Development of a crack with a considerable prefracture zone in a viscoelastic orthotropic plate under variable loads

The study is made of the delayed fracture of a viscoelastic orthotropic plate caused by subcritical advancement of a rectilinear microcrack, which is located along one of the orthotropic axes. The crack develops because of stretching of the plate by uniformly distributed increasing and cyclic external forces perpendicular to the crack line. The investigation is carried out within the framework of the Boltzmann-Volterra theory for resolvent integral operators of difference type, which describe the deformation of a material with time-dependent rheological properties. The analytical form of the kernel of an irrational function of a linear combination of the above integral operators is determined by the method of operator continued fractions. Numerical calculations are conducted for resolvent bounded integral operators with a kernel in the form of Rabotnov's fractional-exponential function. The kinetics of growth of a crack with tip regions commensurable with the crack length is studied. A comparison with the results obtained within the framework of the concept of the thin structure of the crack tip is given. S. P. Timoshenko Institute of Mechanics, National Academy of Sciences of Ukraine, Kiev. Translated from Prikladnaya Mekhanika, Vol. 36, No. 6, pp. 121–129, June, 2000.     

The delayed fracture of an isotropic viscoelastic plate with a microcrack under a varying load

The delayed fracture of an isotropic viscoelastic plate due to subcritical growth of a rectilinear microcrack of normal separation is studied. The paper deals with the development of the crack due to the stretching of the plate by uniformly distributed increasing and cyclic external loads applied perpendicularly to the crack line. The investigation is carried out within the framework of the Boltzmann-Volterra theory for resolvent integral operators of difference type, which describe the deformation of materials with time-dependent rheological properties. Numerical calculations are performed for resolvent integral operators with a kernel in the form of Rabotnov's fractional-exponential function. The kinetics of a crack with a tip zone commensurable with the crack length is studied. The results are compared with those obtained on the basis of the hypothesis on the thin structure of the crack tip. S.P. Timoshenko Institute of Mechanics, National Academy of Sciences of Ukraine, Kiev. Translated from Prikladnaya Mekhanika, Vol. 36, No. 5, pp. 114–121, May, 2000.     

Minimal and maximal fixed point theorems and iterative technique for nonlinear operators in product spaces

In this paper, we study minimal and maximal fixed point theorems and iterative technique for nonlinear operators in product spaces. As a corollary of our result, some coupled fixed point theorems are obtained, which generalize the coupled fixed point theorems obtained by Guo Da-jun and Lankshmikanthamt and the results obtained by Lan in, and.     

Delayed fracture of a transversally isotropic viscoelastic material with a crack under monotonically increasing loading

The delayed fracture of a transversally isotropic viscoelastic material due to slow subcritical growth of a flat normal-fracture macrocrack with a circular cross-section under monotonically increasing load is examined. The calculations employ the modified δ_C of fracture, which is based on the concept of constancy of the prefailure region. The investigation is carried out within the framework of the Boltzmann-Volterra theory for difference-type bounded resolvent operators, which describe the transversal isotropy of the viscoelastic deformational properties of the material. To find the analytical form of the kernel of an irrational function of a linear combination of the above-mentioned integral operators, the method of operator continued fractions is used. Analytical and numerical calculations are carried out for difference-type bounded resolvent operators with the kernel in the form of Rabotnov's fractional-exponential function. S. P. Timoshenko Institute of Mechanics. National Academy of Sciences of Ukraine, Kiev. Translated from Prikladnaya Mekhanika, Vol. 35, No. 10, pp. 54–60, October, 1999.     

On deforming of a linear viscoelastic orthotropic half-space under the turning rigid cylindrical roller

In this paper we consider the problem of rigid cylinder turning on a linear viscoelastic orthotropic half-space with Coulomb's friction acting along the contact area. Results for extents of contact area and pressure under the cylinder are obtained using Volterra's principle. The obtained functions of viscoelastic operators are interpreted by a method based on expansion of such functions in operator continued fractions. A solution is given for the general type of resolvent viscoelastic operators expressing rheological properties of half-space material. Algebra of resolvent Volterrian operators is used to facilitate the calculations. An example is given to illustrate the results for real viscoelastic material with the rheological properties expressed by the operators of Yu.N. Rabotnov.     

