1. 
 Li, Zhiyuan, 1974, et al.
(författare)

Fatigue damage assessment of container ships concerning waveinduced torsion
 2010

Ingår i: Proceedings of the ASME 29th International Conference on Ocean, Offshore and Arctic Engineering (OMAE 2010) in Shanghai, China, June 611, 2010.  9780791849101 ; 2, s. 151158201020140

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 waveinduced 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 fullscale measurements made on a similar type of container vessel.


2. 
 Mao, Wengang, 1980, et al.
(författare)

Development of a fatigue model useful in ship routing design
 2010

Ingår i: Journal of Ship Research.  00224502. ; 54:4, s. 281293

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 narrowband approximation. It is assumed that the significant response range, hs, has a linear relationship with encountered significant wave height, Hs. The mean stress upcrossing 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 wellknown and accurate rainflow analysis. Influence of nonlinearities, e.g. whipping, on fatigue damage predictions and extreme responses is also discussed.


3. 
 Mao, Wengang, 1980, et al.
(författare)

Estimation of wave loading induced fatigue accumulation and extreme response of a container ship in severe seas
 2010

Ingår i: Proceedings of the ASME 29th International Conference on Ocean, Offshore and Arctic Engineering (OMAE 2010) in Shanghai, China, June 611, 2010.  9780791849101 ; 2, s. 133141201020125

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 narrowband approximation, which has been validated in previous work with good accuracy by fullscale 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 narrowband approximation. In addition, extreme response is defined by the level upcrossing 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.


4. 
 Mao, Wengang, 1980, et al.
(författare)

The effect of whipping/springing on fatigue damage and extreme response of ship structures
 2010

Ingår i: Proceedings of the ASME 29th International Conference on Ocean, Offshore and Arctic Engineering (OMAE 2010) in Shanghai, China, June 611, 2010.  9780791849101 ; 2, s. 123131201020124

Konferensbidrag (refereegranskat)abstract
 Waveinduced 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 narrowband approximation for Gaussian load, is employed to include the damage contribution from waveinduced vibrations. In this model, the significant response range hs and the mean stress upcrossing frequency fz are simplified using only the waveinduced 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 whippinginduced 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 100year stress, based on a halfyear fullscale measurement. It is found that a more complicated nonGaussian model is required to consider the contribution from whipping.

