共查询到20条相似文献,搜索用时 78 毫秒
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以Duffing系统为研究对象,探讨常数激励与简谐激励联合作用下系统的骨架曲线及幅频响应特性,重点考察常数激励的影响。采用谐波平衡法求解该系统的振动方程,得到幅频响应关系,并给出了骨架曲线以及周期解的稳定性分析。采用幅频响应曲线和骨架曲线表征系统的基本动力学性质,讨论了常数激励和简谐激励幅值对系统幅频曲线性态和骨架曲线形态的影响。研究发现,系统振动响应中直流分量与谐波分量的振幅同步变化,但变化趋势相反。此外,两者骨架曲线的形态均是先向左微偏后转为向右弯曲,因此,在某些参数条件下,对应一个激励频率的周期解可能有5组,其中3组为稳定性,2组为不稳定解。进一步通过增大常数激励发现其能够对该系统造成的“刚度增强”效应,但同时也会伴随着愈加显著的“刚度渐软”特性。相应地,对于特定的简谐激励幅值,随着常数激励的增大,系统的幅频曲线能够由纯硬特性转变为软硬特性共存,甚至纯软特性。但是,在大尺度下观察,常数激励对系统骨架曲线的影响主要表现在骨架曲线根部的形态上,即随着简谐激励幅值的增大,常数激励对系统共振频率的影响变弱,不同常数激励下的骨架曲线趋于一致。 相似文献
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微风振动常造成架空导线疲劳断股断线、金具脱落等破坏.考虑大跨越导线所处风场的切变特性,采用局部激励模型研究大跨越导线的微风振动机理,建立了长柔导线在档内任意局部位置激励下的动力学模型,基于导线系统的小阻尼特性,得到了局部周期激励下长柔导线波动的格林函数解;依据振动波沿展向的衰减特性,将导线内的波动过程分为驻波振动、行波... 相似文献
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随机激励下高维包装振动系统的可靠性分析 总被引:6,自引:6,他引:0
研究了两自由度包装振动系统在受高斯白噪声外激励下的可靠性.利用由随机平均法导出的关于系统的独立运动积分的随机平均方程,通过系统本身的特性以及对漂移与扩散系数作出的一些假定,给出了系统的可靠性函数以及首通损坏的条件转移概率密度函数所满足的后向柯尔莫哥洛夫方程和福克-普朗克方程,并进一步详细地讨论了其边界与可解性条件.数值结果表明,关于系统的可靠性函数以及首通损坏的条件转移概率密度函数方面的结果是比较合理的,这也表明文中的分析方法是正确的. 相似文献
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参外激励作用下非线性振动系统的混沌 总被引:1,自引:1,他引:0
用多尺度法给邮了van der Pol-Duffing振子在参数激励与外部激励联合作用下的主亚谐联合共振条件,用Melnikov方法研究了与之对应的平衡系统的同、异宿轨道相变的条件,证明了原系统的的振幅与相位存在类随机运动,并结合数值结果给出由概周期运动通向混沌的两种方式。 相似文献
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本文提出了一类线性振动系统X(t) 2ζω_0X(t)十ω_0~2X(t)=F(t),在工程振动中常见的一种功率谱密度为φ_0/(ω~2 α~2)的Gauss平稳激励下,系统响应的时域解和频域解。并且证明了初始响应是一个演变的随机过程,指出响应的初始破坏的可能性是不容忽视的。今后的工作是进一步提出减少这种初始破坏的具体方案。 相似文献
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We study the recently reported energy bursts that take place in a granular system confined to a vertically vibrated shallow box containing two types of grains of equal size but different mass (Rivas in Phys Rev Lett 106:088001?C1?C088001?C4, 2011). In a quasi one dimensional configuration, it is possible to characterize the propagating fronts. The rapid expansion and the subsequent compression of the energy bursts take place at roughly constant velocities. The expansion velocity is 40 times larger than the compression velocity. Starting from an initially segregated configuration it is possible to determine the instants at which the energy bursts begin and the mechanisms that trigger them. Two mechanisms are identified: an oblique collision of a heavy grain with a light one in contact with one of the horizontal walls and a slow destabilization produced by light grains that are surrounded by heavy ones. 相似文献
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We examine the spontaneous formation of numerous previously unreported patterns in deep beds of fine grains vibrated at frequencies
ranging from 10 to 100 Hz and accelerations ranging from 1 to 14 times gravity. Similarly to shallow beds, we find stripes,
closed cells and labyrinthine patterns. In addition, we observe traveling waves, cannibalizing cells and other behaviors that
are unexpected and remain unexplained. All of these patterns vary spatiotemporally, and unlike shallow bed patterns, are harmonic
rather than subharmonic.
