Pestelli C., Palloni F., Bregant L., Castellani F.

As in all industries, also for the production of Large diesel engines the development and manufacturing costs have to be minimized to improve the net margins. Due to the importance and the life dependency related to these products, high level of performances and reliability are main priority in the process. Wartsila as world leader in energy systems devotes a lot of efforts to improve the quality of its methodologies and procedures. Large diesel engines represent for engineers a challenging product: they are big, heavy, dangerous. Testing them is expensive and requires specific techniques and procedures. The authors would like to highlight these problems and their influences and at the same time show that, with the appropriate techniques, good match between numerical simulations and test can be achieved. The paper reports about the analysis of a “genset”, an aggregate formed by tree main parts: the diesel engine, the electric generator and the common base. These three elements combined weight roughly 200 tons, occupying a space of about 260 cubic meters. The finite elements model and the measured FRFs acquired during a modal test in cold conditions were available. Due to the presence of many modes with small frequencies differences and the overlapping of rigid body modes of the different subcomponents with the flexible modes of the complete genset, the influence of the resilient mounting stiffness among the different part and elastic coupling joint between engine and alternator have been considered with special care. In order to compare the experimental mode shapes with the calculated ones and to perform the sensitivity and updating analysis, the commercial software FEMTools has been used both in fully automated and manually controlled procedure. The paper shows the accuracy obtained in the different cases and highlights the sensible spots where modelling and the testing require more care.