use GenGeo to construct a regular structured packing as loading platen

Hi everyone,

I'm trying to use GenGeo to construct a shear cell composed of three layers: the lower and upper layers are loading platens and the middle one is the granular packing to be sheared. I wish the loading platens have a regular structure or at least densely packed. But now GenGeo always gives me two randomly and loosely packed loading platens. What can I do? The script is pretty much like the 2D shear case provided in the Example folder. I also found addPlane (or addLine) in the script is not necessary, isn't it?

from GenGeo import Vector3, BoxWithPlanes3D, CircMNTable3D, InsertGenerator3D, Plane

# Define domain:
length = 20.0; width = 16.0; height = 20.0
platen = 2.0

minPoint = Vector3(-0.5*length,-platen,-0.5*width)
maxPoint = Vector3(0.5*length,height+platen,0.5*width)
minRadius = 0.3
maxRadius = 0.5

mntable = CircMNTable3D (
   minPoint = minPoint,
   maxPoint = maxPoint,
   gridSize = 2.5*maxRadius,
   numGroups = 3
)

platenSph = InsertGenerator3D (
   minRadius = minRadius,
   maxRadius = minRadius,
   insertFails = 5000,
   maxIterations = 5000,
   tolerance = 1.0e-6,
   seed = False
)

lbox = BoxWithPlanes3D (
   minPoint = minPoint,
   maxPoint = Vector3(0.5*length,0.0,0.5*width)
)
lbox.addPlane(Plane(minPoint, Vector3(1,0,0)))
lbox.addPlane(Plane(minPoint, Vector3(0,1,0)))
lbox.addPlane(Plane(minPoint, Vector3(0,0,1)))
lbox.addPlane(Plane(Vector3(0.5*length,0.0,0.5*width), Vector3(-1,0,0)))
lbox.addPlane(Plane(Vector3(0.5*length,0.0,0.5*width), Vector3(0,-1,0)))
lbox.addPlane(Plane(Vector3(0.5*length,0.0,0.5*width), Vector3(0,0,-1)))
platenSph.generatePacking( volume = lbox, ntable = mntable, groupID = 0, tag = 3)
mntable.generateBonds(groupID = 0, tolerance = 1.e-5, bondID = 1)

ubox = BoxWithPlanes3D (
   minPoint = Vector3(-0.5*length,height,-0.5*width),
   maxPoint = maxPoint
)
ubox.addPlane(Plane(Vector3(-0.5*length,height,-0.5*width), Vector3(1,0,0)))
ubox.addPlane(Plane(Vector3(-0.5*length,height,-0.5*width), Vector3(0,1,0)))
ubox.addPlane(Plane(Vector3(-0.5*length,height,-0.5*width), Vector3(0,0,1)))
ubox.addPlane(Plane(maxPoint, Vector3(-1,0,0)))
ubox.addPlane(Plane(maxPoint, Vector3(0,-1,0)))
ubox.addPlane(Plane(maxPoint, Vector3(0,0,-1)))
platenSph.generatePacking( volume = ubox, ntable = mntable, groupID = 1, tag = 4)
mntable.generateBonds(groupID = 1, tolerance = 1.e-5, bondID = 1)

packer = InsertGenerator3D (
   minRadius = minRadius,
   maxRadius = maxRadius,
   insertFails = 5000,
   maxIterations = 5000,
   tolerance = 1.0e-6
)

mbox = BoxWithPlanes3D (
   minPoint = Vector3(-0.5*length,0.0,-0.5*width),
   maxPoint = Vector3(0.5*length,height,0.5*width)
)
mbox.addPlane(Plane(Vector3(-0.5*length,0.0,-0.5*width), Vector3(1,0,0)))
mbox.addPlane(Plane(Vector3(-0.5*length,0.0,-0.5*width), Vector3(0,1,0)))
mbox.addPlane(Plane(Vector3(-0.5*length,0.0,-0.5*width), Vector3(0,0,1)))
mbox.addPlane(Plane(Vector3(0.5*length,height,0.5*width), Vector3(-1,0,0)))
mbox.addPlane(Plane(Vector3(0.5*length,height,0.5*width), Vector3(0,-1,0)))
mbox.addPlane(Plane(Vector3(0.5*length,height,0.5*width), Vector3(0,0,-1)))
packer.generatePacking( volume = mbox, ntable = mntable, groupID = 2, tag = 0)

mntable.write(
   fileName = "threelayer.geo",
   outputStyle = 1
)

mntable.write(
   fileName = "threelayer.vtu",
   outputStyle = 2
)