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Research Papers: Ocean Engineering

Response Based Identification of Critical Wave Scenarios

[+] Author and Article Information
Marco Klein

e-mail: klein@naoe.tu-berlin.de
Ocean Engineering Division,
Technical University Berlin,
Berlin 10623, Germany

Nuno Fonseca

Centre for Marine Technology and Engineering,
Technical University of Lisbon,
Lisbon 1049-001, Portugal

1Corresponding author.

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 16, 2012; final manuscript received April 10, 2013; published online June 6, 2013. Assoc. Editor: Wei Qiu.

J. Offshore Mech. Arct. Eng 135(3), 031107 (Jun 06, 2013) (10 pages) Paper No: OMAE-12-1069; doi: 10.1115/1.4024269 History: Received July 16, 2012; Revised April 10, 2013

In the past few years the identification and investigation of critical wave sequences in terms of offshore structure responses became one of the main topics in the ocean engineering community. Thereby the area of interest covers the entire field of application spectra at sea—from efficient and economic offshore operations in moderate sea states to reliability as well as survival in extreme wave conditions. For most cases, the focus lies on limiting criteria for the design, such as maximum global loads, maximum relative motions between two or more vessels, or maximum accelerations, at which the floating structure has to operate or to survive. These criteria are typically combined with a limiting characteristic sea state (Hs, Tp) or a rogue wave. For the investigation of offshore structures as well as the identification of critical wave sequences, different approaches are available—most of them are based on linear transfer functions as it is an efficient procedure for the fast holistic evaluation. But, for some cases the linear method approach implies uncertainties due to nonlinear response behavior, in particular in extreme wave conditions. This paper presents an approach to these challenges, a response based optimization tool for critical wave sequence detection. This tool, which has been successfully introduced for the evaluation of the applicability of a multibody system based on the linear method approach, is adjusted to a nonlinear task—the vertical bending moment of a chemical tanker in extreme wave conditions. Therefore a nonlinear strip theory solver is introduced into the optimization routine to capture the nonlinear effects on the vertical bending moment due to steep waves. The goal of the procedure is to find a worst case wave sequence for a certain critical sea state. This includes intensive numerical investigation as well as model test validation.

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Copyright © 2013 by ASME
Topics: Waves , Optimization , Ships , Stress
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Figures

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Fig. 1

Scheme of the response based optimization procedure

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Fig. 2

JONSWAP energy density spectrum

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Fig. 3

Progress of the objective function

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Fig. 4

Results of the optimizations. The results are shifted in the time domain for a better comparability.

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Fig. 5

Results of the optimizations with maximum wave steepness constraint. The results of the first optimization runs (runs 1–5, cf. Fig. 4) are indicated in light gray. The results are shifted in time domain for a better comparability.

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Fig. 6

Results of random phase simulation

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Fig. 7

Model of the investigated chemical tanker

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Fig. 8

Comparison of the measured and calculated RAOs

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Fig. 9

Model test results versus results of the optimizations. The results are shifted in time domain for a better comparability.

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