Conditions

5.1.2 Conditions

This section discusses the settings of the parameters and properties common to all the modules.

Click Common in the Model Panel, the following parameters are available in the Properties Panel:

Solution Control Parameters

Number of Iterations: This user input limits the total number of iterations for a steady-state simulation or total number of iterations per time-step for a transient simulation.
Time Definition: Simerics-MP/Simerics-MP+ can solve the conservation equations in two modes: Transient and Steady State Simulation.

For a transient simulation, the following solver parameters are required to determine the time-step (in s):
- Simulation Time (Duration): It is specified in seconds.
- Number of Time Steps: This user input, along with the Simulation Time, decides the size of time-step.
- Cycle Computation Interval: It determines the frequency (time-steps) to update the mesh if it applies.
For a steady-state simulation, the following solver parameter is specified:
- Mesh Update Frequency (Iterations): It determines the frequency (number of iterations) to update the mesh if it applies.
Result Saving Frequency: It determines the frequency to save the solution files (.sres). For a steady-state simulation, it is the number of iterations, while it is the number of time-steps in a transient simulation.
Cycle Computation Interval: This denotes a “Period” during which the average/maximum/minimum of the variables encountered is computed for. It also determines the frequency (time-steps) to update the distributed values of average/maximum/minimum variables.

Understanding the average values

This is NOT a "Moving" average. Each “Period” is exclusive from the previous and the next “Period”.
The values will only be updated once for each “Period” at the end of that “Period”. In the middle of a “Period”, the values shown are the fixed results of the previous “Period”, or (artificial) initial values if this is the first “Period”.
The starting time step of a “Period” for a specific variable is when the user turns that specific output on.
“Period” is a global setting, which has the same value for all the outputs, but the starting time steps can be different for different variables depending on when the user turns the output on for each variable.
When the user loads previous simulation results, the last updated time average/time maximum values will be loaded. If the user starts a continuation run, the starting time step for all the pre-defined time outputs will reset to the starting time step of the continuation run.

Users are recommended to use the physical period (eg: Time step for one Pump pocket rotation or a complete revolution) as the “Period” whenever possible.

Additional Output Files: In addition to the standard file format, Simerics-MP allows the outputs in EnSight format to be compatible with the EnSight® post processing software. It can be activated by the option EnSight Format.

Parallel Simulation: It specifies whether to run the simulation in serial or parallel mode using one of the following:

Running on all cores: Uses all available cores by default
User Defined Number of Cores: Specify the number of cores
Multi-Threads (Version 4 Mode): To run in serial mode.

Figure 5.2 - Common Module settings

Note: For Steady-state simulations, the EnSight output are:

filename_ensight.case

filename_geo_ensight.data

For transient simulations, the EnSight output are:

filename_geo_1_xxxx_ensight.data

filename_sca_1_xxxx_ensight.data

filename_sca_2_xxxx_ensight.data

filename_vec_1_xxxx_ensight.data

where xxxx is the time-step.

Density

Density is a volume condition pertaining to a selected Volume. For a single fluid, or an individual component in a Multicomponent mixture or Multiphase flow, the density is a material property with the unit of kg/m³. It follows one of the four density laws available in Simerics-MP:

As for the mixture density of multiple components, it is a weighted average of the component densities, where the weighting factors depend on the physical processes/models:

Multicomponent Mixing: The mixture density is computed using Mass Fraction Average (Multicomponent module) or User Specified.
Multiphase flow: The mixture density is computed using Vol. Fraction Average (Multiphase module) or User Specified.

Porosity

Porosity is a volume condition pertaining to a selected Volume. It has a value between 0 and 1. Zero porosity indicates a solid, while a porosity of 1 corresponds to a fully open flow domain.

Note that Simerics-MP adopts the superficial velocity formulation to account for the effects of porous media (Flow module). This modelling approach has the follows characteristics:

The velocity solved is the product of porosity and the physical velocity (superficial velocity). Hence, the porosity does not appear explicitly in (and thus does not affect directly) the momentum equations.
The momentum resistance forces induced by the porosity and the permeability of a porous medium are modelled by the addition of a momentum sink to the standard flow equations. Again, the superficial velocity is used to compute the resistance forces. The change of porosity does not directly affect the momentum resistance and thus the flow field.
For heat transfer, under the assumption of thermal equilibrium between the fluid flow and the solid pore structures, porosity affects the heat transfer in the flow by reducing the fluid volume, or the effective volume (product of porosity and physical/cell volume) is used to discretize the energy equation.
In Multicomponent and Multiphase models, the porous medium model applies for both Mixture and Components.

Volume Remesh

Volume remesh feature of Simerics-MP enables the time dependent change of volume mesh to solve transient flows. This is discussed in detail in Mesh Movement.