A discrete orientation defines a spatially varying orientation at the centroid of each mesh element. The orientation can be based on the topology of the part, allowing you to define a continually varying orientation. You define the normal axis and a primary axis, and Abaqus/CAE uses these axes to construct a right-handed Cartesian coordinate system. For two-dimensional and axisymmetric parts, the normal axis is always the out-of-plane direction and represents the positive 3-axis of the coordinate system. Discrete orientations can be used for material orientations and composite layup orientations.
A variety of selection methods are available to define the desired axes. The datum axis and vector value methods define a constant axis direction, whereas the region selection methods allow for varying orientations. For example, you may want to select a curved surface and allow the normal to follow the shape of the curve.
Abaqus/CAE uses the normal axis and primary axis that you specify and the following algorithm to calculate the discrete orientation:
Abaqus/CAE preserves the normal axis direction and uses the specified primary axis direction as a construction direction. If the specified primary axis direction and the normal axis direction form a 90° angle, the final primary axis direction will be the same as the one specified. Otherwise, the primary axis direction will be adjusted to form a Cartesian system.
If you define the normal axis by selecting a surface or face, Abaqus/CAE finds the closest point on the surface or face and uses the surface normal at that point as the normal axis direction (
).
If you define the primary axis by selecting an edge, Abaqus/CAE finds the closest point on the edge and uses the edge tangent at that point as the primary axis construction direction (
).
Abaqus/CAE computes the secondary axis direction (
) by taking the cross product of the primary axis direction and the normal axis direction (
).
Abaqus/CAE computes the final primary axis direction (
) by taking the cross product of the secondary axis direction and the normal axis direction (
).
To define a discrete orientation:
To display the Edit Discrete Orientation dialog box, do the following:
Assign a material orientation or create a composite layup.
Display the Edit Material Orientation dialog box using the procedure described in “Assigning a material orientation or rebar reference orientation,” Section 12.15.4.
Display the composite layup editor using one of the procedures described in “Creating and editing composite layups,” Section 12.14.
Click the arrow to the right of the Definition field, and select Discrete from the list that appears.
Click 
.
For three-dimensional parts, choose the coordinate system axis that you want the Normal axis direction to represent in the resultant orientation.
For three-dimensional parts, define the normal axis of the orientation using one of the following methods:
Select Surface/Faces to select a region, and do the following:
Click 
.
From the prompt area, select individually or select by angle and enter an angle. For more information, see “Using the angle and feature edge method to select multiple objects,” Section 6.2.3.
Identify the regions that define the normal axis of the material orientation by selecting the regions in the viewport or by clicking Surfaces or Sets in the prompt area and selecting an existing surface or set.
Select Datum axis to select datum geometry, and do the following:
To create a datum axis, click 
and select two points in the viewport that define the axis.
Click .
Select the datum axis that defines the normal axis of the material orientation.
Select Vector (i,j,k), and enter the values for the vector components.
Abaqus/CAE displays arrows in the viewport that indicate your selections and axis direction; for example, arrows labeled N-3. If necessary, you can click Flip Direction to obtain the desired direction.
Choose the coordinate system axis that you want the Primary axis direction to represent in the resultant orientation.
Define the primary axis of the orientation using one of the following methods:
Select Edges to select a region, and do the following:
Click .
From the prompt area, select individually or select by edge angle and enter an angle.
Identify the regions that define the primary axis of the material orientation by selecting the regions in the viewport or by clicking Sets in the prompt area and selecting an existing set.
Select Datum axis to select datum geometry, and do the following:
To create a datum axis, click and select two points in the viewport that define the axis.
Click .
Select the datum axis that defines the primary axis of the material orientation.
Select Vector (i,j,k), and enter the values for the vector components.
Abaqus/CAE displays arrows in the viewport that indicate your selections and axis direction; for example, arrows labeled P-1. If necessary, you can click 
to obtain the desired direction.
Click Continue to save the discrete orientation definition and to close the Edit Discrete Orientation dialog box.
