Statistical Analysis of Stress Histories for Fatigue Damage Design of Floating Fish Cages
Publication: Journal of Waterway, Port, Coastal, and Ocean Engineering
Volume 138, Issue 1
Abstract
Floating fish cages provide the main production utilities for salmon farming. However, despite their pivotal role in production safety as well as in protection of the environment, much room exists for further development in relation to verified structural design procedures and computerized tools for structural analysis. In this paper, a statistical analysis of stress range histories is presented and compared with results from rainflow counting. The study is based on a structure being applied by the Norwegian fish farming industry today. The floater is made of steel cylinders configured as a square. The fatigue design analysis is based on time domain analysis of the structure in irregular waves. The statistical properties of the stress range histories are investigated using Weibull plots, histograms, damage plots, and, finally, estimation of short- and long-term distributions and evaluation of its applicability in relation to simplified methods. The Rayleigh distribution and the two-parameter Weibull distribution are applied. A visual inspection of the short-term Weibull plots indicates a quite good fit, and the shape parameter is typically between 0.6 and 0.8. However, a closer inspection of the histograms shows that the process seems to be a combination of a high-frequency/low stress range level process with a Weibull shape parameter and a low-frequency/high stress range level process with a Weibull shape parameter .
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Acknowledgments
The software developed and used for the preparation of this paper was based on the finite-element framework developed by Dr. Jae Won Jang and Professor Gregory R. Miller, Univ. of Washington. The authors want to thank them for making their source code and competence available. Professor Odd M. Faltinsen, NTNU, Professor Ludvig Karlsen, NTNU, and Professor Dag Myrhaug, NTNU gave valuable suggestions regarding the hydrodynamic model, structural modeling aspects, and the wave model, respectively.
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Information & Authors
Information
Published In
Journal of Waterway, Port, Coastal, and Ocean Engineering
Volume 138 • Issue 1 • January 2012
Pages: 30 - 41
Copyright
© 2012 American Society of Civil Engineers.
History
Received: Mar 17, 2011
Accepted: Jul 15, 2011
Published online: Jul 16, 2011
Published in print: Jan 1, 2012
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