To define an amplitude curve using equally spaced data:

1. Display the Edit Amplitude dialog box as described in “Selecting an amplitude type to define,” Section 57.3.

2. Click the arrow to the right of the Time span field, and specify how you want to define the amplitude as a function of time:

   • Select Step time for time that is measured from the beginning of each step.

   • Select Total time for total time accumulated over all non-perturbation analysis steps.

3. Indicate how you want to define Smoothing:

   • Choose Use solver default to accept a default value of 0.25 in Abaqus/Standard and 0.0 in Abaqus/Explicit.

   • Choose Specify to enter a value for the smoothing parameter in the adjacent field. A value of 0.05 is suggested for amplitude definitions that contain large time intervals to avoid severe deviation from the specified definition.

   The Smoothing parameter is the fraction of the time interval before and after each time point during which the piecewise linear time variation is replaced by a smooth quadratic time variation. This parameter is applicable only when time derivatives are needed (for displacement or velocity boundary conditions in a direct integration dynamic analysis) and is ignored for all other uses of this option.

4. Display the Amplitude Data tabbed page.

5. In the Fixed interval field, enter the fixed time or frequency interval at which you will provide the amplitude data.

6. In the first row of the Time/Frequency column in the data table, enter the time (or lowest frequency) at which you will enter the first amplitude.

7. Enter the Amplitude values for each time or frequency. For detailed information on how to enter data, see “Entering tabular data,” Section 3.2.7.

8. If desired, display the Baseline Correction tabbed page.

   When you use an amplitude definition to define an acceleration history in the time domain (a seismic record of an earthquake, for example), the integration of the acceleration record through time may result in a relatively large displacement at the end of the event. This behavior typically occurs because of instrumentation errors or a sampling frequency that is not sufficient to capture the actual acceleration history. In Abaqus/Standard it is possible to compensate for it by using “baseline correction.” For more information, see “Baseline correction in Abaqus/Standard” in “Amplitude curves,” Section 34.1.2 of the Abaqus Analysis User's Guide.

9. Click the arrow to the right of the Correction field, and select one of the following options:

   • Select None for no baseline correction.

   • Select Single interval to treat the entire time of the amplitude definition as a single correction interval.

   • Select Multiple intervals to treat the entire time of the amplitude definition as multiple correction intervals. If you select this option, enter the time points defining the different correction intervals (i.e. in the first row enter the time point defining the end of the first correction interval and the beginning of the section correction interval; in the second row enter the time point defining the end of the second correction interval and the beginning of the third correction interval, etc.).

10. Click OK to save your amplitude definition and to close the Edit Amplitude dialog box.