力学学报

DIRECT NUMERICAL SIMULATION OF THREE DIMENSIONAL TEMPORALLY EVOLVING COMPRESSIBLE MIXING LAYER 1)

The three dimensional temporally evolving compressible mixing layer is simulated directly with the Navier Stokes equations. The discretization method has high order accuracy with group velocity control. The viscous terms of the equations are discretized with the sixth order accurate symmetrical compact difference method, the convection terms are discretized with the fifth order accurate upwind compact difference approximation, and three stage Runge Kutta method is used in advance of time. The time develo...

1998, 30(2): 129-137. doi: 10.6052/0459-1879-1998-2-1995-108

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A STUDY ON THE STABILITY OF GAS LIQUID TWO PHASE VORTEX STREET 1)

通过气液两相涡街试验研究和理论分析，首次得出了当有稳定的气液两相涡街发生时，气液两相涡街结构参数的取值及变化规律

1998, 30(2): 138-144. doi: 10.6052/0459-1879-1998-2-1995-109

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SECTIONAL FRACTURING OF POROUS MEDIA CONTAINING PRESSURIZED GAS UPON UNLOADING —— FOREWARNING INFORMATION OF OUTBURST 1)

A series of one dimensional simulation experiments (coal shock tube) showed that two kinds of damage, fracturing or outburst, could take place, when a porous medium containing pressurized gas and bearing compressive stress was suddenly unloaded. The critical condition of outburst is stronger than that of damage. In other words, outburst is a strong kind of damage. Therefore, there exists the case in which the damage condition is met while the outburst condition has not yet been met. Experiments showed a ...

1998, 30(2): 145-150. doi: 10.6052/0459-1879-1998-2-1995-110

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STUDY OF THE CONSTITUTIVE RELATIONSHIP OF RIGID POLYURETHANE FOAM 1)

Rigid Polyurethane Foam is a material with cellular structure. It has excellent properties for cushioning and energy absorbing and is used in packaging and protective padding. So it is important to study its dynamic mechanical behaviour and to propose its constitutive relation including stress, strain, strain rate and density. In this paper, the high strain rate experiment of rigid polyurethane foam of four kinds of density by Split Hopkinson Pressure Bar was introduced, and the strain rate is 1 000/s, 1 5...

1998, 30(2): 151-156. doi: 10.6052/0459-1879-1998-2-1995-111

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CALCULATION OF RESIDUAL STRESSES IN INJECTION MOLDED PRODUCTS FOR POLYMER MATERIALS 1)

Temperature distribution, microstructure of materials and stress strain are known to change in a complicated manner during mold cooling of semicrystalline thermoplastic polymers due to the coupling effects between them. These complex interaction and the factors which will induce the deformation in the final product, such as temperature variations, cry stallization and frozen in orientation are carefully discussed in the first part of this paper. The cons titutive relations of the thermoelastic plastic bod...

1998, 30(2): 157-167. doi: 10.6052/0459-1879-1998-2-1995-112

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THREE DIMENSIONAL EXACT ANALYSIS FOR FREE VIBRATION OF SIMPLY SUPPORTED PIEZOELECTRIC COMPOSITE LAMINATES 1)

In recent years, piezoelectric materials have been widely used as sensors and actuators in structural shape control, vibration suppression,noise attenuation and damage monitoring. Exact study can provide better understanding of the mechanical and electric behaviors of piezoelectric structures. An analysis for the three dimensional solutions of piezoelectric laminated plates has been conducted by several researchers. The exact solution methods, used in the papers before, mostly follow the strategy of Pagano...

1998, 30(2): 168-177. doi: 10.6052/0459-1879-1998-2-1995-113

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PRINCIPAL RESPONSE OF DUFFING OSCILLATOR TO COMBINED DETERMINISTIC AND NARROW BAND RANDOM PARAMETERIC EXCITATION 1)

The principal resonance of a Duffing oscillator to combined deterministic and narrow band random parametric excitations is investigated. In particular, the case in which the parametric terms sharing close frequencies is examined. For the first time, the method of multiple scales is used to determine the equations of modulation of amplitude and phase. The behavior, stability and bifurcation of steady state response are studied by means of qualitative analyses. Jumps are shown to occur if the random excita...

1998, 30(2): 178-185. doi: 10.6052/0459-1879-1998-2-1995-114

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THEORY AND APPLICATION OF NEW WAVELET PACKETS ALGORITHM WITH RESULTS IN THE ORDER OF FREQUENCY BANDS 1)

Wavelet analysis is a focus of international research. The result of Mallat algorithm is included in the result of wavelet packet algorithm. Old algorithm of wavelet packet put the results in the order of wavelet packet. It is good for mathematics, but not good enough for engineering. In many applications, we wish the result of algorithm can correspond to simple physics. As an example the Shannon wavelet Packets are discussed in detail, and Wavelet packets algorithm which put result in the order of frequenc...

1998, 30(2): 186-192. doi: 10.6052/0459-1879-1998-2-1995-115

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ELEMENT FREE METHOD AND ITS APPLICATION IN ENGINEERING 1)

Element free method(EFM), which is based on moving least squares method,is a gridless method to treat boundary value problems in geotechnique engineering such as dam stability analysis, slope analysis and progressive crack growth. Different from traditional numerical methods such as finite element method, EFM requires only nodes and a description of the external and internal boundaries and interfaces of the model, no element connectivity is needed. The mathematical basis of EFM is moving least squares met...

