Asymptotic behavior of an elastic beam fixed on a small part of one of its extremities

We study the asymptotic behavior of the solution of an anisotropic, heterogeneous, linearized elasticity problem in a cylinder whose diameter $\epsilon$ tends to zero. The cylinder is assumed to be fixed (homogeneous Dirichlet boundary condition) on the whole of one of its extremities, but only on a small part (of size $\epsilon r^\epsilon$) of the second one; the Neumann boundary condition is assumed on the remainder of the boundary. We show that the result depends on $r^\epsilon$, and that there are 3 critical sizes, namely $r^\epsilon=\epsilon^3$, $r^\epsilon=\epsilon$, and $r^\epsilon=\epsilon^{1/3}$, and in total 7 different regimes. We also prove a corrector result for each behavior of $r^\epsilon$.Comment: Preliminary version of a Note to be published in a slightly abbreviated form in C. R. Acad. Sci. Paris, Ser. I, 338 (2004), pp. 975-98

Comportamiento asintótico de una viga elástica fijada en pequeñas zonas de uno de sus extremos

Estudiamos el comportamiento asintótico de una viga elástica delgada cuando su anchura, ε, tiende a cero. La viga está fijada en la totalidad de una de sus bases, mientras que en la otra, sólo lo está en la unión de N pequeñas zonas de talla εrε , r ε tendiendo a cero. Sobre el resto de la frontera se impone una condición de Neumann. El comportamiento depende de r ε , el número de zonas de fijación y su distribución. Para N = 1 aparecen tres tallas críticas, ε 3 , ε y ε 1/3 y por tanto siete regímenes distintos. Si r ε ¿ ε 3 el comportamiento es el mismo que cuando no existe la pequeña zona de sujeción. Si r ε À ε 1/3 el comportamiento es el que obtendríamos si fijáramos en toda la base. En los demás casos aparecen comportamientos intermedios. Para N ≥ 2 el resultado es diferente. Así, si las zonas se concentran alrededor de tres puntos no alineados sólo aparecen dos tallas críticas, ε 3 y ε. Esto prueba que es preferible fijar la viga alrededor de tres puntos no alineados de una base a hacerlo alrededor de tan sólo uno, aún cuando usemos una zona de mucho mayor grosor

Comportement asymptotique d’une poutre élastique fixée sur une petite partie de l’une de ses extremités

We study the asymptotic behavior of the solution of an anisotropic, heterogeneous, linearized elasticity problem in a cylinder whose diameter ε tends to zero. The cylinder is assumed to be fixed (homogeneous Dirichlet boundary condition) on the whole of one of its extremities, but only on a small part (of size εrε) of the second one; the Neumann boundary condition is imposed on the remainder of the boundary. We show that the result depends on rε, and that there are 3 critical sizes, namely rε=ε3, rε=ε, and rε=ε1/3, and in total 7 different regimes. We also prove a corrector result for each behavior of rε.Nous étudions le comportement asymptotique de la solution d'un problème d'élasticité linéaire anisotrope et hétérogène dans un cylindre dont le diamètre ε tend vers zéro. Le cylindre est fixé (condition de Dirichlet homogène) sur la totalité de l'une de ses extrémités, mais seulement sur une petite partie (de taille εrε) de l'autre base ; sur le reste de la frontière on a la condition de Neumann. Nous montrons que le résultat depend de rε, et qu'il existe 3 tailles critiques, à savoir rε=ε3, rε=ε et rε=ε1/3, et au total 7 comportements différents. Nous donnons un résultat de correcteur pour tous les comportements de rε.Dirección General de Investigació

Asymptotic behavior of nonlinear systems in varying domains with boundary conditions on varying sets

For a fixed bounded open set Ω ⊂ RN , a sequence of open sets Ωn ⊂ Ω and a sequence of sets Γn ⊂ ∂Ω ∩ ∂Ωn, we study the asymptotic behavior of the solution of a nonlinear elliptic system posed on Ωn, satisfying Neumann boundary conditions on Γn and Dirichlet boundary conditions on ∂Ωn \ Γn. We obtain a representation of the limit problem which is stable by homogenization and we prove that this representation depends on Ωn and Γn locally.Ministerio de Educación y CienciaJunta de Andalucí

