力学学报

AIRFLOW OVER MOUNTAIN AND CONVECTIVE BOUNDARY LAYER

In this paper,an analytical model coupling the convective boundary layerwith the free atmosphere is built up,The influences of the convective boundary layer on theairflow over mountain are discussed by this model.

1994, 26(1): 1-11. doi: 10.6052/0459-1879-1994-1-1995-516

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EXPERIMENTAL RESEARCH FOR FLUID FORCE OF TWO ELASTIC CIRCULAR CYLINDERS IN SIDE BY SIDE ARRANGEMENTS WHEN SUBJECTED TO UNIFORM CROSSFLOW

This paper presents the experimental investigation into hydrodynamicforce of two elastic circular cylinders in side by side arrangements under various gap ratiosT/D in the range of 4.19 ×10￣4 < Re < 9.1×10￣4. The steady and fluctuating pressuredistributions,steady drag and lift and fluctuating drag and lift force were obtained.Theresults show that as V_r>V_(rc),the oscillations of the cylinders affect not only the steadydrag and lift coefficients,but fluctuating drag and lift coefficients as well.There were...

1994, 26(1): 12-19. doi: 10.6052/0459-1879-1994-1-1995-517

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A DELAY-DIFFUSION DESCRIPTION FOR TWO-DIMENSIONAL CONTAMINANT DISPERSION

In the earlier stage of dispersion process,the rate of dispersion aSsociatedwith earlier discharge is relatively large because the memory term extends further back intime。 In order to investigate the early properties of two-dimensional dispersion,we proposethe delay-diffusion equation as following:which is based on the ansatz derived by Smith(198 1).The analytical expressions forD_(xx):,D_(yx),D_(xy) ,D_(yy) and,are obtained.

1994, 26(1): 20-30. doi: 10.6052/0459-1879-1994-1-1995-518

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SHEAR-BAND BIFURCATION

A diffuse type of theorctical solution,interrelatedwith experimental ob-servations?is given to reveal the characteristics of shear-band bifurcation. This effort is usedto distinguish material bifurcation from structural buckling(bifurcation).It is demonstratedthat the rate of porosity development is governing the process of shear banding,instead ofattributing to the amount of porosity itself.

1994, 26(1): 31-38. doi: 10.6052/0459-1879-1994-1-1995-519

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ELASTIC-PLASTIC FIELDS NEAR THE GROWING CRACK TIP

In this paper,the propagation process of a crack in the power-law hardeningmaterials is accurately calculated by the elastic- plastic finite element method under planestrain and Mode I conditions. The elaistic-plastic fields near the growing crack tip are givenin detail.A unified three term solutions of stress fields ahead of the growing crack tip are firstpresented. The firs t term is t he H RR singularity solut io n. T he second t erm describes thetriaxiality The third term includes a linear term of t...

1994, 26(1): 39-48. doi: 10.6052/0459-1879-1994-1-1995-520

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THE STRESS-STRAINLAW OF ELASTIC BODY WITH MICROCRACKS

The st ress- strain law of elastic body with microcracks is derived in which craick closing and crack surface friction are taken into consideration.An explicit expressionof flexibility tensor increment is found.The equivalent engineering moduli are given for thecases of two dimensional plane stress and plane strain.Numerical results show the noticeableinfluence of crack closing and crack surface friction on the stress-strain law of elastic bodywith micracracks.

1994, 26(1): 49-59. doi: 10.6052/0459-1879-1994-1-1995-521

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SEPARATION OF PRINCIPAL STRESSES IN DYNAMIC PHOTOELASTICITY

A new and effective method that is used to separate the transient prin-cipal st resses for dynamic photoelast ic ity was. prop osed.This is a hybrid met ho d combin-ing the optical method of dynamic caustics and the boundary element numerical method.Firstlyt a modified Cranz-Schardin spark camera is presented to record simultaneously theisochromatic fringe patterns of photoelasticity and the shadow spot patterns in the dynamicprocess. By means of the isochromatic fringe patterns,the difference between trans...

