Meshing union of shapes

Hello everyone,

I am trying to create a mesh of a nanorod in water. I am intending for the nanorod to be a cylinder with two hemispherical endcaps inside a larger cylinder of water inside a larger cylinder of PML. However, when I run my script, I get an error. I have determined that the problem is when I try to add the endcaps of the nanorod to its main cylindrical body. Specifically, I get the error

File “”, line 2
SyntaxError: (unicode error) ‘unicodeescape’ codec can’t decode bytes in position 1-2: malformed \N character escape
Start Findpoints

at which point, Netgen will hang permanently. I would really appreciate it if you could help me figure out why I am getting this error.

Thank you
Thank you



you can just add the whole sphere to the cylinder. It seems the mesher has problems identifiying the edge of the cylinder with the one of the hemisphere.

from ngsolve import *
from netgen.csg import *

def Nanorod(aeff,ratio):

geo = CSGeometry()

radius = aeff*(2/(3*ratio-1))**(1/3)
length = 2 * radius * ratio 
cyl_length = length/2 - radius

physical_space = length + 100
domain = physical_space + 150

sphere1 = Sphere(Pnt(0,-cyl_length,0),radius)
sphere2 = Sphere(Pnt(0,cyl_length,0),radius)

cyl1 = Cylinder(Pnt(0,-2*cyl_length,0),Pnt(0,2*cyl_length,0),radius)
cyl2 = Cylinder(Pnt(0,-2*physical_space,0),Pnt(0,2*physical_space,0),radius+100)
cyl3 = Cylinder(Pnt(0,-2*domain,0),Pnt(0,2*domain,0),radius+200).bc('outer')

box2 = OrthoBrick(Pnt(-physical_space,-physical_space,-physical_space),Pnt(physical_space,physical_space,physical_space)) 
box3 = OrthoBrick(Pnt(-domain,-domain,-domain),Pnt(domain,domain,domain)).bc('outer')

plane1 = Plane(Pnt(0,-cyl_length,0),Vec(0,-1,0))
plane2 = Plane(Pnt(0,cyl_length,0),Vec(0,1,0))

middle = cyl1*plane1*plane2

AuNP = (middle+sphere1+sphere2).mat('gold')
water = (cyl2*box2 - AuNP).mat('water')
pmldom = (cyl3*box3 - water).mat('pml')


ngmesh = geo.GenerateMesh()

mesh = Mesh(ngmesh)
return mesh

mesh = Nanorod(40,1.6)


That did the trick. Thank you very much for your help and quick reply.