The first step in using the GA is to load the characteristic matrices from Nastran using the File à Load à Nastran option to select the file containing the DMIG matrices previously discussed in Exporting the Candidate Set DOF TAM. After loading, the user will be prompted with the following dialog box:
Figure 3. Source of Shapes dialog box
This box allows the user to select how the shapes and frequencies are obtained. The default option Calculate Shapes causes an eigensolution to be performed using the loaded mass and stiffness matrices, resulting in the candidate set TAM shapes and frequencies. Alternatively, the full FEM shapes can be read directly from a separate Nastran punch (.pch) or OP2 (.op2) file by selecting the Read FEM Shapes option. The OP2 file containing the FEM shapes must be written using the PARAM,POST,-1 option. The Nastran output file is the result of a normal modes analysis on the full FEM structure (with no ASET cards) which must contain shapes for at least all DOF in the candidate set. The benefit of reading the full FEM shapes is to avoid any slight inaccuracies of the candidate set TAM as compared to the full FEM. Reading the full FEM shapes, however, is not a replacement for the rigorous requirement on the candidate set TAM discussed in Candidate Set DOF TAM. Even if the full FEM modeshapes are loaded into the GA the candidate set TAM must still be a good representation of the full FEM because the candidate set mass matrix is used throughout the GA process.
The File à Load à Nastran process should be performed for as many FEM configurations as will be processed simultaneously. The mode table will display the mode numbers and frequencies of the FEM(s) for each FEM configuration that is loaded. The Config # drop-down allows the user to toggle the mode table and target mode table between the different FEM configurations, and the Desc input box allows the user to assign a descriptive tag to each FEM configuration. This description is purely for user reference and is optional.
The File à Save option allows the user to save intermediate checkpoints or resume from a previous GA run. Saved checkpoints can be recovered by using File à Load à Matlab. It is recommended that once all FEMs have been loaded and all target modes and solution parameters set that a preliminary checkpoint be saved as a recovery point.