A ramp function is defined by three points (time, function value). Those three points, in order, are (0, 0), (Ramp time, Amplitude) and (Maximum time, Amplitude).
Add a ramp time history function as follows:
Time History Function Name edit box. Use the default or specify another name for the time history function by typing directly in the edit box.
Parameters
Ramp Time edit box. Enter the time that it takes for the ramp function to initially reach its maximum value. It is usually set to one second.
Amplitude edit box. Enter the maximum value of the ramp function. It is usually set to 1.
Maximum Time edit box. Enter the time at the end of the ramp function. It is usually between 10 and 20 seconds.
Define Function area. This area displays the time and values for the function. They cannot be edited and are provided for review purposes only. These values update when changes are made to the items in the Parameters area of the form. If manual changes to this area are necessary, click the Convert to User-Defined button to convert the function to a user-defined function, which will make this area editable.
Function Graph area. This area displays a graph of the function. It updates automatically as additional points are defined for the function. In some cases it may be necessary to click the Display Graph button after making changes to the form to display or update the graphical display.
Run the mouse pointer over the function graph and a dot appears along the line representing the time history function. The coordinates of the dot are reported in the box just below the graph.
Access the Time History Function Definition - Ramp form as follows:
Click the Define menu > Functions > Time History command to access the Define Time History Functions form. Then do one of the following:
Select Ramp from the Choose Function Type to Add drop-down list; click the Add New Function button.
Highlight an existing Ramp function definition in the Functions display area and click the Modify/Show Spectrum button.