共查询到16条相似文献,搜索用时 171 毫秒
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随着深度的增加竖直圆筒容器中的颗粒物质会把自己的重量逐渐转移到容器的侧墙壁上,使容器底部的压力出现不随筒中颗粒材料高度的增加而增加的饱和现象.但值得注意的是,圆筒中的颗粒柱体并不总是表现为这个称为粮仓效应的力学状态.例如当改变侧墙壁的力学环境使其无法承担颗粒的重量时,柱底部的压力显然将随其高度的增加而线性地增加.本文分析讨论了Janssen模型假设对这类处于静力平衡下,但违反粮仓效应的颗粒系统的行为预测.
关键词:
颗粒物质
粮仓
静摩擦
应力 相似文献
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基于侧壁分为上下两部分的装置,测量了圆柱对称颗粒系统(竖直粮仓)的压力随高度的变化,并讨论了测得的仓内压力与Janssen理论模型的偏离情况.实验结果显示无论是否对粮仓进行Vanel等建议的让"侧壁摩擦力充分动员"的底座缓慢下沉操作处理,测得的仓内压力都有不同程度的偏离Janssen现象.另外如果没有沉降处理,在填充颗粒的荷载下上侧壁会发生微弱下沉,从而显著增大压力偏离的程度,但沉降处理可将其消除.这些结果表明,粮仓的颗粒重量在仓底和沿侧壁边界上的分配情况受制备方式和装置变形的影响明显,具体分布情况复杂多样.因此颗粒物质的静应力弹性理论分析应该取应力边界条件. 相似文献
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为了便于从理论上探究粮仓效应产生的机理,处理筒仓中颗粒介质的应力分布等问题,将二维颗粒堆积简化为格点系统,并且以随机堆积为物理背景提出了一个由吸收系数p及侧向传递系数q决定的力传递模型.给出了矩阵形式的力传递方程,提出基于二阶差分方程的方法同时求解传递系数矩阵的特征值和特征向量,从理论上导出了一种典型情况下容器底部压力分布与顶部压力分布的关系式.对有效质量随总质量变化关系的理论分析表明,该模型可以给出与Janssen模型类似的结果.对无负载情况下的底部应力分布进行了理论计算,结果表明容器底部中央应力最大,离中央越远应力越小.运用数值计算讨论了p与q对容器底部压力随堆积高度变化曲线的影响. 相似文献
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报导了不同尺寸的大球缓慢压入颗粒床过程中所受阻力随深度变化的实验测量结果,发现阻力曲线在不同的深度区域有不同的增长规律,存在凹—凸转变.阻力在较浅的区域满足1.3次方的幂率增长,而在较深的区域趋向0.3次方的幂率增长.通过研究凹凸转变中拐点的性质,发现这种阻力增长速度趋缓的转变不是来源于前人认为的器壁支撑导致的介质压强饱和,而是来源于侵入物自身的体积效应.此外,适用于颗粒介质快速阻力的静水压力描述并不适用于阻塞态颗粒介质的慢速阻力行为,实验表明慢速阻力对深度的依赖关系不是线性,且测得的静水压力系数也远大于理论估算值.
关键词:
颗粒介质
阻力
力链重组 相似文献
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颗粒物质是大量颗粒聚集在一起的软凝聚态物质, 其微观结构与宏观力学性质的联系非常复杂. 本文用实验的方法观测了二维竖直晶格堆积颗粒, 在竖直方向外加正压力作用下其侧壁的受力分布情况, 根据实验结果详细讨论和分析了颗粒体系中正压力的转向行为. 实验结果表明: 在缓慢压缩颗粒体系的过程中, 正压力的变化呈现非线性和线性两段不同的规律; 对于确定堆积结构的颗粒体系, 竖直方向施加的正压力通过颗粒力链转向, 且水平方向不同堆积高度处所受压力值不同, 中部的压力大于顶部和底部的压力; 转向系数k的饱和值随堆积角θ 的增大而减小. 对颗粒堆的几何结构与受力情况进行分析, 给出了转向系数与堆积角之间的数学表达式, 理论值与实验值符合较好. 相似文献
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回顾了颗粒介质中应力的分布和传播模式以及物体在颗粒介质中运动所受阻力的研究进展,并报道了我们对颗粒体系中代表离散特性的颗粒尺寸效应对颗粒介质特性影响的研究.研究发现物体由于自身重量在颗粒介质中下沉的深度随着颗粒尺寸的增大单调减小;球体在下陷过程中受到的颗粒床的支撑力,除了在约1 mm范围的表面作用区域以外,与下陷深度之间满足很好的幂率关系,幂值在1.5—1.0之间,并且此幂值随着颗粒尺寸的增大而单调减小.颗粒床的支撑力与下陷深度的幂率关系可解释为颗粒介质内部应力结构重组的宏观反应结果.
