This section defines structure types for describing the grid coordinates, element data, and flow solution data pertaining to a zone. Entities of each of the structure types defined in this section are contained in the Zone_t
structure.
GridCoordinates_t
¶The physical coordinates of the grid vertices are described by the
GridCoordinates_t
structure. This structure contains a list for the data arrays of the individual components of the position vector. It also provides a mechanism for identifying rindpoint data included within the positionvector arrays.
GridCoordinates_t< int IndexDimension, int VertexSize[IndexDimension], int PhysicalDimension> :=
{
DataArray_t<DataType, PhysicalDimension, 2> BoundingBox ; (o)
List( Descriptor_t Descriptor1 ... DescriptorN ) ; (o)
Rind_t<IndexDimension> Rind ; (o/d)
List( DataArray_t<DataType, IndexDimension, DataSize[]>
DataArray1 ... DataArrayN ) ; (o)
DataClass_t DataClass ; (o)
DimensionalUnits_t DimensionalUnits ; (o)
List( UserDefinedData_t UserDefinedData1 ... UserDefinedDataN ) ; (o)
} ;
Note
Default names for the Descriptor_t
, DataArray_t
, and UserDefinedData_t
lists are as shown; users may choose other legitimate names. Legitimate names must be unique within a given instance of GridCoordinates_t and shall not include the names DataClass
, DimensionalUnits
, or Rind
.
There are no required fields for GridCoordinates_t
. Rind
has a default if absent; the default is equivalent to having a Rind
structure whose RindPlanes
array contains all zeros.
The structure parameter DataType must be consistent with the data stored in the DataArray_t
substructures.
GridCoordinates_t
requires two structure parameters: IndexDimension
identifies the dimensionality of the gridsize arrays, and VertexSize
is the number of vertices in each index direction excluding rind points. For unstructured zones, IndexDimension
is always 1 and VertexSize
is the total number of vertices, excluding rind points.
The gridcoordinates data is stored in the list of DataArray_t
entities; each DataArray_t
structure entity may contain a single component of the position vector (e.g., three separate DataArray_t
entities are used for x, y, and z).
Standardized dataname identifiers for the grid coordinates are described in Conventions for DataName Identifiers.
Rind
is an optional field that indicates the number of rind planes (for structured grids) or rind points (for unstructured grids) included in the gridcoordinates data. If Rind
is absent, then the DataArray_t
structure entities contain only “core” vertices of a zone; core refers to all interior and bounding vertices of a zone  VertexSize
is the number of core vertices. Core vertices in a zone begin at [1,1,1] (for a structured zone in 3D) and end at VertexSize
. If Rind
is present, it will provide information on the number of “rind” points in addition to the core points that are contained in the DataArray_t
structures. Indices in DataArray_t
structures have the range \([1  a,1  c,1  e]\) to \([II + b,JJ + d,KK + f]\) where VertexSize = [II,JJ,...]
and RindPlanes = [a,b,...]
(see the Rind_t
structure for the definition of RindPlanes
).
DataClass
defines the default class for data contained in the DataArray_t
entities. For dimensional grid coordinates, DimensionalUnits
may be used to describe the system of units employed. If present, these two entities take precedence over the corresponding entities at higher levels of the CGNS hierarchy, following the standard precedence rules. An example that uses these gridcoordinate defaults is shown under Grid Coordinates Examples.
The UserDefinedData_t
data structure allows arbitrary userdefined data to be stored in Descriptor_t
and DataArray_t
children without the restrictions or implicit meanings imposed on these node types at other node locations.
The BoundingBox
array is optional and provides a measure within which all the grid points lie. It stores minima and maxima of Coordinates values sorted by alphabetical order for Cartesian and Cylindrical coordinate systems while Spherical and Auxiliary coordinate systems retain a specific order to be coherent with the existing SIDS notation:
System 
Bounding Box 

Cartesian 3D 
\[\begin{split}[[Min(CoordinateX), Min(CoordinateY), Min(CoordinateZ)], \\
[Max(CoordinateX), Max(CoordinateY), Max(CoordinateZ)]]\end{split}\]

Cylindrical 3D 
\[\begin{split}[[Min(CoordinateR), Inf(CoordinateTheta), Min(CoordinateX)], \\
[Max(CoordinateR), Sup(CoordinateTheta), Max(CoordinateX)]]\end{split}\]
or
\[\begin{split}[[Min(CoordinateR), Inf(CoordinateTheta), Min(CoordinateY)], \\
[Max(CoordinateR), Sup(CoordinateTheta), Max(CoordinateY)]]\end{split}\]
or
\[\begin{split}[[Min(CoordinateR), Inf(CoordinateTheta), Min(CoordinateZ)], \\
[Max(CoordinateR), Sup(CoordinateTheta), Max(CoordinateZ)]]\end{split}\]

Spherical 
\[\begin{split}[[Min(CoordinateR), Inf(CoordinateTheta), Inf(CoordinatePhi)], \\
[Max(CoordinateR), Sup(CoordinateTheta), Sup(CoordinatePhi)]]\end{split}\]

Auxiliary 3D 
\[\begin{split}[[Min(CoordinateXi), Min(CoordinateEta), Min(CoordinateZeta)], \\
[Max(CoordinateXi), Max(CoordinateEta), Max(CoordinateZeta)]]\end{split}\]

