力学学报

NUMERICAL STUDY OF THREE-DIMENSIONAL SEPARAIED FLOW OVER A BLUNT BODY AT HYPERSONIC SPEED

The study of three-dimensional separation over a capsule-type vehicle at hy- personic speed are carried out using the finite difference numerical method with M_∞= 7.0,Re_∞=4.5 ×10￣5. Five kinds of topological pattern on the vehicle surface are found when the angle of attack is increased from 10°to 40°,and the transition process from regular open separation to close separation on leeward surface are sliown. Analysis shows that different separation patterns are caused by same pressure condition adverse pres...

1995, 27(2): 129-136. doi: 10.6052/0459-1879-1995-2-1995-415

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ON THE MODELLING OF EDDY VISCOSITY TENSOR FOR SHEAR TURBULENCE

This paper considers the new eddy viscosity modelling of shear turbulence,where the eddy viscosity is a forth-order tensor.Based on the concept of Moore-Penrose’s generalized inverse matrices,the computational formula is obtained for the components of eddy viscositv tensor. The checking calculation is completed for a plane back-facing step flow. A proposal is offered for application of the eddy viscosity tensor modelling.

1995, 27(2): 137-142. doi: 10.6052/0459-1879-1995-2-1995-416

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EFFECTS OF VELOCITY DISTRIBUTION ON THE STRUCTURE OF BOTTOM BOUNDABY MIXED LAYER IN A STRAIIFIED FLOW

The problem of bottom boundary mixed layer growth in a stratified flow is dealt with in this paper in terms of a new vertically integrated model.A parameter depending on the distribution of velocity in the vertical direction appears in a new energy balance equation. This energy balance equation is equivalent to the Richardson number closure model used byPollar et al.￣[21] and Thompson￣[13] when the velocity distribution is uniform in the verticaldirection within the layer.The analytic solutions are obtai...

1995, 27(2): 143-150. doi: 10.6052/0459-1879-1995-2-1995-417

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A VARIATIONAL METHOD TO SOLUTION OF LINEAR ELASTIC PROBLEM WITH VOID

Changqing Chen

This paper utilizes two Laurrent’s series which satisfy the conditions of notraction on inner elliptical boundary,and sets up functions.It turns out that the otherboundary conditions can be satisfied provided that the variation of the functions equals zero.With the variational approaching,the elastic problem with void is resovled.Furthermore,this method is applied to the model of periodical distributed void,the effective modulus andthe effctive Poisson’s ratios have been obtained.

1995, 27(2): 151-160. doi: 10.6052/0459-1879-1995-2-1995-418

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DYNAMIC BEHAVIOUR OF SOFTENING BEAMS

Due to thstrain-softening of materials or due to the cross-sectional distortion of thin-walled beams in their large deflection,the moment-curvature relation of beams may display a hardening-softening characteristic.The recent work carried out by a research groupin Peking University has confirmed that when a semi-infinite beam with softening property is subjected to a suddenly applid constant velocity at its tip,softening may develop into asegment of finite length and travel along the beam. Meanwhile,in ord...

1995, 27(2): 161-172. doi: 10.6052/0459-1879-1995-2-1995-419

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ANALYTICAL-GENERALIZED VARIATIONAL METHOD OF MULTI-REGION ON SOLUTION OF SMALL SCALE DELAMINATION OF LAMINAIE

In the case of small scale delamination,the cross section of laminate is divided into two regions Ⅰ and Ⅱ,including and excluding delamination(interface crack)respectively. In each region,the eigen expansions of displacement and stress fields satisfying all of govern- ing equations,boundary conditions along delamination surfaces and conditions of continuity along undelaminated portion of interface are derived.The other boundary conditions and conditions of continuity between the two regions are satisfied b...

1995, 27(2): 173-179. doi: 10.6052/0459-1879-1995-2-1995-420

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SENSITIVITY ANALYSIS OF DISCRETE VIBRATORY SYSTEMS

A new method for analyzing the sensitivity of dicrete structures has been demonstrated.The algorithm of eigen-derivatives is accurate,and only involves the degen- erate modes to be differentiated.

1995, 27(2): 180-188. doi: 10.6052/0459-1879-1995-2-1995-421

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A LINEAR COMPLEMENTARITY METHOD FOR ELASTIC CONTACT PROBLEMS BASED ON THE PRINCIPLE OF VIRTUAL WORK

In this paper,a linear complementary contact condition is first derived,and then,base on the principle of virtual work and FEM,a linear complementarity method for elastic problems with friction is proposed.This method can avoide the tiresome iteration procedure used in previous work,and if there is no unloading,only one incremental step is needed for a solution. An exemple is given to demonstrate tlie correctness and effectiveness of the method.

1995, 27(2): 189-197. doi: 10.6052/0459-1879-1995-2-1995-422

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AN ANALYTICAL METHOD OF PIN LOAD COMPUTATIONS FOR JOINTS OF FINITE DIMENSIONS WITH MULTI-FASTENERS

A new analytical method of pin load computation for Joints with multi-rivets or multi-bolts is presented by means of mathematical theory of elasticity and classical principle of structural mechanics.A system of linear algebraic equations of the unknown pin loads is establiqLhed and several numerical examples are given. In this method,the connected plates are considered as elastic bodies and not rigid ones,then the accuracy weakness of traditional method used in machine design can be overcome. Furthermore,th...

