To set global time history parameters
To set the parameters that apply to all time history definitions and loads in your structure model, use the following procedure.
The program uses some parameters for all time history load definitions. These are set in the program Options dialog.
 Select the File ribbon tab and then select Options from the backstage menu. The Options dialog opens.
 Select the Dynamics tab.

Set the Modal Analysis options used for all dynamic loads:

Select the Eigen Method option:
 Subspace – the default subspace iteration method
 Arnoldi/Lanczos – Instructs the solver to use Arnoldi/Lanczos method for extraction of eigen vectors.
 Ritz Vector – Use load dependent Ritz vectors method for extraction of eigen vectors.
 (Optional) To specify the highest frequency to be considered for the dynamic analysis, check the Set Number of Modes option and then type the Value in cycles/sec.
 (Optional) (for when Set Number of Modes is checked) To specify a number of eigen vectors per shift, check the Shift Modes option and type the integer Value for the shift. This option is used when the solver fails to extract the Set Number of Modes due to insufficient memory.
 (Optional) (for Arnoldi/Lanczos method only) To specify the frequency to be used as an initial shift, check the Set Shift Frequency and then type the Value in Hertz. The solver will look for eigenvalues close to the shift. The eigenvalues found may not necessarily be the smallest values (i.e., closest to zero). If a full scale eigen solution is required, then this option should not be used.
 (Optional) To set the highest frequency (cycle/sec) to be considered for dynamic analysis, check the Set Max Frequency and then type the Value in Hertz.

Select the Eigen Method option:

Set the Time History options:
 Type the solution Time Step used in the stepbystep integration of the uncoupled equations. Values smaller than 0.00001 will be reset to the default value of 0.0013888 seconds.
 (Optional) Check the Include Missing Mass to use the missing mass procedure in the time history analyses.
 (Optional) To specify an ending time for a time history analysis, check the Set Max Time History option and then type the Value in seconds. If not specified, the time history will end when the last forcing function ends.

Set the Damping options:
 Select the Modal Damping method to use.
 For Single, Specify, and Evaluate options, specify the damping values or parameters to use.
 Click OK.