Transient

!syntax description /Executioner/Transient

Normal Usage

The Transient Executioner is the primary workhorse Executioner in MOOSE. Most simulations will use it.

At its most basic the Transient Executioner allows a simulation to step through multiple steps in _time_... doing one nonlinear solve per timestep. Most of the time this type of execution will utilize one or more TimeDerivative Kernels on the variables to solve for their time evolution.

Primary Parameters

The most important parameters for Transient (beyond what Steady already provides) are:

- dt: The initial timestep size - num_steps: Number of steps to do - end_time: Finish time for the simulation - scheme: The TimeIntegrator to use (see below) - defaults to Implicit/Backward Euler.

See down below for the full list of parameters for this class.

TimeIntegrators

It's important to note that transient simulations generally use a TimeIntegrator. As mentioned above, there is a scheme parameter that is shortcut syntax for selection of that TimeIntegrator. However, there is also a whole TimeIntegrator system for creating your own or specifying detailed parameters for time integration.

TimeSteppers

Similarly, the choice of how to move through time (the choice of timestep size) is important as well. The default TimeStepper is ConstantDT but many other choices can be made using the TimeStepper system.

Load Steps

Transient can also be used for simulations that don't necessarily need _time_. In this context a "transient" calculation can simply be thought of as a series of nonlinear solves. The time parameter will move forward - but what you do with it, or what it means is up to you.

One good example of this is doing "load steps" for a solid mechanics calculation. If the only thing that is desired is the final, steady state, solution, but getting to it is extremely difficult, then you might employ "load steps" to slowly ramp up a boundary condition so you can more easily solve from the initial state (the "initial condition") to the final configuration. In this case you would use "time" as a parameter to control how much of the force is applied (for instance, by using FunctionDirichletBC).

In this case you don't use any TimeDerivative Kernels. The "transient" behavior comes from changing a condition based on "time". What that "time" means is up to you to identify (generally, I like to just step through time = 1,2,3,4.. and define my functions so that at time = end_steps the full load is applied.

Quasi-Transient

Similarly to Load Steps, you can use Transient to do "Quasi-Transient" calculations. This is where some variables are evolving with time derivatives, while others are solved to steady state each step.

A classic example of this is doing coupled thermo-mechanics. It's very normal for the heat flow to move much more slowly than the solid mechanics. Therefore, classically, it is normal to have a time derivative for your heat conduction equation but none for the solid mechanics so that at each timestep the solid-mechanics is solved to a full steady state based on the current configuration of heat.

This idea works perfectly in MOOSE with Transient: just simply only apply TimeDerivative Kernels to the equations you want and leave them off for the others.

Solving To Steady State

Another use-case is to use Transient to solve to a steady state. In this case there are a few built-in parameters to help detect steady state and stop the solve when it's reached. You can see them down below in the "Steady State Detection Parameters" section.

It is important to know that you must turn _on_ steady state detection using steady_state_detection = true before the other two parameters will do anything.

Input Parameters

  • reset_dtFalseUse when restarting a calculation to force a change in dt.

    Default:False

    C++ Type:bool

    Options:

    Description:Use when restarting a calculation to force a change in dt.

  • snesmf_reuse_baseTrueSpecifies whether or not to reuse the base vector for matrix-free calculation

    Default:True

    C++ Type:bool

    Options:

    Description:Specifies whether or not to reuse the base vector for matrix-free calculation

  • line_search_packagepetscThe solver package to use to conduct the line-search

    Default:petsc

    C++ Type:MooseEnum

    Options:petsc moose

    Description:The solver package to use to conduct the line-search

  • verboseFalsePrint detailed diagnostics on timestep calculation

    Default:False

    C++ Type:bool

    Options:

    Description:Print detailed diagnostics on timestep calculation

  • update_xfem_at_timestep_beginFalseShould XFEM update the mesh at the beginning of the timestep

    Default:False

    C++ Type:bool

    Options:

    Description:Should XFEM update the mesh at the beginning of the timestep

  • petsc_options_inameNames of PETSc name/value pairs

    C++ Type:MultiMooseEnum

    Options:-ksp_atol -ksp_gmres_restart -ksp_max_it -ksp_pc_side -ksp_rtol -ksp_type -mat_fd_coloring_err -mat_fd_type -mat_mffd_type -pc_asm_overlap -pc_factor_levels -pc_factor_mat_ordering_type -pc_hypre_boomeramg_grid_sweeps_all -pc_hypre_boomeramg_max_iter -pc_hypre_boomeramg_strong_threshold -pc_hypre_type -pc_type -snes_atol -snes_linesearch_type -snes_ls -snes_max_it -snes_rtol -snes_type -sub_ksp_type -sub_pc_type

    Description:Names of PETSc name/value pairs

  • petsc_optionsSingleton PETSc options

    C++ Type:MultiMooseEnum

    Options:-dm_moose_print_embedding -dm_view -ksp_converged_reason -ksp_gmres_modifiedgramschmidt -ksp_monitor -ksp_monitor_snes_lg-snes_ksp_ew -ksp_snes_ew -snes_converged_reason -snes_ksp -snes_ksp_ew -snes_linesearch_monitor -snes_mf -snes_mf_operator -snes_monitor -snes_test_display -snes_view

    Description:Singleton PETSc options

  • max_xfem_update4294967295Maximum number of times to update XFEM crack topology in a step due to evolving cracks

    Default:4294967295

    C++ Type:unsigned int

    Options:

    Description:Maximum number of times to update XFEM crack topology in a step due to evolving cracks

  • splittingTop-level splitting defining a hierarchical decomposition into subsystems to help the solver.

