力学学报

分层流体中栅格湍流的特性

The present experimental study investigates the properties and evolutions of grid turbulence in stratified fluid. By moans of computer image proccesing of particle streak pattern and relavent statistics, it is possible to obtain the flow structure details, turbulence decay of kinetic energy, various turbulent lengthscales, dissipation rate and spectrum. The experimental results further confirm the conclusion that the stratification of fluid mainly supre-sses the vertical turbulent velocity (increases its de...

1991, 23(3): 257-264. doi: 10.6052/0459-1879-1991-3-1995-836

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HYDRODYNAMIC FORCES ACTING ON A CIRCULAR CYLINDER NEAR A WAVY BOUNDARY IN STEADY FLOW

The characteristics of drag and lift forces on a circular cylinder model near a wavy boundary have been experimentally investigated in a water tunnel, tn the range of the Reynolds numbers, based on the diameter of cylinder model, from 104 to 1.9104, the drag, lift force on the cylinder and lift force frequencies have been measured at the wave crest and trough and various distances from the wavy boundary. Flow visualization experiments revealed the wake structure varying with the gap-to-diameter ratio (G/D) ...

1991, 23(3): 265-273. doi: 10.6052/0459-1879-1991-3-1995-837

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INVESTIGATION OF CONTROL LAWS FOR THE SUPPRESSION OF WING/STORE FLUTTER

Control laws for the suppression of wing/store flutter are investigated in this paper. The wing tunnel test was conducted for three control laws used. It shows that the design of control laws is successful and an excellent agreement between the calculated and test results is achieved.Two kinds of flutter suppression control laws based on modern control theory are presented emphatically. State feedback are obtained by the combination of optimal control theory and state-space method used in flutter analysis, ...

1991, 23(3): 274-282. doi: 10.6052/0459-1879-1991-3-1995-838

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A GENERALIZED REYNOLDS EQUATION BASED ON NONNEWTONIAN FLOW IN LUBRICATION MECHANICS

A generalized Reynolds equation based on non-Newtonian flow is derived in this paper. This equation is suitable for a number of non-Newtonian flow models, can be solved numerically to obtain pressure fields in thermal hydrodynamically or thermal elastohy-drodynamically lubricated fluid films. A mathematical approach is given for solving simultaneously the shear stress, shear rate, velocity and equivalent viscosity. To show the application of this equation, two rheological models which have been widely used ...

1991, 23(3): 283-289. doi: 10.6052/0459-1879-1991-3-1995-839

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FORMULATION OF STATISTICAL EVOLUTION OF MICROCRACKS IN SOLIDS

The paper presents a principal formulation of statistical evolution of mic-rocracks, occurring in solids, subjected to external loading. In particular, the concept of ideal microcracks is elaborated, in order to describe the fundamental features of damage resulting from nucleation and extension of microcracks. Relevant average damage functions are also discussed.The paper presents a principal formulation of statistical evolution of mic-rocracks, occurring in solids, subjected to external loading. In particu...

1991, 23(3): 290-298. doi: 10.6052/0459-1879-1991-3-1995-840

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A MICROMECHANICS CONSTITUTIVE MODEL FOR FORWARD TRANSFORMATION PLASTICITY WITH SHEAR AND DILATATION EFFECT: Ⅰ, GENERALIZED NONPROPORTIONAL LOADING HISTORY

Based on micromechanics, thermodynamics and microscale t→m transformation mechanism considerations, amicromechanics constitutive model which takes into account both the dilatation and shear effects of the transformation is proposed to describe the macroscopic plastic behavior of structure ceramics during forward transformation under different temperatures. Under some basic assumptions, the analytic expressions of the Helmholtz and complementary free energy of the constitutive element is derived in a self-co...

1991, 23(3): 299-308. doi: 10.6052/0459-1879-1991-3-1995-841

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A NEW BOUNDARY INTEGRAL FORMULATION WITH NO SINGULARITY

The paper presents how the higher order singularity of a boundary integral equation can be reduced. The approach will be discussed in some detail with the plane elasticity. Numerical results for the meshes of unequal length boundary elements are reported. Higher precision both for deflection and force is obtained than that for general boundary element method.The paper presents how the higher order singularity of a boundary integral equation can be reduced. The approach will be discussed in some detail with ...

1991, 23(3): 309-314. doi: 10.6052/0459-1879-1991-3-1995-842

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STRESS INTENSITY FACTORS FOR CORNER CRACKS AT HOLE UNDER REMOTE TENSION

The three dimensional weight function method developed in [4,5] is used to determine stress intensity factors for corner cracks at a hole in finite thickness plates subjected to remote tensile loading. The geometry parameters considered are r/t=0.5,l,2;a/c = 0.2,0.5,1,2;a/t= 0.2,0.5 within c/r≤2.The results are compared where possible, with other solutions available in the literature. Generally good agreement is observed. The effect of two dimensional unflawed stress distribution on the weight function resu...

