Here is a Matlab script and its supporting function for identifying the frequencies and amplitudes for one or more sine functions.

sinefind.zip

Trial-and-error curve-fitting is used with some convergence techniques.

Here is measured accelerometer data from a channel beam excited by an impulse force. channel.txt

The data has two columns: time(sec) & accel(G)

The response is largely free vibration.

The data shows a beat frequency effect with two superimposed sine functions, which can be identified using the sinefind.m script. The resulting frequencies are natural frequencies.

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Here is a similar script for curve-fitting a time history with one or more damped sine functions: sinefdam.zip

Here is a measured acceleration time history to practise with. Try the curve-fit over the time segment 0.4 to 4.5 seconds.

drop.txt

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See also:

A Time Domain, Curve-Fitting Method for Accelerometer Data Analysis: AIAA_7667_slide.ppt

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If you have any questions on how to use these scripts, please send your data sample via Email to: tom@irvinemail.org or use the contact form below.

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– Tom Irvine

Contact Form:

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