Thus, all coordinate systems are handled in a deterministic way. For 2D coordinate system, the order is kept the same as for 3D. Angle coordinate part of a bounding box is defined by \(Inf(CoordinateTheta)\) and \(Sup(CoordinateTheta)\) (respectively \(Inf(CoordinatePhi)\) and \(Sup(CoordinatePhi)\) for spherical coordinate angle) where \(Inf\) and \(Sup\) operators ensure unicity of the angle interval. The constraints for valid angle bounding box limits are:
\(Inf(CoordinateTheta)\) is included in \([0; 2 π]\)
\(Inf(CoordinateTheta) < Sup(CoordinateTheta)\)
\(Sup(CoordinateTheta)  Inf(CoordinateTheta) ≤ 2 π\)
onedimensional int
array of length IndexDimension
IndexDimension
, VertexSize[]
, Rind
GridCoordinates_t
requires a single structure function, named DataSize
, to identify the array sizes of the gridcoordinates data. A function is required for the following reasons:
the entire grid, including both core and rind points, is stored in the
DataArray_t
entities;the
DataArray_t
structure is simple in that it doesn’t know anything about core versus rind data; it just knows that it contains data of some given size;to make all the
DataArray_t
entities syntactically consistent in their size (i.e., by syntax entities containing x, y and z must have the same dimensionality and dimension sizes), the size of the array is passed onto theDataArray_t
structure as a parameter.
if (Rind is absent) then
{
DataSize[] = VertexSize[] ;
}
else if (Rind is present) then
{
DataSize[] = VertexSize[] + [a + b,...] ;
}
where RindPlanes = [a,b,...]
(see the Rind_t
structure for the definition of RindPlanes
).
This section contains examples of grid coordinates. These examples show the storage of the gridcoordinate data arrays, as well as different mechanisms for describing the class of data and the system of units or normalization.
This example uses Cartesian coordinates for a 2D grid of size 17 × 33; the data arrays include only core vertices, and the coordinates are in units of feet.
! IndexDimension = 2
! VertexSize = [17,33]
GridCoordinates_t<2, [17,33]> GridCoordinates =
{{
DataArray_t<real, 2, [17,33]> CoordinateX =
{{
Data(real, 2, [17,33]) = ((x(i,j), i=1,17), j=1,33) ;
DataClass_t DataClass = Dimensional ;
DimensionalUnits_t DimensionalUnits =
{{
MassUnits = MassUnitsNull ;
LengthUnits = Foot ;
TimeUnits = TimeUnitsNull ;
TemperatureUnits = TemperatureUnitsNull ;
AngleUnits = AngleUnitsNull ;
}} ;
}} ;
DataArray_t<real, 2, [17,33]> CoordinateY =
{{
Data(real, 2, [17,33]) = ((y(i,j), i=1,17), j=1,33) ;
DataClass_t DataClass = Dimensional ;
DimensionalUnits_t DimensionalUnits =
{{
MassUnits = MassUnitsNull ;
LengthUnits = Foot ;
TimeUnits = TimeUnitsNull ;
TemperatureUnits = TemperatureUnitsNull ;
AngleUnits = AngleUnitsNull ;
}} ;
}} ;
}} ;
From the Conventions for DataName Identifiers, the identifiers for \(x\) and \(y\) are CoordinateX
and CoordinateY
, respectively, and both have a data type of real
. The value of DataClass
in CoordinateX
and CoordinateY
indicate the data is dimensional, and DimensionalUnits
specifies the appropriate units are feet. The DimensionalExponents
entity is absent from both CoordinateX
and CoordinateY
; the information that \(x\) and \(y\) are lengths can be inferred from the dataname identifier conventions for coordinate systems.
Note that FORTRAN multidimensional array indexing is used to store the data; this is reflected in the FORTRANlike implied doloops for x(i,j)
and y(i,j)
.
Because the dimensional units for both \(x\) and \(y\) are the same, an alternate approach is to set the data class and system of units using DataClass
and DimensionalUnits
at the GridCoordinates_t
level, and eliminate this information from each instance of DataArray_t
.
GridCoordinates_t<2, [17,33]> GridCoordinates =
{{
DataClass_t DataClass = Dimensional ;
DimensionalUnits_t DimensionalUnits =
{{
MassUnits = MassUnitsNull ;
LengthUnits = Foot ;
TimeUnits = TimeUnitsNull ;
TemperatureUnits = TemperatureUnitsNull ;
AngleUnits = AngleUnitsNull ;
}} ;
DataArray_t<real, 2, [17,33]> CoordinateX =
{{
Data(real, 2, [17,33]) = ((x(i,j), i=1,17), j=1,33) ;
}} ;
DataArray_t<real, 2, [17,33]> CoordinateY =
{{
Data(real, 2, [17,33]) = ((y(i,j), i=1,17), j=1,33) ;
}} ;
}} ;
Since the DataClass
and DimensionalUnits
entities are not present in CoordinateX
and CoordinateY
, the established rules for dimensional data dictate that DataClass
and DimensionalUnits
specified at the GridCoordinates_t
level be used to retrieve the information.
This example uses cylindrical coordinates for a 3D grid whose core size is 17 × 33 × 9; the grid contains a single plane of rind on the minimum and maximum k faces. The coordinates are nondimensional.
! IndexDimension = 3
! VertexSize = [17,33,9]
GridCoordinates_t<3, [17,33,9]> GridCoordinates =
{{
Rind_t<3> Rind =
{{
int[6] RindPlanes = [0,0,0,0,1,1] ;
}} ;
! DataType = real
! IndexDimension = 3
! DataSize = VertexSize + [0,0,2] = [17,33,11]
DataArray_t<real, 3, [17,33,11]> CoordinateRadius =
{{
Data(real, 3, [17,33,11]) = (((r(i,j,k), i=1,17), j=1,33), k=0,10) ;
DataClass_t DataClass = NormalizedByUnknownDimensional ;
}} ;
DataArray_t<real, 3, [17,33,11]> CoordinateZ = {{ }} ;
DataArray_t<real, 3, [17,33,11]> CoordinateTheta = {{ }} ;
}} ;
The value of RindPlanes
specifies two rind planes on the minimum and maximum k faces. These rind planes are reflected in the structure function DataSize
which is equal to the number of core vertices plus two in the k dimension. The value of DataSize
is passed to the DataArray_t
entities. The value of DataClass
indicates the data is nondimensional. Note that if DataClass
is set as NormalizedByUnknownDimensional
at a higher level (CGNSBase_t
or Zone_t
), then it is not needed here.
Note that the entities CoordinateZ
and CoordinateTheta
are abbreviated.
This example uses Cartesian grid coordinates for a 3D unstructured zone where VertexSize
is 15.
GridCoordinates_t<1, 15> GridCoordinates =
{{
! DataType = real
! IndexDimension = 1
! DataSize = VertexSize = 15
DataArray_t<real, 1, 15> CoordinateX =
{{
Data(real, 1, 15) = (x(i), i=1,15) ;
}} ;
DataArray_t<real, 1, 15> CoordinateY =
{{
Data(real, 1, 15) = (y(i), i=1,15) ;
}} ;
DataArray_t<real, 1, 15> CoordinateZ =
{{
Data(real, 1, 15) = (z(i), i=1,15) ;
}} ;
}} ;
Elements_t
¶The
Elements_t
data structure is required for unstructured zones, and contains the element connectivity data, the element type, the element range, the parent elements data, and the number of boundary elements.
Elements_t :=
{
List( Descriptor_t Descriptor1 ... DescriptorN ) ; (o)
Rind_t<IndexDimension> Rind ; (o/d)
IndexRange_t ElementRange ; (r)
int ElementSizeBoundary ; (o/d)
ElementType_t ElementType ; (r)
DataArray_t<int, 1, ElementDataSize> ElementConnectivity ; (r)
DataArray_t<int, 1, ElementSize + 1> ElementStartOffset ; (r)
DataArray_t<int, 2, [ElementSize, 2]> ParentElements; (o)
DataArray_t<int, 2, [ElementSize, 2]> ParentElementsPosition; (o)
List( UserDefinedData_t UserDefinedData1 ... UserDefinedDataN ) ; (o)
} ;
Note
Default names for the Descriptor_t
and UserDefinedData_t
lists are as shown; users may choose other legitimate names. Legitimate names must be unique within a given instance of Elements_t
and shall not include the names ElementConnectivity
, ElementRange
, ParentElements
, ParentElementsPosition
, or Rind
.
IndexRange_t
