CDATA : Question about HRR variation (Gamma distribution)

[L.Rami]

Hello,

I have a question concerning the choice of the distribution for parameter variations on CDATA, I based myself on data from NUREG 2178 VOL2 section 5 which gives HRR values for motors fires using the gamma distribution function, which I tried to reproduce on CDATA, using the following code :

  &MRND ID = 'Peak HRR', DISTRIBUTION_TYPE ='GAMMA ' , ALPHA = 1.1 ,  BETA = 24.19 /
&MRND ID = 'End of Fire HRR' DISTRIBUTION_TYPE = 'CONSTANT' CONSTANT = 0 /
&MRND ID = 'Peak HRR Time Interval' DISTRIBUTION_TYPE = 'CONSTANT' CONSTANT = 500 /
&MRND ID = 'Fire Time Interval' DISTRIBUTION_TYPE = 'CONSTANT' CONSTANT = 10/
&MRND ID = 'Fire Time Decay' DISTRIBUTION_TYPE = 'CONSTANT' CONSTANT = 10/

&MFIR ID = 'Fire_generator' FIRE_ID = 'Armoire'  
FIRE_TIME_GENERATOR_IDS = 'Fire Time Interval' 'Peak HRR Time Interval' 'Fire Time Decay'
FIRE_HRR_GENERATOR_IDS = 'Peak HRR' 'Peak HRR' 'End of Fire HRR'  /  

From what I could understand the gamma distribution is defined by two parameters ALPHA and BETA, on table 5-3 of NUREG 2178 we have for class c motors an ALPHA= 1.1 and BETA= 24.19 the HRR at the 98th Percentile is 100kw, but what I got in the parametre.csv file was a HRR variation between [0 ; 0.15]kw which doesn't match with the 100kw given in the NUREG 2178, moreover the HRR distribution is a set of point clouds not compatible with a GAMMA distribution law.

I don't understand how CDATA uses the Gamma probability law to generate a distribution. Could you please clarify this point for me ? 

Thank you,
Best regards

[L.Rami]

Hello again,

 
I've noticed that on CDATA, the parameters that characterizing the gamma probability function are not defined in the same way as in the literature. For CDATA to work properly, you need to use 1/BETA rather than BETA directly.

I did the test for the motor fire example using NUREG 2178 data (ALPHA ; 1/BETA) and i got the same values as in Table 5-3 (NUREG 2178 VOL2).