International Journal of Maritime Technology (Mar 2015)
VIV of Tapered Cylinders: 3D LES Numerical Simulation
Abstract
In the present study, the author’s previous experimental investigations on the vortex induced vibration of uniform and tapered circular cylinders are numerically simulated. The circular cylinders have medium mass ratios (5.93, 6.1), low mass-damping parameters (0.0275, 0.0279) a mean diameter of 0.028m and an aspect ratio of about 14. A fully coupled two-way fluid-structure interaction (FSI) analysis is used to simulate the phenomena of vortex induced vibration in vicinity of the lock-in range. The 3D computational fluid dynamic (CFD) model is employed to solve the incompressible transient Navier-Stokes equations. LES-Smagorinsky turbulent model is considered within all simulations. Structural displacements are calculated through transient structural analysis in mechanical application (Computational Structural Dynamics-CSD). The transverse vibrations of uniform and tapered cylinders are compared against the experimental results. The comparison reveals that the model is capable to reasonably well predict the initial and upper branches of the responses. It, however, falls short to properly predict the lower branch. The simulation results of the fixed and elastically mounted tapered cylinders indicate that the flow field, in the case of the elastically mounted tapered cylinder, is completely different from that for the equivalent fixed tapered cylinder. For the case of the elastically mounted tapered cylinder no vortex cell fond to be forming in the lock-in region and a single frequency response dominated the entire length of the cylinder.