Homogenization of very thin elastic reticulated structures

This work is devoted to the homogenization of the anisotropic, linearized elasticity system posed on thin reticulated structures involving several parameters. We show that the result depends on the relative size of the parameters. In every case, we obtain a limit problem where both the microscopic and macroscopic scales appear together. From this problem, we get an asymptotic development which gives an approximation in L2 of the displacements and the linearized strain tensor.Ministerio de Ciencia y Tecnologí

Asymptotic behavior of the Navier-Stokes system in a thin domain with Navier condition on a slightly rough boundary

We study the asymptotic behavior of the solutions of the Navier–Stokes system in a thin domain Ωε of thickness ε satisfying the Navier boundary condition on a periodic rough set Γε ⊂ ∂Ωε of period rε and amplitude δε, with δε rε ε. We prove that the limit behavior as ε goes to zero depends on the limit λ of δεε 1 2 /r 3 2 ε . Namely, if λ = +∞, the roughness is so strong that the fluid behaves as if we had imposed the adherence condition on Γε. If λ = 0, the roughness is too weak and the fluid behaves as if Γε were a plane. Finally, if λ ∈ (0, +∞), the roughness is strong enough to make a new friction term appear in the limit.Ministerio de Economía y Competitividad (España) MTM2011- 24457Junta de Andalucía FQM30

On the Navier boundary condition for viscous fluids in rough domains

In this paper we review some recent results concerning the study of the asymptotic behavior of viscous fluids in rough domains assuming Navier boundary conditions on the rough boundary. Our main interest is to study the relation between both the adherence and the Navier boundary conditions in the case of a boundary with weak rugosities. We show that the roughness acts on the fluid as a friction term. In particular, if the roughness is sufficiently strong, Navier condition implies adherence condition. This generalizes previous results of other authors.Ministerio de Ciencia e InnovaciónJunta de Andalucí

Numerical approximation of a one-dimensional elliptic optimal design problem

We address the numerical approximation by finite-element methods of an optimal design problem for a two phase material in one space dimension. This problem, in the continuous setting, due to high frequency oscillations, often does not have a classical solution, and a relaxed formulation is needed to ensure existence. On the contrary, the discrete versions obtained by numerical approximation have a solution. In this article we prove the convergence of the discretizations and obtain convergence rates. We also show a faster convergence when the relaxed version of the continuous problem is taken into account when building the discretization strategy. In particular it is worth emphasizing that, even when the original problem has a classical solution so that relaxation is not necessary, numerical algorithms converge faster when implemented on the relaxed version.Ministerio de Ciencia e InnovaciónJunta de Andalucí

Gamma-convergence of equi-coercive nonlinear energies defined on vector-valued functions, with non-uniformly bounded coefficients

The present paper deals with the asymptotic behavior of equi-coercive sequences {Fn} of nonlinear functionals defined over vector-valued functions in W1,p 0 (Ω)M , where p > 1, M ≥ 1, and Ω is a bounded open set of RN , N ≥ 2. The strongly local energy density Fn(·, Du) of the functional Fn satisfies a Lipschitz condition with respect to the second variable, which is controlled by a positive sequence {an} which is only bounded in some suitable space L r(Ω). We prove that the sequence {Fn} Γ-converges for the strong topology of Lp(Ω)M to a functional F which has a strongly local density F(·, Du) for sufficiently regular functions u. This compactness result extends former results on the topic, which are based either on maximum principle arguments in the nonlinear scalar case, or adapted div-curl lemmas in the linear case. Here, the vectorial character and the nonlinearity of the problem need a new approach based on a careful analysis of the asymptotic minimizers associated with the functional Fn. The relevance of the conditions which are imposed to the energy density Fn(·, Du), is illustrated by several examples including some classical hyper-elastic energies.Ministerio de Economía y CompetitividadInstitut de Recherche Mathématique de Renne