We experimentally investigated nonlinear combination resonances in two graphite-epoxy cantilever plates having the configurations (90/30/-30/-30/30/90L and (-75/75/75/-75/75/-75)~. As a first step, we compared the natural frequencies and modes shapes obtained from the finite-element and experimental-modal analyses. The largest difference in the obtained frequencies for both plates was 6%. Then, we transversely excited the plates and obtained force-response and frequency-response curves, which were used to characterize the plate dynamics. We acquired time-domain data for specific input conditions using an A/D card and used them to generate time traces, power spectra, pseudo-state portraits, and Poincarg maps. The data were obtained with an accelerometer monitoring the excitation and a laser vibrometer monitoring the plate response. We observed the external combination resonance f~ ~ a)2 -t-037 in the quasi-isotropic plate and the external combination resonance f~ ~ (1/2) (a~2 + cJs) and the internal combination resonance f~ ~ w8 ~ (1/2)(co2 + w13) in the +75 plate, where the wi are the natural frequencies of the plate and fZ is the excitation frequency. The results show that a low-amplitude high-frequency excitation can produce a high-amplitude low-frequency motion.
We demonstrate a compact extrinsic Fabry-Perot interferometer-based fiber-optic sensor that uses magnetostrictive amorphous metallic wire Unitika AF-10 (Fe77.5B15Si7.5) as a sensor gauge for measuring dc magnetic fields. We present a theoretical model based on a Gaussian electric field distribution to analyze the sensor operation as a function of longitudinal air-gap separation. The model shows good agreement with the experimental results. A resolution of 50 nT over a range of 50-40,000 nT with a simple passive temperature-compensation method is obtained.
The objective of the present article is to experimentally observe and characterize the transfer of energy from low-amplitude, high-frequency modes to high-amplitude, low-frequency modes. The subject of the study is a three-beam frame. The excitation amplitude is restricted to below 2 g peak. The authors have focused on observing, characterizing, and documenting the excitation of the first mode by high-frequency forcing. The energy-transfer processes are identified by power spectra and characterized further by frequency and amplitude sweeps. The energy-transfer routes observed in the experiment are subharmonic resonance of order one-half, combination resonance of the additive type, and interaction between widely spaced modes. In the latter route, an excitation at a frequency that is more than 100 times the first-mode frequency has been observed to excite the first mode.
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