How much are Whippings Contributing to Fatigue and Extreme Responses in Ship Structure Details
The work presented in this thesis concerns the fatigue estimation tools, the investigation of whip-pings, and the prediction for the responses in the future. The data we use is measured from the onboard hull monitoring system of a 2800 TEU container vessel operated in the North Atlantic. To make the...
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| Language: | English |
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2009
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.504.9670 http://www.fcc.chalmers.se/risk/articles_new/how-much-are-whippings-contributing-to-fatigue-and-extreme-responses-in-ship-structure-details/files/fileinnercontentproxy.2009-07-03.8835982804 |
| Summary: | The work presented in this thesis concerns the fatigue estimation tools, the investigation of whip-pings, and the prediction for the responses in the future. The data we use is measured from the onboard hull monitoring system of a 2800 TEU container vessel operated in the North Atlantic. To make the investigation more economical, efficient, and accurate, we use 30 minutes stationary stresses as a sea state and take away ones with significant wave height Hs < 4m. For the fatigue estimation, two main methods are used in the thesis, rain-flow algorithm and narrow-band approximation. Rain-flow damage is considered as the true damage, and the narrow-band damage is the upper bound of it, which is needed for fatigue damage estimations when stress measurements are not available. To decrease the conservatism of the upper bound, we improve the narrow-band approximation to calculate a new damage estimate which is more closed to the rain-flow damage. The aim of this thesis is to investigate how much are whippings contributing to fatigue and ex-tremes of responses. At first, we give the mathematical definition of whippings. Through the compar-ison of damages made by different frequency stresses, we got the whipping influence roughly. Crossing spectrum is used to predict the future. We got the crossing spectrum of a half year to predict 100 years response, which is the response that happens in average once during 100 years under assumption of stationary shipping. |
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