Abdelkader N., Nouredine C., M.Said B., M. Ouali S.

Influence of Frahm’s damping on the vibro-acoustic characteristics of a rotor structure The present Work consists to evaluate by the method of the opposites and retiming the influence of damping of Frahm in its borderline case, on the vibroacoustic of a rotor structure. The structure is dynamically balanced by small masses fixed on the discs of the rotor. The rotor coupled with the engine is rigidly fixed at a platform. The platform is provided with a device of calibration of range dynamic absorbers. The variable exitation of the rotor is obtained through a variable speed transmission which makes it possible to have the parameters of the critical modes of the system. The external coupling is a condensation of the acoustic pressure on the structural equation of balance. It is the load which depends directly on the displacement and the elastic modes of the structure. This makes it possible to establish the matrix structure between the displacement and the acoustic excitation on one hand and on the other hand, the transfer function between the constraints and the acoustic excitation. A study and a temporal and frequential representation of the vibratory behaviour of the platform with and without the dynamic shock absorber with an experimental validation on the Eigen frequencies obtained by the finite element method. Also, the determination of the shock absorber of Frahm, starting from a given range of dampers of vibration and the evaluation of its first pulsation. Keys words: damping absorber of Frahm / transfer function/damping/Dynamic loads / vibro-acoustic.