关键词:
颗粒物质
离散介质力学 相似文献
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A. Qadir H. Guo X. Liang Q. Shi G. Sun 《The European physical journal. E, Soft matter》2010,31(3):311-314
We present the apparent mass measurements at the bottom of granular packings for different bead and silo sizes. The redirection
parameter K in Janssen theory is found to increase with the ratios of the diameter of the silo to the bead. We attribute this feature
to the friction between the beads and the confining wall of silo; it is the role of friction that leads to variations in the
shielding of vertical stresses as well as pressure screening. 相似文献
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J. F. Wambaugh R. R. Hartley R. P. Behringer 《The European physical journal. E, Soft matter》2010,32(2):135-145
We have made experimental observations of the force networks within a two-dimensional granular silo similar to the classical
system of Janssen. Models like that of Janssen predict that pressure within a silo saturates with depth as the result of vertical
forces being redirected to the walls of the silo where they can then be carried by friction. We use photoelastic particles
to obtain information not available in previous silo experiments --the internal force structure. We directly compare various
predictions with the results obtained by averaging ensembles of experimentally obtained force networks. We identify several
differences between the mean behavior in our system and that predicted by Janssen-like models: We find that the redirection
parameter describing how the force network transfers vertical forces to the walls varies with depth. We find that changes
in the preparation of the material can cause the pressure within the silo to either saturate or to continue building with
depth. Most strikingly, we observe a nonlinear response to overloads applied to the top of the material in the silo. For larger
overloads we observe the previously reported “giant overshoot” effect where overload pressure decays only after an initial
increase (G. Ovarlez et al., Phys. Rev. E 67, 060302(R) (2003)). For smaller overloads we find that additional pressure propagates to great depth. Analysis of the differences
between the inter-grain contact and force networks suggests that, for our system, when the load and the particle weight are
comparable, particle elasticity acts to stabilize the force network, allowing deep propagation. For larger loads, the force
network rearranges, resulting in the expected, Janssen-like behavior. Thus, a meso-scale network phenomenon results in an
observable nonlinearity in the mean pressure profile. 相似文献
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《中国物理 B》2021,30(6):64205-064205
We investigate optical force on a graphene-coated gain microparticle by adopting the Maxwell's stress tensor method.It is found that there exists a threshold gain in obtaining the Fano-profile optical force which indicates the reversal of optical pushing and pulling force. And giant pushing/pulling force can be achieved if the gain value of the material is in the proximity of the threshold gain. Our results show that the threshold gain is more sensitive to the relaxation time than to the Fermi energy of the graphene. We further study the optical force on larger microparticle to demonstrate the pulling force occurring at octupole resonance with small gain value and then it will appear at quadrupole resonance by increasing gain value. Our work provides an in-depth insight into the interaction between light and gain material and gives the additional degree of freedom to optical manipulation of microparticle. 相似文献
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The wall stresses and insert load in a two‐dimensional flat‐bottomed bin with a flow corrective insert were investigated. The static wall stress distributions produced by the granular solids were measured and compared with the theoretical prediction using the differential slice method. The variations in the dynamic wall stresses and the dynamic response of the insert load with time were obtained. The comparison of the experimental insert load to the theoretical prediction was demonstrated. In addition, the effect of the flow corrective insert upon the wall stress and insert load was investigated. As the insert half‐angle increases, the effect of disrupting the contact force network above the insert decreases, and the insert load produced by the granular solids increases. Employing the results obtained using stress measurements, the pulsation phenomena of wall stress and insert load in a bin with a triangle flow corrective insert may be further understood. 相似文献
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Pacheco-Vázquez F Caballero-Robledo GA Solano-Altamirano JM Altshuler E Batista-Leyva AJ Ruiz-Suárez JC 《Physical review letters》2011,106(21):218001
An object falling in a fluid reaches a terminal velocity when the drag force and its weight are balanced. Contrastingly, an object impacting into a granular medium rapidly dissipates all its energy and comes to rest always at a shallow depth. Here we study, experimentally and theoretically, the penetration dynamics of a projectile in a very long silo filled with expanded polystyrene particles. We discovered that, above a critical mass, the projectile reaches a terminal velocity and, therefore, an endless penetration. 相似文献