Craig-Bampton Method, Fixed Interface Model

The Craig-Bampton method is method for reducing the size of a finite element model, particularly where two or more subsystems are connected. It combines the motion of boundary points with modes of the subsystem assuming the boundary points are held fixed.

Here is a tutorial paper.

Craig-Bampton Method for a Two Component System: CB_two_component.pdf

See also:

Assembly of subsystem matrices: assembly_subsystem_matrices.pdf

Component Mode Synthesis, Fixed Interface Model:  component_mode_synthesis.pdf

Mass Condensation, Guyan Reduction:  mass_condensation.pdf

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Here are Matlab scripts used for the examples in the paper.

This script sets up the initial mass and stiffness matrices for each system: spring_mass_series.m

This script and its supporting function perform the Craig-Bampton transformation on the subsystem mass and stiffness matrices:

Craig_Bampton.m
CB_partition.m

This script is used to assemble the Craig-Bampton transformed mass and stiffness matrices and then calculated the natural frequencies and modes shapes: mass_stiffness_assembly.m

Here is a supporting function used by the scripts:  Generalized_Eigen.m

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See also:

Scott Gordon, The Craig-Bampton Method

John Young, Primer on the Craig-Bampton Method

Structural Dynamics – Finite Element Method Page

FRF Substructuring

Combined Ascent Loads for Launch Vehicle Analysis

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– Tom Irvine

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