Particles

[kidder]

From discussion with @nilsdeppe @wthrowe @kidder

• Particles can move from one Element to another during a step (or sub-step)
  • With subcell already communicate neighbor info in case an Element needs to switch
  • We will need Voronoi neighbors (this will also needed for subcell on unstructured meshes) as particles can move diagonally
  • Add particles to the DgElementArray and transfer them to neighbors as needed
  • Need Event to observe particles and infrastructure to read into parview
• In addition, for particles that can feedback to the fluid additional things are needed.
  • For subcell, particles contribute to the subcell they are in
  • For DG, need to weight particles based on their location within the element. Could use spectral volumes or projecting basis against delta functions (do literature search...)