力学学报

THE EFFECT OF ORGANIZED WAVE DISTURBANCES ON COHERENT STRUCTURE IN WALL TURBULENCE

Organized wave disturbances were artificially introduced in log law region of turbulent boundary layers, and were found damping when propagated downstream, the damping ratios measured were qualitatively in good agreement with the results of Landahl (1967) [5] . As the disturbance wave evolved downstream, its harmonics appeared and the average bursting periods of inner layer decreased because of the outer region disturbances.Organized wave disturbances were artificially introduced in log law region of turbul...

1991, 23(4): 385-392. doi: 10.6052/0459-1879-1991-4-1995-854

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AN INVISCID MODEL FOR THE BASE PRESSURE OF TRANSONIC TURBINE CASCADE

An inviscid base pressure model for transonic turbine blade is presented It is shown that for a given back pressure the base pressure at the trailing edge and the profile toss of the blade are fixed and the base pressure can be calculated using an inviscid numerical scheme. A parametric study shows that positive curvature downstream of the throat is advantageous for generating less loss.An inviscid base pressure model for transonic turbine blade is presented It is shown that for a given back pressure the ba...

1991, 23(4): 393-399. doi: 10.6052/0459-1879-1991-4-1995-855

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MOLECULAR ORIENTATION IN STEADY FLOW FIELDS

The finite element method to solve the Navier-Stokes equation is generalized to combine with a molecular model, the multibead rod, so that the flow problems of rigid rodlike suspensions can be simulated properly.The solutions of flow fields and the most probable orientations of multibead rods have been obtained for several steady flow problems and both shown in figures of this paper. The interesting results prove the treatment of this method reasonable.The finite element method to solve the Navier-Stokes eq...

1991, 23(4): 400-410. doi: 10.6052/0459-1879-1991-4-1995-856

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THE DISTRIBUTION OF PARTICLES IN A SHOCK-INDUCED BOUNDARY LAYER OF A DUSTY GAS OVER A SOLID SURFACE

The laminar boundary layer behind a constant-speed shock wave moving through a dusty gas along a solid surface is studied. The Saffman lift force acting on a spherical particle in a gas boundary layer is taken into account. A method for calculating the density profile of dispersed phase near the wall is proposed and some numerical results are given. It is shown that behind the shock wave, there exists a curved thin layer where the density of particles is many times higher than the original one. This dust co...

1991, 23(4): 411-417. doi: 10.6052/0459-1879-1991-4-1995-857

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A TRANSFORMATION OF THE CONVECTIVE DIFFUSION EQUATION WITH CORRESPONDING FINITE DIFFERENCE METHOD

An analytical transformation with corresponding finite difference method of the convective diffusion equation into a diffusion equation coupled with a so-called upwind convection function is proposed in this paper. Reflecting the upwind effect in convective diffusion phenomena with a brief exponential representation, the upwind convection function reduces in essence the difficulty due to the non-symmetrical convection operator, and thus can bring great convenience to the numerical aspect of the convective d...

1991, 23(4): 418-425. doi: 10.6052/0459-1879-1991-4-1995-858

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NATURE OF THE SURFACE HEAT TRANSFER FLUCTUATION IN A HYPERSONIC SEPARATED TURBULENT FLOW

This paper presents the results of an experimental study of the unsteady nature of a hypersonic separated turbulent flow. The nominal test conditions were a freestream Mach number of 7.8 and a unit Reynolds number of 3.5×107/m. The separated flow was generated using finite span forward facing steps. An array of flush mounted high spatial resolution and fast response platinum film resistance thermometers was used to make multi-channel measurements of the fluctuating surface heat transfer within the separated...

1991, 23(4): 426-432. doi: 10.6052/0459-1879-1991-4-1995-859

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A MATHEMATICAL PROGRAMMING ALGORITHM FOR LIMIT ANALYSIS

It is well known from plasticity theory that there are two fundamental theore-ms, static and kinematic theorem, which can be used to determine lower and upper bounds of the collapse multipliers of proportionally loaded structures. According to these theorems the lower and upper bounds can be got by the maximization and minimization procedures, respectively. Both of the procedures can be formulated in mathematical programming forms, and related algorithm are constructed on these forms.In this paper attention...

1991, 23(4): 433-442. doi: 10.6052/0459-1879-1991-4-1995-860

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MOLECULAR DYNAMICS SIMULATION OF ENTROPY AND SURFACE TENSION FOR GRAIN BOUNDARY OF α-Fe

The grain boundary is an interface, and the surface tension is one of its important thermodynamic property. In this paper, the surface tension of the grain boundary for α-Fe,Σ= 9 at various temperatures and pressures is calculated by means of Computer Molecular Dynamics (CMD). The results agree satisfactorily with the experimental data. It is shown that the contribution of entropy to surface tension of- grain boundary can be ignored.The grain boundary is an interface, and the surface tension is one of its i...

1991, 23(4): 443-447. doi: 10.6052/0459-1879-1991-4-1995-861

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THE NEAR-TIP FIELDS FOR A PLANE STRESS MODE Ⅰ STATIONARY CRACK IN AN ELASTIC-PERFECTLY ORTHOTROPIC PLASTIC MATERIAL

In this paper, based on a phenmenological plasticity theory for orthotropicmaterial proposed by Hill, the near-tip field solution for a plane stress mode-Ⅰ stationary crack in an elastic-perfectly orthotropic plastic material is discussed in detail. There is not any discontinuous line of stress and solutions are not unique for problem of plane stress stationary crack in an elastoplastic medium with pastic orthortopy. It is found that the order of singularity of the stresses and strains in the vicinity of th...

