Simulation Parameters
The first section defines the global simulation parameters such as simulation time and output settings.
simulationParameters
{
t_begin 0.
t_end 10.
maxitsteps 10000000
energy_transport false
viscTempCoupling false
surften_model NONE
freesurface true
transportvelocity true
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
ignoreParticlesOutOfBounds false
ref_vel_factor 1.5
dt_simulation -1
aeroViscMode NOMODE
aeroViscCoeff 10.0
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
}
- t_begin
- Time at start of simulation
- t_end
- End-time of simulation
- maxitsteps
- In nanoFluidX, the numerical time-step is calculated internally based on stability criteria using the 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. Note, this parameter is usually used for performance benchmarks where the simulation is performed for a given number of steps.
- energy_transport
- This model flag switches on/off the energy equation model. If ON, additional fields such as temperature are included in the simulation and corresponding phase parameter, reference values and output flags need to be set.
- viscTempCoupling
- This is a Boolean switch that enables temperature-viscosity coupling. It can only be turned on, if the energy_transport flag is turned on, otherwise it makes no sense, as the temperature is not even calculated.
- surften_model
- This flag can be used to switch on the surface tension model according Adami et al. 1 or enable single phase surface tension. If ADAMI or SINGLE_PHASE is chosen, additional parameter in the phase properties need to be defined.
- freesurface
- This flag essentially prevents occurrence of negative pressure values due to lack of support in single phase cases. In single phase cases the free surface of the fluid is in contact with what we refer to as “particle vacuum” (absence of particles) which in classic SPH formulation would cause unphysical behavior. Generally, we recommend keeping this option set to true at all times, unless you are familiar with the consequences of turning it off.
- transportvelocity
- This flag enables the so called transport velocity formulation of Adami. 1 Transport velocity has a series of beneficial influences on the numerical behavior of the SPH method. It introduces a velocity correction term which actively keeps particle distribution isotropic and prevents the pairing instability as well. In one work by Adami et al. 2 it is speculated that transport velocity can behave essentially like a turbulence model.
- verbosityLevel
- During a simulation, nanoFluidX prints some log-information about the current status of the simulation. Depending on this parameter the amount of output can be controlled.
- freq_log
- This increment gives the frequency of log information, i.e. every #freq_log steps the log output is written.
- ns_phaseinfo
- This value (integer) determines how often will the forces/torques and other phase information be measured. It is 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 (e.g. 100 samples per dt_phaseinfo).
- output_type
- This parameter defines the type of the output.
- dt_output
- This is the time increment when the particle output is written.
- t_output_offset
- Time delay to start of writing particle data output.
- t_output_file
- Using the command (providing the particle output file) enables the user to specify a file in which the exact times of the desired particle output are specified.
- dt_output_restart
- How often do you want to output restart files? If you do not want to output restart, you should enter -1.
- t_output_restart_offset
- Delay start of writing restart output.
- t_output_restart_file
- This is a similar command to t_output_file. Using this command enables the user to specify exact times at which the restarts will be written.
- dt_output_restart_wallclock
- A wallclock time interval to write recon files, in hours.
- dt_phaseinfo
- This is the time increment when the additional phase-info output is written (if any of the phases has print_info == true)
- 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.
- restart_keep_count
- If restart_purge is true, restart_keep_count is the number of restart/continue files to keep.
- restart
- Is this run a continuation of a previous simulation? Is it starting from a restart file? If it is, then set to true. If it is a new run, set it to false.
- 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.
- output_vel
- If 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. Note, the order of the flags is not important.
- output_wallvel
- This flag switches on/off the velocity field of wall particles for the output.
- output_temp
- This flag switches on/off the temperature field for the output.
- output_acc
- This flag switches on/off the acceleration field for the output.
- 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.
- output_phaseID
- This flag switches on/off the phase ID (phase number) of each particle for the output.
- output_rho
- This flag switches on/off the density field for the output.
- 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.
- 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.
- 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.
- dt_simulation
- Allows for manual override of the internally calculated (recommended)
time step.Note: Use with extreme caution, especially if using larger than recommended time step.
- aeroViscMode
- Switch for enabling coupling between aeration of oil and apparent viscosity of the oil. More information about the models can be found in Aeration-Viscosity Models.
- aeroViscCoeff
- Linear coefficient in the aeration-viscosity coupling model. It effects how much more viscous will the fluid get as a function of oil-air mixing. More information about the models can be found in Aeration-Viscosity Models.
- adhesionmodel
- Boolean switch for enabling primitive adhesion models, based on the model of Akinci et al. [4]. For more information, refer to Adhesion Model and Single Phase Surface Tension.
- output_data_dir
- Specify a relative or absolute path for the output folder. The data output will be stored in this folder.
- restart_from_dir
- Specify from which folder should the case be restarted.
- operationMode
- Switch which serves as a shortcut to optimize the solver performance for maximum speed, normal operation, or optimize for accuracy.
- damping_type
- Choice of the damping (ramping) function.
- interactionscheme
- Choice of the particle interaction scheme of the solver.
- APD_coeff
- APD particle position correction scheme parameter for intensity of the correction.
- APD_cutoff_factor
- Determines the radius (as a function of dx) of the sphere of influence of the APD corrections scheme.
- APD_cutoff_factor
- Determines the radius (as a function of dx) of the sphere of influence of the APD corrections scheme.
- RM_rho_filtering
- The density filtering (also referred as density re-initialization) operation. The density filtering procedure improves the mass-area-density consistency and filters out small-scale pressure oscillations.
- RM_freq_rho_reinit
- The frequency, that is, number of timesteps, of utilizing the density-filtering scheme (selected by the command RM_rho_filtering).
- RM_coeff_vel_limiter
- Limiter parameter which sets the upper limit on the maximum velocity experienced by a particle.
- wrnFailLevel
- nanoFluidX has improved warning information such that it includes 5 different warning levels, going from 0 as benign to 5 as severe.
- nFXcTandemInterp
- Setting this command to true enables tandem operation between nanoFluidX and nFX[c], where nFX[c] in that case interpolates the data from nFX as it becomes available (output).
- valKeychains
- Keychain validator compares the keychains in the cfg file with valid nanoFluidX keychains, when activated.
- filesys_topo
- Define filesystem topology for multi-node runs.
- print_memusage
- Prints memory usage (host/device) in log output.