Abnormal Wave-Induced Load Effects in Ship Structures
The paper presents an approach to determine the global load effects induced on ship structures by abnormal, freak, or episodic waves. It refers to the present procedure of determining extreme values of wave-induced responses, including the recent advances of adopting time series of wave elevation as reference design conditions to calculate the wave-induced structural loads on ships in heavy weather. It is shown how this procedure can be extended to account for abnormal or episodic waves. Reference is made to what is presently known about abnormal or freak waves, showing that although it is possible to determine the loads induced by these waves in floating and fixed structures, the present knowledge about the probability of occurrence of these waves is not enough to allow a wave design criterion to be defined in a way consistent with the present probabilistic approaches. However, it is suggested that at the present stage of knowledge it is possible to determine the loads induced by abnormal waves similar to ones that have been measured at various ocean locations and that are thus realistic; a method is described to perform such calculations. Although this information cannot replace the wave-induced loads calculated with the presently established procedures, it can serve as guidance for the design. An application example is presented of a containership subjected to a wave trace that includes an episodic wave that was measured during a severe storm in Central North Sea. The measured wave time history is modified in order to investigate the influence of the wave steepness on the induced vertical motions and loads. The loads induced by the abnormal wave are compared for the first time with extreme values from long-term distributions.
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Document Type: Research Article
Publication date: March 1, 2008
More about this publication?
- The Journal of Ship Research is a quarterly publication providing highly technical papers on applied research in hydrodynamics, propulsion, ship motions, structures, and vibrations. While the Journal requires that papers present the results of research that advances ship and ocean science and engineering, most contributions bear directly on other disciplines, such as civil and mechanical engineering, applied mathematics, and numerical analysis. High quality papers are contributed from the U.S., Canada and overseas, with representation from established authorities as well as new researchers.
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