FEM Modal Analysis of a satellite appendage

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?

Answer 1

[Kartik]

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.