Numéro : 2498 - Year : 2007
Implementation of numerical methods for the vibration and acoustic analysis of ships
Jean-Marc SANCHEZ, DCN Ingénierie – Division Coque Structure et Emménagement – Département Analyse des Structures– Lorient (France)
Sébastien BOITEAU, DCN Ingénierie – Division Coque Structure et Emménagement – Département Analyse des Structures– Lorient (France)
Yann LE BRAS, DCN Ingénierie – Division Navire Armée – Environnement Militaire – Lorient (France)
In the course of the last few years, driven by increasingly precise requirements of clients, DCN has done a great deal for the control of the acoustic discretion of submarines and surface vessels concerned by anti-submarine warfare. Besides the performance in terms of noise in rooms (habitability), this article intends to present the activities of DCN in the field of decreasing noise radiated by the vibrations of the hull in the water.
Concerning the vibration and acoustic behaviour of a mechanical system subjected to excitation, it is usually allowed that its response be broken down into three distinct problems by their phenomenology and thus their method for numerical modelling. The first domain, called "modal" between 0 and 50 Hz will be illustrated by a comparison between calculation by finite elements and tests on the frigate. The second domain, that of medium frequencies, will be covered by the presentation of the optimisation of a frigate arch on a finite elements model. Finally the calculation by finite elements does not allow exceeding some hundreds of hertz; the high frequency field (between 300 Hz and 10 kHz) is commonly analysed using SEA (Statistical Energy Analysis) methods. The implementation at DCN of this numerical method will be illustrated by a parametric study of the hull-propulsor interaction on a La Fayette class frigate. The results of such studies finally allow retaining certain architectural concepts contributing to the reduction of the acoustic signature of ships.
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