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research-article

ON THE SIGNIFICANCE OF THE HIGHER ORDER STRESS IN RISER VIV RESPONSES

[+] Author and Article Information
Jie Wu

SINTEF Ocean, Otto Nielsen veg 10, 7052, Trondheim, Norway
jie.wu@sintef.no

Decao Yin

SINTEF Ocean, Otto Nielsen veg 10, 7052, Trondheim, Norway
decao.yin@sintef.no

Halvor Lie

SINTEF Ocean, Otto Nielsen veg 10, 7052, Trondheim, Norway
lie.halvor@sintef.no

Carl M. Larsen

NTNU, Otto Nielsen veg 10, 7052, Trondheim, Norway
carl.m.larsen@ntnu.no

Rolf Baarholm

Equinor, Strandvegen 4, 7500 Stjørdal, Norway
rolbaa@equinor.com

Stergios Liapis

Shell International Exploration and Production Inc., 3333 Highway 6 South - Mg 148. Houston, TX 77210, Texas, USA
liapis101@gmail.com

1Corresponding author.

ASME doi:10.1115/1.4040798 History: Received July 19, 2017; Revised July 01, 2018

Abstract

Vortex-induced vibrations (VIV) can lead to fast accumulation of fatigue damage and increased drag loads for slender marine structures. VIV responses mainly occur at the vortex shedding frequency, while higher harmonics can also be excited. Recent VIV model tests with flexible pipes have shown that higher harmonics in crossflow (CF) direction can contribute to the fatigue damage significantly due to its higher frequency. Rigid cylinder experiments shown that the CF third-order harmonics are more pronounced when the motion orbit is close to a 'figure 8' shape and the cylinder is moving against the flow at its largest CF motion. However, there is still lack of understanding of when and where higher harmonics occur for a flexible pipe. Therefore, significant uncertainty remains on how to account for fatigue damage due to higher harmonics in VIV prediction. In the present paper, representative VIV data from various riser model test campaigns are carefully studied and analyzed. The key parameters that influence the magnitude of the third-order harmonic stress are found to be the bending stiffness, the reduced velocity and the orbit stability. The experimental data is analyzed in order to assess the impact of each parameter on the third-order harmonic stress. A preliminary empirical response model to estimate the maximum CF third-order harmonic stress based on these identified structural and hydrodynamic parameters has been proposed. The results of this study will contribute to reduce the uncertainty and unnecessary conservatism in VIV prediction.

Copyright (c) 2018 by ASME
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