Meshing union of shapes

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1

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

https://ngsolve.org/media/kunena/attachments/1252/Nanorod Question.py
Thank you

Attachment: NanorodQuestion.py

2

Hello,

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.

[code]
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')

geo.Add(AuNP)
geo.Add(water)
geo.Add(pmldom)

ngmesh = geo.GenerateMesh()

mesh = Mesh(ngmesh)
return mesh

mesh = Nanorod(40,1.6)
Draw(mesh)[/code]

Best,
Matthias

3

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