How to place random CNT's in a box domain with random curves and orientation ?

Hi all, what i want is a code that can actually place random carbon nanotubes in a cube domain so that i can use it in comsol livelink MATLAB bellow is a code that puts spheres which i found in this forum i need it based on that.. :

function P = GetRandomSpheres(nWant, Width, Radius)
% INPUT:
%   nWant:  Number of spheres
%   Width:  Dimension of 3d box as [1 x 3] double vector
%   Radius: Radius of spheres
% OUTPUT:
%   P:      [nWant x 3] matrix, centers

P = zeros(nWant, 3);

R2     = (2 * Radius) ^ 2;   % Squared once instead of SQRT each time
W      = Width - 2 * Radius; % Avoid interesction with borders
iLoop  = 1;                  % Security break to avoid infinite loop
nValid = 0;
while nValid < nWant && iLoop < 1e12
  newP = rand(1, 3) .* W + Radius;
  % Auto-expanding, need Matlab >= R2016b. For earlier versions:
  % Dist2 = sum(bsxfun(@minus, P(1:nValid, :), newP) .^ 2, 2);
  Dist2 = sum((P(1:nValid, :) - newP) .^ 2, 2);
  if all(Dist2 > R2)
    % Success: The new point does not touch existing sheres:
    nValid       = nValid + 1;  % Append this point
    P(nValid, :) = newP;
  end
  iLoop = iLoop + 1;
end
% Stop if too few values have been found:
if nValid < nWant
  error('Cannot find wanted number of points in %d iterations.', iLoop)
end
end



n = 100;
R = 5;
P = GetRandomSpheres(n, [100, 100, 100], R);
figure
axes('NextPlot', 'add', ...
    'XLim', [0, 100], 'YLim', [0, 100], 'ZLim', [0, 100]);
view(3);
[X, Y, Z] = sphere();
for k = 1:n
    surf(X * R + P(k, 1), Y * R + P(k, 2), Z * R + P(k, 3));
end

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Answer 1

[Torsten]

https://uk.mathworks.com/matlabcentral/fileexchange/93250-generate-thick-fibers?s_tid=srchtitle

[Polydoros]

Wow thats pretty close to what i wanted thank you! do you know if it will straight away run in comsol or if there is any way to make curved cnts in an DXF or STL file so that i can load them in comsol ?

[Torsten]

I have no experience with this MATLAB code. I think the best you can get is a list of points that define the cylinders. Maybe loading it in a CAD program can help to get DXF or STL files from it.

If you want to use this as geometry in a fluid-dynamics application, I can only advice against it. You will never get a converged flow field in such a random structure, and the mesh must be that fine to resolve the geometry that usual RAM capacity will not suffice.