Discussion Forum

How is the geometry defined in matlab? What kind of modelling did you do with it?

I modeled spheres randomly in space

You tell me what kind of geometry you have modelled. My question was how you have written down this geometry in matlab code.

Matlab code
%Make random s p h e r e s with in a bar and p l o t
function [x1,y1,z1]=creatingspheres (x)
clc
clear all
%Volumefraction(percent)
Volumefraction=7 ;
%Volume fraction(decimal)
vf = Volumefraction/100;
%Dimensions of bar
l = 20 ;
w = 4 ;
h = 4 ;
Vbar =l*w*h;
%Numer of spheres
q = 50 ;
%Radius of spheres
r =((3*vf*(Vbar ))/(4*q*pi))^(1/3) ;
%Create initial random coordinates
x1 = (rand*(w-2*r))+r;
y1 = (rand*(h-2*r))+r ;
z1 = (rand*(l-2*r))+r ;

%Create non overlapping coordinates
m = 1 ;
t = 0 ;
while m < q
if t>1e6
error ('could not compute non over lapping co-ordinates');
break
end
Xm =(rand*(w-2*r))+r ;
Ym =(rand*(h-2*r))+r ;
Zm =(rand*(l-2*r))+r ;
C1 =(x1-Xm).^2+(y1-Ym).^2+(z1-Zm).^2;

if any(C1<4*(r ^2))
t = t+1;
continue
end
m = m+1;
x1 =[x1;Xm];
y1 =[y1;Ym];
z1 =[z1;Zm];
end
%Output sphe r e c o o r d ina t e s
[x1 y1 z1];
%Plot
[xs,ys,zs] = sphere (30);
for n = 1:m
surf ( xs*r+x1(n),ys*r+y1(n),zs*r+z1(n),'FaceColor','g','EdgeColor','r');
hold on;
camlight('left');
material dull;
end
axis equal
xlim([0 w]);
ylim([0 h]);
zlim([0 l]);
hold off;

So basically you create the folowing data:
- width, lenght and height of a bar
- a radius that is the same for all balls
- an (x,y,z)-coordinate for each of the balls

A COMSOL geometry can be drawn using Matlab code which uses the above data. How exactly the LiveLink works and what the specific matlab commands are for creating spheres and bars I don't know, but you can read it in the COMSOL help/manual.

Hello,

You may also find this approach (new to version 5.3) helpful:
www.comsol.com/blogs/how-to-create-a-randomized-geometry-using-model-methods/

Best Regards,