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The average dynamics of a single solid sphere in a liquid-filled cylindrical cavity in the presence of high-frequency rotational oscillation about the axis of symmetry is studied experimentally. In the cavity there is an impermeable membrane which forces the liquid as a whole to vibrates together with the cavity. Various orientations of the vessel in the gravity force field are considered. The action of an average force of vibrational nature on the sphere and the dependence of this force on the vibration parameters and the body dimensions and density are studied. The force is measured with respect to the floating threshold for the heavy body, when the average vibrational force balances or exceeds the action of the gravity force. 相似文献
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Basing upon the assumption on the solenoidality of the field of the time-average body force produced by a surface dielectric barrier discharge analytical expressions for the spatial distributions of the components of this force are proposed. The calculations of the dischargegenerated near-surface jet are in good agreement with the experiment. The distinctive features of spatial distributions of the body force components calculated from the data of the velocity field measurements are physically explained. 相似文献
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本文基于动态散斑场的相关统计特性,发展了一种系统识别技术,这是一条有效的用来分析超小型物体动态特性的途径.我们对重为8g的微型悬臂梁,实时记录了梁振动的自由响应时间域信号,对其进行了动态特性计算机分析和实验研究。 相似文献
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The rigidity of a body usually is characterized by the kinematical assumption that the mutual distance between any two of its particles remains unaltered in any possible deformation. However, from this alone nothing can be said about the internal contact forces exerted between adjacent sub-bodies. Therefore, the determination and form of an internal state of stress for a rigid body is problematical. Here, we will show that by considering such a kinematical characterization as an internal constraint for an elastic body, the constrained body inherits the mechanical structure of the elastic parent theory, i.e., the internal constraint generates an associated set of Lagrange multiplier fields which can be interpreted as an internal constraint reaction pseudo-stress field with the same structure as the state of stress in the parent elastic body. Thus, although the final deformation is the same for both the rigid body and the rigidly constrained elastic body, the latter corresponds to a richer model and, to emphasize this distinction, we refer to it as a quasi-rigid body. While in equilibrium the pseudo-stress field of a quasi-rigid body will satisfy equations identical to the equilibrium equations for the stress field in the elastic parent theory, such equations are not, in general, sufficient to assure uniqueness. In order to overcome this indeterminacy, we consider the quasi-rigid body as the limit of a sequence of deformable bodies, where each member of the sequence is identified by a material parameter such that, as this parameter tends to infinity, the body to which it refers is rigidified. Our approach is variational, i.e., we consider a sequence of minimization problems for hyperelastic bodies whose elastic strain energy is multiplied by a penalty term, say 1/ε . As ε→?0, body distortions are more and more penalized so that the sequence of the displacement fields tends to a rigid displacement field, whereas the sequence of the associated stress fields tends to a definite non-zero limit. It will be shown that among all pseudo-stress fields that satisfy the equilibrium equations for the quasi-rigid body, the unique limit of the sequence as ε→0 minimizes a functional analogous to the complementary energy functional in classical linearized elasticity. This result permits its unique determination without having to consider the whole sequence of penalty problems. 相似文献
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In 1997, H. Nozaki and M. Taya found numerically that for any regular polygonal inclusion except for a square, both the Eshelby tensor at the center and the average Eshelby tensor over the inclusion domain are equal to the Eshelby tensor for a circular inclusion and independent of the orientation of the inclusion. Then in 2001, these remarkable properties were mathematically justified by Kawashita and Nozaki. In this paper, a more radical property is presented for a rotational symmetrical inclusion: For any N-fold (N is an integer greater than 2 and unequal to 4) rotational symmetrical inclusion, the arithmetic mean of the Eshelby tensors at N rotational symmetrical points in the inclusion is the same as the Eshelby tensor for a circular inclusion and independent of the orientation of the inclusion. It follows that the Eshelby tensor at the center and the average Eshelby tensor over the rotational symmetrical inclusion domain are identical to the Eshelby tensor for a circular inclusion and independent of the orientation of the inclusion as well. This paper shows that although the Eshelby property does not hold for non-ellipsoidal inclusions, the Eshelby tensor for a rotational symmetrical inclusion satisfies the arithmetic mean property.
Mathematics Subject Classifications (2000) 73C02. 相似文献
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G. P. Parry 《Journal of Elasticity》2009,94(2):147-166
I use the theory of Lie groups/algebras to discuss the symmetries of crystals with uniform distributions of defects.
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对旋转组合壳体的各个子区的位移场进行双三次B样条插值,同时对子区交界处的广义力向量以单三次B样条展开,推导出以广义向量表示的组合壳体的平衡方程,然后从Beti互换定理和虚功原理出发推导出离散的壳体结构中可能的塑性应变率循环,从而给出了组合壳体安定上限分析的有限元列式,把组合壳体的安定上限分析归结为求解一个数学规划问题,文末给出了算例 相似文献
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Abstract. We will consider nonlinear rotational galloping for two mechanically coupled seesaw oscillators in steady cross-flow, where mechanical coupling consists of a torsion spring. This oscillator system may be viewed as a mechanical two d.o.f. model for the study of rotational galloping of a continuous elastic structure. Using a quasi-steady modelling approach as model equations two coupled nonlinear oscillators are obtained. Depending on the stiffness of the torsion spring and the natural frequencies of the two oscillators either a non-resonant or 1:1 internal resonant system is found. Assuming the windforce to be relatively small an asymptotic analysis based on averaging is presented for both cases.Sommario: Vengono considerate le oscillazioni galoppanti rotazionali non lineari di due oscillatori disposti in bilico su un fulcro (seesaw oscillators) soggetti a un flusso trasversale stazionario e accoppiati meccanicamente attraverso una molla di torsione. Questo sistema oscillatorio può essere interpretato come un modello meccanico a due gradi di libertà per studiare il galoppo rotazionale di una struttura continua elastica. Modellando le azioni indotte dal flusso in modo quasi-statico, si ottengono due oscillatori non lineari accoppiati. A seconda della rigidezza della molla di torsione e delle frequenze naturali dei due oscillatori, si ottiene un sistema non risonante o in risonanza interna 1:1. Assumendo che le forze del vento siano relativamente piccole, viene presentata per entrambi i casi un'analisi asintotica basata sul metodo della media. 相似文献