    C++ Type:std::vector

    Options:

    Description:Top-level splitting defining a hierarchical decomposition into subsystems to help the solver.

  • line_searchdefaultSpecifies the line search type (Note: none = basic)

    Default:default

    C++ Type:MooseEnum

    Options:basic bt contact cp default l2 none shell

    Description:Specifies the line search type (Note: none = basic)

  • num_steps4294967295The number of timesteps in a transient run

    Default:4294967295

    C++ Type:unsigned int

    Options:

    Description:The number of timesteps in a transient run

  • contact_line_search_ltolThe linear relative tolerance to be used while the contact state is changing between non-linear iterations. We recommend that this tolerance be looser than the standard linear tolerance

    C++ Type:double

    Options:

    Description:The linear relative tolerance to be used while the contact state is changing between non-linear iterations. We recommend that this tolerance be looser than the standard linear tolerance

  • petsc_options_valueValues of PETSc name/value pairs (must correspond with "petsc_options_iname"

    C++ Type:std::vector

    Options:

    Description:Values of PETSc name/value pairs (must correspond with "petsc_options_iname"

  • solve_typePJFNK: Preconditioned Jacobian-Free Newton Krylov JFNK: Jacobian-Free Newton Krylov NEWTON: Full Newton Solve FD: Use finite differences to compute Jacobian LINEAR: Solving a linear problem

    C++ Type:MooseEnum

    Options:PJFNK JFNK NEWTON FD LINEAR

    Description:PJFNK: Preconditioned Jacobian-Free Newton Krylov JFNK: Jacobian-Free Newton Krylov NEWTON: Full Newton Solve FD: Use finite differences to compute Jacobian LINEAR: Solving a linear problem

  • mffd_typewpSpecifies the finite differencing type for Jacobian-free solve types. Note that the default is wp (for Walker and Pernice).

    Default:wp

    C++ Type:MooseEnum

    Options:wp ds

    Description:Specifies the finite differencing type for Jacobian-free solve types. Note that the default is wp (for Walker and Pernice).

  • dt1The timestep size between solves

    Default:1

    C++ Type:double

    Options:

    Description:The timestep size between solves

  • schemeimplicit-eulerTime integration scheme used.

    Default:implicit-euler

    C++ Type:MooseEnum

    Options:implicit-euler explicit-euler crank-nicolson bdf2 explicit-midpoint dirk explicit-tvd-rk-2 newmark-beta

    Description:Time integration scheme used.

  • contact_line_search_allowed_lambda_cuts2The number of times lambda is allowed to be cut in half in the contact line search. We recommend this number be roughly bounded by 0 <= allowed_lambda_cuts <= 3

    Default:2

    C++ Type:unsigned int

    Options:

    Description:The number of times lambda is allowed to be cut in half in the contact line search. We recommend this number be roughly bounded by 0 <= allowed_lambda_cuts <= 3

  • end_time1e+30The end time of the simulation

    Default:1e+30

    C++ Type:double

    Options:

    Description:The end time of the simulation

Optional Parameters

  • l_abs_step_tol-1Linear Absolute Step Tolerance

    Default:-1

    C++ Type:double

    Options:

    Description:Linear Absolute Step Tolerance

  • nl_abs_tol1e-50Nonlinear Absolute Tolerance

    Default:1e-50

    C++ Type:double

    Options:

    Description:Nonlinear Absolute Tolerance

  • nl_max_its50Max Nonlinear Iterations

    Default:50

    C++ Type:unsigned int

    Options:

    Description:Max Nonlinear Iterations

  • l_max_its10000Max Linear Iterations

    Default:10000

    C++ Type:unsigned int

    Options:

    Description:Max Linear Iterations

  • compute_initial_residual_before_preset_bcsFalseUse the residual norm computed *before* PresetBCs are imposed in relative convergence check

    Default:False

    C++ Type:bool

    Options:

    Description:Use the residual norm computed *before* PresetBCs are imposed in relative convergence check

  • l_tol1e-05Linear Tolerance

    Default:1e-05

    C++ Type:double

    Options:

    Description:Linear Tolerance

  • nl_rel_tol1e-08Nonlinear Relative Tolerance

    Default:1e-08

    C++ Type:double

    Options:

    Description:Nonlinear Relative Tolerance

  • nl_max_funcs10000Max Nonlinear solver function evaluations

    Default:10000

    C++ Type:unsigned int

    Options:

    Description:Max Nonlinear solver function evaluations

  • nl_rel_step_tol1e-50Nonlinear Relative step Tolerance

    Default:1e-50

    C++ Type:double

    Options:

    Description:Nonlinear Relative step Tolerance

  • nl_abs_step_tol1e-50Nonlinear Absolute step Tolerance

    Default:1e-50

    C++ Type:double

    Options:

    Description:Nonlinear Absolute step Tolerance

Solver Parameters

  • steady_state_start_time0Minimum amount of time to run before checking for steady state conditions.

