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Structures and Safety Reliability

On the Extreme Value Analysis of the Response of a Turret Moored FPSO

[+] Author and Article Information
L. V. S. Sagrilo1

Laboratory of Analysis and Reliability of Offshore Structures, Department of Civil Engineering, COPPE, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil, 21945–970sagrilo@coc.ufrj.br

A. Naess

Centre for Ships and Ocean Structures,  Norwegian University of Science and Technology, Trondheim, Norway, NO7491; Department of Mathematical Sciences,  Norwegian University of Science and Technology, Trondheim, Norway, NO7491

Z. Gao

Centre for Ships and Ocean Structures,  Norwegian University of Science and Technology, Trondheim, Norway, NO7491

1

Corresponding author.

J. Offshore Mech. Arct. Eng 134(4), 041603 (Sep 17, 2012) (9 pages) doi:10.1115/1.4006759 History: Received September 28, 2010; Revised February 09, 2012; Published September 17, 2012; Online September 17, 2012

One of the standardized procedures used in the design of floating systems and their mooring and production lines is the so-called short-term design approach where the system is analyzed for some specific extreme environmental conditions. Along with this procedure, a nonlinear time-domain coupled dynamic analysis, considering the floater and its risers and mooring lines, can nowadays be incorporated as a feasible part of the design practice. One very important and challenging aspect of this process is concerned with the estimation of the characteristic short-term extreme values of the system response parameters based on the sampled time-series. In this paper a common procedure used to establish these extreme values for floater system response parameters, which is based upon a Weibull distribution model for the peaks of the time-series, is reviewed in the light of a recently proposed approach based on a general parametric model for the average conditional exceedance rate of peaks. It is shown that the former model corresponds to a particular case of the latter one. Numerical results are presented for the response parameters of a turret-moored Floating, Production, Storage and Offloading (FPSO) unit considering a short-term coupled analysis of the whole system under an extreme environmental condition of wind, wave, and current. Specifically, the extreme response of surge motion, top tension of the most loaded mooring line, and Det norske Veritas (DnV) codes utilization factor for the most critical section of an 0.20 m outer diameter SLWR (steel lazy wave riser) are investigated.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Turret-moored FPSO in 914 m water depth

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Figure 2

Surge motion spectral density

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Figure 3

3-h extreme surge motion prediction: most probable value

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Figure 4

3-h extreme surge motion prediction: 90% fractile

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Figure 5

3-h extreme surge motion prediction: CoV of the most probable value estimates

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Figure 6

3-h extreme surge motion prediction: CoV of the 90% fractile estimates

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Figure 7

3-h extreme surge motion prediction: CoV curve fitting for ACER estimates

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Figure 8

Line top tension spectral density

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Figure 9

3-h extreme line tension prediction: most probable value

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Figure 10

3-h extreme line tension prediction: normalized 90% fractile

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Figure 11

3-h extreme line top tension prediction: CoV of the most probable value estimates

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Figure 12

3-h extreme line top tension prediction: CoV of the 90% fractile estimates

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Figure 13

3-h extreme line top tension prediction: CoV curve fitting for ACER estimates

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Figure 14

0.20 m outer diameter SLWR configuration

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Figure 15

DnV-LRFD utilization ratio: peaks cumulative distribution on the Rayleigh distribution plot

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Figure 16

3-h extreme DnV-LRFD utilization ratio prediction: most probable value

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Figure 17

3-h extreme DnV-LRFD utilization ratio prediction: CoV of the most probable value estimates

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Figure 18

3-h extreme DnV-LRFD utilization ratio prediction: CoV curve fitting for ACER estimates

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