Creating a Cutting Plane

Creating a cutting plane

The first step in creating a cutting plane is to choose how you are going to define it.

A plane is defined by its origin and its local X', Y' and Z' vectors.

The top two options permit the section to be arbitrarily oriented in space, the lower three align it exactly with the model X, Y and Z axes respectively.

Regardless of how it is defined initially the internal definition of the plane is the same, and it may be translated and rotated at will later.

Ansys LS-DYNA Method

This option allows import of definitions in the format used by the Ansys LS-DYNA *DATABASE_CROSS_SECTION keyword:

• Normal vector tail coordinate
• Normal vector head coordinate
• Edge vector head coordinate

If you have written a .ZTF file from PRIMER than any database cross sections in your original input deck can be imported by using the Import DATABASE_SECTION option.

Note: Ansys LS-DYNA cross sections use lagrangian ("basic" in D3PLOT terminology) space.

When you define a cut section using this method you will be asked if you want to swap to "basic" space for compatibility with Ansys LS-DYNA. This is explained in more detail below in Defining a space system for the plane . (See Appendix B for an oa_pref option that will allow you to set this as your default definition method.)

Origin and Vectors Method

This definition requires the user to enter (in model coordinate space) the:

• coordinates of the origin for the plane
• the local x-axis vector
• any vector lying in the local XY plane.

N3: Three nodes method

This method requires you to pick three nodes which form the local axis system as follows:

• Node 1 is the origin
• Node 2 gives the local X axis from the vector |N1N2|.
• Node 3 gives the local X axis from the vector |N1N2|.

Normally the coordinates of the nodes at the current state form the basis of the plane definition, but if you choose " Section follows nodes " you can update the plane at every state as the nodes move.

Constant X,Y,Z Method

The three "constant" values allow you to define the coordinate along the model X, Y or Z axes respectively at which a plane of that constant axis value will be defined. Locally:

• The origin will be [0,0] on the other two axes.
• Local Z is in the +ve direction down the axis chosen.
• The other two axes are chosen for you, aligned with the two unchosen model axes.

If you use a node here then normally the coordinates of that node at the current state are used, but if you choose " Section follows nodes " you can update the plane at every state as the nodes move.