Driving Point Transfer Functions Research Articles

Alternate methods for characterizing spectral energy inputs based only on driving point mobilities or impedances

This article analyses three characterization methods for spectral energy inputs to a linear time-invariant system. Analytical frequency domain formulations are examined for discrete vibratory systems and one-dimensional continuous structure (undergoing longitudinal or flexural motions) given a harmonic force excitation. Two existing methods that have been proposed by prior researchers are first critically examined. In particular, the driving point transfer functions and their derivatives with respect to frequency are analyzed for an appropriate application to the energy characterization scheme and to determine the sources of error. Then, a new (third) scheme is proposed that is more suitable over low and mid frequency regimes, based on a proper interpretation of the driving point mobilities or impedances and their derivatives. The new method is found to be insensitive to the driving point mobility or impedance formulations, unlike the existing methods. It does yield consistent results, without requiring a prior knowledge of the transfer functions. Finally, the role of structural loss factor has been clarified in the context of the stated problem.

프로펠러 날개의 진동특성에 대한 실험적 연구

An experiment method has been developed to analyse the vibration characteristics of marine propeller blades, and vibration tests have been carried out on the model scale propeller in air and in water. The driving point transfer function(acceleration/excitation force) has been measured and modified by compensating the attachment effect of the impedance head. The measured natural frequencies in air have been compared with the theoretical results by an in-house FEM code PROSTEC. The added masses have been derived by comparing the measured natural frequencies in air and in water, and the results have been compared to the results using existing formula based on experience.

Development of a new spectral energy formulation based on structural driving point mobilities or impedances

A new approximate method is proposed here that characterizes harmonic kinetic and potential energies of a system based on the driving point impedance or mobility. The proposed complex-valued formulation is compared with an existing, real-valued dynamic energy approximation method [J. Sound Vib. 217, 351–386; 247, 683–702]. The scope of this study is limited to the frequency domain analysis and harmonic excitation is applied to a linear time-invariant (LTI) system. Longitudinal and flexural motions of a finite beam along with some discrete system examples are employed to illustrate the proposed scheme. Our method is based on an alternate interpretation of the associated driving point transfer functions and it approximates total time-averaged harmonic kinetic and potential energies. Numerical results show that our method yields a more accurate estimate than the existing method. Further, the proposed scheme is found to be insensitive to the driving point measures as consistent results using either impedance or mobility formulations, unlike the existing method, are predicted. Our characterization method is suitable for a moderately damped system at low and mid-frequencies, like the existing method.

Equivalent network synthesis for via holes discontinuities

A methodology is presented for the synthesis of the passive equivalent circuit of via holes in multilayer printed circuit boards. The paper describes the network synthesis starting from the extraction of the poles and residues from the driving point transfer functions for two port networks. The via hole is partitioned into elementary structures assumed not electromagnetically coupled and the scattering parameters for each one of them are evaluated by using a numerical approach suitably validated by comparison with results computed by other independent numerical methods. The equivalent circuit of the complete via hole is given by the cascading of the circuits of the elementary structures. The proposed technique is validated by comparing the computed scattering parameters with those from measurements for real test boards.

A note on the damping measurement of a composite steel sheet using beam specimens.

Free-free beams excited at the center are commonly used as the specimens of the measurement of damping performance of sheet materials. The antiresonances appearing in the driving point transfer function of the free-free beams are studied, and it is shown that resonance modes of a cantilever beam of a half length is observed at the antiresonances. The damping ratio estimated from the antiresonance trough is compared with the one evaluated from the resonance peak introducing a lumped parameter system. They coincide if the damping is assumed to be hysteretic, which agrees with the experimental results on a composite steel sheet with a viscoelasitc core layer.