I made some small changes to how things are calculated.
I have also discovered that the issue with different density when
changing injection is not related with the node volume but with the way
injection is carried out. When loading particles from a file, all
provide the same density regardless the cell (node) volume.
I am doing testing in 2DCart as it is easier to set up.
Basically things do not work. I've added a correction to the node volume
in the axis which gives okays results but still this is not perfect. I
need to find a better way to do things.
Also, I've noticed that the density changes with the size of the cells,
which should not happen! I'vw to check this issue.
Trying to have a very simple volume per node assuming a rectangle and
the density at the axis it higher than it should (kinda like when using
the more accurate volume calculation).
This is still weird. I also suspect that the size of the first cell in
the axis will also affect this...
So now each edge has the same number of particles and the weight of each
particle is calculated based on the surface of each edge compared to the
total one.
Only in 2DCyl, still to extend to other geometries.
Not perfect constant density, but the issue might be the node volume.
The number of particles per cell can be defined when giving an initial
distribution fora species. If not, the typical method of using the
species weight is used. This is particularly useful for cylindrical
coordinates in which very little particles might end up in the axis if a
constant weight is used.
Fixed an issue with random integer numbers.
Cylindrical coordinates are not perfect yet:
- Box (cylinder) with initial constant density loses particles at r =
0
- Injection density still low in r = 0
I have to change the injection of particles. Each edge will receive a
similar number of particles and their weight will change to have a
constant density based on the geometry.
Still testing.
I think that the volume of the nodes is not being well calculated, maybe
we need a better volume calculation for this, using multiple points (as
it is done for K)
The random position for edges in the axis is corrected so that there is
a more uniform charge density in the axis.
Still, things are not perfect and this is something to really look into
in the future.
WARNING: This current denstiy will be multiplied by the reference
length, no the surface area that is being used for injection!
New units in the injection of particles 'Am2' to inject a density
current. Manual has been modified accordingly.
Reference parameters are now also printed in the case folder.
Fixing an issue with reading tables led me to other issues with
collisions that I think are fixed right now. I am testing with the 1D
ionization model for ALPHIE and things seems to be working properly.
Coulomb scattering is now fully conservative thanks to the method in
lemos2009small.
The trick was to conserve the momentum and energy of ALL particles
involved in the scattering in each cell.
The substeps in Coulomb collisions have been removed as they are no
longer necessary.
Still some issues with e-i, but I don't know right now.
In an attempt to make the operator fully conservarive I have combined ij
and ji collisions (when i/=j).
Now the matter is to find a way that makes this conserve momentum and
energy for intraspecies.
Now per each Coulomb collision process there is the possibility to do
sub-steps. This helps in improving accuracy without reducing the time
step of the problem.
There was an issue with the calculation of theta and phi for the
rotation from W to C. This was causing some velocities not being
correct.
Now the angles are properly computed. Still unsure about the e-i
collisions as they seem to be quite small. Probably a numerical issue
with the mass ratios still exists.
The code is still not fully conservative in intra-species collisions
(small error) but at least now is working.
I have to test species with different weight.
I have to implement a fully conservation for intra-species.
I had to go back to sherlock2008montecarlo to properly understand the
change in frame of reference and how to translate that into the code.
The language there is clear and understandable for a dumb person like
me.
Now I have a Coulomb linear operator that at least works.
However, still not fully 100% conservative, need to fix this with a
correction for intra-species collisions.
I skip gym today because I was unable to focus on other things than
this.
I was having tones of issues with the previous implementation. I think
the problem was the velocity vector and how it was returning to the
normal reference frame.
I hope this new implementation works better.
I found no way to ensure conservation in the linear Coulomb operator.
Thus, now two collisions have to be declared if sp_i /= sp_j: collision
ij and collision ji.
This does not conserve energy so please use under your own risk, like
everything else.
Still, I think something is wrong with this implementation and I'm
really tired.
After fixing all possible divisions by zero I was able to find in the
Coulomb collision I think that this is a first working implementation of
a Coulomb operator based on moments.
Still to test a few things, modify the manual but I would say that I'm
satisfiyed right now. This operator won't be used that often but maybe
improving efficiency is still needed.
In the future a binary operator is required to be able to study cases
out of Maxwellian equilibrium.
I was having a lot of issues trying to get quasi-neutrality with the
injection of electrons and ions. Main issue was a definition of the
direction of injection. This should be fixed now (tested in 1D).
Added a definition for Half-Maxwellian velocity distribution.
WARNING: I'm still not happy at all about the definition of the
direction of injection and the velocity definition to be in that
direction so I might change it at some point (for example take into
account the sign of each direction in the thermal part of the velocity)
When the relative velocity between a charged particle and the background
for Coulomb collisions (W in the code) was low, there was a
segmentation fault. This is fixed now as if the norm of the relative
velocity (normW) in the code is too low, no collision is applied.
I am doing a trick in which I ensure that energy is conserved for
Coulomb collisions. This was not happening and what an issue for
different mass ratios. Still, this can cause an issue on getting the
right relaxation rates, still necessary to check it.
