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Research Papers: Structures and Safety Reliability

Alternative Environmental Contours for Marine Structural Design—A Comparison Study1

[+] Author and Article Information
Erik Vanem

Strategic Research and Innovation,
DNV-GL,
Høvik 1363, Norway
e-mail: Erik.Vanem@dnvgl.com

Elzbieta M. Bitner-Gregersen

Strategic Research and Innovation,
DNV-GL,
Høvik 1363, Norway
e-mail: Elzbieta.Bitner-Gregersen@dnvgl.com

1Paper presented at the 2014 ASME 33rd International Conference on Ocean, Offshore and Arctic Engineering, San Francisco, CA, June 8–13, 2014, Paper No. OMAE2014-23252.

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received June 18, 2014; final manuscript received July 3, 2015; published online August 6, 2015. Assoc. Editor: Carlos Guedes Soares.

J. Offshore Mech. Arct. Eng 137(5), 051601 (Aug 06, 2015) (8 pages) Paper No: OMAE-14-1064; doi: 10.1115/1.4031063 History: Received June 18, 2014

A new approach to estimate environmental contours in the original physical space by direct Monte Carlo simulations rather than applying the Rosenblatt transformation has recently been proposed. In this paper, the new and the traditional approach to estimating the contours are presented and the assumptions on which they are based are discussed. The different results given by these two methods are then compared in a number of case studies. Simultaneous probability density functions are fitted to the joint distribution of significant wave height and wave period for selected ocean locations and environmental contours are estimated for both methods. Thus, the practical consequences of the choice of approach are assessed. Particular attention is given to mixed sea systems. In these situations, the two approaches to environmental contours may be very different while for other wave conditions the contours are similar.

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Figures

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Fig. 1

Approximate locations for the fitted wave height and period distributions

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Fig. 2

Environmental contours for one-, ten-, and 25-yr environmental conditions of West Shetland obtained with the traditional method: total sea (top), wind sea (middle), and swell (bottom)

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Fig. 3

Environmental contours for one-, ten-, and 25-yr environmental conditions of West Shetland obtained from 5 × 106 samples: total sea (top), wind sea (middle), and swell (bottom)

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Fig. 4

Environmental contours for one-, ten-, and 25-yr environmental conditions of Western Africa obtained from the traditional method: swell component only

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Fig. 5

Environmental contours for one-, ten-, and 25-yr environmental conditions of Western Africa obtained from 5 × 106 samples: swell component

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Fig. 6

Environmental contours for one-, ten-, and 25-yr environmental conditions of NWS Australia obtained from the traditional method: total sea (top), wind sea (middle), and swell (bottom)

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Fig. 7

Environmental contours for one-, ten-, and 25-yr environmental conditions of NWS Australia obtained from 5 × 106 samples: total sea (top), wind sea (middle), and swell (bottom)

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Fig. 8

Illustration of how even remote samples in the parameter space contribute in estimation of the contour segments with the new approach

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Fig. 9

A possible modification of the new approach in areas with mixed sea, include only samples within a specified sector in the estimation of the contour segments

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