how to curve fit a sine wave to some data

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Matt Thomas 2023-8-12

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https://ww2.mathworks.cn/matlabcentral/answers/2007812-how-to-curve-fit-a-sine-wave-to-some-data

评论： Matt Thomas 2023-8-13

I have been using a open source software package called openFAST to generate some binary files of wind turbine simulations. I then use MATLAB to view the results of the 5MW_Land_DLL.outb files generated by openFAST using the following code:

%% Run this command first
%% Read a binary output file
% Read file
outbfile = '5MW_Land_DLL_WTurb.outb';
[Channels, ChanName, ChanUnit, FileID, DescStr] = ReadFASTbinary(outbfile);
time = Channels(:,1);

This code organizes the data into the matrices etc. like in the image below:

I then use the plot function to generate a graph:

%%CHange the plot number to reflect the parameter in channel names matrix generated from above command.
% Plot Channel 34
iChan=34
figure()
plot(time, Channels(:,iChan))
xlabel('Time (s)')
ylabel([ChanName(iChan) ChanUnit(iChan)])

That looks like :

What I would like to do now is curve fit a sine wave to this plot above so I can get the frequency, the amplitude, phase, and the equation from it.

Is this possible to do?

I have zero experience in MATLAB. The above code was given to me. 🙂 I am not a coder at all.

Thanks

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Matt Thomas 2023-8-13

ok, ill try to figure that out. ill google the syntax. thank you much

Matt Thomas 2023-8-13

i keep getting an error when using fft.

y=fft( time, Channels(:,iChan))

FFT length must be a nonnegative integer scalar.

thanks

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采纳的回答

Matt J 2023-8-12

1
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2007812-how-to-curve-fit-a-sine-wave-to-some-data#answer_1286852

在 MATLAB Online 中打开

One way, assuming you have the Curve Fitting Toolbox:

fobj = fit( time, Channels(:,iChan) ,'sin1')

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Matt Thomas 2023-8-13

编辑：Matt Thomas 2023-8-13

well, it plots it and works but for sure NOT the results i had in my head haha. I thought it would be more of a tighter and faster sin wave but its nice and slow haha.

when i look at my graph i see a tighter sin wave IE from time 0-15 seconds is a peak, then 15-25 is another peak, and 25-35 is another.

thanks for this. ill see if i can use the data to help me out