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<div class="section abstract"><div class="htmlview paragraph">Local nonlinearities can affect the global dynamics of their linear host structures. In the context of fixed-wing aircraft, failure of store mounting can result in strong local nonlinearities. In this work, we experimentally mimic store mounting failure conditions in a model airplane subject to harmonic excitation. Two identical stores are mounted under the wings and are placed symmetrically opposite each other. The configuration where both stores are “locked”, i.e., mounting is very stiff, serves as the baseline linear system. The second configuration involves unlocking one of the stores, enabling a geometrically nonlinear flexure connection between the unlocked store and the wing. The flexure lets the store interact with the first flexible mode of the airplane, resulting in large relative displacements between the store and wing. In addition, the configuration allows for vibro-impacts between the wing and store. Results show that the strong local vibro-impacts enable excitation of high-frequency modes unexcited in the baseline linear system. This is indicative of energy transfer from low to high frequency modes of the primary structure.</div></div>

Technique for measuring and reducing industrial fan vibration and noise is detailed. A method used to characterize the vibration signature for 100% industrial fan systems shipped is described. A fan system consists of motor, propeller and cage. We measure triax accelerometer vibration, microphone (both sound pressure level in dBA and raw signal in Pa) along with the current of three phase power for each fan shipped. Comparisons are done immediately with the ISO 14694:2003 standard and troubleshooting and design changes are implemented if vibration limits are exceeded. The method and results are provided for several cases. Troubleshooting and best practices are described for various designs. A portable system takes measurements in the field which are compared to the factory baseline characterization in real time to solve installation problems.

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