Error in importing ASCII VTK Unstructured Grid Mesh File

Submitted by Utsav on Sat, 09/23/2023 - 07:48

I am trying to import a ASCII VTK unstructured grid mesh file (as required) while using electrostatics in LIGGGHTS simulation (coupled with TCLB, an open-source Lattice Boltzmann code package) using the below code (following https://www.cfdem.com/media/DEM/docu/region.html).

### Add DLVO forces for particle-fibre interactions
region LvdW_cyl_01 mesh/tet file models/tutorial/Val_Xiong/Fibre_N.vtk scale 0.5 move 20e-4 11e-4 10e-4 rotate 11 11 11 units box side out
fix LvdW_wall1 all wall/region LvdW_cyl_01 colloid -18.7e-21 0.5e-7 0.7e-4 0.6003e-4 # final arg is inner cutoff

I got certain errors (like [Expecting ASCII VTK mesh file, cannot continue (input_mesh_tet.cpp:198)]; [Expecting ASCII VTK unstructured grid mesh file, cannot continue (input_mesh_tet.cpp:204)]; [Expecting 'CELLS' section in ASCII VTK mesh file, cannot continue (input_mesh_tet.cpp:247)]), but kind of more or less resolved them someway. But now, I am getting the below error.

ERROR on proc 0: This feature is not available for tet mesh regions (region_mesh_tet.cpp:204)

Anyone has any idea about how to resolve this? What "feature" it might be talking about (which is probably not compatible with tet mesh)? It happened just after completion of Particle Insertion. So, does it have any link to particle insertion?

Kindly please help me on this. Thank you in advance.

Forums:

Utsav | Sat, 09/30/2023 - 08:49

Thanks a lot Daniel for your kind, prompt, and informative response.

I am running simulations with TCLB and LIGGGHTS coupled (for CFD and DEM respectively). My computational domain is shown in this image: https://drive.google.com/file/d/12bub7EjFFu37AZwuhkuTIBu-B2xZ5rgJ/view?u.... The cylinder shown there is a "wall" for CFD (TCLB) and DEM both, and has been inserted as a "STL file" in both input files. It works fine there (particles do not enter the cylinder). Now, I am using ELECTROSTATICS to capture these particles at the surface of cylinder, as soon as the particles touch the cylinder (or come in the respective cut-off distance from the cylinder's outer surface). I am able to run the simulation successfully when the cylinder axis is oriented either along x, or y, or z direction, by defining the cylinder within the LIGGGHTS input file using the command [region void cylinder dim c1 c2 radius lo hi]. But now I need to run simulations with Cylinder oriented at different angles with respect to x axis, or, y axis, or, z axis. Unfortunately, I could not find any direct way to rotate this cylinder around any of the axes (x, or, y, or, z). So, I was trying to insert/import a file externally for the cylinder so that I could use the command [region mesh/tet file filename scale s move offx offy offz rotate phix phiy phiz] from here: https://www.cfdem.com/media/DEM/docu/region.html to rotate it as required. But, when I am importing a cylinder meshed with Unstructured Tetrahedral Mesh (as ASCII VTK file), it shows the error as "ERROR on proc 0: This feature is not available for tet mesh regions (region_mesh_tet.cpp:204)", as mentioned in my previous comment. So, what do I do to resolve it? What exactly i should do to run my simulation with an Inclined Cylinder? What's the alternate way to define or insert an Inclined Cylinder for ELECTROSTATICS the way it has been shown in my computational domain?

I define the ELECTROSTATICS parameters (like Hamaker Constant, stern layer thickness, etc) after defining/inserting the Cylinder.

By the way, this error goes away if I comment-out the code of "particle insertion", but I can't do that for my intended simulations

Daniel Queteschiner | Sat, 09/30/2023 - 18:39

There are several things you could try:

-) Make the primitive cylinder region you had dynamic by adding the rotate option with rotation angle v_theta and rotation point/axis. Simply setting v_theta to the desired rotation angle should do the trick.

-) If that doesn't work, you could try adding the missing functions to the RegTetMesh class, an example of a crude approximation can be found here
https://github.com/ParticulateFlow/LIGGGHTS-PFM/blob/master/src/region_m...
Note, that we just use this for particle insertion so this might not be good enough for your needs

-) If that also doesn't work out for you, you could implement a fix that uses surface meshes instead of regions such as fix wall/gran just with your desired interaction instead of the granular interaction forces ...