SURF

Bulk Data Entry Defines a face of a shell or solid (3D solid, axisymmetric solid, or plane-strain solid) element as part of a surface.

Format

(1)	(2)	(3)	(4)	(5)
SURF	`SRFID`	`ELFACE`
	`EID1`	`GA1`	`GB1`	`NORMAL1`
	`EID2`	`GA2`	`GB2`	`NORMAL2`
	`EID3`	etc.	etc.	etc.
	etc.	etc.

Alternative Format (faceted surface)

For a 3D space model: In this format, surface is represented as a collection of 3- or 4-noded polygons (facets). Each facet is defined by 3 or 4 GRID IDs.

For a 2D space model: In this format, surface is represented as a collection of 2-noded line segments (facets). Each facet is defined by 2 Grid IDs.

(1)	(2)	(3)	(4)	(5)
SURF	`SRFID`	`FACE`
	`GA1`	`GB1`	`GC1`	`GD1`
	`GA2`	`GB2`	`GC2`	GD2
	`GA3`	etc.	etc.	etc.
	etc.	etc.

Alternative Format (SET Format)

A surface may also be defined using a form of the SET Bulk Data Entry. With this approach, the surface is composed of all selected shell elements and the external faces of all selected solid elements; that is, those faces that are not connected to any other solid element faces in the model.

To use this format, the SURF keyword is used in place of the SET keyword and the TYPE must be ELEM. All methods for defining a set of type ELEM are valid for this form of surface definition. Refer to the SET Bulk Data Entry.

Definitions

Field	Contents	SI Unit Example
`SRFID`	Surface identification number. Integer Specifies an identification number for this entity. <String> Specifies a user-defined string label for this entity. 4 No default (Integer > 0 or <String>)
`ELFACE`	Flag indicating that the surface is composed of an element face.
`EID#`	Shell or solid element identification number. No default (Integer > 0)
`GA#`	Grid point identification number at the corner of the desired face of a solid element. This field must be blank for shell elements. Default = blank (Integer > 0, blank)
`GB#`	Optional grid point identification number. Used to identify face of solid elements. 1 Default = blank (Integer > 0, blank)
`NORMAL`	Identifies the normal direction for a face of the surface. The normal of a face of a surface may be different from the normal of the underlying elements. 0 (Default) Normal matches the normal of the underlying element. For solid elements, this is pointing into the element. 1 Normal direction is opposite of the underlying element. For solid elements, this is pointing out of the element.
`FACE`	Flag indicating that the surface is composed of 3-noded or 4-noded polygons (facets) for a 3D space model, or, 2-noded line segments (facets) for a 2D space model.
`GA#`, `GB#`, `GC#`, `GD#`	Grid point identification numbers at the corners of the facet. 3D space model If only `GA#`, `GB#`, and `GC#` are specified, it references a 3-noded facet. If `GA#`, `GB#`, `GC#`, and `GD#` are specified, it references a 4-noded facet. 2D space model `GA#` and `GB#` should be specified, and `GC#` and `GD#` should be blank. The normal direction of a facet is defined with the sequence of grids `GA#`, `GB#`, and so on. 2 No default (Integer > 0)

Comments

GB is used to identify faces of solid elements based on the following table:

For HEXA Elements	Grid point identification number at a corner of the desired face that is diagonally opposite GA.
PENTA elements	Quad faces:	Grid point identification number at a corner of the desired face that is diagonally opposite `GA`.
PENTA elements	Tria faces:	Leave blank.
TETRA elements	Grid point identification number at the corner opposite the desired face.
PYRA elements	Quad faces:	Leave blank
PYRA elements	Tria faces:	`GA` and `GB` must specify the grids on the edge of the face that borders the quadrilateral face, and the grids must be ordered so that they define an inward normal using the right-hand rule.
CQUAXI, CTAXI, CTRIAX6, CQPSTN, and CTPSTN elements	`GA` and `GB` should specify the corner grids on the line segment.

For the “FACE” format, the normal direction of a facet is defined as:

Figure 1.
ELIST is an alternative to SET and SURF, but ELIST is intended only to provide compatibility with Nastran decks. It is recommended to use SURF/SET instead of ELIST. Additionally,
- The SURF and SET entries may not be combined with ELIST entries to define damp elements.
- ELIST entries are internally converted to SET entries. If ELIST is referenced on a minimum of one MFLUID entry, then all MFLUID entries in a model must reference ELIST entries. In such cases, if an MFLUID entry references a particular Set Identification Number (<SID>) to define WSURF1/WSURF2 fields without a corresponding ELIST,<SID> in the model, then OptiStruct will not search for a SET/SURF,<SID>.
String based labels allow for easier visual identification, including when being referenced by other entries. For more details, refer to String Label Based Input File.
This card is represented as a contact surface in HyperMesh.