LQR control for a system describing the interaction between a floating solid and the surrounding fluid

TL;DR

This paper develops an LQR control framework for a coupled fluid-solid system with unbounded fluid domain, overcoming stability challenges to enable feedback control design using Riccati equations.

Contribution

It introduces a novel approach to define a well-posed LQR problem for an unbounded fluid-solid interaction system despite the lack of exponential stability.

Findings

Successfully formulated a well-posed LQR problem

Developed Riccati-based feedback control for the system

Addressed stability challenges in unbounded fluid domains

Abstract

This paper studies an infinite time horizon LQR optimal control problem for a system describing, within a linear approximation, the vertical oscillations of a floating solid, coupled to the motion of the free boundary fluid on which it floats. The fluid flow is described by a viscous version of the linearized Saint-Venant equations (shallow water regime). The major difficulty we are facing is that the domain occupied by the fluid is unbounded so that the system is not exponentially stable. This fact firstly raises challenges in proving the wellposedness, requiring the combined use of analytic semigroup theory and of an interpolation technique. The main contribution of the paper is that we show that, in spite of the lack of exponential stabilizability, we can define a wellposed LQR problem for which a Riccati based approach to design feedback controls can be implemented.