Vortex dislocations and force distribution of long flexible cylinders subjected to sheared flows

We present DNS results of vortex-induced vibrations (VIV) of flexible cylinders with aspect ratio greater than 500, subjected to linear and exponential sheared flows. The maximum Reynolds number is Re_m = 1000 resulting in a turbulent near-wake. The first case corresponds to lock-in of the third mode (n = 3), while the second case is a multi-mode response with excited modes as high as n = 12 and 14. We observed vortex dislocations similar to the structures visualized in experiments for stationary cylinders, and obtained corresponding force distributions. Strong vortex dislocations can result in substantial modulation of the forces on the body, and such effects have to be taken into account when constructing low-dimensional predictive models.