ac274: particles in cell ( phase-space fluids)
Post on 01-Jan-2016
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Systems with soft (long-range) interations:
Grazing collisions (small deflections)
Each particle feels a collective soft interaction
Plasmas, AstrophysicsBiological fluids,Electrophoresis,
Phase-space fluids
1. Charge assign to the grid (P2G)
2. Solve field eq.s on the grid (GG)
3. Compute forces on the particles (G2P)
4. Move particles (PP)
PIC: solution procedure
PwL: -a*(1-a)+(1-a)*a; = 0 for any a
PwC: -a*1/2+(1-a)*1/2=1/2-a; = 0 only for a=1/2
NGP: -a*1, or (1-a)*1; = 0 never
BUT: if <a>=1/2 both pwc and ngp give zero on average!
Spurious forces
PIC methods scale like NP*NG instead of NP*NP
Very useful for phase-space fluids with soft interactions: plasmas, astrophysics, electro-bioflows
Modern developments:Unstructured, Moving Grids, parallel solvers, totrack STRONG inhomogeneities
P3M: Particle-Particle (dense) + Particle-Mesh
Summary
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