RE: Numerical Instability
Gary Bennett
Hi, I am fairly new to FDS and have tried to run the following simulation with a message of numerical instability coming up fairly early on in the simulation (between 107 & 127s). I have tried moving the inlet positions and the location of fire as well as extraction rates and inlet sizes but with no success.
I have looked at other posts to make sure my HOLES & OBSTS are okay & I think they are but I am obviously still doing something wrong.
Can anyone help please.
&HEAD CHID='Exercise1'/ Single point extraction plus jet fans
&MESH ID='stair',IJK=4,20,33,XB=0.00,2.00,23.00,33.00,0.00,3.30/
&MESH ID='cp1',IJK=270,26,24,XB=2.00,56.00,20.00,33.00,0.00,2.40/
&MESH ID='cp2',IJK=170,30,21,XB=8.00,42.00,5.00,20.00,0.00,2.10/
&MESH ID='cp3',IJK=75,10,21,XB=27.00,42.00,0.00,5.00,0.00,2.10/
&TIME TWFIN=600/
&OBST XB=0.00,0.10,23.00,33.0,0.00,3.30, RGB=153,153,153, TRANSPARENCY=0.80, SURF_ID='INERT'/
&OBST XB=0.00,2.00,23.00,23.1,0.00,3.30, RGB=153,153,153, TRANSPARENCY=0.80, SURF_ID='INERT'/
&OBST XB=0.00,2.00,29.90,33.0,0.00,3.30, RGB=153,153,153, TRANSPARENCY=0.80, SURF_ID='INERT'/
&OBST XB=2.00,2.10,20.00,33.0,0.00,3.30, RGB=153,153,153, TRANSPARENCY=0.80, SURF_ID='INERT'/
&OBST XB=2.00,56.00,32.90,33.0,0.00,2.40,SURF_ID='INERT'/
&OBST XB=2.00,56.00,20.0,20.1,0.00,2.40,SURF_ID='INERT'/
&OBST XB=55.90,56.00,20.00,33.0,0.00,3.30, RGB=153,153,153, TRANSPARENCY=0.80, SURF_ID='INERT'/
&OBST XB=26.00,26.10,5.0,20.00,0.00,2.10, SURF_ID='INERT',COLOR='GRAY 60'/
&OBST XB=8.00,27.00,5.00,5.10,0.00,2.40, RGB=153,153,153, TRANSPARENCY=0.80, SURF_ID='INERT'/
&OBST XB=27.00,27.10,0.00,5.00,0.00,2.10, RGB=153,153,153, TRANSPARENCY=0.80, SURF_ID='INERT'/
&HOLE XB=1.90,2.20,26.00,27.00,0.00,2.00, COLOR='GREEN'/
&HOLE XB=12.0,13.0,19.90,20.10,0.00,2.00, COLOR='GREEN'/
&HOLE XB=16.0,23.0,19.90,20.10,0.00,2.10, COLOR='GREEN'/
&HOLE XB=31.0,38.0,19.90,20.10,0.00,2.10, COLOR='GREEN'/
&HOLE XB=0.50,1.50,27.90,28.20,3.20,3.40, COLOR='YELLOW'/
&HOLE XB=26.90,27.20,0.2,4.80,0.00,2.10,COLOR='GREEN'/
&OBST XB=10.00,12.00,16.00,18.00,0.40,1.50, COLOR='RED', SURF_IDS='fire','INERT','INERT'/ fire
&DUMP RENDER_FILE='Exercise1', PLOT3D_QUANTITY='HRRPUV','MIXTURE FRACTION','TEMPERATURE','VELOCITY','VISIBILITY'/
&REAC ID='polyurethane',C=6.20,H=7.20,O=2.10,N=1.00,SOOT_YIELD=0.0250/
&SURF ID='fire',
FYI='s1. polyurethane fire + vent',
COLOR='RED',
HRRPUA=800.00, RAMP_Q='RAMP_Q_ignition'/
&RAMP ID='RAMP_Q_ignition' T=0.00 F=0.00/
&RAMP ID='RAMP_Q_ignition' T=100.00 F=0.10/
&RAMP ID='RAMP_Q_ignition' T=200.00 F=0.30/
&RAMP ID='RAMP_Q_ignition' T=300.00 F=0.60/
&RAMP ID='RAMP_Q_ignition' T=400.00 F=0.90/
&RAMP ID='RAMP_Q_ignition' T=500.00 F=0.40/
&RAMP ID='RAMP_Q_ignition' T=600.00 F=0.20/
&RAMP ID='RAMP_Q_ignition' T=700.00 F=0.15/
&RAMP ID='RAMP_Q_ignition' T=800.00 F=0.10/
&RAMP ID='RAMP_Q_ignition' T=900.00 F=0.10/
&SURF ID='fan',RGB=26,128,26,VOLUME_FLUX=10.0,RAMP_V='fan_RAMP_V'/
&RAMP ID='fan_RAMP_V', T=10.00, F=0.00/
&RAMP ID='fan_RAMP_V', T=60.00, F=1.00/
