Numerical Modeling of High Length-to-Diameter Ratio Riser Subjected to VIV

Abstract

Abstract Modeling of long marine risers subjected to VIV is a challenging problem to solve using 3D Computational Fluid Dynamics (CFD) due to the high length-to-diameter ratio and usage of different VIV suppression devices. The scale of the problem can also get extremely large as the risers may have lengths up to thousands of meters, which makes it hard to use 3D CFD simulations. However, CFD is unique to capture complex flow around bluff structures and able to model risers with and without suppression devices and involve effects of nonlinear structural response inherently. ExxonMobil's high quality data on the behavior of high length-to-diameter ratio (L/D) risers subjected to vortex induced vibrations (VIV) in uniform and sheared flow (Marintek, 2003) exposes some of the physical details of full-scale riser response and compares the multi-mode VIV response of risers without suppression devices to that of risers with varying lengths of suppression coverage. In this paper, ExxonMobil data is investigated and validated using CFD code AcuSolveTM, which uses a strongly coupled numerical method that simultaneously solves fluid phase equations and structural equations of motion through modal analysis to predict the vibration response. Numerical simulations for high L/D bare riser response show that the method provides a good estimation of VIV responses in both in-line and crossflow directions by comparing numerical results against available field data.