力学学报

ABSOLUTE INSTABILITY IN CRICULAR CYLINDER WAKES

The stability of circular cylinder wake at low Reynolds numbers has been studied experimently. The experiments were separatly carried out in a propeller-driven water channel and in a gravity-driven low turbulence water tunnel. The test section of water channel was 15 cm in width, 10cm in depth and 100 cm in length, and the test section of water tunnel was 4 cm in width.10cm in height and 100 cm in length. The cylinder model used in channel and tunnel were 15 cm long, 0.2 cm in diameter and 4cm long, 1 cm in...

1999, 31(1): 1-9. doi: 10.6052/0459-1879-1999-1-1999-001

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STUDY OF ONE NUMERICAL METHOD FOR SOLVING THE UNSTEADY EQUATIONS OF STREAM AND VORTICITY FUNCTIONS

The method for solving the unsteady equations of stream and vorticity functions has been improved. The Hermitian formulas of forth-order accuracy are adopted for first partial derivatives of stream function (i.e. velocities). The forth-order accuracy finite difference is used for the convective terms instead of the second-order central difference. The ADI successive method is used for solving the equations which contain the temperature equation to obtain the steady solutions.Second-order central difference ...

1999, 31(1): 10-20. doi: 10.6052/0459-1879-1999-1-1999-002

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STABILITY OF MULTIPLE EQUILIBRIA IN THERMOHALINE DOUBLE-DIFFUSIVE SYSTEM

Stability of multiple equilibria in the thermohaline double-diffusive system is studied here with numerical method in a body-fitted curvilinear coordinate system by introducing nonlinear equation of state, temperature-flux boundary condition and variable limit of forced boundary condition into this system. With heat-to-salt buoyancy ratio A larger than, equal to and smaller than 1, the flow is divided into temperature-dominated regime, temperature-salinity equilibrant regime and salinity-dominated regime. F...

1999, 31(1): 21-28. doi: 10.6052/0459-1879-1999-1-1995-001

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RELATIVE VELOCITIES OF LARGE PARTICLES SUSPENDED IN A VERTICAL TURBULENT LIQUID FLOW

A dimensionless formula for estimating the time-mean velocity differences between fluid and large particles has been given. The Particles are suspended in a homogeneous turbulent liquid flow. and their sizes are larger than the size of the micro-eddy of the turbulent liquid flow.A comparison between the orders of the accelerations of the eddy and the gravity shows that in a flow with considerable high Reynolds number, the dynamic force of eddy is dominant and the influence of the gravity to the motion of th...

1999, 31(1): 29-37. doi: 10.6052/0459-1879-1999-1-1995-002

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PROPERTIES OF THE STATISTICAL DAMAGE EVOLUTION EQUATION AND ITS NUMERICAL SIMULATION

Damage mechanics has become a very helpful tool for engineers to deal with failure problems. Actually the physical essence of damage is the population of distributed microdamage in a continuum element. When one intends to correlate the damage evolution to the mesoscopic dynamics of microstructure of a particular material, it becomes necessary to investigate the statistical evolution of distributed microdamage. Based on the analysis and numerical simulation of one kind of statistical damage evolution equati...

1999, 31(1): 38-48. doi: 10.6052/0459-1879-1999-1-1995-003

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EFFECT OF THE ELASTIC-T-TERM ON THE CRACK-TIP PARAMETERS AND THE STABILITY OF CRACK GROWTH PATH

The so-called elastic T-term is the third term of Williams expansion for the linear elastic crack tip field, which is constant along the crack plane over a large distance in front of or behind the crack tip and has been introduced as an another independent crack tip parameter. It was shown that the T-stress has no direct effect on the crack tip parameters, such as the J-integral,in linear deviation. However, the T-stress influences significantly the shape and size of the plastic zone under the small-scale y...

1999, 31(1): 49-57. doi: 10.6052/0459-1879-1999-1-1995-004

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SHAPE SENSITIVITY ANALYSIS OF THE EIGENPROBLEM

This paper deals with eigenproblem sensitivity analysis with respect to boundary shape. It shows how to obtain the distributed parameter differential equations plus boundary conditions which govern the eigenproblem sensitivity before the structure is discretized, and how to obtain the solution to them using finite element methods. This paper points out that the distributed parameter differential equations plus boundary conditions, which govern the eigenproblem sensitivity, are just the non-homogeneous ones...

1999, 31(1): 58-67. doi: 10.6052/0459-1879-1999-1-1995-005

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THE CHARACTERISTICS OF TIMOSHENKO BEAM DURING THE PROCESS OF ELASTIC IMPACT AND CONTACT

In this paper, the semi-analytical solutions for a particle impacting on simply-supported Timoshenko beam with finite length is obtained by using the method of mode superposition. The characteristics of impact loads varying with respect to time is given, several interesting conclusions about the impact loads are presented, and the exact values of impact loads at initial moment of impact is derived and verified. The propagating characteristics of longitudinal waves and shear waves in a finite-length beam is ...

