#### 2.1.14.4. Cut-off Geometry

The Cut-off Geometry feature uses CAD geometries to shape the Solid Model by cutting off elements. The operation is analogous to machining a composite part after curing. See Guide to Solid Modeling for more information. The Cut-off Geometry feature is illustrated in the following figures:

Figure : Extruded Solid Model

Figure : Cut-off Geometries Shown Alongside Extruded Solid Model

Figure : Solid Model with Cut-off Features

##### 2.1.14.4.1. Defining Cut-off Geometry

A Cut-off Geometry is added by selecting Create CutOffGeometry in the context menu of the Cut-off Geometry folder.

The cut-off operation can be defined with either a CAD surface geometry of CAD body geometry. The orientation flag specifies on which side of the surface or the body the elements are cut off. The up orientation specifies that elements in the reverse normal direction of the geometry are cut off. A visualization of the surface normal direction of a CAD body geometry can be displayed with the Show Normals button in the toolbar.

Multiple Cut-Off Geometries can be used for one solid model. The cut offs are applied sequentially in the order of creation of the Cut-Off Geometries.

The following properties must be defined in the Cut-Off Geometry Properties dialog:

###### Cut-off Geometry Properties

- CAD Geometry: CAD geometry for surface or body geometry.

- Orientation: Determines the cutting orientation of a surface/body geometry.

  Figure : Cut-off Geometry Normal Direction

- Relative Merge Tolerance: Set the merging tolerance for neighboring nodes relative to the element size. If two nodes fall within this tolerance they are merged, thus avoiding very small element edges.

##### 2.1.14.4.2. Decomposition of Degenerated Elements

The cutting operation can reshape elements in such a way that they are no longer able to be handled by the solver. The cut-off elements are therefore decomposed into homogenous prism and tetrahedral elements following the cut-off operation. An example of such a decomposition is shown in the figure below. The decomposition takes place automatically during Solid Model generation.

Figure : A Degenerated Hexahedral Element (left) is Decomposed into Several Tetrahedral Elements (right)

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