Normal Modes Analysis

There are two ways to use Normal Mode response in an Optimization run:

1. Set the ATTA field on DRESP1 entry equal to the Normal Mode number(s) that you want to use as a response. In this process, you will identify and provide the mode number(s) that are to be optimized.
2. You can also source the mode number of the mode with largest modal participation at the peak loading frequency by adding a separate Modal Frequency Response Subcase, in addition to the existing Normal Modes subcase. The ATTA field should identify the number of modes and the ATTi field should be set equal to the subcase ID of the Modal Frequency Response subcase. The Modal Frequency Response Analysis subcase should contain a PEAKOUT entry that identifies peak identification criteria. OptiStruct will internally identify the modes to be optimized based on Modal Frequency Response Analysis, by picking the modes (ATTA) for each peak response which contributes the most to the corresponding response. Therefore, the maximum number of modes identified for the optimization is equal to: number of modes (ATTA) * NPEAK (on PEAKOUT).