4.8.1. Solution Control

All Aria input files must include a Solution Control Description block in the Procedure section of the input file. This description contains directives for executing a steady-state (sequential) or transient analysis ranging from simple single-region analyses to more complicated multi-region execution including transfer, nested nonlinear iterations, and/or subcycling.

A solution control block has three parts:

System

Controls how the simulation is advanced

Parameters

Parameters to inform how each region is handled by system

Initialization

Additional actions to do at startup before system-defined behavior

See the command reference for details on all possible commands.

The system block controls how the analysis progresses by advanceing the relevant region(s). For a Transient Analysis this corresponds to taking a step, whereas for a Steady Analysis this corresponds to solving the steady problem (i.e. taking the ONLY step).

When there are multiple regions involved in an analysis, it is often necessary to transfer information between them. Once a transfer block is set up, this is accomplished with the transfer directive. These more complex analyses may also require explicitly initialization of fields. Depending on the simulation types, various parameters are required, as is demonstrated in the sections below.

Typically, regions control their own postprocessing when they during advance. In rare cases, one may wish to trigger the postprocessors manually (e.g. adaptivity). To do so, one can explicitly postprocess at any point in a solution control block.

4.8.1.1. Steady Analysis

To set up a simple steady analysis, a Sequential block can be used to advance a region. As a simple example

Simple Sequential Input

Begin Sierra myJob

  # Materials, Solvers, Finite Element Model, etc
  ...

  Begin Procedure myProcedure

    Begin Solution Control Description
      # Note that the description calls out the system to use
      Use System Main
      Begin System Main
        Begin Sequential MySolveBlock
          Advance steadyRegion
        End
      End
    End

    Begin Aria Region steadyRegion
      # ICs, BCs, equations, output, etc
      ...
    End Aria Region steadyRegion

    ...
  End Procedure myProcedure
End Sierra myJob

Though its often more favorable to solve fully-coupled physics within a single application, this is not always possible. As an alternative, loose-coupling is often carried out by exchanging solution information across multiple applications. Solution control provides various means of carrying out these analyses depending upon the strength of physics coupling within a solution step.

Note

This section refers to coupling within the Sierra ecosystem, e.g. coupling Aria and Adagio via Arpeggio. For weak coupling with apps outside of the Sierra ecosystem, see File Based Coupling. For stronger coupling, see MPMD Coupling.

When the different problem physics are weakly-coupled, one is assuming that for each solution step it is sufficient to supply current values of variables involved in the coupling. In this case, the regions can be sequentially advanced with information exchanged in between via transfers. Below, an example of a weakly coupled Aria-Adagio simulation is provided

Weakly Coupled Sequential Input

Begin Sierra myJob

  # Materials, Solvers, Finite Element Model, etc
  ...

  Begin Procedure myProcedure

    Begin Solution Control Description
      Use System Main
      Begin System Main
        Begin Sequential MySolveBlock
          Advance ariaRegion
          transfer aria_to_adagio
          Advance adagioRegion
          transfer adagio_to_aria
        End
      End
    End

    Begin Aria Region ariaRegion
      # ICs, BCs, equations, output, etc
      ...
    End Aria Region ariaRegion

    Begin Adagio Region adagioRegion
      # ICs, BCs, equations, output, etc
      ...
    End Adagio Region adagioRegion

    Begin transfer adagio_to_aria
      # transfer commands
      ...
    End transfer adagio_to_aria

    Begin transfer aria_to_adagio
      # transfer commands
      ...
    End transfer aria_to_adagio

    ...
  End Procedure myProcedure
End Sierra myJob

For a stronger coupling, one may chose to iterate within a solution step until the interaction between physics has converged. This is accomplished by specifying a Nonlinear command block within the sequential block. Here the nonlinear iteration will continue until user specified criteria Parameters for Nonlinear Iteration is satisfied

Stronger Coupled Sequential Input

Begin Sierra myJob

  # Materials, Solvers, Finite Element Model, etc
  ...

  Begin Procedure myProcedure

    Begin Solution Control Description
      Use System Main
      Begin System Main
        Begin Sequential MySolveBlock
          Begin Nonlinear Iteration
            Advance ariaRegion
            transfer aria_to_adagio
            Advance adagioRegion
            transfer adagio_to_aria
          End
        End
      End
    End

