Hi Hossam,
Controlling the mesh density with the options "Mesh.CharacteristicLengthMin"
and "Mesh.CharacteristicLengthMax" may be too stringent. It may be better to
use the "mesh size field" feature if you want to impose a mesh density.
Also, (I'm not sure about that) the last fragment operation with "Delete"
specified might mess up the physical group.
I convert your .geo file to a python script in order to test your code via the
gmsh python API. You can find attached this .py file.
What you are trying to do seems somehow similar to what I do with gmsh and
FEniCS (periodic homogenization for linear elasticity). You could be interested
by some features of the python package HO-homog that we develop (
https://gitlab.enpc.fr/baptiste.durand/HO_homog ).
Regards,
Baptiste Durand
–––––
Baptiste Durand
Doctorant – Laboratoire Navier
[email protected] – 01 64 15 37 21 ( 06 58 88 05 41 ) – linkedin.com/in/
bd1747
Today's Topics:
1. Composite RVE (Hossam Ragheb)
----------------------------------------------------------------------
Message: 1
Date: Thu, 10 Dec 2020 13:34:34 +0000
From: Hossam Ragheb <[email protected]>
To: [email protected]
Subject: [Gmsh] Composite RVE
Message-ID: <[email protected]>
Content-Type: text/plain; charset="utf-8"; Format="flowed"
Hi,
I am new to gmsh, so apologies if the answer to my question is obvious.
I coded a .geo file (Attached) to create 3D RVE with fibers in a matrix
that includes voids.
The process simply is :
??? 1- Create box of the matrix material.
??? 2- Create voids using Sphere command and BooleanDifference to
remove these from the matrix material.
??? 3- Create fibers as Cylinders and and utilise BooleanFragments to
include the cylinders in the matrix.
I have one persistent problem, once the mesh is created the fibers are
meshed as hollow cylinders, however i need them to be solid.
Its interesting behavior. Last thing to note that mesh size affects the
outcome, for example when the min/max mesh size is 2, the result is
solid cylinders, but with mesh size of 1, it becomes hollow.
It there a way to force the meshing algorithm to mesh the cylinder as
solid object?
I have attached the .geo file, please let me know if you can help.
Any suggestions?
Thanks,
Hossam Ragheb
-------------- next part --------------
//------------------------------------------------------------------------------
//
// Gmsh Stochastic Composite RVE
//
// Constructive Solid Geometry, OpenCASCADE geometry kernel
//
//------------------------------------------------------------------------------
SetFactory("OpenCASCADE");
Mesh.Tetrahedra = 1;
Mesh.Triangles = 1;
fac = 1;
Mesh.CharacteristicLengthMin = 2*fac;
Mesh.CharacteristicLengthMax = 2*fac;
voiden = 0.01;
Vf = 0.7;
// Coefficent of variation of the fibre diameter
cvf = 0.17;
Vlratio = 20;
Cube = 75*fac;
frmean = 5.0 * fac;
frmin = frmean - (frmean*cvf);
frmax = frmean + (frmean*cvf);
vrmin = 2.5*fac;
vrmax = 5.0*fac;
R = Cube;
nSvoid = Floor((voiden*2*R*2*R*2*R)/((4/3)*3.1415926*vrmax*vrmax*vrmax));
nFibre = Floor((Vf*2*R*2*R*2*R)/(3.1415926*frmax*frmax*2*R));
dims = Floor(Sqrt(nFibre));
Box(1) = {-R,-R,-R, 2*R,2*R,2*R};
For s In {2:nSvoid}
If (s < nSvoid)
r = vrmin +Rand(vrmax-vrmin);
x = -R + Rand(2*R);
y = -R + Rand(2*R);
z = -R + Rand(2*R);
Sphere(s) = {x, y, z, r};
EndIf
If (s == nSvoid)
r = vrmin +Rand(vrmax-vrmin);
x = -R + Rand(2*R);
y = -R + Rand(2*R);
z = -R + Rand(2*R);
Sphere(s) = {x, y, z, r};
Dilate {{x, y, z}, {Vlratio, 1, 0.5}} { Volume{s}; }
EndIf
Physical Volume(s) = {s};
EndFor
BooleanDifference(nSvoid+1) = { Volume{1}; Delete; }{ Volume{2:nSvoid}; Delete;
};
dx = (2*R)/dims;
count = 0;
For i In {0:dims-1}
For j In {0:dims-1}
// Fibre diameter
Fr = frmin +Rand(frmax-frmin);
// Center of grid box in the RVE
cgx = (-R + 0.5*dx) + j * dx;
cgy = (-R + 0.5*dx) + i * dx;
// Center of cylinder base
xF = (cgx - 0.5*dx + Fr) + Rand(dx-2*Fr);
yF = (cgy - 0.5*dx + Fr) + Rand(dx-2*Fr);
zF = -R;
