Numerical Dynamic Analysis of a Composite Pleasure Craft for Comfort Improvement

Abstract

Comfort on board is one of the most important design aspects of present pleasure boats, in addition to performance and aesthetics. In order to reduce construction costs and improve quality, it is necessary to deal with vibration and noise issues in the early stages of design to obtain preliminary information about the structure's response to vibrations before the project reaches a stage in which it is difficult to make structural modifications. In this paper, the modal and harmonic analyses of a 25 m motor yacht made of composite materials are performed to investigate the structure's dynamic behavior and improve the comfort level. The numerical verification is carried out by conducting a series of dynamic analyses on a finite element model based on sequential phases and taking into account the model with and without added mass. The modal analysis is carried out for two configurations, that is the engines installed with rigid connections and with elastic connections) in order to determine all the global and local natural frequencies and to check the possibility of the occurrence of the resonance phenomenon. The harmonic analysis is executed first by applying an explorative load at the after keel line of the boat to determine the response peaks and estimate the correct damping coefficients, and secondly by applying the load generated by the main propulsion sources to verify the onboard comfort. The vibration velocity spectra obtained by the numerical model of the boat are compared with guideline limits and the results showed that the vibration velocity in different areas of the boat remains within the limit levels imposed by the British Standard ISO 20283-5:2016 concerning habitability, and the limits set by RINA Rules concerning comfort.