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排序方式: 共有450条查询结果,搜索用时 203 毫秒
441.
Ivan Giorgio Antonio Culla Dionisio Del Vescovo 《Archive of Applied Mechanics (Ingenieur Archiv)》2009,79(9):859-879
In this paper a new approach is presented to reduce vibrations for one- and two-dimensional mechanical structures, as beam
or thin plates, by means of several piezoelectric transducers shunted with a proper electric network system. The governing
equations of the whole system are coupled to each other through the direct and converse piezoelectric effect. More in detail,
the mechanical equations are expressed in accordance with the modal theory considering n vibration modes and the electrical equations reduce to the one-dimensional charge equation of electrostatics for each of
n considered piezoelectric transducers. In this electromechanical system, a shunting electric device forms an electric subsystem
working as multi degrees of freedom (dof’s) damped vibration absorber for the mechanical subsystem. Herein, it is introduced
a proper transformation of the electric coordinates in order to approximate the governing equations for the whole shunted
system with n uncoupled, single mode piezoelectric shunting systems that can be readily damped by the methods reported in literature. A
further numerical optimisation problem on the spatial distribution of the piezoelectric elements allows to achieve a better
performance. Numerical case studies of two relevant systems, a double clamped beam and a fully clamped plate, allow to take
into account issues relative to the proposed approach. Laboratory experiments carried out in real time on a beam clamped at
both ends consent to validate the proposed technique. 相似文献
442.
The possibility of transverse galloping of a square cylinder at low Reynolds numbers (Re≤200, so that the flow is presumably laminar) is analysed. Transverse galloping is here considered as a one-degree-of-freedom oscillator subjected to fluid forces, which are described by using the quasi-steady hypothesis (time-averaged data are extracted from previous numerical simulations). Approximate solutions are obtained by means of the method of Krylov-Bogoliubov, with two major conclusions: (i) a square cylinder cannot gallop below a Reynolds number of 159 and (ii) in the range 159≤Re≤200 the response exhibits no hysteresis. 相似文献
443.
We have investigated gapless edge states in zigzag-edge graphene nanoribbons under a transverse electric field across the opposite edges by using a tight-binding model and the density functional theory calculations. The tight-binding model predicted that a quantum valley Hall effect occurs at the vacuum-nanoribbon interface under a transverse electric field and, in the presence of edge potentials with opposite signs on opposite edges, an additional quantum valley Hall effect occurs under a much lower field. Dangling bonds inevitable at the edges of real nanoribbons, functional groups terminating the edge dangling bonds, and spin polarizations at the edges result in the edge potentials. The density functional theory calculations confirmed that asymmetric edge terminations, such as one having hydrogen at an edge and fluorine at the other edge, lead to the quantum valley Hall effect even in the absence of a transverse electric field. The electric field-induced half-metallicity in the antiferromagnetic phase, which has been intensively investigated in the last decade, was revealed to originate from a half-metallic quantum valley Hall effect. 相似文献
444.
445.
Frans P. van der Meer Carlos G. Dávila 《International Journal of Solids and Structures》2013,50(20-21):3308-3318
This study aims to bridge the gap between classical understanding of transverse cracking in cross-ply laminates and recent computational methods for the modeling of progressive laminate failure. Specifically, the study investigates under what conditions a finite element model with cohesive X-FEM cracks can reproduce the in situ effect for the ply strength. It is shown that it is possible to do so with a single element across the thickness of the ply, provided that the interface stiffness is properly selected. The optimal value for this interface stiffness is derived with an analytical shear lag model. It is also shown that, when the appropriate statistical variation of properties has been applied, models with a single element through the thickness of a ply can predict the density of transverse matrix cracks. 相似文献
446.
A novel type of transverse surface wave propagating in a layered structure consisting of a piezoelectric layer attached to an elastic half-space 下载免费PDF全文
Sohichi Hirose 《Acta Mechanica Sinica》2010,26(3):417-423
The existence and propagation of transverse surface waves in piezoelectric coupled solids is investigated, in which perfect bonding between a metal/dielectric substrate and a piezoelectric layer of finite-thickness is assumed. Dis- persion equations relating phase velocity to material con- stants for the existence of various modes are obtained in a simple mathematical form for a piezoelectric material of class 6mm. It is discovered and proved by numerical examples in this paper that a novel Bleustein-Gulyaev (B-G) type of transverse surface wave can exist in such piezoelectric cou- pled solid media when the bulk-shear-wave velocity in the substrate is less than that in the piezoelectric layer but greater than the corresponding B-G wave velocity in the same pie- zoelectric material with an electroded surface. Such a wave does not exist in such layered structures in the absence of pie- zoelectricity. The mode shapes for displacement and electric potential in the piezoelectric layer are obtained and discussed theoretically. The study extends the regime of transverse sur- face waves and may lead to potential applications to surface acoustic wave devices. 相似文献
447.