, ElementType_t
, and ElementConnectivity
are the required fields within the Elements_t
structure. ElementStartOffset
is required only for MIXED
, NGON_n
and NFACE_n
element type. Rind
has a default if absent; the default is equivalent to having a Rind
structure whose RindPlanes
array contains all zeros.
Rind
is an optional field that indicates the number of rind elements included in the elements data. If Rind
is absent, then the DataArray_t
structure entities contain only core elements of a zone. If Rind
is present, it will provide information on the number of rind elements, in addition to the core elements, that are contained in the DataArray_t
structures.
Note that the usage of rind data with respect to the size of the DataArray_t
structures is different under Elements_t
than elsewhere. For example, when rind coordinate data is stored under GridCoordinates_t
, the parameter VertexSize
accounts for the core data only. The size of the DataArray_t
structures containing the grid coordinates is determined by the DataSize
function, which adds the number of rind planes or points to VertexSize
. But for the element connectivity, the size of the DataArray_t
structures containing the connectivity data is just ElementDataSize
, which depends on ElementSize
, and includes both the core and rind elements.
ElementRange
contains the index of the first and last elements defined in ElementConnectivity
. The elements are indexed with a global numbering system, starting at 1, for all element sections under a given Zone_t
data structure. The global numbering insures that each element, whether it’s a cell, a face, or an edge, is uniquely identified by its number. They are also listed as a continuous list of element numbers within any single element section. Therefore the number of elements in a section is:
ElementSize = ElementRange.end  ElementRange.start + 1
The element indices are used for the boundary condition and zone connectivity definition.
ElementSizeBoundary
indicates if the elements are sorted, and how many boundary elements are recorded. By default, ElementSizeBoundary
is set to zero, indicating that the elements are not sorted. If the elements are sorted, ElementSizeBoundary
is set to the number of elements at the boundary. Consequently:
ElementSizeInterior = ElementSize  ElementSizeBoundary
ElementType_t
is an enumeration of the supported element types:
ElementType_t := Enumeration(
ElementTypeNull, ElementTypeUserDefined, NODE, BAR_2, BAR_3,
TRI_3, TRI_6, QUAD_4, QUAD_8, QUAD_9,
TETRA_4, TETRA_10, PYRA_5, PYRA_14,
PENTA_6, PENTA_15, PENTA_18, HEXA_8, HEXA_20, HEXA_27,
MIXED, PYRA_13, NGON_n, NFACE_n,
BAR_4, TRI_9, TRI_10, QUAD_12, QUAD_16,
TETRA_16, TETRA_20, PYRA_21, PYRA_29, PYRA_30,
PENTA_24, PENTA_38, PENTA_40, HEXA_32, HEXA_56, HEXA_64 );
The conventions for element numbering for the various supported types are described in Unstructured Grid Element Numbering Conventions.
For all element types except MIXED
, ElementConnectivity
contains the list of nodes for each element. If the elements are sorted, then it must first list the connectivity of the boundary elements, then that of the interior elements.
ElementConnectivity = Node1_{1}, Node2_{1}, ... NodeN_{1}, Node1_{2}, Node2_{2}, ... NodeN_{2}, ... Node1_{M}, Node2_{M}, ... NodeN_{M}
where M
is the total number of elements (i.e. ElementSize
), and N
is the number of nodes per element.
ElementDataSize
indicates the total size (number of integers) of the array ElementConnectivity
. For all element types except MIXED
, NGON_n
, and NFACE_n
, ElementDataSize
is given by:
ElementDataSize = ElementSize * NPE[ElementType]
where NPE[ElementType]
is a function returning the number of nodes for the given ElementType
. For example, NPE[HEXA_8]=8
.
When the section ElementType
is MIXED
, the data array ElementConnectivity
contains
one extra integer per element, to hold each individual element type:
ElementConnectivity = Etype_{1}, Node1_{1}, Node2_{1}, ... NodeN_{1}, Etype_{2}, Node1_{2}, Node2_{2}, ... NodeN_{2}, ... Etype_{M}, Node1_{M}, Node2_{M}, ... NodeN_{M}
where again M
is the total number of elements, and \(\scriptsize\mathsf{N}_\mathrm{i}\) Ni
is the number of nodes in element i
.
The data array ElementStartOffset
contains the starting positions of each element in the ElementConnectivity
data array
and its last value corresponds to the ElementConnectivity
total size:
ElementStartOffset = 0, NPE[Etype_{1}] + 1, ... ElementStartOffset[n1] + NPE[Etype_{n}] + 1, ..., ElementStartOffset[M1] + NPE[Etype_{M}] + 1 = ElementDataSize
In the case of MIXED
element section, ElementDataSize
is given by:
ElementDataSize = ∑(NPE[ElementType_{n}] + 1)
where the summation is over n
, and n
represents a specific element type.
Arbitrary polyhedral elements may be defined using the NGON_n
and NFACE_n
element types. The NGON_n
element type is used to specify all the faces in the grid, and the NFACE_n
element type is then used to define the polyhedral elements as a collection of these faces. Except for boundary faces, each face of a polyhedral element must be shared by another polyhedral element.
For example, for NGON_n
, the data array ElementConnectivity
contains a list of nodes making up each face in the grid while ElementStartOffset
provides the starting position of each face in the ElementConnectivity
array:
ElementConnectivity = Node1_{1}, Node2_{1}, ... NodeN_{1}, Node1_{2}, Node2_{2}, ... NodeN_{2}, ... Node1_{M}, Node2_{M}, ... NodeN_{M} ElementStartOffset = 0, Nnodes_{1}, Nnodes_{1} + Nnodes_{2}, ... ..., ElementStartOffset[i1] + Nnodes_{i}, ..., ElementStartOffset[M1] + Nnodes_{M} = ElementDataSize
where here M
is the total number of faces, and Nnodesi
is the number of nodes in face i
.
The ElementDataSize
is the total number of nodes defining all the faces.
Note that the number of nodes in face i
is given by:
Nnodes_{i} = ElementStartOffset[i+1]  ElementStartOffset[i]
Then for NFACE_n
, ElementConnectivity
contains the list of face elements making up each polyhedral element,
while ElementStartOffset
provides the starting position of each polyhedral element in the ElementConnectivity
array:
ElementConnectivity = Face1_{1}, Face2_{1}, ... FaceN_{1}, Face1_{2}, Face2_{2}, ... FaceN_{2}, ... Face1_{M}, Face2_{M}, ... FaceN_{M} ElementStartOffset = 0, Nfaces_{1}, Nfaces_{1} + Nfaces_{2}, ... ..., ElementStartOffset[i1] + Nfaces_{i}, ..., ElementStartOffset[M1] + Nfaces_{M} = ElementDataSize
where now M
is the total number of polyhedral elements, and Nfacesi
is the number of faces in element i
.
The sign of the face number determines its orientation (i.e., the direction of the face normal, constructed as defined by the convention for 2D elements). If the face number is positive, the face normal is directed outward; if it’s negative, the face normal is directed inward. The ElementDataSize is the sum of the number of faces defining each polyhedral element.
Note that the number of faces in element i
is given by:
Nfaces_{i} = ElementStartOffset[i+1]  ElementStartOffset[i]
For face elements in 3D, or bar element in 2D, additional data may be provided for each element in ParentElements
and ParentElementsPosition
.
The element numbers of the two adjacent cells for each face are given in ParentElements
.
The corresponding canonical positions of the face in the two parent cells is given in ParentElementsPosition
