# [Gmsh] Boundary Layer around hemi sphere in a cube

Christophe Geuzaine cgeuzaine at ulg.ac.be
Wed Oct 11 08:44:55 CEST 2017

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> On 30 Sep 2017, at 11:33, Nilanka Indunil Kumari Ekanayake <nekanayake at student.unimelb.edu.au> wrote:
>
> Hi,
>
> I've created the following mesh. For the boundary layer I've used extrude command. As I need to define physical volume for the farfield (bounded by the box and hemisphere). Here I considered two volumes created by a seperate Surface loops. One is volume is the extruded volume and the other volume is outside extruded surface (bounded by the block).
>
> However, when I check the surface face, I see some overlapping in the boundary and around it (specially in volume surface).
>
> Also I would like to have have qaud dominated mesh in the volume? Any method to get it ?
>

These algorithms are still in development, and not ready for production use. For your simple geometry I would advise generating a fully structured grid.

> The critical task was to define the cut plane.
>
> Volume faces - Non uniformity around  boundary layer (Due to face overlapping?)

No: it's just that without an explicit extrusion direction, Extrude uses the (smoothed) normal field computed on the surface triangles to compute the extrusion direction. Here you then extrude "not quite" in the symmetry plane.

For such a simple geometry, I would recommend explicitly extruding a 2D mesh (and thus creating the boundary layer directly) using e.g. a rotation.

Christophe

> <image.png>
> <image.png>
>
> Cheers,
> Nilanka
>
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--
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
http://www.montefiore.ulg.ac.be/~geuzaine

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