VOLUME_SET

Specifies topological information for a set of volumetric elements.

Type

AcuSolve Command

Syntax

VOLUME_SET ("name") { parameters...}

Qualifier

User-given name.

Parameters

Shape (enumerated) [no default]
Shape of the elements.
four_node_tet or tet4
Four-node tetrahedron.
five_node_pyramid or pyramid5
Five-node pyramid.
six_node_wedge or wedge6
Six-node wedge (prism).
eight_node_brick or hex8
Eight-node brick (hexahedron).
ten_node_tet or tet10
Ten-node tetrahedron.
elements (array) [no default]
A set of element connectivity.

Description

The purpose of the VOLUME_SET command is to simply act as a container that is later referenced by other commands that take volume elements as an input. All elements in a given VOLUME_SET have the same shape. The VOLUME_SET container enables subsequent commands to accept mixed topologies. For example, consider a simulation which contains tetrahedra and prism elements. These volume elements are read into separate VOLUME_SET containers, and are then referenced in a single ELEMENT_SET command as follows:
VOLUME_SET( "tetrahedra" ) {
    elements     = { 1, 1, 2, 4, 3 ;
                       2, 3, 4, 6, 5 ;
                       3, 5, 6, 8, 7 ; }
    shape        = four_node_tet
}
VOLUME_SET( "prisms" ) {
    elements     = { 1, 1, 2, 4, 9, 10, 11 ;
                       2, 3, 4, 6, 12, 13, 14 ;
                       3, 5, 6, 8, 15, 16, 17 ; }
    shape        = six_node_wedge
}
ELEMENT_SET( "fluid elements" ) {
   volume_sets   = { "tetrahedra", "prisms" }
   medium        = fluid
   ...
}

The elements and shape parameters of the VOLUME_SET command are mandatory. shape specifies the shape (topology) of the elements in the set. elements provides the element connectivity. This parameter is a multi column array, with one row per element. The first column corresponds to the element numbers, which are unique numbers within each volume set. Negative values are acceptable. The remaining columns are the element nodes. The number of element nodes and their order must match the shape of the volume set. The element node numbers must be valid numbers, as given by the COORDINATE command.

A four-node tetrahedron element requires four nodes ordered with the local node numbering order shown below:
Figure 1. Four-node Tetrahedron Element


A five-node pyramid element requires five nodes ordered with the local node numbering order shown below:
Figure 2. Five-node Pyramid Element


A six-node wedge (or prism) element requires six nodes ordered with the local node numbering order shown below:
Figure 3. Six-node Wedge Element


An eight-node brick (or hexahedron) element requires eight nodes ordered with the local node numbering order shown below:
Figure 4. Eight-node Brick Element


A ten-node tetrahedron element requires ten nodes ordered with the local node numbering order shown below:
Figure 5. Ten-node Tetrahedron Element


The element nodes may also be read from a file. For the above example, the element nodes may be placed in "tetrahedra.cnn":
1      1         2            4               3
2      3         4            6               5
3      5         6            8               7
and "prisms.cnn":
1      1         2            4               9                  10                     11
2      3         4            6              12                  13                     14
3      5         6            8              15                  16                     17
then read from the file in the volume set commands:
VOLUME_SET( "tetrahedra" ) {
   elements  = Read("tetrahedra.cnn")
shape        = four_node_tet
}
VOLUME_SET( "prisms" ) {
   elements  = Read("prisms.cnn")
shape        = six_node_wedge
}

Each VOLUME_SET command must be referenced in an ELEMENT_SET command in order to have the elements participate in the solution. For example, it is not possible to define a VOLUME_SET strictly for ELEMENT_OUTPUT purposes without using it in an ELEMENT_SET command.