The first step in using the selectASET GUI is to load the Nastran data using File à Load TAM. The user will be prompted to select the file containing the candidate set TAM mass and stiffness matrices, which can be exported from Nastran using standard functionality as shown in the sample Nastran file in Figure 2. There are other ways to output the characteristic matrices from Nastran, but this is the most straightforward. The red lines in the figure indicate the changes to a standard modes solution (SOL 103) necessary to export the mass and stiffness matrices into the punch (.pch) file in DMIG format. Note that this method assumes that the user has already selected a set of candidate DOF (generally no more than about 2,000) that is an excellent representation of the full detailed FEM. For a detailed discussion of the process of selecting the candidate set DOF and generating the TAM, see the “Model Preparation” section of the Genetic Algorithm for Accelerometer Placement user’s guide here.
Figure 2. Sample Nastran deck showing changes to a modes solution to export the mass and stiffness matrices in DMIG format.
After selecting the punch file with the TAM matrices, the user will be prompted to select another Nastran output file containing the full FEM displacement mode shapes. This separate run should output the mode shape coefficients of all DOF for at least all target modes. To get the full FEM mode shapes, this run should not include ASET cards. Results can be read from a punch (.pch) or OP2 (.op2) file; however, if read from an OP2, the user must use PARAM, POST, -1.
The File à Load à TAM process should be performed for as many FEM configurations as will be processed simultaneously. The mode table will display the mode number and frequencies for each FEM configuration that is loaded. The Config # drop-down box 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 for user reference and is optional.
File à Save can be used to save intermediate checkpoints or results. Saved checkpoints can be reloaded into the GUI using File à LoadàMATLAB .