(

- 11.1 Iterative Data Structure Definitions
- 11.2 Rigid Grid Motion Structure Definition:
`RigidGridMotion_t` - 11.3 Arbitrary Grid Motion Structure Definition:
`ArbitraryGridMotion_t` - 11.4 Zone Grid Connectivities
- 11.5 Examples for Time-Dependent Flow

This section describes structure types intended primarily for time-dependent flows. Data structures are presented for storing time-dependent or iterative data, and for recording rigid and arbitary grid motion. The section concludes with several examples.

In order to keep a record of time dependent or iterative data, the data
structures `BaseIterativeData_t` and `ZoneIterativeData_t`
are used.

The `BaseIterativeData_t` data structure is located directly under
the `CGNSBase_t` node.
It contains information about the number of time steps or iterations
being recorded, and the time and/or iteration values at each step.
In addition, it may include the list of zones and families for each step
of the simulation, if these vary throughout the simulation.

The `BaseIterativeData_t` data structure is defined as follows:

BaseIterativeData_t := { int NumberOfSteps (r) DataArray_t<real, 1, NumberOfSteps> TimeValues ; (o/r) DataArray_t<int, 1, NumberOfSteps> IterationValues ; (r/o) DataArray_t<int, 1, NumberOfSteps> NumberOfZones ; (o) DataArray_t<int, 1, NumberOfSteps> NumberOfFamilies ; (o) DataArray_t<char, 3, [65, MaxNumberOfZones, NumberOfSteps]> ZonePointers ; (o) DataArray_t<char, 3, [65, MaxNumberOfFamilies, NumberOfSteps]> FamilyPointers ; (o) List( DataArray_t<> DataArray1 ... DataArrayN ) ; (o) List( Descriptor_t Descriptor1 ... DescriptorN ) ; (o) DataClass_t DataClass ; (o) DimensionalUnits_t DimensionalUnits ; (o) List( UserDefinedData_t UserDefinedData1 ... UserDefinedDataN ) ; (o) }

- Default names for the
`DataArray_t`,`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`BaseIterativeData_t`and shall not include the names`DataClass`,`DimensionalUnits`,`FamilyPointers`,`IterationValues`,`NumberOfFamilies`,`NumberOfZones`,`TimeValues`, or`ZonePointers`. -
`NumberOfSteps`is a required element of the`BaseIterativeData_t`data structure. It holds either the number of time steps or the number of iterations being recorded. -
`TimeValues`or`IterationValues`must be defined. If both are used, there must be a one-to-one correspondence between them.

`TimeValues` and `IterationValues` are data-name identifiers
corresponding to the time and iteration values stored in the file.
When `IterationValues` are used, the iterative data stored in the
database correspond to values at the end of the associated iteration.

The data-name identifiers `NumberOfZones` and `ZonePointers`
are only used if different zone data structures apply to different steps
of the simulation.
(See the Adapted Unstructured Mesh
example.)

Similarly, if the geometry varies with time or iteration, then the
data-name identifiers `NumberOfFamilies` and `FamilyPointers`
are used to record which `Family_t`
data structure(s) correspond(s) to which step.

The `DataArray_t` nodes for
`ZonePointers` and `FamilyPointers` are defined as
three-dimensional arrays.
For each recorded step, the names of all zones and families being
used for the step may be recorded.
Note that the names are limited to 65 characters;
this is the
maximum size of a name of a zone from another base: 32 chars + '/' + 32 chars.
Only one '/' character is allowed, then the first token before the '/' is
the CGNSBase name and the second token is the Zone or Family name.
If no '/' is found, the name is a Zone or a Family name of the current
CGNS Base.
The variables `MaxNumberOfZones` and `MaxNumberOfFamilies`
represent the maximum number of zones and families that apply to
one step.
So if `NumberOfSteps` = 5 and `NumberOfZones` = {2,2,3,4,3},
then `MaxNumberOfZones` equals 4.

When `NumberOfZones` and `NumberOfFamilies` vary for
different stored time steps, the name `Null` is used in
`ZonePointers` and `FamilyPointers` as appropriate for
steps in which the `NumberOfZones` or `NumberOfFamilies`
is less than the `MaxNumberOfZones` or `MaxNumberOfFamilies`.

Any number of extra `DataArray_t`
nodes are allowed.
These should be used to record data not covered by this specification.

