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Title
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Operational modal analysis and model updating with a cyclostationary input
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| Author(s) |
Hanson, David, Mechanical & Manufacturing Engineering, Faculty of Engineering, UNSW
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| Resource Type |
Thesis
PhD Doctorate
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| Keyword(s) |
Modal analysis; structural dynamics -- mmathematical models; cyclostationary waves; finite element method.
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| Date |
2006 |
| School/Centre |
University of New South Wales. School of Mechanical and Manufacturing Engineering |
| Description/Abstract |
This thesis addresses the problem of identifying the modal properties of a system based
only on measurements of the system responses. This situation is frequently encountered
in structural dynamics and is particularly relevant for systems where the in-service
excitation is not artificially reproducible. The inherent non-linearities in these systems
mean that the modal properties estimated using traditional input/output techniques will
be different to those exhibited in operation. A common example from the literature is an
aircraft in flight where the modal properties are heavily influenced by the operating
point, i.e. the combination of load, speed, altitude etc., at which the aircraft is travelling.
The process of identifying the modal properties of systems in-service is called
Operational Modal Analysis (OMA).
Not knowing the input complicates the analysis. Most of the techniques in the literature
overcome the lack of knowledge about the unmeasured excitations by assuming they are
both spatially and frequentially white, i.e. of equal magnitude and with a flat autospectrum.
This thesis presents a new technique for OMA which relaxes these
constraints, requiring only that the system is excited by a so called cyclostationary input
with a unique cyclic frequency, and that the log spectrum of the second order
component of this input is frequentially smooth, as will be explained. Such systems
include vehicles with internal combustion engines as the vibration from such an engine
exhibits cyclostationary statistics. In this thesis, the technique is applied to a laboratory
test rig and a passenger train both using an artificial input, and to a race car using the
engine as the excitation.
By combining cyclostationary signal processing and the concept of the cepstrum, the
technique identifies the resonances and anti-resonances in the transfer functions
between each response and the cyclostationary source. These resonances and antiresonances
can be used to regenerate Frequency Response Functions (FRFs) and it is
shown how the unknown scaling of the system can be recovered by employing finite
element model updating in conjunction with this regeneration. In addition, the
contribution made to model updating by the anti-resonances is also investigated.
Finally, the potential of OMA to inform a model updating process is demonstrated using
an experimental case study on a diesel railcar. |
| Language |
EN |
| Rights |
Please click here to view the rights |
| Citation Link |
Please use this identifier to cite or link to this item: http://handle.unsw.edu.au/1959.4/31199 |
| Full Text | 
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| Total Attachment(s) | 2 |
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