Experimental Investigation of Vertical Forces in Pure Sway Motion for a Free Surface Roll Damping Tank
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- Institutt for marin teknikk 
In this thesis the objective was to perform experiments in pure sway motion of a model roll damping tank, to try and locate a connection between the vertical forces that develop in such condition, and several influential parameters such as excitation frequency, excitation amplitude and water filling level. The frequency spectrums of the vertical forces that develops at these differing parameters were instrumental in the investigation. If a relationship existed, it was attempted to get a full mathematical description of this connection. First an in depth investigation of the theoretical aspects of a free surface roll damping tank was performed. Here important subjects were discussed, such as the different main roll damping tank configurations available. Furthermore, as a free surface tank was the main area of focus, the thesis goes on to perform a thorough theoretical investigation of the function and design of such a tank. Lastly, as the tank was a model of a full scale version, the thesis proceeds to discuss different theoretical aspects related to scaling in a hydrodynamic problem. After a thorough literature review of the free surface tank, the proceeding chapters goes on to discuss the overall setup, and the general preparation procedure applied before the experimental investigation. Described first is the model rig and the instrumentation applied in the setup. Then, the experiment strategy used when conducting the investigation is explained, as well as the preparation procedure of the equipment in the setup. Finally, the thesis proceeds to describe the filtering procedure, including the study performed of the accuracy of the experimental data; as part of ensuring that the results are trustworthy these procedures were necessary. In the closing chapters of this thesis the post-processing of the experimental data is performed. Here the results are analyzed, and it is found that a connection exists between the vertical forces and the parameters tested. A full mathematical description was not established, however, the relationship was partially expressed by a Gaussian model which were a function of the excitation frequency.