Merge pull request #24873 from joshuahansel/time-sequence-stepper-las…

…t-step

Added extrapolation option to TimeSequenceStepperBase

framework/doc/content/source/timesteppers/CSVTimeSequenceStepper.md

@@ -1,17 +1,17 @@
 # CSVTimeSequenceStepper
 
-Imports a time sequence from a CSV file, or similar delimited text files.
-The CSVTimeSequenceStepper uses a [DelimitedFileReader](MooseUtils.md#delimitedfilereader)
+This time stepper derives from [TimeSequenceStepperBase.md] and provides the
+sequence of time values from a CSV file or similarly delimited text file.
+A [DelimitedFileReader](MooseUtils.md#delimitedfilereader) is used
 to read the CSV file.
 
 The file is always read in columns. The column can either be accessed by name
 (using the "column_name" parameter, provided that the CSV file has a header
 containing the names of the different columns) or by index (using the
 "column_index" parameter, with 0 the index of the first column).
 
-If the solve fails to converge during a time step, the behavior of the
-`CSVTimeSequenceStepper` is the same as the [TimeSequenceStepper.md]. The
-time step will be cut then the time stepper will attempt to return to the original sequence.
+See [TimeSequenceStepperBase.md#failed_solves] for information on the behavior
+of this time stepper for failed time steps.
 
 !syntax parameters /Executioner/TimeSteppers/CSVTimeSequenceStepper
 

framework/doc/content/source/timesteppers/ExodusTimeSequenceStepper.md

@@ -1,10 +1,12 @@
 # ExodusTimeSequenceStepper
 
-!syntax description /Executioner/TimeSteppers/ExodusTimeSequenceStepper
+This time stepper derives from [TimeSequenceStepperBase.md] and provides the
+sequence of time values from an Exodus file.
 
 The Exodus file is read by the first process (rank 0), and the time step sequence is then broadcast to all other processes.
 
-If the solve fails to converge during a time step, the behavior of the `ExodusTimeSequenceStepper` is the same as the [TimeSequenceStepper.md]. The time step will be cut then the time stepper will attempt to return to the original sequence.
+See [TimeSequenceStepperBase.md#failed_solves] for information on the behavior
+of this time stepper for failed time steps.
 
 ## Example input file
 

framework/doc/content/source/timesteppers/TimeSequenceStepper.md

@@ -1,12 +1,11 @@
 # TimeSequenceStepper
 
-!syntax description /Executioner/TimeSteppers/TimeSequenceStepper
+This time stepper derives from [TimeSequenceStepperBase.md] and provides the
+sequence of time values from a user-specified list, given by
+[!param](/Executioner/TimeSteppers/TimeSequenceStepper/time_sequence).
 
-If the solver fails to obtain a converged solution for a given
-step, the executioner cuts back the step size and attempts to advance the time
-from the previous step using a smaller time step. The time step is cut back by
-multiplying the time step by the cutback factor, defaulting to 0.5. If this is successful,
-the time stepper will then attempt to use the next time in the sequence, adjusting the time step to "get back on track".
+See [TimeSequenceStepperBase.md#failed_solves] for information on the behavior
+of this time stepper for failed time steps.
 
 ## Example input syntax
 

framework/doc/content/source/timesteppers/TimeSequenceStepperBase.md

@@ -0,0 +1,34 @@
+# TimeSequenceStepperBase
+
+`TimeSequenceStepperBase` is a base class for time steppers that use a sequence
+time values $t_i$ to produce time step sizes.
+
+## Failed solves id=failed_solves
+
+If the solver fails to obtain a converged solution for a given
+step, the executioner cuts back the step size and attempts to advance the time
+from the previous step using a smaller time step. The time step is cut back by
+multiplying the time step by the cutback factor, defaulting to 0.5. If this is successful,
+the time stepper will then attempt to use the next time in the sequence,
+adjusting the time step to "get back on track".
+
+## Choosing the time step size past the final time value
+
+Suppose that $t_N$ is the maximum time value provided in the sequence. This value
+may be less than the simulation end time $t_\text{end}$ given by the
+[!param](/Executioner/Transient/end_time) parameter. If this is true and the current simulation
+time $t$ is past $t_N$, then by default, there will be a single, final time step
+that jumps to the end time:
+
+!equation
+\Delta t = t_\text{end} - t_N \,.
+
+However, in many cases this is undesirable, such as when a steady state condition
+is used to terminate a transient, in which case an arbitrarily large end time
+is specified, leading to a very large time step size. This behavior can be
+altered with [!param](/Executioner/TimeSteppers/TimeSequenceStepper/use_last_dt_after_last_t).
+If set to `true`, this uses the final time step size in the sequence instead
+for all time past $t_N$:
+
+!equation
+\Delta t = t_N - t_{N-1} \,.

