Estimation of Hydrodynamic Forces on Cylinders Undergoing FlowInduced Vibrations Based on Modal Analysis

Abstract

The objective of the present study is estimating hydrodynamic forces acting on cylinders undergoing vortexinduced 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 twodimensional unsteady Reynoldsaveraged 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 largescale 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.