To define a time history type using spectral parameters, use the following procedure.

1. On the Loading ribbon tab, select the Time History > Forcing Function tool in the Dynamic Specifications group.
   
   The Add New: Time History Definitions dialog opens.
2. Type an Integration Time Step value in seconds.
3. (Optional) Select the Consider Missing Mass Mode option if necessary.
4. (Optional) Select the Save option to generate a file with time history data.
5. Select the Loading Type for your data:

   Acceleration

   or

   Force

   or

   Moment

6. Select the Spectrum option in the Function Options group.
7. Specify the time data:
   1. Enter the maximum time (in second) in the generated time history in the Tmax field.
   2. Enter the time step (in seconds) in the DeltaT field.
   3. Enter the time at the end of rising acceleration in the T1 field.
   4. Enter the time at the end of the steady acceleration in the T2 field.
   5. Enter the time at the end of the acceleration decay in the T3 field.
   Note: The value of T1 must be greater than zero. Further, T3 > T2 > T1 and Tmax must be greater than T3.
8. Enter the damping ratio in the Damp field.
9. Specify the options:
   1. (Optional) Type a Random Seed value. Enter a positive integer (in the range of 1 to 2,147,483,647) to be used as a unique random number generation "seed." A unique time history will be produced for each seed value. Change this value when you want to produce a "different (from the time history generated with the prior seed value)" but statistically equivalent time history.
   2. Enter the No of digitized Freq. This is the number of equally spaced frequencies at which the input shock spectrum is re-digitized (by interpolation).
   3. Enter the No. of Iteration which will be used to perfect the computed time history.
10. Click Add.