Active noise control procedures in a generic composite helicopter cabin

Abstract

Composite materials are used more and more in the helicopter domain, instead of metal structures, which leads toward a degradation of the acoustic comfort in the cabin because of the decreasing mass and low performances of composites. So, active control procedures can be used in addition to passive treatments. The paper deals with the feasibility of active noise control procedures in order to reduce the radiated noise generated in a composite helicopter cabin, through the mechanical deck. A generic composite fuselage is excited by four shakers to simulate the noise produced by the four gear box fastenings. Four decorrelated random signals are generated to produce forces equal to about 1 N into the 500–3000 Hz band. Modal analysis and structural intensity measurements are achieved on the mechanical deck, and pressure fields are acquired in two parallel planes. Moreover, theoretical acoustic modes of the cavity are computed with a FEM model. These different data allow one to analyze the structural behavior of the mechanical desk and the structure–cavity coupling. Four piezoelectric actuators, located in front of the excitations, are controlled by feedforward algorithms to reduce the pressure fields with different types of error sensors and cost functions.