共查询到20条相似文献,搜索用时 140 毫秒
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颗粒物质由离散的固体颗粒组成, 受到周期性振动时可以表现出复杂的动力学行为. 这些行为往往受众多因素的影响, 如空气阻力和器壁摩擦力等. 针对受振颗粒体系中冲击力的倍周期分岔现象, 通过抽真空或将容器底镂空消除空气阻力, 单独研究器壁滑动摩擦力的影响. 结果表明在仅有器壁摩擦力作用的情况下, 倍周期分岔过程仅受约化振动加速度的控制, 与颗粒的尺寸、颗粒层数及振动频率无关. 将器壁摩擦力处理成一个大小恒定、方向与颗粒和器壁相对速度反向的阻力, 并包含到完全非弹性蹦球模型中, 能够对所观察到的现象给出很好的解释. 通过对倍周期分岔点测量平均值的拟合, 得到器壁滑动摩擦力的大小约为颗粒总重量的10%.
关键词:
颗粒物质
器壁摩擦力
倍周期分岔
冲击力 相似文献
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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
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实验研究了竖直振动情况下,窄容器中颗粒的运动模式.发现运动模式与颗粒床厚度及振动加速度有很强的依赖关系.实验表明横向尺寸较小的容器可以抑制对流卷及拱起现象.对于足够厚的颗粒床,即使振动加速度很大,颗粒床下部仍然存在着颗粒聚集态.出现聚集态时,颗粒床对容器底的冲击力是倍周期分岔的.实验表明倍周期分岔点与颗粒床厚度无关.对于较薄的颗粒床,颗粒可以是聚集态或对流卷,视颗粒尺寸而定.如果使用尺寸分布非常窄的球形颗粒,可以观察到颗粒的有序排列.出现同心的圆筒形“壳”结构,每个“壳”上的颗粒是二维六角密排列的.
关键词:
颗粒物质
倍周期分岔
颗粒聚集态
球堆积 相似文献
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实验研究了竖直振动颗粒床中,倍周期运动对尺寸分离的影响.实验中,当振动加速度足够大时,系统中出现稳定的对称对流,进一步增大振动加速度到某个临界值时,还会出现倍周期运动.观察表明,背景颗粒的对流运动对分离过程起主导作用,对流速度决定着分离过程的快慢,而在2倍周期和4倍周期分岔之后,分离时间有所减慢.对引起对流运动的起因进行了分析,以此为基础分析了倍周期运动产生影响的物理机理,并对分离时间进行了定量计算,结果与实验值符合很好.
关键词:
颗粒物质
“巴西果”效应
倍周期分岔
对流 相似文献
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A. V. Popov 《Russian Physics Journal》2005,48(9):947-953
Equations of fractal motion of electrons with variable weak memory and nonlocality are investigated. It is demonstrated that
the fractal dimension of time changes by a harmonic law for stationary electron motion. The fractal nonlocality has been established
for the free electron; it also changes by a harmonic law. The fractal nonlocality of the electron bound with the hydrogen
atom nucleus differs radically. In this case, the fractal dimension of radial electron motion is everywhere less than unity.
It can be greater than unity in regions well away from the nucleus.
