  In this work, we introduce a novel data-driven formulation, the
Koopman-Linearly-Time-Invariant (Koopman-LTI) analysis, for analyzing
Fluid-Structure Interactions (FSI). An implementation of the Koopman-LTI on a
subcritical free-shear flow over a prism at Re=22,000 corroborated a
configuration-wise universal Koopman system, which approximated the
configuration's nonlinear dynamics with stellar accuracy. The Koopman-LTI also
successfully decomposed the entwined morphologies of raw measurement into a
linear superposition of frequency-based constituents. Most importantly, with
random and anisotropic turbulence, the Koopman-LTI yielded frequency-wise
identical modes for structure response and fluid excitation, thus establishing
direct constitutive relations between the phenomenology of fluid and structure.
