Existence of martingale solutions to a nonlinearly coupled stochastic fluid-structure interaction problem

We study a nonlinear stochastic fluid-structure interaction problem with a multiplicative, white-in-time noise. The problem consists of the Navier-Stokes equations describing the flow of an incompressible, viscous fluid in a 2D cylinder interacting with an elastic lateral wall whose elastodynamics is described by a membrane equation. The flow is driven by the inlet and outlet data and by the stochastic forcing. The noise is applied both to the fluid equations as a volumetric body force, and to the structure as an external forcing to the deformable fluid boundary. The fluid and the structure are nonlinearly coupled via the kinematic and dynamic conditions assumed at the moving interface, which is a random variable not known a priori. The geometric nonlinearity due to the nonlinear coupling requires the development of new techniques to capture martingale solutions for this class of stochastic FSI problems. Our analysis reveals a first-of-its-kind temporal regularity result for the solutions. This is the first result in the field of SPDEs that addresses the existence of solutions on moving domains involving incompressible fluids, where the displacement of the boundary and the fluid domain are random variables that are not known a priori and are parts of the solution itself.