On probabilistic norm of a linear operators and space of operators

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Noether symmetry method for Birkhoffian systems in terms of generalized fractional operators

Compared with the Hamiltonian mechanics and the Lagrangian mechanics, the Birkhoffian mechanics is more general. The Birkhoffian mechanics is discussed on the basis of the generalized fractional operators, which are proposed recently. Therefore, differential equations of motion within generalized fractional operators are established. Then, in order to find the solutions to the differential equations, Noether symmetry, conserved quantity, perturbation to Noether symmetry and adiabatic invariant are investigated. In the end, two applications are given to illustrate the methods and results.     

Interfacial discontinuity relations for coupled multifield phenomena and their application to the modeling of thin interphases as imperfect interfaces

Interfacial continuity and discontinuity relations are needed in dealing with a variety of mechanical and physical phenomena in heterogeneous media. The present work consists of two parts. In the first part concerned with perfect interfaces, two orthogonal projection operators reflecting the interfacial continuity and discontinuity of the field variables of coupled mechanical and physical phenomena are introduced and some coordinate-free interfacial relations involving the surface decomposition of a generic linear constitutive law are deduced. In the second part dedicated to the derivation of a general imperfect interface model for coupled multifield phenomena by applying Taylor's expansion to a 3D curved thin interphase perfectly bonded to its two neighboring phases, the interfacial operators and relations given in the first part are used directly so as to render the derivation more direct and to write the final interfacial jump relations characterizing the model in a unified and compact way. The general imperfect interface model obtained in the present work includes as special cases all the relevant ones reported in the literature.     

Adequacy of a nonlinear theory of viscoelasticity

Some features of the behavior of viscoelastic materials whose existence leads to the choice of nonlinear constitutive relations are discussed. A classification of such constitutive relations is given and a number of requirements imposed by practice on their adequacy are formulated. A nonlinear theory of viscoelasticity is proposed; this theory offers the advantages over the theory in which stresses are expressed in terms of strains by integral operators of increasing multiplicity. By a one-dimensional example, it is shown that the constitutive operator relations are reciprocal.     

Bruck formula for a perturbed Lipschitzian iteration of Lipschitz pseudocontractive maps

Introduction InRef.[1],BrowderdefinedpseudocontractivemappinginBanachspaceand mentionedtherelationshipofthisclassofmappingtoanimportantclassofmappingknown asaccretive(monotoneinHilbertspace)operator.ThemappingAisaccretiveiffI-Ais pseudocontractive.Themapp…     

Some theorems on Gabor operators

The object of this study is the class of closable Gabor operators. That is the set of operators which map a Gabor function (or note) into a multiple of a Gabor function. By using the Bargman space (sometimes called Bargman representation) some general properties of these operators are derived. It is shown that the set of Gabor operators whose adjoint is also a Gabor operator establishes a six-dimensional complex manifold with a partial Lie-group structure and with an involution. The corresponding Lie-algebra and the infinitesimal generators are calculated. Further it turns out that, at least locally, a Gabor operator with a Gabor adjoint results from an evolution process. The proofs of the theorems are a hybridization of Hilbert space techniques and classical complex analysis (theorems of Osgood, Montel, etc.). The proofs will be published elsewhere in a wider context.     

Random directional contractors and their applications

In this paper, as the generalizations of Altman’s directional contractors[4,5] and Lee and Padgett’s random contractors[1,2] we introduce the concept of random directional contractors for set-valued random operators. Using the new concept and transfinite induction, we show several existence theorems to solutions of nonlinear set-valued random operator equations. Our theorems improve and generalize the corresponding results in [1,2,4,5,11]. Next, some applications of our results to nonlinear random integral and differential equations are given.     

Theory and application of numerical simulation method of capillary force enhanced oil production

A kind of second-order implicit upwind fractional step finite difference methods are presented for the numerical simulation of coupled systems for enhanced(chemical)oil production with capillary force in the porous media.Some techniques,e.g.,the calculus of variations,the energy analysis method,the commutativity of the products of difference operators,the decomposition of high-order difference operators,and the theory of a priori estimate,are introduced.An optimal order error estimate in the l~2 norm is derived.The method is successfully used in the numerical simulation of the enhanced oil production in actual oilfields.The simulation results are satisfactory and interesting.     

