[Gmsh] Composite RVE (Hossam Ragheb)

[Baptiste DURAND]

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 
baptiste.durand at enpc.fr – 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 <har1g15 at soton.ac.uk> 
To: gmsh at onelab.info 
Subject: [Gmsh] Composite RVE 
Message-ID: <8b4e55e8-f24a-5e9e-b0da-b21288631289 at soton.ac.uk> 
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;}; 

------------------------------ 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://onelab.info/pipermail/gmsh/attachments/20201214/b3350e2e/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: mwe_composite_RVE.py
Type: text/x-python
Size: 3662 bytes
Desc: not available
URL: <http://onelab.info/pipermail/gmsh/attachments/20201214/b3350e2e/attachment.py>