The half-power bandwidth method can be used to estimate the damping ratio and corresponding Q value from the frequency response function of a structure which has been excited by base motion or an applied force. The structure may be a multi-degree-of-freedom (MDOF) system as long as the modal frequencies are separated by a sufficient frequency margin so that the spectral peaks are distinct.
Here are some resources.
notes_on_frequency_resolution.pdf
An Introduction to Frequency Response Functions: frf.pdf
(Download and then reopen to see full equations.)
Keyword: frequency, resolution, damping, modal, FRF
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Matlab GUI scripts:
Force or Base Excitation, with Frequency Response Function Magnitude: half_power_bandwidth.zip
Force Excitation, with Complex Frequency Response Function: half_power_bandwidth_fc.zip
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Here is a Matlab script that will perform a modal curve-fit for a multi-degree-of-freedom system. The script extracts modal frequencies and damping from a complex FRF. mdof_frf_curvefit.m
Supporting function: mdof_frf_curvefit_phase1.m
The method in these scripts is described in: mdof_frf_curvefit.pdf
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See also:
Damping Value Conversion Calculator
Vibrationdata Signal Analysis Package – modal FRF option
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Here is a newsletter with an example of the half-power bandwidth method applied to the Ares-1X roll-out: May2010_NL.pdf
– Tom Irvine
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