Creating FRF with Multi Degree of Freedom System

Hi,

I have 50*8 Amplitude vs Rotor Speed Data and also 50*8 Frequency vs Rotor Speed Data. 50 means the rotor speed limit.

8 means that degree of freedom is eight.

I don't know how can I create FRF for my case. Can you give me some suggestions.

Answer 1

[SOUMNATH PAUL]

Hi,

As per my understanding you have two sets of data matrices, each matrix is 50*8 which means you have data for 50 different rotor speeds and for each rotor speed there are 8 different degrees of freedom.

Since you have 8 degrees of freedom, we need to create 8 FRFs.

Firstly, we need to load the csv data set in the MATLAB workspace. You can go through this page to understand how to load csv data in the workspace: https://in.mathworks.com/help/matlab/ref/readmatrix.html

After the data is loaded, we need to create a script which loops through each degree of freedom and for each one plot the amplitude vs frequency data.

% Assuming your data is loaded into two variables: amplitudeData and frequencyData 

% Each of these variables is a 50x8 matrix. 
% Predefine the figure window size 
figure('Units', 'normalized', 'Position', [0.1, 0.1, 0.8, 0.8]); 
% Loop through each degree of freedom 

for dof = 1:8 
    % Extract the data for the current degree of freedom 
    amplitude = amplitudeData(:, dof); 
    frequency = frequencyData(:, dof); 

    % Create a subplot for each degree of freedom 
    subplot(2, 4, dof); 

    % Plot the FRF for the current degree of freedom 
    plot(frequency, amplitude, 'LineWidth', 1.5); 

    % Label the axes 
    xlabel('Frequency (Hz)'); 
    ylabel('Amplitude'); 

    % Add a title to the plot 
    title(['FRF - DOF ' num2str(dof)]); 

    % Optionally, add grid and set axis limits 
    grid on; 
    xlim([min(frequency), max(frequency)]); 

    % Automatic y-axis limits can be set with 'ylim auto' 

    % If you prefer manual limits, replace 'auto' with [ymin ymax] 
    ylim('auto'); 

end 

% Adjust subplot spacing 

subplot_adjustment = 0.04; 
subplots = get(gcf, 'Children'); 
set(subplots, 'Position', get(subplots, 'Position') + [-subplot_adjustment, -subplot_adjustment, subplot_adjustment*2, subplot_adjustment*2]); 

% Add a super title to the entire figure 

sgtitle('Frequency Response Functions for 8 Degrees of Freedom'); 

Hope it helps!

Regards,

Soumnath