1994 Fiscal Year Final Research Report Summary
Study of Fatigue Design Chart for Ship and Offshore Structures
| Project/Area Number |
05302054
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| Research Category |
Grant-in-Aid for Co-operative Research (A)
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| Allocation Type | Single-year Grants |
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| Research Field |
船舶工学
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| Research Institution | Osaka University |
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Principal Investigator |
TOMITA Yasumitsu Osaka University Faculty of Eng., Professor, 工学部, 教授 (30029251)
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| Co-Investigator(Kenkyū-buntansha) |
TOYOSADA Masahiro Kyushu University Faculty of Eng., Professor, 工学部, 教授 (30188817)
FUJIMOTO Yukio Hiroshima University Faculty of Eng., Professor, 工学部, 教授 (60136140)
OSAWA Naoki Osaka University Faculty of Eng., Research Assistant, 工学部, 助手 (90252585)
HASHIMOTO Kiyoshi Osaka University Faculty of Eng., Research Assistant, 工学部, 助手 (50183554)
FUNAKI Toshihiko Osaka University Faculty of Eng., Professor, 工学部, 教授 (90029174)
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| Project Period (FY) |
1993 – 1994
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| Keywords | fatigue / design chart / time history / wave condition / fatigue limit / real service condition |
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| Research Abstract |
The authors analyzed wave data which ships and offshore structures encountered in real service conditions. The time history of ocean wave conditions are concluded as follows.
(1) In relatively lower wave height conditions - calm sea condition - (lower than twice the height of the mean wave in the area), encountered wave height can be seen as a time independent random process.
(2) In higher wave conditions - storm condition - (higher than twice the height of the mean wave in area), wave height increases over time and reaches a maximum value at one point only before decreasing gradually. That is, encountered wave height is a time dependent prosess.
(3) Conditions (1) and (2) appear alternately in random order.
Above characteristics of time history of encountered wave conditions in any area is the same, but mean wave height, mean storm duration, maximum wave height in the storm condition and the number of storms encountered in service life depend on the sailing route and the sea area. A standard loading model - storm model - applied to fatigue strength analysis has been determined by the collected data.
The fatigue limits for crack initiation and crack propagation under "storm model" conditions are proved to be higher than that of a constant amplitude test which is stress amplitude according to fatigue life of 2 millions cycles and also to be higher than one-third of maximum stress in storm conditions. The storm conditions, therefore, only damage structural members.
Based on above "storm model", new fatigue design method to be applicable to ship and offshore stru ctures is proposed.
Fatigue test under "storm model" were performed for specimens with boxing fillet weldments which one of the most important ship structural components from a view point of fatigue strength. New fatigue design charts applicable to real service sea conditions are obtained.
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