[Fusternino]

I am trying to mesh a geometry that includes both spider-wide like complex geometries as well as simple geometries. Essentially, my problem is a long pipe with a localized flow obstruction.

I require a purely hexahedral mesh. The current strategy is to first use an unstructured tetrahedral mesh and then convert it to a purely hexahedral mesh. This allows for the rapid generation of hexahedral meshes for complex geometries.

The main problem however is that this generates too many elements. In regions of simpler geometry, it would be allowable to use very high aspect ratio hexahedral elements (a ratio of 5-10 would be fine). However, I am having difficulty controlling the growth of the tetrahedral elements and am achieving instead aspect ratios in the range of 2-4. Thus, there is a very large number of elements penalty for using this rapid mesh generation method.

Any ideas as to how to generate elements with aspect ratios in the pipe-like regions (as would easily be done with a block structured hexahedral mesh)? I would like to get the number of elements penalty down to 10-25%, ideally.