    Default:0

    C++ Type:double

    Options:

    Description:Minimum amount of time to run before checking for steady state conditions.

  • steady_state_tolerance1e-08Whenever the relative residual changes by less than this the solution will be considered to be at steady state.

    Default:1e-08

    C++ Type:double

    Options:

    Description:Whenever the relative residual changes by less than this the solution will be considered to be at steady state.

  • steady_state_detectionFalseWhether or not to check for steady state conditions

    Default:False

    C++ Type:bool

    Options:

    Description:Whether or not to check for steady state conditions

Steady State Detection Parameters

    Restart Parameters

    • enableTrueSet the enabled status of the MooseObject.

      Default:True

      C++ Type:bool

      Options:

      Description:Set the enabled status of the MooseObject.

    • start_time0The start time of the simulation

      Default:0

      C++ Type:double

      Options:

      Description:The start time of the simulation

    • use_multiapp_dtFalseIf true then the dt for the simulation will be chosen by the MultiApps. If false (the default) then the minimum over the master dt and the MultiApps is used

      Default:False

      C++ Type:bool

      Options:

      Description:If true then the dt for the simulation will be chosen by the MultiApps. If false (the default) then the minimum over the master dt and the MultiApps is used

    • control_tagsAdds user-defined labels for accessing object parameters via control logic.

      C++ Type:std::vector

      Options:

      Description:Adds user-defined labels for accessing object parameters via control logic.

    • no_fe_reinitFalseSpecifies whether or not to reinitialize FEs

      Default:False

      C++ Type:bool

      Options:

      Description:Specifies whether or not to reinitialize FEs

    • dtmax1e+30The maximum timestep size in an adaptive run

      Default:1e+30

      C++ Type:double

      Options:

      Description:The maximum timestep size in an adaptive run

    • dtmin2e-14The minimum timestep size in an adaptive run

      Default:2e-14

      C++ Type:double

      Options:

      Description:The minimum timestep size in an adaptive run

    • n_startup_steps0The number of timesteps during startup

      Default:0

      C++ Type:int

      Options:

      Description:The number of timesteps during startup

    • abort_on_solve_failFalseabort if solve not converged rather than cut timestep

      Default:False

      C++ Type:bool

      Options:

      Description:abort if solve not converged rather than cut timestep

    • timestep_tolerance2e-14the tolerance setting for final timestep size and sync times

      Default:2e-14

      C++ Type:double

      Options:

      Description:the tolerance setting for final timestep size and sync times

    Advanced Parameters

    • picard_abs_tol1e-50The absolute nonlinear residual to shoot for during Picard iterations. This check is performed based on the Master app's nonlinear residual.

      Default:1e-50

      C++ Type:double

      Options:

      Description:The absolute nonlinear residual to shoot for during Picard iterations. This check is performed based on the Master app's nonlinear residual.

    • relaxation_factor1Fraction of newly computed value to keep.Set between 0 and 2.

      Default:1

      C++ Type:double

      Options:

      Description:Fraction of newly computed value to keep.Set between 0 and 2.

    • relaxed_variablesList of variables to relax during Picard Iteration

      C++ Type:std::vector

      Options:

      Description:List of variables to relax during Picard Iteration

    • picard_max_its1Number of times each timestep will be solved. Mainly used when wanting to do Picard iterations with MultiApps that are set to execute_on timestep_end or timestep_begin

      Default:1

      C++ Type:unsigned int

      Options:

      Description:Number of times each timestep will be solved. Mainly used when wanting to do Picard iterations with MultiApps that are set to execute_on timestep_end or timestep_begin

    • picard_rel_tol1e-08The relative nonlinear residual drop to shoot for during Picard iterations. This check is performed based on the Master app's nonlinear residual.

      Default:1e-08

      C++ Type:double

      Options:

      Description:The relative nonlinear residual drop to shoot for during Picard iterations. This check is performed based on the Master app's nonlinear residual.

    Picard Parameters

    • time_period_startsThe start times of time periods

      C++ Type:std::vector

      Options:

      Description:The start times of time periods

    • time_period_endsThe end times of time periods

      C++ Type:std::vector

      Options:

      Description:The end times of time periods

    • time_periodsThe names of periods

      C++ Type:std::vector

      Options:

      Description:The names of periods

    Time Periods Parameters

    Input Files