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Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 52–57, September, 2005. 相似文献
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Based on the fractal distribution of nanoparticles, a fractal model for heat transfer of nanofluids is presented in the Letter. Considering heat convection between nanoparticles and liquids due to the Brownian motion of nanoparticles in fluids, the formula of calculating heat flux of nanofluids by convection is given. The proposed model is expressed as a function of the average size of nanoparticle, concentration of nanoparticle, fractal dimension of nanoparticle, temperature and properties of fluids. It is shown that the fractal model is effectual according to a good agreement between the model predictions and experimental data. 相似文献
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分形结构对随机取向烟尘团簇粒子光散射特性的影响 总被引:1,自引:0,他引:1
利用蒙特卡罗方法对不同分形维数和分形前向因子的随机取向烟尘团簇粒子的分形结构进行了仿真,采用离散偶极子近似(DDA)方法对随机取向烟尘团簇粒子的缪勒矩阵元进行了数值计算,并与球形粒子模型进行了比较,深入探讨了烟尘团簇粒子的分形维数和分形前因子对其散射特性的影响。研究表明,等效球形粒子的光散射特性与随机取向烟尘团簇粒子的光散射特性存在很大差别,并且此差别随着团簇粒子的分形维数以及分形前向因子的增大而减小;分形维数对表征团簇粒子散射特性的缪勒矩阵元的影响在一定散射角范围内均比较明显,分形前向因子对团簇粒子的缪勒矩阵元角分布的影响与分形维数的影响类似,不过其影响相对分形维数较弱。 相似文献
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Regular and stochastic oscillations in a simple periodically forced vibroacoustic system with a piecewise-linear (bimodular) elasticity are considered from the viewpoint of their statistical properties: oscillation spectra, the largest Lyapunov exponents, and fractal dimension. It is shown that a strange attractor exists in a limited range of parameters together with a triple-period dynamic cycle being absorbed by the latter at some finite value of the parameter. The corresponding bifurcation process is followed in detail. (c) 1995 American Institute of Physics. 相似文献
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It is shown that fractal dimensions along line transects of a stationary, stochastic surface are all identical to one another, save that in one special direction the dimension may be less than in all others. We discuss the implications of this result for practical measurement of surface roughness and for interpretation of fractal dimension. It is argued that the result provides significant new motivation for employing fractal dimension as a canonical measure of surface roughness. Nevertheless, in view of the virtual direction-invariance of fractal dimension, measurement of scale assumes new significance. This matter is addressed. 相似文献
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Self-similarity in multiple processes at high energies is considered. It is assumed that a parton cascade transforms into
a hadron shower with a fractal structure. The box counting (BC) method used to calculate the fractal dimension is analyzed.
The parton shower with permissible 1/3 parts of pseudorapidity space, which corresponds to a triadic Cantor set, was used
as a test fractal. It was found that there is an optimal set of bins (a parameter of the BC method) that allows one to find
the fractal dimension with maximal accuracy. The optimal set of bins is shown to depend on the fractal generation law. The
P-adic coverage (PaC) method is proposed and used in the fractal analysis. This method makes it possible to determine the
fractal dimension of a shower as accurately as possible, the number of fractal levels and partons at each branching point
during the parton shower evolution, the type of cascade (either random or regular), and its structure. It is shown to be applicable
to an analysis of the regular and random N-ary cascades with permissible 1/k parts of the space studied. 相似文献
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Kh. B. Ashurov S. E. Maksimov B. L. Oksengendler O. E. Sidorenko M. B. Guseva 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2011,5(3):587-590
Ion-stimulated growth of a fractal cluster on the substrate is simulated in regimes that are intermediate between diffusion-
and reaction-limited aggregations. It is shown that the fractal dimension of a growing cluster and the type of formed epitaxial
structure are due to the sequence of ion-stimulated processes with different fractal dimensions. The algorithm for revealing
the ion stimulation mechanism of processes based on fractal laws is proposed. 相似文献
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Yu. I. Kuzmin 《Physics of the Solid State》2001,43(7):1199-1206
The effect of morphologic factors on magnetic flux trapping and critical currents in a superconducting structure, which presents a type II percolation superconductor with pinning centers, is considered. The role of pinning centers is played by fractal clusters of the normal phase. The properties of these clusters are analyzed in detail: their statistics is studied, the distribution of critical currents of depinning is found, and the depen-dences of the main statistical parameters on the fractal dimension are obtained. The effect of fractal clusters of the normal phase on the electric field caused by the motion of the magnetic flux after the vortices have been broken away from pinning centers is considered. The current-voltage characteristics of superconducting structures in a resistive state are obtained for an arbitrary fractal dimension. It is found that the fractality of the boundaries of normal-phase clusters forces magnetic flux trapping, thereby increasing the critical current. 相似文献
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A. A. Bykov K. Yu. Terent’ev D. M. Gokhfeld M. I. Petrov 《Physics of the Solid State》2012,54(10):1947-1950
The fractal dimension of the boundaries of clusters formed by pores and granules in polycrystalline materials is shown to be determined by the sample density and crystallite sizes. The dependence of the fractal dimension on the density has a maximum. It is shown that the maximum diamagnetic response can be obtained in a porous high-temperature superconductor with a porosity of 50?C60% and small crystallite sizes. 相似文献