Numerical and experimental analysis of the dynamic behavior of main engine foundations

The value of a super-yacht project can be measured in terms of cost, size, autonomy, design and lately also in terms of comfort on board, since the competition among the various shipyards is now being played on quality of living onboard , as well as on more traditional aspects such as design, cost and performance. Since the on-board comfort has become a performance parameter, the vibration and noise level are topics of increasing interest to ship-owners, ship designers and builders. The engine-mount loading is the primary source of vibrations onboard boats. Indeed, the increased sophistication of the on board outfitting has required lower limits levels on vibration and noise over the last decade. By contrast, the current trend aims at producing faster ships, equipped with increasingly powerful engines, which imply, in the absence of proper measures of contrast, higher levels of vibration and noise. In order to improve the comfort level onboard their superyachts, Azimut|Benetti Shipyards, in cooperation with the Naval Architecture Section of the DITEN Department of the University of Genova and with the DIA Department of the University of Trieste, began an investigation campaign of the dynamic response of the marine Diesel engine foundations. The dynamic behavior of the Diesel engine foundation is a paramount importance to evaluate its effectiveness in the coupling system between the Diesel engine and the ship structures. An accurate study of the dynamic behavior of these elements allows both avoiding high levels of vibrations in the low frequency range and limiting the structure-borne noise levels in the high frequency range. The knowledge of dynamic response of Diesel engine foundations is a key factor for the comfort assessment in the first phase of ship and superyacht design with regards to noise and vibration characteristics. Given the labour time needed to perform a dynamic FE analysis, with particular reference to mobility analyses, in this study a procedure to individuate the optimum dimensional characteristics of engine foundations numerical models has been performed, in order to achieve in reasonable calculation times reliable results. The investigation has been supported by a wide measurement campaign by which it has been possible to make a validation of numerical results