1995, 27(2): 198-212. doi: 10.6052/0459-1879-1995-2-1995-423

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ROBUST STABILITY ANALYSIS OF IMPULSIVE DYNAMICAL SYSTEMS

This paper is concerned with the problem of stability robustness for the k-p periodic solutions of impulsive dynamical systems.First of all,based on the solutions of differential equations, impulsive conditions and loint conditions.necessary and sufficient conditions for the existence of k-p periodic solutions of the system are presented by using the iterative method.Then,utilizing tlie equivalent principle of stability,we derived the stability conditions through the perturbed difference equations of period...

1995, 27(2): 213-221. doi: 10.6052/0459-1879-1995-2-1995-424

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ONE DIMENSIONAL OPTIMAL STRAIN PATHS OF THE NONLINEAR VISCOELASTICITY AND THE VISCOPLASTICITY

In this paper, we presented the equations of the optimal strain paths for the nonlinear viscoelasticity and the viscoplasticity in one dimensional case. We also showed some character of the optimal paths,i.e(1)if the relation of the viscous part and the strain in the nonlinear viscoelastic constitutive equation is cave,the corresponding optimal strain path is cave;(2)the optimal paths of the overstress viscoplasticity and the Bodner-Parton one are that the plastic strain is linear and the plastic strain ra...

1995, 27(2): 222-225. doi: 10.6052/0459-1879-1995-2-1995-425

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CAVITY DAMAGE AND DEFOBMATION LOCALIZATION BEHAVIORS OF THE CONSTRAINED BULGIN OF SUPERPLASTIC METAL SHEETS

In this paper, the cavity damage and deformation localization behaviors of the constrained bulging of the cavity-sensitive superplastic metal sheets into cone-desk shape dies are numerically studied by using a largestrain rigid visco-plastic finite element method. Based on the simulation of practical alloy sheets,the influences of the superimposed pressure Ph,the initial cavity growth rate β_0 and the geomletrical shapes of the dies(the cone angle θ and the die heightHp)on the localization and cavity fract...

1995, 27(2): 226-231. doi: 10.6052/0459-1879-1995-2-1995-426

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ELASTIC-PLASTIC ANALYSIS OF A DYNAMICALLY LOADED DOUBLE NOTCH THIN PLATE

In this paper,dynamic elastic-plastic FEM analyses of a double notch thir plate subjected to the experimentally measured tensile pulse are presented.An invariant finite domain integral expression J(t)employed as dynamic energy release rate is calculated. The analysis demonstrate that J(t)integral can be regarded as the crack tip characterizing parameter for the double notch specimen used in Ref.1. we also calculate the value of the J_(dc)(t)integral from the measured load-calculated displacement curve by us...

1995, 27(2): 232-238. doi: 10.6052/0459-1879-1995-2-1995-427

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FORMULAIION FOR GENERALIZED CONFORMING PLATE ELEMENT WITH FERGUSON’S SURFACE

This paper presents a thin plate element with Ferguson’s surface according to generalized conforming theory,and advances it to moderate thick plate problem,regarding it as two-dimensional deep beam and getting out the functions of element border by using Timoshenko’s beam theorem. Calculation results show it is of high quality.

1995, 27(2): 239-244. doi: 10.6052/0459-1879-1995-2-1995-428

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AN ISOTROPIC DAMAGE ANALYSIS ON BEAMS UNDER CREEP PURE BENDING LOAD

In this paper, based on the assumptions of pure bending damage of beams, the elementary equations on bending damage are developed. Similar to the tensile damage variable defined as reduction of loading area by L.M. Kachanov,the bending damage variable is defined as reduction of moment of inertia. For the simplicity of application in engineering,asimple bending damage model is proposed.At last,an exact creep pure bending damage analysis is made, based on which the materials’constants of the simple bending da...

1995, 27(2): 245-249. doi: 10.6052/0459-1879-1995-2-1995-429

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EFFECTS OF ANHARMONICITY AND MASS FACTOR ON MOLECULAR VIBRATIONAL RELAXATION OF DIATOMICS IN CONDENSED STATE

In this note,we investigate the effects of anharmonicity and mass for diatomicmolecular vibrational relaxation in condensed fluid by computer simulation. We have shownthat the rates of vibrational relaxation increase with the increase of anharmonicity and massfactor. This is in agreement with the data from experiment.

1995, 27(2): 250-252. doi: 10.6052/0459-1879-1995-2-1995-430

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MEASURING TEMPERATURE FIELD WITH THREE-STEP PHASE-SHIFTING

A two-reference phase-shifting method is used to meaisure temperature fieldin this paper.Because the phaise-shifting is introduced during reconstructing,it overcomesdisadvantges which exist in introducing phase-shifting during recording.Using this method,we can measure not only quasi-state field , but also transient field.we also adopt a newmethod to calculate the temperature field distribution in this paper.Experimental resultsillustrate that the method inproves measurement speed and precision.

1995, 27(2): 253-256. doi: 10.6052/0459-1879-1995-2-1995-431

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1995 Vol. 27, No. 2

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