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Performance of ships in waves

Sigmund, Sebastian LSF

Due to environmental, economical and safety related issues, power prediction for operational conditions is desired within the maritime industry. In this context, accurate and reliable predictions of ship performance in waves is essential.

In this thesis, advanced numerical methods based on the solution of the Reynolds-averaged Navier-Stokes (RANS) equations were used to perform extensive and systematic investigations of the performance of ships in regular and irregular waves. In particular, the effects of ship speed, skin friction, wave steepness, and encounter angle on the wave-added resistance, and the interaction between wave radiation and wave diffraction forces were analyzed. Moreover, the influence of waves on the nominal wake fraction and the propulsion characteristics was investigated. Therefore, the ship's resistance, propeller open water characteristics and propulsion forces were computed for calm water and for waves. Additionally, the attainable ship speed of a free-running cruise ship in calm water and in regular and irregular waves was computed, and the speed loss was determined. Grid studies has been performed, mean values and oscillation amplitudes were determined carefully using Fourier analysis, and actual wave heights were monitored and used for normalization. Whenever possible, computational results were compared with the results of scale model test measurements. Overall, very good agreement was obtained.

Generally, it was shown that RANS methods are well suited for the prediction of ship performance in waves considering most nonlinear effects. The findings obtained in this work contribute to the understanding of the fundamental physics related to the wave-added resistance and about the propulsion of ships in waves in a sustainable manner. Furthermore, these findings may be used to further develop efficient prediction tools suitable for the ship design process.

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Sigmund, Sebastian: Performance of ships in waves. 2019.

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