1991, 23(3): 315-322. doi: 10.6052/0459-1879-1991-3-1995-843

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MATHEMATICAL PROGRAMMING METHOD FOR ANALYSIS OF ELASTO-PLASTIC CONTACT PROBLEMS WITH FRICTION

本文提出摩擦接触弹塑性分析的数学规划法,是弹性接触问题解法的推广,使之能处理比例加载时的塑性效应。利用所导出接触问题总刚度阵的逆,结合参变量线性互补公式,仍可消去由接触单元而引入的惩罚因子。于是,可以获得一个弹塑性问题、弹性接触和弹塑性接触问题的有限元参数二次规划法模型。所选的几个实例说明了方法的实用性。

1991, 23(3): 323-331. doi: 10.6052/0459-1879-1991-3-1995-844

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THE PROBLEM ABOUT NECESSARY AND SUFFICIENT CONDITION FOR THE METHOD OF WEIGHTED RESIDUALS AND THE SELECTION OF WEIGHTED FUNCTIONS

本文论证了偏微分方程初-边值混合问题的加权残值方程的充要性条件和有关定理。关于充要性条件的讨论也为正确选择解析函数作为权函数,建立充要的加权残值方程提供了理论指导。重点讨论了边界积分方程的充要性。指出了两种满足充要条件的权函数和相应的边界积分方程。

1991, 23(3): 332-338. doi: 10.6052/0459-1879-1991-3-1995-845

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STATISTICAL ANALYSIS OF BENDING STRESS INTENSITY FACTORS FOR CRACKED PLATE WITH UNCERTAIN PARAMETERS

This paper applies stochastic finite element method based on local averages of random fields to analyse statistical features of bending stress intensity factors for cracked plates with uncertain parameters. The stiffness matrix of a hybrid crack-tip singular element is first derived, then by use of first-order Taylor expansion the mean and variance of stress intensity factors are formulated. As an example the effects of uncertainties of Young's modulus. Possion's ratio and plate thickness on plate bending s...

1991, 23(3): 339-346. doi: 10.6052/0459-1879-1991-3-1995-846

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SECONDARY BIFURCATIONS OF A SLENDER ELASTIC BAR UNDER AXIAL COMPRESSION

Based on the equilibrium equation of an elastic curved bar in [1] , the post-buckling behavior of a slender bar with rectangular cross-section under axial compression is studied. Let the ratio of the lengths of the sides of the cross-section be 1:26. By using Poin-care-Keller's shooting method and introducing rescaling functions, we investigate the case in which 6 is in a neighborhood of δ0= 1. The secondary bifurcations of the equilibrium state of the bar are found whenδ≠1; we also give the asymptotic unfo...

1991, 23(3): 347-354. doi: 10.6052/0459-1879-1991-3-1995-847

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THE STABILITY OF A CHAPLYGIN'S SPHERE ROLLING ON A SLIGHTLY ROUGH HORIZONTAL PLANE

本文利用文献[1]的结果,继续讨论 Chaplygin 球在微粗糙平面上滚动的稳定性。严格证明了在粘性和库仓两种磨擦条件下球绕最大惯量主轴滚动的一致稳定性,和在粘性摩擦条件及球的最大与中间主惯量矩十分接近的前提下球绕最小惯量主轴滚动的不稳定性。

1991, 23(3): 355-360. doi: 10.6052/0459-1879-1991-3-1995-848

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DEVELOPED LONGUET-LENZ'S VECTOR

Besides the angular momentun vector and energy, there is another vector as a constant of motion in the Kepler's problem. In this paper, we deduce rotating voctor of linear central force, rotating vector of inverse cubic force, etc, and discuss their apptications.Besides the angular momentun vector and energy, there is another vector as a constant of motion in the Kepler's problem. In this paper, we deduce rotating voctor of linear central force, rotating vector of inverse cubic force, etc, and discuss their...

1991, 23(3): 361-365. doi: 10.6052/0459-1879-1991-3-1995-849

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CONNEXION OF FIRST INTEGRALS WITH PARTICULAR SOLUTION OF THE VARIATIONAL EQUATIONS FOR NONHOLONOMIC SYSTEMS

The paper presents the variational equations of nonholomic systems and studies their solution. By using a first integral, a particular solution of the variational equations is obtained, and an example is given.The paper presents the variational equations of nonholomic systems and studies their solution. By using a first integral, a particular solution of the variational equations is obtained, and an example is given.

1991, 23(3): 366-370. doi: 10.6052/0459-1879-1991-3-1995-850

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OUTSIDE SINGULAR POINT METHOD FOR THE ELASTOPLASTIC TORSION PROBLEMS

In this paper, the outside singular point method with the aid of sand-heap analogy for solving elastoplastic torsion problems is proposed. This method can reduce the dimensions of the problem and effectively avoid the singularity of the solution and needs no numerical integration. It has the advantages in simplicity, efficiency and accuracy.In this paper, the outside singular point method with the aid of sand-heap analogy for solving elastoplastic torsion problems is proposed. This method can reduce the dim...

1991, 23(3): 371-373. doi: 10.6052/0459-1879-1991-3-1995-851

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A CONSTITUTIVE RELATION OF ELASTO-BRITTLE MATERIAL WITH DAMAGE AND ITS APPLICATION

Based on principle of continuum damage mechanics, the mechanical response of the elasto-brittle material with damage is analyzed theoretically in this paper. Both material and damage are considered to be anisotropic. The expressions for the damage tensor, the effective elasticity tensor, the true stress tensor and the damage energy dissipation rate tenare also derived.Based on principle of continuum damage mechanics, the mechanical response of the elasto-brittle material with damage is analyzed theoreticall...

1991, 23(3): 374-378. doi: 10.6052/0459-1879-1991-3-1995-852

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A CONTENTION TO THE CLASSIC NONHOLONOMIC DYNAMICS

Totally different points to the conclusions in reference [4] are presented in this paper. Some comments on the characteristics of classic Gauss-Appell-hetaeb nonholo-nomic dynamics and Vacco dynamics are given as well.Totally different points to the conclusions in reference [4] are presented in this paper. Some comments on the characteristics of classic Gauss-Appell-hetaeb nonholo-nomic dynamics and Vacco dynamics are given as well.

1991, 23(3): 379-384. doi: 10.6052/0459-1879-1991-3-1995-853

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1991 Vol. 23, No. 3

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