共查询到20条相似文献,搜索用时 15 毫秒
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《ournal of non Newtonian Fluid Mechanics》2005,125(1):71-85
This study looks at the influence of slip at the wall on plane Couette flows of viscous and yield stress fluids with ultrasonic wall motion. These fluids are used in coating processes. A constant speed V at one wall creates the flow, and vibrations and slip take place at the other wall. Isothermal conditions and arbitrary (longitudinal or transverse) vibrations are considered, with negligible vibrational inertia.For the Bingham model, due to its nonlinearity, whatever the vibration direction and the wall slipperiness, significant decreases occur in the average stress as soon as moderate values of the dimensionless vibration velocity amplitude are involved. Such effects are associated with adherent or slippery walls, even with linear friction laws. They do not occur with linear viscous (Newtonian) models.Average stress reductions can reach nearly 100% for very high Oldroyd numbers, i.e. for stress values without vibration close to the yield limit. Slip velocity also decreases. The cost in terms of the power dissipated remains relatively less than in the Newtonian case, and may contribute to a change in the temperature field. Even when the flow without vibration is a pure slip one, large enough amplitude vibrations, either longitudinal or transverse, applied at the wall can reduce the average shear stress and slip velocity, giving rise to an average axial shear flow.Hence vibrations of moderate or high-velocity amplitude applied to adherent or slippery walls enhance plane Couette flow rates for viscoplastic materials. With moderate values of this amplitude, longitudinal vibrations may be 1.5–2 times more efficient than transverse vibrations with an equivalent cost. However, if for technological reasons transverse vibrations have to be preferred, they can also produce significant results. In any case, coating flows should benefit from an adequate application of ultrasound at the wall. 相似文献
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针对裸眼完井中一种新型的螺旋钻孔-射孔套管,结合室内材料试验及有限元法,对不同深度的直井和水平井中套管承受非均匀载荷的力学性能进行分析。结果表明:随井深增加,套管所受应力和最大变形增加;同井深情况下,随着套管孔眼数量和孔眼面积增加,套管最大变形增加,最小应力减小、最大应力增加。应力集中是降低套管承载力的主要因素,选用套管时要考虑到载荷不均匀系数引起的应力破坏和变形引起的失稳破坏。研究结论可为合理选择、设计套管,确定套管钻孔和射孔的孔径、密度、相位,分析钻孔后套管的剩余强度,保证套管使用的安全性提供一定的理论依据。 相似文献
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V. G. Popov 《Mechanics of Solids》2013,48(2):194-202
The paper presents a solution of the problem of determining the stress state in an elastic isotropic half-space with a crack intersecting its boundary under harmonic longitudinal shear vibrations. The vibrations are excited by a regular action of a harmonic shear load on the crack shores. The solution method is based on the use of the discontinuous solution of the Helmholtz equation, which allows one to reduce the original problem to a singular integro-differential equation for the unknown jump of the displacement on the crack surface. The solution of this equation is complicated by the existence of a fixed singularity of its kernel. Therefore, one of the main results is the development of an efficient approximate method for solving such equations, which takes into account the true asymptotics of the unknown function. The latter allows one to obtain a high-precision approximate formula for calculating the stress intensity factor. 相似文献
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细直杆件在压应力作用下会产生横向屈曲即失稳.直杆撞击刚性平面或拉断卸载后将形成压缩波,因承载压缩载荷的长度增加可以引起失稳.冲击速度转换的压应力沿着杆件切线方向,该处弯矩和剪力为零;而众多文献设定的失稳段固支边界条件并不准确.基于精确的杆件变形曲率方程得到端部载荷指向杆件中固定点时的受压失稳条件,得到其极限状态即载荷沿杆端切向作用时失稳长度相当于两端简支的1.5 倍.对于钢丝绳拉断形成的冲击失稳,载荷恒定而长度增加,可以产生高阶屈曲即在侧向出现多次曲折,并基于尼龙-橡胶带的模拟试验给出了定性说明. 相似文献
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《Journal of Fluids and Structures》2008,24(1):75-95
The turbulent flow of air caused by the spinning of a single disk inside a typical hard disk drive casing is calculated using large eddy simulation (LES). The pressure acting on the disk is recorded as a function of time and is used to compute the vibrations of the spinning disk using a self-developed hybrid-spectral finite-difference code. This unidirectional fluid–structure interaction problem is computed for two commonly occurring cases: a disk actuated on one side only (Case 1) and a disk actuated on both sides (Case 2). The pressure loading on the disk is characterized in terms of its mean, root-mean-square (r.m.s.) and its spectral content. The mean pressure acting on the disk is asymmetrical in the case where the disk is actuated on one side only, leading to a mean deformation of the disk to one side. The r.m.s. vibrations of Case 2 are higher than those for Case 1 and their spectral distributions are almost identical. Large pressure fluctuations of the flow are found in the wake of the actuator arm and near the region where the shroud expands to accomodate the actuator. The spectral content of the excitation force due to the pressure is mainly in the low kHz frequency range, while higher frequencies are seen at the disk edge. This typically results in the excitation of the first 3–4 modes of the disk; however, (asymmetric) Case 1 displays the excitation of higher modes compared with (symmetric) Case 2. 相似文献
