# Creating modified cavities in 3D models.

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Luke Benham 2020 年 6 月 14 日
コメント済み: Nathan Welch 2020 年 6 月 30 日
Hi, I wish to create cavities in a cubic model (discrete geometry) similar to that found here.
The only difference is I wish to have more control over the size of the cube and sphere, possibly add multiple, and control the location of the sphere within the 3D space, is any/all of this possible?
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Luke Benham 2020 年 6 月 15 日
Yeah my current idea was to use sphere as used in the mathworks code in the previously supplied hyperlink. The attached shows an idea as a pdegplot that i wish to generate using code. (The figure was created using an imported .stl file however)
Nathan Welch 2020 年 6 月 30 日
I'm having a similar issue that I posted here
However, I wish to mesh the internal cavity and include it in my model. So the cavity mesh must match up with the body mesh, i.e. same nodes and same faces at the interface surface.
Is this possible in MATLAB? The example that you reference above does something close but it isn't very good as the 'mesh' that is used to model the spherical cavity is just a set of terrible tetrahedrals not a delaunay type mesh.
I know about other meshing softwares, GMSH etc, but I want something in MATLAB (even if I have to write it myself) as I need to do a lot of optimisation and solving PDEs, whilst updating meshes and carrying out incremental alterations - rather than entirely recreating them. My BIG stumbling block is just getting even a basic, terribly performing discretization method for an arbitrary geometry.

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### 採用された回答

ADSW121365 2020 年 6 月 15 日

All of this is definitely possible, but the inbuilt CAD capabilities/geometry design in MATLAB aren't its strongest point.
From experience complicated geometries generally fall into two catagories for use in the toolbox:
• Direct Geometry Design Inside an external mesh generator: See a question I asked for nested cubes on stackexchange here. GMSH is free, robust, has inbuilt optimisation and isn't too hard to learn, though finding anything in the documentation is long. There are many other mesh generators, but GMSH also has a direct export to a .m file for MATLAB.
• CAD Design & Creation of an STL/BREP/STEP file depending on the geometry, subsequent external meshing then importing to MATLAB. Some questions I've answered on this forum which maybe helpful to this approach can be found here and here
Edit: The approach via alphashapes mentioned in the comments is actually really good for this type of problem and worth considering.
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Luke Benham 2020 年 6 月 15 日
Thank you, this is very helpful and support the answer seen here.
ADSW121365 2020 年 6 月 15 日
The approach suggested is actually really good - I'm thinking too generally, the CAD approach allows a drag-and-drop type approach to geometry design which is probably more beneficial when you wish to consider complicated embedded stuctures.

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