On vanishing viscosity approximation of conservation laws with discontinuous flux.
Résumé
We characterize the vanishing viscosity limit for multi-dimensional conservation laws of the form $$ u_t + \text¨{div }\mathfrak{f}(x,u)=0, \quad u|_{t=0}=u_0 $$ in the domain $\R^+\times\R^N$. The flux $\mathfrak{f}=\mathfrak{f}(x,u)$ is assumed locally Lipschitz continuous in the unknown $u$ and piecewise constant in the space variable $x$; the discontinuities of $\mathfrak{f}(\cdot,u)$ are contained in the union of a locally finite number of sufficiently smooth hypersurfaces of $\R^N$. We define ``$\mathcal G_{VV}$-entropy solutions'' (this formulation is a particular case of the one of \cite{AKR-I}); the definition readily implies the uniqueness and the $L^1$ contraction principle for the $\mathcal G_{VV}$-entropy solutions. Our formulation is compatible with the standard vanishing viscosity approximation $$ u^\varepsilon_t + \text{div } (\mathfrak{f}(x,u^\varepsilon)) =\varepsilon \Delta u^\varepsilon, \quad u^\varepsilon|_{t=0}=u_0, \quad \varepsilon\downarrow 0, $$ of the conservation law. We show that, provided $u^\varepsilon$ enjoys an $\varepsilon$-uniform $L^\infty$ bound and the flux $\mathfrak{f}(x,\cdot)$ is non-degenerately nonlinear, vanishing viscosity approximations $u^\varepsilon$ converge as $\varepsilon \downarrow 0$ to the unique $\mathcal G_{VV}$-entropy solution of the conservation law with discontinuous flux.
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