共查询到17条相似文献,搜索用时 171 毫秒
1.
2.
对于仓壁不固定的粮仓系统,其底部压力会随颗粒高度线性增加.由于没有Janssen应力饱和现象,其力学状态与通常粮仓系统显然不同.通过上拉和下压这种应力未饱和粮仓系统的仓壁,实验研究了不同顶部负载时颗粒介质与仓壁的最大静摩擦阻力.结果显示阻力随颗粒质量的增加在上拉时呈线性增长关系,但在下压时呈指数增长关系,下压阻力强度比上拉时大一个量级以上.此外阻力与顶部负载呈线性变化关系.这些测量很好地符合了基于应力转向比为常数的假设(即Janssen假设)下给出的连续力学理论计算,表明该假设对于此应力未饱和粮仓系统依然适用.
关键词:
颗粒物质
粮仓
静摩擦
应力转向比 相似文献
3.
4.
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
5.
6.
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
7.
实验研究了竖直振动颗粒床中颗粒对容器底部的压力随振动强度的变化情况.发现压力随振动加速度的增加经历倍周期分岔,典型的分岔序列为:2P,4P,混沌,3P,6P,混沌,4P,8P,混沌.观察表明,伴随倍周期分岔现象,在颗粒床底部出现颗粒的聚集态.聚集态内颗粒密堆积在一起并作整体的上下运动.采用完全非弹性蹦球模型分析了颗粒对容器底的冲击力,并给出了倍周期分岔现象的一种解释.
关键词:
颗粒物质
混沌
倍周期分岔
非弹性碰撞 相似文献
8.
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
9.
运用事件驱动算法研究颗粒混合物在垂直振动容器中的振荡现象.容器被具有一定高度的隔板分成相等大小的两个小室,并采用半径相差一倍的两种颗粒.研究结果表明,颗粒振荡周期随两种颗粒密度比的减少而急剧增加.通过计算在垂直方向上两种颗粒高度之比随颗粒密度的变化关系,说明决定颗粒振荡与否的主要因素并不是"巴西坚果效应"或"反巴西坚果效应".通过计算颗粒温度,发现颗粒振荡取决于颗粒混合气体的小颗粒温度.当小颗粒温度大于一定值时,颗粒混合气体发生颗粒振荡现象.根据Viridi等提出的流体动力学模型,文中对该模型做出相应的修改,加入密度因子,从而可以解释颗粒振荡周期与颗粒密度比的关系. 相似文献
10.
通过分子动力学模拟对聚乙烯/银纳米颗粒复合物的结构、极化率和红外光谱、热力学性质、力学特性进行计算, 分析其随模拟温度和银颗粒尺寸的变化规律. 模拟结果表明: 聚乙烯/银纳米颗粒复合物为各向同性的无定形结构, 温度升高可提高银纳米颗粒的分散均匀性; 银纳米颗粒表面多个原子层呈现无定形状态, 并在银颗粒和聚乙烯基体的界面形成电极化层, 界面区域随颗粒尺寸和温度的增加分别减小和增加; 与聚乙烯体系相比, 聚乙烯/银纳米颗粒复合物的极化率高很多, 且随温度的升高和银颗粒尺寸的减小而增大; 银颗粒尺寸直接影响界面电偶极矩的强度和振动频率, 红外光谱峰强度和峰位随颗粒尺寸发生变化; 聚乙烯/银纳米颗粒复合物具有比聚乙烯体系更高的等容热容和与聚乙烯体系相反的负值热压力系数, 热容随颗粒尺寸的变化较小, 但随温度的升高而明显减小, 具有显著的温度效应; 热压力系数随温度的变化较小, 但随颗粒尺寸的增加而减小, 具有明显的尺度效应, 温度稳定性更好; 聚乙烯/银纳米颗粒复合物的力学特性表现出各向同性材料的弹性常数张量, 具有比聚乙烯体系更高的杨氏模量和泊松比, 并且都随温度的升高和银颗粒尺寸的增大而减小, 加入银纳米颗粒可有效改善聚乙烯的力学性质.
关键词:
分子动力学模拟
聚合物纳米复合物
纳米颗粒 相似文献
11.
L. Vanel E. Clément 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(3):525-533
We report sets of precise and reproducible measurements on the static pressure at the bottom of a granular column. We make
a quantitative analysis of the pressure saturation when the column height is increased. We evidence a great sensitivity of
the measurements with the global packing fraction and the eventual presence of shear bands at the boundaries. We also show
the limit of the classical Janssen model and discuss these experimental results under the scope of recently proposed theoretical
frameworks.
Received 7 September 1998 and Received in final form 28 January 1999 相似文献
12.
The role played by the history of packing in the behaviour of a granular material confined in a column is studied experimentally. The mean pressure applied by the granular assembly to the base is measured as a function of the height of material poured in the column. We obtain reproducible mean vertical normal stress measurements without using a particular procedure to mobilise the wall friction. We focus on the influence of the filling method on the mean vertical normal stress. Filling the column via the edges induces a higher apparent mass of grain than filling it via the centre. Particular attention is devoted to the measurement of the effect of the force sensor stiffness. We show that the lower the base stiffness, the lower the mean pressure on the base. We also vary the packing fraction. We obtain an increasing relation between the apparent mass and the mean packing fraction, and show that this relation depends on the filling method.Received: 4 April 2004, Published online: 20 July 2004PACS:
45.70.Cc Static sandpiles; granular compaction - 81.05.Rm Porous materials; granular materials - 83.80.Fg Granular solidsM. Tixier: Mireille.Tixier@meca.uvsq.fr 相似文献
13.
Vanel L Claudin P Bouchaud J Cates ME Clement E Wittmer JP 《Physical review letters》2000,84(7):1439-1442
We present precise and reproducible mean pressure measurements at the bottom of a cylindrical granular column. If a constant overload is added, the pressure is linear in overload and nonmonotonic in the column height. The results are quantitatively consistent with a local, linear relation between stress components, as was recently proposed by some of us. They contradict the simplest classical (Janssen) approximation, and may rather severely test competing models. 相似文献
14.
We investigate the deflection and the fluctuation of
stresses due to different sizes of granular material in a
cylindrical column. It is experimentally observed that the
saturation mass systemically increases with granule diameter . The
results indicate the shielding of vertical stress in silo is
varying. We show that the ratio between the horizontal and the
vertical stresses, K, decreases with the increase in grainule
diameter D. In addition, it has also been found that the presence
of larger granules leads to stronger stress fluctuation on the
bottom plate of silo. 相似文献
15.
We have performed experiments on narrow granular columns to test
the validity of the Janssen law under such conditions.
The weight at the bottom of the cylinder and the compression and
movement of the packing have been measured.
The apparent mass dependence on height is not in good agreement with
the Janssen law using a one-parameter fit. A two-parameter fit
yielded good results for the apparent mass during upward and downward
movement at constant velocity of the granular column inside the
enclosing cylinder. The dependence of the apparent mass on the
diameter of the column does not follow the Janssen law. Rather, it
depends strongly on details of the packing.
A slow force relaxation was observed when stopping the translational stage
after upward motion. 相似文献
16.
17.
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