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We construct the solution of the problem on the steady-state vibrations of a finite boxed shell of square cross-section with
symmetry conditions at the shell ends. We present the dispersion curves, find the natural frequencies, and study the stress
distribution in the shell. We obtain a simple formula for the approximate analysis of the shell in the case of low-frequency
vibrations on the basis of the expansion of the solution in two small parameters and on the Lagrange interpolation formula. 相似文献
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A plane harmonic problem of vertical vibrations of a rigid permeable stamp on a liquid saturated poroelastic base is considered. The equations of two-phase Biot media, which take into account inertial and viscous interactions of phases, are used. The asymptotic properties of the contact stress at low vibration frequencies are studied. 相似文献
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在对大量的套管全尺寸挤毁试验结果分析的基础上,提出套管外压失稳机理:实际工程中的套管截面不是理想圆,在外压作用下的非圆套管圆周方向上环向应力分布不均匀,有附加弯矩效应;随外压增加,在最大压缩环向应力处达到屈服;当屈服逸到一定程度时,材料由于强度承载力不足而失效,导致套管发生失稳挤毁。基于上述套管强度挤毁准则,分析了理想弹塑性套管在轴向载荷作用下的抗挤强度计算方法,得到较保守的套管挤毁压力计算公式。与试验结果对比表明:导出的计算公式偏差较小,计算精度满足工程要求,失稳强度准则是适用的。 相似文献
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A dynamic behavior of solid propellant motor composite casing under the action of an internal impact pressure is treated. This pressure describes the engine operation. The thin-walled casing consists of the cylindrical shell and two bottoms. These bottoms are truncated hemisphere. The casing is clamped along two edges of the bottoms. A shear, a rotary inertia and stress–strain relations for an orthotropic material are accounted. Semi analytical method is suggested to analyze the structure stress–strain state. The thin-walled casing dynamic is described by large dimension system of the ordinary differential equations. 相似文献
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An experimental analysis using three-dimensional laser Dopplervelocimetery (LDV) measurements and computational analysis usingthe Reynolds stress model of the commercial code, FLUENT, wereconducted to give a clear understanding on the structure of thetip leakage flow in a forward-swept axial-flow fan operating atthe peak efficiency condition, and to emphasize the necessity ofusing an anisotropic turbulence model for the accurate predictionof the tip leakage vortex. The rolling-up of the tip leakage flowwas initiated near the position of the maximum static pressuredifference, which was located at approximately 12% axial tipchord downstream from the leading edge of the blade, and developedalong the centerline of the pressure trough on the casing. Areverse flow between the blade tip and the casing due to the tipleakage vortex acted as a blockage on the through-flow. As aresult, high momentum flux was observed below the tip leakagevortex. As the tip leakage vortex proceeded to the aft part of theblade passage, the strength of the tip leakage vortex decreaseddue to the strong interaction with the through-flow and the casingboundary layer, and the diffusion of the tip leakage vortex byhigh turbulence. Through the comparative study of turbulencemodels, it was clearly shown that an anisotropic turbulence model,e.g., Reynolds stress model, should be used to predict reasonablyan anisotropic nature of the turbulent flow fields inside the tipleakage vortex. In comparison with LDV measurement data, thecomputed results predicted the complex viscous flow patternsinside the tip region in a reliable level. 相似文献
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In [1] a dispersion relation for the vibrations of an elastic rod of circular cross section with an electric current flowing over its surface was obtained, and a detailed study was made of the particular case of axially symmetric vibrations. The present paper is devoted to an examination of the longwave bending vibrations of elastic rods with an electric current flowing over their surface. These vibrations are of special interest since they have the lowest frequency and hence the last stability. 相似文献
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《应用数学和力学(英文版)》2017,(9)
