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On the use of transmissibility functions in operational modal analysis

Friday, 23 April, 2010 - 17:00
Campus: Brussels Humanities, Sciences & Engineering campus
Christof Devriendt
phd defence

In order to identify the dynamic vibration behavior of structures (the modal
parameters) in operational conditions (e.g. airplane during flight) on the basis of
measured response signals output-only system identification techniques exist. This
discipline is called "Operational Modal Analysis (OMA).

Operating conditions can differ significantly from laboratory conditions under
which a structure is tested in the classical Experimental Modal Analysis (EMA). OMA
allows us to obtain a more realistic model. This explains the great interest that exists for
efficient system identification techniques capable of extracting reliable models directly
from operational data.

In this doctoral research a new OMA approach was proposed that increases the
reliability of OMA techniques (more accurate modal parameters) and generalizes their
applicability to arbitrary signals (existing OMA techniques assume that the operational
forces are the result of a stochastic process , white noise).

This innovative OMA approach is based on measured transmissibility functions.
In general transmissibility functions contain no information about the resonance
frequencies of a structure. It is therefore not obvious that one can use transmissibility
functions to obtain modal parameters. It is however demonstrated that it is possible to
identify the modal parameters (resonance frequencies, mode shapes and damping values)
making use of transmissibility functions measured during varying forces.