Norwegian Deepwater Program: Analysis of Vortex-Induced Vibrations of Marine Risers Based on Full-Scale Measurements

Abstract

As a part of the Norwegian Deepwater Program (NDP) three drilling risers have been instrumented with accelerometers and rotation-rate meters for measurement of vortex-induced vibrations (VIV). In addition, current was measured at number of depths. The paper describes how the riser displacements were derived from the measurements and compared with the current. A major task has been to rid the acceleration measurements of the influence of gravity due to the riser's rotations out of the vertical and include the measurements of angular motion in a consistent way. This has been done using modal decomposition and a least-squares method to estimate the modal weights. The main purpose of the work was to provide data for calibration of computer programs for prediction of VIV. Examples of results are given.

Modal analysis of measurements from a large-scale VIV model test of a riser in linearly sheared flow

“…The modal analysis technique has previously been applied to combined measurements of acceleration and angular rate on a full-scale drilling riser (Kaasen et al, 2000). A similar approach has been used by Trim et al (2005).…”

Experimental investigation of vortex-induced vibration of long marine risers

“…Modal analysis has been applied previously to analyse data from other long riser VIV tests; e.g. Kaasen et al (2000), who used rotation-rates and accelerations as input signals, and Lie and Kaasen (2005), who used strain signals. For the present work, the original intent was to use only the measured strains in the modal analysis.…”

A systematic approach to riser VIV response reconstruction

“…Several researchers have considered the response reconstruction problem; the relevant references include Kaasen et al (1997); Trim et al (2005), and Lie and Kaasen (2006). These methods are based on linear structural dynamics techniques combined with the classical mode superposition principle, where the displacements are written as a linear combination of the classical riser free vibration modes weighted by the modal response factors.…”