力学学报

STREAMWISE VORTICES IN A PLANE MIXING LAYER AND RAYLEIGH'S CENTRIFUGAL INSTABILITY

A finite difference scheme is employed to solve the Navier Stokes and continuity equations for a 3 D temporally growing plane mixing layer. The physical mechanism for generation and development of streamwise vortices in the mixing layer is numerically investigated. Rayleigh's theory of centrifugal instability for inviscid axisymmetric flow is extended to analyze the two dimensional primary flows of the mixing layer. Accordingly, a dimensionless group Ray =-(r/υθ)/υθ/r is derived, where υθ is th...

1997, 29(2): 129-135. doi: 10.6052/0459-1879-1997-2-1995-207

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FLUCTUATING SURFACE PRESSURES OF TWO CIRCULAR CYLINDERS IN TANDEM ARRANGEMENTS SUBJECTED TO WAVE AND CURRENT FLOW AT HIGH REYNOLDS NUMBERS

Fluctuating pressures, lift and drag of two circular cylinders in tandemarrangements wave investigated experimentally in this paper. The twocylinders, which were made of a PVC pipe and whose surfaces were smooth,were subjected to wave and current flow in the range of 2 40×10 5≤ Re≤5 40×10 5, 2 94≤Kc≤7 85, 2 54≤L/D≤5 02 . The results show that: the flow pattern around the two cylindersin wave and current flow are similar to those in uniform cross flow atsmall Kc numbers, but the interference ...

1997, 29(2): 136-141. doi: 10.6052/0459-1879-1997-2-1995-208

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ALTERNATIVE FORM OF THE BOUSSINESQ EQUATIONS WITH IMPROVED LINEAR DISPERSION CHARACTERISTICS

Boussinesq type equations, can be used to simulate the nonlinear transformation of surface waves due to the effects of shoaling, refraction, diffraction, reflection and nonlinear action so on. Different linear dispersion charateristics can be obtained by different vertically integrated methods. A new form of the Boussinesq equations is derived by using two different layers the horizontal velocity variable. The 4th order of Pade approximation, that is exact linear dispersion relation of Airy waves, is obta...

1997, 29(2): 142-150. doi: 10.6052/0459-1879-1997-2-1995-209

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1997, 29(2): 151-157. doi: 10.6052/0459-1879-1997-2-1995-210

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ON THE HOPF BIFURCATION SYSTEM IN THE PRESENCE OF PARAMETRIC REAL NOISES

With the aid of the stochastic averaging method,the theory of singular points of diffusion processes and the method of invariant measure, a Hopf bifurcation system in the presence of parametric real noises is studied. It is found that in this nonlinear stochastic system, due tothe presence of the parametric real noises, a change of the type of bifurcation takes place and two bifurcation points appear, which differ from the original Hopf bifurcation one.

1997, 29(2): 158-166. doi: 10.6052/0459-1879-1997-2-1995-211

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RESEARCHES ON TWO EXPRESSIONS ABOUT COMPLEX EIGENVALUE

It is very interesting to study eigenvalues of a linear system by analyzing the properties of its mass matrix, stiffness matrix, damping matrix and so on. After a brief review on the complex mode theory, this paper developed a new set equations about corresponding matrices by recalling the orthogonality between the complex modes of a damped gyroscopic linear system. Based upon this, the applicability of two popular expressions about complex eigenvalues was investigated. The emphasis was given to the questio...

1997, 29(2): 167-174. doi: 10.6052/0459-1879-1997-2-1995-212

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NATURAL CHARACTERISTICS OF WAVE PROPAGATION IN BEAM

The natural characteristics of wave propagation in beam has been studied based on distributed parameter concepts, and the relations between those and the periodic structures are given. The influence of support condition on characteristics of wave propagation has been discussed. It is shown in this paper that some problem would create if an approximate method (such as finite element method) is used. The study results of this paper can be applied to analyse the periodic structures.

1997, 29(2): 175-181. doi: 10.6052/0459-1879-1997-2-1995-213

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A CHAIN NETWORK MODEL SIMULATING MACRO MECHANICAL BEHAVIOR AND MICRO DAMAGE EVOLUTION OF Si 3N 4 CERAMICS

By taking the bridging of elongated grains as a dominant load transfer mechanism across the intrinsic flaws in the matrix, a chain-network model is proposed and used to simulate macro mechanical response and micro damage evolution of in situ reinforced ceramics. Relation between the mechanical parameters of the chains and the geometrical-physical properties of the elongated grains is discussed. Numerical experiments and statistic investigations are carried out.

1997, 29(2): 182-188. doi: 10.6052/0459-1879-1997-2-1995-214

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METHODS FOR RANDOM THERMAL CREEP STRESS ANALYSIS OF MASSIVE CONCRETE STRUCTURES

Stochastic finite element method for random the rmal creep stress inmassive concrete structures is presented. In the proposed method, various kinds of random factors including material physical parameters and random temperature in concrete are taken into account. Owing to the effect of stochastic environmental temperature, hydration heat of concrete and random heat conductivity parameters, the temperature in concrete appears to be non-stationary process. Based on the linear creep law, the effect of temperat...

