Three-dimensional Navier-Stokes-Biot coupling via a moving reticular plate interface: existence of weak solutions

TL;DR

This paper proves the existence of weak solutions for a complex three-dimensional fluid-structure interaction model involving a moving permeable interface, extending previous 2D results to 3D and handling nonlinear free-boundary coupling.

Contribution

It introduces a novel regularization and compactness framework to establish existence of solutions for a fully 3D nonlinear Navier-Stokes-Biot FSI system with a moving interface.

Findings

Established existence of weak solutions for the 3D coupled system.

Developed a regularization method compatible with the nonlinear free boundary.

Extended 2D analysis to the more challenging 3D setting.

Abstract

We prove the existence of finite-energy weak solutions to a regularized three-dimensional fluid-structure interaction (FSI) problem involving an incompressible, viscous, Newtonian fluid and a multilayered poro(visco)elastic structure. The structure consists of a thick layer modeled by the Biot equations and a thin reticular plate with inertia and elastic energy, transparent to fluid flow. The coupling is nonlinear in the sense that it takes place on a moving interface that is not known a priori but is defined by the solution itself, making the problem a moving-boundary problem. This nonlinear free-boundary coupling, combined with the limited regularity of the Biot displacement, renders the classical weak formulation ill-defined at finite energy. To address this, we introduce a minimally invasive regularization based on a suitable extension and convolution of the Biot displacement, chosen so that the regularized problem remains consistent with the original model. We then construct approximate solutions to the regularized problem via a Lie operator-splitting scheme and derive uniform energy bounds. While these bounds ensure weak and weak* convergence, passing to the limit in the nonlinear terms requires refined compactness arguments, including variants of the Aubin-Lions lemma and tools adapted to moving non-Lipschitz interfaces. The result applies in particular to the purely elastic case (without structural damping) as well as the poroviscoelastic case. This work extends the two-dimensional analysis of Kuan-\v{C}ani\'c-Muha 2024 to the fully three-dimensional setting and, to our knowledge, provides the first existence result for a nonlinearly coupled, multilayer 3D Navier-Stokes-Biot FSI system with a permeable interface.