The `ZoneIterativeData_t` data structure is located under the
`Zone_t` node.
It may be used to record pointers to zonal data for each recorded step of
the simulation, and is defined as follows:

ZoneIterativeData_t< int NumberOfSteps > := { DataArray_t<char, 2, [32, NumberOfSteps]> RigidGridMotionPointers ; (o) DataArray_t<char, 2, [32, NumberOfSteps]> ArbitraryGridMotionPointers ; (o) DataArray_t<char, 2, [32, NumberOfSteps]> GridCoordinatesPointers ; (o) DataArray_t<char, 2, [32, NumberOfSteps]> FlowSolutionPointers ; (o) DataArray_t<char, 2, [32, NumberOfSteps]> ZoneGridConnectivityPointers ; (o) DataArray_t<char, 2, [32, NumberOfSteps]> ZoneSubRegionPointers ; (o) List( DataArray_t<> DataArray1 ... DataArrayN ) ; (o) List( Descriptor_t Descriptor1 ... DescriptorN ) ; (o) DataClass_t DataClass ; (o) DimensionalUnits_t DimensionalUnits ; (o) List( UserDefinedData_t UserDefinedData1 ... UserDefinedDataN ) ; (o) }

- Default names for the
`DataArray_t`,`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`ZoneIterativeData_t`and shall not include the names`ArbitraryGridMotionPointers`,`DataClass`,`DimensionalUnits`,`FlowSolutionPointers`,`GridCoordinatesPointers`,`RigidGridMotionPointers`,`ZoneGridConnectivityPointers`, or`ZoneSubRegionPointers`.

The data arrays with data-name identifiers ` xxxPointers`
contain lists of associated data structures for each recorded time value
or iteration.
These data structures contain data at the associated time value, or at
the end of the associated iteration.
There is an implied one-to-one correspondence between each pointer
(from 1, 2, ...,

Any number of extra `DataArray_t`
nodes are allowed.
These should be used to record data not covered by this specification.

The `ZoneIterativeData_t` data structure may not exist without
the `BaseIterativeData_t` under the
`CGNSBase_t` node.
However `BaseIterativeData_t` may exist without
`ZoneIterativeData_t`.

Adding rigid grid motion information to the CGNS file enables an
application code to determine the mesh location without the need to
alter the original mesh definition recorded under
`GridCoordinates_t`.
A data structure named `RigidGridMotion_t` is used to record the
necessary data defining a rigid translation and/or rotation of the grid
coordinates.

The rigid grid motion is recorded independently for each zone of the
CGNS base.
Therefore the `RigidGridMotion_t` data structure is located under
the zone data structure (`Zone_t`).
There may be zero to several `RigidGridMotion_t` nodes under a
`Zone_t` node.
The multiple rigid grid motion definitions may be associated with
different iterations or time steps in the computation.
This association is recorded under the
`ZoneIterativeData_t` data structure.

RigidGridMotion_t := { List( Descriptor_t Descriptor1 ... DescriptorN ) ; (o) RigidGridMotionType_t RigidGridMotionType ; (r) DataArray_t<real, 2, [PhysicalDimension, 2]> OriginLocation ; (r) DataArray_t<real, 1, PhysicalDimension> RigidRotationAngle ; (o/d) DataArray_t<real, 1, PhysicalDimension> RigidVelocity ; (o) DataArray_t<real, 1, PhysicalDimension> RigidRotationRate ; (o) List( DataArray_t DataArray1 ... DataArrayN ) ; (o) DataClass_t DataClass ; (o) DimensionalUnits_t DimensionalUnits ; (o) List( UserDefinedData_t UserDefinedData1 ... UserDefinedDataN ) ; (o) } ;

- 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`RigidGridMotion_t`and shall not include the names`DataClass`,`DimensionalUnits`,`OriginLocation`,`RigidGridMotionType`,`RigidRotationAngle`,`RigidRotationRate`, or`RigidVelocity`. -
`RigidGridMotionType`and`OriginLocation`are the only required elements under`RigidGridMotion_t`. All other elements are optional.

`RigidGridMotionType_t` is an enumeration type that describes
the type of rigid grid motion.