1991, 23(4): 448-457. doi: 10.6052/0459-1879-1991-4-1995-862

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EFFECT OF HYDROGEN ON THE DEFORMATION PROCESS AHEAD OF CRACK TIP IN BCC SINGLE CRYSTAL

The deformation process and the strain field ahead of crack tip in Fe-3% Si single crystal were studied with SEM, grid method and computer image processing The distribution of strain field in plastic band around the crack tip is characterized by εyy= f(x)exp(-Ar) The general feature of the plastic deformation is similar in both charged or uncharged hydrogen specimens. However, the presence of hydrogen enhances the localized plastic band inhomogeneity and significantly increases the plasticity in high deep s...

1991, 23(4): 458-463. doi: 10.6052/0459-1879-1991-4-1995-863

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BIFURCATIONS OF NONLINEAR OSCILLATION SYSTEM UNDER COMBINED PARAMETRIC AND FORCING EXCITATION

In this paper, we study rhe problems of bifurcation in nonlinear oscillation system under combined parametric and forcing excitation for 1/2 su-bharmonic resonance-primary parametric resonance. The eight different diagrams of bifurcating response curve are obtained by using the method of multiple scales.In this paper, we study rhe problems of bifurcation in nonlinear oscillation system under combined parametric and forcing excitation for 1/2 su-bharmonic resonance-primary parametric resonance. The eight dif...

1991, 23(4): 464-474. doi: 10.6052/0459-1879-1991-4-1995-864

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BOUNDARY ELEMENT METHOD OF THE ORTHOTROPIC THICK PLATES

In this paper the fundamental solutions of the orthotropic thick plate involving transvere shear deformation are presented by using Hormander's method and plane wave decomposition. The boundary integral equations of the thick plates are obtained, which are adapted to arbitrary boundary condrions and plane forms. The numerical calculations of the fundamental solutions are discussed in detail. Some of numerical examples are analyzed with B.E.M.In this paper the fundamental solutions of the orthotropic thick p...

1991, 23(4): 475-483. doi: 10.6052/0459-1879-1991-4-1995-865

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THE PARAMETRIC VARIATIONAL PRINCIPLE FOR ELASTOPLASTICITY CONSOLIDATION IN SOIL

based on the effective stress approach by Terzaghi, the paper presents the parametric variational principle for seepage and consolidation with elastoplasticity in sotl-The proposed principle is nciple is free from the restraint of Drucker's postulate of plasticity, consequently suitable for solving the nonassociated plastic flow problems in seepage and consolidation of soil.based on the effective stress approach by Terzaghi, the paper presents the parametric variational principle for seepage and consolidati...

1991, 23(4): 484-490. doi: 10.6052/0459-1879-1991-4-1995-866

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FORCES EXERTED BY NONLINEAR PERIODIC AND BREAKING WAVES ON PILES

, Jiachun Li

本文采用十五阶 Stokes 波的 Pade 逼近,获得了与实验较为一致的流场,并且利用已有的破碎波的速度、加速度场,计算了非线性波和破碎波对各种杆件作用力,比较了它们的主要特征,为海洋工程设计提供依据。

1991, 23(4): 491-196. doi: 10.6052/0459-1879-1991-4-1995-867

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INFLUENCES OF LOAD DWELLS ON CRACK GROWTH RETARDATION OF STEELS

Effects of load dwells on crack growth might be significant in correlating laboratory data from accelerated life tests ro real life fatigue perfomance of engineering structures. In this study, the dwells following an averload effects on fatigue crack retardation behaviors in two structureal steels-ASTM A537 and 16Mn are primarily investigated. Influences of different dwell times (holding times) and dwell loads are examined. It is shown that as the holding time at zero load increased, the number of delay cyc...

1991, 23(4): 497-502. doi: 10.6052/0459-1879-1991-4-1995-868

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VISCOSITY-INDUCED MODE BIFURCATIONS IN AN INFINITE CAPILLARY LIQUID CYLINDER

This paper points out that viscosity can induce mode splitting (or called bifurcation) of the type of one-to-infinity in an infinite capillary liquid cylinder This phenomenon is similar to the Zeeman and Stark effects in atomic physics, although of different importance. After splitting there occur stable modes with negative potential energy, which are opposite to Hare and Chandrasekhar's energy principle.This paper points out that viscosity can induce mode splitting (or called bifurcation) of the type of on...

1991, 23(4): 503-506. doi: 10.6052/0459-1879-1991-4-1995-869

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EXPERIMENTAL STUDY ON SOME MECHANICAL PARAMENTERS OF ROCK

In this paper, the testing data of friction factor between syenitic blocks under static and dynamic conditions are presented. Dynamic tests are performed on a vibro-stand. The results show that the static friction factor under static condition is lager than that under dynamic condition. The variations of the friction factor in these two conditions are also quite different.In this paper, the testing data of friction factor between syenitic blocks under static and dynamic conditions are presented. Dynamic tes...

1991, 23(4): 507-512. doi: 10.6052/0459-1879-1991-4-1995-870

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1991 Vol. 23, No. 4

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