Simulation
Defines the global simulation parameters, such as simulation time and output settings.
Commands
simulationParameters
{
t_begin 0.
t_end 10.
maxitsteps 10000000
energy_transport false
surften_model NONE
freesurface true
velcorrScheme T_VCORR
verbosityLevel VERBOSITY_STANDARD
freq_log 100
ns_phaseinfo 20
output_type VTUBINARY
dt_output 0.01
t_output_offset 0.5
t_output_file /path/to/outputtimes.txt
dt_output_restart 0.1
t_output_restart_offset 0.5
t_output_restart_file /path/to/outputtimes.txt
dt_output_restart_wallclock 2.5
dt_phaseinfo 0.1
restart_purge false
restart_keep_count 1
restart false
restart_from_step 200
output_vel false
output_wallvel false
output_temp false
output_acc false
output_prtlID true
output_phaseID true
output_rho true
output_press true
output_rank false
output_viscosity false
ignoreParticlesOutOfBounds false
ref_vel_factor 1.5
dt_simulation -1
adhesionmodel false
output_data_dir /path/to/output
restart_from_dir /path/to/sim/to/restart
operationMode NORMAL
damping_type HARMONIC
interactionscheme WEIGHTED
APD_coeff 0.001
APD_cutoff_factor 3.0
RM_freq_rho_reinit 20
RM_rho_filtering INSTANT
RM_coeff_vel_limiter 1.25
wrnFailLevel 5
nFXcTandemInterp true
valKeychains false
filesys_topo AUTO
print_memusage false
cleandir_opt MODIFY
enforce_operation_order false
varvisc_temperature false
varvisc_non_Newtonian false
output_comp true
output_comp_level 6
}
Definitions
Command | Contents | SI Unit Example |
---|---|---|
t_begin | Time at start of simulation Default = 0 |
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t_end | End-time of simulation Default = 1.0 |
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maxitsteps | In nanoFluidX, the numerical time-step is
calculated internally based on stability criteria using input values
like reference velocity. Depending on the resulting time-step and
the time to simulate (t_end –
t_begin), a huge number of iterations might
be necessary. In order to avoid an infinite loop this parameter can
be used to stop a simulation after a given number of
iterations. Tip: This parameter is typically used for
performance benchmarks where the simulation is performed for a
given number of steps.
Default = 1000000000 |
|
energy_transport | This model flag switches on/off the energy equation model. If
enabled, additional fields such as temperature are included in the
simulation and corresponding phase parameter. Reference values and
output flags need to be set. Options
Related Commands
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surften_model | This flag can be used to switch on the surface tension model1 or enable single phase surface tension. Options
Warning: If ADAMI,
TARTAKOVSKY2016_F1, or
SINGLE_PHASE is chosen, an additional
parameter in the phase properties must be
defined.
Related Options
|
|
freesurface | This flag prevents the occurrence of negative pressure values due
to lack of support in single phase cases. Options
Tip: In single phase cases, the free
surface of the fluid is in contact with a particle vacuum
(absence of particles) which in classic SPH formulation would
cause unphysical behavior. It is recommended to keep this option
set to true.
CAUTION: Changing this flag without an advanced understanding could have
undesired consequences.
Related Commands
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velcorrScheme | Particle velocity correction schemes, also referred to as
reuniformization schemes or shifting schemes, are used to improve
particle (discretization point) distribution in nanoFluidX and the quality of results.
nanoFluidX uses transport velocity
(TV) and artificial particle displacement (APD) methods to produce
well arranged particle distributions. While TV and APD themselves are not tied to a specific interaction scheme, the current implementation in nanoFluidX means that TV is more suited for Weighted interaction scheme and APD is intended for use with Riemann interaction scheme. Options
Default = The default value is set according to the interaction scheme. Related Commands
|
|
verbosityLevel | During a simulation, nanoFluidX prints some
log-information about the current status of the simulation. The
amount of output can be controlled with this parameter. Options
|
|
freq_log | This increment gives the frequency of log information, that is,
every #freq_log steps the log output is
written. Default = 100 |
|
ns_phaseinfo | This value (integer) determines how often the forces/torques, and
other phase information, are measured. Tip: This command
is slightly different from dt_phaseinfo, as
dt_phaseinfo determines the frequency of
the output. For example, you may want to output
dt_phaseinfo every 0.1 s, in the
meantime, there might be 10000 simulation steps in that time
period. ns_phaseinfo then allows you to
specify the number of measurement samples in that period. For
example, 100 samples per
dt_phaseinfo.
Attention: Changing this value can speed up the simulation substantially,
while having a minor impact on the output information
quality.
