力学学报

NUMERICAL STUDY ON DRAG COEFFICIENT OF AIR OVER WELL-DEVELOPED WIND WAVE

Turbulent air flow over well-developed wind waves in air-sea boundary layer is numerically simulated without considering wave breaking. Wind wave model is constructed according to the Donelan's idea. We have adopted the k - ε model to calculate the turbulent flow. The results of drag coefficient and turbulence characteristics agree well with observations.

1997, 29(4): 385-394. doi: 10.6052/0459-1879-1997-4-1995-243

PDF

LDV DIAGNOSIS OF FLOW FIELD IN LIQUID LIQUID HYDROCYCLONE WITH DOUBLE CYLINDER AND SINGLE CONE

The whole velocity and turbulence fields in a liquid liquid hydrocyclone with double cylinder and single cone were diagnosed with atwo dimensional LDV system under five testing conditions. The resultsshow that fluid flow in the hydrocyclone is a very strongly swirling turbulent flow. The fluid flows in tangentialdirection are composed of inner and outer swirling flows. The tangential velocity in the inner region is in accordance with therelation of Rankine's forced vortex . The flow field in theouter regi...

1997, 29(4): 395-405. doi: 10.6052/0459-1879-1997-4-1995-244

PDF

THE MAXIMUM ENERGY CRITERION FOR IDENTIFYING BURST EVENTS IN WALL TURBULENCE USING WAVELET ANALYSIS

In this paper, the wavelet analysis method is used to perform the time frequency double local decompositions for the signal of streamwise fluctuating velocity both in time space and in frequency space. The signal is obtained from a hot film anemometer output in an experimental study of turbulent boundary layer over a smooth flat surface. The energy evolution of fluctuating velocitywith scales is studied using the wavelet coefficients. The maximum energy criterion is proposed to determine the time scale th...

1997, 29(4): 406-412. doi: 10.6052/0459-1879-1997-4-1995-245

PDF

CRACK TRAPPING PHENOMENA IN DYNAMIC CRACK PROPAGATION

Using the mode I weight function of Willis et al. (1995)for a moving crack in combination with the model method of Rice et al. the instabilityphenomena of the crack front, how does it begin to surround andpenetratevarious arrays of asperities are investigated. The numerical results showthat the oscillatory crack tip motion through brittle, locallyheterogeneous materials results from constructive destructiveinterference of stress waves that can lead to continuing fluctuation of the crack front and propagat...

1997, 29(4): 413-420. doi: 10.6052/0459-1879-1997-4-1995-246

PDF

A CYLINDRICAL INTERFACE CRACK IN FIBER REINFORCED COMPOSITES

The problem of a cylindrical interface crack is reduced to a system of singular integral equations with the aid of two unknown dislocation functions at the interface crack surface. By using Muskhelishvili theory of singular integral equations, the interface stress field at the tips of the composites cylindrical interface is worked out. The stress singularity at the interface crack tips is determined in which two cases are considered, i.e....

1997, 29(4): 421-428. doi: 10.6052/0459-1879-1997-4-1995-247

PDF

A MICROMECHANICAL MODEL FOR ELASTIC BEHAVIOUR ANALYSIS OF WOVEN FABRIC COMPOSITES

A micromechanical model for elastic behaviour analysis of woven fabric composites is proposed in this paper. This model takes into account the actual fabric structure by considering the fibre undulation and continuity along both the warp and weft directions, the gaps between adjacent yarns and the actual cross sectional geometry of the yarn. The effect of the voids in the interyarn space and two cases of fabric stacking arrangements to the composite elastic properties have been investigated. A comparison o...

1997, 29(4): 429-438. doi: 10.6052/0459-1879-1997-4-1995-248

PDF

一类刚-柔耦合系统的建模与稳定性研究

For the simple Rigid Flexible Coupling system with a central rigid body and a mounted cantilever beam, the mathematical models of Euler Bernoulli beam in earlier papers have serious defect. In the present work, a nonlinear mathematical model of the system with a finite deforming beam on the assumption that its constitutive relation in linearly elastic, using the Differential Element Method and Variational Method, is obtained. In using strict method to analyse this nonlinearly coupling dynamic system, we u...

1997, 29(4): 439-447. doi: 10.6052/0459-1879-1997-4-1995-249

PDF

STUDY OF CRACK TIP SINGULARITY OF MODULE BY MICRO MULTIPLICATION MOIRE INTERFEROMETRY

A micro multiplication moire interferometry method with high spatial resolution and superhigh sensitivity is proposed by combining the traditional moire interferometry with magnification and multiplication techniques. The interference theory is given and the demonstrated experiment is conducted successfully. Then, this new method is applied to the study of the displacement fields and singularity around interlayer crack tip of the simulated microelectronic module under different thermal loadings.

1997, 29(4): 448-455. doi: 10.6052/0459-1879-1997-4-1995-250

PDF

A MATHEMATICAL MODEL FOR IMPACT HAMMERS AND IT'S GLOBAL BIFURCATIONS

By the method of modern dynamical systems, we studied the dynamicsof impact hammers by maps of circle and investigated the propreties ofthese maps. With the increasing of the frequency of excitation,the bifurcations that take place in this system are different from that inone dimensional maps. Under extreme conditions, the motions of the impacthammer are chaotic.