1999, 31(1): 68-74. doi: 10.6052/0459-1879-1999-1-1995-006

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POSTBUCKLING RESPONSE OF THIN CIRCULAR PLATES AND ENERGY RELEASE RAf E OF CIRCULAR DELAMINATION

In the present paper, the problem of the axisymmetric postbuckling response has been investigated for thin circular plates and delaminated circular films under the action of inplane compression. Especially, the problem of the asymmetric bifurcation buckling occuring at the stage of the axisymmetric postbuckling deformation has beed investigated for the first time.The regular solutions of the axisymmetric buckling and postbuckling equations are derived by the use of power series expansions, and the solutions...

1999, 31(1): 75-83. doi: 10.6052/0459-1879-1999-1-1995-007

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THEORETICAL AND EXPERIMENTAL ANALYSES OF THERMAL BUCKLING PROBLEMS OF LINER SHELLS (II) -EXPERIMENTAL PART

The buckling problem of the liner shells is a major problem in reactor containment's design, but few experimental results have been published. In this paper, we carry out the experimental research for the local 1:1 models of the 200MW RCCV. Buckling temperature and strain loads of liner shells are given. The relation of temperature and deflection or membrane strain during buckling are also presented. The results show that the liners are easier to buckle in the local area than in the whole area between two ...

1999, 31(1): 75-83. doi: 10.6052/0459-1879-1999-1-1995-008

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POINCARE-LIKE CELL MAPPING METHOD AND ITS APPLICATION

A Poincare-like Cell Mapping method fit for both autonomous and periodic nonautonomous nonlinear dynamic systems is presented in this paper. Compared with the traditional Cell Mapping method, the new one has apparent advantages in practice due to introduction of Poincare section, and can be widely used in high dimension nonlinear dynamic systems. Using this new method, the global characteristic of balanced and unbalanced bearing rotor nonlinear dynamic systems are analyzed in this paper. The periodic solut...

1999, 31(1): 91-99. doi: 10.6052/0459-1879-1999-1-1995-009

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LARGE EDDY SIMULATION OF THE TURBULENT FLOW AROUND A CIRCULAR CYLINDER AT SUB-CRITICAL REYNOLDS NUMBERS

The performance of the Smagorinsky eddy-viscosity subscale grid model and the suitability of second-order accurate finite volume scheme for large eddy simulations of complex flows are investigated in the case of turbulent wake behind a nominally two-dimension cylinder at subcritical Reynolds number 20000 based on freestream velocity and cylinder diamter. The numerical method is applied to the incompressible Navier-Stokes equation written in generalized nonorthogonal coordinates, which has the following main...

1999, 31(1): 100-105. doi: 10.6052/0459-1879-1999-1-1995-010

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FATIGUE RELIABILITY ANALYSIS UNDER TWO STAGE LOADING

Based on two-dimensional probabilistic Miner's rule, a new method of fatigue reliabilityanalysis under two-stage loading is established, and a very successful experimental verification is made in terms of eight large samples of low-high as well as high-low two-stage fatigue experimental data given by Tanaka, et al.For a two-stage cyclic loading, let the first loading level be denoted by (Sa1, Sm1), and the second level by (Sa2, Sm2). Each individual in the specimen population is first subjected to n1 cycle...

1999, 31(1): 106-112. doi: 10.6052/0459-1879-1999-1-1995-011

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EQUIVALENT ELASTIC PARAMETERS OF THE HONEYCOMB CORE

The result of Gibson's formula that describes equivalent elastic parameters of cellular material is simple and applied easily. However because the stiffness corresponding with extension or contraction deformation of honeycomb wallboard is neglected, it causes indeterminedness shown by the elastic matrix of material of core in numeral analyzing honeycomb sandwich panels. In this paper it is again discussed that the influence of extension or contraction deformation of honeycomb wallboard on in-plane stiffness...

1999, 31(1): 113-118. doi: 10.6052/0459-1879-1999-1-1995-012

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COORDINATED DYNAMIC LOAD DISTRIBUTION FOR MULTIPLE ROBOT MANIPULATORS CARRYING A COMMON OBJECT SYSTEM

This paper presents an efficient real-time dynamic load (force) distribution method for multiple robot manipulators carrying a common object system. In the coordination for several manipulators sharing an object, a proper load (force) distribution is important. Particularly,to effectively manipulate the object without slipping and crushing, a force that required for the object to follow. the given trajectory must be properly distributed among the manipulators. The dynamic load distribution for cooperating m...

1999, 31(1): 119-125. doi: 10.6052/0459-1879-1999-1-1995-013

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1999 Vol. 31, No. 1

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