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Research Papers: Structures and Safety Reliability

Truncation Design and Model Testing of a Deepwater FPSO Mooring System

[+] Author and Article Information
Hongwei Wang, Gang Ma, Liping Sun, Zhuang Kang

College of Shipbuilding Engineering,
Harbin Engineering University,
Harbin 150001, China

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received July 7, 2015; final manuscript received January 20, 2016; published online February 15, 2016. Assoc. Editor: Ron Riggs.

J. Offshore Mech. Arct. Eng 138(2), 021603 (Feb 15, 2016) (10 pages) Paper No: OMAE-15-1065; doi: 10.1115/1.4032605 History: Received July 07, 2015; Revised January 20, 2016

Limitation of offshore basin dimensions is a great challenge for model tests of deepwater mooring system. The mooring system cannot be modeled entirely in the basin with a reasonable model scale. A classical solution is based on hybrid model tests for the truncated mooring system. An efficient truncation method is proposed in this paper taking advantage of the mechanical characteristics of catenary mooring system. Truncation procedures are presented both in vertical and horizontal directions. A turret moored floating production storage and offloading (FPSO) is analyzed, and its mooring system is truncated from the original 914 m water depth to 736 m and 460 m, respectively. Numerical simulations are performed based on catenary theory and lumped mass model to these three systems, including the original untruncated system and two truncated systems. The static characteristics and dynamic response are investigated, and the results are compared between the truncated and untruncated system, and good agreements are obtained, verifying the preliminary truncation design. Model tests are conducted to the three mooring system configurations in the deepwater basin of the Harbin Engineering University. The static and dynamic properties are found to be mostly consistent between the untruncated system and two truncated systems, except for some discrepancy in 460 m system. It indicates that the truncation design is successful when the truncation factor is large, while difference still exists when the truncation factor is small. Numerical reconstruction to the model test in 460 m and extrapolation to 914 m are also implemented. The results are found to be consistent with those in 914 m, verifying the robustness and necessity of the hybrid model testing, especially for the mooring system with large truncation.

Copyright © 2016 by ASME
Topics: Design , FPSO , Mooring , Water
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Figures

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Fig. 1

Schematic of the truncated and untruncated mooring lines

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Fig. 2

Diffraction model of an FPSO

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Fig. 3

(a) Bird's eye view of the FPSO mooring system and (b) plan view of the FPSO mooring system

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Fig. 4

Vertical truncated mooring force–displacement

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Fig. 5

Horizontal truncated mooring force–displacement

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Fig. 6

X force on turret—X displacement

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Fig. 7

Surge in coupled analysis

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Fig. 8

Force on line 2 in coupled analysis

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Fig. 9

Horizontal layouts of the mooring lines in (a) 10 m, (b), 8 m, and (c) 5 m water depth

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Fig. 10

(a) An FPSO model after calibration, (b) turret model after calibration, and (c) mooring line model after calibration

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Fig. 11

(a) Mooring piles and (b) mooring piles with horizontal troughs

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Fig. 12

Schematic of the mooring lines fixed to piles in selected water depths

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Fig. 13

Restoring forces of single line in selected water depths

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Fig. 14

X restoring force on turret—surge

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Fig. 15

Comparison of target and measured wave spectrum

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Fig. 17

Tension in line 2

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