Powder Generation

Powder Simulation

The powder generation software runs simulation of powder deposition. Then a knife moves along x axis at the specified height.

The parameters are set in the same JSON file that is used in simulation. This helps with the consistency of simulation sizes.

Input Configuration

To start a simulation with internally generated powder layer, prepare a JSON file for your simulation as usual, but include the powder generation setting. As usual, if the setting is not included, the default value is used.

First, look at the Sizes and PowderBedGenerator sections of the input JSON file. Here is the example

"sizes": {
  "FullXapprox": 0.010,
  "FullYapprox": 0.010,
  "FullZapprox": 0.005,
  "substrate"  : 0.00456
},
"PowderBedGenerator": {
  "Type": "PowDEM",
  "RandomSeed": 0,
  "GroundSurface": "",
  "PSDsizes":
 [[0, 45e-6], [5, 50e-6], [30, 60e-6], [50,70e-6], [70,80e-6], [90,90e-6], [100,100e-6]],
  "KnifeZposition": 0.00466
  },

Here are the solver options.

Key	Value Type	Value
Type	string	PowDEM
The name of the powder generator software.
RandomSeed	integer	0
To generate different configurations of powder with same parameters, change this number to any other number.
KnifeZposition	float	0.00466
The height of the powder spreading knife (m).
GroundSurface	string	“”
Leave empty for powder deposition on a flat surface, specified with the sizes.substrate parameter in JSON. Fill in the file path to the surface geometry if the substrate is not flat.
PSDsizes	list of value pairs	[[0, 45e-6], [5, 50e-6],…}
The distribution of powder sizes is set in the form \([[p_1,d_1],[p_2,d_2], ...]\), where \(p_i\) is the volume fraction of powder particles which have diameter less than \(d_i\). The pairs should be listed in order of increasing diameter.

Here are the geometry options.

Key	Value Type	Value
FullXapprox	float	0.010
FullYapprox	float	0.010
FullZapprox	float	0.005
substrate	float	0.00456

The FullXapprox\(\times\) FullYapprox (Here, 10 mm \(\times\) 10 mm) area is filled with powder. The height of the powder layer has to be (much) less than FullZapprox (m). The powder is set on the substrate, the height of the substrate is substrate (m). These are the same fields that are used in the KiSSAM simulation. The height of the powder layer is KnifeZposition-substrate (here, 0.1 mm).

\(0<\) substrate \(<\) KnifeZposition \(<\) FullZapprox.

PowDEM run

Launch the powder deposition simulation with :

/share/bin/PowDEM [<default.json>] <input.json> [-n] [-v]

If the fields which are required by the program are absent from the input.json file, they can be provided in the default file default.json

-v

verbose output.

-n

turn off interactrive graphics.

Output Files

• spheres.dat contains the complete data of the generated powder geometry.

This is a text file and it contains four columns. For each sphere, its position (\(x\), \(y\), \(z\)) and radius (\(r\)) in μm are in one row.

27.4911 27.4917 27.4911 27.5
44.7133 79.1247 63.0167 37.5
87.07 32.4956 32.4953 32.5
166.9 34.6008 27.4979 27.5
128.672 75.4377 27.498 27.5
...

Before including the generated script in the KiSSAM simulation, spheres have to be rasterized with the rasterizeSpheres.x script.

• powder_evolution.log contains the detailed info of the particles dynamics and its relaxation to a steady-state solution.

It is a file in text format with several columns. Rows starting wit # are comments. Check this file during the simulation to check the integral values of the current powder geometry.

Example:

# Powder simulation convergence:
# t_sim Xmean Ymean Zmean Ymin Ymax Vmean V_Ymax V_0.99N maxV_traj maxV_insta Num_Particles
0 497.62 349.225 501.327 0 582.428 1 1 1 1 1 2098
...
1957.13 1234.56 494.681 41.2317 499.222 0 100.166 0.00786938 -0.0049597 0.0404546 0.0800193 0.147372 1084

The columns contain:

Column Key	Description
t_sim	time in seconds
X	Knife position in \(x\) coordinate
Xmean	mean \(x\) position of particles
Ymean	mean \(y\) position of particles
Zmean	mean \(z\) position of particles
Ymin	minimal \(y\) coordinate (\(y\) is the vertical axis)
Ymax	maximal \(y\) coordinate (\(y\) is the vertical axis)
Vmean	mean velocity of particles
V_Ymax	velocity of max height change
V_0.99N	velocity of 99% fastest particle
maxV_traj	maximum trajectory velocity (\(\Delta x/\Delta t\) for a given time step Delta t)
maxV_insta	maximum instantaneous velocity
Num_Particles	number of spheres in the simulation

• powder_stats.log is a text log file which contains statistic information of the powder.

It might be useful in case of further powder analysis. This file contains the final thickness of the powder (the difference between the highest and lowest point of the powder by the vertical axis), the integral filling factor. It is followed by a table of three columns: particle size, distribution density by volume, distribution density by total amount, respectively. The file header is as follows:

# Final characteristics of the powder:
# Powder thickness (max) = 119.23 um, filling factor (mean) = 50.8124%. For more details please use spheres-analyze utility.
# PSD statistics:
# size_i(um) fi_volumetric fi_number

Use Powder in the Simulation

To use the prepared powder in the simulation, prepare the volumetric data from the spheres.dat file. To do this, use the rasterizeSpheres.x script. For example,

/opt/KiSSAM/scripts/rasterizeSpheres.x 3 spheres.dat

Here, 3 is the mesh step in μm. The same mesh step should be used in the KiSSAM simulation in the NumericalParams.dr field (see JSON file description).

The file that is generated by the script should be specified as initial powder geometry is the simulation.

"Powder": {
  "initSpheresVDBfile": "init_spheres.vdb"
}

Visualization controls

The visualization is interactive. The following keyboard and mouse actions control the run.

• Space is to pause the simulation. Press Space again to resume the run.

• Press w/e is to zoom in/out the picture.

• Mouse buttons and actions

  • Press the middle mouse button (wheel) and move mouse to translate the picture.

  • Press the left mouse button and move the mouse to rotate the picture.