    Begin Parameters for Nonlinear Iteration
      Converged when "adagioRegion.MaxInitialNonlinearResidual(0) < 1E-1 && \$
                        ariaRegion.MaxInitialNonlinearResidual(0) < 1E-1 "
    End

    Begin Aria Region ariaRegion
      # ICs, BCs, equations, output, etc
      ...
    End Aria Region ariaRegion

    Begin Adagio Region adagioRegion
      # ICs, BCs, equations, output, etc
      ...
    End Aria Region adagioRegion

    Begin transfer adagio_to_aria
      # transfer commands
      ...
    End transfer adagio_to_aria

    Begin transfer aria_to_adagio
      # transfer commands
      ...
    End transfer aria_to_adagio

    ...
  End Procedure myProcedure
End Sierra myJob

4.8.1.2. Transient Analysis

Similar to a sequential block, a Transient block defines the way transient region(s) advance. A simple example of a transient solution control block will look similar to that of a sequential analog, except that additional parameters are required to describe the time range of the simulation. Additionally, parameters defining the time integration for each Region must also be supplied by the user. The example below demonstrates both a fixed and adapative timestep transient. See Time Step Selection for guidance on setting these parameters.

Simple Transient Input

Begin Sierra myJob

  # Materials, Solvers, Finite Element Model, etc
  ...

  Begin Procedure My_Aria_Procedure

    Begin Solution Control Description

      Use System Main

      Begin System Main
        Simulation Start Time            = 0.0
        Simulation Termination Time      = 10.0
        Simulation Max Global Iterations = 1000

        Begin Transient Time_Block_1
          Advance My_Aria_Region
        End
        Begin Transient Time_Block_2
          Advance My_Aria_Region
        End
      End

      #Parameters for Time_Block_1 behavior
      Begin Parameters For Transient Time_Block_1
        Start Time      = 0.0
        Number of steps = 8
        Begin Parameters For Aria Region My_Aria_Region
          Time Step Variation    = Fixed
          Initial Time Step Size = 0.001
        End
      End

      #Parameters for Time_Block_2 behavior
      Begin Parameters For Transient Time_Block_2
        Begin Parameters For Aria Region My_Aria_Region
          Time Step Variation           = Adaptive
          Initial Time Step Size        = 0.001
          Predictor-Corrector Tolerance = 1e-3
          Minimum Time Step Size        = 1e-6
        End
      End
    End

    ...
  End Procedure My_Aria_Procedure
End Sierra myJob

Note

Note that for each named Begin Transient [NAME] command block there should be a corresponding Begin Parameters for Transient [NAME] command block which defines its parameters.

Similar to the sequential case, multiple regions can be tied together either in a weak or strong coupling using transfers and Nonlinear command blocks. The stronger case is demonstrated below. Here, the time step for advancement to the next solution step is negotiated between the coupled Regions based upon their respective Transient parameters.

Coupled Transient Input

Begin Sierra myJob

  # Materials, Solvers, Finite Element Model, etc
  ...

  Begin Procedure My_Aria_Procedure

    Begin Solution Control Description

      Use System Main

      Begin System Main
        Simulation Start Time            = 0.0
        Simulation Termination Time      = 10.0
        Simulation Max Global Iterations = 1000

        Begin Transient Time_Block
            Begin Nonlinear Iteration
              Advance myAriaRegion
              transfer aria_to_adagio
              Advance myAdagioRegion
              transfer adagio_to_aria
            End Nonlinear Iteration
        End
      End

      Begin Parameters for Nonlinear Iteration
        Converged when "myAdagioRegion.MaxInitialNonlinearResidual(0) < 1E-1 && \$
                          myAriaRegion.MaxInitialNonlinearResidual(0) < 1E-1 "
      End

      Begin Parameters For Transient Time_Block_1
        Start Time      = 0.0
        Termination Time = 10.0

        #Aria region-specific parameters for Time_Block_1
        Begin Parameters For Aria Region myAriaRegion
            Time Step Variation    = adaptive
            Initial Time Step Size = 0.001
            Predictor-Corrector Tolerance = 1e-3
            Minimum Time Step Size        = 1e-6
        End

        #Adagio region-specific parameters for Time_Block_1
        Begin Parameters For Adagio Region myAdagioRegion
            Time increment = 0.001
        End
      End

    End Solution Control Description

    Begin transfer adagio_to_aria
      # transfer commands
      ...
    End transfer adagio_to_aria

    Begin transfer aria_to_adagio
      # transfer commands
      ...
    End transfer aria_to_adagio

    ...
  End Procedure My_Aria_Procedure
End Sierra myJob

Note

Note here that a subblock for parameters of each region participating in the transient is present in the Parameters block of the transient.