;
these canonical face positions are defined in the section Unstructured Grid Element Numbering Conventions.
For faces on the boundary of the domain, the second parent is set to zero.
The UserDefinedData_t
data structure allows arbitrary userdefined data to be stored in Descriptor_t
and
DataArray_t
children without the restrictions or implicit meanings imposed on these node types at other node locations.
This section contains four examples of elements definition in CGNS.
The first example is for a simple threeelement tetrahedral grid, using the TETRA_4
element type.
The second example is for the same grid as the first example, but the elements are treated as general polyhedra to illustrate the use of the NGON_n
and NFACE_n
element types.
The third and fourth examples are for an unstructured zone with 15 tetrahedral and 10 hexahedral elements, with the third example defining the elements in separate sections for the TETRA_4
and HEXA_8
element types, and the fourth example combining them using the MIXED
element type.
This example uses the simple threeelement tetrahedral grid shown below.
The element type is TETRA_4
, and the connectivity is defined in ElementConnectivity
by specifying the four nodes comprising each element, with the order consistent with the numbering conventions for tetrahedral elements. The data in ElementConnectivity
is grouped by element; note that the parentheses are added here for presentation purposes only.
Zone_t UnstructuredZone =
{{
Elements_t TetraElements =
{{
IndexRange_t ElementRange = [1,3] ;
ElementType_t ElementType = TETRA_4 ;
DataArray_t<int, 1, NPE[TETRA_4] × 3> ElementConnectivity =
{{
Data(int, 1, NPE[TETRA_4] × 3) =
(1, 2, 3, 4), (2, 5, 3, 6), (2, 6, 3, 4) ;
}} ;
}} ;
}} ;
This example uses the same grid as in the previous example, but treats the elements as general polyhedra to illustrate the use of the NGON_n
and NFACE_n
element types. The grid consists of three volume elements, each made up of four face elements, with each face defined by three nodes.
For each face, the nodes comprising that face are listed in ElementConnectivity
for the NGON_n
element type.
The ElementRange
is [1,10]
, corresponding to the 10 total faces in the grid. The ElementDataSize
is 30, corresponding to the total of 30 nodes defining the 10 faces.
The faces making up the three volume elements are then listed in ElementConnectivity
for the NFACE_n
element type. The ElementRange
is [11,13]
, corresponding to the three volume elements. The ElementDataSize
is 12, corresponding to three volume elements with four faces per element. Note that the face numbers for faces 3 and 8 are negative in the definition of volume element 3, since their normals point inward for that element. Again, the parentheses in ElementConnectivity
are for presentation purposes only.
Zone_t UnstructuredZone =
{{
Elements_t NgonElements =
{{
IndexRange_t ElementRange = [1,10] ;
ElementType_t ElementType = NGON_n ;
DataArray_t<int, 1, 30> ElementConnectivity =
{{
Data(int, 1, 30) =
(1, 3, 2), (1, 2, 4), (2, 3, 4), (3, 1, 4),
(2, 3, 5), (2, 5, 6), (5, 3, 6), (3, 2, 6),
(2, 6, 4), (6, 3, 4) ;
}} ;
DataArray_t<int, 1, 11> ElementStartOffset =
{{
Data(int, 1, 11) =
0, 3, 6, 9,
12, 15, 18, 21,
24, 27, 30 ;
}} ;
}} ;
Elements_t NfaceElements =
{{
IndexRange_t ElementRange = [11,13] ;
ElementType_t ElementType = NFACE_n ;
DataArray_t<int, 1, 12> ElementConnectivity =
{{
Data(int, 1, 12) =
( 1, 2, 3, 4),
( 5, 6, 7, 8),
(8, 9, 10, 3) ;
}} ;
DataArray_t<int, 1, 4> ElementStartOffset =
{{
Data(int, 1, 4) =
0, 4, 8, 12 ;
}} ;
}} ;
}} ;
In this example, elements are defined for an unstructured zone with 15 tetrahedral and 10 hexahedral elements. The elements are written in two separate sections, one for the tetrahedral elements and one for the hexahedral elements.
Zone_t UnstructuredZone =
{{
Elements_t TetraElements =
{{
IndexRange_t ElementRange = [1,15] ;
int ElementSizeBoundary = 10 ;
ElementType_t ElementType = TETRA_4 ;
DataArray_t<int, 1, NPE[TETRA_4] × 15> ElementConnectivity =
{{
Data(int, 1, NPE[TETRA_4] × 15) = (node(i,j), i=1,NPE[TETRA_4], j=1,15) ;
}} ;
}} ;
Elements_t HexaElements =
{{
IndexRange_t ElementRange = [16,25] ;
int ElementSizeBoundary = 0 ;
ElementType_t ElementType = HEXA_8 ;
DataArray_t<int, 1, NPE[HEXA_8] × 10> ElementConnectivity =
{{
Data(int, 1, NPE[HEXA_8] × 10) = (node(i,j), i=1,NPE[HEXA_8], j=1,10) ;
}} ;
}} ;
}} ;
In this example, the same unstructured zone described in the previous example is written in a single element section of type MIXED
(i.e., an unstructured grid composed of mixed elements).
Zone_t UnstructuredZone =
{{
Elements_t MixedElementsSection =
{{
IndexRange_t ElementRange = [1,25] ;
ElementType_t ElementType = MIXED ;
DataArray_t<int, 1, ElementDataSize> ElementConnectivity =
{{
Data(int, 1, ElementDataSize) = (etype(j),(node(i,j),
i=1,NPE[etype(j)]), j=1,25) ;
}} ;
}} ;
DataArray_t<int, 1, 26> ElementStartOffset =
{{
Data(int, 1, 26) =
0, (NPE[etype(j)]+ElementStartOffset[j]+1, j=1,25) ;
}} ;
}} ;
Axisymmetry_t
¶The
Axisymmetry_t
data structure allows recording the axis of rotation and the angle of rotation around this axis for a twodimensional dataset that represents an axisymmetric database.
Axisymmetry_t :=
{
List( Descriptor_t Descriptor1 ... DescriptorN ) ; (o)
DataArray_t<real,1,2> AxisymmetryReferencePoint ; (r)
DataArray_t<real,1,2> AxisymmetryAxisVector ; (r)
DataArray_t<real,1,1> AxisymmetryAngle ; (o)
DataArray_t<char,2,[32,2]> CoordinateNames ; (o)
DataClass_t DataClass ; (o)
DimensionalUnits_t DimensionalUnits ; (o)
List( UserDefinedData_t UserDefinedData1 ... UserDefinedDataN ) ; (o)
} ;
Note
Default names for the Descriptor_t
and UserDefinedData_t
lists are as shown; users may choose other legitimate names. Legitimate names must be unique within a given instance of Axisymmetry_t and shall not include the names AxisymmetryAngle, AxisymmetryAxisVector, AxisymmetryReferencePoint, CoordinateNames, DataClass, or DimensionalUnits.
AxisymmetryReferencePoint
and AxisymmetryAxisVector
are the required fields within the Axisymmetry_t
structure.
AxisymmetryReferencePoint
specifies the origin used for defining the axis of rotation.
AxisymmetryAxisVector
contains the direction cosines of the axis of rotation, through the AxisymmetryReferencePoint
. For example, for a 2D dataset defined in the \((x,y)\) plane, if AxisymmetryReferencePoint
contains \((0,0)\) and AxisymmetryAxisVector
contains \((1,0)\), the xaxis is the axis of rotation.
AxisymmetryAngle
allows specification of the circumferential extent about the axis of rotation. If this angle is undefined, it is assumed to be 360°.
CoordinateNames
may be used to specify the first and second coordinates used in the definition of AxisymmetryReferencePoint
and AxisymmetryAxisVector
. If not found, it is assumed that the first coordinate is CoordinateX
and the second is CoordinateY
. The coordinates given under CoordinateNames
, or implied by using the default, must correspond to those found under GridCoordinates_t
.
DataClass
defines the default class for numerical data contained in the DataArray_t
entities. For dimensional data, DimensionalUnits
may be used to describe the system of units employed. If present, these two entities take precedence over the corresponding entities at higher levels of the CGNS hierarchy, following the standard precedence rules.
