Simulation of Riser VIV Using Fully Three Dimensional CFD Simulations

Abstract

Fully three dimensional computational fluid dynamics (CFD) solutions are combined with structural models of a tensioned riser to predict riser vortex induced motion. The use of three dimensional CFD solutions overcomes many of the shortcomings of combining a series of strip or two dimensional simulations to calculate the fluid forces on the riser. Three dimensional vortex structures are treated correctly and straked risers and variations in angle of attack can be studied directly. The proposed method uses finite element methods that are tolerant of sparse meshes and high element aspect ratios. This allows economical solutions of large fluid domains while retaining the important features of the large fluid vortex structures which drive risers. Long risers can be treated with readily available computers and examples of simulations of riser with L/D over 1400 are given and compared with previously published experimental data. These examples are used to illustrate several points regarding the effects of the treatment of the riser structure as well as the efficacy of rotating frame or pinned riser experiments used to simulate sheared currents. The method can also be extended to sheared currents whose heading varies with depth.

Analysis of two-dimensional and three-dimensional wakes of long circular cylinders

“…Also in this fashion, S. Holmes, O.H. Oakley and Y. Constantinides [5] studied a similar case and concluded that the coarse resolution of the grid yields discrepancies on the prediction of the forces on the cylinder. The use of such a coarse spanwise spacing is usually justified by stating that the cross-flow vibrations of the risers extends the spanwise correlation length significantly and hence lower resolutions are required.…”

“…Even though this has been proven for the spanwise length of the excited structural vibration mode (which can go to the order of the cylinder extent), the largest spanwise correlation length of the turbulent wake of the flow is below the order of the diameter. Since only very large scale structures in the spanwise direction are captured and these are much bigger than the actual largest spanwise scale of the turbulent wake, the underresolution of the wake in the axial direction leads to unphysical effects [5].…”

Effect of bidirectional internal flow on fluid.structure interaction dynamics of conveying marine riser model subject to shear current

“…The reason that some numerical simulations of vortex-induced vibration have been failing to accurately duplicate experimental processes is mostly due to the complexity of physics involved in the real problem. In addition, the grid topology, mesh density, boundary condition, and coupling scheme between the flow governing equations and structure motion equations commonly have strong influence on the quality of numerical results (Holmes, et al, 2006). Due to calculation disability and some deficiencies of CFD software package itself, most numerical results depended on 2D vortex simulation and then integrate the hydrodynamic forces to 3D fluid domain (Yamamotoa, et al, 2004).…”

“…Due to calculation disability and some deficiencies of CFD software package itself, most numerical results depended on 2D vortex simulation and then integrate the hydrodynamic forces to 3D fluid domain (Yamamotoa, et al, 2004). Some attempts to simulate vortex-induced vibration with very large aspect ratio are indeed a 2D numerical simulation (Holmes, et al, 2006).…”

Numerical investigation of vortex shedding and vortex-induced vibration for flexible riser models

“…Some attempts to simulate VIV with very large aspect ratio are indeed 2D simulations (Holmes and Owen, 2006). Kim and Rheem (2009) measured the cross flow response of a cylinder under local shear flow.…”