Study of a new solution to reduce vibration transmission through pillars on board ships

In the last decades, the demand for higher comfort levels on board of ships has increased year by year. Comfort has always been a key factor in cruise ships and pleasure yachts, though recently, the attention to the condition of seafarers has also increased. Several studies in the last years focused on how to improve comfort on board, suggesting methods and analytical instruments for the prediction of vibration and noise levels during the ship design process. Other studies investigated how to reduce the vibration transmitted from the machinery to the ship or how to reduce the vibration of radiating surfaces with the aim of reducing the noise levels on board. Some early studies, addressed pillars as a key factor in vibration transmission, this viewpoint was shared also by shipbuilding companies. Aim of this work is to study a device for the reduction of vibration transmission through the pillars. This research is a first step in the development of such device. The main element of the isolator is a resilient element. In order to guarantee the structural capability of the device, the design loads acting on the pillars have been evaluated on a reference yacht and on a cruise ship using both scantling rules and direct FE calculation. Prototypes with different designs have been built and their dynamic characteristics have been studied in a laboratory experimental facility basing on the ISO 10846 standard for the laboratory measurement of the vibro-acoustic properties of isolators. The prototype design showing the lowest transmissibility has been tested on a real scale mock-up representing a portion of two decks with the typical structure of a cruise ship. The real scale test shows the effectiveness of the isolator in the reduction of the vibration transmitted through the pillar. In addition, a simplified finite element model of the isolator has been set up using the data measured on the mock-up structure and the simplified model has been used to study the isolator effectiveness on a superyacht finite element model. The comparative numerical study and most of all the experimental tests led to very positive results which could pave the way to promising developments in the future.