1998, 30(2): 193-202. doi: 10.6052/0459-1879-1998-2-1995-116

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DIFFUSION MOTIONS AND QUANTIZATION OF MECHANICAL SYSTEMS

Stochastic mechanics has gradually drawn much attention in the area of physics and mechanics since it was established by Nelson in 1966. In stochastic mechanics, quantum fluctuational phenomena are described in terms of diffusion processes instead of wave functions. The importance of stochastic mechanics can be shown from the fact that stochastic mechanics and orthodox quantum mechanics make the same predictions for the same position measurements. Since all measurements ultimately consist of position on...

1998, 30(2): 203-212. doi: 10.6052/0459-1879-1998-2-1995-117

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STRUCTURAL STATE DETECTION WITH FIBEROPTIC SENSING ARRAY AND NEURAL NETWORK SIGNAL PROCESSING TECHNIQUES 1)

In this paper, a type of simple and excellent crank type etched fiberoptic intensity sensor is presented. A three dimension sensing network, which is composed of etched fiberoptic sensors, is embedded in the laminated composite material structure of vertical tail wing of training 11 plane for the purpose of nondestructive evaluation of structural states in smart composite material and structures. The composite specimens in which sensing network is embedded are tested with stretch and bending in three poi...

1998, 30(2): 213-219. doi: 10.6052/0459-1879-1998-2-1995-118

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STUDY ON THE RELIABILITY OF RESIDUAL STRENGTH IN FATIGUE

Reliability study of fatigue problems can be divided into two types. The first type is that we can only consider the final results of fatigue process fracture. The failure probability is P f(N)=P(N fN) . The second type is that we must consider the fatigue process and take the component's strength (i.e. residual strength) as the function of cyclic number N . It's failure probability is P f(N)=P . We assume that the stage of the crack initiation is finished. Then the residual strength R a...

1998, 30(2): 220-228. doi: 10.6052/0459-1879-1998-2-1995-119

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AN IMPROVEMENT OF TRANSIENT SOLUTIONS OF AXISYMMETRIC DYNAMICS PROBLEM FOR TWO PHASE MEDIA

In Reference , the linear differential equations of axisymmetric dynamic problem for two phase media are derived by means of Laplace Hankel mixed transforms. To obtain a set of solutions in transform space for one layer in the form of initial parameters the fluid specific flux vector should be introduced. Based on the solutions of one layer, the solutions of multi layered system are achieved by employing the transfer matrix methed, but the flux boundary condition should be provided and the inversion of ...

1998, 30(2): 229-232. doi: 10.6052/0459-1879-1998-2-1995-120

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BUCKLING OF ELASTIC ANNULAR PLATE WITH PIEZOELECTRIC MATERIAL 1)

Because piezoelectric material has electromechanical effect of coupling,it has been applied to many important technical fields. It may be applied to the induction and control of integral intelligent structure system. After piezoelectric material is utilized, it may easily be applied to accurate monitor measurement of flexible structure, then the structure can be controlled effectively. Because there are piezoelectric material in structure, the research for integral structure became more complex and difficu...

1998, 30(2): 233-237. doi: 10.6052/0459-1879-1998-2-1995-121

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THE ANALYSIS OF FRACTURE OF BRITTLE ROCK MATERIAL BY USING THE BOUNDARY COLLOCATION METHOD 1)

Based on the conceptions of the microcrack controlling fracture and asymptotic failure, Griffith proposed the theory of the material brittle fracture in 1921. The underground rock masses are generally subjected tocompressive loading, consequently, the cracks in rock masses are forced to be closed and the crack surfaces are subjected to the loading. Maclintock and Wash established a modified Griffith Maximum Tensile Stress Theory in 1924, which only inspected the friction force τ n=νσ x(ν is the fr...

1998, 30(2): 238-246. doi: 10.6052/0459-1879-1998-2-1995-122

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EFFECTS OF THE SURFACE ENERGY ON THE LATTICE CONTRACTION AND EIGENFREQUENCY OF A NANO GRAIN

Nano grains are single phase or multiphase polycrystals with a grain size in the range of 1 to 100 nm. Compared with bulk materials with the same chemical composition, nano grains exhibit rather high surface energy due to the large volume fraction of particles (atoms and molecules) residing in the grain boundaries. Therefore, the influence of surface energy to the mechanical properties of grain, such as Young's modules, lattice size and eigenfrequency, is not negligible. This is confirmed by experiments....

1998, 30(2): 247-251. doi: 10.6052/0459-1879-1998-2-1995-123

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A STANDARD SOLUTION FOR THE DYNAMICS OF MULTI POINT COLLISION 1)

The impact problem between bodies is an important research task in the domain of modern engineering. Most previous researching work has focused on the impact problem of multi rigid body systems. In this kind of multi rigid body systems, two rigid bodies are connected by a hinge. But there is another kind of impact systems. In this kind of impact systems, there is no hinge among the colliding bodies. All of bodies may be free or constrained by their surroundings but for the hinges among them. This collisio...

1998, 30(2): 252-256. doi: 10.6052/0459-1879-1998-2-1995-124

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1998 Vol. 30, No. 2

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