Best Way to simulate a Hexagonal Lattice, as well as Moltres Input File.

[Jeremyb8707bigbrain]

Hey friends!

I currently have a unit cell, a hexagon with an apothem of 7cm, 15cm tall, and an inner circle radius 5 cm. I plan to do a parametric study on how the thickness of the graphite affects the neutronics and thermal-hydraulics for FLiBe-UF4 Salt.

My issue is simulating a meaningful hexagonal lattice without having to build one on Gmsh, which would be a pain to tag all the surfaces correctly, as well as explode the DOF count. I was wondering if there was any way with the BCs to simulate a sort of lattice where to the simulation is not just 1 singular cell.

As well as using the Input File for MOOSE/Moltres, I know I am supposed to do a steady state simulation to find out the initial conditions for a transient, but I am having a very hard time figuring out what I should/shouldn't include and how everything on that front works.
My initial temperature would be a 973K inlet temp, with 4 energy groups and 6 delayed. I saw some sources say you must set a power threshold, how would I do such things?

Thank you Moltres Experts 🙏

[smpark7]

Hey @Jeremyb8707bigbrain you can refer to https://mooseframework.inl.gov/source/meshgenerators/HexagonConcentricCircleAdaptiveBoundaryMeshGenerator.html for generating hexagonal unit cells using MOOSE MeshGenerators. I find MOOSE to be quite powerful for generating meshes as long as you stick to regular shapes. You can stack multiple sequences of MeshGenerator steps (e.g., renaming a boundary after generating the hexagon) by setting the 'input' parameter to the name of the previous MeshGenerator object.

As for getting steady state results, you can refer to cases in https://github.com/arfc/moltres/tree/devel/problems/2021-cnrs-benchmark/phase-1 and its associated publication https://www.sciencedirect.com/science/article/pii/S0306454922001463. I used full-coupling.i to generate steady-state results. Then I ran transient cases in phase-2.

[Jeremyb8707bigbrain]

Thank you so much for these resources! I see the mesh generator there is only for 2D meshes (or so it says in the documentation), would there be such a mesh generator type that could adapt the boundaries of a 3D mesh? Or would I have to do this in 2D and then extrude it into 3D?

I ask this because I have already made a 3D mesh in gmsh for 1 unit cell and I would love to make a small ring around that hexagon with more cells, but in Gmsh this is to pricey and not worth it, do you believe doing it in MOOSE would be the better option?

[smpark7]

I'm not sure if you already found the answers, but yes you can create the mesh in 2D and extrude using AdvancedExtruderGenerator or MeshExtruderGenerator.

You can load your gmsh file into MOOSE using FileMeshGenerator and add rings to it using PeripheralRingMeshGenerator or PeripheralTriangleMeshGenerator.

[Jeremyb8707bigbrain]

Yep I got my answers thank you! Apparently MeshExtruderGenerator is deprecated so I am using the advanced one, so far its working great!