&HOLE XB=20.00,22.00,4.90,5.10,0.00,2.00,COLOR='GREEN'/inlet air
&VENT XB=54.00,55.00,20.00,20.00,1.30,2.30,SURF_ID='fan'/
&SURF ID='BLOW', POROUS=.TRUE., VOLUME_FLUX=0.50, RAMP_V='BLOWER RAMP FAN',/
&RAMP ID='BLOWER RAMP FAN',T=0.0,F=0.0/
&RAMP ID='BLOWER RAMP FAN',T=40.00,F=0.5/
&RAMP ID='BLOWER RAMP FAN',T=80,F=1/
&OBST XB=10.00,11.00,26.00,26.00,2.10,2.40, COLOR='BLUE', / Fan Shroud
&OBST XB=10.00,11.00,26.30,26.30,2.10,2.40, COLOR='BLUE', / Fan Shroud
&OBST XB=10.00,11.00,26.00,26.30,2.40,2.40, COLOR='BLUE', / Fan Shroud
&OBST XB=10.00,11.00,26.00,26.30,2.10,2.10, COLOR='BLUE', / Fan Shroud
&OBST XB=10.40,10.40,26.00,26.30,2.10,2.40, COLOR='RED', SURF_ID='BLOW'/
&OBST XB=25.00,26.00,26.00,26.00,2.10,2.40, COLOR='BLUE', / Fan Shroud
&OBST XB=25.00,26.00,26.30,26.30,2.10,2.40, COLOR='BLUE', / Fan Shroud
&OBST XB=25.00,26.00,26.00,26.30,2.40,2.40, COLOR='BLUE', / Fan Shroud
&OBST XB=25.00,26.00,26.00,26.30,2.10,2.10, COLOR='BLUE', / Fan Shroud
&OBST XB=25.40,25.40,26.00,26.30,2.10,2.40, COLOR='RED', SURF_ID='BLOW'/
&OBST XB=40.00,41.00,26.00,26.00,2.10,2.40, COLOR='BLUE', / Fan Shroud
&OBST XB=40.00,41.00,26.30,26.30,2.10,2.40, COLOR='BLUE', / Fan Shroud
&OBST XB=40.00,41.00,26.00,26.30,2.40,2.40, COLOR='BLUE', / Fan Shroud
&OBST XB=40.00,41.00,26.00,26.30,2.10,2.10, COLOR='BLUE', / Fan Shroud
&OBST XB=40.40,40.40,26.00,26.30,2.10,2.40, COLOR='RED', SURF_ID='BLOW'/
&OBST XB=34.40,34.40,12.0,13.0,1.80,2.10, COLOR='BLUE', / Fan Shroud
&OBST XB=34.70,34.70,12.0,13.0,1.80,2.10, COLOR='BLUE', / Fan Shroud
&OBST XB=34.40,34.70,12.0,13.0,2.10,2.10, COLOR='BLUE', / Fan Shroud
&OBST XB=34.40,34.70,12.0,13.0,1.80,1.80, COLOR='BLUE', / Fan Shroud
&OBST XB=34.40,34.70,12.50,12.50,1.80,2.10, COLOR='RED', SURF_ID='BLOW'/
&OBST XB=19.40,19.40,12.0,13.0,1.80,2.10, COLOR='BLUE', / Fan Shroud
&OBST XB=19.70,19.70,12.0,13.0,1.80,2.10, COLOR='BLUE', / Fan Shroud
&OBST XB=19.40,19.70,12.0,13.0,2.10,2.10, COLOR='BLUE', / Fan Shroud
&OBST XB=19.40,19.70,12.00,13.00,1.80,1.80, COLOR='BLUE', / Fan Shroud
&OBST XB=19.40,19.70,12.5,12.50,1.80,2.10, COLOR='RED', SURF_ID='BLOW'/
&BNDF QUANTITY='RADIATIVE HEAT FLUX'/
&BNDF QUANTITY='WALL TEMPERATURE'/
&ISOF QUANTITY='TEMPERATURE', VALUE=60.00,100.00/
&ISOF QUANTITY='VELOCITY', VALUE=5.00/
&ISOF QUANTITY='VISIBILITY', VALUE=5.00,10.00/
&TAIL /
dr_jfloyd
"... Common causes of such instabilities are mesh cells that have an aspect
ratio larger than 2 to 1..."
You have aspect ratios of 5:1.
Did you load the plot3d file (*.q) written at the last timestep to see where the solution is going unstable?
Peter
In addition to Dr Floyd's comments you have no inlet air. The 'HOLE'
you have created makes a hole in your obstruction but not through the
boundary. You can't use '&HOLE' in boundaries (page 50 of the
manual). You need to add an OPEN VENT at that location to let FDS
know that is open to the outside. In essence as you are extracting a
significant volume you're generating a vacuum which is probably the
source of the instability.
Hope that helps.
regards
Peter
>
> - Show quoted text -