Received: 17 May 1999 相似文献
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The temperature of a granular medium is defined, in a manner analogous to that of a molecular gas, as the root mean squared kinetic energy of the grains. Using a novel two-layer granular experiment, we have made a systematic study of the granular temperature as a function of driving parameters in order to determine whether the behavior of the granular temperature is truly analogous to the temperature of a molecular gas. By examining the behavior of this particular system in detail, where two fluctuating granular media are in thermal contact, we also suggest general conditions under which such analogies can be extended to other driven systems. 相似文献
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Piroz Zamankhan 《Advanced Powder Technology》2013,24(6):1070-1085
A series of experiments are described in which air-immersed grains within different containers are exposed to vertical vibrations. When the peak acceleration relative to gravity exceeded Γ = 6 at 49 Hz), tilted cavitating beds were formed. Then, when a large, low-density object was put onto the free surface, the vigorous granular convection dragged it into the bed. The large object was not being dragged into the bed at Γ > 6 when the air pressure inside the container fell well below1 Torr. These findings, as well as those from computer simulations, confirm the key role played by large air cavities such as swallow holes in submerging large, low-density objects into a granular bed. 相似文献
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The stationary state eventually reached by a vibrated granular gas with a piston on the top, and in presence of gravity, is considered. The relationship between the second velocity moments of the piston and of the gas just below it is investigated by using event driven molecular dynamics simulations. It is concluded that velocity correlations between the piston and the gas play a crucial role in determining the velocity fluctuations of the piston, that can be much larger than estimated by energy equipartition. 相似文献
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J. Badreddine M. Micoulaut E. Rouhaud S. Remy D. Retraint M. François 《Granular Matter》2013,15(3):367-376
The properties of a ultrasonic vibrated granular gas are investigated by using an event-driven Molecular Dynamics simulation of inelastic hard spheres that are fluidized by a vibrating bottom wall (sonotrode) in boxes with different geometries showing either no or an increased confinement. It appears that geometry controls dramatically not only the distribution of wall impacts and their velocity and impact angles, but also more fundamental properties of the granular gas such as temperature and density. For geometries displaying an acute angle (prism), stacking is found, which induces a strong temperature and density gradient. The underlying origin of such phenomena for the granular gas arises from the spatial limitation, confinement, combined with the inelastic collisions induced by closely located side walls. It underscores the possibility that kinetic and thermodynamic properties of granular gases can be changed by simple geometries inducing spatial limitation. 相似文献
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A. Karrech D. Duhamel G. Bonnet F. Chevoir J.-N. Roux J. Canou J.-C. Dupla 《Granular Matter》2008,10(5):369-375
This paper deals with the vibration of granular materials due to cyclic external excitation. It highlights the effect of the
acceleration on the settlement speed and proves the existence of a relationship between settlement and loss of contacts in
partially confined granular materials under vibration. The numerical simulations are carried out using the Molecular Dynamics
method, where the discrete elements consist of polygonal grains. The data analyses are conducted based on multivariate autoregressive
models to describe the settlement and permanent contacts number with respect to the number of loading cycles. 相似文献
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As a densely packed granular material begins to flow through a constriction, dilatant waves are often observed. These waves initiate at the constriction and propagate outward into the granular material with an increase in the porosity of the material behind the wave front. As a model for dilatant waves, we consider curved waves carrying a jump in the gradient of porosity in the context of the continuum theory for the flow of granular materials presented by Goodman and Cowin. Their speed of propagation is determined and it is shown that such waves carry a jump in the stress acting on planes transverse to their direction of propagation. For the case when a wave of dilatancy propagates into a uniform region at rest, an explicit formula for the amplitude of the wave is derived for waves of general shape and then specialized to give results for plane, cylindrical, and spherical waves. In this case, the wave is purely longitudinal. 相似文献
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P F Lourens 《Accident; analysis and prevention》1989,21(5):419-426
This paper presents an overview of the field of error analysis. Section 1 shows why discussions about human error are relevant for societal safety. With regard to safety research, it is important to predict abnormal events. At the machine side, reliability studies proved their value, but to predict failures in the human factor has been shown to be very difficult. Therefore, problems in how to define the notion of human error (Section 2) and how to classify different types of error (Section 3) are discussed. Some researchers started to use systematical classifications of human error types based on a recent, hierarchical model of human task performance. The outline of the model is presented. Examples of error analysis studies from the field of transportation research (Section 4) provide some basic suggestions on how to reduce error rates. Some conclusions on error control are given in Section 5. The responsibility of managers and system designers in this respect is strongly emphasized. 相似文献