力学学报

The study of turbulent properties in stable flexuous blow-suck boundary channel flow

In non-equilibrium turbulent flows, the properties betweenReynolds stress and rate of strain is different, the phase difference of theReynolds stress and rate of strain are stable in a sizable range. This isuseful to understand Reynolds stress and rate of strain, and posed greatproblem to non-equilibrium turbulent models and sub-grade Reynolds stressmodels in LES. Distribution of the disturbance and its non-line term andrelation of the phase were also studied with laminar model in this paper.

2005, 37(6): 673-681. doi: 10.6052/0459-1879-2005-6-2004-212

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The study of the characteristic of vortex wave in an asymmetric channel

It has been received much attention that the dispersionphenomena can be produced by unsteady flows in a channel during the past fewdecades because of their usages in chemical, biochemical and medicalengineering. As the study of fluid mechanics has evolved from steady stateinvestigations towards the reality of unsteady phenomena, it has becomeincreasingly clear that instantaneous whole field non-intrusive flowmeasurement techniques are required. In the past few years particle imagevelocimetry (PIV) has developed rapidly as a means for obtaining wholefields of fluid velocities. It has capitalized on recent computer hardwareand software developments, to the extent that it now is practicable fordetermining and mapping fields of unsteady movement, especially at thenarrow flow channels.This study makes the use of PIV to capture the vortex wave motion and theirstructures during oscillatory flows through a two-dimensional asymmetricchannel. The vortex wave is a relatively recently discovered fluid structurewhere a standing wave of vortices can be generated either by an unsteadymotion of a channel wall or by unsteady flow through an asymmetric channelexpansion. The vortex wave, which evolved at low speed, can enhance the masstransfer of boundary layer in channels and consequently maintain very lowwall shear rates for some shear sensitive microorganism or mammalian cells.In this paper, a set of experimental equipment was established for vortexwave flow. Unsteady incompressible flow, flowing at low-Reynolds-number inperiodic oscillatory pattern, in a two-dimensional channel with backwardsidestep structure was investigated by using PIV. The generation,development and disappear of the vortex wave about oscillatory flow in anasymmetric channel has been analyzed quantificationally. A series ofvelocity vector figures at different phases have been obtained. The velocityprofile and the vorticity of vortex wave have been tested and calculated inthis paper in order to analyze the mechanisms of strengthening masstransfer. The results show that the vortex wave flow-field is periodical andthe waves will be brought as the fluid periodically flows. It indicates thatthe main feature of vortex wave is that it is a two-dimensional standingwave formed during the deceleration period and the core flow follows acurving path with a sequence of vortices forming alternately on each wallbetween the core flow and the walls of the channel. In addition, therelationship between Reynolds number and vortex wave has been investigated.The experimental results corresponded satisfactorily with the analysingresults of the vorticity equation. It has showed that the vortex strengthenhances but the size of the vortices and the wave is almost changeless asReynolds number increases.

2005, 37(6): 682-688. doi: 10.6052/0459-1879-2005-6-2004-402

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Three dimensional numerical simulation of natural curved river

2005, 37(6): 689-696. doi: 10.6052/0459-1879-2005-6-2004-223

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Interaction effect in energy absorption of porous material filled thin-walled structure

The mechanism of "interaction effect" raised in porous material filled thin-walled structure is studied, and quantitative partition in energy absorption is reached with the proposed model in this paper. Taking aluminum foam filled hat section as example, we found three characteristic regions in the crushed foam filler, i.e., densified region, extremely densified region and undeformed region. An analytical model according to the experimental observation was built to find the volume reduction and volumetric strain in each region of the crushed porous material filler, based on the ideally crushable assumption. Combining with the superfolding element model for thin-walled hat structures, the contribution of each component of the filled structure, i.e., hat section, porous filler; densified region and extremely densified region to the overall energy absorption was quantitatively partitioned. The study shows that little increase in energy absorption is found in the thin-walled structure, while the augmentation in porous material filler is 40% or so. The extremely densified region accounts for mainly to the interaction effect.

