How to get the cross-sectional area of a PDE model

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Hanshun Yu 2020-5-18

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https://ww2.mathworks.cn/matlabcentral/answers/526274-how-to-get-the-cross-sectional-area-of-a-pde-model

回答： DGM 2025-3-29

Now I have a 3D model of a rebar as a .stl file and I want to calculate the cross-sectional area of this rebar at different places. My point is to calculate the area so the contour or slice function doesn't work for me.

I have imported this model to MATLAB as a PDEModel. But when I searched for the cross-sectional area of a PDEModel, I just got how to plot the PDE solution.

Then I used the generateMesh function to get a FEMesh. I think maybe the Surface Intersection function can do it but I don't know how to build a surface from the FEMesh.

So is there any way I can do this?

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darova 2020-5-18

Can you attach the data? Can you show position you want to get crossection?

Hanshun Yu 2020-5-18

Cylinder.zip

Thanks for your concern. I attached the .stl file here. It's just a cylinder.

About the positoin, I'd like to get cross-sectional area of any section perpendicular to x-axis so it's not so important I think.

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darova 2020-5-18

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https://ww2.mathworks.cn/matlabcentral/answers/526274-how-to-get-the-cross-sectional-area-of-a-pde-model#answer_433114

在 MATLAB Online 中打开

See this solution

f1 = stlread('Cylinder.stl');
[y,z] = meshgrid(-2:2);             % meshgrid for plane
h = surf(y*0+2,y,z);                % crossection plane
f2 = surf2patch(h,'triangles');     % convert to patch
f2.facecolor= 'r';
patch(f1,'facecolor','y')           % display cylinder
patch(f2)                           % display crossection plane
[~,ff] = SurfaceIntersection(f1,f2);% find crossection line
ff = rmfield(ff,'edges');           % remove edges
patch(ff,'linew',2)                 % display crossection line
alpha(0.3)                          % make surfaces transparent
axis vis3d equal

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darova 2021-2-9

在 MATLAB Online 中打开

Do you know why the function is throwing an error when I place the intersection plane at 0 or 50 (lower and upper limit of the cone) ?

I believe the answer is:

Error: in IntersectionPolygon: key is out of bound

Try

h2 = surf(y,z,z*0+50-0.01);
h2 = surf(y,z,z*0+0.01);

This is what my crosse sections look like. Is there a command that fills the cross section with a certain color?

Sure, use patch or fill

Matt 2023-4-24

Hey I'm having a similar issue with this method, I can't find why it doesn't work on my side when trying to "convert" the points/Clist to vertices and faces.

I run the following code :

f1 = stlread('OBJECT.stl');

[y,z] = meshgrid(-20:20);

h = surf(y*0+20,y,z);

f2 = surf2patch(h,'triangles');

f2.facecolor= 'r';

f1.vertices = f1.Points;

f1.faces = f1.ConnectivityList;

f1 = rmfield(f1,'Points','ConnectivityList');

patch(f1,'FaceColor','y')

patch(f2)

but I get this error : Unrecognized property 'vertices' for class 'triangulation'.

and also it seems to Matlab that I don't have enough arguments for patch(f1,'FaceColor','y').

Would appreciate any help !

~Matt

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Mathematics and Optimization Partial Differential Equation Toolbox Geometry and Mesh

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