Fourier Series 2

[tcarrillo]

Hi - Can any anyone help me graph the 1st harmonic. Please see attached data.

Thanks,

 

[GregLocock]

Incidentally you might want to fiddle the data slightly - runout at 360 should equal runout at 0

OK, first thing to do is to interpolate the data so that you have 64 samples, not 36

Then you need to install the data analysis add-in

then you need to use the Fourier Analysis in that menu.

Then you need the magnitude, use imabs

Then you need to read up on the scale factor used in Fourier.

Eyeballing I'd expect an amplitude of somewhat less than 3 mm for the first order component, and get 2.24 mm



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[tcarrillo]

Thanks! Greg

 

[catiaguy12]

Hi Greg - I've done all the math (I think) but i still don't see how am i may going to graph it. Please help

See attached file.

Thanks a lot.
Thomas

 

[GregLocock]

I think you've just calculated the centreing error, ie the DC component of the fourier series.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[GregLocock]

Sorry, I was wrong, you are working the Fourier coefficnts out the old fashioned way (nice to see). Incidentally your x axis is screwy, the first value is 11 degrees, not 0

If you've done it right you have calculated the amplitude of the sine and cosine parts of the first order, so now generate a sine wave and multiply it by a, and a cos wave and mutliply it by b, and add them up, and that should be the first order component.

You've got a - sign problem in b,

the correct formula is 0.34*cos(x)-1.83*sin(x), and it looks OK

I don't know where I got 2.24 before, that is wrong.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[catiaguy12]

Thanks for taking the time to review my problem. Thank you!

TC

 

[patprimmer]

If someone is truly helpful, the traditional way to thank them is to award a star. It cost you nothing but a few seconds.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[crysta1c1ear]

I'll do it, LOL!

 

[tcarrillo]

My apologies, I'm new to the forum and I don't know how to give someone a star.

Greg - thank you once again.

 

[crysta1c1ear]

Just click
[highlight]Thank GregLocock
for this valuable post![/highlight]

 

[tcarrillo]

Thanks guys! Awarded Grag with star