meshing two slabs with an intersecting object

[Chris W]

Dear iso2mesh users,

i am currently stuck at a seemingly easy problem. I want to mesh a domain, consisting of two layered slabs, the lower

of which has a hemisphere sitting on the boundary, that "sticks" into the domain of the lower slab, like this:

The picture shown is my current workaround, but as mentioned, i would like the turquoise and yellow domain to be directly

on top of each other, like shown here:

I tried the following code (with various tweaks):

clear;clc;
tb1 = [-1 -1 5]; tb2 = [21 16 11]; % Tissue Slab "Box" (2 corner nodes)
bb1 = [0 0 0]; bb2 = [20 15 10]; % Bounding Box (2 corner nodes)
detpos = [11.27, 7.5, 0];        % Detector Position
radius = 0.8;

% mesh the tissue slab (slightly bigger, so it overlaps):
[node_box,faces_box] = meshabox(tb1,tb2,0.1,1);
% mesh the sphere:
[node_hs,faces_hs] = meshasphere(detpos,0.8,1,1);
% mesh the bounding box:
[node_bb,faces_bb] = meshabox(bb1,bb2,0.1,1);
% merge tissue slab and sphere
[node_merged,faces_merged] = mergemesh(node_hs,faces_hs,node_box,faces_box);
% sphere should be inside the domain of the bounding box:
[cnode,cface] = surfboolean(node_bb,faces_bb,'first',node_hs,faces_hs);

subplot(1,2,1)
plotmesh(cnode,cface,'x>11.27'); % looks reasonable
% the tissue slab should be inside of (bounding box + hemisphere)
[newnode,newface] = surfboolean(cnode,cface,'first',node_box,faces_box); % doesn't look right

subplot(1,2,2)
plotmesh(newnode,newface,'x>11.27');

but whenever i try to concatenate the two boxes to a sandwich, something is wrong

(I tried to adapt the procedure from the issue "issue merging meshes" asked a few month ago).

What would be an appropriate way to mesh this? I also looked into latticegrid(), but could not find a way

to intersect/concatenate the spherical geometry with the two layered slab.

I might haven't fully understood, how iso2mesh's mesh generation works. From what i think (please correct me if

this is wrong), all functions like surfboolean() etc. work on surfaces (hence the name :>); it is not possible to merge meshes

directly into each other. So one would try to intersect/merge etc. different geometries' surfaces and only in the

final step generate the actual tetrahedral mesh.

Any help is highly appreciated, thanks!

Christoph Wagner

[Qianqian Fang]

hi Chris

please checkout the below example

https://github.com/fangq/mmc/blob/master/mmclab/example/demo_mcxyz_skinvessel.m#L12-L23

it meshes a two-layered slab using latticegrid(), and then use surfboolean to combine with a cylindrical mesh to create an inclusion.

in your case, if you want to combine with a sphere, you can simply replace the meshacylinder by meshasphere. Here is my quick tweak of that script




%% create the skin-vessel benchmark mesh
[no,fc]=latticegrid([0 200],[0 200],[20 32 200]); % create a 3-layer tissue
fc2=cell2mat(fc);
fc=[fc2(:,[1 2 3]); fc2(:,[1 3 4])];

%[ncy,fcy]=meshacylinder([-1,99.5,99.5],[201,99.5,99.5],20,5); % add the vessel
[ncy,fcy]=meshasphere([100 100 200],20,4,5); % add the vessel
[newnode,newelem]=surfboolean(no,fc,'first',ncy,fcy);  % merge the two domains

%c0=[10,100,150,26]';

c0=[10 100 199 26]';

seeds=[ones(4,2)*100, c0];  % define the regions by index

%ISO2MESH_TETGENOPT='-Y -A'
[cfg.node,cfg.elem]=s2m(newnode,newelem(:,1:3),1,30,'tetgen',seeds); % creating the merged mesh domain
plotmesh(cfg.node,cfg.elem,'x>100')


the output mesh cross section is attached. you can modify the sphere location/radius/mesh density according to your needs.

Qianqian

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[Chris W]

Dear Qianqian,

perfect, I must have missed that example code. Thank you so much!

Best Wishes,

Chris

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