力学学报

A COUPLING MODEL OF WATER-HEAT MOVEMENT IN THE SOIL OF SAND-FIXATION AREA

, Jiachun Li

Based on the Phillips & Vriès' theory, we have suggested a coupling model for simulating water-heat movement in the sand soil with vegetation. The effects of temperature and vegetation roots on the exchange of water and heat between atmosphere and land are firstly analyzed. Then, we have provided the formulae to estimate soil evaporation, canopy transpiration, water-absorbing rate of root system and heat flux in soil. A Crank-Nicolson difference scheme is constructed to solve nonlinear diffusion equation to...

1996, 28(5): 513-521. doi: 10.6052/0459-1879-1996-5-1995-364

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THE PHENOMENON OF DRAG REDUCTION IN FLOWS OF CLAY SUSPENSIONS

Experiments with clay suspensions flowing over smooth, gravel and stone beds prove that resistance of the flow may be considerably reduced by the suspended sediment if the flow boundary is rough The measured mean velocity of clay suspensions is much higher than the flow of water The friction factor of flows of high clay concentrations over the gravel bed was less than half of the clear water flow on the same hydraulic conditions The high viscosity and yield stress of clay suspensions suppressed the de...

1996, 28(5): 522-531. doi: 10.6052/0459-1879-1996-5-1995-365

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COMPLETENESS AND NONUNIQUENESS OF GENERAL SOLUTIONS OF ELASTIC SHALLOW SHELLS WITH CONSTANT CURVATURE

A new general solution of elastic shallow shells with constant curvature is derived its completeness and nonuniqueness are proved Famous Vlasov solution is one of its special case Furthermore it is proved that Vlasov solution does not suit for shallow spherical shells And we give a new general solution of shallow spherical shells

1996, 28(5): 532-541. doi: 10.6052/0459-1879-1996-5-1995-366

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DOUBLE SCALAR FORMULATION OF ISOTROPIC ELASTIC DAMAGE

Description of damage state and damage evolution are of fundamental importance that have not been completely resolved This paper focuses on a most simple case, i e , isotropic elastic damage for initially isotropic elastic materials We note some limitations of the classical isotropic damage theory based on the strain equivalence hypothesis, in which the damage state is described by a single scalar damage variable In the present paper, it is shown that the complete description for isotropic elastic ...

1996, 28(5): 542-549. doi: 10.6052/0459-1879-1996-5-1995-367

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CONSTITUTIVE BEHAVIOR OF THE COMPOSITES WITH BOTH MATRIX CREEP AND SLIGHT INTERFACE CREEP

Under certain temperature and stresses metal matrix composites can exhibit pronounced creep deformation When the interfaces of composite are imperfect and viscoelastic, they also considerably contribute to the global creep behavior Based on the Mori Tanaka method for composites with imperfect interfaces, this paper studies the constitutive behavior of the composites with both matrix creep and slight interface creep The effects of various microstructural parameters are carefully examined

1996, 28(5): 550-557. doi: 10.6052/0459-1879-1996-5-1995-368

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THE LIAPUNOV’S METHOD FOR THE INVERSE DYNAMICS OF A SPACE MANIPULATOR

The inverse dynamics of a space manipulator is discussed in this paper. It is shown that as the result of the nonholonomic behavior of the system,the Liapunov's method with the joint angles as variables is infeasible in the practice,owing to the theoretical incorrectness and the appearance of dead point in computation. The Liapunov's method using the configuration of the payload as variables is suggested,and a numerical example is given. The improved method of path-planning can ensure the asymptotic stabili...

1996, 28(5): 558-563. doi: 10.6052/0459-1879-1996-5-1995-369

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DEFORMATION LOCALIZATION FOR PLANE STRAIN TENSION OF POLYMERS

A kind of BPA eight chain molecular chain network model based on strain softting glassy polymers is introduced into the Updating Lagrange finite element formulation A driving stress finite element method of elastic plastic large deformation suitable for the deformation localization analysis is proposed Using this method, the plastic flow localizing propagation for the plane strain tension of initial isotropic polymers is numerically simulated Adaptation of the BPA model to crystal...

1996, 28(5): 564-574. doi: 10.6052/0459-1879-1996-5-1995-370

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FINITE ELEMENT ANALYSIS FOR GRADIENT PLASTICITY AND MODELLING OF STRAIN LOCALIZATION

A finite element method for gradient plastic continuum is presented The Laplacian of the internal state variable is determined on the basis of a least square polynomial approximation of the internal state variable around each integration point A mixed strain element with one point guadrature and hourglass control derived from the Hu-Washizu principle and the average von Mises yield criterion are particularly considered The consistent element stiffness matrix and consistent algorithm for the integratio...

1996, 28(5): 575-584. doi: 10.6052/0459-1879-1996-5-1995-371

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EXPERIMENTAL RESEARCH ON FLOW BEHAVIORS OF AN ELECTRORHEOLOGICAL FLUID BETWEEN TWO PARALLEL ELECTRODES

The flow behaviors of an electrorheological (ER) fluid between two parallel transparent electrodes are studied experimentally Some new phenomena caused by electric field induced non homogeneously solification ae found, such as solid phase accumulation and saturation process, instability and anisotropism, of ER rivers, which has provided the experimental basis for further understanding of the mechanical behaviors of ER fluids and setting up a new theoretical model of ER valves instead of the present iso...

