Adhesive contact problem for viscoplastic materials

We examine a mathematical model that describes a quasistatic adhesive contact between a viscoplastic body and deformable foundation. The material’s behaviour is described by the rate-type constitutive law which involves functions with a non-polynomial growth. The contact is modelled by the normal compliance condition with limited penetration and adhesion, a subdifferential friction condition also depending on adhesion, and the evolution of bonding field is governed by an ordinary differential equation. We present the variational formulation of this problem which is a system of an almost history-dependent variational–hemivariational inequality for the displacement field and an ordinary differential equation for the bonding field. The results on existence and uniqueness of solution to an abstract almost history-dependent inclusion and variational–hemivariational inequality in the reflexive Orlicz–Sobolev space are proved and applied to the adhesive contact problem.     

Bénard instabilities in polar fluids

This paper employs continuum theory of polar fluids to investigate the onset of roll-type instabilities in a fluid confined between horizontal rigid boundaries and subject to a vertical temperature gradient. A Fourier series method is used to obtain an exact expression for the determination of the critical temperature gradient for the particular type of instability. Results are presented for a wide range of the various parameters in the theory.

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Résumé Cet article utilise la théorie du continuum des fluides polaires en vue d'étudier le début d'instabilités de type cellulaire dans un fluide compris entre des limites horizontales rigides et soumis à un gradient de température vertical. Afin de déterminer exactement le gradient de température critique pour le type d'instabilité en question, on utilise une méthode basée sur les séries de Fourier. On présente des résultats pour une large gamme des différents paramètres utilisés dans la théorie.

     

Analysis of two frictional viscoplastic contact problems with damage

In this work we study two quasistatic frictional contact problems arising in viscoplasticity including the mechanical damage of the material, caused by excessive stress or strain and modelled by an inclusion of parabolic type. The variational formulation is provided for both problems and the existence of a unique solution is proved for each of them. Then a fully discrete scheme is introduced using the finite element method to approximate the spatial domain and the Euler scheme to discretize the time derivatives. Error estimates are derived and, under suitable regularity assumptions, the linear convergence of the algorithm is deduced. Finally, some numerical examples are presented to show the performance of the method.     

Shape optimization in two-dimensional viscous compressible fluids

We present a method for solving the optimal shape problems for profiles surrounded by viscous compressible fluids in two space dimensions. The class of admissible profiles is quite general including the minimal volume condition and a constraint on the thickness of the boundary. The fluid flow is modelled by the Navier-Stokes system for a general viscous barotropic fluid with the pressure satisfying p（o） = aQlog^d（o） for large Q. Here d 〉 1 and a 〉 0.     

A quasistatic viscoplastic contact problem with normal compliance and friction

We consider a quasistatic contact problem between a viscoplasticbody and an obstacle, the so-called foundation. The contactis modelled with normal compliance and the associated versionof Coulomb's law of dry friction. We derive a variational formulationof the problem and, under a smallness assumption on the normalcompliance functions, we establish the existence of a weak solutionto the model. The proof is carried out in several steps. Itis based on a time-discretization method, arguments of monotonicityand compactness, Banach fixed point theorem and Schauder fixedpoint theorem.     

On a viscoplastic approximation in finite plasticity

We are concerned with a phenomenological model of isotropic finite elasto‐plasticity valid for small elastic strains applied to polycrystalline material. We prove a local in time existence and uniqueness result. To the best of our knowledge this is the first rigorous result concerning classical solutions in geometric nonlinear finite visco‐plasticity.     

CABARET scheme in velocity-pressure formulation for two-dimensional incompressible fluids

The CABARET method was generalized to two-dimensional incompressible fluids in terms of velocity and pressure. The resulting algorithm was verified by computing the transport and interaction of various vortex structures: a stationary and a moving solitary vortex, Taylor-Green vortices, and vortices formed by the instability of double shear layers. Much attention was also given to the modeling of homogeneous isotropic turbulence and to the analysis of its spectral properties. It was shown that, regardless of the mesh size, the slope of the energy spectra up to the highest-frequency harmonics is equal ?3, which agrees with Batchelor’s enstrophy cascade theory.     

Optimal control of a two-dimensional contact problem

We consider a frictionless contact problem with unilateral constraints for a 2D bar. We describe the problem, then we derive its weak formulation, which is in the form of an elliptic variational inequality of the first kind. Next, we establish the existence of a unique weak solution to the problem and prove its continuous dependence with respect to the applied tractions and constraints. We proceed with the study of an associated control problem for which we prove the existence of an optimal pair. Finally, we consider a perturbed optimal control problem for which we prove a convergence result.     

