1994

Linjama, Jukka

This study deals with the measuring techniques for estimating and characterising vibration propagation in thin beams and plates. The measurement method applied was the vibrational intensity technique for bending waves, which uses two or four motion sensors. This thesis contributes to method development and to the experimental verification of the methods. The aim of the experiments was (a) to test the accuracy and limitations of the known methods in controlled conditions and (b) to verify the alternative forms and extensions to the known methods that were developed. For bending vibration of beams, estimates for the moment and shear force components of power and the impedance are derived, and new estimates for the reflection coefficient are given. The frequency response technique with one reference signal is introduced and applied in experiments. For bending waves in plates, the applicability of the approximative two-transducer intensity method in practice is investigated, paying particular attention to the effect of the nearfields. The applicability of commercial laser-doppler vibrometers as motion sensors for use in vibrational intensity measurements is assessed. New energetic quantities, apparent intensities and field descriptors, are proposed to be used in connection with intensity measurements. Approximations for these quantities, which may be regarded as extensions of the two-transducer method, are derived and implemented in the experiments.