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Molflow webinar

Bookmarks to different parts (detailed in the bullet points below) are in the video description:

2020-01-23 16_40_05-Molflow webinar - Selecting facets (basics) - YouTube.png



Introduction to Monte Carlo simulations

If you're new to these Monte Carlo tools, this presentation is a good overview of the special physics at very low pressures, how it's related to Monte Carlo simulations, and how Molflow actually works.

  • Short explanation of the high vacuum physics
  • The Monte Carlo method
  • History of Molflow and Synrad
  • Typical Molflow workflow




Interface basics

The interface is your first encounter with Molflow, this video shows the basic controls and also some tips and tricks.

  • Loading a simple pipe
  • Mouse commands (zoom, pan, rotate)
  • Default views and area zoom
  • View options, view parameters, light options
  • Additional parts of the interface, global settings, white background
  • Screenshot tool
  • Toggling coordinate axes
  • Advanced: 4 split views

Selecting facets (basics)

Highly recommended to watch: shows the different techniques to select facets, then memorize them as groups. Mastering these will save you a lot of time later.

  • Creating a 100-sided pipe
  • Select by clicking on geometry
  • Cycle through overlapping facets
  • Select by facet number in list
  • Options for selection display in volume view
  • Select multiple facets
  • Selection box
  • Multi-select from facet list
  • Add overlapping facets to selection
  • Memorizing selections
  • Recalling and combining selections
  • Smart select tool

Selecting facets and vertices (advanced)

Tips and tricks useful for geometry editing and large geometries where using traditional techniques are cumbersome.

  • Select by number (facet id)
  • Invert selection
  • Select vertices
  • Select in circle
  • Move selection box/circle anchor
  • TAB to switch facet/vertex modes
  • Difference between add/remove logic
  • Restrict selectable facets by Caps Lock

Create geometry with built-in tools

As opposed to importing a geometry from an external editor, you can now create your geometry from scratch. This tutorial walks you through the steps to assemble a basic vacuum system, consisting of two pumping ports and a variable diameter pipe.

Result geometry:

  • Starting with an empty geometry
  • Create a circle and extrude it to a pipe
  • Create a larger diameter circle at end of pipe
  • Create difference of two circles
  • Adding vertical pumping ports
  • Rotating a circle (using an axis)
  • Rotating a circle (using 2 vertices)
  • Move a circle by fixed offset
  • Move a circle up to an existing facet
  • Mirroring a pipe to a plane
  • Fixing a 0-area facet with the Collapse command
  • Building T intersections between pipes
  • Fixing the T intersection by scaling down vertical pipe
  • Clear isolated vertices

A simple vacuum simulation

Finishing the example from the previous video by adding physics and comparing the pressure result with the published paper

Source geometry:
Solved exercise: (with symmetry:

  • Adding outgassing
  • Adding the pumps
  • Setting up textures
  • Setting up profiles
  • Advanced: taking advantage of symmetry


Basic simulation of an RF cavity

An example of a vacuum simulation of a realistic geometry. You can get the source files from this tutorial's page.

  • Importing the STL file to Molflow
  • Adding outgassing
  • Adding pumps
  • Starting the simulation
  • Adding textures (pressure color maps)
  • Playing with mesh resolution
  • Manual texture color scaling
  • Single counter facet instead of texturing all
  • Measuring distances in Molflow
  • Setting counter facet parameters and texture
  • Visualization techniques
  • Adding a profile (pressure along a direction)
  • Adding a new profile facet by scaling
  • Exporting profiles and textures
  • Splitting the geometry horizontally

Conductance calculations

Conductance, part 1: theory and a simple (round pipe) example:

  • Theory and formulae for conductance
  • Simple round pipe example + analytic solutions
  • Constructing the geometry, adding sticking and outgassing
  • Using formulas to determine transmission probability
  • Monte Carlo vs analytic results
  • Calculating conductance from transmission probability


Conductance, part 2: real-life CAD example

2020-02-14 09_04_27-CATIA V5 R27 64 -  CERN _  Large Assembly _ started 2020-02-14 at 9_03_31 on PCT.png
2020-02-14 10_43_43-Molflow+ 2.7.10 (Dec 19 2019) [].png

  • Importing the geometry, collapsing and rotating
  • Setting up pumping, desorption and sampling planes
  • Creating plugs
  • Starting simulation, extracting results
  • Using formulas to get average pressure
  • Verifying results: changing the pumping speed
  • Detailed results after more simulation time

CAD000567144.stl (Geometry) (Solution)


Advanced vacuum diagnostics

Additional tools to get deep insight into the behavior of your system

  • Angular profiles
  • Direction vector textures
  • Velocity profile
  • Histograms
  • Particle logger

Non-isothermal systems

Vacuum systems with different facet temperatures

  • Governing equations
  • Accomodation factor
  • Thermal creep example

Sequential simulations (intro)

Simulating a vacuum system with a large pressure difference in multiple steps

Sequential simulations (angle maps)

Recording an angular distribution and generating gas with it

Sequential simulations (superstructures)

Gaining ray-tracing speed from sectioning the geometry to smaller parts

Symmetry and similarity

Advanced tools taking advantage of symmetries in the system and similar structures

  • Symmetry plane
  • Periodic systems and teleports
  • Inverse teleports

Time-dependent simulations (basic)

  • Acoustic delay line example
  • Timewise plotter
  • Pressure evolution plotter
  • Time-dependent physical parameters

Source geometry: adl1.stl
Solved result:


Time-dependent simulations (advanced)

  • Radioactive decay
  • Surface sojourn time

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