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 cylindersundergoing vortex-induced vibration (VIV) using dynamic mode decomposition (DMD).The cylinders are subjected to a uniform incomingflow at a laminar Reynolds number(Re=250) and an upper transition Reynolds number (Re=3.6 x 10(6)) (Re=U infinity D/nu defined based on the incomingflow U-infinity, the diameter of the cylinder D, and the viscosityof thefluid nu). Both a single cylinder and a configuration of piggyback cylinders are con-sidered. Numerical simulations based on two-dimensional unsteady Reynolds-averagedNavier-Stokes (URANS) equations combined with the k-omega SST turbulence model arecarried out to obtain the snapshots of the surroundingflowfields for DMD analysis. TheDMD method is a powerful tool to obtain the spatial-temporal evolution characteristicsof the coherent structures in the wakeflow behind the cylinders. In the present study, thismodal decomposition method is combined with a moving reference frame around the cylin-ders. The dominant DMD modes with their corresponding frequencies of the wakeflows areidentified and are used to reconstruct theflowfields. The large-scale shedding vortices arecaptured by the dominant modes. The reconstructed wakeflow behind the cylinders is usedto estimate the drag and lift forces on the cylinders combined with a force partitioning anal-ysis.

Automated summary

The present study aims to estimate the hydrodynamic forces acting on cylinders undergoing vortex-induced vibration (VIV) using dynamic mode decomposition (DMD). Numerical simulations are conducted to obtain flow field snapshots for DMD analysis, and the reconstructed flow fields are used to estimate the drag and lift forces on the cylinders. The DMD method proves to be a powerful tool in capturing the coherent structures in the wake flow.