2005, 37(6): 697-703. doi: 10.6052/0459-1879-2005-6-2004-255

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Reflection and refraction of longitudinal displacement wave at an interface between two different micropolar magneto-thermoelastic solid in welded contact

The general governing equations of micropolar generalized magneto-thermoelasticitic solid affected by multi-physical field,such as magnetic field ,thermal field and elastic field,are presented in this paper. The magnetic effect, thermal effect and mechanical effect are included in the general equations. Also the coupled thermalelasticity and its five extended theories are in its generalized heat conduction equation. The five extended theories are the Lord-Shulman theory with one relaxation time(L-S), the Green-Lindsay theory with two relaxation times(G-L), the Green-Naghdi theories of type II(without energy dissipation,G-N II) and of type III(G-N III),and the Chandrasekharaiah and Tzou theory(dual-phase-lag,C-T). Using this general governing equations, the reflection and refraction at the plane interface of two-welded semi-infinte micropolar elastic solid are studied for incident longitudinal displacement wave in the presence of a constant magnetic field and an uniform initial temperature field. Using continuous conditions at the interface, the amplitude ratios of reflected and/or refracted thermal wave,longitudinal displacement wave(LD wave) and coupled transverse and microrotational wave(CD I and CD II ) to incident LD wave are studied and described graphically with the incident angle,which variates from 0 degree to 90 degree. The thermal effect, the magnetic effect and the affection of thermal relaxation on them are discussed. The numerical results show that all reflected and refracted waves are affected by thermal field, magnetic field and thermal relaxtion. And there is a striking discrepancy between different type wave for thermal effect, such as that for the effect of magnetic field or thermal relaxtion,but it is similar for reflected and refracted waves of the same type.

2005, 37(6): 704-712. doi: 10.6052/0459-1879-2005-6-2004-373

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Interval algorithm for membership-set identification of linear time-invariant system

An interval algorithm was presented for parameter set estimation of a linear time-invariant system with the Unknown-But-Bounded (UBB) noise. In virtue of interval mathematics, the algorithm objective is in seeking the minimal hyper-rectangle (or interval vector) of parameters which is compatible with the measurements and the bounded noise, and its recursive formula were derived. Convergence of the algorithm was analyzed. The center estimation of parameters can not only be obtained, but also the uncertain bounds on them. Numerical examples illustrate its small computation efforts and higher accuracy in comparison with Fogel's algorithm and the least squares algorithm.

2005, 37(6): 713-718. doi: 10.6052/0459-1879-2005-6-2004-370

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THE MOVING LEAST-SQUARE APPROXIMATION WITH COMPLEX VARIABLES AND ITS APPLICATION IN BOUNDARY ELEMENT-FREE METHOD FOR ELASTICITY

Based on the moving least-square (MLS) approximation, the moving least-square approximation with complex variables (MLSCV) is presented in this paper. And the moving least-square approximation with complex variables based on the orthogonal basis function is discussed in detail. The method can not form an ill-conditioned system of equations. The meshless method obtained from the moving least-square approximation with complex variables has greater computational efficiency. Then, combining the moving least-square approximation with complex variables and the boundary element-free method (BEFM) for elasticity, the boundary element-free method with complex variables (BEFMCV) for elasticity is presented, and the corresponding formulae are obtained. The boundary element-free method with complex variables is a direct numerical method of the meshless method of boundary integral equation. And the boundary condition can be applied easily. The boundary element-free method with complex variables has a greater precision. Some numerical examples are given at last.

2005, 37(6): 719-723. doi: 10.6052/0459-1879-2005-6-2004-314

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Experimental Research of Dynamic Mechanical Behaviors of Frozen soil

Frozen soil samples at 4 different temperatures were investigated in 4 different high strain rates on Split Hopkinson Pressure Bar (SHPB). The test results indicated that temperature and strain rate each have an effect on floating stress, this shows the time-temperature equivalence property of frozen soil. And the time-temperature equivalence property also show its dynamic brittleness and frozen brittleness. The oscillation and convergence of strain-stress curves are also aroused by its time-temperature equivalence property.

