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Structural Monitoring and Maintenance
  Volume 6, Number 4, December 2019, pages 365-387
open access

A parametric study on fatigue of a top-tensioned riser subjected to vortex-induced vibrations
Do Kyun Kim, Eileen Wee Chin Wong and Mala Konda Reddy Lekkala

    This study aims to provide useful information on the fatigue assessment of a top-tensioned riser (TTR) subjected to vortex-induced vibration (VIV) by performing parametric study. The effects of principal design parameters, i.e., riser diameter, wall thickness, water depth (related to riser length), top tension, current velocity, and shear rate (or shear profile of current) are investigated. To prepare the base model of TTR for parametric studies, three (3) riser modelling techniques in the OrcaFlex were investigated and validated against a reference model by Knardahl (2012). The selected riser model was used to perform parametric studies to investigate the effects of design parameters on the VIV fatigue damage of TTR. From the obtained comparison results of VIV analysis, it was demonstrated that a model with a single line model ending at the lower flex joint (LFJ) and pinned connection with finite rotation stiffness to simulate the LFJ properties at the bottom end of the line model produced acceptable prediction. Moreover, it was suitable for VIV analysis purposes. Findings from parametric studies showed that VIV fatigue damage increased with increasing current velocity, riser outer diameter and water depth, and decreased with increasing shear rate and top tension of riser. With regard to the effects of wall thickness, it was not significant to VIV fatigue damage of TTR. The detailed outcomes were documented with parametric study results.
Key Words
    vortex-induced vibration (VIV); fatigue; top-tensioned riser (TTR); parametric study; offshore
Do Kyun Kim: Marine Offshore and Subsea Technology (MOST) Group, School of Engineering,
Newcastle University, NE1 7RU Newcastle upon Tyne, UK;
Graduate Institute of Ferrous Technology, POSTECH, 37673 Pohang, Republic of Korea
Eileen Wee Chin Wong and Mala Konda Reddy Lekkala: Ocean and Ship Technology Research Group (Department of Civil and Environmental Engineering),
Universiti Teknologi PETRONAS, 32610 Seri Iskandar, Perak, Malaysia

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