270 research outputs found
Sharp interface limit for a phase field model in structural optimization
We formulate a general shape and topology optimization problem in structural
optimization by using a phase field approach. This problem is considered in
view of well-posedness and we derive optimality conditions. We relate the
diffuse interface problem to a perimeter penalized sharp interface shape
optimization problem in the sense of -convergence of the reduced
objective functional. Additionally, convergence of the equations of the first
variation can be shown. The limit equations can also be derived directly from
the problem in the sharp interface setting. Numerical computations demonstrate
that the approach can be applied for complex structural optimization problems
Approximations of Shape Metrics and Application to Shape Warping and Empirical Shape Statistics
International audienceThis chapter proposes a framework for dealing with two problems related to the analysis of shapes: the definition of the relevant set of shapes and that of defining a metric on it. Following a recent research monograph by Delfour and ZolĂ©sio [8], we consider the characteristic functions of the subsets of â2 and their distance functions. The L 2 norm of the difference of characteristic functions and the Lâ and the W 1,2 norms of the difference of distance functions define interesting topologies, in particular that induced by the well-known Hausdorff distance. Because of practical considerations arising from the fact that we deal with image shapes defined on finite grids of pixels, we restrict our attention to subsets of â2 of positive reach in the sense of Federer [12], with smooth boundaries of bounded curvature. For this particular set of shapes we show that the three previous topologies are equivalent. The next problem we consider is that of warping a shape onto another by infinitesimal gradient descent, minimizing the corresponding distance. Because the distance function involves an inf, it is not differentiable with respect to the shape. We propose a family of smooth approximations of the distance function which are continuous with respect to the Hausdorff topology, and hence with respect to the other two topologies. We compute the corresponding GĂąteaux derivatives. They define deformation flows that can be used to warp a shape onto another by solving an initial value problem. We show several examples of this warping and prove properties of our approximations that relate to the existence of local minima. We then use this tool to produce computational de.nitions of the empirical mean and covariance of a set of shape examples. They yield an analog of the notion of principal modes of variation. We illustrate them on a variety of examples
Linear Quadratic Zero-Sum Two-Person Differential Games
International audienceAs in optimal control theory, linear quadratic (LQ) differential games (DG) can be solved, even in high dimension, via a Riccati equation. However, contrary to the control case, existence of the solution of the Riccati equation is not necessary for the existence of a closed-loop saddle point. One may " survive " a particular, non generic, type of conjugate point. An important application of LQDG's is the so-called Hâ-optimal control, appearing in the theory of robust control
Formal asymptotic limit of a diffuse-interface tumor-growth model
We consider a diffuse-interface tumor-growth model which has the form of a phase-field system. We characterize the singular limit of this problem. More precisely, we formally prove that as the coefficient of the reaction term tends to infinity, the solution converges to the solution of a novel free boundary problem. We present numerical simulations which illustrate the convergence of the diffuse-interface model to the identified sharp-interface limit
Moving frames applied to shell elasticity
Exterior calculus and moving frames are used to describe curved elastic
shells. The kinematics follow from the Lie-derivative on forms whereas the
dynamics via stress-forms.Comment: 20 pages, 1 figur
hp-adaptive Galerkin Time Stepping Methods for Nonlinear Initial Value Problems
This work is concerned with the derivation of an a posteriori error estimator for Galerkin approximations to nonlinear initial value problems with an emphasis on finite-time existence in the context of blow-up. The structure of the derived estimator leads naturally to the development of both h and hp versions of an adaptive algorithm designed to approximate the blow-up time. The adaptive algorithms are then applied in a series of numerical experiments, and the rate of convergence to the blow-up time is investigated
Le palĂ©olithique infĂ©rieur et moyen en Midi toulousain : nouvelles donnĂ©es et perspectives de lâarchĂ©ologie prĂ©ventive
Depuis quelques annĂ©es, les opĂ©rations dâarchĂ©ologie prĂ©ventive menĂ©es en Midi toulousain ont permis de rĂ©actualiser certaines donnĂ©es relatives Ă la gĂ©omorphologie des sites palĂ©olithiques infĂ©rieur et moyen. Ainsi, plusieurs contextes peuvent ĂȘtre considĂ©rĂ©s comme plus favorables que dâautres pour la conservation du matĂ©riel. Par ailleurs, les rĂ©sultats prĂ©liminaires dâĂ©tudes typo-technologiques des industries mises au jour rĂ©cemment, offrent de nouvelles perspectives de recherche pour la constitution dâun cadre chrono-culturel plus prĂ©cis.In the last years, preventive archeology projects conducted in the Midi toulousain Region (southern France) allowed to update data concerning the geomorphology of Early and Middle Palaeolithic sites. It became apparent that certain contexts can be considered as more favorable to vestige conservation than others. Besides, preliminary results of typo-technological studies of recently discovered artifacts offer new research perspectives for the definition of a more precise chrono-cultural frame
Le palĂ©olithique infĂ©rieur et moyen en Midi toulousain : nouvelles donnĂ©es et perspectives de lâarchĂ©ologie prĂ©ventive
Depuis quelques annĂ©es, les opĂ©rations dâarchĂ©ologie prĂ©ventive menĂ©es en Midi toulousain ont permis de rĂ©actualiser certaines donnĂ©es relatives Ă la gĂ©omorphologie des sites palĂ©olithiques infĂ©rieur et moyen. Ainsi, plusieurs contextes peuvent ĂȘtre considĂ©rĂ©s comme plus favorables que dâautres pour la conservation du matĂ©riel. Par ailleurs, les rĂ©sultats prĂ©liminaires dâĂ©tudes typo-technologiques des industries mises au jour rĂ©cemment, offrent de nouvelles perspectives de recherche pour la constitution dâun cadre chrono-culturel plus prĂ©cis.In the last years, preventive archeology projects conducted in the Midi toulousain Region (southern France) allowed to update data concerning the geomorphology of Early and Middle Palaeolithic sites. It became apparent that certain contexts can be considered as more favorable to vestige conservation than others. Besides, preliminary results of typo-technological studies of recently discovered artifacts offer new research perspectives for the definition of a more precise chrono-cultural frame
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