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DAMAGE OF POROUS MEDIA CONTAINING PRESSURIZED GAS BY UNLOADING AND THE MAXIMUM DAMAGE PRINCIPLE FOR CRITICAL OUTBURST

Damage of porous media containing pressurized gas by unloading is formulated using a simple failure model and neglecting percolation. The damage can be shown to be caused by a discontinuous rarefaction wave—— a “damage wave”. Also, there exists a maximum damage wave,which satisfies C J condition as in the case of steady deflegration.A maximum damage principle for critical outburst is proposed.

1997, 29(6): 641-646. doi: 10.6052/0459-1879-1997-6-1995-279

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ON THE EQUIVALENCE BETWEEN THE FREE SURFACE DISTRIBUTION PRESSURE PULSATING AND WAVEMAKING BY A FLAT PLATE TYPE WAVE GENERATOR

An inverse problem aimed to find the equivalence relationship between the free surface pressure distribution and floating body motionis considered in the present paper. We choose a simple wave generation problem in a 2 D wave tank for analysis, in the linear potential regime,a Fredholm integral equation of the first kind with a complex kernel that determines the free surface pressure distribution is obtained.Regularization approach is adopted to tackle this ill posed integral equation. The present stu...

1997, 29(6): 647-654. doi: 10.6052/0459-1879-1997-6-1995-280

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PERIODIC AND CHAOTIC SOLUTIONS OF CONVECTION IN POROUS MEDIA

Convective heat transfer in a porous medium with uniform internal heat generation per unit volume q is studied. Evolution of convection with the lapse of time at various Rayleigh numbers is investigated by higher order defference techniques (effect of tilted angle is properly studied for comparison). Convection is computed up to about Ra=16 000 . The results show that the convection is stable at small Ra , and becomes periodic when Ra is increased to 4 600, as Ra is further increased there...

1997, 29(6): 655-661. doi: 10.6052/0459-1879-1997-6-1995-281

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THERMAL STRESS RESPONSE OF A FINITE LENGTH THICK WALL TUBE UNDER SUBCOOLING BOILING BOUNDARY CONDITION

Based on a transient temperature distribution of finite length thick wall tube, which is obtained by solving the governing equations with phase transformation, shape coefficients and subcooling boiling boundary conditions considered, the increment form of thermal elastoplastic constitutive equation is derived and solved by means of Finite Element Method. The transient thermal stresses and residual stresses are obtained and the influencing factors on the thermal stresses are analyzed and discussed.

1997, 29(6): 662-668. doi: 10.6052/0459-1879-1997-6-1995-282

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NORMAL FORM OF THE MULTIPLE HOPF BIFURCATIONS IN NONINTERNAL RESONANCE CASES

By a newly developed method for finding the normal form, this paper deduces the normal form for the mutiple Hopf bifurcations of a high dimensional nonlinear dynamical system in noninternal resonance cases when its Jacobian matrix has many pairs of imaginary eigenvalues, and gives the expressions of the coefficients in the normal form by those inthe original system.

1997, 29(6): 669-675. doi: 10.6052/0459-1879-1997-6-1995-283

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THE CONVERGENCE PROOF OF THE PLANE RATIONAL FINITE ELEMENT

The rational finite element formulates directly in the physical domain and interpolates with the solutions, rather than using the iso parametric technique and interpolates with polynomials in the computational plane. Because of its analytical feature, the convergence can still be proved even if the element is incompatible. The present proof makes use of the method in applied mechanics, and is easier to be understood. The method can be extended to structures with multi types of elements. The convergence pr...

1997, 29(6): 676-685. doi: 10.6052/0459-1879-1997-6-1995-284

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THE TRANSVERSE DEFLECTION ANALYSIS OF UNSYMMETRICAL COMPOSITE LAMINATED PLATES

The nonlinear governing equations of composite laminated plates with elastical restraint are established by use of energy variational principle and nonlinear geometric equations in this paper. The governing equations are solved by means of generalized Fourier series method,subsequently the corresponding load deflection curves are obtained. The analysis in this paper is focused on the transverse deflection of unsymmetrical laminates.

1997, 29(6): 686-691. doi: 10.6052/0459-1879-1997-6-1995-285

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A GENERALIZED CONFORMING QUADRILATERAL MEMBRANE ELEMENT INSENSITIVE TO GEOMETRIC DISTORTION

In numerical analysis many finite element models have acceptable performance when the computing meshes are regular. However, as the level of mesh distortion increases, their accuracy of solutions descends rapidly. Therefore, how to formulate an element that is less sensitive to geometric distortion was an important question for study for a long period. In this paper, a simple quadrilateral membrane element with rotational degrees-of-freedom is developed with the approach of the generalized conforming elemen...

1997, 29(6): 692-700. doi: 10.6052/0459-1879-1997-6-1995-286

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INVESTIGATION OF THE STIFFNESS OF TRABECULAE BY REPRESENTATIVE VOLUME ELEMENT (RVE) APPROACH

Based on the concept of the fabric tensor to represent the microstructure of the cancellous bone, a more sophisticated idealized representative volume element (RVE) model is introduced for cancellous bone. It is assumed that the trabeculae distribution in the principal direction of the fabric tensor is proportional to the associated eigenvalue of the tensor. With this understanding, the present model provides a consistent and quantitative way to describe various kinds of microstructures from rod like trab...

