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.


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.

Copyright © 2010 by American Society of Mechanical Engineers
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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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