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Research Papers: Structures and Safety Reliability

Effects of Waves and Currents on Extreme Loads on a Jacket

[+] Author and Article Information
Kjersti Bruserud

Statoil ASA,
Forusbeen 50,
Stavanger 4035, Norway;
Institute of Marine Technology,
Norwegian University of Science and
Technology (NTNU),
Otto Nielsens vei 10,
Trondheim 7491, Norway
e-mail: kjbrus@statoil.com

Sverre Haver

Department of Mechanical and Structural
Engineering and Materials Science,
University of Stavanger,
Kjell Arholms gate 41,
Stavanger 4036, Norway;
Institute of Marine Technology,
Norwegian University of Science and
Technology (NTNU),
Otto Nielsens vei 10,
Trondheim 7491, Norway
e-mail: sverre.k.haver@uis.no

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received February 13, 2015; final manuscript received May 20, 2015; published online August 20, 2015. Assoc. Editor: Hideyuki Suzuki.

J. Offshore Mech. Arct. Eng 137(5), 051603 (Aug 20, 2015) (9 pages) Paper No: OMAE-15-1011; doi: 10.1115/1.4031099 History: Received February 13, 2015

In lack of simultaneous data of metocean parameters such as wind, waves, and currents, Norwegian design regulations presently recommend a conservative combination of metocean parameters for estimation of characteristic metocean loads on offshore structures. A simplified parametric load model for a jacket, based on waves and currents, is assumed. Several approaches to load estimation are investigated and the following are considered: different averaging length of extreme currents, the effect of peak-over-threshold approach for estimation of extreme wave and currents compared to all-sea states approach and extreme load estimation directly from a load time series. When compared to the recommended approach, all other approaches yield a reduced estimated characteristic metocean load. The purpose of this study is to indicate the possible conservatism in the Norwegian design regulations for estimation of quasi-static loads on a jacket. The results are intended to be illustrative and not suitable for use in specific design calculations.

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References

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Figures

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Fig. 1

Illustration of different current data

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Fig. 2

Empirical (dots) and fitted (line) distributions of Hs

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Fig. 3

(a) Empirical (dots) and fitted (line) distributions of Cs, 10 min Cs, (b) empirical (dots) and fitted (line) distributions of Cs, 3 hrs mean Cs, and (c) empirical (dots) and fitted (line) distributions of Cs, 3 hrs max Cs

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Fig. 4

Extreme (a) Hs and (b) Cs for different thresholds

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Fig. 5

Empirical (dots) and fitted (line) distributions of Hs

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Fig. 6

(a) Empirical (dots) and fitted (line) distributions of Cs, 10 min Cs, (b) empirical (dots) and fitted (line) distributions of Cs, 3 hrs mean Cs, and (c) empirical (dots) and fitted (line) distributions of Cs, 3 hrs max Cs

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Fig. 7

Scatter diagram of Hs and maximum 3 hrs Cs

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Fig. 9

Empirical (dots) and fitted (line) distributions of V

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Fig. 8

Empirical (dots) and fitted (line) distributions of H˜

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Fig. 10

(a) Empirical (dots) and fitted (line) distributions of L based on most probable H, 10 min Cs, (b) empirical (dots) and fitted (line) distributions of L based on most probable H, 3 hrs mean Cs, and (c) empirical (dots) and fitted (line) distributions of L based on most probable H, 3 hrs max Cs

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Fig. 11

(a) Fitted distributions of L, based on Monte Carlo H, 10 min Cs, (b) fitted distributions of L, based on Monte Carlo H, 3 hrs mean Cs, and (c) fitted distributions of L, based on Monte Carlo H, 3 hrs max Cs

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