力学学报

ASYMPTOTIC EXPANSIONS OF TRANSONIC FLOW ABOUT THIN AIRFOIL AND WING WITH BLUNT NOSE

Matched asymptotic expansions are used in the analyses of transonic flow about thin airfoils and wings with blunt nose in this paper. The potential equations and boundary conditions for first and second approximations, which represent, the flow near the leading edge, are derived and the corresponding analytical solutions are developed. The composite solutions for the velocity on the surface are constructed, and the singularities of TSD approximation at the leading edge are removed.

1990, 22(3): 257-265. doi: 10.6052/0459-1879-1990-3-1995-943

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INSTABILITY OF NON-NEWTONIAN OPEN CHANNEL FLOW

, The mechanism of instability of non-Newtonian flow in an. open channel is studied by means of experiment and theoretical analysis. It is proved that the instability of non-Newtonian flow results essentially from the Bingham yield stress τB of the fluid. The larger the yield stress, is and the smaller the rigidity coefficient η is, the more unstable the non-New-t.onian flow will be. Based on the theory, the phenomena of "river clogging" in hypercon-centrated flow in the Yellow River and its tributories, th...

1990, 22(3): 266-275. doi: 10.6052/0459-1879-1990-3-1995-944

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MODELING OF BITUMINOUS COAL AND LEAN COAL COMBUSTION IN A COMBUSTOR OF CO-FLOWING JETS WITH LARGE VELOCITY DIFFERENCE

The two-dimensional turbulent re irculating two-phase flow, mixing ancl combustion in a combustor of coflowing jets with large velocity difference for two types of pulverized coal-bituminous coal and lean coal are predicted by the trajectory model of particle phase with some improvements in the solution technique. The prediction results show the particle motion pattern and the mixing of the particles with the reverse gas flow. The stabilization of pulverized coal fla.ne is realized mainly by volatile combus...

1990, 22(3): 276-284. doi: 10.6052/0459-1879-1990-3-1995-945

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挤出胀大流动的有限元方法研究

Yurun Fan

An essential improvement has been made upon the stream-line finite element method proposed by Luo-Tanner. Instead of integrating a constitutive equation along the elements' boundaries as Luo-Tanner did, one can integrate the equation along the stream lines passing through the elements' Gauss points. Thus the difficulties of discontinuous velocity gradients and the stress singularity at the exit line are avoided and the amount of computation is considerably reduced. A stricter enforcement of the incompressib...

1990, 22(3): 285-292. doi: 10.6052/0459-1879-1990-3-1995-946

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ELASTIC-PLASTIC FIELDS NEAR CRACK TIP GROWINGSTEP-BY-STEP IN A COMPRESSIBLE-PERFECTLYPLASTIC SOLID

The elastic-plastic fields near the crack tip growing step-by-step in a compressf-ble-perfectly plastic solid are analysed based on the fundamental equations for plane strain pro-blem of perfectly plastic solid, and the asymptotic solutions for stress field near the crack tip are obtained. The solutions show both the evolution process of elastic unloading domain and predict the possibility of the secondary plastic domain. The classical central fan domain must be rec-tified and the stress deviatoric stress n...

1990, 22(3): 293-301. doi: 10.6052/0459-1879-1990-3-1995-947

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BIFURCATION AND FRACTURE IN SHEET-METAL FORMING WITH VOID GROWTH EFFECT

A plane-stress finite element void model has been employed to simulate the void growth damage during the proportional straining process of a dual-phase sheet metal. The ov-erall and local responses of the model are carefully handled to accord with some existing testing results This procedure provides the means of determining the constitutive parameters that characterize ductile damage. Then, bifurcations intothe modes of localized shear bands and diffuse necking are investigated. The critical strains determ...

1990, 22(3): 302-310. doi: 10.6052/0459-1879-1990-3-1995-948

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THE SPECTROSCOPIC DIAGNOSTICS ON VECUUM ARC

In this paper, according to multi-thermodyoamic equilibium, the electron density and temperature and atom density of the vacuum arc are measured through spectroscopic,measurement. The results show that the vacuum arc is in non-thermodynamic equilibrium.

1990, 22(3): 311-317. doi: 10.6052/0459-1879-1990-3-1995-949

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NUMERICAL STUDY ON PROJECTILE PENETRATIONMECHANISM

In this paper, the numerical study is carried out for three test problems of projectile penetration; a tungsten projectile impacting on a steel target at 1000 m/s, a steel projectile impacting on a steel target at 1000m/s. and a steel projectile impacting on a. aluminium target at 1000 m/s. The basic equations of compressible fluid and elactic-plastic flow in two dimensions and Eulerian typical CPG-LTDL code are used in the numerical calculation. The results of computation are in good agreement with the exp...

1990, 22(3): 318-327. doi: 10.6052/0459-1879-1990-3-1995-950

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FUZZY MATHEMATICAL METHOD IN ROCK MECHANICS

In view of the marked "Fuzziness" in the factors that have effect on the problems of rock mechanics, the deformation failure of rock mass in mining engineering is studied by using the Fuzzy mathematical theory in the paper. In accordance with the deformation failure of rock mass in open-pit mines, by applying the theory of Fuzzy probability measures, the Fuzzy probability formula is derived for the deformation failure of rock masses, and the numerical method is given to calculate the Fuzzy probability. The ...

