Section: time

This section deals with parameters that control the time stepping of the simulation. This section also addresses the time-dependent nature of checkpoint files, plot files, and regridding.

Primary location in code: amr-wind/core/SimTime.cpp.

time.stop_time

type: Real number

The time (in seconds) when the simulation should stop. This parameter is related to time.max_step depending on whether the user provides a positive or negative value for this input. If the user provides a positive value, then the stop criteria is such that the simulation stops when it reaches the stop_time. If the user specifies a negative value, then the simulation stops when it has completed the prescribed number of steps as determined by time.max_step.

time.max_step

type: Integer

The number of timesteps to run before termination. See also time.stop_time.

time.fixed_dt

type: Real number

Fixed timestep size (in seconds) used to advance the simulation. If this parameter is negative, then time.cfl is used to determine the adaptive timestep during the simulation.

time.initial_dt

type: Real number

Initial timestep size (in seconds) used to initialize the simulation. Only activated if time.fixed_dt is negative (signalling CFL controlled time stepping) and if time.initial_dt is positive. This parameter can be useful for starting CFL-controlled simulations like Rayleigh-Taylor flow that initialize with zero velocity.

time.cfl

type: Real number, optional, default = 0.5

The maximum CFL allowed during the simulation. Adaptive timestepping algorithm is used to ensure that the maximum CFL condition is not violated while using the largest allowable timestep to advance the simulation.

time.init_shrink

type: Real number, optional, default = 0.1

init_shrink indicates a reduction factor applied to the timestep size during initialization phased used to perform the initial iterations to determine pressure. This factor must be a value greater than zero but less than or equal to 1.0.

time.max_dt_growth

type: Real number, optional, default = 0.1

max_dt_growth indicates a growth limit factor applied to the timestep size whenever it increases during a variable dt simulation. This factor must be a value greater than zero but less than or equal to 1.0. In most cases a value of 0.1 is sufficient, but if dt is forced to shrink harshly and often due to time.enforce_plot_time_dt or time.enforce_checkpoint_time_dt being active, a larger growth factor may be more practical.

time.regrid_interval

type: Integer, optional, default = -1

If amr.max_level is greater than zero, this parameter indicates the frequency (in timesteps) at which the mesh is adaptively refined based on various user-specified criteria. If this value is negative, the mesh is only refined once during initialization and remains constant for the rest of the simulation.

time.plot_interval

type: Integer, optional, default = -1

If this value is greater than zero, it indicates the frequency (in timesteps) at which outputs (plot files) are written to disk.

time.plot_time_interval

type: Real number, optional, default = -1.0

If this value is greater than zero, it indicates the frequency (in seconds) at which outputs (plot files) are written to disk. This cannot be specified in conjunction with time.plot_interval. Because the size of time steps (dt) do not automatically correspond to the size of the plot time interval, additional parameters are available if desired: time.plot_time_interval_reltol, time.enforce_plot_time_dt, and time.enforce_plot_dt_reltol. These additional parameters are only relevant for simulations with a variable time step size (dt).

time.plot_delay

type: Integer, optional, default = 0

If time.plot_interval is greater than zero, then the plot delay specifies how long (in timesteps) to wait before writing a plot file. The implementation waits until this threshold is reached to check if the interval allows for a file to be written. For example, if the plot delay is specified to be “1000”, and the plot interval is “10”, then the first plot file written would be at timestep “1000”. If the plot delay is “1001” and the plot interval is still “10”, then the first plot file file would be at timestep “1010”.

time.plot_time_delay

type: Real number, optional, default = 0.0

If time.plot_time_interval is greater than zero, then the plot time delay specifies how long (in seconds) to wait before writing a plot file. Similar to time.plot_delay, the implementation waits until this threshold is reached to check if the time interval allows for a file to be written.

time.checkpoint_interval

type: Integer

If this value is greater than zero, it indicates the frequency (in timesteps) at which checkpoint (restart) files are written to disk.