2005, 37(6): 724-728. doi: 10.6052/0459-1879-2005-6-2004-450

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Generalized nonlinear strength theory for rock materials

Based on generalized nonlinear strength theory that has been proposed by author, combined with mechanics characteristics of rock materials, a generalized nonlinear strength theory for rock is proposed. The failure function of the theory is a smooth curve between SMP criterion and Mises criterion in the π plane and is a exponential curve in the meridian plane. The generalized nonlinear strength theory for rock is validated by the triaxial compression test data for different rocks that have been published. The generalized nonlinear strength theory for rocks can be widely applied to all kind of rocks and can describe the characteristics of nonlinear strength in the π plane and the meridian plane. Compared with the Hoek-Brown criterion using test results of five different rock types under the three-dimensional stress states, the superiority of the nonlinear strength theory for rock materials has been embodied in this paper.

2005, 37(6): 729-736. doi: 10.6052/0459-1879-2005-6-2004-270

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Effect of lateral undulatory support stiffness of rail on initiation and evolution of rail corrugation

A model of rail corrugation calculation is put forward. The model considers a combination of a theory of wheel/rail in rolling contact, an undulatory wear model of rail material and a dynamical performance of railway vehicle coupled with a curved track. A computer code for rail corrugation is developed, and the model is verified with a full scale test facility. The effects of the uneven lateral support stiffness of rail, due to discrete sleeper support, and the different curving speed of the vehicle on the initiation and development of rail corrugation are numerically investigated in detail. In the calculation the damage on the running surface of rail, concerning rail corrugation formation, is restricted to wear mechanism of rail material. Through the numerical analysis it is found that: (1) The uneven lateral support stiffness of rail, due to discrete sleeper support, easily causes the initiation and development of rail corrugation; (2) The corrugation mainly contains the same wave-length as a sleeper bay and 28~35 mm wave-lengths. The undulatory wear with 28~35 mm wave-lengths and very small depth trough is caused by a contact vibration of the wheel and rail at high frequencies; (3) The distribution of the maximum depth of undulatory wears on the rails under the 4 wheels of the same bogie is different; (4) The change of the curving speeds doesn't decrease the growth of the rail corrugation caused by the discrete sleeper support.

2005, 37(6): 737-749. doi: 10.6052/0459-1879-2005-6-2004-153

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Plannar motion and stability for a rigid body with a flexible attachment in a field of central gravitational force

2005, 37(6): 750-755. doi: 10.6052/0459-1879-2005-6-2004-232

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Contact Dynamics of the Rotor and Bearing Hub in Electrostatic Micromotor

A mathematical model of the contact between the rotor and bearing hub of electrostatic micromotor, which actuated MEMS, is constructed to investigate the contact dynamics. It is illustrated that in what way the contact problem of the contact stress and strain equations can be presented under the scaling effects of micro-scale. The parameters, the geometries of the micromotor, the electrostatic force, the material characteristics, and the applied gap voltages, which are related to the contact, are discussed in detail. The discriminations between unchanged gap and maximum changed gap under different applied voltages and various materials are studied. Some results of the contact width, the contact stress, the contact strain, are compared with finite element model (FEM) solutions of an equivalent problem. The 1st principal stress and strain and whole contact stress for expressing the distributions are shown. The small differences between the both methods, showing characteristic features of FEM and the theoretical assumptions, are explained.