RigidGridMotionType_t := Enumeration( RigidGridMotionTypeNull, RigidGridMotionTypeUserDefined, ConstantRate, VariableRate ) ;

The characteristics of the grid motion are defined by the following
data-name identifiers:

Data-Name Identifier |
| Description |
| Units |
---|---|---|---|---|

OriginLocation | Physical coordinates of the origin before and after the rigid grid motion | L
| ||

RigidRotationAngle | Rotation angles about each axis of the translated coordinate
system.
If rotating about more than one axis, the rotation is performed first
about the x-axis, then the y-axis, then the z-axis.
If not specified, RigidRotationAngle is set to zero. | α | ||

RigidVelocity | Grid velocity vector of the origin translation | L/T
| ||

RigidRotationRate | Rotation rate vector about the axis of the translated coordinate system | /αT
| ||

Any number of `DataArray_t`
nodes are allowed.
These may be used to record data not covered by this specification.

"Rigid grid motion" implies relative motion of grid zones.
However, no attempt is made in the `RigidGridMotion_t` data
structure to require that the
`ZoneGridConnectivity_t`
information be updated to be consistent with the new grid locations.
Whether the `ZoneGridConnectivity_t` information refers to the
original connectivity (of
`GridCoordinates`) or
the latest connectivity (of the moved or deformed grid) is currently
left up to the user.

When a grid is in motion, it is often necessary to account for the
position of each grid point as the grid deforms.
When all grid points move at the same velocity, the grid keeps its
original shape.
This particular case of grid motion may be recorded under the
`RigidGridMotion_t` data structure.
On the other hand, if the grid points have different velocity, the grid
is deforming.
The `ArbitraryGridMotion_t` data structure allows the CGNS file to
contain information about arbitrary grid deformations.
If not present, the grid is assumed to be rigid.

Note that multiple
`GridCoordinates_t`
nodes may be stored under a `Zone_t`.
This allows the storage of the instantaneous grid locations at different
time steps or iterations.

The arbitrary grid motion is recorded independently for each zone of the
CGNS base.
Therefore the `ArbitraryGridMotion_t` data structure is located
under the zone data structure
(`Zone_t`).
There may be zero to several `ArbitraryGridMotion_t` nodes under a
single `Zone_t` node.
The multiple arbitrary grid motion definitions may be associated with
different iterations or time steps in the computation.
This association is recorded under the
`ZoneIterativeData_t` data structure.

ArbitraryGridMotion_t< int IndexDimension, int VertexSize[IndexDimension], int CellSize[IndexDimension] > := { ArbitraryGridMotionType_t ArbitraryGridMotionType ; (r) List(DataArray_t<real, IndexDimension, DataSize[]> GridVelocityX GridVelocityY ... ) ; (o) List( Descriptor_t Descriptor1 ... DescriptorN ) ; (o) GridLocation_t GridLocation ; (o/d) Rind_t<IndexDimension> Rind ; (o/d) DataClass_t DataClass ; (o) DimensionalUnits_t DimensionalUnits ; (o) List( UserDefinedData_t UserDefinedData1 ... UserDefinedDataN ) ; (o) }

- 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`ArbitraryGridMotion_t`and shall not include the names`ArbitraryGridMotionType`,`DataClass`,`DimensionalUnits`,`GridLocation`, or`Rind`. - The only required element of the
`ArbitraryGridMotion_t`data structure is the`ArbitraryGridMotionType`. Thus, even if a deforming grid application does not require the storage of grid velocity data, the`ArbitraryGridMotion_t`node must exist (with`ArbitraryGridMotionType`=`DeformingGrid`) to indicate that deformed grid points (`GridCoordinates_t`) exist for this zone. -
`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 grid velocity data. - The
`GridLocation`specifies the location of the velocity data with respect to the grid; if absent, the data is assumed to coincide with grid vertices (i.e.,`GridLocation`=`Vertex`).

`ArbitraryGridMotion_t` requires three structure parameters;
`IndexDimension` identifies the dimensionality of the grid-size
arrays, and `VertexSize` and `CellSize` are the number of
core vertices and cells, respectively, in each index direction.
For unstructured zones, `IndexDimension` is always 1.

`ArbitraryGridMotionType_t` is an enumeration type that describes
the type of arbitrary grid motion.

ArbitraryGridMotionType_t := Enumeration( ArbitraryGridMotionTypeNull, ArbitraryGridMotionTypeUserDefined, NonDeformingGrid, DeformingGrid ) ;

The `DataArray_t` nodes are used
to store the components of the grid velocity vector.
The table below lists the data-name identifiers used to record these
vectors in Cartesian, cylindrical, and spherical coordinate systems.

