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中文核心期刊

1993 Vol. 25, No. 5

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ON PROBLEMS IN THE WEAKLY NONLINEAR THEORY OF HYDRODYNAMIC STABILITY AND ITS IMPROVEMENT
There are three main problems in the weakly nonlinear theory of hydrody-namic stability: (1) The radius of convergence with respect to the perturbation parameter is too small and there is no concrete estimation for it. (2) The solution has a special structure, thus in general, it can not satisfy the initial condition posed by many practical problems. (3) When the linear part of its solution does not correspond to a neutral case, there are more than one way in determining the Landau constants, and actually n...
1993, 25(5): 515-528. doi: 10.6052/0459-1879-1993-5-1995-674
STEADY FREE VORTEX RINGS IN AN INVISCID FLUID
Axisymmetric vortex rings which move steadily through an incompressible unbounded ideal fluid at rest at infinity are investigated. A general spectral scheme is proposed for seeking solutions of steady axisymmetric vortex rings with arbitrary vorticity distribution in the core. The properties of vortex ring are also given a numerical description. Comparison between the numerical results and asymptotic analytic solution is very satisfactory.
1993, 25(5): 529-536. doi: 10.6052/0459-1879-1993-5-1995-675
NUMERICAL SIMULATION OF THE VORTEX STRUCTURES OF A CIRCULAR. CYLINDER OSCILLATING TRANSVERSELY IN UNIFORM FLOWS
Vortex shedding from a circular cylinder oscillating transversely in uniform flows is numerically investigated using the Navier-Stokes equations for different oscillating frequencies, amplitudes and Reynolds numbers. The emphasis of this study is put on the complicated vortex structures in the near wake and their influence on the force on the body. A switch phenomenon in the phase of initial vortex shedding and complex vortex patterns, such as 25, 2P and P + S etc. modes, near the fundamental lock-in region...
1993, 25(5): 537-547. doi: 10.6052/0459-1879-1993-5-1995-676
NORMAL FORM AND CODIMENSION 3 DEGENERATE BIFURCATION OF A NONLINEAR DYNAMICAL SYSTEM
In this paper we use matrix representation method to compute the higher order normal form of a nonlinear dynamical system with Z2-symmetry. We obtain universal unfoldings corresponding to normal forms for codimension 2 and codimension 3 degenerate cases. Finally we use obtained normal form and universal unfolding to discuss codimension 3 degenerate bifurcations of nonlinear dynamical system.
1993, 25(5): 548-559. doi: 10.6052/0459-1879-1993-5-1995-677
THE CONSTITUTIVE RELATION OF SUPERPLASTICITY OF METAL WITH UNIFORM EQUIAXED FINE GRAIN
Based on the metallographical research results for the mechanism of super-plastic deformation, a costitutive relation of superplasticity of metal with uniform equiaxed fine grain is developed here by using the method of micro-cell model. The three micro-mechanism of superplastic deformation are included in the constitutive relation. An analysis of basic experimental phenomina of superplastic deformation, such as the influences of grain size and strain rate on stress-strain rate curve and strain rate sensiti...
1993, 25(5): 560-568. doi: 10.6052/0459-1879-1993-5-1995-678
A STUDY ON TWO SURFACE MULTIAXIAL CONSTITUTIVE MODEL OF CYCLIC PLASTICITY
A two-surface constitutive model, which considers the effects of cyclic hardening / softening, plastic strain amplitude history and nonproportional cyclic loading, is presented. In the model, the evolution equations of limit and yield surfaces are introduced, the nonproportionality of cyclic strain paths is denned, and a rational method to determine the modal parameters is proposed. The predictions of the model, for 42CrMo steel with quenched and tempered treatment, agree with the experimental results very ...
1993, 25(5): 569-574. doi: 10.6052/0459-1879-1993-5-1995-679
A DIRECT EIGENSYSTEM REALIZATION ALGORITHM FOR MODAL PARAMETER IDENTIFICATION IN TIME DOMAIN
A new method called direct eigensystem realization algorithm (DERA) is developed for structural modal parameter identification. A direct procedure is presented for obtaining the minimum realization of a multiple-input multiple output time-invariant discrete system from observations of the input and output in time domain, and then modal parameters are obtained from the eigenvalues and eigenvectors of the system transition matrix. Because of the use of direct input-output observations, some weaknesses of the ...
1993, 25(5): 575-581. doi: 10.6052/0459-1879-1993-5-1995-680
THE SOLUTION OF STRESS INTENSITY FACTORS FOR NON-SYMMETRIC DOUBLE EDGE CRACKS IN ANISOTROPIC PLATES BY COMPLEX VARIABLE- GENERALIZED VARIATIONAL METHOD
Description is given of a complex variable-generalized variational method to investigate the stress intensity factors(S.I.F.) associated with the non-symmetric double edge cracks in anisotropic plates. In this work a cracked plate is decomposed into two subregions with edge cracks. According to the theory of anisotropic elasticity, the stress and displacement series which satisfy all basic equations and stress-free boundary conditions on crack surfaces are established. By using a generalized variational pri...
