Use the smooth step definition method to define the amplitude, a, between two consecutive data points 
and 
as
. This definition is intended to ramp up or down smoothly from one amplitude value to another. For more information, see “Defining smooth step data” in “Amplitude curves,” Section 34.1.2 of the Abaqus Analysis User's Guide.To define an amplitude curve using smooth step data:
Display the Edit Amplitude dialog box as described in “Selecting an amplitude type to define,” Section 57.3.
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.
In the data table, enter the tabular data. For detailed information on how to enter data, see “Entering tabular data,” Section 3.2.7.
Click OK to save your amplitude definition and to close the Edit Amplitude dialog box.