| 1. |
- Mao, Wengang, 1980, et al.
(författare)
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A regression and beam theory based approach for fatigue assessment of containership structures including bending and torsion contributions
- 2015
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Ingår i: Marine Structures. - : Elsevier BV. - 0951-8339. ; 41:1, s. 244-266
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Tidskriftsartikel (refereegranskat)abstract
- Container shipping has been expanding dramatically during the last decade. Due to their special structural characteristics, such as the wide breadth and large hatch openings, horizontal bending and torsion play an important role to the fatigue safety of containerships. In this study the fatigue contributions from vertical bending, horizontal bending and torsion are investigated using full-scale measurements of strain records on two containerships. Further, these contributions are compared to results from direct calculations where a nonlinear 3D panel method is used to compute wave loads in time domain. It is concluded that both bending and torsion have significant impacts on the fatigue assessment of containerships. The stresses caused by these loads could be correctly computed by full-ship finite element analysis. However, this requires large computational effort, since for fatigue assessment purposes the FE analysis needs to be carried out for all encountered sea states and operational conditions with sufficient time steps for each condition. In this paper, a new procedure is proposed to run the structure finite element analysis under only one sea condition for only a few time steps. Then, these results are used to obtain a relationship between wave loads and structural stresses through a linear regression analysis. This relation can be further used to compute stresses for arbitrary sea states and operational conditions using the computed wave loads (bending and torsion moments) as input. Based on this proposed method for structure stress analysis, an efficient procedure is formulated and found to be in very good agreement with the full-ship finite element analysis. In addition it is several orders of magnitude more time efficient for fatigue assessment of containership structures.
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| 2. |
- Ogeman, Viktor, 1988, et al.
(författare)
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Comparison of computational methods for evaluation of wave-load-induced fatigue damage accumulation in a containership structure detail
- 2013
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Ingår i: Proceedings of The 5th International Conference on Computational Methods in Marine Engineering (MARINE 2013). - 8494140744 ; , s. 342-353
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Konferensbidrag (refereegranskat)abstract
- In this study different methods, from linear strip theory to more complex non-linear panel methods, are employed to estimate the hydrodynamic loads on a 4400TEU container ship. Subsequently, the structural stresses are computed using the finite element method and engineering beam theory. The calculated stresses are used to evaluate the fatigue damage in a detail of the ship structure using the rainflow counting method and different spectral methods. It is concluded that, for the studied part of the structure with governing uniaxial stresses due to wave loading, disregarding vibrational responses, it is sufficient to evaluate the fatigue damage using a spectral method, i.e. the so-called narrow band approximation, without any compensation.
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| 3. |
- Ogeman, Viktor, 1988, et al.
(författare)
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Uncertainty in stress concentration factor computation for ship fatigue design
- 2014
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Ingår i: Proceedings of The ASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering (OMAE 2014). - 9780791845424 ; 4A, s. 1-9
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Konferensbidrag (refereegranskat)abstract
- The stress concentration factor is often used to compute the local stress of ship structures when the hot-spot approach is chosen for fatigue assessment, where the computed damage is proportional to the power 3 or 5 of the stress concentration factor (SCF). It means a little change of the SCF value could lead to a huge difference in fatigue life predictions. Hence the methodology of computing the SCF should be defined clearly in classification society guidelines. In this study, different methods to compute SCF based on class guidelines are firstly surveyed. Then some fuzzy explanations in the computation methods are identified. The consequences of the fuzzy definitions may lead to large variation of SCF computations. A rather simple structural detail with cracks observed is used for this investigation. To this structural detail, two alternatives to compute the local stress for fatigue assessments are compared. Some recommendations to reduce the SCF to increase its fatigue life are also taken into account to guide the local design of such structural details. The difference of fatigue life predictions using these proposed approaches is compared, while at least 50% difference is expected even though the guidelines from the same classification are employed. Further, it is supposed to have more impacts to the final results if a more complex detail is chosen.
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