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FieldForcer

Mesh doesn't show up in solution

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Hi,

 

I imported a mesh from stl file in CADFEKO. When I right click on properties of this geometry, it shows that Front and Back medium are assigned White_matter property, but Face Medium is set to arbitrary Dielectric boundary. I didn't define Dielectric boundary, but I did define White_matter property. Problem is Face medium drop down list does not show White_matter, and I can't select it. As a result mesh has some arbitrary Dielectric boundary. 

image.thumb.png.7f5214d8609ceb7467f514e7d3c9b7d3.png

When I mesh model, I receive a Warning 16097.

image.png.9b8b390dab826a2aae4872eebe836c1c.png

Next, I executed a frequency sweep solution with following option:

image.png.b0dd70302ccbc7968b062d1701066d0f.png

CEM validate didn't detect any issue.

image.png.18c8b6cd8caea1b86ca9513016bd2541.png

After execution, the solution obtained doesn't show any mesh.  

image.thumb.png.4323e408d504f7c014a64b2fd5436bb8.png

What is solution to such a problem?

I have attached both cfx, pfs, and stl file.

 

Thanks in advance,

FieldForcer 

P.S.: Earlier Peter Futter suggested I write lua script. I don't understand workflow of writing such a file to solve mesh issue.

 

Figures8Coil_MIDA.cfx

Figures8Coil_MIDA.pfs

Brain_White_Matter.stl

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Hi Fieldforcer

 

You need to tell CADFEKO what is on the outside and inside of this surface mesh. The outside is the triangle normals side, which point outwards for this mesh.

 

The inside will be white_matter, the outside is free space. And this is a dielectric surface, not a PEC surface, I presume.

Set the following below on the Face properties and Save.

 

To quickly see if the mesh displays in POSTFEKO, rather just run PREFEKO. If it displays, then you can run FEKO to solve completely.

 

image.png

 

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Hi mel,

 

Your presumption is correct. I changed Front medium to Free Space, and turned off Low Frequency Stabilization in Solver Settings because low frequency stabilization and dielectric bodies (SEP) are not allowed in the same model. Mesh gives same warning as before meaning I dont' have control over mesh of BrainWhiteMatter.

image.png.cd93b9fe31ef30e0e79310f14fa807ba.png

When I execute simulation, solution requires enormous memory because BrainWhiteMatter mesh is too fine.

image.png.2005a7e94f0c13db9c204a8380bdf430.png

I used coarse mesh for wires, and can't play with White_Matter mesh. How to scale down memory requirement?

 

Thanks,

FieldForcer

P.S.: Attached is updated cfx file.

 

Figures8Coil_MIDA.cfx

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Unfortunately there's not much to do here. It is a surface mesh of many dielectric triangles.

You should like into running this on a bigger computer, one with 1 TByte of RAM.

 

The best solver for this application would be hybrid FEM/MoM, but then you would need to mesh the brain into tetrahedra. FEKO unfortunately cannot create a tetrahedral mesh from a surface mesh. 

You can view the concept behind the solution in the below videos:

https://altairuniversity.com/learning-library/23068/

https://altairuniversity.com/learning-library/stacked-dielectric-resonator-antenna-2/

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You could try to remesh as Torben suggests, but with the small geometric details, I don't think you are going to reduce the memory to a practical level for your machine.

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Hi Torben,

 

With Use model mesh option, remeshed geometry has too many triangles.

image.thumb.png.b6b0a7a154337cc9a2bf12ae98a1fe80.png

I agree with mel. This simulation will require enormous RAM. When I executed simulation, I received following error:

image.thumb.png.d557049c1953f0178c74f329e6e8c84d.png

I tried to find if something is wrong with geometry, and if mesh could be repaired with following options.

image.png.49ef876ab4a2c56d4acc689e9b05c771.png

No clashes were detected.

image.png.e970cad89466d344a19b8ecb6b78c9df.png

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Hi mel,

 

I don't have wave-guide port, and video suggests using FEM modal port. Does it mean I change voltage port to FEM modal port?

Also video mentions applying FEM to dielectric regions, but that option is unavailable in Properties of brainwhitematter mesh. What am I missing?

 

Is there a method to define better mesh, and apply FEM/MoM solver?

Figures8Coil_MIDA.cfx

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You can use the FEM current source which is applied on a FEM line port. The FEM line port is very similar to the wire port for voltage sources.

 

You need a tetrahedral volume mesh to use FEM. Your existing mesh is a surface mesh.

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Hi Mel,

I converted surface mesh (stl) model of BrainWhiteMatter to tetrahedral mesh(wrl) in Gmsh. Following were the options to export volume mesh:

image.png.4a07204c66f73aedaa09b1b0e5a899c5.png

Then I imported BrainWhiteMatter.wrl mesh in FEKO. and received following error:

image.png.7297a7fdc4ed3d0eb2f787f61a15f621.png

 

Clearly this wasn't a good format for volume mesh. Which format should I use? 

It seems that Gmsh can import other formats. If I want to select few elements, and measure total volume, it might be possible to do it in Gmsh.

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