Name

elements — Elements definition block

Synopsis

elements
  eltype ...
  attributes ...
  id n1 n2 ... nnne ...
  attributes ...
  id n1 n2 ... nnne ...
  eltype ...
  attributes ...
  id n1 n2 ... nnne ...
end

Description

elements specifies elements on a one by one basis. To generate elements (and nodes) for various simple geometries, make use of the epatch command.

An element is defined by the element type, a set of attributes, and the node connectivity list.

Element types

eltype et

Specifies the element type (required if attributes are defined). All elements defined thereafter will be of type et until a new et is specified. eltype always undefines all required attributes and resets all optional attributes to their default values.

It is possible to initially specify a dummy element type when defining the element connectivities and to change it later. This can be useful when the mesh and the elementsets are created by an external program, or when the mesh definition shall be independent of the operator. In this case, the correct element type and the element attributes need to be set at a later stage (see below). The following dummy element types are available:

  • P for point elements.

  • L2 and L3 for linear and quadratic line elements, respectively.

  • T3 and T6 for linear and quadratic triangular elements, respectively.

  • Q4, Q8, and Q9 for quadrilateral elements.

  • TE4 and TE10 for linear and quadratic tetrahedral elements, respectively.

  • PR6 and PR15 for linear and quadratic prismatic elements, respectively.

  • HE8, HE20, and HE27 for hexahedral elements.

Specifying the element type and element attributes

Required and optional element attributes depend on the element type and can be consulted in the elements section of the user manual. Attribute definitions apply to all subsequently defined elements, until the attributes are re-defined or the eltype command is specified.

The element type and any element attribute may be specified after the definition of the elements, and may be changed anytime, by specifying a new elements block as shown below. The elements whose attributes shall be set or changed need to be defined in elementlists or elementsets.

Synopsis:

elements
  eltype et
  attributes... elementlist name
  attributes... elementset name
  attributes... epatch id
  ...
end

Element definition

id "[" n1 n2 ... nnne [nodeset id] "]"

Specifies an element. The positive integer number id identifies the element and must be unique within the current branch.

The node connectivity list can be specified in several ways, depending on the element type. Most elements have a fixed number of nodes, in this case, the brackets [ ] around the node indices ni may be omitted:

eltype Q4.S.MITC  mid 1  thickness 2.
1  1 2 4 5
2  2 3 5 6

For elements with a variable number of nodes (i.e. some connector elements), the brackets are mandatory:

eltype RBE
1001  [100001  1 2 3 4 5 6 7 8 9]

For elements with a potentially very large number of nodes, the use of one or several nodesets may be convenient:

eltype RBE
1001  [100001  nodeset left]
1002  [100002  nodeset right]
1003  [100002  nodeset front  nodeset back]

Examples

  • Define a four node quadrilateral shell element with the external number 10001, having a constant shell thickness of 1.3. The element nodes are 1 2 11 12:

    elements
      eltype Q4.S.MITC  mid 2  thickness 1.3
      10001 1 2 11 12
    end

  • Specify 4 elements: Two four node quadrilateral shell elements with a constant thickness of 1.3, and two elements of the same element type with a constant thickness of 1.5:

    elements
      eltype Q4.S.MITC  mid 1  thickness 1.3
      10001 1 2 11 12
      10002 2 3 12 13
      thickness 1.5
      10003 3 4 13 14
      10004 4 5 14 15
    end

  • Like the previous example, but this time, the element type and element attributes are specified after the element connectivities:

    elements
      eltype Q4
      10001 1 2 11 12
      10002 2 3 12 13
      10003 3 4 13 14
      10004 4 5 14 15
    end
    
    elementset thin
      10001 10002
    end
    
    elementset thick
      10003 10004
    end
    
    elements
      eltype Q4.S.MITC  mid 1  thickness 1.3  elementset thin
      eltype Q4.S.MITC  mid 1  thickness 1.5  elementset thick
    end