Comparison Between Component Mode Synthesis Methods

Christopher_Fadanelli

MotionView provides several advanced component mode synthesis (CMS) methods for structural analysis: Craig Bampton, Craig Bampton with Geometric Stiffness, Craig Chang, and Craig Chang with Contact.

 

1. Craig Bampton Method: This technique involves computing mode shapes by applying unit displacements at each interface node while constraining the remaining degrees of freedom. It produces mode shapes from static interface constraints and from fixed-interface eigenmodes where all interface nodes are restrained.
2. Craig Bampton with Geometric Stiffness: This method builds upon the Craig Bampton approach but incorporates geometric stiffness effects into the mode shape calculations, offering a more comprehensive analysis.
3. Craig Chang Method: This approach derives mode shapes from an inertial relief analysis with unit forces applied, as well as from free-free eigenmode analysis (unconstrained normal modes). It provides a detailed understanding of the structure's dynamics.
4. Craig Chang with Contact: This variant enhances accuracy at predefined contact interfaces, refining stress and strain predictions where components interact. For more information, please visit our help site.

In this example, we compare the results of a flexible body modeled using the Craig Bampton and Craig Chang methods. The model in question is a dual-slot component used in a four-bar linkage. Flexprep was utilized to generate the flexbodies, and mode shapes were visualized by loading the H3D file into HyperView. Additionally, mode shapes and natural frequencies were compared by opening the .out file in a text editor.

 

 

 

Up to mode 16, both methods yield similar natural frequencies and eigenvalues. However, deviations in mode shapes become apparent beyond this point.

 

Deformation, Stress, and Strain Comparison: The dual-slot component was analyzed with one end fixed and the other allowed to rotate about the Y Global axis, with a velocity of 3.14 rad/s applied to the crank. Comparing results in HyperView shows that both flexbodies produced similar outcomes, demonstrating that both methods yield comparable results in this context.