Vent not attached to an obstruction - but it is!!

[Glen]

Hello,
I always seem to have some issues with getting my vents sitting
snuggly with the roof obstructions and what not, so i have taken to
simply adding a obstruction on top of the vent so that there is always
something solid for it to be attached to.

Which usually works fine. However I am having a heap of trouble
getting a group of vents working.

the code looks a little something like this


&VENT SURF_ID='20Ms', XB=293,294.5,111,112.5,15.4,15.4,
CTRL_ID='NewSmokeZone13' / Mall Fan 2
&OBST XB=293,294.5,111,112.5,15.4,15.6/

So the obstruction has the same dimensions as the vent, but obviously
has a thickness.

The error i get is:

ERROR: VENT 23 must be attached to a solid obstruction

I am using multi mesh with a ijk of aprox 400mm.

It is driving me up the wall, I have moved the vent and obstruction
higher and lower, left and right, and its still giving me the issue.

Anyone have any ideas?

Cheers
Glen.

[TimoK]

Well, you have about 0.4 m grid spacing and try to make
an obst that is 0.2 m thick. Might be that FDS makes
this obst as thin obst. Vents should have at least one
grid cell thick obsts.

Remedy: add "THICKEN=.TRUE." to the obst line.

Additional help: add also "PERMIT_HOLE=.FALSE." to the
obst line, so no hole will take it away (by accident).

TimoK

[Steve]

Glen,

This happened to me recently as well when working with roof vents. I
believe I had
attached the vents to the underside of the thickness of the roof and
they were never
"seen" by FDS as being attached to an obstruction. I finally moved
them to the top
side of the roof obstruction (taking the thickness into account) and
that seemed to
solve the issue. Hope it works for you.

Steve