Cumulative quantities
Molflow's time-dependent mode allows to measure the system state at various moments. By default, these system states are independent of each other, since MolFlow simulations are event-driven - in other words, tracing of the molecules isn't done in chronologic order.
However, certain simulations (for example, measuring contamination of a surface) require tracking the history of the surface - whoch allows to get additional data.
Example
A typical physical quantity requiring cumulative quantities is the number of resident particles on a facet. This can be calculated by integrating all incident hits up to a certain moment (all particles that arrived), and subtracting all particles that were pumped and that left the surface up to that moment.
Defining moments for the time domain
First, the time domain has to be covered without overlaps, nor gaps, in the Moments Editor. In the example below, the system state is recorded every 1 second from t=0s to t=100s:
The Check gaps button allows to verify if the time domain is fully covered:
If not, it displays the first 10 gaps:
Integration
Calculating the cumulative quantities over a large number of time moments might be a heavy operation, so it is not done at every 1-second update as the simulation progresses. Instead, it has to be performed from the Time menu:
At this point, at every moment, the moment-specific hits, desorptions, reflections and absorptions are calculated up to the actual moment.
About the last moment of integration
User-defined moments are in fact time intervals spanning from t-window/2 to t+window/2 where t is the moment centerpoint and window is the time moment. Because of this, the last moment's recorded hits are only taken into account with a 0.5 multiplier.
For example, if the user has window=1s and requests integrated quantities at t=1.5s, then...
- The first moment's hits (t=0.5s, corresponding to the interval [0 .. 1s] are added
- Half of the second moment's hits (t=1.5s, corresponding to the interval [1 .. 2s]) are added
Cumulative quantities
Cumulative quantities are calculated for facets - they are not available in profiles or textures. They can be visualized in the...
- Formula Editor
- Facet details window
- Evolution Plotter
The following quantities are available:
- Cumulative incident MC hits: all incident hits integrated up to the given moment
- Cumulative desorbed MC hits: all desorbed hits integrated up to the given moment. This refers to the particles created on a facet (outgassing).
- Cumulative absorbed MC hits: all pumped (absorbed) particles up to the given moment
- Cumulative reflected MC hits: all reflected (or re-desorbed) particles up to the given moment. Re-desorbed particles arrived from elsewhere, and optionally spent a small residence time on the facet (if this is enabled in the facet advanced properties).
- MC hit balance: calculated as "Cumulative incident hits" - "Cumulative absorbed hits" - "Cumulative reflected hits"
- Particle balance (absolute, or per m2): The same as above, converted to physical particles