1990, 22(3): 328-336. doi: 10.6052/0459-1879-1990-3-1995-951

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CONDITION FOR OCCURENCE OF CIRCULAR PENETRATION DURING IMPACT OF A FALLING DROPLET WITH A FLUID

In observing the impact of a free falling droplet with a fluid, Cai discovered what he called the circular penetration phenomenon, whose occurence had a periodic dependence on the height of free fall. Empirical formulas were developed by Cai to correlate his experimental measurements. This note shows that formulas in better agreement with experiment can be derived from the theory of free oscillation of droplets, thus providing a physical basis for circular penetration.

1990, 22(3): 337-340. doi: 10.6052/0459-1879-1990-3-1995-952

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PRELIMINARY SIMULATIONS OF THE FUNCTIONS OF PROT ECTION CONSTRUCTIONS AGAINST EROSION

The practical problems of wind erosion damages of railway embarkment and the effectiveness of the engineering designs of protection constructions were explored by means of laboratory simulations.The simulation results, which are described in the present paper, show the rationality of various engineering designs for wind damage prelection used in Northwest China area. The experimental results are of help, as well, in understanding the processes of wind erosion, wind dri-ft and the functions of various protec...

1990, 22(3): 341-346. doi: 10.6052/0459-1879-1990-3-1995-953

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VORTEX STRUCTURE IN THE WAKE OF THE AXISYMMETRIC BLUFF BODIES

Vortex structure in the wake of a sphere and a bluff body with a slanted base were investigated by both flow visualization and hot wire measurement. Flow visualization showed that wake configuration consisted of a series interlocking loops. Each vortex element looks like "hairpin vortex", which connect each other in chains. It was found that slanting the base could fix the orientation of the rolling up of vortex sheet as well as the position of vortex shedding, and vortex structure is quite regular. As for ...

1990, 22(3): 347-350. doi: 10.6052/0459-1879-1990-3-1995-954

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EXPERIMENTAL STUDY OF CHAOTIC PHENOMENA IN A CIRCULAR COUETTE FLOW SYSTEM

In this paper, we observed and measured the chaotic phenomena in a circular Couette flow system by means of flow visualizations arid Laser light scattered power spectra.Two routes to turbulence have been found: the first one viafrom quasiperiodic motion to chaos, the second one via intermittency.A new idea that the weak nonlinear,interaction may locally have an effect on Taylor vortices is introduced in explanation of the great difference in transition threshold values between the Above two routes.

1990, 22(3): 351-355. doi: 10.6052/0459-1879-1990-3-1995-955

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ANALYSIS ON A KIND OF STRONG NONLINEAR SYSTEM

In this paper, a kind of strong nonlinear system is investigated, which can be treated as extension of the system of T. D. Burton and M. N. Harridan. At first, the qualitative behaviour of the system is analysed. The bifurcation value of this system is obtained. Then the Dai Shiqiang's perturbation method is applied to analyse the qualitative behaviour of this system.

1990, 22(3): 356-361. doi: 10.6052/0459-1879-1990-3-1995-956

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THE INTERFACE CRACK PROBLEM OF THE BI-MATERIAL ELASTIC BODY

In the paper, the stress singularhy and stress intensity factors of bimaterial clastic body with a semi-infinite plane crack in the interface of two materials are considered. Using the general solutions of displacement field in elasticity and the kontorovitch-lebedev integral transformation, we have obtained the exact forms of the stress sigularhy and intensity factors at the crack tip when a pair of symmetric normal concentrated forces are applied on the surface of the crack.

1990, 22(3): 362-365. doi: 10.6052/0459-1879-1990-3-1995-957

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MAGNETOHYDRODYNAMIC PIPE FLOW IN A DUCT WITH ELLIPTIC CROSS SECTION

The analytic solution is obtained to the problem of the steady one-dimension-al flow of an incompressible, viscous, .electrically conducting fluid through a pipe with elliptic cross section, in the presence pf an applied transverse uniform magnetic field. A no-slip condi-tion on the velocity is assumed at the non-conducting wall

1990, 22(3): 366-373. doi: 10.6052/0459-1879-1990-3-1995-958

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AN EXPERIMENTAL STUDY OF DYNAMIC BEHAVIOR OF STRUCTURES UNDER IMPACT LOADS

The dynamic behavior of arches, frames, and shallow spherical shells under concentrated impact loads at high rate of strain is examined using a split Hopkinson Pressure Bar (SHPB), apparatus. Some new phenomenon is observed at different strain rates.

1990, 22(3): 374-379. doi: 10.6052/0459-1879-1990-3-1995-959

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A RESEARCH ON THE ROLLING RESISTANCE COEFFICIENT OF THE CYLINDRICAL ROLLER ROLLING FREELY

Xu Furen

In this paper, the rolling resistance of the cylindrical roller rolling freely on the horizontal base is studied theoretically using the viscoelasticity theory and Hertz's contact principle, and the equations to determine the rolling resistance coefficient and contact width of the roller are proposed.

1990, 22(3): 380-384. doi: 10.6052/0459-1879-1990-3-1995-960

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1990 Vol. 22, No. 3

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