Article
Topological Sensitivity Analysis for the Location of Small Cavities in Stokes Flow
SIAM Journal on Control and Optimization (Impact Factor: 1.46). 01/2009; 48(5):28712900. DOI: 10.1137/070704332
Source: DBLP
ABSTRACT
The moulds' filling process may generate flaws consisting of small gas bubbles trapped inside the material, which weaken the solidity of the casted piece. We consider here the inverse problem of determining these small size flaws' locations from velocities boundary measurements. The fluid flow is described by a simplified model based on the Stokes system. A numerical algorithm based on the topological sensitivity analysis applied to an energylike misfit functional is worked out to that end.

 "Motivations. This obstacle inverse problem arises, for example, in mold filling during which small gas bubbles can be created and trapped inside the material (as it is mentioned in [10]). We can also mention the fact that the most common devices used to spot immersed bodies, such as submarines or banks of fish, are sonars, using acoustic waves: Active sonars emit acoustic waves (making themselves detectable), while passive sonars only listen (and can only detect targets that are noisy enough). "
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ABSTRACT: We consider the inverse problem of detecting the location and the shape of several obstacles immersed in a fluid flowing in a larger bounded domain Ω from partial boundary measurements in the two dimensional case. The fluid flow is governed by the steadystate Stokes equations. We use a topological sensitivity analysis for the KohnVogelius functional in order to find the number and the qualitative location of the objects. Then we explore the numerical possibilities of this approach and also present a numerical method which combines the topological gradient algorithm with the classical geometric shape gradient algorithm; this blending method allows to find the number of objects, their relative location and their approximate shape. 
 "We make a boundary measurement on the part of the exterior boundary ∂Ω and then study a KohnVogelius type cost functional. The topological asymptotic expansion of this kind of functional has studied by Ben Abda et al. in [15] but they impose Neumann boundary conditions on the boundary of the objects. Here, we have to deal with Dirichlet boundary conditions on the inclusions boundaries and the KohnVogelius approach leads to consider Dirichlet and mixed boundary conditions on the exterior boundary. "
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ABSTRACT: We want to detect small obstacles immersed in a fluid flowing in a larger bounded domain Ω in the threedimensional case. We assume that the fluid motion is governed by the steadystate Stokes equations. We make a measurement on a part of the exterior boundary ∂Ω and then take a Kohn–Vogelius approach to locate these obstacles. We use here the notion of the topological derivative in order to determine the number of objects and their rough locations. Thus we first establish an asymptotic expansion of the solution of the Stokes equations in Ω when we add small obstacles inside. Then, we use it to find a topological asymptotic expansion of the considered Kohn–Vogelius functional which gives us the formula of its topological gradient. Finally, we make some numerical simulations exploring the efficiency and the limits of this method.Inverse Problems 10/2012; 28(10). DOI:10.1088/02665611/28/10/105007 · 1.32 Impact Factor 
 "Its aim is twofold: (i) to establish the expressions of coefficients T 2 , T 3 , T 4 for a crack of size a embedded in a 2D medium characterized by a scalar conductivity, permitting computationally efficient methods for evaluating smallcrack expansions of cost functionals, and (ii) to demonstrate the effectiveness of the resulting expansion (1) for crack identification purposes. Since the sensitivity of cost functionals (rather than field variables ) is emphasized here, an adjoint solutionbased approach is formulated as it avoids the (involved and costly) evaluation of higherorder sensitivities of field variables, following what is now common practice in usual sensitivity analyses and previous works on topological sensitivity [3] [6] [9] [10] [16] [22]. Coefficients T 2 , T 3 , T 4 are hence found to be expressed in terms of the free and adjoint fields (i.e. the response of the reference medium to the applied and adjoint excitations), and also (for T 4 ) on the Green's function associated with the geometry and boundary condition structure under consideration. "
Article: Fast identification of cracks using higherorder topological sensitivity for 2D potential problems
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ABSTRACT: This article concerns an extension of the topological sensitivity (TS) concept for 2D potential problems involving insulated cracks, whereby a misfit functional J is expanded in powers of the characteristic size a of a crack. Going beyond the standard TS, which evaluates (in the present context) the leading O(a2) approximation of J, the higherorder TS established here for a small crack of arbitrarily given location and shape embedded in a 2D region of arbitrary shape and conductivity yields the O(a4) approximation of J. Simpler and more explicit versions of this formulation are obtained for a centrally symmetric crack and a straight crack. A simple approximate global procedure for crack identification, based on minimizing the O(a4) expansion of J over a dense search grid, is proposed and demonstrated on a synthetic numerical example. BIE formulations are prominently used in both the mathematical treatment leading to the O(a4) approximation of J and the subsequent numerical experiments.Engineering Analysis with Boundary Elements 02/2011; 35(235):223235. DOI:10.1016/j.enganabound.2010.08.007 · 1.39 Impact Factor
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