The UserDefinedData_t
data structure allows arbitrary userdefined data to be stored in Descriptor_t
and DataArray_t
children without the restrictions or implicit meanings imposed on these node types at other node locations.
RotatingCoordinates_t
¶The
RotatingCoordinates_t
data structure is used to record the rotation center and rotation rate vector of a rotating coordinate system.
RotatingCoordinates_t :=
{
List( Descriptor_t Descriptor1 ... DescriptorN ) ; (o)
DataArray_t<real,1,PhysicalDimension> RotationCenter ; (r)
DataArray_t<real,1,PhysicalDimension> RotationRateVector ; (r)
DataClass_t DataClass ; (o)
DimensionalUnits_t DimensionalUnits ; (o)
List( UserDefinedData_t UserDefinedData1 ... UserDefinedDataN ) ; (o)
} ;
Note
Default names for the Descriptor_t
and UserDefinedData_t
lists are as shown; users may choose other legitimate names. Legitimate names must be unique within a given instance of RotatingCoordinates_t
and shall not include the names DataClass
, DimensionalUnits
, RotationCenter
, or RotationRateVector
.
RotationCenter
and RotationRateVector
are the required fields within the RotatingCoordinates_t
structure.
RotationCenter
specifies the coordinates of the center of rotation, and RotationRateVector
specifies the components of the angular velocity of the grid about the center of rotation. Together, they define the angular velocity vector. The direction of the angular velocity vector specifies the axis of rotation, and its magnitude specifies the rate of rotation.
For example, for the common situation of rotation about the xaxis, RotationCenter
would be specified as any point on the xaxis, like \((0,0,0)\). RotationRateVector
would then be specified as \((ω,0,0)\), where ω is the rotation rate. Using the righthand rule, ω would be positive for clockwise rotation (looking in the +x direction), and negative for counterclockwise rotation.
Note that for a rotating coordinate system, the axis of rotation is defined in the inertial frame of reference, while the grid coordinates stored using the GridCoordinates_t
data structure are relative to the rotating frame of reference.
DataClass
defines the default class for data contained in the DataArray_t
entities. For dimensional data, DimensionalUnits
may be used to describe the system of units employed. If present, these two entities take precedence over the corresponding entities at higher levels of the CGNS hierarchy, following the standard precedence rules.
The UserDefinedData_t
data structure allows arbitrary userdefined data to be stored in Descriptor_t
and DataArray_t
children without the restrictions or implicit meanings imposed on these node types at other node locations.
If rotating coordinates are used, it is useful to store variables relative to the rotating frame. Standardized dataname identifiers should be used for these variables, as defined for flowsolution quantities in the section Conventions for DataName Identifiers.
FlowSolution_t
¶The flow solution within a given zone is described by the
FlowSolution_t
structure. This structure contains a list for the data arrays of the individual flowsolution variables, as well as identifying the grid location of the solution. It also provides a mechanism for identifying rindpoint data included within the data arrays.
FlowSolution_t< int CellDimension, int IndexDimension,
int VertexSize[IndexDimension],
int CellSize[IndexDimension] > :=
{
List( Descriptor_t Descriptor1 ... DescriptorN ) ; (o)
GridLocation_t GridLocation ; (o/d)
Rind_t<IndexDimension> Rind ; (o/d)
IndexRange_t<IndexDimension> PointRange ; (o)
IndexArray_t<IndexDimension, ListLength[], int> PointList ; (o)
List( DataArray_t<DataType, IndexDimension, DataSize[]>
DataArray1 ... DataArrayN ) ; (o)
DataClass_t DataClass ; (o)
DimensionalUnits_t DimensionalUnits ; (o)
List( UserDefinedData_t UserDefinedData1 ... UserDefinedDataN ) ; (o)
} ;
Note
Default names for the Descriptor_t
, DataArray_t
, and UserDefinedData_t
lists are as shown; users may choose other legitimate names. Legitimate names must be unique within a given instance of FlowSolution_t
and shall not include the names DataClass
, DimensionalUnits
, GridLocation
, PointList
, PointRange
, or Rind
.
There are no required fields for FlowSolution_t
. GridLocation
has a default of Vertex
if absent. Rind
also has a default if absent; the default is equivalent to having an instance of Rind
whose RindPlanes
array contains all zeros.
Both of the fields PointList
and PointRange
are optional. Only one of these two fields may be specified.
The structure parameter DataType
must be consistent with the data stored in the DataArray_t
structure entities; DataType
is real
for all flowsolution identifiers defined in the section Conventions for DataName Identifiers.
For unstructured zones GridLocation
options are limited to Vertex
or CellCenter
, unless one of PointList
or PointRange
is present.
Indexing of data within the DataArray_t
structure must ne consistent with the associated numbering of vertices or elements.
FlowSolution_t
requires four structure parameters; CellDimension
identifies the dimensionality of cells or elements, IndexDimension
identifies the dimensionality of the gridsize arrays, and VertexSize
and CellSize
are the number of core vertices and cells, respectively, in each index direction, excluding rind points. For structured zones, core vertices and cells begin at [1,1,1]
(in 3D) and end at VertexSize
and CellSize
, respectively. For unstructured zones, IndexDimension
is always 1.
The flow solution data is stored in the list of DataArray_t
entities; each DataArray_t
structure entity may contain a single component of the solution vector. Standardized dataname identifiers for the flowsolution quantities are described in the section Conventions for DataName Identifiers. The field GridLocation
specifies the location of the solution data with respect to the grid; if absent, the data is assumed to coincide with grid vertices (i.e., GridLocation = Vertex
). All data within a given instance of FlowSolution_t
must reside at the same grid location.
For structured grids, the value of GridLocation
alone specifies the location and indexing of the flow solution data. Vertices are explicitly indexed. Cell centers and face centers are indexed using the minimum of the connecting vertex indices, as described in the section Structured Grid Notation and Indexing Conventions.
For unstructured grids, the value of GridLocation
alone specifies location and indexing of flow solution data only for vertex and cellcentered data. The reason for this is that elementbased grid connectivity provided in the Elements_t
data structures explicitly indexes only vertices and cells. For data stored at alternate grid locations (e.g., edges), additional connectivity information is needed. This is provided by the optional fields PointRange
and PointList
; these refer to vertices, edges, faces or cell centers, depending on the values of CellDimension
and GridLocation
. The following table shows these relations. The NODE
element type should not be used in place of the vertex. A vertex GridLocation
should use the GridLocation = Vertex
pattern, which implies an indexing on the grid coordinates arrays and not a NODE Elements_t
array.
CellDimension 
GridLocation 


