Katsuyoshi Nagayasu

Vibration distribution reconstruction and control of a thin plate by using distributed PVDF sensors affixed to the plate

In this study, vibration distribution of a thin plate is detected using outputs from a number of long-span piezoelectric films that serve as distributed vibration sensors affixed on the plate. Using long-span piezoelectric films, only the integrated strains along the direction of the sensor span could be obtained. However, in the case that plural sensors were affixed and a kind of transformation was used, the vibration distribution could be obtained. We are considering applying the method for vibration control of space structures, namely antennas and/or solar battery paddles. In this study, basic technology for realizing the applications is presented. The strain distributions and the sensor outputs are predicted and calculated using NASTRAN (Finite Element Method). The strain distributions of a vibrating rectangular thin plate to which a number of long-span PVDF films were affixed are detected by experiment. These PVDF films are cut into several kinds of sinusoidal shapes and the outputs of the films are composed to the vibration distribution. This method is based on the theory that waves of any kind are composed by the sum of trigonometric function series. The usefulness of this approach is confirmed by comparing the calculational and experimental results.

Cavity resonances in a multi-coupled pipe system with equally spaced connecting holes.

Cavity resonances sometimes occur in pipe-like structures such as boiler exhaust ducts or heat exchangers. They are due to the self-sustaining oscillation mechanism. The noise is often eliminated by shifting the resonant frequencies away from the frequencies of the vortex generation. Thus the estimation of the resonant frequencies is of great importance in a practical sense. The calculation method of the resonant frequencies on the multi-coupled pipe system with equally spaced connecting holes was studied. It is found that the simultaneous equations derived by the acoustic modal analysis method can be divided into several independent groups due to the structural periodicity.