Abstract
In prior work by the author and others [1–3], a new method was demonstrated to extract fixed base modes from a modal test performed on a test article mounted on a vibration slip table. This paper addresses uncertainty that was apparent in frequency and damping estimates in previous work [3]. After reviewing the method based on substructure coupling, additional testing indicates that some of the frequency error was due to different size attachment bolts in the seismic mass truth test and the slip table test. In the previous work, the largest errors in prediction of the truth data were associated with damping. A procedure to subtract significant low frequency slip table damping is implemented and the resulting corrected damping estimate presented.
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the U.S. Department of Energy under Contract DE-AC04-94AL85000.
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Abbreviations
- dof:
-
Degree of freedom
- f :
-
Applied force
- FRF:
-
Frequency response function
- q :
-
Generalized coordinate
- B :
-
Reduction matrix applying the constraint to equations of motion
- Φ c :
-
The mode shape matrix of the slip table at dof to be constrained
- \( \zeta \) :
-
Modal damping ratio
- ω :
-
Angular frequency (rad/s)
- \( \Psi \) :
-
Mass normalized real mode shapes
- c :
-
Subscript for degrees of freedom to be constrained to zero
References
Mayes RL, Bridgers LD (2009) Extracting fixed base modal models from vibration tests on flexible tables. In: Proceedings of the 27th international modal analysis conference, Orlando, paper 67
Allen MS, Gindlin HM, Mayes RL (2010) Experimental modal substructuring to extract fixed-base modes from a substructure attached to a flexible fixture. In: Proceedings of the 28th international modal analysis conference, Jacksonville, paper 164
Mayes RL, Allen MS (2011) Converting a driven base vibration test to a fixed base modal analysis. In: Proceedings of the 29th international modal analysis conference, Jacksonville, paper 36
Hensley DP, Mayes RL (2006) Extending SMAC to multiple references. In: Proceedings of the 24th international modal analysis conference, St. Louis, pp 220–230
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© 2012 The Society for Experimental Mechanics, Inc. 2012
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Mayes, R.L. (2012). Refinements on Estimating Fixed Base Modes on a Slip Table. In: Allemang, R., De Clerck, J., Niezrecki, C., Blough, J. (eds) Topics in Modal Analysis I, Volume 5. Conference Proceedings of the Society for Experimental Mechanics Series. Springer, New York, NY. https://doi.org/10.1007/978-1-4614-2425-3_32
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DOI: https://doi.org/10.1007/978-1-4614-2425-3_32
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