1997, 29(2): 189-202. doi: 10.6052/0459-1879-1997-2-1995-215

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HIGHER ORDER SINGULAR TERMS AND J -INTEGRAL FORMULATIONS

从４种典型裂纹情况的特征展开式出发，运用其微分性质和伪正交性质得到了含有高阶奇异项的Ｊ积分表达式．它们是通用的显函数表征的．本研究支持了Ｈｕｉ和Ｒｕｉｎａ的杰出研究和重要观点，即高阶奇异项和非奇异项一样在小范围屈服描述中扮演着重要角色．研究表明，常规柔度方法确定的Ｊ积分已隐含了高阶奇异项的贡献．断裂准则有可能由含高阶奇异项和非奇异项的Ｊ积分的临界值来描述

1997, 29(2): 203-214. doi: 10.6052/0459-1879-1997-2-1995-216

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THE LARGE PERTURBATION INVERSION METHOD ON 2 D MEDIUM PARAMETERS

The problem of parameter inversion in inhomogeneous medium was studied and a generalized ray approximation method to inverse 2-D medium parameters was introduced in this paper. By use of the referential variables and perturbational variables the medium parameters of wave equation were rewritten. Using the Green function theory, the integral equation of perturbational parameters was obtained. Based on the local principles of wave function in inhomogeneous medium, a generalized ray approximation form of total...

1997, 29(2): 215-219. doi: 10.6052/0459-1879-1997-2-1995-217

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A UNIFIED HOMOGENIZATION MODEL FOR THE INTERACTION BETWEEN TUBES AND FLUID

Two equivalent homogenized equations presenting the dynamic behaviour of tubes in fluid are developed. Correspondently, the relation between parameters in the both equations are given too. It is interesting that both the equations are just the ones obtained by Schumann and Benner in 1981 and Brochard and Hammami in 1991, respectively. In fact, a unified homogenization theory for the interaction between tubes and fluid has been presented in the paper.

1997, 29(2): 220-223. doi: 10.6052/0459-1879-1997-2-1995-218

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STABILITY ANALYSIS OF A TWO-DIMENTIONAL DISLOCATION CRACK MODEL

Based on the one-dimensional dislocation crack model and the energy calculations, a two-dementional dislocation crack model is presented,which is an elliptical crack caused by the dislocation pile-up groups.The total potential energy of this model is obtained. Following the principle of conservation of energy, the equilibrium length of the crack and the critical stresses for growing cracks are given. All results are compared with Griffith's solutions for Mode-I through crack and the elliptical embedded crac...

1997, 29(2): 224-230. doi: 10.6052/0459-1879-1997-2-1995-219

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LARGE-SCALE NONLINEAR PROBLEM OF ELASTIC SPHERICAL SHELLS SUBJECTED TO CONCENTRATED LOAD

The large-scale axisymmetrical nonlinear problem of elastic spherical shells subjected to concentrated load is studied by the pseudo-arclength algorithm of the finite element method. The range of the deformation is from the initial states to the complete retroflexion of shells. The calculated results are compared with the experiment results.

1997, 29(2): 231-235. doi: 10.6052/0459-1879-1997-2-1995-220

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NONLINEAR FORCED VIBRATION OF LAMINATED COMPOSITE SHALLOW SPHERICAL SHELLS

A nonlinear forcde vibration problem of a symmetrically laminated cylindrically orthotropic shallow spherical shell including transverse shear has been studied. Period solutions of resonance and nonresonance are also obtained. Finally, this paper discusses the effects of transverse shear on characteristic curves of forcing frequency and amplitude of vibration.

1997, 29(2): 236-241. doi: 10.6052/0459-1879-1997-2-1995-221

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AN EXPERIMENTAL ANALYSIS OF FRACTURE MECHANICS FOR CRACK TIP NORMAL TO INTERFACIAL

The problems of an interfacial crack with the crack tip normal to interface are investigated by experiment. High-resolution moire interferometry methods are employed to get displacement fields surrounding cracks. The order of singularity of displacement faction of angular displacement and stress intensity factor are determined from experimental results and it also be compared and discussed with some theoretical results.

1997, 29(2): 242-247. doi: 10.6052/0459-1879-1997-2-1995-222

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A NOVEL FIBEROPTIC STRESS SENSOR

Based on the effect of mismatch of mode volume and principle of microbending. A novel intensity fiberoptic stress sensor is presented.The responses of the optical fiber stress sensors are linear,repeatable, have a high cyclic endurance and no measurable hysteresis.

1997, 29(2): 248-251. doi: 10.6052/0459-1879-1997-2-1995-223

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THE HAMILTON SYSTEM AND ANALYTICAL SYMPLECTIC SOLUTION FOR REISSNER PLATES

Based on the Reissner plate theory, and by modifying the mixed variational principle, the Hamilton type generalized variational principle is established, and the Hamilton canonical equations and the analytical symplectic solution are also presented.

1997, 29(2): 252-256. doi: 10.6052/0459-1879-1997-2-1995-224

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1997 Vol. 29, No. 2

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