On the linearization of systems of conservation laws for fluids at a material contact discontinuity

In order to investigate the linearized stability or instability of compressible flows, as it occurs for instance in Rayleigh–Taylor or Kelvin–Helmholtz instabilities, we consider the linearization at a material discontinuity of a flow modeled by a multidimensional nonlinear hyperbolic system of conservation laws. Restricting ourselves to the plane-symmetric case, the basic solution is thus a one-dimensional contact discontinuity and the normal modes of pertubations are solutions of the resulting linearized hyperbolic system with discontinuous nonconstant coefficients and source terms. While in Eulerian coordinates, the linearized Cauchy problem has no solution in the class of functions, we prove that for a large class of systems of conservation laws written in Lagrangian coordinates and including the Euler and the ideal M.H.D. systems, there exists a unique function solution of the problem that we construct by the method of characteristics.     

Optimal control for two-dimensional stochastic second grade fluids

This article deals with a stochastic control problem for certain fluids of non-Newtonian type. More precisely, the state equation is given by the two-dimensional stochastic second grade fluids perturbed by a multiplicative white noise. The control acts through an external stochastic force and we search for a control that minimizes a cost functional. We show that the Gâteaux derivative of the control to state map is a stochastic process being the unique solution of the stochastic linearized state equation. The well-posedness of the corresponding stochastic backward adjoint equation is also established, allowing to derive the first order optimality condition.     

On free boundary problems with moving contact points for the stationary two-dimensional Navier-Stokes equations

Solvability of the problem of slow drying of a plane capillary in the classical setting (i. e., with the adherence condition on a rigid wall) is established. The proof is based on a detailed study of the asymptotics of the solution near a point of contact of the free boundary with a moving wall, including estimates of the coefficients in well known asymptotic formulas. It is shown that the only value of the contact angle admitting a solution of the problem with finite energy dissipation equals π. Bibliography: 18 titles. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 213, 1994, pp. 179–205. Translated by E. V. Frolova.     

On Burgers fluids

We investigate several qualitative aspects concerning the solutions to the flow of a Burgers fluid, a model that has been used to describe a variety of materials: polymeric liquids, asphalt and asphalt mixtures, and the earth's mantle. Continuous dependence of the solutions with respect to initial data and supply terms, uniqueness of solutions and the impossibility of localization of the solutions are proved. Exponential stability and structural stability are analysed. We also consider uniaxial shear flows. We prove instability of solutions whenever the constitutive parameters do not satisfy certain relations. Also we study the spatial behaviour of the solutions. Copyright © 2006 John Wiley & Sons, Ltd.     

On dynamics of fluids in meteorology

We consider the full Navier-Stokes-Fourier system of equations on an unbounded domain with prescribed nonvanishing boundary conditions for the density and temperature at infinity. The topic of this article continues author’s previous works on existence of the Navier-Stokes-Fourier system on nonsmooth domains. The procedure deeply relies on the techniques developed by Feireisl and others in the series of works on compressible, viscous and heat conducting fluids.     

On dynamics of fluids in astrophysics

The object of this article is to show the existence of weak solutions to the Navier–Stokes–Fourier Poisson system on (in general) unbounded domains. The topic is a natural continuation of the author’s results on the existence of weak solutions to the problem on Lipschitz domains and to the Oxenius system on unbounded domains. Technique of the proof is based on the tools developed in a series of works by Feireisl (Oxford lecture series in mathematics and its applications, 26, Oxford University Press, Oxford) and others during the recent years. The weak solution’s sensitivity to a change of the domain is discussed as well.     

Certain nonlocal problems for two-dimensional equations of motion of Oldroyd fluids

The solvability of a boundary-value problem on the semi-axis t0 is studied for two-dimensional equations of motion of Oldroyd fluids (1), and with trivial problem data a proof is given of the existence of a solution which is periodic with respect to t and has the period . This solution has an absolute term which is also periodic with respect to t and has the period . Substantiation is given for the principle of linearization (first Liapunov method) in the theory of the exponential stability of solutions at t.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 189, pp. 101–121, 1991.     

On a method of solving two-dimensional integral equations of axisymmetric contact problems for bodies with complex rheology

A two-dimensional integral equatin appearing in axisymraetric contact problems for bodies with complex rheology is studied. A method of constructing the solution of this equation in proposed, based on inspecting the non-classical spectral properties of an integral operator. A contact problem for a non-uniformly aging viscoelastic foundation is solved as an example.     

A remark on the inviscid limit for two-dimensional incompressible fluids

In this article, we shall study the inviscid limit of two dimensional fluids with bounded voticity. We prove that the solution of incompressible Navier-Stokes system converges strongly in L² to the solution of the Euler incompressible system in the case of two-dimensional fluids in the whole space.