STATISTICAL CHARACTERISTICS OF LONG-TERM WAVE-INDUCED LOAD FOR FATIGUE STRENGTH ANALYSIS FOR SHIPS

Fatigue strength is one of the most important factors taken into consideration in the design of ships. When analysing the fatigue strength of ship hull structures, it is necessary to obtain both the long-term distribution and the time history of wave-induced loads. Recent investigations have found that short-term distribution over a short period, of the order of about one hour, is closely approximated by the Rayleigh distribution, while long-term distribution, which consist of a large number of short-term random conditions, has not yet been completely clarified. Up to now, designers have assumed it to be an exponential distribution. Finally, the time history of wave-induced loading during an actual sailing condition has not been clarified. The purpose of this study is to clarify the two lesser known factors mentioned above by analysing data collected from 38 ships that sailed the North Pacific over a period of 14 years (1976-1989). The main points made in this study are as follows: 1) Various wave conditions were recorded in the same sea zone during the same period, allowing clarification of their scatter band. 2) The distribution function of long-term wave-induced loading can be analytically described by the Weibull distribution function, with an expected shape parameter value close to one. 3) The time history of wave conditions during real sailing can be divided into two types. One is the calm sea condition, and the other consists of various storm conditions. These two kinds of conditions appear alternately in random order. Also discussed, based on the above results, its fatigue strength analysis of ship structural members.

• Supplemental Notes:
  • PRADS '92, 5th Intl Symp on the Practical Design of Ships and Mobile Units; 17-22 May 1992; Newcastle upon Tyne, U.K. Pprs. Publ by Elsevier Science Pubs Ltd., U.K., Vol 2, p 2.792 [14 p, 7 ref, 4 tab, 11 fig]
• Authors:
  • Tomita, Y
  • Kawabe, H
  • Fukuoka, T
• Publication Date: 1992

Language

• English

Subject/Index Terms

• TRT Terms: Fatigue strength; Loads; Water waves
• Old TRIS Terms: Random loads; Wave data; Wave loads
• Subject Areas: Hydraulics and Hydrology; Marine Transportation;

Filing Info

• Accession Number: 00703606
• Record Type: Publication
• Source Agency: British Maritime Technology
• Files: TRIS
• Created Date: Aug 14 1995 12:00AM