Karlsen, Kenneth H.Risebro, Nils H.Towers, John D.2020-08-212020-08-212002-10-27Karlsen, K. H., Risebro, N. H., & Towers, J. D. (2002). On a nonlinear degenerate parabolic transport-diffusion equation with a discontinuous coefficient. <i>Electronic Journal of Differential Equations, 2002</i>(93), pp. 1-23.1072-6691https://hdl.handle.net/10877/12450We study the Cauchy problem for the nonlinear (possibly strongly) degenerate parabolic transport-diffusion equation ∂tu + ∂x (γ(x)ƒ(u)) = ∂2x A(u), A'(·) ≥ 0, where the coefficient γ(x) is possibly discontinuous and ƒ(u) is genuinely non-linear, but not necessarily convex or concave. Existence of a weak solution is proved by passing to the limit as ε ↓ 0 in a suitable sequence {uε}ε > 0 of smooth approximations solving the problem above with the transport flux γ(x)ƒ(·) replaced by γε(x)ƒ(·) and the diffusion function A(·) replaced by Aε(·), where γε(·) is smooth and A'ε(·) > 0. The main technical challenge is to deal with the fact that the total variation |uε|BV cannot be bounded uniformly in ε, and hence one cannot derive directly strong convergence of {uε}ε > 0. In the purely hyperbolic case (A' ≡ 0), where existence has already been established by a number of authors, all existence results to date have used a singular mapping to overcome the lack of a variation bound. Here we derive instead strong convergence via a series of a priori (energy) estimates that allow us to deduce convergence of the diffusion function and use the compensated compactness method to deal with the transport term.Text23 pages1 file (.pdf)enAttribution 4.0 InternationalDegenerate parabolic equationNonconvex fluxWeak solutionDiscontinuous coefficientViscosity methoda priori estimatesCompensated compactnessArticleThis work is licensed under a Creative Commons Attribution 4.0 International License.