[Gmsh] Error generating quadrangular structured mesh between 2 volumes

Hernandez Pereira, Cristina cristina.hernandez-pereira17 at imperial.ac.uk
Wed Jun 27 17:13:19 CEST 2018

My objective is to simulate the flow around a rounded cube in a domain using OpenFOAM. To do this, I want to create a structured mesh with quadrangular elements in the volume between the outer cube (volume 1) and the inner rounded cube, which has to be empty (volume 2). I have attached the .geo file.

I adapted the example in demos\simple_geo\transfinite and I tried 2 alternatives. First, I applied Transfinite Volume to all the volumes  (Transfinite Volme "*") in order to get a quadrangular mesh. When doing the 3D mesh in GUI, the volumes corresponding to the lateral corners, which are shaped as wedges (3,5,6,7,8,10,11,12) are not meshed inside and I get 8 errors:

Error   : Incompatible surface 22 in transfinite volume 3
Error   : Incompatible surface 36 in transfinite volume 5
Error   : Incompatible surface 36 in transfinite volume 6
Error   : Incompatible surface 34 in transfinite volume 7
Error   : Incompatible surface 28 in transfinite volume 8
Error   : Incompatible surface 32 in transfinite volume 10
Error   : Incompatible surface 32 in transfinite volume 11
Error   : Incompatible surface 30 in transfinite volume 12

To solve this, I applied Transfinite Volume toall the volumes except 3,5,6,7,8,10,11,12 (Transfinite Volume {4,9,13,14,15,16};). After doing this, I didn't get the previous errors, all the volumes were meshed inside but the meshing in volumes 3,5,6,7,8,10,11,12 (wedges at corners) is really irregular (see attached photo of section of mesh converted to OpenFOAM).

A part from these errors, in both cases, when I apply Mesh > 3D, a window appears with the following warning: "You are trying to generate a mixed structured/unstructured grid using the 3D Delaunay algorithm...". I pressed continue and, as a result of this,  I repeteadly got: "Error: Cannot build pyramids on non manifold faces"

Could anyone clarify what this means or how I could solve this? Is this related to the fact that I am not getting a quadrangular structured mesh in all the volumes, included the wedges at the corners?

I would appreciate if you could help me with this, maybe suggesting another way to generate the mesh I want between these 2 volumes.

Thanks in advance,

Cristina Hernandez Pereira
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