Vertex 
EdgeCenter 
*FaceCenter 
CellCenter 

1 
vertices 
 
 
cells (line elements) 
2 
vertices 
edges 
 
cells (area elements) 
3 
vertices 
edges 
faces 
cells (volume elements) 
Note
In the table, *FaceCenter stands for the possible types: IFaceCenter
, JFaceCenter
, KFaceCenter
, or FaceCenter
.
Although intended for edge or facebased solution data for unstructured grids, the fields PointRange/List
may also be used to (redundantly) index vertex and cellcentered data. In all cases, indexing of flow solution data corresponds to the element numbering as defined in the Elements_t
data structures.
Rind
is an optional field that indicates the number of rind planes (for structured grids) or rind points or elements (for unstructured grids) included in the data. Its purpose and function are identical to those described for the GridCoordinates_t
structure. Note, however, that the Rind
in this structure is independent of the Rind
contained in GridCoordinates_t
. They are not required to contain the same number of rind planes or elements. Also, the location of any flowsolution rind points is assumed to be consistent with the location of the core flow solution points (e.g., if GridLocation = CellCenter
, rind points are assumed to be located at fictitious cell centers).
DataClass
defines the default class for data contained in the DataArray_t
entities. For dimensional flow solution data, DimensionalUnits
may be used to describe the system of units employed. If present, these two entities take precedence over the corresponding entities at higher levels of the CGNS hierarchy, following the standard precedence rules.
The UserDefinedData_t
data structure allows arbitrary userdefined data to be stored in Descriptor_t
and DataArray_t
children without the restrictions or implicit meanings imposed on these node types at other node locations.
int
PointRange
, PointList
FlowSolution_t
requires the structure function ListLength
, which is used to specify the number of entities (e.g. vertices) corresponding to a given PointRange
or PointList
. If PointRange
is specified, then ListLength
is obtained from the number of points (inclusive) between the beginning and ending indices of PointRange
. If PointList
is specified, then ListLength
is the number of indices in the list of points. In this situation, ListLength
becomes a user input along with the indices of the list PointList
. By user we mean the application code that is generating the CGNS database.
onedimensional int
array of length IndexDimension
IndexDimension
, VertexSize[]
, CellSize[]
, GridLocation
, Rind
, ListLength[]
The function DataSize[]
is the size of flow solution data arrays. If Rind
is absent then DataSize
represents only the core points; it will be the same as VertexSize
or CellSize
depending on GridLocation
. The definition of the function DataSize[]
is as follows:
if (PointRange/PointList is present) then
{
DataSize[] = ListLength[] ;
}
else if (Rind is absent) then
{
if (GridLocation = Vertex) or (GridLocation is absent)
{
DataSize[] = VertexSize[] ;
}
else if (GridLocation = CellCenter) then
{
DataSize[] = CellSize[] ;
}
}
else if (Rind is present) then
{
if (GridLocation = Vertex) or (GridLocation is absent) then
{
DataSize[] = VertexSize[] + [a + b,...] ;
}
else if (GridLocation = CellCenter)
{
DataSize[] = CellSize[] + [a + b,...] ;
}
}
where RindPlanes = [a,b,...]
(see the Rind_t
structure for the definition of RindPlanes
).
This section contains an example of the flow solution entity, including the designation of grid location and rind planes and datanormalization mechanisms.
Conservationequation variables (\(\rho, \rho U, \rho V \text{ and } \rho e_0\)) for a 2D grid of size \(11 \times 5\). The flowfield is cellcentered with two planes of rind data. The density, momentum and stagnation energy (\(\rho e_0\)) data is nondimensionalized with respect to a freestream reference state whose quantities are dimensional. The freestream density and pressure are used for normalization; these values are \(1.226\,kg/m^3\) and \(1.0132 \times 10^5\,N/m^2\) (standard atmosphere conditions). The dataname identifier conventions for the conservationequation variables are Density
, MomentumX
, MomentumY
and EnergyStagnationDensity
.
! CellDimension = 2
! IndexDimension = 2
! VertexSize = [11,5]
! CellSize = [10,4]
FlowSolution_t<2, [11,5], [10,4]> FlowExample =
{{
GridLocation_t GridLocation = CellCenter ;
Rind_t<2> Rind =
{{
int[4] RindPlanes = [2,2,2,2] ;
}} ;
DataClass_t DataClass = NormalizedByDimensional ;
DimensionalUnits_t DimensionalUnits =
{{
MassUnits = Kilogram ;
LengthUnits = Meter ;
TimeUnits = Second ;
TemperatureUnits = TemperatureUnitsNull ;
AngleUnits = AngleUnitsNull ;
}} ;
! DataType = real
! Dimension = 2
! DataSize = CellSize + [4,4] = [14,8]
DataArray_t<real, 2, [14,8]> Density =
{{
Data(real, 2, [14,8]) = ((rho(i,j), i=1,12), j=1,6) ;
DataConversion_t DataConversion =
{{
ConversionScale = 1.226 ;
ConversionOffset = 0 ;
}} ;
DimensionalExponents_t DimensionalExponents =
{{
MassExponent = +1 ;
