The use of flexible structures in the marine environment has increased significantly in the recent past. Their design under harsh conditions of wind, waves, current and ice requires complex Fluid-Structure Interaction (FSI) analyses that must contemplate large structural deformations and nonlinear fluid dynamics effects. Vortex Induced Vibration (VIV) is a common FSI occurrence in marine risers used in petroleum production, mooring cables, moored structures, tethered structures and spar hulls. VIV can produce large amplitude resonant motions leading to structural failure.
Our study focuses on computer aided numerical simulations to analyse VIV effects on an experimental rig when towed under water at various operating conditions. Computational Fluid Dynamics (CFD) investigation of the dynamic characteristics of pressure and velocity fields for viscous fluid flow reveal significant time and space scales for convergence and accuracy of our Finite Volume (FV) calculations. The iterative CFD numerical procedure involves solving the three dimensional Navier-Stokes equation on a mixed structured-unstructured mesh containing millions of FV elements for the fluid domain with second order accuracy in time. The effects of the lift and drag fluid forces are studied by a structural analysis performed on the entire rig by means of the Finite Element Method (FEM). We examine non-linear stress distributions due to bending and torsional loads, as well as time-history records of the dynamic response of the structure. To assess performance of both fluid and structural analyses using parallel processing at ACEnet’s Placentia cluster, simulations are conducted using 1, 2, 4, 8 and 16 cores for various levels of discretization of the fluid and structural domains requiring hundreds of Gb of data manipulation. Processor speed-up and efficiency results are presented.
The computational tool we are developing will aid in the safe and efficient design and operation of submerged structures used in the offshore Oil and Gas industry. Our tool integrates advanced solutions to improve performance and safety while mitigating risk to the environment, infrastructure and people.
