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Research Papers: Piper and Riser Technology

Statistical Uncertainty Analysis in Time-Domain Fatigue Assessment of Steel Risers

[+] Author and Article Information
Rodrigo C. da Costa

Laboratory of Analysis and Reliability of
Offshore Structures,
Department of Civil Engineering,
Federal University of Rio de
Janeiro COPPE/UFRJ,
Av. Pedro Calmon, s/n,
Rio de Janeiro RJ 21941-596, Brazil
e-mail: rccosta.ec@gmail.com

Luis. V. S. Sagrilo

Professor
Laboratory of Analysis and Reliability of
Offshore Structures,
Department of Civil Engineering,
Federal University of Rio de
Janeiro COPPE/UFRJ,
Av. Pedro Calmon, s/n,
Rio de Janeiro RJ 21941-596, Brazil
e-mail: sagrilo@coc.ufrj.br

1Corresponding author.

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received June 6, 2016; final manuscript received November 16, 2017; published online January 2, 2018. Assoc. Editor: Lance Manuel.

J. Offshore Mech. Arct. Eng 140(3), 031701 (Jan 02, 2018) (9 pages) Paper No: OMAE-16-1057; doi: 10.1115/1.4038583 History: Received June 06, 2016; Revised November 16, 2017

This paper addresses the statistical uncertainty in long-term fatigue damage in offshore structures due to the short-term simulation length used in time domain analysis of stresses. The paper focuses on steel risers applications. A new simulation-based estimator for the variance of the short-term fatigue damage is presented. The proposed estimator is based on a variation of the original nonparametric bootstrap. It works with blocks of data instead of discrete values, in order to better account for the autocorrelation of the stress cycles in the stress time series. This versatile estimator can be applied in time-domain fatigue analyses to assess the variance of the fatigue damage using a single stress time series and does not require any previous assumptions on the stochastic stress process.

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References

DNV, 2010, “ Fatigue Design of Offshore Steel Structures,” Det Norske Veritas, Hovik, Norway, Standard No. DNV-RP-C203. https://rules.dnvgl.com/docs/pdf/DNV/codes/docs/2011-10/RP-C203.pdf
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Dirlik, T. , 1985, “ Application of Computers in Fatigue Analysis,” Ph.D. thesis, University of Warwick, Coventry, UK. http://wrap.warwick.ac.uk/2949/
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Costa, R. C. D. , 2015, “ Statistical Uncertainty Analysis in Time-Domain Fatigue Assessment of Steel Risers,” Master's thesis, COPPE, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil. https://www.researchgate.net/profile/Rodrigo_Costa15/publication/302988764_Statistical_Uncertainty_Analysis_in_Time-Domain_Fatigue_Assessment_of_Steel_Risers/links/5734b3b608aea45ee83ae04b/Statistical-Uncertainty-Analysis-in-Time-Domain-Fatigue-Assessment-of-Steel-Risers.pdf

Figures

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Fig. 1

Stress time series divided into blocks of data

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Fig. 2

Spectral densities for the bandpass case study

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Fig. 3

Estimated COV for the scaled and normalized fatigue damage for δω = 0.03 and m = 3

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Fig. 4

Estimated COV for the scaled and normalized fatigue damage for δω = 0.03 and m = 6

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Fig. 5

Estimated COV for the scaled and normalized fatigue damage for δω = 0.35 and m = 3

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Fig. 6

Estimated COV for the scaled and normalized fatigue damage for δω = 0.35 and m = 6

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Fig. 7

SLWR geometric configuration

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Fig. 8

Expected fatigue life for the SLWR (based on 10800 s-long simulations)

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Fig. 9

Estimated COV for the scaled and normalized fatigue damage at the TDP

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Fig. 10

Estimated COV for the scaled and normalized fatigue damage at the buoyancy zone

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Fig. 11

Estimated COV for the scaled and normalized fatigue damage at the connection point

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