| 11. |
- Mao, Wengang, 1980, et al.
(författare)
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The effect of whipping/springing on fatigue damage and extreme response of ship structures
- 2010
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Ingår i: Proceedings of the ASME 29th International Conference on Ocean, Offshore and Arctic Engineering (OMAE 2010) in Shanghai, China, June 6-11, 2010. - 9780791849101 ; 2
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Konferensbidrag (refereegranskat)abstract
- Wave-induced vibrations, also known as whipping and springing, are defined as high frequency response of ship structures. In this paper, the fatigue damage caused by whipping and springing is presented by investigating the amidships section of a 2800 TEU container ship that operates in the North Atlantic Ocean. A simplified fatigue model, originally from the generalized narrow-band approximation for Gaussian load, is employed to include the damage contribution from wave-induced vibrations. In this model, the significant response range hs and the mean stress up-crossing frequency fz are simplified using only the wave-induced loading and encountered wave frequency, respectively. The capacity and accuracy of the model is illustrated by application on the measurements of the 2800 TEU container ship for different voyages during 2008. The whipping-induced contribution to the extreme response is investigated by means of the level crossing approach. It shows that the level crossing model for Gaussian load cannot be used for the prediction of extreme responses, such as the 100-year stress, based on a half-year full-scale measurement. It is found that a more complicated non-Gaussian model is required to consider the contribution from whipping.
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| 12. |
- Mao, Wengang, 1980, et al.
(författare)
-
Theoretical development and validation of a fatigue model for ship routing
- 2012
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Ingår i: Ships and Offshore Structures. - : Informa UK Limited. - 1754-212X .- 1744-5302. ; 7:4, s. 399-415
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Tidskriftsartikel (refereegranskat)abstract
- Fatigue cracks are observed much earlier than expected in ships and marine structures due to uncertainties in the fatiguedesign process, such as encountered sea environments and variability in S-N curves, etc. The current study presents thetheoretical development and validation of a fatigue model useful for ship routing which may contribute to better utilisationof the materials and structures by more wise operation of them. During the theoretical development of the ship routingfatigue model, various models to estimate fatigue damage intensity, including both cycle counting calculations and spectralapproximations, are reviewed. The proposed ship routing fatigue model is a function of operation profiles, i.e., heading angleand ship speed, as well as encountered wave environments (significant wave height), which are easily available in today’scommercial routing tool systems. Concerning the characteristics of ship response, the so-called narrow-band approximationis adopted and further simplified in order to estimate the fatigue damage in ships under an arbitrary stationary sea state.Long-term fatigue damage is estimated by a summation of fatigue damages in all encountered sea states during, for example,one voyage or a period of several years. Further, fatigue damage due to wave-induced vibrations (whipping and springing)and fatigue damage caused by various stress components are also studied and discussed. A validation using response fromfull-scalemeasurements and numerical analysis is presented. It shows that the proposed model works very well in comparisonwith the rainflow counting method. Finally, the proposed ship routing fatigue model is applied on real case scenarios, whereits applicability in shipping industry is demonstrated.
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| 13. |
- Mao, Wengang, 1980, et al.
(författare)
-
What is the potential of using ship fatigue routing in terms of fatigue life extension?
- 2012
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Ingår i: Proceedings of the Twentysecond International Offshore and Polar Engineering Conference (ISOPE2012) on Rhodes, Greece, June 17-22, 2012. - 1098-6189 .- 1555-1792. - 9781880653944 ; 4, s. 681-687
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Konferensbidrag (refereegranskat)abstract
- Fatigue damage accumulation in ship structures is a continuous random process, which together with several sources of uncertainties in the fatigue analysis make the fatigue life prediction complex and difficult. It may be a plausible explanation to why fatigue cracks are found earlier than expected in many ocean-crossing vessels. The existence of fatigue cracks brings great challenges to the safety of ship structures, maintenance issues and costs. Various means should therefore be implemented to extend ships’ fatigue service life, for example, decrease cargo loadings and reduce ship speeds. Another alternative is to employ a ship routing design which can reduce/minimize the fatigue damage accumulation, denoted as ship fatigue routing here. This investigation presents a ship fatigue routing procedure, using a simple spectral method developed by the authors, and the analysis of long-term fatigue assessment of a typical container vessel. The potential benefits of using the proposed ship fatigue routing procedure is demonstrated by a case study of a 2,800TEU container ship, using data from full-scale measurements, hindcast data and numerical analysis. It is found that, at least for the current vessel, the fatigue life can be extended by at least 50% by choosing more well-suited “optimum” ship routings.
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