1996, 28(5): 585-590. doi: 10.6052/0459-1879-1996-5-1995-372

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STUDIES ON STRONGLY SWIRLING TURBULENT GAS PARTICLE FLOWS BY A PHASE DOPPLER PARTICLE ANEMOMETER

The axial and tangential time averaged and RMS fluctuation velocities of gas particle phases and particle concentration for strongly swirling turbulent gas particle flows in a cyclone chamber with tangential inlets and central axial exit are measured using a 2 D Phase Doppler Particle Anemometer(PDPA) The results show the behavior of gas particle turbulence interaction in this kind of flows, different from that of weakly swirling gas particle flows

1996, 28(5): 591-596. doi: 10.6052/0459-1879-1996-5-1995-373

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CORRELATION MEASUREMENT OF TURBULENT FLUCTIONS IN CURVED CHANNEL USING A TWO POINT LDV SYSTEM

Laser doppler velocimetry (LDV) measurements have been carried out in fully developed curved channel flows Reynolds number based on bulk velocity U and half the channel width δ is about 5 000 Streamwise velocity fluctuation of two points arranged either in streamwise, spanwise or lateral direction is measured by a two point LDV system specially designed for this experiment The data were used to calculated the correlation coefficients in three directions Conditional sampling (VITA) was employed to d...

1996, 28(5): 597-602. doi: 10.6052/0459-1879-1996-5-1995-374

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NEAR TIP SINGULAR FIELDS FOR MODE I CRACK DYNAMICALLY PROPAGATING IN A POWER LAW COMPRESSIBLE MATERIAL

Near tip singular stress and strain fields of a mode I crack dynamically propagating in a power law compressible material under plane strains are considered. With J 2 flow theory and the rectangular components, this paper obtains the near tip asymptotic fields in which the singularities of stress and strain are different and the angular variations of field quantities are the same as those in elastic perfectly plastic materials.

1996, 28(5): 603-608. doi: 10.6052/0459-1879-1996-5-1995-375

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SPECIFIC THERMOELASTIC PROPERTIES OF COMPOSITES REINFORCED BY COATED SPHERICAL PARTICLES

Based on the proposed concept of uniform fields in matrix, exact relations between the effective thermoelastic properties of composites reinforced by coated spherical particles are derived in the present paper

1996, 28(5): 609-612. doi: 10.6052/0459-1879-1996-5-1995-376

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CONTACT SURFACE ELEMENT METHOD FOR THREE DIMENSIONAL ELASTIC CONTACT PROBLEMS

The stiffness matrix of three dimensional contact surface element is deduced basing on the principle of virtual work in this paper In order to evade rearranging nodes and elements due to variation of contact surface during contact procedure, the presetting elements are presented The method is validated by numerical examples

1996, 28(5): 613-619. doi: 10.6052/0459-1879-1996-5-1995-377

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NUMERICAL SIMULATION OF THE STRESSES DISTRIBUTION ON NORMAL AND CALCIFIED NON UNIFORM THICKNESS BIOPROSTHETIC HEART VALVES

The stress distributions on the porcine aortic valves in closed position are simulated with nonlinear finite element Eight node super parametric shell element is used during the analysis The difference of the stress distribution between non uniform thickness leaflet and uniform thickness leaflet is analyzed It is found that the leaflet thickness has influence on the stress distribution Further the stress distributions of normal leaflet and the leaflet with a few calcified areas are analyzed It ...

1996, 28(5): 620-626. doi: 10.6052/0459-1879-1996-5-1995-378

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THE DRIFT INSTABILITY OF LOCAL TRANSMITTING BOUNDARY IN TIME DOMAIN

In this paper, an instability of Multi transmitting Boundary differing from the high frequency oscillation instability is discovered based on the analyses of the properties and computing results in application, and the concept of the drift instability of Multi transmitting Boundary is introduced for the first time The drift instability phenomenon and its mechanism are studied, the drift instability condition is discussed, and a simple and effective measure is suggested for eliminating the drift instabi...

1996, 28(5): 627-632. doi: 10.6052/0459-1879-1996-5-1995-379

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GLOBAL DYNAMICS SIMULATION OF MULTIBODY SYSTEMS WITH VARIABLE TOPOLOGY

New concepts, a basic system and a current system for a multibody system with variable topology, are proposed for the global dynamics simulation of the complex mechanical systems By use of technology of activation of passive constraints, the exchange of topologies of a system is automatically completed in the simulation process The software DAMB, developed by the authors is extended to simulate the whole dynamic process of a system An example, the simulation of launching of a rocket gun system, is giv...

1996, 28(5): 633-637. doi: 10.6052/0459-1879-1996-5-1995-380

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DISPLACEMENT METHOD OF ELASTIC/VISCOPLASTIC TORSIONAL COLUMN

The displacement general solution is used to discuss the torsion of elastic/viscoplastic column

1996, 28(5): 638-638. doi: 10.6052/0459-1879-1996-5-1995-381

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1996, 28(5): 639-639. doi: 10.6052/0459-1879-1996-5-1995-382

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1996 Vol. 28, No. 5

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