Assertion `coarse(cs,child.x,child.y) && coarse(cs,child.x,0,child.z) && coarse(cs,0,child.y,child.z) && coarse(cs,child.x,child.y,child.z)' failed.

[SigmaYot Zeta]

Dear all,

I want to simulate fluid flow in a fixed bed, so I generated some spherical particles and imported them into Basilisk.

When I used the `adapt_wavelet` function to refine the initial mesh, I encountered some problems. I set the refinement tolerance to 1/3 of the particle diameter, and the mesh refinement process succeeded without errors. However, when I further set it to 1/10, 1/100, and 1/1000 of the particle diameter, I encountered Error as follow,

```

/home/zousiyu/bin/basilisk/src/embed-tree.h:312: Assertion `coarse(cs,child.x,child.y) && coarse(cs,child.x,0,child.z) && coarse(cs,0,child.y,child.z) && coarse(cs,child.x,child.y,child.z)' failed.
./nptl/pthread_kill.c:44:error: This GDB supports auto-downloading debuginfo from the following URLs:
./nptl/pthread_kill.c:44:error:   <https://debuginfod.ubuntu.com>
./nptl/pthread_kill.c:44:error: Enable debuginfod for this session? (y or [n]) [answered N; input not from terminal]
./nptl/pthread_kill.c:44:error: Debuginfod has been disabled.
./nptl/pthread_kill.c:44:error: To make this setting permanent, add 'set debuginfod enabled off' to .gdbinit.
./nptl/pthread_kill.c:44:error: [Thread debugging using libthread_db enabled]
./nptl/pthread_kill.c:44:error: Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
./nptl/pthread_kill.c:44:error: [Detaching after vfork from child process 45685]
./nptl/pthread_kill.c:44:error: [Detaching after vfork from child process 45698]
./nptl/pthread_kill.c:44:error: [Detaching after vfork from child process 45711]
./nptl/pthread_kill.c:44:error: Program received signal SIGABRT, Aborted.

```

I set different levels of mesh refinement tolerance, but none of them seem to yield good results. Therefore, I plotted VOF, CS, and cell plots at different mesh refinement levels (see image attachments). Strangely, when the mesh refinement tolerance decreases (such as 1/10, 1/100, and 1/1000 of the particle diameter), holes appear in the mesh.

My stl file and code see attachments.

Thanks for your attention.

[Stephane Popinet]

Dear SigmaYotZeta,

Have you tried:

fractions_cleanup (cs, fs);

To be applied after initialisation and after calls to adapt_wavelet().
See here for an example:

https://basilisk.fr/src/examples/porous3D.c

cheers,

Stephane

PS: please do not send images in proprietary formats (e.g. pptx), use
open formats: jpeg, png etc.