Numerical Simulation of Vortex-Induced Vibrations of Free Span Pipelines Including Nonlinear Soil Models

Abstract

This thesis introduces a fully three dimensional (3D) numerical simulation method of the VIV behaviors of free span pipelines by considering the nonlinear pipe-soil interaction effect. The pipeline is modeled as a tensioned beam of which the governing equations are numerically solved by applying a fully implicit discretization scheme. Reynolds Averaged Navier-Stokes (RANS) equations are numerically solved to compute the fluid domain. An overset grid method is utilized in discretizing the fluid field around the pipeline. Six computational blocks and nearly 1 million grid points are needed in the simulation. It is a good strategy to generate finer grid in the near body regions and relatively coarse grid in the far field. By exchanging motions and forces between the pipeline motion solver and the fluid solver, fluid-structure interaction is achieved. This research also includes a nonlinear soil model to simulate the pipe-soil interaction which is considered as a spring-pipeline system while the stiffness characteristics are expressed by using a nonlinear force-displacement (P-y) curves.

The simulation results are compared with model tests or other numerical simulations for validation in two cases: (1) a free span pipeline of G/D=2.0 at different reduced velocities including linear and nonlinear soil models; (2) a free span pipeline of different G/D which ranges from 1.2 to 3.0.