Differences in Predicted Flow-Induced Vibration of Submarine Pipelines Considering Cross-Flow and Inline Oscillations and its Influence in Fatigue-Life

Abstract

In offshore facilities, the most widely spread way to transport fluids in relatively short distances is through submarine pipelines. These structures are subject to internal and external forces. Nowadays, most of the proposed models to study submarine pipelines subjected to vortex induced vibrations feature a circular cylinder, submitted to a cross-flow, and are able to display oscillations in just the transverse direction to the fluid flow velocity. In this paper three different models that consider a two-dimensional fluid flow around a pipeline were studied via ANSYS CFX®, for Reynolds numbers between 100 and 700, with the purpose of determining the limitations of the 1-DOF models based on the Strouhal number and lift and drag coefficients and account its influence in fatigue lifespan. These models consisted of a static cylinder — i.e. no oscillations —, a cylinder with 1-DOF — i.e. cross-flow oscillations — and a cylinder with 2-DOF — i.e. cross-flow and inline oscillations —. It was found that, although fluid flow Reynolds numbers were very small as to make the submarine pipeline models fall within the finite-life region, a 1-DOF model is accurate enough to predict fatigue lifespan, since it presents respect to the 2-DOF model little deviation in the chosen comparison parameters.

Numerical modelling of the oscillatory flow effect around submarine pipeliness

“…These equations were solved numerically using the ANSYS-CFX software, which has been intensively validated in this type of flow by [17] who studied the variation of the Strouhal number, the lift coefficient and the resistance coefficient for the flow around of a static cylinder in a laminar regime and thus obtained a sensitivity analysis of its values in regards to the proximity of the domain boundaries to the cylinder.…”