Phase Parameters

In the “phases”-section the material parameters are defined for different SPH components.

The name of the phases as given/used in SimLab is not important, only the material ID (in SimLab) that relates to the phase number as defined here! The first phase definition in the configuration file defines the properties of the SPH particles with the material ID “1”, the second group for the material ID “2” etc.
          name                       Water
          type                       FLUID
          rho_0                      1000.
          dyn_visc                   1.e-3
          surf_ten                   0.1
          temp_0                     0.
          heat_cond                  0.
          heat_cap                   0.
          evolve_temp                false
          rho_compr                  0.01
          pc_factor                  1.0
          print_info                 false
          print_phase                true
          cs                         100     
          rm_rho_theta               1.1
          init_vel		      “0.0 0.0 0.0”
          name                       Housing
          type                       WALL				
          heat_cond                  0.0
          heat_cap                   0.0
          temp_0                     0.0
          evolve_temp                false
          noSlip                     true
          print_info                 true
          print_phase                true
          adhesionCoeff              0.01            
          fluidContactPhase          1      
          makesubphase               true
          init_vel		      “0.0 0.0 0.0”
          name                        Something_moving
          type                        MOVINGWALL
          rho_0                       1.0
          heat_cond                   0.0
          heat_cap                    0.0
          temp_0                      0.0
          evolve_temp                 false	
          noSlip                      true
          print_info                  true
          print_phase                 true	
          adhesionCoeff               0.01            
          fluidContactPhase           1   
          makesubphase                true   
          init_vel		       “0.0 0.0 0.0”
The name of this phase.
Note: This does not need to match with the component name in SimLab.
Options: This can be any string value like “water,” for example, or “mixedfluid.”
The type of the phase defines the physical behavior.
This property is mandatory and defines if a group of SPH particles behaves as:
  • FLUID: the forces acting on these particles define the motion according the Navier-Stokes equation.
  • WALL: these particles do not change their position during the entire simulation as they define a static rigid wall boundary. They have no-slip boundary condition associated at the fluid-wall interface, which can be overridden by the noSlip command.
  • MOVINGWALL: these particles can change their position based on how is their motion defined, unless specified as a rigid body. As explained later, moving walls can move according to an imposed velocity or imposed rotation (see Imposed Motions). They also have no-slip boundary condition associated at the FLUID-MOVINGWALL interface. If the MOVINGWALL is designated as a rigid body (see fluidCoupledMotion), then it interacts freely with the fluid and is subject to buoyancy forces etc. (for example, ships and similar floating objects can be simulated as rigid bodies).
  • MASSFLOW: starting with the 2021.0 nanoFluidX release - this phase type no longer exists. Please use the Probe functionality for extracting the mass flow.
The reference density of this phase.
This is the initial density of all particles of this phase.
In case that the body is defined as rigid (fluidCoupledMotion), this value is overridden by a density which is calculated based on the specified mass of the body (body_mass) and the total number of particles representing the phase in question.
Default: 1.0
The dynamic viscosity of this phase in [kg / (m s), Pa s].
If viscTempCoupling (temperature-viscosity coupling) is set to true, this value will be ignored since it is specially defined by temperature-viscosity models which determine the viscosity of the fluid (see Viscosity-temperature Dependence Models).
Default: 0.0
The specific heat capacity at constant pressure (Cp) of this phase.
Related options/commands: energy_transport, heat_cond, evolve_temp, temp_0, Energy equation
Unit: [J/kg/K]
Default: 0.0
The heat conductivity of this phase.
Related options/commands: energy_transport, heat_cap, evolve_temp, temp_0, Energy equation
Unit: [W/m/K]
Default: 0.0
This flag can be used to set the temperature of a phase constant or to allow it to evolve according the energy equation.
Related options/commands: energy_transport, heat_cap, heat_cond, temp_0, Energy equation
Options: true / false
Default: false
Switch to enable the wall or moving wall to become a slip or no-slip boundary condition.
Options: true / false
Default: true
The initial temperature of a phase in Kelvin [K].
Related options/commands: energy_transport, heat_cap, heat_cond, evolve_temp, Energy equation
Default: 273.15
The surface tension coefficient [N/m].
For ADAMI surface tension model, this needs to be the physical value of the surface tension coefficient. For lubricating oil, the common oil-air surface tension value is 0.03 N/m.