1994, 26(1): 60-69. doi: 10.6052/0459-1879-1994-1-1995-522

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THE SCATTERING OF DISPLACEMENT STE SH-WAVES BY A SEMI-CYLINDRICAL CANYON

The problem of scattering of a plane displacement step SH-wave by a semi-cylindrical c anyon is considered analyt ic alytically Expressions for the displacement field inducedare derived by means of an integral transform technique and expansion of wave funct ions.Numerical results are presented for the points on the surface of the canyon and the halfspace: This result is expected to be used as influence coefficients of Duhamel integral in thesolution of the displacement field due to the time-varying scatter...

1994, 26(1): 70-80. doi: 10.6052/0459-1879-1994-1-1995-523

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EIGENVECTOR DERIVATIVES OF GENERALIZED NONDEFECTIVE EIGENPROBLEMS WITH REPEATED EIGENVALUES

This p ap er present s a met ho d for comput ation of t he eigenvalue andeigenvector derivat ives a8so c iated with repeat ed eigenvalues of the generalized nondefectiveeigenproblem,This met ho d requires the knowledge of only t hose eigenvectors to be dif-ferentiated.A complete set of formulations has been presented covering the case wheresome groups of repeated first eigenvalue derivatives occur.A numerical exaniple is given todemonstrate t he effect iveness of the prop osed met ho d.

1994, 26(1): 81-89. doi: 10.6052/0459-1879-1994-1-1995-524

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THE MODIFIED SIMPLEX METHOD FOR TOPOLOGY OPTIMlZATION OF SPACE TRUSS STRUCTURE WITH MULTIPLE LOADING CONDITIONS

In this paper , the member forces are considered as design variables, andconvex quadratic programming model of topology optimization for space truss structure isgiven under mutiple loading conditions. The linear interdependent problem for memberforces and K-T multipliers is formed by making use of its K-T condition)and can be solvedby the modified simplex method.

1994, 26(1): 90-98. doi: 10.6052/0459-1879-1994-1-1995-525

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THE STUDY OF THE APPARATUS OF TENSION SHB USED AT HIGH STRAIN RATE AND MEASURING TECHNIQUE

This paper provides t he tensio n S HB apparatus used at high st rain rate.Rom the theory of one-dimentional elastic stress wave,the paper derives the general equa-tions of dynamic stress-straln relationship. Using the tension SHB apparatus, We haveperformed tension tests at high strain rate and obtained the stress-strain relationship curvesof hard aluminum LC.

1994, 26(1): 99-105. doi: 10.6052/0459-1879-1994-1-1995-526

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SPECTRAL ANALYSIS AND TWO -DIMENSIONAL SIMULATION OF THE INJECTION OF THE INJECTION MOLD-FILLING PROCESS FOR A NON-NEWTONIAN FLUID

The C hebyshev collocat ion met hod and Fast Fourier Transform ( FFT)is employed for computing the temperature,pressure, and velocity fields in a flat thin center-fed disk-cavity for the flow of thermoplastic materials. The cavity-filling process is treatedas a transient and non-isothermal flow of a non-Newtonian flnid with moving bonndary Inthe nnmerical scheme the spatial discretization is spectral but the temporal discretizationuses covent ional Crank-Nicolson finite-difference,Goo d agreement is obtain...

1994, 26(1): 106-112. doi: 10.6052/0459-1879-1994-1-1995-527

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STEP INDUCED HYPERSONIC TURBULENT BOUNDARY-LAYER SEPARATION

This report describes detailed heating distribution data and the study of oilflow and liquid crystal thermograph in turbulent separated regions induced by cylindrical,square and two-dimensional steps in an impusle wind tunnel at Mach number range of 5-9,Reynolds number(2-5)×10￣7/m,Step heights ranged from 0.06-2.5 times boundarylayer thickness. The results indicate that surface pressure and heating peaks occur at thereattachment line which is at a distance of 0.15 times its height ahead of the step,and for...

1994, 26(1): 113-120. doi: 10.6052/0459-1879-1994-1-1995-528

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THE CONE-SHAPED VORTEXX STRUCTURE IN FLAT PLATE BOUNDARY AYER

The quasi-3D flow visualization method is used to study the coherentstructure in tiie flat plate boundary layer at low Revnolds number,It was found that theformation of the cone-shaped vortex plas an important role in the large eddy structures ofturbulent boundary layer,

1994, 26(1): 121-127. doi: 10.6052/0459-1879-1994-1-1995-529

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1994 Vol. 26, No. 1

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