Boundary-layer corrections for stress and strain fields in randomly heterogeneous materials

Boundary-layer effects on the effective response of fibre-reinforced media are analysed. The distribution of the fibres is assumed random. A methodology is presented for obtaining non-local effective constitutive operators in the vicinity of a boundary. These relate ensemble averaged stress to ensemble averaged strain. Operators are also developed which re-construct the local fields from their ensemble averages. These require information on the local configuration of the medium. Complete information is likely not to be available, but averages of these operators conditional upon any given local information generate corresponding conditional averages of the fields. Explicit implementation is performed within the framework of an approximation of Hashin-Shtrikman type. Two types of geometry are considered in examples: a half-space and a crack in an infinite heterogeneous medium. These are representative, asymptotically, of the field in the vicinity of any smooth boundary, and in the vicinity of a crack tip, respectively. Results have been obtained for the case of anti-plane deformation, realized by the imposition of either Dirichlet or Neumann conditions on the boundary; those for the Neumann condition are presented and discussed explicitly. The stresses in both fibre and matrix adjacent to a crack tip are shown to differ substantially from the values that would be predicted by ordinary homogenization.     

Study of the Deformation of Anisotropic Viscoelastic Bodies

A study is made of methods for solving linear viscoelastic problems on the basis of the Volterra concept — representation of irrational functions of integral operators as operator power series (analogues of Taylor series). It is pointed out that these series converge weakly. The results of development and substantiation of a new mathematical method for solution of the above problems are summarized. It is based on representing irrational functions of integral operators by operator continued fractions, which converge well. Solutions to certain linear viscoelastic problems for anisotropic bodies are given     

Footbridge between finite volumes and finite elements with applications to CFD

The aim of this paper is to introduce a new algorithm for the discretization of second‐order elliptic operators in the context of finite volume schemes on unstructured meshes. We are strongly motivated by partial differential equations (PDEs) arising in computational fluid dynamics (CFD), like the compressible Navier–Stokes equations. Our technique consists of matching up a finite volume discretization based on a given mesh with a finite element representation on the same mesh. An inverse operator is also built, which has the desirable property that in the absence of diffusion, one recovers exactly the finite volume solution. Numerical results are also provided. Copyright © 2001 John Wiley & Sons, Ltd.     

A generalization of recursion operators of differential equations

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Modified characteristic finite difference fractional step method for moving boundary value problem of nonlinear percolation system

A fractional step scheme with modified characteristic finite differences running in a parallel arithmetic is presented to simulate a nonlinear percolation system of multilayer dynamics of fluids in a porous medium with moving boundary values. With the help of theoretical techniques including the change of regions, piecewise threefold quadratic interpolation, calculus of variations, multiplicative commutation rule of difference operators, multiplicative commutation rule of difference operators, decomposition of high order difference operators, induction hypothesis, and prior estimates, an optimal order in l ² norm is displayed to complete the convergence analysis of the numerical algorithm. Some numerical results arising in the actual simulation of migration-accumulation of oil resources by this method are listed in the last section.     

A study of eigenvalue sensitivity for hydrodynamic stability operators

The eigenvalue sensitivity for hydrodynamic stability operators is investigated. Classical matrix perturbation techniques as well as the concept of -pseudospectra are applied to show that parts of the spectrum are highly sensitive to small perturbations. Applications are drawn from incompressible plane Couette flow, trailing line vortex flow, and compressible Blasius boundary-layer flow. Parameter studies indicate a monotonically increasing effect of the Reynolds number on the sensitivity. The phenomenon of eigenvalue sensitivity is due to the nonnormality of the operators and their discrete matrix analogs and may be associated with large transient growth of the corresponding initial value problem.This work was started at NASA Langley Research Center, Hampton, VA (LaRC), at the Institute for Computer Applications in Science and Engineering (ICASE). The first author gratefully acknowledges financial support from both ICASE and LaRC during the course of this work. Partial support for the second author was provided by the Aeronautical Research Institute of Sweden (FFA). Support for the third and fourth authors was provided by NASA Langley Research Center under Contract NAS1-18240. Computer time was provided by LaRC.     

Modified characteristic finite difference fractional step method for moving boundary value problem of percolation coupled system

For the coupled system with moving boundary values of multilayer dynamicsof fluids in porous media,a characteristic finite difference fractional step scheme appli-cable to the parallel arithmetic is put forward.Some techniques,such as the change ofregions,the calculus of variations,the piecewise threefold quadratic interpolation,themultiplicative commutation rule of difference operators,the decomposition of high orderdifference operators,and the prior estimates,are adopted.The optimal order estimatesin the l2norm are derived to determine the error in the approximate solution.This nu-merical method has been successfully used to simulate the flow of migration-accumulationof the multilayer percolation coupled system.Some numerical results are well illustratedin this paper.