Volume region definition for head loss for hollow cylinder

[plaza]

Hi, I need to define a volume region for head loss. The shape of the region is a hollow cylinder with its axis along the z axis (vertical), i.e a cylinder volume which has had a cylinder of smaller radius but same height cut out of it. Can I use the geometric function 'cylinder' and basic operators such as 'and' or 'or' to define the volume region for head loss? What would be the expression for the hollow cylinder (xo,yo,zo,x1,y1,z1,radiusa) with the cylinder cut out of it (x2,y2,z2,x3,y3,z3,radiusb) ?
Regards,
Floren

[Yvan Fournier]

Hello,

Yes, just use "and not" to indicate you are in the big cylinder but not in the small one.

Regards,

Yvan

[plaza]

Hi Yvan, thanks very much. Unfortunately I have a situation where I need to model a head loss region about 0.1 m thick with a pressure drop of about 800 Pa for a water velocity through the region of about 0.0173 m/s. It is also near an outlet, but I don't think that is the main problem as when I move the region away from the outlet I still have the same problem of divergence. I have set icalhy to 0 in cs_user_parameters.f90, with no gravity. I can get a converged solution easily for small pressure drops of about 8 Pa but when I increase alpha from 5000 to near 5000000 which I believe I need, inflow starts at the outlet, blocking of the outlet and the solution diverges. If necessary I can make the region thicker but i don't think I can move the region away from the outlet. I have reproduced the problem in a simple vertical pipe problem, it is attached. Would you be able to comment?
Regards,
Floren

[plaza]

Hi Yvan, sorry, misprint in my previous post, should be 0.00173 m/s.
Regards,
Floren