Approximation of a compressible Navier-Stokes system by non-linear acoustical models

We analyse the existing derivation of the models of non-linear acoustics such as the Kuznetsov equation, the NPE equation and the KZK equation. The technique of introducing a corrector in the derivation ansatz allows to consider the solutions of these equations as approximations of the solution of the initial system (a com-pressible Navier-Stokes/Euler system). The validation of the approximation ansatz is given for the KZK equation case

Perturbative numeric approach in microwave imaging

21 pagesIn this paper, we show that using measurements for different frequencies, and using ultrasound localized perturbations it is possible to extend the method of the imaging by elastic deformation developed by Ammari and al. [Electrical Impedance Tomography by Elastic Deformation SIAM J. Appl. Math. , 68(6), (2008), 1557–1573.] to problems for the Helmholtz equations with Neumann boundary conditions, and to reconstruct by a perturbation method both the conductivity and the permittivity, provided that the conductivity function is coercive and the wave number in the Helmholtz equation is not a resonant frequency

Controllability of the moments for Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation

Recalling the proprieties of the Khokhlov-Zabolotskaya-Kuznetsov(KZK) equation, we prove the controllability of moments result for the linear part of KZK equation. Then we prove the local controllability result for the full KZK equation applying a known method of perturbation for the nonlinear inverse problem

Short time heat diffusion in compact domains with discontinuous transmission boundary conditions

We consider a heat problem with discontinuous diffusion coefficientsand discontinuous transmission boundary conditions with a resistancecoefficient. For all compact $(\epsilon,\delta)$-domains $\Omega\subset\mathbb{R}^n$ with a $d$-set boundary (for instance, aself-similar fractal), we find the first term of the small-timeasymptotic expansion of the heat content in the complement of$\Omega$, and also the second-order term in the case of a regularboundary. The asymptotic expansion is different for the cases offinite and infinite resistance of the boundary. The derived formulasrelate the heat content to the volume of the interior Minkowskisausage and present a mathematical justification to the de Gennes'approach. The accuracy of the analytical results is illustrated bysolving the heat problem on prefractal domains by a finite elementsmethod

Equation de Khokhlov-Zabolotskaya-Kuznetsov. Analyse Mathématique, Validation de l'approximation et Méthode de Contrôle

This work consists of two parts. In the first part we consider the Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation $(u_t - u u_x -\beta u_{xx})_x -\gamma \Delta_y u =0$ in Sobolev spaces of functions periodic on $x$ and with mean value zero. The derivation of KZK from the nonlinear isentropic Navier Stokes equations and approximation their solutions (for viscous and non viscous cases), the results of the existence, uniqueness, stability and blow-up of solution of KZK equation are obtained, also a result of existence of a smooth solution of Navier-Stokes system in the half space with periodic in time mean value zero boundary conditions. In the second part we prove the local controllability of moments for two systems described by a nonlinear evolution equation in Banach space and by a nonlinear heat equation when the control is a multiplier on the right-hand side. For this two systems with integral overdetermination we obtain sufficient conditions on the size of the neighborhood from which we can take the function from the overdetermination condition so that the inverse problem is uniquely solvable. We also prove the controllability result for linearized KZK equation.Ce travail se compose de deux parties. Dans la première, nous considérons l'équation de Khokhlov-Zabolotskaya-Kuznetsov (KZK) $(u_t - u u_x -\beta u_{xx})_x -\gamma \Delta_y u =0$ dans les espaces de Sobolev des fonctions p\ériodiques sur $x$ de valeur moyenne nulle. La déivation de l'\équation KZK à partir des équations de Navier-Stokes isentropiques non linéaires et de l'approximation de leurs solutions (pour les cas visqueux et non visqueux), les résultats de l'existence, de l'unicité, de la stabilité et du blow-up de la solution de KZK sont obtenus ainsi qu'un résultat sur l'existence d'une solution régulière du syst\éme de Navier-Stokes dans le demi espace avec conditions aux limites péiodiques en temps et de valeur moyenne nulle. Dans la deuxième partie, nous prouvons la contrôabilitélocale des moments de deux systèmes décrits par une équation non-linéaire d'evolution dans un espace de Banach et par une équation non-linéaire de la chaleur quand le contrôle est un multiplicateur du membre de droite. Pour les deux systémes avec une surdétermination intégrale nous obtenons des conditions suffisantes sur la taille du voisinage duquel nous pouvons prendre la fonction de la condition de surdétermination de sorte que le problème inverse ait une solution unique. Nous prouvons également le résultat de contrôlabilité pour l'équation KZK linéarisée