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颗粒物质(上) 总被引:57,自引:0,他引:57
颗粒物质是地球上存在最多、最为人们所熟悉的物质类型之一.大量颗粒组成的离散态物质体系具有特别的性质和运动规律.颗粒物质表现出许多不同于固、液、气物质的奇特现象和独特的运动规律.由于对颗粒物质运动规律的理解具有重要科学意义和应用背景,近十年来颗粒物质研究逐步成为物理学研究中的一个活跃领域.文章综述了颗粒物质的一些主要特性,如颗粒物质的静态性质、振动行为、流动特性等,其中也包括文章作者的一些新近研究结果.限于篇幅,文章分为上、下两部分发表.第一部分在对颗粒物质作一般介绍后讨论颗粒物质的静态特性,第二部分则主要讨论颗粒物质振动时的行为和流动性质. 相似文献
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针对颗粒介质力学特性的颗粒尺度效应研究,选用土矿物颗粒制备不同颗粒尺度的抗剪试样,进行一系列直剪快剪和三轴抗剪试验,测得了不同颗粒粒径和体分比试样的变形曲线及剪应力强度;基于颗粒间微观作用力与重力比值和胞元体模型,首次从微观和细观角度解释颗粒尺度效应的物理机理.结果表明,随着介质中粗颗粒的比例增加和粒径减小,介质变形特性增强,剪应力强度也随之提高;体分比对变形和强度特性的影响比粒径的影响更加显著.基于介质特性尺度效应物理机理分析,提出衡量介质颗粒聚集和摩擦效应的微重比判别参数以及应变梯度和变形协调微裂纹引起颗粒尺度效应的细观机理解释;文中提出的胞元体模型大大减少了颗粒物质体系的计算自由度,为工业和工程设计的计算建模提供一种可行途径. 相似文献
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在对垂直振动下的铜颗粒和氧化铝颗粒混合物的研究中,除了观测到巴西果分层和混合分层外,还发现了一种新的随时间周期变化的分离形态. 此分离形态可随着时间的演化,在巴西果、反巴西果和三明治这几种分层构型之间进行动态的循环反转. 给出了这种反转态出现的相区,并且观测了其动态转变的规律. 根据碰撞、磨擦及空气的耗散作用所产生的耗散结构对循环反转态的出现给出了定性的解释,并通过实验证实这种分层构型与空气的存在有密切的关系.
关键词:
颗粒物质
巴西果效应
相分离 相似文献
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颗粒物质是由众多离散颗粒组成的软凝聚态物质,涉及多个物理层次结构和机制,是多尺度问题. 首先阐述了颗粒物质多尺度力学的研究框架,指出颗粒间接触力链构成的细观尺度是核心,颗粒物质显示出的独特静态堆积特性和动态流变特性都与细观尺度力链的复杂演变规律直接相关. 围绕着定量描述力链特征这一目标,采用严格的球形颗粒Hertz法向接触理论和Mindlin-Deresiewicz切向接触理论,对重力作用下12000个球心共面的二维等径颗粒静态堆积进行了离散动力学模拟,对力链分布特征、接触力规律等做了量化分析,考察了颗粒
关键词:
颗粒物质
力链
离散模型
多尺度力学 相似文献
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在竖直振动两种颗粒的混合物的实验中,观察到了一种新的分离现象——“三明治”式分离,即大而重的颗粒被夹在两层小的轻颗粒之间.这不同于“巴西果”效应导致的大而重的颗粒在上的两层有序结构.实验表明当振动加速度大于某个临界值时这种三层有序将取代两层结构,而且是稳定的.实验中观察到导致“三明治”式分离的两种不同的分离过程.对这两种过程的物理机理及其与振动加速度、振动频率及颗粒尺寸等因素的关系做了研究,并给出了相图.