Data-Name Identifier |
| Description |
| Units |
---|---|---|---|---|

GridVelocityX | x-component of grid velocity | L/T
| ||

GridVelocityY | y-component of grid velocity | L/T
| ||

GridVelocityZ | z-component of grid velocity | L/T
| ||

GridVelocityR | r-component of grid velocity | L/T
| ||

GridVelocityTheta | θ-component of grid velocity | /αT
| ||

GridVelocityPhi | φ-component of grid velocity | /αT
| ||

GridVelocityXi | ξ-component of grid velocity | L/T
| ||

GridVelocityEta | η-component of grid velocity | L/T
| ||

GridVelocityZeta | ζ-component of grid velocity | L/T
| ||

The field `GridLocation`
specifies the location of the grid velocities with respect to the
grid; if absent, the grid velocities are assumed to coincide with grid
vertices (i.e., `GridLocation = Vertex`).
All grid velocities within a given instance of
`ArbitraryGridMotion_t` must reside at the same grid location.

`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` or
`FlowSolution_t`.
They are not required to contain the same number of rind planes or
elements.
Also, the location of any rind points is assumed to be consistent
with the location of the core data points (e.g., if
`GridLocation = CellCenter`,
rind points are assumed to be located at fictitious cell centers).

`DataClass` defines the
default for the class of data contained in the
`DataArray_t` entities.
For dimensional grid velocities,
`DimensionalUnits`
may be used to describe the system of dimensional units employed.
If present, these two entities take precedence over all corresponding
entities at higher levels of the hierarchy, following the standard
precedence rules.

The `UserDefinedData_t`
data structure allows arbitrary user-defined 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.

Point-by-point grid velocity implies a deformation (or potentially only
motion) of the grid points relative to each other.
Because the original grid coordinates definition remains unchanged with
the name `GridCoordinates`,
any deformed coordinates must be written with a different name (e.g.,
`MovedGrid#1` or another used-defined name) and are pointed
to using `GridCoordinatesPointers` in the data structure
`ZoneIterativeData_t`.

Point-by-point grid velocity may also lead to relative motion of grid
zones, or movement of grid along abutting interfaces.
However, no attempt is made here to require that the
`ZoneGridConnectivity_t`
information be updated to be consistent with the new grid locations.
Whether the `ZoneGridConnectivity_t` information refers to the
original connectivity (of
`GridCoordinates`) or
the latest connectivity (of the moved or deformed grid) is currently
left up to the user.

dependencies:

The function `DataSize[]` is the size of the `DataArray`s
containing the grid velocity components.
It is identical to the function
`DataSize[]` defined for
`FlowSolution_t`.

In this example, the whole mesh moves rigidly, so the only
time-dependent data are the grid coordinates and flow solutions.
However, since the mesh moves rigidly, the grid coordinates need not be
recorded at each time step.
Instead, a `RigidGridMotion_t`
data structure is recorded for each step of the computation.

The number of steps and time values for each step are recorded under
`BaseIterativeData_t`.

CGNSBase_t { BaseIterativeData_t { NumberOfSteps = N ; TimeValues = time1, time2, ..., timeN ; } ; } ;

The multiple rigid grid motion and flow solution data structures are
recorded under the zone.
`RigidGridMotionPointers` and `FlowSolutionPointers` keep the
lists of which `RigidGridMotion_t`
and `FlowSolution_t` nodes
correspond to each time step.

Zone_t Zone {--- Time independent dataGridCoordinates_t GridCoordinates ZoneBC_t ZoneBC ZoneGridConnectivity_t ZoneGridConnectivity--- Time dependent dataRigidGridMotion_t RigidGridMotion#1 RigidGridMotion_t RigidGridMotion#2 ... RigidGridMotion_t RigidGridmotion#N FlowSolution_t Solution#0 FlowSolution_t Solution#1 FlowSolution_t Solution#2 ... FlowSolution_t Solution#N ZoneIterativeData_t { RigidGridMotionPointers = {"RigidGridMotion#1", "RigidGridMotion#2", ..., "RigidGridMotion#N"} FlowSolutionPointers = {"Solution#1", "Solution#2, ..., "Solution#N"} } }

Note that there may be more solutions under a zone than those pointed to
by `FlowSolutionPointers`.
In this example, `Solution#0` could correspond to a restart solution.