framework/include/timesteppers/TimeSequenceStepperBase.h

@@ -38,6 +38,9 @@ class TimeSequenceStepperBase : public TimeStepper
   virtual Real computeDT() override;
   virtual Real computeFailedDT() override;
 
+  /// Whether to use the final dt past the last t in sequence
+  const bool _use_last_dt_after_last_t;
+
   /// the step that the time stepper is currently at
   unsigned int & _current_step;
 

framework/src/timesteppers/TimeSequenceStepperBase.C

@@ -18,11 +18,17 @@ InputParameters
 TimeSequenceStepperBase::validParams()
 {
   InputParameters params = TimeStepper::validParams();
+  params.addParam<bool>(
+      "use_last_dt_after_last_t",
+      false,
+      "If true, uses the final time step size for times after the last time in the sequence, "
+      "instead of taking a single step directly to the simulation end time");
   return params;
 }
 
 TimeSequenceStepperBase::TimeSequenceStepperBase(const InputParameters & parameters)
   : TimeStepper(parameters),
+    _use_last_dt_after_last_t(getParam<bool>("use_last_dt_after_last_t")),
     _current_step(declareRestartableData<unsigned int>("current_step", 0)),
     _time_sequence(declareRestartableData<std::vector<Real>>("time_sequence"))
 {
@@ -129,7 +135,19 @@ TimeSequenceStepperBase::computeInitialDT()
 Real
 TimeSequenceStepperBase::computeDT()
 {
-  return _time_sequence[_current_step + 1] - _time_sequence[_current_step];
+  const auto standard_dt = _time_sequence[_current_step + 1] - _time_sequence[_current_step];
+
+  if (_use_last_dt_after_last_t)
+  {
+    // last *provided* time value index; actual last index corresponds to end time
+    const auto last_t_index = _time_sequence.size() - 2;
+    if (_current_step + 1 > last_t_index)
+      return _time_sequence[last_t_index] - _time_sequence[last_t_index - 1];
+    else
+      return standard_dt;
+  }
+  else
+    return standard_dt;
 }
 
 Real

modules/doc/content/newsletter/2023/2023_07.md

@@ -0,0 +1,23 @@
+# MOOSE Newsletter (July 2023)
+
+!alert! construction title=In Progress
+This MOOSE Newsletter edition is in progress. Please check back in August 2023
+for a complete description of all MOOSE changes.
+!alert-end!
+
+## MOOSE Improvements
+
+## libMesh-level Changes
+
+## PETSc-level Changes
+
+## Bug Fixes and Minor Enhancements
+
+### New option for time-stepping past the last time in time sequence steppers
+
+The various time sequence steppers ([TimeSequenceStepper.md], [CSVTimeSequenceStepper.md],
+and [ExodusTimeSequenceStepper.md]) compute time step size from a sequence of
+time values. Past the final time value, they previously could only make a single
+time step directly to the simulation end time. Now an option
+`use_last_dt_after_last_t` has been added, which when true, will instead use
+the final time step size in the provided sequence past the last time in the sequence.

test/tests/time_steppers/timesequence_stepper/gold/timesequence_last_dt_out.csv

@@ -0,0 +1,8 @@
+time,dt
+0,0
+1,1
+3,2
+4,1
+8,4
+12,4
+16,4

test/tests/time_steppers/timesequence_stepper/tests

@@ -1,5 +1,5 @@
 [Tests]
-  issues = '#9698 #6353 #6795'
+  issues = '#9698 #6353 #6795 #24868'
   design = 'TimeSequenceStepper.md'
 
   [time_sequence]
@@ -63,7 +63,15 @@
       input = 'csvtimesequence.i'
       exodiff = 'csvtimesequence_out.e'
 
-      detail = 'when reading the sequence from a comma-separated input file.'
+      detail = 'when reading the sequence from a comma-separated input file, and'
+    []
+
+    [use_last_dt]
+      type = CSVDiff
+      input = 'timesequence_last_dt.i'
+      csvdiff = 'timesequence_last_dt_out.csv'
+
+      detail = 'allowing the last time step size to be used past the final time in the sequence.'
     []
   []
 

test/tests/time_steppers/timesequence_stepper/timesequence_last_dt.i

@@ -0,0 +1,28 @@
+[Mesh]
+  type = GeneratedMesh
+  dim = 1
+[]
+
+[Problem]
+  solve = false
+[]
+
+[Executioner]
+  type = Transient
+  num_steps = 6
+  [TimeStepper]
+    type = TimeSequenceStepper
+    time_sequence = '0 1 3 4 8'
+    use_last_dt_after_last_t = true
+  []
+[]
+
+[Postprocessors]
+  [dt]
+    type = TimestepSize
+  []
+[]
+
+[Outputs]
+  csv = true
+[]