Depending on the two physics being coupled, the two regions can have differing time scales. In this case a Subcycle command block can be used to subcycle the region with a smaller timescale, rather than forcing the larger timestep region to follow this smaller step. The solution will advance when the two time applications arrive at the same solution time.

Subcycled Transient Input

Begin Sierra myJob

  # Materials, Solvers, Finite Element Model, etc
  ...

  Begin Procedure My_Aria_Procedure

    Begin Solution Control Description

      Use System Main

      Begin System Main
        Simulation Start Time            = 0.0
        Simulation Termination Time      = 10.0
        Simulation Max Global Iterations = 1000

        Begin Transient Time_Block_1
          Transfer Adagio_to_Aria
          Advance My_Aria_Region
          Transfer Aria_to_Adagio
          Begin Subcycle AdagioSubcycle
            Advance AdagioRegion
          End
        End

      End

      Begin Parameters For Transient Time_Block_1
        Start Time      = 0.0
        Number of steps = 8

        Begin Parameters For Aria Region My_Aria_Region
          Time Step Variation    = Fixed
          Initial Time Step Size = 0.001
        End

        Begin Parameters for Adagio Region AdagioRegion
          initial time step = 1.0e-6
          # time step scale factor = 1.0
          time step increase factor = 10.
          # step interval = 500
        End
      End

    End

    Begin transfer adagio_to_aria
      ...
    End transfer adagio_to_aria

    Begin transfer aria_to_adagio
      ...
    End transfer aria_to_adagio

    Begin Aria Region myAriaRegion
      ...
    End Aria Region myAriaRegion

    Begin Adagio Region myAdagioRegion
      ...
    End Adagio Region myAdagioRegion

  End Procedure myProcedure
End Sierra myJob

4.8.1.3. Variable Initialization

In the case of transient analysis it is sometimes necessary to initialize a distribution of values before the analysis actually begins. This can be useful, for example, to transfer a field containing initial conditions to a coupled region. This is accomplished by using an Initialize command block. An example of this case is provided below

Initialization Transient Input

Begin Sierra myJob

  # Materials, Solvers, Finite Element Model, etc
  ...

  Begin Procedure My_Aria_Procedure

    Begin Solution Control Description

      Use System Main

      begin initialize init
        Advance AdagioRegion
        Transfer Adagio_to_Aria
      end initialize init

      Begin System Main

        # Note that the system calls out the initialize to use
        Use initialize init

        Simulation Start Time            = 0.0
        Simulation Termination Time      = 10.0
        Simulation Max Global Iterations = 1000

        Begin Transient Time_Block_1
          Advance My_Aria_Region
          Transfer Aria_to_Adagio
          Begin Subcycle AdagioSubcycle
            Advance AdagioRegion
          End
          Transfer Adagio_to_Aria
        End

      End

      Begin Parameters For Transient Time_Block_1
        Start Time      = 0.0
        Number of steps = 8

        Begin Parameters For Aria Region My_Aria_Region
          Time Step Variation    = Fixed
          Initial Time Step Size = 0.001
        End

        Begin Parameters for Adagio Region AdagioRegion
          initial time step = 1.0e-6
          # time step scale factor = 1.0
          time step increase factor = 10.
          # step interval = 500
        End
      End
    End

    Begin transfer adagio_to_aria
      ...
    End transfer adagio_to_aria

    Begin transfer aria_to_adagio
      ...
    End transfer aria_to_adagio

    Begin Aria Region myAriaRegion
      ...
    End Aria Region myAriaRegion

    Begin Adagio Region myAdagioRegion
      ...
    End Adagio Region myAdagioRegion

  End Procedure myProcedure
End Sierra myJob