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An algorithm for the identification of fronts prescribed by Signorini type boundary conditions. (Un algorithme d’identification de frontières soumises à des conditions aux limites de Signorini.) (French) Zbl 0954.65050
The purpose of this paper is to study a question concerning the geometrical inverse problem, which consists in finding the shape of an unknown part $$\gamma$$ of the boundary $$\partial\Omega$$ of a two-dimensional body $$\Omega$$, by using thermal measurements of some part $$M$$ of the boundary. The two extremal points of the unknown boundary $$\gamma$$ are supposed to be fixed, while Signorini type boundary conditions are prescribed on $$\gamma$$. The problem is turned into an optimal shape one, by constructing a Kohn-Vogelius-like cost function, the only minimum of which is proved to be the unknown boundary.
Main result: The authors prove that the derivative of this cost functional with respect to a direction $$\theta$$ depends only on the state function $$u^0$$ and not on its Lagrangian derivative $$u^1(\theta)$$. Expressions which allow to implement a gradient algorithm to solve the inverse problem are proposed. The authors obtain very good numerical results by linearization (from Signorini to mixed obundary conditions on the auxiliary Dirichlet problem) and by the use of gradient expressions, which do not depend on the derivatives of the solution.
The main interest of this work lies in the way used to overcome the difficulties arising from the nonlinear boundary conditions. It appears that this approach may be extended to the thermoelastic coupled problem, which is a more relevant problem from a physical point of view.

##### MSC:
 65K10 Numerical optimization and variational techniques 49J20 Existence theories for optimal control problems involving partial differential equations 49N45 Inverse problems in optimal control 34H05 Control problems involving ordinary differential equations 35R30 Inverse problems for PDEs 49Q12 Sensitivity analysis for optimization problems on manifolds
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