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ON THE SLOW INSTABILITY OFKARMAN VORTEX STREET

The KarmAn vortex street being linearly stable for an isolated case according to it’s classical point-vortex model has been shown numerically to hold also for other more complicated models. The stability of the Karman vortex street verified by using point-vortex model when perturbed infinitesimally is however a “slow instability”as shown by the simulation when the street is to be perturbed by finite disturbances.The concept of“slow instability” was verified to exist also in the case of wake flow by using th...

1996, 28(2): 129-134. doi: 10.6052/0459-1879-1996-2-1995-312

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DEVELOPMENT OF NND SCHEME ON UNSTRVCTURED GRIDS

A second order cell-centered NND finite volume algorithm on unstructured triangular grids is presented for solving the Euler equations.A self-adaptive mesh technique is employed to improve the efficiency of the calculation.Two examples,shock reflection from a wall and flow in ZD wind tunnel with a step,are solved, and the results show that the present algorithm possesses good stability characteristics and capability of capturing the shock waves.

1996, 28(2): 135-142. doi: 10.6052/0459-1879-1996-2-1995-313

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NUMERICAL RESEARCH ON NONEQUILIBRIUM CHEMISTRY BOUNDARY LAERS OVER ABLATING TEFLON SURFACES

The chemically nonequilibrium boundary layers over ablating Teflon surface are numerically analysed.The effects of the gas models,the reaction rate constants and the wall catalysis on boundary layer properties are investigated.The results indicate that:the gas models have strong effects on the magnitude sequence of the species concentrations but the maximum difference of electron densities between the two models is only of one order of magnitude; the different floarocarbon reaction rate constants have much ...

1996, 28(2): 143-150. doi: 10.6052/0459-1879-1996-2-1995-314

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FLUIDELASTIC INSTABILITY IN TUBE ARRMS OF HEAT EXCHANGERS

In this paper the authors focus to discuss the fluidelastic instability in tube arrays of heat exchangers.From the viewpoint of practical application,the tube-in-channel model ofLever and Weaver are utilized. However, the vibration of tube is considered as periodic damping(or divergent)motion and the fundamental equations are solved by means of complex method.According to the relation between reduced flow velocity and mass damping parameter, the stability map will be drawn out, which may be used to predict ...

1996, 28(2): 151-158. doi: 10.6052/0459-1879-1996-2-1995-315

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SINGLE POINT SUBDOMAIN PRECISE INTEGRATION AND FINITE DIFFERENCE

Comparisons are made on stability analysis,explicit versus implicit integration schemes, to show the superiority of single point subdomain precise integration method proposed in this paper to the finite difference integration schemes.

1996, 28(2): 159-163. doi: 10.6052/0459-1879-1996-2-1995-316

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NUMERICAL ANALYSIS FOR MATERIAL BIFURCATION

By comparing with the results given by analytic method,the advantages of employing numerical method to analyse material bifurcations are displayed in this paper.Under the loading conditions of uniaxial and slightly biaxial tension,the characteristics of material bifurcations(plane shear banding and surface wrinkling)are demonstrated. Uniaxial tension testings justify that the critical stresses given by calculations are reasonably fair.

1996, 28(2): 164-170. doi: 10.6052/0459-1879-1996-2-1995-317

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A RATE-INDEPENDENT CONSTITUTIVE LAW FOR NONPROPORTIONAL CYCLIC PLASTICITY

A new constitutive law for rate-independent nonproportional cyclic plasticity is proposed, with proper consideration of discrete memory in plastic strain space and of nonproportional loading. Comparisons are made between the theoretical predictions and the experimental results for copper.

1996, 28(2): 171-180. doi: 10.6052/0459-1879-1996-2-1995-318

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MAGNETOELASTIC BUCKLING AND POST-BUCKLING OF SIMPLY-SUPPORTED CONDUCTING ROD

The magnetoelastic buckling and post-buckling of a simply-supported conducting rod in a magnetic field are studied.The magnetic field is produced by currents flowing in a pair of infinitely long paraelle wires and the natural state of the rod is in the plane of the wires and equidistant from the two wires. Under the spatial deformation, the mathematical model of theproblem is derived,and the linearized equations are studied. It is shown that the buckled states of the rod are always in planar deformations. S...

1996, 28(2): 181-190. doi: 10.6052/0459-1879-1996-2-1995-319

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STRESS-STRAIN FIELD NEAR THE NOTCH TIP OF A RUBBER SHEET

Analized in this paper is the elastostatic field near a notch tip in a rubber-like thin sheet.The asymptotic equations for the notch tip field are derived based on the constitutive relation given by Ref.[1].Near field solutions are obtained in regions that decreases and increases in size as the notch tip is approached.Their singular character depends on the constitutive parameters as well as the angle of notch that is evaluated numerically.

