  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 structure displacement enjoys improved
regularity by utilizing the dissipation effects of the fluid onto the structure
and that all FEWS satisfy the relative energy inequality. 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.