1993, 25(5): 582-591. doi: 10.6052/0459-1879-1993-5-1995-681
MATHEMATICAL ANALYSES OF STRESS AND STRAIN FIELDS IN FRACTURE PROCESS ZONE
本文将条状分离区看作是位错连续分布区域,利用复变函数理论及切比雪夫多项式级数展开提出了一种统一的数学分析的方法,用以对均匀材料裂纹前方分离过程区的非线性效应进行有效的,精确的解析分析。避免以前各种模型一般都需要借助于有限元法或其他离散方法才能得到数值解答的难点。本文利用这一新方法,对断裂过程区是内聚力模型,条状屈服区模型的裂纹问题,受约束金属薄膜的裂纹问题,进行了分析计算,并与已有的结果进行了比较,得到了满意的结果。
1993, 25(5): 591-605. doi: 10.6052/0459-1879-1993-5-1995-682
A MICROMECHANICAL STUDY ON THE NONLINEAR VISCOELASTIC CONSTITUTIVE RELATION OF HIGH RIGIDITY PARTICULATE-FILLED POLYMERS
In this paper, a micromechanical theory is used to study the nonlinear vis-coelastic constitutive relation of high rigidity particulate-filled polymers. It is demonstrated that the linear Eshelby's equivalent inclusion method and the relevant macroscopic average method can be generalized to research the constitutive relation of the composites, when the deformation of the materials is describled with linear strain and the particle's rigidity is very much higher than the matrix's.
1993, 25(5): 606-614. doi: 10.6052/0459-1879-1993-5-1995-683
STABILITY, BIFURCATIONS AND CATASTROPHE OF STEADY ROTATION OF SYMMETRIC GYROSCOPE WITH VISCOUS-LIQUID-FILLED CAVITY ON PLANE
The number, the angles of orientation and the stability in Rumyantsev-Movchan's sense of steady rotations of a symmetric gyroscope with a cavity completely filled with a uniform viscous liquid on a plane are given for various values of the parameters. By taking the square of the upright component of the angular momentum M2 as a control parameter, three types of bifurcation diagrams of the steady rotation with two types of jumps are obtained. By taking account of the M2-damping owing to the moment of unavoid...
1993, 25(5): 615-622. doi: 10.6052/0459-1879-1993-5-1995-684
MELECULAR DYNAMICAL SIMULATION FOR VIBRATIONAL-TRANSLATIONAL ENERGY RELAXATION IN CONDENSED STATE
本文利用分子动力学计算机模拟方法,研究了稠密态双原子分子振动-平动弛豫速率与分子离解能、密度和温度的关系。发现振动弛豫速率随着分子离解能的增高而下降。这一现象与由光谱数据得到的结果是一致的。它可以用振动频率的下降来解释;分子振动弛豫速率随密度增大而加快,在我们所作的范围内,似乎看不到弛豫速率与温度有关。
1993, 25(5): 623-627. doi: 10.6052/0459-1879-1993-5-1995-685
THE TRAILING-EDGE VORTEX STRUCTURE OF A CONSTANT-RATE AIRFOIL AND MECHANISM OF DYNAMIC STALL
The vortex structure shed from the trailing-dege of a constant-rate pitching airfoil was visualized using hydrogen bubble technique. Its time evolution, and the effects of pitching rate were studied. Combining the trailing-dege vortex structure with the (previously obtained) airfoil upper-surface separated vortex structure, a complete flow structure was obtained. The mechanism of dynamic stall was studied based on the flow structure and vorticity dynamics theory, and insights were provided.
1993, 25(5): 628-631. doi: 10.6052/0459-1879-1993-5-1995-686
THE NUMERICAL SIMULATION OF FLOW AROUND AN AIRFOIL WITH SUCTION AT HIGH ANGLE OF ATTACK
In this investigation, a new phenomenon of stationary vortex was found and some new dynamic process by means of suction on the airfoil surface was studied by numerical method. The full Navier-Stokes equations were solved by the implicit factorized finite difference algorithm. The results show that: (1) The suction can increase the lift force at high incidence. (2) If suction pressure is strong enough, the unsteady vortex shedding phenomenon can be eliminated and steady flow formed. (3) Near the midchord, th...
1993, 25(5): 632-637. doi: 10.6052/0459-1879-1993-5-1995-687
EXACT SOLUTIONS FOR A PARTIALLY LIQUID-FILLED ROTOR TO BE EXCITED LATERALLY
In this paper, the turbulent forces imposing on a rotor partilly filled with a liquid are discussed when the rotor is subjected to lateral excitation. First, we verify that the turbulent flow is irrotational in the rotating coordinate system fixed with the rotor and then the whole flow is resolved into the stable flow with constant vorticity and the irrotational turbulent flow in analysis. The explicit expressions of free surface and resultant forces imposing on the rotor are obtained. It is known that ther...
1993, 25(5): 638-642. doi: 10.6052/0459-1879-1993-5-1995-688