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) (6) (7) (8) (9) (10)
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) (6) (7) (8) (9) (10)
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.

No default (Integer > 0)

  
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

  1. 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.
    Tria faces: Leave blank.
    TETRA elements Grid point identification number at the corner opposite the desired face.
    PYRA elements Quad faces: Leave blank
    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.
  2. For the “FACE” format, the normal direction of a facet is defined as:


    Figure 1.
  3. 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>.
  4. This card is represented as a contact surface in HyperMesh.