Vibration analysis of a 40m ice class motor yacht

Abstract

The purpose of this Master Thesis is the study of vibrations of the hull, deck and structure of an Ice Class motor yacht 40 m in length under construction at Cerri Cantieri Navali. This investigation is carried out because of the shipyard’s necessity to gather information about the vibration behavior of the yacht, regarding that is not a conventional structure because the requirements of the Classification Society to be approved as an Ice class yacht, it is considerably stiffer than regular semi displacement motor yachts of the same size. Vibration analysis during the construction process are of great importance, as soon is it possible to detect any probable vibration issue, sooner the changes on structure could be done. Vibration issues are determinant, not only for structural reasons but also when high standards are expected on comfort and wellbeing. If the limits stablished by the standards are not exceeded, the habitability will be good, which means that no health damage will occur.

At the stage of this study, the hull, structure, deck and upper deck are going to be finished. This is a perfect condition to perform measurements and analyze differences between experimental results and FEM analysis, considering that there is no uncertainties regarding damping, and induced errors on input data. The objective of this study is to determine how accurate this FEM model is, to allow further investigations on this project. Construction plans, technical information and assistance is provided by the shipyard's technical office.

The vibration analysis is developed through the use of the Nastran/ Patran finite element code, the modelling of all the mentioned above was performed to obtain the natural mode and to carry out the dynamic analysis, and after compared with the excitations