Attenuation of acoustic waves and mechanical vibrations at low frequencies by a nonlinear dynamical absorber

International audienceAt the present time, the attenuation of acoustic waves and mechanical vibrations at high and middle frequencies is well known and easily done, especially with dissipative materials. However, this attenua-tion is much more difficult to realize at low frequencies because of the large wavelengths. In the work presented here, we propose to reduce the noise and the vibrations at low frequencies over a broad frequency band by means of nonlinear absorbers allowing a transfer and a dissipation of the energy. These absorbers are randomly arranged in a matrix and have a nonlinear dynamical behavior. The absorber consists of a cantilever beam supporting a concentrated mass at its end. It is designed in order to obtain a nonlinear dynamical behavior in the low-frequency band due to the finite displacements of the beam. This mechanical system is modeled by a mass-spring-damper system with a nonlinear stiffness and a nonlinear damping. Indeed, nonlinearity allows attenuation over a broader frequency band, unlike linear systems which only generate a reduction over a narrow frequency band around the resonance, which makes it possible to reduce the number of absorbers needed for a given attenuation. We will first present the design of the nonlinear absorber optimized using stochastic modeling in order to obtain the most adequate nonlinear response possible. Then, experimental results will be presented as well as their comparisons with the numerical predictions