  The dynamics of a thin low-density polyethylene sheet subject to periodic
forcing due to B\'enard-K\`arm\`an vortices in a long narrow water channel is
investigated here. In particular, the time-averaged sheet deflection and its
oscillation amplitude are considered. The former is first illustrated to be
well-approximated by the static equilibrium between the buoyancy force, the
elastic restoring force, and the profile drag based on the depth-averaged water
speed. Our observations also indicate that the presence of upstream vortices
hinder the overall reconfiguration effect, well-known in an otherwise steady
flow. For the sheet tip oscillations, a simple model based on
torsional-spring-mounted flat plate correctly captures the measured tip
amplitude over a wide range of sheet physical properties and flow conditions.
Furthermore, a rich phenomenology of structural dynamics including
vortex-forced-vibration, lock-in with the sheet natural frequency, flow-induced
vibration due to the sheet wake, multiple-frequency and modal response is
reported.
