FEM Modal Analysis of a satellite appendage

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Joseph Sparka
Joseph Sparka on 24 Mar 2023
Answered: Kartik on 17 May 2023
I am currently working on a Simulink satellite model for which i need to include a flexible appendage. I used Matlab to create the simple appendage cuboid 3D Model and run a FEM analysis to get the required modal data.
However the function structuralModalResults = solve(structuralModal,"FrequencyRange",[omega1,omega2]) returns only the natural frequencies. To add flexibility to the appendage I also need the damping ratio and modal contribution/modal participation factors of the flexible modes. How do I find this data?

Answers (1)

Kartik
Kartik on 17 May 2023
Hi,
You can use the "solve" function of the "structuralModalProperties" object to obtain modal damping ratios and modal participation factors for flexible modes. Here's an example code snippet:
% Create a structural modal properties object and find natural frequencies
structuralModal = structuralModalProperties(loadcase,modalanalysis);
structuralModalResults = solve(structuralModal);
% Specify frequency range of interest for modal damping and participation analyses
omega1 = 0;
omega2 = 1000;
% Get modal damping ratios and participation factors for flexible modes
[modalDamping,modalParticipation] = solve(structuralModal,...
"FrequencyRange",[omega1,omega2],...
"ModalAnalysisDampingMatrix","Full");
% Print modal damping ratios to the console
fprintf("Modal damping ratios:\n");
for i = 1:length(modalDamping)
fprintf("Mode %d: %.6f\n",i,modalDamping(i));
end
% Print modal participation factors to the console
fprintf("Modal participation factors:\n");
for i = 1:size(modalParticipation,2)
fprintf("Mode %d:\n",i);
for j = 1:size(modalParticipation,1)
fprintf(" DOF %d: %.6f\n",j,modalParticipation(j,i));
end
end
The "solve" function is called twice in the above code - once to get the natural frequencies and again to obtain modal damping ratios and modal participation factors for flexible modes.

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