time.checkpoint_time_interval

type: Real number, optional, default = -1.0

If this value is greater than zero, it indicates the frequency (in seconds) at which checkpoint (restart) files are written to disk. This cannot be specified in conjunction with time.checkpoint_interval. Because the size of time steps (dt) do not automatically correspond to the size of the checkpoint time interval, additional parameters are available if desired: time.checkpoint_time_interval_reltol, time.enforce_checkpoint_time_dt, and time.enforce_checkpoint_dt_reltol. These additional parameters are only relevant for simulations with a variable time step size (dt).

time.checkpoint_delay

type: Integer, optional, default = 0

If time.checkpoint_interval is greater than zero, then the checkpoint delay specifies how long (in timesteps) to wait before writing a checkpoint file. The implementation waits until this threshold is reached to check if the interval allows for a file to be written. For example, if the checkpoint delay is specified to be “1000”, and the checkpoint interval is “10”, then the first checkpoint file written would be at timestep “1000”. If the checkpoint delay is “1001” and the checkpoint interval is still “10”, then the first checkpoint file would be at timestep “1010”.

time.checkpoint_time_delay

type: Real number, optional, default = 0.0

If time.checkpoint_time_interval is greater than zero, then the checkpoint time delay specifies how long (in seconds) to wait before writing a checkpoint file. Similar to time.checkpoint_delay, the implementation waits until this threshold is reached to check if the time interval allows for a file to be written.

time.regrid_start

type: Integer, optional, default = 0; default = start index upon restart

This user-specified parameter sets the base timestep onwards which the mesh is adaptively refined.

time.plot_start

type: Integer, optional, default = 0; default = start index upon restart

This user-specified parameter sets the base timestep onwards which the output (plot files) are written to the disk. This parameter is specifically for offsetting the index following a restart.

time.checkpoint_start

type: Integer, optional, default = 0; default = start index upon restart

This user-specified parameter sets the base timestep onwards which the checkpoint (restart) files are written to the disk. This parameter is specifically for offsetting the index following a restart.

time.use_force_cfl

type: Boolean, optional, default = true

If this flag is true then the forces (including the pressure gradient) are included in the CFL calculation.

time.plot_time_interval_reltol

type: Real number, optional, default = 1e-8

When time.plot_time_interval is greater than zero, the implementation compares the current simulation time to the specified time interval in order to output the time step that meets or just passes the time interval. Because this involves a comparison between real numbers, this comparison uses a tolerance, which is relative to the current timestep, which helps avoid skipping time steps which are very close, but just shy, of the time interval. In most cases, this parameter need not be modified, but it can be changed by the user.

time.enforce_plot_time_dt

type: Boolean, optional, default = false

In the case of a variable dt simulation, the simulation time will not likely correspond exactly to the plot time interval. However, by setting this parameter to true, the time step size (dt) will be shortened when necessary to enforce the simulation time to match the plot time interval. Enabling this feature while also enabling time.enforce_checkpoint_time_dt will result in a warning message.

time.enforce_plot_dt_reltol

type: Real number, optional, default = 1e-3

When time.enforce_plot_time_dt is true, a tolerance is needed to determine when it is necessary to shrink the time step size. This tolerance is relative to the plot time interval. In most cases, this parameter need not be modified, but it can be changed by the user.

time.checkpoint_time_interval_reltol

type: Real number, optional, default = 1e-8

This parameter is active when time.checkpoint_time_interval is greater than zero, and it exists for the same reason as time.plot_time_interval_reltol.

time.enforce_checkpoint_time_dt

type: Boolean, optional, default = false

Similar to time.enforce_plot_time_dt, setting this parameter to true will enforce the simulation time to match the checkpoint time interval in the case of a variable dt simulation. Enabling this feature while also enabling time.enforce_plot_time_dt will result in a warning message.

time.enforce_checkpoint_dt_reltol

type: Real number, optional, default = 1e-3

When time.enforce_checkpoint_time_dt is true, a tolerance is needed to determine when it is necessary to shrink the time step size. This tolerance is relative to the checkpoint time interval. In most cases, this parameter need not be modified, but it can be changed by the user.