Damping analysis of a free aluminum plate

An analysis of the energy dissipation sources acting in a vibrating aluminum plate is presented in this paper. In the first step, the contact-free modal analysis of a suspended plate is conducted using a laser vibrometer and an acoustic excitation to obtain reference data. The thin nylon suspension set-up guarantees a low boundary damping, which is assumed to be negligible. In the second step, a number of damping sources are modeled. Acoustic damping due to the noise radiation of the nonbaffled plate is computed using the boundary integral method and a light fluid approximation to express the vibroacoustic coupling in analytical terms. The damping due to the sheared air flow along the free-plate borders is determined on the basis of a simple two-dimensional boundary layer model. Thermoelastic damping is assessed using a Fourier series expression for the temperature field along with a perturbation technique to take thermoelastic coupling into account. Since no robust model is available so far to quantify viscoelastic material damping in aluminum, it is determined in a last step by subtracting measured values of damping from those previously computed. Aluminum viscoelastic damping turns out to be very small and almost independent of frequency.