LengthExponent = 3 ;
TimeExponent = 0 ;
TemperatureExponent = 0 ;
AngleExponent = 0 ;
}} ;
}} ;
DataArray_t<real, 2, [14,8]> MomentumX =
{{
Data(real, 2, [14,8]) = ((rho_u(i,j), i=1,12), j=1,6) ;
DataConversion_t DataConversion =
{{
ConversionScale = 352.446 ;
ConversionOffset = 0 ;
}} ;
}} ;
DataArray_t<real, 2, [14,8]> MomentumY =
{{
Data(real, 2, [14,8]) = ((rho_v(i,j), i=1,12), j=1,6) ;
DataConversion_t DataConversion =
{{
ConversionScale = 352.446 ;
ConversionOffset = 0 ;
}} ;
}} ;
DataArray_t<real, 2, [14,8]> EnergyStagnationDensity =
{{
Data(real, 2, [14,8]) = ((rho_e0(i,j), i=1,12), j=1,6) ;
DataConversion_t DataConversion =
{{
ConversionScale = 1.0132e+05 ;
ConversionOffset = 0 ;
}} ;
}} ;
}} ;
The value of GridLocation
indicates the data is at cell centers, and the value of RindPlanes
specifies two rind planes on each face of the zone. The resulting value of the structure function DataSize
is the number of cells plus four in each coordinate direction; this value is passed to each of the DataArray_t
entities.
Since the data are all nondimensional and normalized by dimensional reference quantities, this information is stated in DataClass
and DimensionalUnits
at the FlowSolution_t
level rather than attaching the appropriate DataClass
and DimensionalUnits
to each DataArray_t
entity. It could possibly be at even higher levels in the hierarchy. The contents of DataConversion
are in each case the denominator of the normalization; this is \(\rho_\infty\) for density, \((p_\infty \rho_\infty)^{1/2}\) for momentum, and \(p_\infty\) for stagnation energy. The dimensional exponents are specified for density. For all the other data, the dimensional exponents are to be inferred from the dataname identifiers.
Note that no information is provided to identify the actual reference state or indicate that it is freestream. This information is not needed for data manipulations involving renormalization or changing the units of the converted raw data.
ZoneSubRegion_t
¶The ZoneSubRegion_t
node allows for the ability to give flowfield or other information over a subset of the entire zone in a CGNS file. This subset may be over a portion of a boundary,
or it may be over a portion of the entire field.
ZoneSubRegion_t< int IndexDimension, int CellDimension > :=
{
List( Descriptor_t Descriptor1 ... DescriptorN ) ; (o)
int RegionCellDimension ; (o/d)
GridLocation_t GridLocation ; (o/d)
IndexRange_t<IndexDimension> PointRange ; (r:o:o:o)
IndexArray_t<IndexDimension, ListLength, int> PointList ; (o:r:o:o)
Descriptor_t BCRegionName ; (o:o:r:o)
Descriptor_t GridConnectivityRegionName ; (o:o:o:r)
Rind_t<IndexDimension> Rind; (o/d)
List( DataArray_t<DataType, 1, ListLength[]> DataArray1 ... DataArrayN ) ; (o)
FamilyName_t FamilyName ; (o)
List( AdditionalFamilyName_t AddFamilyName1 ... AddFamilyNameN ) ; (o)
DataClass_t DataClass ; (o)
DimensionalUnits_t DimensionalUnits ; (o)
List( UserDefinedData_t UserDefinedData1 ... UserDefinedDataN ) ; (o)
} ;
Note
Default names for the Descriptor_t
, DataArray_t
, and UserDefinedData_t
lists are as shown;
users may choose other legitimate names. Legitimate names must be unique within a given instance of ZoneSubRegion_t
and shall not include the names RegionCellDimension
, Rind
, PointRange
, PointList
, BCRegionName
, GridConnectivityRegionName
, FamilyName
, DataClass
or DimensionalUnits
.
RegionCellDimension
must be equal to or less than the cell dimension for the zone. If absent, then its default value is CellDimension
.
GridLocation
has a default value of Vertex
if absent. Permissible values of GridLocation
are determined by RegionCellDimension
(see below). All data within a given instance of ZoneSubRegion_t
must reside at the same grid location.
The extent of the region and distribution of its data is specified by one of PointRange
, PointList
, BCRegionName
, or GridConnectivityRegionName
. One and only one of these must be specified.
The extent of the subregion and the distribution of data within that subregion is determined by RegionCellDimension
, GridLocation
, and one of PointRange/List
, BCRegionName
or GridConnectivityRegionName
. For a 3D subregion (RegionCellDimension
= 3), data can be located at vertices, edges, face centers or cell centers. For a 2D subregion (RegionCellDimension
= 2), data can be located at vertices, edges or cell centers (i.e. area elements). It is anticipated that one of the widest uses for ZoneSubRegion_t
will be to store specific boundaryonly information. For example, in a 3D simulation, one may wish to store additional data on surfaces. In this case, the RegionCellDimension
would be set to 2.
PointRange/List
refer to vertices, edges, faces or cell centers, depending on the values of RegionCellDimension
and GridLocation
. Note that it is both the dimensionality of the zone (CellDimension
) as well as the dimensionality of the subregion (RegionCellDimension
), that determines the types of elements permissible in PointRange/List
. The following table shows these relations.
CellDimension 
RegionCellDimension 
GridLocation 