1996, 28(2): 191-199. doi: 10.6052/0459-1879-1996-2-1995-320

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PRACTICAL StABILITY AND LIAPUNOV STABILITY OF DELAY SYSTEMS

, Zhaolin Wang

This paper deals mainly with practical stability in terms of two measures for nonlinear systems with finite time delay.First,a kind of Ruzumikhin type differential comparison principle and monotone criterion are introduced. Then, based on them a Liapunov- Razumikhin direct method is presented, which results in general direct criteria of pactical stabilty.These criteria reduce the problem to a set of finite dimensional differential or integral inequlities and can be verified directly according to equations o...

1996, 28(2): 200-206. doi: 10.6052/0459-1879-1996-2-1995-321

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EXACT INVARIANT AND ADIABATIC INVARIANT OF A GENERAL DYNAMICAL SYSTEM

This paper studies the exact invariant and the adiabatic invariant of a general dynamical system in the extended phase space and gives the relation between the symmetry and the invariant of the system in the space.It presents the conception and a structure method of the higher order adiabatic invariant for the system,reveals the relation between the higher order adiabatic invariant and the infinitesimal symmetric transformations and discusses the first order adiabatic invariant and corresponding infinitesim...

1996, 28(2): 207-216. doi: 10.6052/0459-1879-1996-2-1995-322

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DYNAMIC PROCESS OF HEARd WORKING -A PRINCIPLE OF LEAST CARDIAC WORK WITH CARDIAC KINETIC ITEM

The principle of least cardiac work is a valid model which describes the dynamic process when the heart is working. In the previous study[1],analytic solutions of the cardiac process were abtained, but during heart working,specially on some pathological conditions,the kinetic power takes certain percent of the total power.So,when we analyse the cardiac dynamic process,we should analyse the total cardiac work.When the kinetic power was calculated,the equations are changed from the initial linear equations to...

1996, 28(2): 217-224. doi: 10.6052/0459-1879-1996-2-1995-323

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THE BOUNDARY INTEGRAL METHOD FOR INCOMPRESSIBLE VISCOUS NAIER-STOKES EQUATION

The first-order time splitting method is used to discretize the Navier-Stokes equations with primitive variables and a conjugate gradient method is used to decouple the variables.The resulted Laplace equations, Possion equations and Helmhotz equations are solved by using Boundary Integral Method and thus a boundary integral formulation for viscous Navier-Stokes equation is established for the first time.The numerical results for the steady and unsteady viscous flow aroulld cylindical body show the method de...

1996, 28(2): 225-232. doi: 10.6052/0459-1879-1996-2-1995-324

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THE COMPUTATION OF THE FREE VISCOUS FLOW ON THE WAV SLOPE

In this paper a time-dependent transformation which maps the moving flow region into a fixed rectangular is offered, by which the effective computational methods may be used to compute very complex free viscous flow. From the results of the example the important difference were discovered in comparing with the results computated by [1] with simplified equations.

1996, 28(2): 233-238. doi: 10.6052/0459-1879-1996-2-1995-325

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SPHERICAL INCLUSION WITH SLIDING INTERFACE

More and more attention has been paid to the influence of the sliding interface on the mechanical behaviors of materials recelltly. But most of the results available based on the assumption that the inclusion interface could not sustain any shear traction(free sliding),which is not suitable for most physical realities.In the present paper the non-zero shear traction at the inclusion interface has been taken into account,and an exact solution is obtained for the eigenstrain problem of spherical inclusion wit...

1996, 28(2): 239-243. doi: 10.6052/0459-1879-1996-2-1995-326

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THEOREM OF WORK RECIPROCITY FOR PYROELECRIC ELASTIC MEDIA WITH APPLICATION

With the linear elastic theory,theory of dielectrics and thermal conduction theory,the equations of work reciprocity similar to Bett’s theorem of work reciprocity are derived for pyroelectric elastic media.According to the equations,the pyroelectric elastic Somigliana’s boundary integral equalities were presented, which can be widely applied to boundary element method.

1996, 28(2): 244-250. doi: 10.6052/0459-1879-1996-2-1995-327

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CONSTITUTIVE MODELING OF ANISOTHERMAL NONPROPORTIONAL CYCLIC VISCOPLASTICITY

In order to describe the nonproportional cyclic deformation behavior at anisothermal condition,a viscoplastic constitutive model is introduced,which considers nonproportional cyclic additional hardening,the effects of nonproportional cyclic loading history and temperature history.In the model, the evolution equations of back stresses with three different evoluting rates are proposed;a new nonproportionality is defined.To consider the influence of nonproportional cyclic loading history and temperature histor...

1996, 28(2): 251-256. doi: 10.6052/0459-1879-1996-2-1995-328

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1996 Vol. 28, No. 2

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