### ASA 124th Meeting New Orleans 1992 October

## 3aSA2. Modeling and numerical method in the medium frequency range for
vibroacoustic predictions using theory of structural fuzzy.

**Christian Soize
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*Structures Dept., ONERA, BP 72, F-92322 Chatillon Cedex, France
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In linear dynamic analysis of complex mechanical systems, the structural
fuzzy is defined as the set of minor subsystems that are connected to the
master structure but are not accessible by classical modeling. The notion of
master structure is presently extended to other elements such as an external
dense compressible fluid strongly coupled with the primary structure. For the
low-frequency (LF) dynamic analysis, the modeling of the structural fuzzy is
commonly made with a system of masses. If the LF modeling of the structural
fuzzy is applied in the medium-frequency (MF) domain, there result some large
differences between calculations and experiment. It is therefore necessary to
take into account internal degrees of freedom of the structural fuzzy. A global
probabilistic modeling of the structural fuzzy is proposed to improve the
calculated estimates of the MF vibrations into the master structure and of the
far field radiated by itself. In this paper, (1) a probabilistic modeling of
the structural fuzzy is presented, (2) a probabilistic behavior law of the
structural fuzzy is built, (3) the random vibrations in the master structure
with a structural fuzzy and the far field radiated are studied, (4) the
numerical analysis needed to implant the method is presented, and (5) numerical
simulations on standard structures and on a complex industrial submarine
structure are shown.