Assessment of Fatigue Safety Factors for Deep-Water Risers in Relation to VIV

[+] Author and Article Information
Bernt J. Leira, Carl M. Larsen

 NTNU, Dept Marine Structures, N-7491 Trondheim, Norway

Trond Stokka Meling

 Statoil, N-4035 Stavanger, Norway

Vidar Berntsen

 SINTEF, Marintek, Div. Struct. Eng., N-7491 Trondheim, Norway

Bernie Stahl

 Consulting Engineer Houston, TX 77059-5544, USA

Andrew Trim

 BP-Exploration, Sunbury-on-Thames, TW167LN, United Kingdom

J. Offshore Mech. Arct. Eng 127(4), 353-358 (Mar 11, 2005) (6 pages) doi:10.1115/1.2087548 History: Received November 26, 2003; Revised March 11, 2005

Safety factors required to control fatigue damage of deepwater metallic risers caused by vortex-induced vibration (VIV) are considered. Four different riser configurations are studied: Cases I and II: Vertical tensioned 12in. risers suspended from a spar buoy at water depths of 500 and 1500m. Cases III and IV: Steel catenary risers suspended from a spar buoy, both at 1000m. For Case III, the riser diameter is 12in., while for Case IV it is 33in. For each riser configuration, relevant design and analysis parameters which are subject to uncertainty are identified. For these quantities, random variables are established also representing model uncertainties. Subsequently, repeated analyses of fatigue damage are performed by varying the input parameters within representative intervals. The results are applied to fit analytical expressions (i.e., so-called response surfaces) utilized to describe the limit state function and to develop the probabilistic model for reliability analysis of the risers. By combining the random variables for the input parameters with the results from the parameter variations, a relationship between the fatigue safety factor and the failure probability is established for each riser configuration.

Copyright © 2005 by American Society of Mechanical Engineers
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Figure 1

Lift coefficient curve in VIVANA

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Figure 2

Standard and alternative added mass curves

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Figure 3

Comparison between results from measurements and numerical predictions for riser stresses based on VIVANA analysis

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Figure 4

(Annual) Failure probability in year 20 versus fatigue safety factor. Case 1.

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Figure 5

(Annual) Failure probability in year 20 versus fatigue safety factor. Case 2.

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Figure 6

(Annual) Failure probability in year 20 versus fatigue safety factor. Case 3.

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Figure 7

(Annual) Failure probability in year 20 versus fatigue safety factor. Case 4.



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