Hi @makeclean - so I’ve reviewed the file and have identified the issues.
The internal “twist” is also not compatible with the curve that partitions the exterior surface (highlighted):
Essentially, this will cause elements to invert in order to respect both this straight curve and the tortuous curves inside the volume.
Volumes with a lot of “twist” often require a bit more assistance (in the form of webcut/partitioning) from the user to assist Cubit in laying down a valid mesh
To remove this external curve we will
regularize the volume:
regularize volume <volume_id>
To webcut this volume we will create additional surfaces that are normal to the faces of the internal faces. We do this by:
- Creating vertices on the midpoints of the rectangle
- Then vertices on the circular curve that are “close to” these midpoint vertices.
- Then we create curves with the vertices on the circular curve that are opposite each other
- Then we sweep these curves, using one of the helical curves as a guide, to create the additional surfaces (sheet bodies)
- Then we webcut using these sheet bodies.
This will result in multiple volumes that more explicitly define the twist for the mesher.
You’ll need to update your boundary layers, but here’s a coarse mesh without the boundary layers, just to give you a feel for how the mesh looks:
Here’s a journal file that runs the commands, starting from the Trelis file you’ve sent:
## Open the file
## Delete mesh entities
delete boundary_layer all
## Block type was TETRA... change it to linear hexes
block 2 element type hex8
## Remove the extraneous, straight curve that will cause problems
regularize vol 1
## Create vertices on / near midpoints of the rectangular feature
create vertex on curve 3 4 1 2 midpoint
create vertex on curve 13 close_to vertex 11 12 13 14
## Create curves to be used for cutting the geometry
create curve vertex 15 17
create curve vertex 16 18
## Sweep the curves along helical path to form cutting surfaces
sweep curve 15 along curve 6
sweep curve 16 along curve 6
## Perform Webcuts
webcut Volume 1 tool Body 2
delete Body 2
webcut Volume 1 4 tool Body 3
delete Body 3
## Delete the free vertices we used for constructing the cut surfaces
delete vertex all
## Imprint and merge volumes
## Demo Mesh
vol all size 0.005
mesh vol all
Let me know if this was helpful!