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Offshore Technology

Gaussian Analysis of an Irregular Wave Impact on Deck

[+] Author and Article Information
Ravikiran S. Kota2

Centre for Ships and Ocean Structures (CeSOS), Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norwayravi.kota@ntnu.no

Torgeir Moan

Centre for Ships and Ocean Structures (CeSOS), Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway

For Zd=0, it is in fact possible to obtain an analytical solution in Eq. 23 and could be used to verify the numerical integration routine.

2

Corresponding author.

J. Offshore Mech. Arct. Eng 132(4), 041302 (Sep 24, 2010) (12 pages) doi:10.1115/1.4001436 History: Received June 18, 2009; Revised October 29, 2009; Published September 24, 2010; Online September 24, 2010

Level-crossing analysis of long-crested, Gaussian waves in space and time are studied in the context of wave loads on a fixed, horizontal deck-box above mean waterline. Vertical wave loads on decks due to insufficient airgap are a major concern for many in-service platforms. Reliable estimation of magnitude and duration of these loads is important in assessing structural and global response of an offshore platform. In the case of an irregular wave-impact on a flat deck of dimensions comparable to mean wavelength of the incident waves, both temporal and spatial variability of wave-kinematics need to be considered during the deck-wetting process. In the present study, we have used a multidimensional Gaussian formulation of incident wave-kinematics to derive a joint probability density function of deck-wetting (or exceedance) duration and its spatial extent. We have also derived a probability density function for initial slam force on deck. A numerical scheme for simulating wave-impact events on a two-dimensional deck is discussed, results from which are compared against corresponding analytical estimates. Vertical force on deck was estimated using the momentum method, which includes a von Kármán slamming model applied over the wetted-length determined from an undisturbed wave profile.

FIGURES IN THIS ARTICLE
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Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Variation in wetted-length and its rate of change for a deck heaving through a regular wave-crest

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Figure 2

Merging of adjacent cycles

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Figure 3

Illustration of a deck-wetting event

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Figure 4

Expected number of deck-wetting events: analytical estimates and simulation

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Figure 5

Analytical distribution of deck-wetting duration τ and its sensitivity

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Figure 6

Probability of event-duration: analytical versus simulation

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Figure 7

Sensitivity of PDF of initial slam force to wave-slope and deck-elevation

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Figure 8

Probability of initial slam force: analytical estimate versus simulation

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Figure 9

Expected variation in wetted-length and vertical force on deck from simulation

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