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TECHNICAL PAPERS

Analysis of Design Wave Loads on an FPSO Accounting for Abnormal Waves

[+] Author and Article Information
C. Guedes Soares1

Unit of Marine Technology and Engineering, Technical University of Lisbon, Instituto Superior Técnico, Lisboa, Portugalguedess@mar.ist.utl.pt

Nuno Fonseca

Unit of Marine Technology and Engineering, Technical University of Lisbon, Instituto Superior Técnico, Lisboa, Portugalnfonseca@mar.ist.utl.pt

Ricardo Pascoal

Unit of Marine Technology and Engineering, Technical University of Lisbon, Instituto Superior Técnico, Lisboa, Portugalrpascoal@mar.ist.utl.pt

Guenther F. Clauss

 Technical University Berlin, Ocean Engineering Section, Berlin, Germanyclauss@ism.tu-berlin.de

Christian E. Schmittner

 Technical University Berlin, Ocean Engineering Section, Berlin, Germanyschmittner@ism.tu-berlin.de

Janou Hennig

 Technical University Berlin, Ocean Engineering Section, Berlin, Germanyhennig@ism.tu-berlin.de

1

Corresponding author.

J. Offshore Mech. Arct. Eng 128(3), 241-247 (Jul 08, 2005) (7 pages) doi:10.1115/1.2166656 History: Received September 23, 2004; Revised July 08, 2005

The paper presents an analysis of structural design wave loads on an FPSO. The vertical bending moment at midship induced by rogue waves are compared with rule values. The loads induced by deterministic rogue waves were both measured in a seakeeping tank and calculated by an advanced time domain method. Two procedures are used to calculate the expected extreme vertical bending moment during the operational lifetime of the ship. The first one relies on a standard linear long term prediction method, which results from the summation of short term distribution of maxima weighted by their probability of occurrence. The short term stationary seastates are represented by energy spectra and the ship responses by linear transfer functions. The second one is a generalization of the former and it accounts for the nonlinearity of the vertical bending moment, by using nonlinear transfer functions of the bending moment sagging peaks which depend of the wave height.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Segmented model of the FPSO during tests in the wave tank (scale 1:81)

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Figure 2

Side view of the FPSO midship-vertical position of the connecting elements can be changed (photo: measuring device at waterline level)

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Figure 3

Comparison of model wave (measured at scale 1:81) with the registered New Year wave presented as full scale data

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Figure 4

Transfer function amplitudes of heave and pitch motions

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Figure 5

Transfer function amplitude of the vertical bending moment at midship

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Figure 6

Measurements and simulations of the wave at midship, heave, pitch, and the vertical bending moment at midship. NYW crest occurs at midship.

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Figure 7

Comparison of experimental and numerical maximum hogging and sagging peaks, which are associated with the large crest passing through the ship. Results presented as function of the large crest position along the ship. Length between perpendiculars is 259.8m.

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Figure 8

Measured (dashed lines) and simulated (continuous lines) time histories of the vertical bending moment at midship for different positions of the NYW crest along the longitudinal direction (indicated by the arrows). Results in kN m.

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Figure 9

Long term distribution of the wave induced bending moment at midship

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