  Proper orthogonal decomposition (POD) is often employed in developing
reduced-order models (ROM) in fluid flows for design, control, and
optimization. Contrary to the usual practice where velocity field is the focus,
we apply the POD analysis on the pressure field data obtained from numerical
simulations of the flow past stationary and oscillating cylinders. Since
pressure mainly contributes to the hydrodynamic forces acting on the structure,
we compute the pressure POD modes on the cylinder surface oscillating in
lock-in and lock-out regions. These modes are then dissected into sine and
cosine magnitudes to estimate their contribution in the development of pressure
lift and drag decomposition coefficients, respectively. The key finding of this
study is that more POD modes are required to capture the flow physics in
nonsynchronous regimes as compared to synchronization case. Engineering
application of this study is the development of reduced-order models for
effective control techniques.
