Index of content:
Volume 126, Issue 3, September 2009
- STRUCTURAL ACOUSTICS AND VIBRATION 
126(2009); http://dx.doi.org/10.1121/1.3183376View Description Hide Description
Contact between sliding bodies can cause vibrations leading to instability. The problem of squeal due to high frequency noise from brake systems is due to unstable vibrations generated at the contact interface between the pad and disk. Squeal noise is characterized by extreme unpredictability due to large uncertainties on the values of parameters of the system. Parametrical complex eigenvalueanalysis is a common tool used to predict squeal instability. In this paper a substructured linear finite element model of a simplified brake system is studied. A parametrical analysis is focused on a test case and compared to experimental results. The analysis is developed as a function of the parameters assumed to be the most influential but also the most uncertain: friction coefficient and the parameters driving the dynamics of the system. The uncertainties are accounted for by considering parameters such as random variables. A Monte Carlo simulation and a probabilistic technique are performed simultaneously to study the probability of squeal occurrence. Finally, a reduced model based on the transfer function calculated at the contact is developed to perform the analysis with reduced computational effort.
126(2009); http://dx.doi.org/10.1121/1.3183368View Description Hide Description
A classical simply-supported beam is modified by tilting the pad constraining the roller. The consequence is that the axial and transverse displacements of the beam are coupled by the boundary conditions. The eigenanalysis methodology is extended to this unusual situation where displacement components are coupled, even though each displacement has a different associated wavenumber. The dependence of the natural frequencies on the tilt angle is evaluated and typical results for the eigenfunctions are presented. The response of the beam to harmonic point force excitation is synthesized by constructing a modal series. Frequency response functions at the drive point for cases where the force is applied in the axial and transverse directions are computed. The results indicate that deviations of the tilt angle from zero affect the displacement in the direction that is orthogonal to the excitation much more than the driven displacement.
126(2009); http://dx.doi.org/10.1121/1.3177262View Description Hide Description
The elastodynamic Green function can be retrieved from the cross correlations of the motions of a diffuse field. To extract the exactGreen function, perfect diffuseness of the illuminating field is required. However, the diffuseness of a field relies on the equipartition of energy, which is usually described in terms of the distribution of wave intensity in direction and polarization. In a full three dimensional (3D) elastic space, the transverse and longitudinal waves have energy densities in fixed proportions. On the other hand, there is an alternative point of view that associates equal energies with the independent modes of vibration. These two approaches are equivalent and describe at least two ways in which equipartition occurs. The authors gather theoretical results for diffuse elastic fields in a 3D full-space and extend them to the half-space problem. In that case, the energies undergo conspicuous fluctuations as a function of depth within about one Rayleigh wavelength. The authors derive diffuse energy densities from both approaches and find they are equal. The results derived here are benchmarks, where perfect diffuseness of the illuminating field was assumed. Some practical implications for the normalization of correlations for Green function retrieval arise and they have some bearing for medium imaging.