1997, 29(4): 456-463. doi: 10.6052/0459-1879-1997-4-1995-251

PDF

NUMERICAL SIMULATION AND A SIMPLIFIED MODEL FOR THE EARLY STAGE RESPONSE OF A MILD STEEL BEAM UNDER IMPACT LOADING

There are both elastic and plastic deformation coupled in the early stage response of a beam under impact loading. The results of finite element simulation indicate that the travelling plastic hinge predicted by the rigid plastic idealisation actually does not exist. The propagation of elastic flexural waves is the dominant deformation mechaism in the early stage. In this paper, a simplified elastic perfectly plastic coupled model is proposed which gives an excellent prediction of the early stage respon...

1997, 29(4): 464-469. doi: 10.6052/0459-1879-1997-4-1995-252

PDF

TRUSS GEOMETRY OPTIMIZATION BASED ON TWO STEP METHOD LINKED WITH SENSITIVITY OF OPTIMAL OBJECTIVE

The problem of the truss geometry optimization is solved by a sequential two step method. After finishing cross section optimization the first and second order derivatives of optimum objective with respect to nodal coordinate variables are calculated to construct a model of the shape optimization. Therefore, an approximate explicit formulation is established to overcome the difficulty of forming the optimization model of the second subproblem. It is easily solved by the sequential quadratic program algori...

1997, 29(4): 470-475. doi: 10.6052/0459-1879-1997-4-1995-253

PDF

AN IMPROVEMENT OF THE APPROXIMATE SOLUTION TO CONVEX MODELS OF UNCERTAINTIES

Zhiping Qiu

In terms of the eigenvalue problem with uncertain parameters,by means of non probabilistic,convex modeling combined with perturbation theory, an improvement is made on the first order approximate solution inconvex models of uncertainties. Without calculating the derivative of eigenvalues, the improved method not only can widen application of convex modeling, but also can greatly increase the efficiency ofcomputations.

1997, 29(4): 476-480. doi: 10.6052/0459-1879-1997-4-1995-254

PDF

HYPERSINGULAR INTEGRAL EQUATIONS AND BOUNDARY ELEMENT METHOD FOR PLANAR CRACK PROBLEMS IN THREE DIMENSIONAL FINITE BODIES

Using the Somigliana representation and the concepts of finite part integrals, a set of hypersingular integral equations of a planar crack in a three dimensional finite body and subjected to arbitrary loads are derived,and a numerical method is proposed by combining the finite part integral method with the boundary element method. According to the analytic theory of hypersingular integral equations, the square root models of displacement discontinuities in the elements near the crack front are applied,...

1997, 29(4): 481-485. doi: 10.6052/0459-1879-1997-4-1995-255

PDF

A GENERALIZED INTERLAYER MODEL FOR INTERFACE FRACTURE ANALYSIS BETWEEN BIMATERIALS

A generalized model of interfacial zone between bimaterials is presented. By virtue of this model, a penny shaped interface crack is investigated under torsion. Stress intensity factor is obtained by solving singular integral equation. Numerical examples are given to show the effects of material properties, interlayer thickness, and especially the distribution parameter k on the stress intensity factor.The comparison between Erdogan's results and our results shows that theinterlayer model presented in this...

1997, 29(4): 486-490. doi: 10.6052/0459-1879-1997-4-1995-256

PDF

SYMBOLIC LINEARIZATION OF NONLINEAR COUPLED DIFFERENTIAL AND ALGEBRAIC DYNAMIC EQUATIONS

This paper presents a symbolic approach for linearization of differential and algebraic dynamic equations. This technique avoids the drawbacks of the numerical perturbation method and eliminates the need to set up thelinearized constraints library. Several examples have been used tovalidate the procedure. Included is the stability analysis of six DOFrailway car model.

1997, 29(4): 491-496. doi: 10.6052/0459-1879-1997-4-1995-257

PDF

A STUDY OF IDENTIFICATION OF NONLINEAR CHARACTERISTICS IN CUSHIONING PACKAGING BASED ON NEURAL NETWORKS

The structural neural network method with fuzzy adaptive controlis applied to the identification of nonlinear characterisics in packaging cushionings in this paper. The simulated results on the two typical models of packaging cushioning materials show that the nonlinear characteristics can be identified perfectly. The combination of the structural neural network method with fuzzy adaptive techniques increases the training speed of the network, reduces the artificial interference to parameters of the network...

1997, 29(4): 497-500. doi: 10.6052/0459-1879-1997-4-1995-258

PDF

ON THE STABILITY OF DISSIPATIVE MECHANICAL SYSTEMS WITH CONSTRAINT DAMPING

, Zhaolin Wang

The paper investigates the stability of a nonlinear dissipative mechanical system subjected to potential force, gyroscopic force, Rayleigh dampingand constraint damping, using direct Liapunov method. Assuming that the gyroscopic force depends on a parameter, two asymptotically stability theorems are obtained, and the lower bounds of the parameter are evaluated.

1997, 29(4): 501-505. doi: 10.6052/0459-1879-1997-4-1995-259

PDF

ON THE APPLICABILITY OF ESHELBY′S EQUIVALENT INCLUSION METHOD IN NONLINEAR CONTINUMM MECHANICS

This note actually is a discussion on the paper′ A Micromechanical Analysis of The Nonlinear Elastic and Viscoelastics Constitutive Relation of a Polymer Filled With Rigid Particles′ published in Acta Mechanica Sinica, Vol.25, No.5, 1993(or Vol.10, No.2, 1994, English Edition). In order to verify the validity of the statement concluded by the paper, two illustrative examples are considered. Analytical solutions for problems of a rigid spherical particle and a spherical void embedded in an infinite...

1997, 29(4): 506-512. doi: 10.6052/0459-1879-1997-4-1995-260

PDF

1997 Vol. 29, No. 4

NoticeMORE+

Exquisite ArticlesMORE+

Download Center

Author Center