This dissertation focuses on nonlinear modal interactions in plates. Our first investigation involved the activation of a two-to-one internal resonance in the response of a metallic cantilever plate. Although the plate was excited around the frequency of its second bending mode, its response contained a contribution from its first torsional mode. The frequency ratio between the bending and torsional modes was nearly two-to-one.
Next, we investigated the energy transfer from high-frequency to low-frequency modes in a cantilever graphite-epoxy composite plate (90/30/ — 30/ — 30/30/90)<sub>s</sub>. The plate was excited around the natural frequency of its seventh (third torsional) mode. For some excitation amplitudes and frequencies, we observed the activation of a low-frequency (first bending) mode accompanied by an amplitude and phase modulation of the seventh mode.
We studied combination resonances in the responses of cantilever composite plates with the layups (90/30/ — 30/ — 30/30/90)<sub>s</sub> and (—75/75/75/ — 75/75/ — 75)<sub>s</sub> to harmonic base excitations. We activated the combination resonance f<sub>e</sub>≈ ω₂ + ω₇ in the (90/30/ — 30/ — 30/30/90)<sub>s</sub> plate, where the w; are the natural frequencies of the plate and f<sub>e<sub> is the excitation frequency. In the (—75/75/75/ — 75/75/ — 75)<sub>s</sub> plate, we activated the external combination resonance f<sub>e<sub>≈ 1/2(ω₂+ω₅) and the combination internal resonance f<sub>e</sub>≈1/2(ω₂+ω₁₃) ≈ ω₈.
We carried out an experimental-modal analysis (EMA) of a nonclassically supported plate with and without a constrained-layer damping (CLD) patch attached on its upper left-hand side surface. The natural frequencies and mode shapes were used to ascertain the effect of the CLD patch. / Ph. D.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/39144 |
| Date | 14 August 2006 |
| Creators | Oh, Kyoyul |
| Contributors | Engineering Mechanics, Nayfeh, Ali, Mook, Dean T., Hyer, Michael W., Hendricks, Scott L., Burns, John A. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation, Text |
| Format | xi, 116 leaves, BTD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 32777934, LD5655.V856_1994.O4.pdf |
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