Structures Dept., ONERA, BP 72, F-92322 Chatillon Cedex, France
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.