,孙业志,刘湘平.散体动力学理论及其应用,北京:冶金工业出版社2002:5-10.
[17]H.Kruggel-Emden,E.Simsek,S.Rickelt,etc.Review and extension of normal force modelsfor the Discrete Element Method,Powder Technology,2007(171),157-173.
[18]王泳嘉,邢纪波.离散元法及其在岩土力学中的应用.辽宁:东北工学院出版社,1991:60-89.
[19]Vemuri B C,Chen l,Vu-Quou L,et al.Efficient and accurate collision detection for granular flow simulation.Graphical Models and Image Processing,1998,60:403-422.
[20]徐泳,孙其诚,张凌.颗粒离散元法研究进展,力学进展,2003(2):251-260.
[21]刘凯欣,高凌天.离散元法在求解三维冲击动力学问题中的应用,固体力学学报,2004(6):181-185.
[22]周健,池永.颗粒流方法及PFC2D程序,岩土力学,2000(9):271-274.
[23]姜泽辉,陆坤权,厚美瑛.振动颗粒混合物中的三明治式分离,物理学报,2003(9):2244-2248.
[24]金建交,杨世春,何根旺.砌块成型机的振动对砌块密实度的影响,机械下程与自动化,2006(1):49-52.
[25]陶为农.超声波法在检测配筋砌体灌芯混凝土密实度中的应用,建筑砌块与砌块建筑,2004(2):17-18.
[26]杨鼎宜,刘平,李琪.应用振动挤压成型工艺生产混凝土空心砌块,混凝土与水泥制品,1998(5):52-54.
[27]吴清松,胡茂彬.颗粒流的动力学模型和实验研究进展,2002(2):250-258.
[28]苑金生.国外混凝土砌块生产设备及发展趋势,中国建筑机械设备,1996(6):41-42.
[29]贾妍,侯书军.振动作用下粘性颗粒动力学行为的实验研究,安徽化工,2005 (3):41-42.
[30]徐茂辉,谢慧才,混凝土密实度的雷达检测方法,四川建筑科学研究,2005(4):100-103.
[31]焦玉勇,葛修润,谷先荣.三维离散元法中的数据结构,岩土力学,1998(19):74-79
[32]姜泽辉,李斌,赵海发.竖直振动颗粒物厚层中冲击力分岔现象,物理学报,2005(3):1273-1278.
[33]张翠兵,邓志勇.抛石散体振动密实过程的离散元数值模拟,岩石力学与工程学报,2004(1):95-100.
[34]P.Van Liedekerke,E.Tijskens,E.Dintwa.A discrete element model for simulation of a spinning discfertilizer spreader I.Single particle simulations,Powder Technology,2005(170):72-85.
[35]J.Theuerkauf,P.Witt,D.Schwesig.Analysis of particle porosity distribution in fixed beds using the discrete element method,Powder Technology,2006(165):92-99.
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[53]付留根,张明莉.砌块成型的振动特点,设计&制造,2004(4):82-83.
[2]Cundall P A,Strack O L.A discrete numerical model for granular assembles.Geotechnique,1979,29(1):47-65.
[3]Thornton C.A direct approach to micromechanically based continuum models for granular material.In Satake M,eds.Mechanics of Granular Material.Japanese SMFE society,1989:145-150.
[4]魏群.散体单元法的基本原理数值方法及程序,科学出版社,1991:8-16.
[5]李艳洁,徐泳.用离散元模拟颗粒堆积问题,农机化研究,2005(2):57-59.
[6]付宏,董劲男,于建群.基于CAD模型的离散元法边界建模方法,吉林大学学报(工学版),2005(6):626-631.
[7]赵跃民,张曙光,焦红光.振动平面上粒群运动的离散元模拟,中国矿业大学学报,2006(9):586-590.
[8]Cundall P A,Hart R D.Development of generalized 2-D and 3-D discrete element programs for modeling jointed rock.ITASCA Consulting Group,Misc.Paper SL 28521,U.S.Army Corps of Engineers,1985.
[9]UDEC news and world report,Official Publication of the UDEC Users Group,ITASCA Consulting Group,Inc.,1985.
[10]User' s Manual of FLAC,ITA SCA Consulting Group,Inc.,1987.
[11]Coetzee M J,etc.FLAC BASICS,ITASCA Consulting Group,Inc.,1993.
[12]Cundall P A,Strack O L.Particle flow code in dimensions.Itasca Consulting Group,Inc.,1999.
[13]Mishra B K,Murty C V R.On the determination of contact parameters for realistic DEM simulation of ball mills.Powder Technol.,2001,115:290-297.
[14]Tsuji Y,Tanaka T,Ishida T.Lagrangian simulation of plug flow of cohesionless particles ina horizontal pipe.Powder Technol.,1992,71: 239-250.
[15]王泳嘉,宋文洲,赵艳娟.离散单元法软件系统 2D-Block的现代化特点.岩石力学与工程学报.2000,19(增):1057-1060.
[16]吴爱祥,孙业志,刘湘平.散体动力学理论及其应用,北京:冶金工业出版社2002:5-10.
[17]H.Kruggel-Emden,E.Simsek,S.Rickelt,etc.Review and extension of normal force modelsfor the Discrete Element Method,Powder Technology,2007(171),157-173.
[18]王泳嘉,邢纪波.离散元法及其在岩土力学中的应用.辽宁:东北工学院出版社,1991:60-89.
[19]Vemuri B C,Chen l,Vu-Quou L,et al.Efficient and accurate collision detection for granular flow simulation.Graphical Models and Image Processing,1998,60:403-422.
[20]徐泳,孙其诚,张凌.颗粒离散元法研究进展,力学进展,2003(2):251-260.
[21]刘凯欣,高凌天.离散元法在求解三维冲击动力学问题中的应用,固体力学学报,2004(6):181-185.
[22]周健,池永.颗粒流方法及PFC2D程序,岩土力学,2000(9):271-274.
[23]姜泽辉,陆坤权,厚美瑛.振动颗粒混合物中的三明治式分离,物理学报,2003(9):2244-2248.
[24]金建交,杨世春,何根旺.砌块成型机的振动对砌块密实度的影响,机械下程与自动化,2006(1):49-52.
[25]陶为农.超声波法在检测配筋砌体灌芯混凝土密实度中的应用,建筑砌块与砌块建筑,2004(2):17-18.
[26]杨鼎宜,刘平,李琪.应用振动挤压成型工艺生产混凝土空心砌块,混凝土与水泥制品,1998(5):52-54.
[27]吴清松,胡茂彬.颗粒流的动力学模型和实验研究进展,2002(2):250-258.
[28]苑金生.国外混凝土砌块生产设备及发展趋势,中国建筑机械设备,1996(6):41-42.
[29]贾妍,侯书军.振动作用下粘性颗粒动力学行为的实验研究,安徽化工,2005 (3):41-42.
[30]徐茂辉,谢慧才,混凝土密实度的雷达检测方法,四川建筑科学研究,2005(4):100-103.
[31]焦玉勇,葛修润,谷先荣.三维离散元法中的数据结构,岩土力学,1998(19):74-79
[32]姜泽辉,李斌,赵海发.竖直振动颗粒物厚层中冲击力分岔现象,物理学报,2005(3):1273-1278.
[33]张翠兵,邓志勇.抛石散体振动密实过程的离散元数值模拟,岩石力学与工程学报,2004(1):95-100.
[34]P.Van Liedekerke,E.Tijskens,E.Dintwa.A discrete element model for simulation of a spinning discfertilizer spreader I.Single particle simulations,Powder Technology,2005(170):72-85.
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