If using the SINGLE_PHASE surface tension model, this value needs to be fine-tuned to suit a particular case. Good start is value of 0.1 N/m.
Related options/commands: surften_model, ref_curv, Multiphase surface tension
Default: 0.0
The compressibility of the fluid.
Following the weakly-compressible approach the admissible density variation is 1%, for example rho_compr = 0.01
Note: Do not change/touch this value unless very sure about the meaning and consequences.
Default: 0.01
Background correction pressure associated with the transport velocity formulation. It can have an arbitrary value, however it is generally recommended to keep it on the same order of magnitude of the p0 (base pressure).
Related options/commands: Transport velocity formulation
Default: 1.0
If this Boolean flag is set to true, an additional file is written during the simulation with the filename name_info.txt (name is the phase name as defined earlier). The content is written every #N steps (see dt_phaseinfo) and contains information on for example the forces, torques, kinetic energy, center-of-mass etc. of this phase.
Options: true / false
Default: false
This Boolean flag switches the output of this phase on or off. This switch is useful to limit the amount of output since wall particles for example, do not change their position in time and might not be necessary in the output.
Options: true / false
Default: false
Specify the speed of sound in the FLUID phases (individually).
Speed of sound can have a profound influence on the overall behavior of the simulation and is generally considered an advanced parameter.
Tip: It is recommended that you leave it out of the phase definition, unless you are absolutely certain you know what you are doing.
By default, this parameter is left out of the phase definition in which case the code will use the automatically calculated speed of sound based on the ref_vel and rho_compr.
Scaling parameter designed to enable local particle density reinitialization once the threshold of rho_0*rm_rho_theta is exceeded.
Restriction: This parameter is only available and meaningful when Riemann scheme is used.
For high density fluids, such as water or oil, best practice is to keep the value very high at, for example, 1e7 (basically meaning that heavy fluids never undergo local density reinitialization).
For low density fluids it is suggested to keep this value low, for example, between 1.1 and 1.2.
Suggested best practices maintain the stability of the Riemann formulation in multiphase simulations.
Numerical parameter used in the low-dissipation Riemann solver. It determines the level of numerical dissipation being introduced in the pair-wise interactions.
Default value is 3.0 and that is the recommended value. Reducing this value increases the amount of dissipation. The value of 3.0 is adopted from academic sources.
User is advised not to modify this value unless they are certain of their understanding of what the parameter does from a theoretical point of view.
Setting this value to -1 allows for reverting the low-dissipation Riemann solver to a linearized Riemann solver. This increases the overall amount of numerical dissipation used and can be enabled on a phase basis.
If the specified phase is a fluid, then the linearized Riemann solver will be applied with particle interaction within the phase; If the specified phase is not a fluid, then any fluid particles that are interacting with this phase will be switched to linearized Riemann solver. This modification essentially increases numerical dissipation so that the stability of inter-phase behavior is improved.
Default: 3.0
Scalar value that determines the strength of adhesion force of the fluid particles to the material. Tested range goes from 0.001 to 2.0.
This is a purely numerical parameter, so it does not have its physical counterpart defined. For more information, see Adhesion Model and Single Phase Surface Tension Models.
Default: 0.0
Specifying this command in the phase definition will automatically enable tracking of time which the WALL or MOVINGWALL phase spends in contact with the specified fluid phase. This tracked output will be written in the respective particle output file.
This command is only valid for WALL and MOVINGWALL type phases, whereas the tracked phase can only be a FLUID.
nanoFluidX has undergone some structural changes and now includes optional use of the sub-phasing. For more details, see Theory and Advanced Features.
Setting this value to true enables more efficient treatment of the phases when executing the main GPU calculations. The performance gain is likely to be more prominent as the number of the phases in the case increases.
Generally we recommend using this capability whenever possible (for use limitations see Theory and Advanced Features).
Default: true
This command can be applied to all phase types, but depending on whether it is a solid or a fluid, it will have different behavior.
If this command is applied to a FLUID phase type – it assigns an initial velocity to the specified FLUID phase.
If this command is applied to a WALL or a MOVINGWALL phase type, it will assign the specified velocity vector to all the particles belonging to that phase. In effect this will behave as a velocity boundary condition on the specified phase.
Default: “0.0 0.0 0.0”