Global Settings
This dialog allows you to set program preferences, as well as physical properties that affect the current file.
Program settings
Autosave
Frequency
Determines how often the autosave feature is triggered. Autosaving only occurs when there is a change compared to the last saved version. To disable autosaving, input a very large number, i.e. 1E6.
Only when simulation is running
Restrict autosaving when calculation is running, and presumably you're not interacting with MolFlow. Pervents to get in your way while editing the file.
Check for updates at startup
Launches the updater utility on every startup. Note that the update information file is on CERN's server that creates an anonymous visitor statistics. If you wouldn't like this, you can disable this option, and use manual updates.
Anti-Aliasing
Enables smoothing of polygon outlines. Improves visibility when many lines are rendered on top of each other. Has some performance price, though. Disabling it might speed up rendering, though tests don't show a significant difference.
White background
Removes background and redraws colors. Useful for printing geometries or making screenshots for articles.
Left-handed coordinate system
Only changes the rendering: some users prefer right-handed coordinates (default), some left-handed:
Example
Left image: left-handed coordinates, Right image: right-handed coordinates
Highlight non-planar facets
Shows non-planar facets, that create a leak.
The warning message at the bottom is always displayed.
Highlight selected facets
Shade face of selected facets, useful when edges of selected facets are shared.
Highlighting on
Highlighting off
Use old XML format
Currently MolFlow's XML files have a root element, as stipulated by the XML standard:
<?xml version="1.0"?>
<SimulationEnvironment type="molflow" version="2925">
...
</SimulationEnvironment>
Older versions didn't have it, and only contained a list of nodes. Enable this setting to save files without the root element - its only use is to open the files in older MolFlow versions. New versions can read the old format (and upgrade on save).
Simulation settings
These settings are specific to the current geometry, i.e. they change when loading a file.
Gas molecular mass
Defines the mass of the simulated gas particles. The value is used for determining the average speed of the molecules, and also at sticking factor / volumetric pumping speed conversion, and finally the pressure and molecular force calculation.
When you change it, if you have sticking facets, MolFlow warns you that the sticking factor is kept constant thus the pumping speed will change.
Gas half life
When the checkbox is enabled, you can define a half-life after which the gas will decay. Time is counted from the particle's creation (i.e. desorption). It is supported both in steady-state and time-dependent modes.
Technically, when the particle is created, a life expectancy is generated randomly, following the exponential distribution. Per definition, the mean of the distribution is \(\frac{1}{\lambda}\), so \(\lambda=\frac{1}{\tau}\) where \(\tau\) is the half life (in seconds) you enter into the checkbox.
MolFlow is event-driven, it only simulates collisions with the walls. Therefore at every wall collision, the particle's flight time is compared to the life expectancy. If at this comparison, it turns out that the particle should have decayed during the last flight in-volume, the exact decay location is calculated and the particle is moved back to that point. Profiles and textures are recorded on eventual transparent facets until the calculated decay location (but not on the target opaque facet), then the particle is eliminiated, showing a light blue hit if Hit display is enabled.
Quick pipe simulation with no decay
Quick pipe with \(\tau\)=5E-5s half-life
Outgassing info
Final outgassing rate
Shows the outgassing at \(t=\infty\)...
- This is the steady-state outgassing, if all your desorptions are constant
- Or uses the last user-defined value (which is kept until \(t=\infty\)) of your time-dependent parameters, if facet outgassing uses a parameter
It is shown in both mbar.l/s and in molecule flux (1/s). The conversion between the two is done by the ideal gas equation, and thus it depends on the desorbing facets' temperature:
\(\frac{d(pV)}{dt}=\frac{dN}{dt}kT\)
Where \(\frac{d(pV)}{dt}\) on the left is the outgassing rate, and \(\frac{dN}{dt}\) is the molecule flux.
Total desorbed molecules
This shows how many molecules desorbed during the entire duration of the time-dependent simulation. The simulation starts at t=0, and ends at the final moment. The final moment is calculated as the last user-defined interval's end: it is the final moment plus half time window. For example, if time window is dt=1s and the final moment is dt=10s, then the final moment is 10 + 1.0/2 = 10.5s.
In the example below (default for quick pipe: room temperature, 10 mbar.l/s outgassing, no moments defined, default time window 1E-10s)
You can see that the final moment is t=0 plus half of the time window (0 + 1E-10 / 2 = 5E-11 s).
If the model changed
Calculating total outgassing is realtively expensive in terms of computing: MolFlow has to go through all facets, and sum the outgassing values, which can be dynamic (outgassing map from SynRad) or even time-dependent.
To speed up the user interface, the recalculation is only done when the simulation is launched. If you see the "model changed" message, you can either launch the simulation, or click the Recalc. outgassing button to get the outgassing.
Worker threads
Here you can define thenumber of threads that will run the simulation, and view their status.
As a thumb rule, you'd probably want to use as many threads as CPU cores, and maybe less for memory-intensive (large or time-dependent) simulations.
Reasons to run a lot of threads
- On a multi-core system, for maximum performance, you should run as many processes as the number of cores in your CPU
- Each process uses a different random number generator seed. Thus, running 4 processes, for example, will eliminate repetations of the random-number generator, which is never perfect. MolFlow uses the Mersenne-Twister algorithm.
Reasons to restrict the number of threads
- Each process keeps the geometry and all result counters (i.e. textures) in the memory. Thus, running 16 processes will keep 16 copies of your system in the memory. For time-dependent simulations, each moment has its own system state - in other words, the memory requirement is multiplied by the number of moments!
- If MolFlow (or your OS altogether) becomes very slow, it is possible that you've run out of memory and swapping happens.
To change the number of threads or restart
Enter the number of threads in the textbox and click Apply and restart processes. Simulation will continue from the current state when you click "Resume".
Limit desorption
You can automatically stop the simulation after desorbing a fixed number of molecules. Click the limit button to set a new number. After the simulation auto-pauses, you can increase the limit or disable it altogether (a limit of 0 means inifnite).