Form: NLLink Local Axis, Link Advanced Axis
Each link/support object has its own element local coordinate system used to define force deformation properties and output. The axes of this local system are denoted 1, 2 and 3. The first axis is directed along the length of the object and corresponds to extensional deformation. The remaining two axes lie in the plane perpendicular to the element and have a user-specified orientation; those directions correspond to shear deformation. It is important to clearly understand the definition of the element local 1- 2-3 coordinate system and its relationship to the global X-Y-Z coordinate system. Both systems are right-handed coordinate systems. It is up to the user to define local systems that simplify data in put and interpretation of results.
Select one or more link objects to be assigned the same local axes.
Click the Assign menu > Link/Support > Local Axes command to access the NLLink Local Axis form:
Angle in Degrees. Type in a value for Angle in Degrees. This is an angle by which the local axis 2 of the element will be rotated around local axis 1. Local axis 1 is along the length of the element. By default local axis 2 is always in the 1-Z plane, except if the element is vertical and then it is parallel to the global X axis. The definition of the local axes follow the right-hand rule. The angle is measured counter-clockwise as positive if local axis 1 is pointing towards you.
If appropriate, check the Advanced Axes check box and click the Advanced button to access the Link Advanced Axes form. Use the Link Advanced Axis form to refine the specification of the local axes for the selected object(s).
Local Plane - Select the local plane for the link/support from the drop-down list.
Local Axes Type options.
Default option. When the Default option is selected, the other areas of the form are not available and no further input is required. This is the default.
Advanced option. When the Advanced option is selected, the input required on the form changes depending on the options selected in the Axial Reference Vector Specified by and Plane Reference Vector Specified by areas of the form.
Axial Reference Vector Specified by - Choose one of the following options to specify how the axial reference vector will be defined. Note that Axial reference vectors apply to zero length links only.
Coordinate Direction - When this option is selected, the form will display an Axial Coordinate Direction area, a Coordinate System drop-down list, and Direction drop-down list. Choose the coordinate system for the reference vector and then the coordinate direction for it from the drop-down list.
Two Joints - When this option is selected, the lower portion of the form will display a Two Joints for Axial Reference Vector area with Axial Joint 1 and Axial Joint 2 drop-down lists. The lists consist of the joints included in the model and a None selection. Choose the two joints to be used to specify the axial reference vector.
User Vector - When this option is selected, the lower portion of the form will display a Coordinate System drop-down list and a User Axial Reference Vector area with edit boxes for Axial Vector X, Axial Vector Y, and Axial Vector Z. Select the coordinate system for the reference vector, and then enter coordinate values in these edit boxes to specify the axial reference vector.
Plane Reference Vector Specified by - Choose one of the following options to specify how the plane reference vector will be specified.
Coordinate Direction - When this option is selected, the form will display a Coordinate System drop-down list and a Plane Coordinate Direction area with Primary and Secondary Dir (Direction) drop-down lists. Choose the coordinate system for the reference vector and then choose a coordinate direction from each drop-down list.
Two Joints - When this option is selected, the lower portion of the form will display a Two Joints for Plane Reference Vector area with Plane Joint 1 and Plane Joint 2 drop-down lists. The lists consist of the joints included in the model and a None selection. Choose the two joints to be used to specify the plane reference vector.
User Vector - When this option is selected, the form will display a Coordinate System drop-down list and a User Plane Reference Vector area with edit boxes for Plane Vector X, Plane Vector Y, and Plane Vector Z. Choose the coordinate system for the reference vector and then enter coordinate values in the edit boxes to specify the plane reference vector.
See Also