Default = 20 (20 samples per dt_phaseinfo) |
|
output_type | This parameter defines the type of the output. Options
|
|
dt_output | This is the time increment when the particle output is
written. Default = 0.1 |
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t_output_offset | Time delay to start of writing particle data output. For example,
setting this command to 0.2 s means that the writing of the particle
output begins at 0.2 s. Note:
Default = -1 (no effect). |
|
t_output_file | Enables you to specify a file in which the exact times of the
desired particle output are specified. The format of the file is a
column of desired time outputs with:
Attention: This command is mutually exclusive with
and takes precedent over dt_output and
t_output_offset.
|
|
dt_output_restart | Defines how often restart files are output. If you do not want to
output restart files, enter -1. Attention: Restart output
is only deactivated if dt_output_restart is
non-positive and a file is not provided.
Default = 10*dt_output |
|
t_output_restart_offset | Delays the start of writing restart output. For example, setting
this command to 0.3 s means that the writing of the restart output
begins at 0.3 s. It is similar to t_output_offset, except that the former is referring to the particle output, and the latter to the restart output. Note:
Default = -1 (no effect) |
|
t_output_restart_file | Enables you to specify exact times at which the restarts will be
written. The format of the file is a column of desired time outputs with:
Attention: This command is mutually exclusive with
and takes precedent over dt_output_restart
and t_output_restart_offset.
|
|
dt_output_restart_wallclock | A wallclock time interval to write recon files, in hours. The
acceptable range is between 1 second and 24 hours. Default = 0.0 (inactive) |
|
dt_phaseinfo | This is the time increment when the additional phase-info output
is written (if any of the phases has print_info
== true). Default = 0.1 |
|
restart_purge | If this switch is set to false, it will keep all the restart
files that have been output. Otherwise, if set to true, it will keep
only the latest restart point. Options
Related Commands
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restart_keep_count | If restart_purge is true,
restart_keep_count is the number of
restart/continue files to keep. This command is optional. Default = 1 |
|
restart | Defines if you are continuing a simulation or starting from a
restart file. Options
Related Commands
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restart_from_step | This specifies from which point does the simulation restart. The
restart numbers with the respective times can be found in the OUTPUT
folder of the case, in the restart.txt
file. Alternatively, you can use the keyword in the command line upon launching and the code automatically picks up from the last available restart file. For more information, refer to Restart a Simulation in the Run nanoFluidX section. Related Commands
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Output Flags | If the particle output is written, the following flags can be used to limit the amount of data that is actually written to the output file. Except for the particle positions, all other variables can be switched on/off for the output. The order of the flags is not important. | |
output_vel | This flag switches on/off the velocity field for the output. Options
|
|
output_wallvel | This flag switches on/off the velocity field of wall particles
for the output. Options
|
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output_temp | This flag switches on/off the temperature field for the output. Options
Warning: When this flag is set to
true and
energy_transport is set to
false, an error occurs.
Related Commands
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|
output_acc | This flag switches on/off the acceleration field for the output. Options
|
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output_prtlID | This flag switches on/off the particle ID field for the output.
This is a unique integer number for each particle to track the
Lagrangian motion in time. Options
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output_phaseID | This flag switches on/off the phase ID (phase number) of each
particle for the output. Options
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output_rho | This flag switches on/off the density field for the output. Options
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output_press | This flag switches on/off the pressure field for the output. | |
output_rank | This flag switches on/off the rank (GPU) of each particle for the
output. This information is only necessary if the particle
distribution on different ranks (GPUs) is of interest. Options
|
|
output_viscosity | This flag enables output of viscosity field in the case that
either varvisc_temperature or
varvisc_non_Newtonian are set to true. Options
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ignoreParticlesOutOfBounds | Check flag to ensure continuation of the run in case there is a
particle out of bounds. If particles are out of bounds the
simulation will not stop. If some kind of outlet is specified for
the boundaries, the particles will get deleted. Otherwise they will
continue to move outside of the domain. Options
|
|
ref_vel_factor | Factor which specifies how much overhead is added to the maximum
detected velocity in order to ensure adequate time step and keep the
simulation stable. Note: This is relevant only if the
ref_vel is set automatically by the
code.
Default = 1.5 |
|
dt_simulation | Allows for manual override of the internally calculated
(recommended) time step. CAUTION: Use with extreme
caution, especially if using larger than recommended time
step.
