  In this paper, we study a nonlinear interaction problem between compressible
viscous fluids and plates. For this problem, we introduce relative entropy and
relative energy inequality for the finite energy weak solutions (FEWS). First,
we prove that for all FEWS, the relative energy inequality is satisfied and
that the structure displacement enjoys improved regularity by utilizing the
dissipation effects of the fluid onto the structure. Then, we show that all
FEWS enjoy the weak-strong uniqueness property, thus extending the classical
result for compressible Navier-Stokes system to this fluid-structure
interaction problem.