关键词:
颗粒物质
振动
有序结构
三明治式分离
巴西果效应 相似文献
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《Physica A》2002,303(1-2):48-56
We considered a flow of a cohesionless granular material in a partially filled three-dimensional rotating container. A variational continuum mechanics model is suggested to describe the profile of the free surface of the granular material. A combination of a level set method and a variational form of energy conservation equation allows us to describe flow of granular material in arbitrary-shaped containers. 相似文献
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在冲击荷载作用下, 颗粒材料通过颗粒间的摩擦及非弹性碰撞可有效进行能量耗散实现缓冲作用. 本文采用离散元方法对冲击载荷下颗粒材料的缓冲过程进行数值分析, 研究不同厚度下颗粒材料的缓冲性能. 计算结果表明: 颗粒层厚度H是影响颗粒材料缓冲性能的关键因素, 并存在一个临界厚度Hc. 当H < Hc时, 冲击力随H的增加而降低; 当H > Hc时, 冲击力对H的变化不敏感并趋于稳定值. 此外, 在不同颗粒摩擦系数和初始密集度下对缓冲过程的离散元分析表明, 光滑和疏松颗粒材料具有更好的缓冲性能. 最后, 对颗粒材料在冲击过程中的力链结构和底板的压力分布进行了讨论, 以揭示颗粒材料缓冲性能的内在机理. 相似文献
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Numerical simulation of two-dimensional granular shearing flows and the friction force of a moving slab on the granular media 下载免费PDF全文
This paper studies some interesting features of two-dimensional granular shearing flow by using molecular dynamic approach for a specific granular system.The obtained results show that the probability distribution function of velocities of particles is Gaussian at the central part,but diverts from Gaussian distribution nearby the wall.The macroscopic stress along the vertical direction has large fluctuation around a constant value,the non-zero average velocity occurs mainly near the moving wall,which forms a shearing zone.In the shearing movement,the volume of the granular material behaves in a random manner.The equivalent friction coefficient between moving slab and granular material correlates with the moving speed at low velocity,and approaches constant as the velocity is large enough. 相似文献
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Granular materials have been conventionally used for acoustic treatment due to their sound absorptive and sound insulating properties. An emerging field is the study of the acoustical properties of multiscale porous materials. An example of these is a granular material in which the particles are porous. In this paper, analytical and hybrid analytical-numerical models describing the acoustical properties of these materials are introduced. Image processing techniques have been employed to estimate characteristic dimensions of the materials. The model predictions are compared with measurements on expanded perlite and activated carbon showing satisfactory agreement. It is concluded that a double porosity granular material exhibits greater low-frequency sound absorption at reduced weight compared to a solid-grain granular material with similar mesoscopic characteristics. 相似文献
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《中国物理快报》2020,(7)
The evolution of energy in subaerial and subaqueous granular column collapses is studied.Employing the refractive index matching method and planar laser-induced fluorescence technique,we obtain granular and liquid images simultaneously in a single experiment of subaqueous flow.Particle image velocimetry and particle tracking velocimetry are used to process the data for the fluid and granular phase.We find stepwise decreases in the total kinetic energy of the granular material.The stage of rapidly falling energy corresponds to large transverse changes in the direction of the massive granular particles.Moreover,in this stage,a major fraction of the granular kinetic energy transferred from the granular potential energy is lost or transferred.Interestingly,compared with dry granular flow,the existence of an ambient liquid seems to reduce the total dissipated energy,which may be the reason why previous studies observed similar granular runout distances in subaqueous and dry granular collapses. 相似文献
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Sergiu C. Dragomir Mathew D. Sinnott S. Eren Semercigil Özden F. Turan 《Journal of sound and vibration》2014
Tuned vibration absorbers may improve the safety of flexible structures which are prone to excessive oscillation magnitudes under dynamic loads. A novel absorber design proposes sloshing of granular material in a rotating cylinder where the granular material is the energy dissipating agent. As the conventional dissipative elements require maintenance due to the nature of their function, the new design may represent a virtually maintenance free alternative. 相似文献
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Granular material is a collection of macroscopic particles that are visible with naked eyes. The non-equilibrium nature of
the granular materials makes their rheology quite different from that of molecular systems. In this minireview, we present
the unique features of granular materials focusing on the shear flow of dry granular materials and granule-liquid mixture. 相似文献
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Hong J 《Physical review letters》2005,94(10):108001
Protecting a big impulse from outside is one of the important issues of our everyday life. A granular medium is often used as a protecting material. The impulse inside a granular medium is a solitary wave which may be confined temporarily to a particular region of the medium, which we call the granular container that plays the role of the protector. We find a universal power-law behavior in time for the leakage of the impulse energy confined inside various granular containers. 相似文献