You can create a velocity/angular velocity boundary condition to prescribe a velocity for the selected degrees of freedom of the selected region's nodes.
Note: To fix the velocity of a region at zero you must define a specific displacement for that region (see “Defining a displacement/rotation boundary condition,” Section 16.10.2).
To create or edit a velocity/angular velocity boundary condition:
Display the velocity/angular velocity boundary condition editor using one of the following methods:
To create a new velocity/angular velocity boundary condition, follow the procedure outlined in “Creating boundary conditions,” Section 16.8.2 (Category: Mechanical; Types for Selected Step: Velocity/Angular velocity).
To edit an existing velocity/angular velocity boundary condition using menus or managers, see “Editing step-dependent objects,” Section 3.4.12. To edit the region to which the boundary condition is applied, see “Editing the region to which a prescribed condition is applied,” Section 16.8.4.
If you want to change the coordinate system (CSYS) in which to apply the boundary condition, click Edit and use one of the following methods:
Select an existing datum coordinate system in the viewport.
Select an existing datum coordinate system by name.
From the prompt area, click Datum CSYS List to display a list of datum coordinate systems.
Select a name from the list, and click OK.
Click Use Global CSYS from the prompt area to revert to the global coordinate system.
This coordinate system editing option is available only in the step in which the boundary condition is created. By default, the global coordinate system is used to define the boundary condition.
If a Distribution field appears in the editor, click the arrow to the right of the field, and select one of the following:
Select Uniform to define a uniform boundary condition.
Select User-defined to define the boundary condition in user subroutine DISP. See the following sections for more information:
If you are defining the boundary condition directly in the editor (and not in user subroutine DISP), perform the following steps:
Use the appropriate method to define the boundary condition:
If no text fields appear next to each degree of freedom:
You can use the following techniques to define the boundary condition:
Toggle on a degree of freedom to fix the value at zero.
Toggle off a degree of freedom to leave the degree of freedom unconstrained.
If text fields appear next to each degree of freedom:
You can use the following techniques to define the boundary condition:
Toggle on a degree of freedom to constrain the degree of freedom. The text field becomes available in which you can specify a value for the degree of freedom. If you are creating the boundary condition in this step, a default value of zero appears in the text field. If you are modifying the boundary condition in this step, the value propagated from the previous step appears in the text field.
Toggle off a degree of freedom to leave the degree of freedom unconstrained. If you toggle off a degree of freedom after modifying the default or propagated value in the text field, the modified value is lost. If you toggle that degree of freedom back on, the default or propagated value reappears in the text field.
Click the arrow to the right of the Amplitude field, and select the amplitude of your choice from the list that appears. Alternatively, you can click Create to create a new amplitude. (See Chapter 38, “The Amplitude toolset,” for more information.)
Click OK to save your data and to exit the editor.
If you are defining the boundary condition in user subroutine DISP, perform the following steps:
If desired, use the following techniques to define the velocity:
Toggle on a degree of freedom to constrain the degree of freedom. If you are in the initial step, that degree of freedom is set to zero. If you are in any step other than the initial step, a text field becomes available in which you can specify a value for the degree of freedom.
Toggle off a degree of freedom to leave the degree of freedom unconstrained.
Click OK to save your data and to exit the editor.
Enter the Job module and display the job editor for the analysis job of interest. (For more information, see “Creating, editing, and manipulating jobs,” Section 18.5.)
In the job editor, click the General tab, and specify the file containing the user subroutine that defines the boundary condition. For more information, see “Specifying general job settings,” Section 18.6.6.
Note: You can specify only one user subroutine file in the job editor; if your analysis involves more than one user subroutine, you must combine the user subroutines into one file and then specify that file.