// Cylinder axis dx,dy,dz
dxF = 0;
dyF = 0;
dzF = 2*R;
Cylinder(nSvoid+2+count) = {xF,yF,zF,dxF,dyF,dzF,Fr};
Physical Volume(nSvoid+2+count) = {nSvoid+2+count};
count = count +1;
EndFor
EndFor
BooleanDifference(1000) =
{Volume{nSvoid+1};Delete;}{Volume{nSvoid+2:nSvoid+1+count};};
Physical Volume("Matrix") = {1000};
Physical Volume("Fibres") = {nSvoid+2:nSvoid+1+count};
f() =
BooleanFragments{Volume{1000};Delete;}{Volume{nSvoid+2:nSvoid+1+count};Delete;};
------------------------------
import gmsh
import math
import random
from subprocess import run
gmsh.initialize()
factory = gmsh.model.occ
gmsh.option.setNumber("Mesh.Tetrahedra", 1)
gmsh.option.setNumber("Mesh.Triangles", 1)
gmsh.option.setNumber("General.Terminal", 1)
gmsh.option.setNumber("General.Verbosity", 5)
gmsh.option.setNumber("Mesh.SaveAll", 0)
gmsh.option.setNumber("Mesh.MshFileVersion", 4.1)
fac = 1
gmsh.option.setNumber("Mesh.CharacteristicLengthMin", 2 * fac)
gmsh.option.setNumber("Mesh.CharacteristicLengthMax", 2 * fac)
# geometry parameters
voiden = 0.01
Vf = 0.7
# Coefficent of variation of the fibre diameter
cvf = 0.17
Vlratio = 20
Cube = 75 * fac
frmean = 5.0 * fac
frmin = frmean - (frmean * cvf)
frmax = frmean + (frmean * cvf)
vrmin = 2.5 * fac
vrmax = 5.0 * fac
R = Cube
nSvoid = math.floor(
(voiden * 2 * R * 2 * R * 2 * R) / ((4 / 3) * math.pi * vrmax * vrmax * vrmax)
)
nFibre = math.floor((Vf * 2 * R * 2 * R * 2 * R) / (math.pi * frmax * frmax * 2 * R))
dims = math.floor(math.sqrt(nFibre))
box_1 = factory.addBox(-R, -R, -R, 2 * R, 2 * R, 2 * R)
spheres = list()
for s in range(2, nSvoid + 1):
if s < nSvoid:
r = vrmin + random.uniform(0.0, vrmax - vrmin)
x = -R + random.uniform(0.0, 2 * R)
y = -R + random.uniform(0.0, 2 * R)
z = -R + random.uniform(0.0, 2 * R)
sphere = factory.addSphere(x, y, z, r)
spheres.append(sphere)
elif s == nSvoid:
r = vrmin + random.uniform(0.0, vrmax - vrmin)
x = -R + random.uniform(0.0, 2 * R)
y = -R + random.uniform(0.0, 2 * R)
z = -R + random.uniform(0.0, 2 * R)
sphere = factory.addSphere(x, y, z, r)
factory.dilate([(3, sphere)], x, y, z, Vlratio, 1, 0.5)
spheres.append(sphere)
phy_gp = gmsh.model.addPhysicalGroup(3, [sphere])
difference = factory.cut(
[(3, box_1)], [(3, tag) for tag in spheres], removeObject=True, removeTool=True
)
# get the tag :
difference = difference[0][0][1]
dx = (2 * R) / dims
count = 0
# parameters for cylinder axis
dxF, dyF, dzF = 0, 0, 2 * R
cylinders = list()
for i in range(0, dims):
for j in range(0, dims):
# Fibre diameter
Fr = random.uniform(frmin, frmax)
# Center of grid box in the RVE
cgx = (-R + 0.5 * dx) + j * dx
cgy = (-R + 0.5 * dx) + i * dx
# Center of cylinder base
xF = (cgx - 0.5 * dx + Fr) + random.uniform(0.0, dx - 2 * Fr)
yF = (cgy - 0.5 * dx + Fr) + random.uniform(0.0, dx - 2 * Fr)
zF = -R
cylinder = factory.addCylinder(xF, yF, zF, dxF, dyF, dzF, Fr)
cylinders.append(cylinder)
phy_cylinders = list()
for cyl in cylinders:
phy_cyl = gmsh.model.addPhysicalGroup(3, [cyl])
phy_cylinders.append(phy_cyl)
matrix = factory.cut(
[(3, difference)], [(3, t) for t in cylinders], removeObject=True, removeTool=False
)
matrix = matrix[0][0][1]
phy_matrix = gmsh.model.addPhysicalGroup(3, [matrix])
gmsh.model.setPhysicalName(3, phy_matrix, "Matrix")
phy_fibres = gmsh.model.addPhysicalGroup(3, cylinders)
gmsh.model.setPhysicalName(3, phy_fibres, "Fibres")
all_entities = gmsh.model.getEntities(3)
# remove the matrix and the fibres :
remove_entities = [e for e in all_entities if e[1] not in cylinders + [matrix]]
gmsh.model.removeEntities(remove_entities, recursive=True)
# factory.fragment([(3, matrix)], [(3, t) for t in cylinders])
factory.synchronize()
gmsh.model.mesh.generate(3)
gmsh.model.mesh.removeDuplicateNodes()
gmsh.model.mesh.renumberNodes()
gmsh.model.mesh.renumberElements()
gmsh.write("rve.msh")
try:
run(f"meshio-convert rve.msh rve.xdmf", shell=True, check=True)
except:
pass
gmsh.fltk.run()
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