CFD Simulation of Vortex–Induced Vibrations of Free Span Pipelines Including Pipe-Soil Interactions

Abstract

This paper presents a three dimensional numerical simulation of free span pipelines under vortex-induced vibrations (VIV) and pipe-soil interactions. Pipeline is simplified as a tensioned beam with uniformly distributed tension. The tensioned beam equations are solved using a fully implicit discretization scheme. The flow field around the pipeline is computed by numerically solving the unsteady Navier-Stokes equations. Fluid domain is discretized using overset grid system consists of several computational blocks and approximate one million grid points in total. Grid points in near-wall regions of pipeline and bottom are of high resolution, while far field flow is in relatively coarse grid. Fluid-structure interaction (FSI) is achieved by communicating forces and motions between fluid solver and pipeline motion solver. Pipeline motion solver inputs drag and lift forces calculated by fluid solver, then computes displacements in both in-line and cross-flow directions and outputs new positions of pipeline back to fluid solver. Soil effect also plays an important role in this simulation. The pipe-soil interactions are modeled as mass-spring system with equivalent stiffness.

Simulation results are compared with experiments for validation in three cases: (a) An isolated pipeline VIV in uniform current without boundary effect; (b) A pipeline horizontally placed close to plane boundary in uniform current at different gap to diameter ratios G/D; (c) A free span pipeline at specific gap-to-diameter ratio with respect to different reduced velocities.