Abstract
This work presents a modal test on a cylindrical bolted structure that initially appeared to be a routine model calibration experiment. However, while reviewing the test data the structure appeared to have two pairs of ovaling modes with identical shapes. Assuming this to be the result of an uninstrumented component of the test article, extensive efforts were conducted to identify this feature. When all options were exhausted, the interaction between the structure and the air contained within was investigated. Contrary to the typical assumption that the fluid-structure interactions are negligible for such a thick walled cylinder, analysis showed that for this test article the acoustic modes of the internal air significantly impacted the structural response. In this case, the acoustic and the structural modes coincided in frequency, causing the first ovaling modes to split into two pairs at different frequencies. Experimental and analytical results are presented that describe this structural-acoustic mode coupling phenomenon.
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Abbreviations
- CMIF:
-
Complex mode indicator function
- FEM:
-
Finite element model
- FRF:
-
Frequency response function
- SMAC:
-
Synthesize modes and correlate (computer program)
- \( \varnothing \) :
-
Mode shape vector
- s :
-
Subscript for structural
- a :
-
Subscript for acoustic
- F :
-
Fractional contribution to mode shape
References
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Hensley, D.P., Mayes, R.L.: Extending SMAC to multiple references. In: Proceedings of the 24th International Modal Analysis Conference, pp. 220–230 (2006)
Structural Dynamics Code Development Team. Sierra Structural Dynamics—User’s Notes. Sandia National Laboratories, Version 4.36.1 (2015)
Acknowledgements
This work was funded by Sandia National Laboratories. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
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Pacini, B., Tipton, G. (2016). Structural-Acoustic Mode Coupling in a Bolted Aluminum Cylinder. In: Mains, M. (eds) Topics in Modal Analysis & Testing, Volume 10. Conference Proceedings of the Society for Experimental Mechanics Series. Springer, Cham. https://doi.org/10.1007/978-3-319-30249-2_35
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DOI: https://doi.org/10.1007/978-3-319-30249-2_35
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