Capsize Risk Assessment using Fredyn Ship Motion Predictions

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Authors
  1. Taggart, K.A.
Corporate Authors
Defence Research Establishment Atlantic, Dartmouth NS (CAN)
Abstract
This report presents a method for predicting capsize risk of intact ships in seaway. Ship speed and heading are assumed to be independent variables, and the joint distribution of significant wave height and peak wave period is obtained from a wave scattergram. For a given set of operating and environmental conditions, the time domain program Fredyn is used to determine the occurrence of hsip capsize. For irregular seas, the dependence of capsize on wave process realization is modelled by fitting a Gumbel distribution to maximum absolute roll angels obtained from several different wave phase seed numbers. Ten simulations of 30 minute duration can adequately provide the distribution of maximum hourly roll angle for a given seaway and ship operating condition. Sample computations for a Canadian Patrol Frigate suggest that the method gives realistic estimates of annual capsize risk. The current implementation conservatively assumes that ship speed and headings are independent of wave conditions. Future work will examine ship operational profiles to include the influence of capsize avoidance action.
Keywords
Computer programs (FREDYN);Capsizing;Time domain;Dynamic stability
Report Number
DREA-TM-1999-149 — Technical Memorandum
Date of publication
01 Sep 1999
Number of Pages
92
DSTKIM No
CA001506
CANDIS No
513150
Format(s):
Hardcopy;Document Image stored on Optical Disk

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