Boundary System

) is a local base vector system on 2D boundaries (t, n) and on 3D boundaries (t1, t2, n). Use it to apply loads and other boundary conditions in a normal or tangential direction on a boundary that is not aligned with the global Cartesian coordinate system.

	For 3D and 2D models, a Boundary System node is automatically added under Definitions.

Common applications for this coordinate system include specifying pressure or normal displacement on a surface.

To specify the boundary coordinate system, you specify the direction of the normal and a direction that is projected onto the boundary, normalized, and used as the first tangent vector. The normal direction is in most cases the outward-pointing normal vector, but you can reverse the normal direction. The general definition of the normal is the direction of the normal vector n, which can be plotted using the variables for its components (typically nx, ny, and nz). See Normal Variables.

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In 2D, the local coordinate system is defined by (t1, n, to), representing the tangential and normal direction of the boundary. This coordinate system is always right-oriented. The second tangent direction (to) is the cross product between normal vector (n) and the first tangent direction (t1). This method always gives a right-oriented orthonormal system, unless the tangent direction is parallel to the normal.

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In 3D, the local coordinate system is defined by (t1, t2, n), representing two tangential directions (t1 and t2) and one normal direction (n). This coordinate system is always right-oriented but not always orthogonal. The second tangent direction (t2) is the cross product between the specified normal vector (n) and the first tangent vector (t1). This method always gives a right-oriented orthonormal system, unless the tangent direction is parallel to the normal.

You can also reverse the normal on some boundaries and switch the domain normal on the exterior of some domains by right-clicking the node and selecting and , respectively. See Reverse Normal and Domain Normal.

Select a : (the default), , or . The deformed configuration follows the material whereas the reference configuration has fixed basis directions in the spatial frame. The geometry configuration is used to specify normal and tangential components of boundary conditions and refers to the undeformed geometry when using a Deformed Geometry interface.

In the table, the default names are entered — t1, t2, and n (for 3D models) or t1, n, and to (for 2D models). Click the table cells to edit the names. To reverse the direction of the normal for the boundary system, select the check box.

Select an option from the list: (the default), , , or any other applicable coordinate system that you have added. If is selected,select , , or from the list. If is selected from the list, default values are displayed for the local tangent variables root.t1x, root.t1y, and root.t1z (3D) or root.t1x and root.t1y (2D). Enter other values as needed to define a tangent direction by specifying directions for a local tangent plane in the , , and fields.