Finding the frequency of an arbitrary, time-varying load

[GoshDarn]

Hi everyone,

So I have time-varying force data. The force acts as a concentrated load. The force does not vary periodically/harmonically, it just has a general variation with time. My main question is: How do I determine the corresponding frequency of this force data?

Also, if I'm using MATLAB and I have a data vector of this force's time variation, how do I use MATLAB to determine the corresponding frequency data? Do I use the fft() function?

Any help/insight would be appreciated! Let me know if you need any more details and I will happily provide them.

Thanks

 

[mfb]

If it is not periodic, it does not have a single frequency.

Do I use the fft() function?

That looks like a Fourier transformation: Good. It will show you the main frequency components of your signal.

 

[GoshDarn]

Thanks for the helpful reply, I appreciate it.

What exactly does fft() give me? For instance, say I define my force vector as V=[2 6 2 9 10 3 . . . .] then plug in fft(V) in MATLAB. What is the physical significance of the resulting numbers? Are they the frequency of the data of the vector?


Basically my goal is to first plot my force as a function of time from the given data, F(t). I have this data so its very easy. Then I want to plot the force as a function of its frequency, F(f) using a Fourier transform. How do I do this?

Any help/advice would be greatly appreciated. Let me know if you need my to provide more info.

 

[mfb]

What exactly does fft() give me?

Check the documentation?
The mathematical interpretation of a Fourier transformation (FT): If you see a peak at some value x, your data has an oscillating signal with a frequency of x. If you see multiple peaks (or even some broad distribution), you have multiple different oscillations in your signal at the same time (or chaos).

How do I do this?

Should be somewhere in the manual.

 

[sardar]

for your question! Determining the frequency of an arbitrary, time-varying load can be a challenging task, but there are several methods that can be used to do so. One approach is to use the Fast Fourier Transform (FFT) algorithm, as you mentioned. This algorithm allows you to analyze the frequency components of a signal by converting it from the time domain to the frequency domain. In MATLAB, you can use the fft() function to perform this conversion and obtain the frequency data for your force signal.

Another approach is to use a spectrogram, which is a visual representation of the frequency components of a signal over time. This can be helpful for identifying any changes or patterns in the frequency of your force data. MATLAB also has a spectrogram function that you can use for this purpose.

It's important to note that the results you obtain from these methods may not be exact, as your force data may not have a clear and consistent frequency. However, they can still provide valuable information about the frequency content of your signal.

Additionally, if you have access to the physical system that is producing the force data, you may be able to measure the frequency directly using sensors or other equipment. This would provide the most accurate frequency information.

I hope this helps and please let me know if you have any further questions or need more details. Good luck with your analysis!