In this example, velocity vectors are node dependent allowing for mesh deformation. In such a case, it is difficult or even impossible to recompute the mesh at each time step. Therefore the grid coordinates are recorded for each step.

Multiple `GridCoordinates_t` and `FlowSolution_t` data
structures are recorded under the zone.
In addition, the data structure
`ArbitraryGridMotion_t` is
recorded for each step.
`GridCoordinatesPointers`, `FlowSolutionPointers`, and
`ArbitraryGridMotionPointers_t` keep the list of which grid
coordinates definition, flow solution, and arbitrary grid motion
definition correspond to each time step.

Zone_t Zone {--- Time independent dataZoneBC_t ZoneBC ZoneGridConnectivity_t ZoneGridConnectivity--- Time dependent dataList ( GridCoordinates_t GridCoordinates MovedGrid#1 MovedGrid#2 ... MovedGrid#N ) List ( FlowSolution_t Solution#0 Solution#1 Solution#2 ... Solution#N ) List ( ArbitraryGridMotion_t ArbitraryGridMotion#1 ArbitraryGridMotion#2 ... ArbitraryGridMotion#N ) ZoneIterativeData_t { GridCoordinatesPointers = {"MovedGrid#1", "MovedGrid#2", ..., "MovedGrid#N"} FlowSolutionPointers = {"Solution#1", "Solution#2, ..., "Solution#N"} ArbitraryGridMotionPointers = {"ArbitraryGridMotion#1", "ArbitraryGridMotion#2", ..., "ArbitraryGridMotion#N"} } }

In this example, the mesh size varies at each remeshing, therefore new
zones must be created.
`ZonePointers` is used to keep a record of the zone definition
corresponding to each recorded step.
Let's assume that the solution is recorded every 50 iterations, and the
grid is adapted every 100 iterations.

The number of steps, iteration values for each step, number of zones
for each step, and name of these zones are recorded under
`BaseIterativeData_t`.

CGNSBase_t { BaseIterativeData_t { NumberOfSteps = 4 IterationValues = {50, 100, 150, 200} NumberOfZones = {1, 1, 1, 1} ZonePointers = {"Zone1", "Zone1", "Zone2", "Zone2"} } }

Each zone holds 2 solutions recorded at 50 iterations apart.
Therefore the `ZoneIterativeData_t`
data structure must be included to keep track of the
`FlowSolutionPointers`.

Zone_t Zone1 {--- Constant dataGridCoordinates_t GridCoordinates Elements_t Elements ZoneBC_t ZoneBC--- Variable dataList ( FlowSolution_t InitialSolution Solution50 Solution100 ) ZoneIterativeData_t { FlowSolutionPointers = {"Solution50", "Solution100", "Null", "Null"} } } Zone_t Zone2 {--- Constant dataGridCoordinates_t GridCoordinates Elements_t Elements ZoneBC_t ZoneBC--- Variable dataList ( FlowSolution_t RestartSolution Solution150 Solution200 ) ZoneIterativeData_t { FlowSolutionPointers = {"Null", "Null", "Solution150", "Solution200"} } }

- If the solution was recorded every 100 iterations instead of
every 50 iterations, then each zone would have only one
`FlowSolution_t`node and the data structure`ZoneIterativeData_t`would not be required. - Note that
`FlowSolutionPointers`is always an array of size`NumberOfSteps`even if some of the steps are defined in another zone.

The following is an example demonstrating the use of the rigid grid motion,
arbitrary grid motion, and time-accurate data nodes in CGNS.
The example is a 3-zone case.
Zone 1 is rigidly rotating about the *x*-axis at a constant rate, with
no translation.
Zone 2 is a deforming zone.
Zone 3 is a fixed zone.
This is a time-accurate simulation with two solutions saved at times
15.5 and 31.0, corresponding to iteration numbers 1000 and 2000.

No units are given in this example, but a real case would establish them. Also, a real case would include connectivity, boundary conditions, and possibly other information as well. Each indentation represents a level down (a child) from the parent node.