The interacting capillary bundle model proposed by Dong et al. [Dong, M., Dullien, F.A.L., Zhou, J.: Trans. Porous Media 31, 213–237 (1998); Dong, M., Dullien, F.A.L., Dai, L., Li, D.: Trans. Porous Media 59, 1–18 (2005); Dong, M., Dullien, F.A.L., Dai, L., Li, D.: Trans. Porous Media 63, 289–304 (2006)] has simulated correctly various aspects of immiscible displacement in porous media, such as oil production
histories at different viscosity ratios, the effects of water injection rate and of the oil–water viscosity ratio on the shape
of the displacement front and the independence of relative permeabilities of the viscosity ratio. In the interacting capillary
bundle model pressure equilibrium was assumed at any distance x measured along the bundle. Interaction between the capillaries also results in transfer of fluids across the capillaries.
In the first part of this paper the process of fluid transfer between two capillaries is analysed and an algebraic expression
for this flow is derived. Consistency with the assumption of pressure equilibration requires that all transfer must take place
at the positions of the oil/water menisci in the tubes without any pressure drop. It is shown that fluid transfer between
the tubes has no effect on the predictions obtained with the model. In the second part of the paper the interacting tube bundle
model is made more realistic by assuming fluid transfer between the tubes all along the single phase flow regions across a
uniform resistance, resulting in pressure differences throughout the single phase regions between the fluids present in the
different tubes. The results of numerical simulations obtained with this improved interacting capillary bundle model show
only small differences in the positions of the displacement front as compared with the predictions of the idealized model. 相似文献
448.
In this paper the non-linear analysis of a composite Timoshenko beam with arbitrary variable cross section undergoing moderate large deflections under general boundary conditions is presented employing the analog equation method (AEM), a BEM-based method. The composite beam consists of materials in contact, each of which can surround a finite number of inclusions. The materials have different elasticity and shear moduli with same Poisson's ratio and are firmly bonded together. The beam is subjected in an arbitrarily concentrated or distributed variable axial loading, while the shear loading is applied at the shear center of the cross section, avoiding in this way the induction of a twisting moment. To account for shear deformations, the concept of shear deformation coefficients is used. Five boundary value problems are formulated with respect to the transverse displacements, the axial displacement and to two stress functions and solved using the AEM. Application of the boundary element technique yields a system of non-linear equations from which the transverse and axial displacements are computed by an iterative process. The evaluation of the shear deformation coefficients is accomplished from the aforementioned stress functions using only boundary integration. Numerical examples are worked out to illustrate the efficiency, the accuracy, the range of applications of the developed method and the influence of the shear deformation effect. 相似文献
449.
Holm Altenbach Victor A. Eremeyev 《Archive of Applied Mechanics (Ingenieur Archiv)》2008,78(10):775-794
The classical plate theory can be applied to thin plates made of classical materials like steel. The first theory allowing
the analysis of such plates was elaborated by Kirchhoff. But this approach was connected with various limitations (e.g., constant
material properties in the thickness direction). In addition, some mathematical inconsistencies like the order of the governing
equation and the number of boundary conditions exist. During the last century many suggestions for improvements of the classical
plate theory were made. The engineering direction of improvements was ruled by applications (e.g., the use of laminates or
sandwiches as the plate material), and so new hypotheses for the derivation of the governing equations were introduced. In
addition, some mathematical approaches like power series expansions or asymptotic integration techniques were applied. A conceptional
different direction is connected with the direct approach in the plate theory. This paper presents the extension of Zhilin’s
direct approach to plates made of functionally graded materials.
The second author was supported by DFG grant 436RUS17/21/07. 相似文献
450.
采用2mm宽REBCO超导带材,通过堆叠、圆化和拉拔等成型技术制备了多种规格的堆叠型股线,并利用试验手段研究了不同结构股线的横向抗压性能。经研究发现,超导股线在带面方向的抗压性能最好,侧面方向最差。而对比测试表明,股线带材和铜带的分布对其抗压性能影响不大,增加包壳壁厚可提高股线的抗压性能,而增大股线直径,可部分改善抗压能力,但股线扭转则会降低其抗压效果。 相似文献