Default = -1 (Or the value the code calculates as appropriate) |
|
adhesionmodel | Boolean switch for enabling primitive adhesion models, based on
the model of Akinci et al. For more information, refer to
Adhesion Model and Single Phase Surface Tension. Options
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|
output_data_dir | Specifies a relative or absolute path for the output folder. The
data output will be stored in this folder. Format:
path/to/directory. Default = Folder which contains the .cfg file. This is also a reference if relative path is provided. |
|
restart_from_dir | Specify from which folder should the case be restarted. Format:
path/to/the/restart. Default = Folder which contains the .cfg file. This is also a reference if relative path is provided. |
|
operationMode | A switch that serves as a shortcut to optimize the solver
performance for maximum speed, normal operation, or optimize for accuracy. Options
Attention: A proficient user can achieve
either the DESIGN or
CONSERVATIVE modes manually by setting the
correct parameters. For more information, refer to Operation Modes.
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damping_type | Choice of damping (ramping) function. Options
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interactionscheme | Choice of the particle interaction scheme of the solver. Options
|
|
APD_coeff | APD particle position correction scheme parameter for intensity
of the correction. Tip: APD is an efficient algorithm for
particle regularization.
Default = 0.001 |
|
APD_cutoff_factor | Determines the radius (as a function of dx) of the sphere of
influence of the APD corrections scheme. This factor plays an
important role in balancing the intensity of the APD correction and
potential local instabilities and therefore consequent behavior of
the Riemann solver. Tip: Best practice is to use a value
between 2 and 3. Set as 2.0 to have less local instabilities
(hot particles), but less intensity in particle positioning, and
3.0 for stronger APD correction (less particle vacuum), but
potentially more local instabilities.
Default = 3.0 |
|
RM_rho_filtering | The density filtering (also referred to as density
re-initialization) operation. The density filtering procedure
improves the mass-area-density consistency and filters out
small-scale pressure oscillations. Options
Important: This command is only applicable
to the RIEMANN solver (obsolete when using
WEIGHTED).
Tip:
For more information, refer to Particle Interaction Schemes in the Theory Manual. |
|
RM_freq_rho_reinit | The frequency (number of timesteps) utilizing the density
filtering scheme (selected by the command
RM_rho_filtering). Default = 20 |
|
RM_coeff_vel_limiter | Limiter parameter that sets the upper limit on maximum velocity
experienced by a particle. Attention: Particles whose
velocity exceeds the value of the reference velocity, multiplied
by the RM_coeff_vel_limiter, will have their
velocity reset to the reference velocity value.
Default = 1.25 |
|
wrnFailLevel | Allows you to specify at which level a warning becomes an error
and stops the simulation. nanoFluidX has
5 warning levels where 5 is the most severe. Default = 5 (no warning produces an error) |
|
nFXcTandemInterp | Enables tandem operation between nanoFluidX and nanoFluidX[c] where nanoFluidX[c] interpolates the data from
nanoFluidX as it becomes available
in the output. This tandem operation is done through a pipe file
(FIFO) that is created inside the working
case folder. Options
For more information, refer to the Theory Manual. |
|
valKeychains | Keychain validator compares the keychains in the
cfg file with valid nanoFluidX keychains, when activated.
Keychain validator is meant to help address typographical errors in
the .cfg file. Options
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filesys_topo | Defines the file system topology for multi-node runs. Options
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print_memusage | Prints memory usage (host/device) in log output. Attention: The derivation of the values slightly differs
between device on host based on the information available. The
device value is calculated from the difference between total
memory on a single GPU and the amount of free memory on that
GPU. This gives the correct value for all supported
configurations.
For the unsupported case of a GPU being oversubscribed and multiple MPI ranks residing on it, the value is the sum of all processes on this MPI rank. For host memory, the amount of memory used is represented by the resident set size of every MPI rank. The amount of memory is correct although multiple MPI ranks usually reside in the shared RAM on a single machine. Additionally, if there is not enough host memory available and memory is swapped to the disk, the amount of swapped memory is not included in the printed value.Default =
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cleandir_opt | Treatment of output data directory in a clean run. Options
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enforce_operation_order | Enforces summation order in the GPU calculations and effectively
allows for full run reproducibility provided the same hardware and
software platform. Options
Note: When enabling operation order, you can expect a
small computational penalty ranging from 0 to 20 percent
reduction in performance. The exact performance drop is
difficult to generalize as it depends on the exact numerical
setup and number of particles on each of the
GPUs.
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varvisc_temperature | Set to true to request temperature dependent viscosity. Options
Attention:
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varvisc_non_Newtonian | Enables non-Newtonian behavior modeling. Options
Attention:
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output_comp | Enables compressed binary data output. Options
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output_comp_level | Output data compression level. Options
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