Index of content:
Volume 118, Issue 2, August 2005
- STRUCTURAL ACOUSTICS AND VIBRATION 
Theoretical and experimental vibration analysis for a piezoceramic disk partially covered with electrodes118(2005); http://dx.doi.org/10.1121/1.1940468View Description Hide Description
Using the linear two-dimensional electroelastic theory, the vibration characteristics of partially electrode-covered thin piezoceramic disks with traction-free boundary conditions are investigated by theoretical analysis, numerical calculation, and experimental measurement. Four types of piezoceramic disks are discussed owing to the different electrode-covered distribution and electrical boundary conditions. It is found that when an alternating electrical potential is applied to the piezoceramic disk with axisymmetric partial electrodes, not only extensional but also transverse vibrations occur in resonance. The electrode-covered distribution influences the extensional vibration characteristics of piezoceramic disks; however, this phenomenon is not present for the transverse vibration. In this paper the optical speckle interferometry and electrical impedance analysis are employed to validate the theoretical analysis. Numerical calculations based on the finite element method are performed to make comparison with the theoretical and experimental results. According to the theoretical calculation, the variations of extensional resonant frequencies and dynamic electromechanical coupling coefficients depending on the various electrode-covered ratios are also investigated in this work. For the type with circular partial electrodes being connected, it is shown that the coupling coefficients will reach a maximum at the fundamental mode and drop to zero at the overtone mode for certain electrode-covered ratios.
118(2005); http://dx.doi.org/10.1121/1.1953227View Description Hide Description
Congruent coordinate transformations are used to convert second-order models to a form in which the mass, damping, and stiffness matrices can be interpreted as a passive mechanical system. For those systems which can be constructed from interconnected mass, stiffness, and damping elements, it is shown that the input–output preserving transformations can be parametrized by an orthogonal matrix whose dimension corresponds to the number of internal masses—those masses at which an input is not applied nor an output measured. Only a subset of these transformations results in mechanically realizable models. For models with a small number of internal masses, complete discrete mapping of the transformation space is possible, permitting enumeration of all mechanically realizable models sharing the original model’s input–output behavior. When the number of internal masses is large, a nonlinear search of transformation space can be employed to identify mechanically realizable models. Applications include scale modelvibration testing of complicated structures and the design of electromechanical filters.
118(2005); http://dx.doi.org/10.1121/1.1932212View Description Hide Description
The paper describes a model to calculate the transmission loss of both curved laminate and sandwich composite panels within statistical energy analysis (SEA) context. The vibro-acoustic problem is developed following a wave approach based on a discrete lamina description. Each lamina is considered to consist of membrane, bending, transverse shearing and rotational inertia behaviors. Moreover, the orthotropic ply angle of each lamina is considered. Using such a discrete lamina description, the dispersion behaviors of the panel are correctly represented. Using the dispersion curves, the radiation efficiency, the modal density, as well as, the nonresonant and the resonant transmission are computed. Moreover, expression for the evaluation of the ring frequency and the critical frequencies of such panels is given. The described model is shown to handle accurately, both laminate and sandwich composite shells. Additionally, a transmission loss test is presented to confirm the validity of the presented model.
Experimental investigation of targeted energy transfers in strongly and nonlinearly coupled oscillators118(2005); http://dx.doi.org/10.1121/1.1944649View Description Hide Description
Our focus in this study is on experimental investigation of the transient dynamics of an impulsively loaded linear oscillator coupled to a lightweight nonlinear energy sink. It is shown that this seemingly simple system exhibits complicated dynamics, including nonlinear beating phenomena and resonance captures. It is also demonstrated that, by facilitating targeted energy transfers to the nonlinear energy sink, a significant portion of the total input energy can be absorbed and dissipated in this oscillator.
118(2005); http://dx.doi.org/10.1121/1.1940449View Description Hide Description
A state-space coupling method is presented for the direct solution of fluid-loaded natural frequencies and mode shapes of plates. This method expands the frequency-dependent term in the Rayleigh integral in a power series on circular frequency. After factoring out the frequency term from the integrands, integration involved in setting up the acoustic impedance coefficient matrices is confined to a frequency-independent part. The acoustic impedance coefficient matrices are therefore frequency-independent and can be coupled directly with the structural matrix into a canonical state-space form to yield the fluid-loaded modes via the direct eigenvalueanalysis. A fluid-loaded stiffened plate is involved to demonstrate the method. Numerical results of the fluid-loaded natural frequencies, mode shapes, and modal damping ratios are given to show the efficacy of the state-space coupling method.