Development of an NVH Methodology for Superyacht Structure

One of the most important aspect of superyacht design is the comfort on-board in terms of vibration and noise performance. While NVH (Noise Vibration Harshness) analysis has been well established in the automotive industry, it is a recent concern to the marine industry, reflected in the new rules and regulations issued by the Classification Societies for the evaluation of maximum noise and vibration. In order to improve the comfort level onboard their superyachts, a famous italian superyacht shipyard, in cooperation with the European Boat Design Innovation Group (EBDIG) partners, Genoa University and Coventry University, developed an NVH methodology for superyacht superstructures. This began with a comprehensive investigation into the dynamic behaviour of superyacht structures and a review of existing comfort rules. The investigation involved FEA of a 60m superyacht. The results of modal and transient analyses were compared with experimental data gathered during the vessels construction to validate the FEA model. A reliable predictive analysis is critical to avoid problems with the completed hull, due to the significant challenges of modifying the dynamic behaviour of the hull structure after construction. Any action towards vibration and noise reduction generally implies a significant increase in structure weight. The reduction of which continues to be a key objective of superyacht design. Even when the general structural vibration issues are solved, some vibration problems can persist at a local level. To address this a post construction solution was developed, which involved the application of a "Tuned Mass Damper" system. A 60m super yacht after refitting, exhibited unpleasant vibrations on the highest decks, which were mitigated by the application of a TMD. In this paper the NVH methodology is presented starting from the initial natural frequencies analysis and ending with the FEA simulation and optimisation of a passive control device, designed to be easily adapted to the deck geometry.