In this paper, we present an analytical method for evaluating the stress field within a casing-cement-formation system of oil/gas wells under anisotropic in-situ stresses in the rock formation and uniform pressure within the casing. The present method treats the in-situ stresses in the formation as initial stresses since the in-situ stresses have already developed in the formation before placement of cement and casing into the well. It is demonstrated that, via this treatment, the present method excludes additional displacements within the formation predicted by the existing method, and gives more reasonable stress results. An actual tight-oil well is analyzed using the present and existing analytical methods, as well as the finite element method. Good agreement between the analytical results and the finite element analysis(FEA) results is obtained, validating the present method. It is also evident that, compared with the present method, the existing method overestimates the compressive stress level within the casing and the cement.Finally, the effects of elastic properties of the formation, cement, and inner pressure of casing on stresses within the casing and cement are illustrated with a series of sensitivity analyses. 相似文献
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Interaction of a plane harmonic wave with a thin rigid inclusion of the shape of a cylindrical shell
V. G. Popov 《Mechanics of Solids》2012,47(2):187-194
The paper presents the solution of the problem of determining the stress state in an elastic matrix containing a rigid inclusion
of the shape of a thin cylindrical shell. It is assumed that harmonic vibrations occur in the matrix under the conditions
of axial symmetry (the symmetry axis is the inclusion axis) and the conditions of full adhesion between the inclusion and
the matrix are satisfied. The vibrations are caused by the propagation of a plane wave whose front is perpendicular to the
inclusion axis. The solution method is based on representing the displacements in the matrix as discontinuous solutions of
the equations of axisymmetric oscillations of an elastic medium with unknown stress jumps on the inclusion surface. The realization
of the boundary conditions for these jumps leads to a system of integral equations. Its solution is constructed numerically
by the mechanical quadrature method with the use of special quadrature formulas for specific integrals. It is numerically
investigated how the ratio of the inclusion geometric dimensions and the propagating wave frequency affect the stress concentration
near the inclusion. 相似文献
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A. D. Zamanov 《International Applied Mechanics》2001,37(9):1189-1195
A problem on the forced vibrations of a rectangular composite plate with locally curved structures is formulated using the exact three-dimensional equations of continuum mechanics and continuum theory. A technique for numerical solution of the problem is developed based on the semianalytic finite-element method. Numerical results are given for the stress distribution in the plate under forced vibrations. The results obtained are analyzed to study the effect of the curvature in the structure of the plate on the distribution of stress amplitudes. It is shown that the curvatures change significantly the stress pattern under either static or dynamic loading 相似文献
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The vibrations of a vessel strongly influence the behavior of the interface of the fluids in it. Thus, vertical vibrations
can lead both to the parametric excitation of waves (Faraday ripples) and to the suppression of the Rayleigh-Taylor instability
[1–2]. At the present time, the influence of vertical vibrations on the behavior of a fluid surface have been studied in sufficient
detail (see, for example, review [3]). The behavior of an interface of fluids in the case of horizontal vibrations has been
studied less. An interesting phenomenon has been revealed in the experimental papers [4, 5]: in the case of fairly strong
horizontal vibrations of a vessel containing a fluid with a free surface, the fluid collects near one of the vertical vessel
walls, the free surface being practically plane and stationary with respect to the vessel, while its angle of inclination
to the horizon depends on the vibration rate. But if there is a system of immiscible fluids with comparable but different
densities in the vessel, horizontal vibrations lead to the formation of a steady wave relief at the interface. An explanation
of the behavior of a fluid with a free boundary was given in [6] on the basis of averaged equations of fluid motion in a vibrational
field. The present paper is devoted to an analysis of the behavior of the interface of fluids with comparable densities in
a high-frequency vibrational field.
Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 8–13, November–December, 1986. 相似文献