2005, 37(6): 756-763. doi: 10.6052/0459-1879-2005-6-2004-141

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Applications of optimization methods in fluid mechanics

2005, 37(6): 764-768. doi: 10.6052/0459-1879-2005-6-2004-207

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2005, 37(6): 769-776. doi: 10.6052/0459-1879-2005-6-2004-317

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Numerical study of the dynamics performance of the supersonic inlet for air-breathing pulse detonation engine

A series of numerical computation have been conducted to characterize the movement of the terminal shock inside an axisymmetric supersonic inlet under different outlet conditions: sinusoidal perturbation pressure, experimental gauge pressure history at the head wall of a PDE and blockage of outlet of inlet. The relationship between the movement of terminal shock and the outlet conditions is demonstrated. The governing equations are discretized by finite volume method. The inviscid flux at the interfaces of control volumes is computed using three order upwind interpolation, while the corresponding viscous flux is computed using two order centered difference scheme. The minmod limiter is introduced to eliminate the non-physical elements of solutions. For steady computation, time-dependent method is used; for unsteady computation, dual time stepping method is used. The discretized algebraic equations are solved using alternate direction iteration method.

2005, 37(6): 777-782. doi: 10.6052/0459-1879-2005-6-2004-421

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Water flooding microscopic seepage mechanism research based on three-dimension network model

Water flooding microscopic seepage mechanism was researched by stochastic simulation on percolation network model at microcosmic level. The validity of network model was testified by the comparison of simulation and experiment of water-oil relative permeability steady flooding. Then, the microscopic distribution laws of remaining oil were discussed at different stages of water flooding and at different wetting situations. The forms of remaining oil distribution were divided into single grain (or single drop) shape, fleck shape, network shape and oil-water mixed shape. Research results show that the blocks of network shape remaining oil are less than other forms while occupying more volumes. Pores with max network shape remaining oil are reduced together with the reducing of remaining oil saturation and are reduced rapidly at about forty percent to fifty percent of remaining oil saturation. Wettability not only influences sweep efficiency, but also influences remaining oil distribution. The general change tendency of remaining distribution is becoming more and more dispersive.

2005, 37(6): 783-787. doi: 10.6052/0459-1879-2005-6-2004-361

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Three-dimensional progressive damage analysis of composite laminates containing a hole subjected to tensile loading

A three-dimensional parametric progressive damage model has been developed by integrating damage mechanisms for composite laminates containing an open hole subjected to static tensile loading. The model is capable of simulating the whole processs of failure initiation, propagation and catastrophic failure of the structure, which is also capable of predicting ultimate strength of composite laminates containing an open hole and assessing the four damage mechanisms and the relationship among them that are fibre breakage, fibre-matrix shearing, matrix cracking and delamination. The analysis method mainly includes the components of stress analysis, failure analysis, material property degradation. Finally, nine different types of laminates containing an open hole were used to predict the ultimate strength of the laminates and analyze damage progression. An excellent agreement was found between the analytical predictions and the experimental data of the document.

2005, 37(6): 788-795. doi: 10.6052/0459-1879-2005-6-2004-393

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The free vibration characteristics of nonlocal continuum bar and a boundary of material constant in Eringen's nonlocal model

2005, 37(6): 796-798. doi: 10.6052/0459-1879-2005-6-2004-201

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FORM in structural reilianbility analysis and chaotic dynamics

2005, 37(6): 799-804. doi: 10.6052/0459-1879-2005-6-2004-244

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Bone Growth Equation and Parameters Identification

This study presents a method to identify the main parameters(B and K) in bone growth and remodeling equation which is based on the animal Experiment of rapid-growing Rats in Different Stress Environment. The results are proved to be of good stability and identification precision with the numerical method of BFGS by analysis. It suggests that B and K are variables changing with time and space. The research shows that solving the uncertainty and unknown properties of life phenomenon with inversion theory and method is an effective way. The thought and method used in the research of bone growth and remodeling adaptation and quantification of unknown parameters of bone growth equation in this paper also provide clue and reference to establish human model of bone growth and remodeling.

2005, 37(6): 805-809. doi: 10.6052/0459-1879-2005-6-2004-275

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2005 Vol. 37, No. 6

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