Vertex 
EdgeCenter 
*FaceCenter 
CellCenter 

1 
1 
vertices 
 
 
cells (line elements) 
2 
1 
vertices 
edges 
 
 
2 
2 
vertices 
edges 
 
cells (area elements) 
3 
1 
vertices 
edges 
 
 
3 
2 
vertices 
edges 
faces 
 
3 
3 
vertices 
edges 
faces 
cells (volume elements) 
Note
In the table, *FaceCenter stands for the possible types: IFaceCenter
, JFaceCenter
, KFaceCenter
, or FaceCenter
.
For both structured and unstructured grids, GridLocation = Vertex
means that PointRange/List
refers to vertex indices. For structured grids, edges, faces and cell centers are indexed using the minimum of the connecting vertex indices, as described in the section Structured Grid Notation and Indexing Conventions. For unstructured grids, edges, faces and cell centers are indexed using their element numbering, as defined in the Elements_t
data structures.
If the vertices or elements of the subregion are continuously numbered, then PointRange
may be used. Otherwise, PointList
should be used to list the vertices/elements. Alternatively, if the data locations and range of the subregion coincide with an existing BC region or zonetozone GridConnectivity region, then BCRegionName
or GridConnectivityRegionName
may be used. BCRegionName
is a string giving the name of an existing BC_t
node of the current zone. GridConnectivityRegionName
is a string giving the name of an existing GridConnectivity1to1_t
or GridConnectivity_t
node of the current zone. The name referred to should be unambiguous.
Consistent with FlowSolution_t
, the subregion’s solution data is stored in the list of DataArray_t
entities; each DataArray_t
structure entity contains a single quantity. Standardized dataname identifiers for solution quantities are described in the section Conventions for DataName Identifiers. As noted above, all solution data within a given subregion must reside at the same grid location.
DataClass
defines the default class for data contained in the DataArray_t
entities. For dimensional flow solution data, DimensionalUnits
may be used to describe the system of units employed. If present, these two entities take precedence over the corresponding entities at higher levels of the CGNS hierarchy, following the standard precedence rules.
ZoneSubRegion_t
requires the structure function ListLength[]
, which is used to specify the number of data points (e.g. vertices, cell centers, face centers, edge centers) corresponding to the given PointRange/List
. If PointRange
is specified, then ListLength
is obtained from the number of points (inclusive) between the beginning and ending indices of PointRange
. If PointList
is specified, then ListLength
is the number of indices in the list of points. In this situation, ListLength
becomes a user input along with the indices of the list PointList
. By user we mean the application code that is generating the CGNS database.
Rind
is an optional field that indicates the number of rind planes (for structured grids) or rind points (for unstructured grids). If Rind
is absent, then the DataArray_t
structure entities contain only core data of length ListLength
, as defined for this region. If Rind
is present, it will provide information on the number of rind elements, in addition to the ListLength
, that are contained in the DataArray_t
structures. The bottom line is that Rind
simply adds a specified number to ListLength
, as used by the DataArray_t
structures.
The UserDefinedData_t
data structure allows arbitrary userdefined data to be stored.
There may be multiple instances of ZoneSubRegion_t
in a given zone. These may simply be multiple regions defined for a single solution, or they may be associated with different times / different solutions in a timedependent simulation (in which case ZoneIterativeData_t
should be used to associate them).
All FamilyName
and AdditionalFamilyName
entries should respect the rules defined in Base Level Families and Zone_t
.
This section contains four examples of Zone Subregions, including the use of PointList
, PointRange
and BCRegionName
.
For this example, it is assumed that a 1zone 3D structured grid exists of size (\(197\times97\times33\)). Inside of this zone, the user wishes to output a special subset region of interior data (say, temperature and kinematic viscosity) at the specific cellcenter locations \(i = 121149\), \(j = 1745\), \(k = 2123\). Even though this same data may possibly exist under FlowSolution_t
(which holds the flowfield data for the entire zone), this particular location may represent a special region of interest where the user wants to focus attention or output different types of flowfield variables or userdefined data. Note that for structured grids, the location list always references grid nodes; in this case with GridLocation = Cellcenter
the cell centers are indexed by the minimum \(i\), \(j\), and \(k\) indices of the connecting vertices.
Under Zone_t
:
ZoneSubRegion_t<3,3> Region1 =
{{
GridLocation_t GridLocation = CellCenter ;
int RegionCellDimension = 3;
IndexRange_t<3> PointRange =
{{
int[3] Begin = [121,17,21];
int[3] End = [149,45,21];
}};
! ListLength = (149121+1)*(4517+1)*(2321+1) = 29*29*3 = 2523
DataArray_t<real,1,2523> Temperature =
{{
Data(real,1,2523) = temperature at the cell centers specified
}} ;
DataArray_t<real,1,2523> ViscosityKinematic =
{{
Data(real,1,2523) = kinematic viscosity at the cell centers specified
}} ;
}} ; ! end Region1
This example is like the previous one, except it is for an unstructured zone. Inside of this zone, the user wishes to output a special subset region of data (say, temperature and kinematic viscosity) at a specific list of 2523 element cellcenter locations, located somewhere within the (larger) field of elements. Recall that when GridLocation
is anything other than Vertex
in conjunction with unstructured grids, then the location list represents element numbers and not grid node numbers.
Under Zone_t
:
ZoneSubRegion_t<1,3> Region1 =
{{
GridLocation_t GridLocation = CellCenter ;
int RegionCellDimension = 3;
IndexArray_t<1,2523,int> PointList =
{{
int[1] ElementList = list of 3D element numbers where region data given
}} ;
! ListLength = length of the element list = 2523
DataArray_t<real,1,2523> Temperature =
{{
Data(real,1,2523) = temperature at the element cell centers specified
}} ;
DataArray_t<real,1,2523> ViscosityKinematic =
{{
Data(real,1,2523) = kinematic viscosity at the element cell centers specified
}} ;
}} ; ! end Region1
In this example, boundary data is output on a 2D surface subregion of a 3D problem. Because this is data on a topologically 2D boundary (in a 3D simulation), RegionCellDimension
is set to 2. GridLocation
is specified as FaceCenter
. Recall that when GridLocation
is anything other than Vertex
in conjunction with unstructured grids, then the location list represents element numbers and not grid node numbers. Thus, the PointList/Range
indicates particular surface elements (or boundary elements) that need to have been defined in the file under their own Elements_t
node(s), separate from the 3D volume elements that make up the grid. In this case, we assume that the surface element numbers at which we are outputting data are 5568 through 5592 inclusive. Because the numbers occur in sequential order, we can make use of PointRange
.
Under Zone_t
:
ZoneSubRegion_t<1,3> Region1 =
{{
GridLocation_t GridLocation = FaceCenter ;
int RegionCellDimension = 2;
IndexArray_t<1,25,int> PointRange =
{{
int[1] Begin = [5568];
int[1] End = [5592];
}} ;
! ListLength = length of the element list = 25
DataArray_t<real,1,25> Temperature =
{{
Data(real,1,25) = temperature at the specific face element locations specified
}} ;
DataArray_t<real,1,25> ViscosityKinematic =
{{
Data(real,1,25) = kinematic viscosity at the specific face element locations specified
}} ;
}} ; ! end Region1
In this example, boundary data is output at the same locations where the BCs are specified in a particular BC_t
node (in this case the ListLength
is 25). Note that because this is data on a topologically 2D boundary (in a 3D simulation), RegionCellDimension
is set to 2. GridLocation
is not specified, because it is inherited from the BC_t
node along with the ListLength
.
Under Zone_t
:
ZoneSubRegion_t<1,3> Region1 =
{{
int RegionCellDimension = 2;
Descriptor_t BCRegionName = "name of a ZoneBC/BC_t node" ;
! ListLength = length of the point/element list from BC_t = 25
DataArray_t<real,1,25> Temperature =
{{
Data(real,1,25) = temperature at the specific BC locations specified
}} ;
DataArray_t<real,1,25> ViscosityKinematic =
{{
Data(real,1,25) = kinematic viscosity at the specific BC locations specified
}} ;
}} ; ! end Region1