4.9.4. Transfer

Transfer allows you to send fields from one region to another. There are two kinds of transfer - copy and interpolate. Copy transfer requires identical meshes (same node/element locations and same global IDs), while interpolation interpolates fields on dissimilar meshes. The benefit of the copy transfer is that a search is not required to transfer the information. With interpolation on the other hand, the sender and receiver need not be of same topology but the source and target destinations should overlap geometrically so that a search can be performed to find entities to interpolate.

The specification of this choice is as follows

Begin Transfer Transfer_name
  [TRANSFER_TYPE] [PART_TYPE] [TOPOLOGY] From [SRC_REGION] To [DST_REGION]
  ...
End

Here SRC_REGION/DST_REGION are the participating regions, TRANSFER_TYPE can be COPY or INTERPOLATE, PART_TYPE can be SURFACE or VOLUME, and TOPOLOGY can be CONSTRAINTS, ELEMENTS, or NODES. The remainder of this section discusses the major components that must be present in a Transfer block. See the command reference for a detailed list of all possible options.

4.9.4.1. Field

First, one must specify which quantities are to be transferred across regions. Each field transfer will have the general form

Send Field [SRC_FIELD] State [SRC_STATE] To [DST_FIELD] State [DST_STATE]

The SRC_FIELD/DST_FIELD can be any Aria field, including Aria Solution Fields, User Fields, and Postprocess Value Fields. Note that when receiving a solution field, the corresponding equation must be specified with a type of XFER so that the DOF field is created appropriately (see Equation Specification). See the command reference for more details on specifying a send field.

The SRC_STATE/DST_STATE refer to the state of the field (or NONE if the field is not stated). See Internal Field Definition for more information on field states.

For example, to transfer a postprocessed quantity in one region to a user field in another, one could do

# Scope: Sierra > Procedure
Begin Aria Region first_region
  use finite element model same_model

  ...

  postprocess value of function "temperature - 273.15" on all_blocks as tempC
End

Begin Aria Region second_region
  use finite element model same_model

  ...

  user field real node scalar first_temp on all_blocks
End

Begin Transfer temp_transfer
  copy volume nodes from first_region to second_region
  send field tempC state none to first_temp state none
End

4.9.4.2. Location

The source and destination parts dictate what portion of the domain is transferred. These parts be specified using the Send Blocks line command. Note that for copy transfer, each part must be specified in unique send block lines

# Scope: Sierra > Procedure
Begin Transfer foo
  Send Block block_1 to block_1
  Send Block block_2 to block_2
  ...
End

For interpolation transfer on the other hand, they must be specified in one line

# Scope: Sierra > Procedure
Begin Transfer foo
  Send Block block_1 block_2 to block_3 block_4
  ...
End

Note that in either case, assemblies can be used to simplify the definitions. Alternatively, the transfer send and receive blocks can be specified in block form using Send Blocks and Receive Blocks respectively. This form is useful when one wishes to send or receive all blocks in the mesh, since it allows the use of the Include All Blocks alias instead of having to list them manually.

# Scope: Sierra > Procedure
Begin Transfer foo
  Begin Send Blocks
    Include All Blocks
  End
  Begin Receive Blocks
    Include Block = block_3 block_4
  End
  ...
End

Note that if these lines are omitted, the transfer is performed over the entire domain.

4.9.4.2.1. Search Tolerance

In cases of interpolation, a search over the two meshes must be performed to communicate values. By default, the tolerance used in this search is a function of the geometric problem size. For cases in which the source and destination do not overlap, one should specify tolerancing in order to guarantee that values will be mapped to the destination. If the the separation between source and destination varies, then one should specify a Geometric Tolerance consistent with the largest separation distance.

4.9.4.2.2. Extrapolation Handling

When source and destination entities partially overlap, then by default source values will be extrapolated to the destination. This behavior can be explicitly controlled with the Nodes Outside Region command. The most common options for the command are described below:

EXTRAPOLATE

This is the default behavior. The sending field is extrapolated beyond the bounds of the sending mesh. This can lead to extrapolation error, such as when a large gradient at the surface causes a negative values when only positive values are acceptable. If this happens, upper and lower bounds can be set per field within the SEND FIELD command.

Send Field field1 State none To field2 State none Lower Bound 0.0 Upper Bound 1.0

TRUNCATE

The receiving coordinate is projected back to the surface of the sending mesh to determine a value. This ensures that the receiving value is not outside of the field values in the sending mesh.

ABORT

If any receiving point is outside the sending mesh by more than the geometric tolerance, abort the simulation. Do not attempt to project, extrapolate, or otherwise handle the point. This can be useful for detecting problem setup errors that otherwise may have been silently extrapolated.

IGNORE

The receiving mesh object can be ignored and will receive no value. This is usually not recommended as it can cause mesh objects just outside to have a zero value when the nodes just inside the mesh might have very large values.

4.9.4.3. Skeleton Examples

Since several different uses of transfer can arise, some examples are included below.

Note

While this example shows only steady problems, the same basic setup of transfer would apply to transient problems as well.

A skeleton outline of one-way transfer between two regions

# Scope: Sierra > Procedure
Begin Solution Control Description
  Use System Main
  Begin System Main
    Begin Sequential MySolveBlock
      Advance first_Region
      transfer my_transfer
      Advance second_Region
    End
  End
  ...
End

Begin Aria Region first_region
  Use Finite Element Model fem_model_A

  eq energy for temperature On block_1 using q1 with lumped_mass diff
  ...
End

Begin Aria Region second_region
  Use Finite Element Model fem_model_B

  eq energy for temperature On block_1 using q1 with xfer
  ...
End

Begin Transfer my_transfer
  interpolate volume nodes from first_region to second_region
  send block block_1 to block_1
  send field solution->temperature state new to solution->temperature state new
End

A skeleton outline of two-way transfer between two regions:

# Scope: Sierra > Procedure
Begin Solution Control Description
  Use System Main
  Begin System Main
    Begin Sequential MySolveBlock
      Advance RegionA
      Transfer AtoB
      Advance RegionB
      Transfer BtoA
    End
  End
  ...
End

Begin Aria Region RegionA
  Use Finite Element Model same_model

  eq energy for temperature On block_1 using q1 with diff
  eq species for species of 3 On block_2 using q1 with xfer
  ...
End

Begin Aria Region RegionB
  Use Finite Element Model same_model

  eq energy for temperature On block_1 using q1 with xfer
  eq species for species of 3 On block_2 using q1 with diff
  ...
End

Begin Transfer AtoB
  copy volume nodes from first_region to second_region
  send block block_1 to block_1
  send field solution->temperature state new to solution->temperature state new
End

Begin Transfer BtoA
  copy volume nodes from second_region to first_region
  send block block_2 to block_2
  send field solution->species_3 state new to solution->species_3 state new
End

Transfer is not exclusive to Aria regions. For example, an IO Region can be used to distribute data from external mesh databases. See Using Transfer for a complete example of this use case.