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Entropy solutions to the macroscopic incompressible porous media equation

Ángel Castro, Daniel Faraco and Björn Gebhard

Vol. 18 (2025), No. 9, 2241–2292
Abstract

We investigate maximal potential energy dissipation as a selection criterion for subsolutions (coarse- grained solutions) in the setting of the unstable Muskat problem. We show that both (a) imposing this criterion on the level of convex integration subsolutions and (b) the strategy of Otto based on a relaxation via minimizing movements lead to the same nonlocal conservation law. Our main result shows that this equation admits an entropy solution for unstable initial data with an analytic interface.

Keywords
incompressible porous media, Saffman–Taylor instability, relaxation, subsolutions, nonlocal hyperbolic conservation law, mixing zone, level sets
Mathematical Subject Classification
Primary: 76E17, 76S05
Secondary: 35L65, 35Q35
Milestones
Received: 20 December 2023
Revised: 20 August 2024
Accepted: 29 October 2024
Published: 5 September 2025
Authors
Ángel Castro
Consejo Superior de Investigaciones Científicas
Instituto de Ciencias Matemáticas-CSIC
ICMAT-CSIC-UAM-UCM-UC3M
Madrid
Spain
Daniel Faraco
Departamento de Mathemátics
Universidad Autónoma de Madrid
Instituto de Ciencias Matemáticas
CSIC-UAM-UC3M-UCM
Madrid
Spain
Björn Gebhard
Angewandte Mathematik Münster
Universität Münster
Münster
Germany

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