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TECHNICAL PAPERS

A Methodology to Simulate Floating Offshore Operations Using a Design Wave Theory

[+] Author and Article Information
Lee O’Neill, Emmanuel Fakas, Mark Cassidy

 University of Western Australia, Perth Wa 6009, Australia

J. Offshore Mech. Arct. Eng 128(4), 304-313 (Jun 02, 2005) (10 pages) doi:10.1115/1.2166654 History: Received October 26, 2004; Revised June 02, 2005

Numerical techniques are extensively used to predict vessel motions and associated contact forces for offshore operations such as lift and floatover deck installations. The accuracy of such predictions however is highly dependent on the comprehensive modeling of sea state conditions, which is often limited by computational power and time constraints. A time-efficient methodology, suitable for modeling large numbers of installation sea states, is developed to alleviate this problem. The methodology is based on the Constrained New Wave model which has been previously used to overcome similar problems. However this has only been for individual, extreme storm conditions. The accuracy, time-efficiency, and practicality of the revised methodology is demonstrated by means of direct comparison of simulation results obtained for a floatover deck installation on the North West Shelf of Australia. The ability to perform a large number of simulations in a time and cost efficient manner is of paramount importance in assessing the system limitations to varying installation conditions, a case that has always been challenging to designers during the development of oil and gas projects. Such flexibility improves confidence in the overall system, necessary for the accurate assessment of the commercial viability of marginal developments.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Typical new wave with crest elevation of 1m located at 250s

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Figure 2

(A) New wave; (B) random wave; (C) constrained new wave

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Figure 3

Maximum response as function of crest elevation (50 constrained new waves for each crest elevation) (P-M spectrum, Hs=1 and Tz=10s)

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Figure 4

FOD installation

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Figure 5

Input wave train and mating line response for a FOD system

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Figure 6

Convergence test of maximum response for different numbers of constrained new waves

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Figure 7

Cumulative distribution for Hs=1.25, Tz=10s, θ=30deg by interpolation between Hs=1m, 1.5m. (A) Fender force; (B) mating line force; (C) vertical contact force; and (D) horizontal contact force.

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Figure 8

Cumulative distribution for Tz=11s, Hs=1.25, θ=37.5deg by interpolation between Tz=10s, 12s. (A) Fender force, (B) mating line force; (C) vertical contact force, and (D) horizontal contact force.

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Figure 9

Cumulative distribution for Hs=1.5m, Tz=8s, and θ=37.5deg by interpolation between θ=30deg, 45deg. (A) Fender force, (B) mating line force, (C) vertical contact force, and (D) horizontal contact force.

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Figure 10

Cumulative distribution for Hs=1.5m, Tz=11s, and θ=37.5deg by interpolation between Hs=1m, 1.5m and Tz=10s, 12s. (A) Fender force, (B) mating line force, (C) vertical contact force, and (D) horizontal contact.

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Figure 11

Cumulative distribution for Hs=1.5m, Tz=11s, and θ=37.5deg by interpolation between Hs=1m, 1.5m, Tz=10s, 12s, and θ=30deg, 45deg. (A) Fender force, (B) mating line force, (C) vertical contact force, and (D) horizontal contact.

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