| 1. |
- Li, Zhiyuan, 1974, et al.
(författare)
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Fatigue damage assessment of container ships concerning wave-induced torsion
- 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
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Konferensbidrag (refereegranskat)abstract
- The traditional method to assess fatigue damage of ship structures assumes moderate wave amplitudes and linear responses. This method can be questioned when applied on container ships that are characterized by large deck openings, because the low torsion rigidity of this type of ship makes it sensitive to oblique waves. In this paper, the 3D hydrodynamic code WASIM is used to simulate a 4400 TEU container ship operating in the North Atlantic Ocean. Nonlinear wave loads are utilized for direct calculation of the stress histories under severe sea states. The warping stress from wave-induced torsion is separated from the stress components from vertical and horizontal bending. The contribution to fatigue damage accumulation from warping stresses is evaluated. For comparison, the results from the numerical simulations and fatigue calculations are verified with full-scale measurements made on a similar type of container vessel.
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| 2. |
- Mao, Wengang, 1980, et al.
(författare)
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Development of a fatigue model useful in ship routing design
- 2010
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Ingår i: Journal of Ship Research. - 1542-0604 .- 0022-4502. ; 54:4, s. 281-293
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, a simple fatigue estimation model, only using encountered significant wave height, is used for predicting fatigue accumulation of a vessel during a voyage. The formulation of the model is developed based on the narrow-band approximation. It is assumed that the significant response range, hs, has a linear relationship with encountered significant wave height, Hs. The mean stress up-crossing frequency, fz, is represented by the corresponding encountered wave frequency and it is expressed as a function of Hs. The capacity and accuracy of the model is illustrated by application on one container vessel’s fatigue damage accumulation in an amidships detail, operating in the North Atlantic during 2008. For this vessel, all the necessary data needed in the fatigue model, and for verification of it, was obtained by measurements. The results from the proposed fatigue model are compared with the well-known and accurate rainflow analysis. Influence of nonlinearities, e.g. whipping, on fatigue damage predictions and extreme responses is also discussed.
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| 3. |
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| 4. |
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| 5. |
- Mao, Wengang, 1980, et al.
(författare)
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Estimation of wave loading induced fatigue accumulation and extreme response of a container ship in severe seas
- 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
- The hydrodynamic analysis of a 4400 TEU container ship with constant forward speed is carried out by the nonlinear numerical code WASIM in the time domain under severe sea states. Straightforward fatigue estimation is performed using the rainflow counting approach based on simulated time series of stresses. The narrow-band approximation, which has been validated in previous work with good accuracy by full-scale measurement of a 2800 TEU container ship, is implemented to estimate the fatigue damage based on the same responses. It is concluded that a slight deviation from the Gaussian process does not influence the fatigue estimation by narrow-band approximation. In addition, extreme response is defined by the level up-crossing approach. The Gaussian crossing model using Rice’s formula is employed to predict the extreme response based on the responses from above numerical analysis. It shows that the Gaussian model is not suitable for this prediction. A more complicated level crossing model is proposed which is based on the Laplace Moving Average method. Its accuracy in prediction of extreme responses is analyzed and presented with good agreement by means of numerical simulations.
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| 6. |
- Mao, Wengang, 1980
(författare)
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Fatigue Assessment and Extreme Response Prediction of Ship Structures
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, a simplified narrow-band approximation model is proposed to estimate fatigue damage of ship structures, and an efficient method for extreme response predictions is also developed using upcrossing spectrums of ship responses. The proposed fatigue model includes two main parameters, significant stress range hs and zero upcrossing frequency fz. The first parameter is assumed to be proportional to significant wave height Hs through a factor C, derived from a linear hydrodynamic theory. The value of C depends on the mission conditions. The zero upcrossing frequency is approximated by the encountered wave frequency, where the wave period Tz is deduced to be an explicit function of Hs. The fatigue model is validated by the “accurate” rainflow method with less than 10% of discrepancy. The uncertainties of fatigue life predictions are studied by the safety index, employing the proposed fatigue model. It is shown that the safety index computed using the fatigue model agrees well with that computed from the measurements. With respect to the fact that ship responses are non-Gaussian, the Laplace Moving Average (LMA) method and a transformed Gaussian approach are studied to model the non-Gaussian responses. The transformed Gaussian approach is adopted for the computation of the upcrossing spectrums. The extreme ship responses are then estimated from the upcrossing spectrums. The standard deviation, zero upcrossing frequency, skewness and kurtosis of responses are needed to compute the upcrossing spectrums. It is shown that the extreme responses computed by the proposed method agree well with those computed by the standard engineering method using the measured responses.
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| 7. |
- Mao, Wengang, 1980, et al.
(författare)
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Safety Index of Fatigue Failure for Ship Structure Details
- 2010
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Ingår i: Journal of Ship Research. - 1542-0604 .- 0022-4502. ; Vol. 54:No, 3, s. pp. 197-208
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Tidskriftsartikel (refereegranskat)abstract
- One way to assess the uncertainty in fatigue damage analysis is to use a so-called safety index. In the computation of such an index, the variation coefficient for the accumulated damage is required. In this paper the expected fatigue damage and its coefficient of variation are firstly estimated from measured stress. Secondly, when suitable stress measurements are not available these are computed from models for damage accumulation and sea states variability. Stresses during the ship sailing period are regarded as the nonstationary, slowly changing, Gaussian processes, and hence damage accumulation, during encountered sea state, can be approximated by an algebraic function of significant wave height, ship speed, and heading angle. Further, the space time variability of significant wave height is modeled as a log normal field with parameters estimated from the satellite measurements. The proposed methods to estimate uncertainties in the damage accumulation process are validated using full-scale measurements carried out for a container vessel operating in the North Atlantic.
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| 8. |
- 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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