RMS output

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Kelliann L

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Sep 26, 2022, 10:06:02 PMSep 26
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Hi all, I have have modified the simple_test example by adding thermocouples above the burner with the following devcs (please see the code attached):

&DEVC ID='INSTANT TEMPERATURE', XYZ= 0.2,1.2,0.3, QUANTITY='TEMPERATURE', TEMPORAL_STATISTIC='INSTANT VALUE' /
&DEVC ID='TIME AVERAGE TEMPERATURE', XYZ= 0.2,1.2,0.3, QUANTITY='TEMPERATURE', TEMPORAL_STATISTIC='TIME AVERAGE' /
&DEVC ID='RMS TEMPERATURE', XYZ= 0.2,1.2,0.3, QUANTITY='TEMPERATURE', TEMPORAL_STATISTIC='RMS' /

Examining the results (please see the excel attached), the RMS value is not consistent with the hand calc or anywhere near the instantaneous values. Please let me know what you think. I do not understand how the RMS is being calculated in FDS 6.7.9. Thank you!



simple_test_devc.xlsx
simple_test.fds

dr_jfloyd

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Sep 27, 2022, 7:09:34 AMSep 27
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Your spreadsheet column G formula is incorrect. 
=(D3-$J$2)^2
should be
=(B3-$J$2)^2

The average should be changed as well.

The RMS calculation uses the instantaneous temperature (INSTANT VALUE) and is computed using every FDS timestep and not just the DT_DEVC interval. 

Kelliann L

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Sep 27, 2022, 9:11:38 AMSep 27
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That worked great, thank you!
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