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Research Papers: CFD and VIV

Toward a Probabilistic Approach to Determine Nominal Values of Tank Sloshing Loads in Structural Design of Liquefied Natural Gas FPSOs

[+] Author and Article Information
Jeom Kee Paik

The Korea Ship and Offshore Research Institute
(The Lloyd's Register Foundation
Research Centre of Excellence),
Pusan National University,
Busan 609-735, Korea;
Department of Mechanical Engineering,
University College London,
London WC1E 6BT, UK

Sang Eui Lee, Bong Ju Kim, Jung Kwan Seo, Yeon Chul Ha

The Korea Ship and Offshore Research Institute
(The Lloyd's Register Foundation
Research Centre of Excellence),
Pusan National University,
Busan 609-735, Korea

Toshiyuki Matsumoto

Nippon Kaiji Kyokai,
Tokyo 267-0056, Japan

Su Hwan Byeon

STX Offshore and Shipbuilding Co., Ltd.,
Jinhae 641-060, Korea

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received May 9, 2014; final manuscript received January 7, 2015; published online February 24, 2015. Assoc. Editor: Thomas E. Schellin.

J. Offshore Mech. Arct. Eng 137(2), 021801 (Apr 01, 2015) (17 pages) Paper No: OMAE-14-1053; doi: 10.1115/1.4029666 History: Received May 09, 2014; Revised January 07, 2015; Online February 24, 2015

The aim of this study is to develop a new probabilistic approach to determine nominal values for tank sloshing loads in structural design of LNG FPSO (liquefied natural gas, floating production, storage, and offloading units). Details of the proposed procedure are presented in a flow chart showing the key subtasks. The applicability of the method is demonstrated using an example of a hypothetical LNG FPSO operating in a natural gas site off a hypothetical oceanic region. It is noted that the proposed method is still under development for determining reliable estimates of extreme sloshing induced impact loads. It is concluded that the developed method is useful for determining the sloshing design loads in ship-shaped offshore LNG installations in combination with virtual metocean data and operational conditions.

Copyright © 2015 by ASME
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References

Figures

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Fig. 1

Procedure to determine sloshing design loads

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Fig. 2

An example of the motion selection

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Fig. 3

An impact pressure profile [1]

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Fig. 4

An example of probability plot for the variable V1

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Fig. 5

An example of maximum mean and minimum COV criterion

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Fig. 6

Target vessel and tank arrangements

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Fig. 7

Probability density function of metocean data and their best-fit distribution (solid line)

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Fig. 8

Coordinate system of wind and current

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Fig. 9

Results of mesh convergence tests for wind (left) and current (right) load simulations

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Fig. 10

Results of speed tests for wind (left) and current (right) load simulations

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Fig. 11

Numerical mesh model of wind (left) and current (right) load simulations

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Fig. 12

Wind load coefficients of forces (left) and moments (right)

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Fig. 13

Current load coefficients of forces (left) and moments (right)

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Fig. 14

Results of RAOs for 6DOF

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Fig. 15

An example of the wind and current effects on FLNG motion time series for scenario-10

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Fig. 16

An example of 6DOF motions extracted from the time series for scenario-12

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Fig. 17

Mesh modeling of areas of local refinement (left) and cross sections (right) for sloshing simulations

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Fig. 18

Results of convergence tests in terms of number of inner iterations and the time step for scenario-12

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Fig. 19

An example of the summed and average velocity at the free surface for scenario-12

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Fig. 20

An example of the pressure distribution inside the LNG tank in terms of time for scenario-12

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Fig. 21

Examples of the time histories of sloshing impacts inside the LNG tank

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Fig. 22

Summary of identified locations where sloshing impact occurs

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Fig. 23

Best-fit of 6DOF based on the results of GOF tests with the 95% confidence interval

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Fig. 24

Interval studies of 6DOF motion for motion probabilities

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Fig. 25

Results of motion probabilities for the 30 scenarios

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Fig. 26

Sloshing probability of exceedance curves for peak pressure (left), impulse (center), and rise time (right)

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