Base (CGNSBase_t) SimulationType (SimulationType_t) Data=TimeAccurate BaseIterativeData (BaseIterativeData_t) Data=NumberOfSteps=2 TimeValues (DataArray_t) Data=(15.5, 31.0) IterationValues (DataArray_t) Data=(1000, 2000) Zone#1 (Zone_t) GridCoordinates (GridCoordinates_t) CoordinateX (DataArray_t) CoordinateY (DataArray_t) RigidGridMotion#1(RigidGridMotion_t) Data=RigidGridMotionType=ConstantRate OriginLocation (DataArray_t) Data=(0,0,0), (0,0,0) RigidRotationAngle (DataArray_t) Data=(5., 0., 0.) RigidGridMotion#2(RigidGridMotion_t) Data=RigidGridMotionType=ConstantRate OriginLocation (DataArray_t) Data=(0,0,0), (0,0,0) RigidRotationAngle (DataArray_t) Data=(10., 0., 0.) ZoneIterativeData (ZoneIterativeData_t) RigidGridMotionPointers (DataArray_t) Data=(RigidGridMotion#1, RigidGridMotion#2) FlowSolutionPointers (DataArray_t) Data=(Soln#1, Soln#2) Soln#1 (FlowSolution_t) Density (DataArray_t) VelocityX (DataArray_t) Soln#2 (FlowSolution_t) Density (DataArray_t) VelocityX (DataArray_t) Zone#2 (Zone_t) GridCoordinates (GridCoordinates_t) CoordinateX (DataArray_t) CoordinateY (DataArray_t) MovedGrid#1 (GridCoordinates_t) CoordinateX (DataArray_t) CoordinateY (DataArray_t) MovedGrid#2 (GridCoordinates_t) CoordinateX (DataArray_t) CoordinateY (DataArray_t) ArbitraryGridMotion#1 (ArbitraryGridMotion_t) Data=ArbitraryGridMotionType=DeformingGrid ArbitraryGridMotion#2 (ArbitraryGridMotion_t) Data=ArbitraryGridMotionType=DeformingGrid GridVelocityX (DataArray_t) GridVelocityY (DataArray_t) ZoneIterativeData (ZoneIterativeData_t) ArbitraryGridMotionPointers (DataArray_t) Data=("ArbitraryGridMotion#1", "ArbitraryGridMotion#2") GridCoordinatesPointers (DataArray_t) Data=("MovedGrid#1", "MovedGrid#2") FlowSolutionPointers (DataArray_t) Data=("Soln#1", "Soln#2") Soln#1 (FlowSolution_t) Density (DataArray_t) VelocityX (DataArray_t) Soln#2 (FlowSolution_t) Density (DataArray_t) VelocityX (DataArray_t) Zone#3 (Zone_t) GridCoordinates (GridCoordinates_t) CoordinateX (DataArray_t) CoordinateY (DataArray_t) ZoneIterativeData (ZoneIterativeData_t) FlowSolutionPointers (DataArray_t) Data=("Soln#1", "Soln#2") Soln#1 (FlowSolution_t) Density (DataArray_t) VelocityX (DataArray_t) Soln#2 (FlowSolution_t) Density (DataArray_t) VelocityX (DataArray_t)

- Under
`BaseIterativeData_t`, one can give either`TimeValues`, or`IterationValues`, or both. In the example, both have been given. - The nodes
`NumberOfZones`and`ZonePointers`are not required under the`BaseIterativeData_t`node in this example because all existing zones are used for each time step. - Under
`ArbitraryGridMotion`, the`GridVelocity`data is optional. In the example, it was put under one of the nodes but not under the other. Hence,`"ArbitraryGridMotion#1"`in the example has no children nodes, while`"ArbitraryGridMotion#2"`does. - The pointers under
`ZoneIterativeData_t`point to names of nodes within the same zone. Thus, for example,`Soln#1`refers to the flow solution named`Soln#1`in the same zone, even though there are flow solution nodes in other zones with the same name. - The name
`GridCoordinates`always refers to the*original*grid. Thus, when a grid is deforming, the deformed values must be put in`GridCoordinates_t`nodes of a different name. In the example, the deformed grids (for`Zone#2`) at the two times of interest were put into`"MovedGrid#1"`and`"MovedGrid#2"`. - Because the node
`"ArbitraryGridMotion#1"`doesn't really add any information in the current example (since it was decided not to store`GridVelocity`data under it), one has the option of not including this node in the CGNS file. If it is removed, then under`Zone#2`'s`ZoneIterativeData`, the`ArbitraryGridMotionPointers`data would be replaced by:Data = (Null, ArbitraryGridMotion#2)