Estimation of Hydrodynamic Forces on Cylinders Undergoing Flow-Induced Vibrations Based on Modal Analysis

The objective of the present study is estimating hydrodynamic forces acting on cylinders undergoing vortex-induced vibration (VIV) using dynamic mode decomposition (DMD). The cylinders are subjected to a uniform incoming flow at a laminar Reynolds number (Re = 250) and an upper transition Reynolds number (Re = 3.6 × 10⁶) (Re = U_∞D/ν defined based on the incoming flow U_∞, the diameter of the cylinder D, and the viscosity of the fluid ν). Both a single cylinder and a configuration of piggyback cylinders are considered. Numerical simulations based on two-dimensional unsteady Reynolds-averaged Navier–Stokes (URANS) equations combined with the k−ω SST turbulence model are carried out to obtain the snapshots of the surrounding flow fields for DMD analysis. The DMD method is a powerful tool to obtain the spatial–temporal evolution characteristics of the coherent structures in the wake flow behind the cylinders. In the present study, this modal decomposition method is combined with a moving reference frame around the cylinders. The dominant DMD modes with their corresponding frequencies of the wake flows are identified and are used to reconstruct the flow fields. The large-scale shedding vortices are captured by the dominant modes. The reconstructed wake flow behind the cylinders is used to estimate the drag and lift forces on the cylinders combined with a force partitioning analysis.