Electron. J. Differential Equations, Vol. 2026 (2026), No. 61, pp. 1-19.

Interface condition for the Poisson equation in a partially porous medium

Tomislav Fratrovic, Eduard Marusic-Paloka

Abstract:
In this article, we derive a new effective interface condition between two parts of a partially porous medium. We study the steady-state Poisson equation in a two-dimensional domain that combines an upper porous part with a periodic microstructure and a lower free region. Using the homogenization approach and a formal asymptotic expansion, we establish a second-order correction to the classical interface condition that accounts for microscale effects, including those arising from both the local flux and the source term redistribution across the interface. This refinement is essential for high-precision applications in which the pore size is small but not negligible compared to the system scale.

Submitted July 15, 2026. Published August 17, 2026.
Math Subject Classifications: 35B27, 35J05, 74Q05, 80M40.
Key Words: Homogenization; asymptotic expansion; boundary layers; macroscopic model; effective interface condition.
DOI: 10.58997/ejde.2026.61

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Tomislav Fratrovic
Faculty of Transport and Traffic Sciences
University of Zagreb, Croatia
email: tfratrovic@fpz.unizg.hr
Eduard Marusic-Paloka
Department of Mathematics
Faculty of Science
University of Zagreb, Croatia
email: emarusic@math.hr

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