DiscreteNucleationTimeStep

Return a time step limit for nucleation event to be used by IterationAdaptiveDT

Supply this postprocessor to an IterationAdaptiveDT via the postprocessor_dtlim parameter.

The timestep limit computed by this postprocessor is computed according to two different criteria.

Time step limit at nucleus insertion

If a nucleus has just been added to the nucleus list by the DiscreteNucleationInserter the timestep limit is set to the value supplied using the dt_max parameter for one timestep. In conjunction with IterationAdaptiveDT this causes the time step to be cut to dt_max from which it will slowly have to grow back.

Nucleation rate based timestep limit

Between nucleation event onsets the timestep is limited based on the user supplied upper bound on the probability (p2nucleus) to have _more than two_ nueceation events to occur during a single timestep. This probability is calculated as

(1)

where is the total nucleation rate over the whole simulation cell that results in the probability . To obtain for a given equation Eq. (1) is numerically inverted. is then divided by the integrated nucleation rate per unit time to obtain the largest possible time step that keeps the probability for two or more nuclei to form below the user specified upper bound.

Timestep (dt) in a nucleation simulation with a DiscreteNucleationTimeStep limited time step. The green curve (dtnuc) shows the time step limit. The envelope of that curve is determined by the upper bound on the two or more nucleus probability. The sharp downward spikes are the time step cut-backs during nucleation events.

This addresses two issues with poisson statistics sampling. At every sampling point in the domain the rate is sufficiently low to stay in the rare event regime (i.e where either zero or one event are happening). At higher rates the time resolution is insufficient to capture all possible nucleation events. Controlling the probability of multiple nuclei forming also reduces the chance of overlapping nuclei to form.

The DiscreteNucleationTimeStep postprocessor is part of the Discrete Nucleation system.

Input Parameters

  • inserterDiscreteNucleationInserter user object

    C++ Type:UserObjectName

    Options:

    Description:DiscreteNucleationInserter user object

  • dt_maxTime step to cut back to at the start of a nucleation event

    C++ Type:double

    Options:

    Description:Time step to cut back to at the start of a nucleation event

Required Parameters

  • execute_onTIMESTEP_ENDThe list of flag(s) indicating when this object should be executed, the available options include NONE, INITIAL, LINEAR, NONLINEAR, TIMESTEP_END, TIMESTEP_BEGIN, FINAL, CUSTOM.

    Default:TIMESTEP_END

    C++ Type:ExecFlagEnum

    Options:NONE INITIAL LINEAR NONLINEAR TIMESTEP_END TIMESTEP_BEGIN FINAL CUSTOM

    Description:The list of flag(s) indicating when this object should be executed, the available options include NONE, INITIAL, LINEAR, NONLINEAR, TIMESTEP_END, TIMESTEP_BEGIN, FINAL, CUSTOM.

  • p2nucleus0.01Maximum probability for more than one nucleus to appear during a time step. This will limit the time step based on the total nucleation rate for the domain to make sure the probability for two or more nuclei to appear is always below the chosen number.

    Default:0.01

    C++ Type:double

    Options:

    Description:Maximum probability for more than one nucleus to appear during a time step. This will limit the time step based on the total nucleation rate for the domain to make sure the probability for two or more nuclei to appear is always below the chosen number.

Optional Parameters

  • enableTrueSet the enabled status of the MooseObject.

    Default:True

    C++ Type:bool

    Options:

    Description:Set the enabled status of the MooseObject.

  • use_displaced_meshFalseWhether or not this object should use the displaced mesh for computation. Note that in the case this is true but no displacements are provided in the Mesh block the undisplaced mesh will still be used.

    Default:False

    C++ Type:bool

    Options:

    Description:Whether or not this object should use the displaced mesh for computation. Note that in the case this is true but no displacements are provided in the Mesh block the undisplaced mesh will still be used.

  • outputsVector of output names were you would like to restrict the output of variables(s) associated with this object

    C++ Type:std::vector

    Options:

    Description:Vector of output names were you would like to restrict the output of variables(s) associated with this object

  • 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.

  • allow_duplicate_execution_on_initialFalseIn the case where this UserObject is depended upon by an initial condition, allow it to be executed twice during the initial setup (once before the IC and again after mesh adaptivity (if applicable).

    Default:False

    C++ Type:bool

    Options:

    Description:In the case where this UserObject is depended upon by an initial condition, allow it to be executed twice during the initial setup (once before the IC and again after mesh adaptivity (if applicable).

  • force_preauxFalseForces the GeneralUserObject to be executed in PREAUX

    Default:False

    C++ Type:bool

    Options:

    Description:Forces the GeneralUserObject to be executed in PREAUX

Advanced Parameters

Input Files

References