1997, 29(6): 701-710. doi: 10.6052/0459-1879-1997-6-1995-287

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THE AXIALLY SYMMETRIC MIXED BOUNDARY-VALUE PROBLEM OF THE VERTICAL VIBRATION OF A RIGID BODY ON FLUID-SATURATED POROUS HALF SPACE

Vertical vibration of a rigid body on fluid saturated porous half space is studied. At first governing equations of dynamic problem for fluid saturated solid (Biot's wave equations) are solved by Hankel transform. Then the dual integral equations of vertical vibration of a rigid body on fluid saturated porous half space are established according to the mixed boundary value condition. By applying Abel transform the dual integral equations are reduced to Fredholm integral equation of the second kind. The d...

1997, 29(6): 711-719. doi: 10.6052/0459-1879-1997-6-1995-288

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A NEW NON CONTACT METHOD FOR MEASURING ELASTIC CONSTANTS OF MATERIALS

A new non contact method for measuring elastic constants of materials was presented and practised. The elastic constants were calculated by measuring the velocities of longitudinal and surface waves generated by a ruby pulsed laser. The experimental results show that the method is suitable and feasible for measuring in environments where high temperature, ionizing radiation or rapid movement make the use of contact sensors difficult if not impossible.

1997, 29(6): 720-725. doi: 10.6052/0459-1879-1997-6-1995-289

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THREE-DIMENSIONAL IMPACT OF A RIGID ELLIPSOID ON FIXED SURFACE WITH FRICTION

The three dimensional impact of a rigid ellipsoid on a fixed surface with friction is discussed in this paper. The differential equations of tangential velocity of contact point in the duration of impact are formulated with the normal impulse as argument. A qualitative analysis on the global behavior of tangential sliding motion is given by use of the singularity theory of phase plane. The analytical solution determining the sliding motion is also obtained.

1997, 29(6): 726-732. doi: 10.6052/0459-1879-1997-6-1995-290

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TRIPLE RESONANCES OF TORSIONAL VIBRATION OF A SHAFTING SYSTEM SIMULATING A GENERATOR SET ROTOR

A mathematical model of torsional vibration of the shafting system which has quadratic nonlinearities and harmonic excitation is established. By using of the improved averaging method for nonlinear oscillation, under the conditions ω 3≈2ω 2, ω 2≈2ω 1,and  Ω ≈ω 2, the first approximation solution and its corresponding steady-state solution of the triple resonances are obtained. The steady-state response curves are obtained and the singularity analysis is carried out. It is pointed out that the tr...

1997, 29(6): 733-739. doi: 10.6052/0459-1879-1997-6-1995-291

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THE ANALYSIS OF REGULATION CHARACTERISTICS AND THE DESIGN CRITERIA FOR THE COLLAPSIBLE TUBE FLOW REGULATOR

The flow regulation behavior of collapsible tubes under high Reynolds number are analyzed. The flow rate as a function of downstream pressure, namly the flow regulation characteristic curve is derived. The design criteria for the flow regulator with a collapsible tube as its active element are presented.

1997, 29(6): 740-744. doi: 10.6052/0459-1879-1997-6-1995-292

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QUASI-HIGH ORDER GALERKIN BEM FOR ELASTO-PLASTIC ANALYSIS

A two-stage interpolation Galerkin boundary element method called the Quasi-High Order Element Method (QHOEM) is proposed for solving elastoplastic problems. In the initial stage, it uses high order elements to interpolate the coordinates and the variables. For the numerical integration involved, it further uses interpolation to decompose the high order elements into low order elements so that the existing analytical integration formulas can be applied. By doing this, the proposed method yields good adaptab...

1997, 29(6): 745-750. doi: 10.6052/0459-1879-1997-6-1995-293

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SOLUTION TO BI LAYER BEAMS ON ELASTIC FOUNDATION

Based on Goodman model, which is used for simulating the touching condition between beams, a diffirential equation group of composite beams on Winkler foundation and its theoretical solution have been induced. The shear, tension and compression deformation in beam section due to the horizontal and vertical force in interlayer are considered through introducing a ``generalized interlayer reaction modulus''. This method raises the calculation accuracy, especially in the case of broken bi layer beams.

1997, 29(6): 751-754. doi: 10.6052/0459-1879-1997-6-1995-294

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DYNAMIC ANALYSIS OF CONSTRAINED MULTIBODY SYSTEMS IN RIEMANNIAN CONFIGURATION SPACE

The dynamic problem of constrained multibody systems in Riemannian configuration space is researched. The orthonormal bases of normal subspace and tangent subspace of the system manifold are constructed adopting the singular value decomposition of the constraint matrix and a modified Gram-Schmidt process. The dynamic equations of the system are projected along the dual bases, and new formulas of the system dynamic response are obtained. A numerical analysis method is also given. A numerical example is prese...

1997, 29(6): 755-760. doi: 10.6052/0459-1879-1997-6-1995-295

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1997 Vol. 29, No. 6

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