DEVC is not within any mesh - Measuring HEATFLUX in a volume specified by XB

[ramsampath]

Hello,

I would like to output a max value of heatflux in a volume specified by XB .... where some of that volume intersects or overlaps a solid surface.

The FDS manual says the following.

"...
&DEVC XB=..., QUANTITY='TEMPERATURE', ID='maxT', SPATIAL_STATISTIC='MAX' /
causes FDS to write out the maximum gas phase temperature over the volume bounded by XB. Other
SPATIAL_STATISTIC’s are discussed below. Some are appropriate for gas phase output quantities, some
for solid phase, and some for both. Note that if XB is used for a point device without a SPATIAL_STATISTIC,
then FDS will define XYZ to be the center of the volume defined by XB.
"

In my case

However when I run fds I get the following warnings and the HEAT_FLUX is not output.

DEVC A1_HEATFLUX is not within any mesh

Could you guide me on how to get the max heat flux among in a volume specified by XB where XB overlaps the solid ?

and also similarly WALL_TEMPERATURE.

Attached is the sample FDS file (as txt) and I get the following warnings and don't get the heat flux value output.
Would really appreciate some help on this.

Thank you
Ram.
FSource_1_FDS.txt

[drjfloyd]

&DEVC ID='A1_HEATFLUX', XB=3.0273, 3.2265, 2.0669, 2.094, 2.1115, QUANTITY='NET HEAT FLUX' SPATIAL_STATISTIC='MAX' /

XB need six values.

[ramsampath]

Apologies for the overlook, it was a syntax error on my part @drjfloyd thank you for pointing out. The correct values are as follows and attached in the following fds file. I got past that error .

&DEVC ID='A1_HEATFLUX', XB=3.0273, 3.2265, 2.0669, 2.0904, 2.094, 2.1115, QUANTITY='NET HEAT FLUX' SPATIAL_STATISTIC='MAX' /

Based on a visual overlook it should overlap some solid cells.

• However this time it gives me values for MAX Heat flux as -10000000000. Wondering what I am doing wrong, maybe I overlooked another detail . Would really appreciate help on this.

FSource_1_FDS.txt

[mcgratta]

I will run this case and check it out.

[mcgratta]

I ran the case with the latest source code and I do not see this large negative value. What version of FDS are you using?

[ramsampath]

Thank you @mcgratta . The version of FDS I am using is 6.9
Fire Dynamics Simulator

Current Date : December 9, 2024 09:14:16
Revision : FDS-6.9.1-0-g889da6a-release
Revision Date : Sun Apr 7 17:05:06 2024 -0400
Compiler : Intel(R) Fortran Intel(R) 64 Compiler Classic for applications running on Intel(R) 64, Version 2021.9.0 Build 20230302_000000
Compilation Date : Tue 04/09/2024 01:25 PM

[drjfloyd]

6.9.1 release:

<style> </style>

s	C	kW/m2	C	C	kW/m2
Time	A1_TEMP	A1_HEATFLUX	DCP-A-EC_TEMP	DCP-A-EC_WALLTEMP	DCP-A-EC_HEATFLUX
0	20	-10000000000	20	-10000000000	-10000000000

[drjfloyd]

I haven't looked to see if the DEVC actually includes any wall cells but if it does, then with the current source the DCP-A-EC_WALLTMEP doesn't look right:

<style> </style>

s	C	kW/m2	C	C	kW/m2
Time	A1_TEMP	A1_HEATFLUX	DCP-A-EC_TEMP	DCP-A-EC_WALLTEMP	DCP-A-EC_HEATFLUX
0	20	0	20	0	0

[ramsampath]

@drjfloyd - are the second set of values with a different version of fds ? I was getting the big negative numbers with FDS 6.9 .

Also, attached is a representation of the volume

which defines the XB of DEVC device. It seems to be just bordering the face of the OBST. Perhaps that's the issue ? Does it need to penetrate the OBST in order to correctly measure ? If so I can increase the bounds of the XB.

Thank you.

[drjfloyd]

As noted in my post the second set was "the current source"

It is best if the XB slightly overlaps the wall cells. As noted in the User's Guide

"You can further limit the search by using the sextuplet of coordinates XB to force FDS to only compute statistics for
surface cells within the given volume. Be careful to account for the fact that the solid surface might shift
to conform to the underlying numerical grid."

[mcgratta]

I'm going to see if I can create an ERROR if there are no values found within the search volume. That is what is happening here.

[ramsampath]

Thank you Jason and Kevin - @drjfloyd and @mcgratta - let me try to reposition the bounds so that they overlap.

[ramsampath]

Thank you much. I repositioned the bounds to make sure that they overlap in the following fds file and after a couple of adjustments I was able to get values for both WALL_TEMPERATURE and HEAT_FLUX .

This specific case had this geometry bound which was attached to the device exactly lined up with the grid ? and when i placed the device on the boundary of that wall it fell on the adjacent grid cell, so this may have been the reason it wasn't finding the surface ?

Anyway, I was able get values after making sure there was considerable overlap.

Thank you again.

[mcgratta]

I am working to check to ensure that there is at least one point included in any SPATIAL_STATISTIC evaluation. FDS includes surface cells whose centers fall within the XB volume. If it is exactly at the boundary of the volume, there is a chance that it might not be included. Best to make the volume a bit bigger to make sure you get at least one point.