Use mode tracking to keep track of the natural (resonance) frequencies. The options for mode tracking are listed below:

As the design changes throughout the design process, the order of the mode shapes can change. For example, suppose the first bending mode of a structure is at 7 Hz and the first torsional mode is at 10 Hz. After the design is modified, the first bending mode is 11 Hz and the first torsional mode is at 9 Hz. If a constraint was originally placed on the first bending mode, it is now on the first torsional mode. Using mode tracking, GENESIS can reorder the modes so that the constraint remains on the first bending mode.

If a constrained mode that is being tracked is not found during a design cycle analysis, then a fatal error occurs and GENESIS stops.

If a constrained mode that is being tracked switches with another mode, then a warning message appears after design convergence. In this case, check the results of the last analysis to make sure that the correct mode shape is constrained.

If modes switch position during the design process, the frequencies and mode shapes in the output and postprocessing files are not in order of increasing frequency.

Mode tracking information is printed in the analysis results section of the output file. It is important to examine this data if you are restarting the optimization. This is because the mode numbers, which are referenced in the definition of objective or constraint, need to change if the mode switches order. The mode number in the design cycle from which you are restarting will be the position of the mode when all of the modes are ordered from lowest to highest frequency.

You usually need to use mode tracking whenever frequencies or Eigenvector components are used as objective or constraints.