{"action":"created","issue":{"url":"https://api.github.com/repos/firemodels/fds-smv/issues/2949","labels_url":"https://api.github.com/repos/firemodels/fds-smv/issues/2949/labels{/name}","comments_url":"https://api.github.com/repos/firemodels/fds-smv/issues/2949/comments","events_url":"https://api.github.com/repos/firemodels/fds-smv/issues/2949/events","html_url":"https://github.com/firemodels/fds-smv/issues/2949","id":110730129,"number":2949,"title":"Bulk density and heat output","user":{"login":"mattbilson76","id":15055988,"avatar_url":"https://avatars.githubusercontent.com/u/15055988?v=3","gravatar_id":"","url":"https://api.github.com/users/mattbilson76","html_url":"https://github.com/mattbilson76","followers_url":"https://api.github.com/users/mattbilson76/followers","following_url":"https://api.github.com/users/mattbilson76/following{/other_user}","gists_url":"https://api.github.com/users/mattbilson76/gists{/gist_id}","starred_url":"https://api.github.com/users/mattbilson76/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/mattbilson76/subscriptions","organizations_url":"https://api.github.com/users/mattbilson76/orgs","repos_url":"https://api.github.com/users/mattbilson76/repos","events_url":"https://api.github.com/users/mattbilson76/events{/privacy}","received_events_url":"https://api.github.com/users/mattbilson76/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":{"login":"mcgratta","id":11333911,"avatar_url":"https://avatars.githubusercontent.com/u/11333911?v=3","gravatar_id":"","url":"https://api.github.com/users/mcgratta","html_url":"https://github.com/mcgratta","followers_url":"https://api.github.com/users/mcgratta/followers","following_url":"https://api.github.com/users/mcgratta/following{/other_user}","gists_url":"https://api.github.com/users/mcgratta/gists{/gist_id}","starred_url":"https://api.github.com/users/mcgratta/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/mcgratta/subscriptions","organizations_url":"https://api.github.com/users/mcgratta/orgs","repos_url":"https://api.github.com/users/mcgratta/repos","events_url":"https://api.github.com/users/mcgratta/events{/privacy}","received_events_url":"https://api.github.com/users/mcgratta/received_events","type":"User","site_admin":false},"milestone":null,"comments":1,"created_at":"2015-10-09T20:25:01Z","updated_at":"2015-10-16T20:20:01Z","closed_at":null,"body":"Note - input file with a results summary follows this text.\r\n\r\nI am using the BULK_DENSITY feature now, and getting some mixed results.\r\n\r\nIt appears that once the value of BULK_DENSITY goes above some threshold that the total heat release is capped.\r\n\r\nI have an object 0.1 m * 0.1 m * 0.2 m, with a density of 100 kg/m3, total mass is 0.2 kg.  The object occupies one grid cell.  I initially thought that BULK_DENSITY = 100 kg/m3 would be a sensible limit.  Heat of combustion of my material is 30000 kJ/kg.  So this should have given about 6000 kJ of heat.    \r\n\r\nWhen I run this model I observe the following:\r\n\r\n- Total heat released at BULK_DENSITY varying from 100 kg/m3 to (about) 25 kg/m3 is around 1200 kJ (i.e. the number does not change at different values of BULK_DENSITY).\r\n- Total heat released is less than what I expected (around 6000 kJ).\r\n- The above result was based on the top face igniting (0.1 m * 0.2 m).  If I change the face to the side of the object (0.1 m * 0.1 m) the heat realeased halves.\r\n- The volume of the domain is 2.4 m by 2.4 m by 1.0 m, and therefore I don't believe I am getting near to consuming all the oxygen.\r\n- When I decrease the BULK_DENSITY to 1.0 kg/m3 I start to see the behavior I expected.\r\n\r\nIt appears to me that FDS is limiting the total heat released in some way.\r\n\r\nMy hypothesis is that it is doing the following to limit the total heat available:\r\n\r\n1) Maximum total mass of combustible fuel = area of face burning * thickness of material * density of material = A (kg).\r\n2) Maximum energy release is then capped as follows: If OBST volume * BULK_DENSITY exceeds A (see above), then the heat release is capped.\r\n\r\nThis seems too complex but it does reflect the behavior I am seeing when I run simple test cases.  I was applying BULK_DENSITY simply to compute the mass of combustible material as OBST volume * BULK_DENSITY, but something seems to be different to this if the BULK_DENSITY goes above some limit?\r\n\r\n\r\n\r\n*****INPUT FILE - RESULTS SUMMARY AT END*****\r\n\r\n&HEAD CHID='WBP-04-32', TITLE='test' /\r\n\r\n&MESH IJK=24,5,24, XB=0.0,2.4,0.0,1.0,0.0,2.4 /\r\n\r\n&TIME T_END=900.0 /\r\n\r\n&MISC INITIAL_UNMIXED_FRACTION=0.0 /\r\n\r\n&REAC FUEL='MYFUEL',FORMULA='C8H8',HEAT_OF_COMBUSTION=40000.0,SOOT_YIELD=0.01 /\r\n\r\n***\r\nMaterial density is set here, it is 100 kg/m3\r\n***\r\n\r\n&MATL ID                    = 'FABRIC'\r\n      FYI                   = 'Properties completely fabricated'\r\n      SPECIFIC_HEAT         = 1.0\r\n      CONDUCTIVITY          = 0.1\r\n      DENSITY               = 100.0\r\n      N_REACTIONS           = 1\r\n      NU_SPEC               = 1.0\r\n      SPEC_ID               = 'MYFUEL'\r\n      REFERENCE_TEMPERATURE = 200.0\r\n      HEAT_OF_REACTION      = 500.0 \r\n      HEAT_OF_COMBUSTION    = 30000.0 /\r\n \r\n&MATL ID            = 'GYPSUM PLASTER'\r\n      FYI           = 'Quintiere, Fire Behavior'\r\n      CONDUCTIVITY  = 0.48\r\n      SPECIFIC_HEAT = 0.84\r\n      DENSITY       = 1440.0 /\r\n\r\n***\r\nMaterial thickness is set here, it is 0.02 m\r\n***\r\n\r\n&SURF ID             = 'UPHOLSTERY'\r\n      FYI            = 'Properties completely fabricated'\r\n      COLOR          = 'PURPLE'\r\n      BURN_AWAY      = .TRUE.\r\n      MATL_ID        = 'FABRIC'\r\n      BACKING        = 'EXPOSED'\r\n      THICKNESS      = 0.02 /\r\n\r\n&SURF ID             = 'WALL'\r\n      DEFAULT        = .TRUE.\r\n      RGB            = 200,200,200\r\n      MATL_ID        = 'GYPSUM PLASTER'\r\n      THICKNESS      = 0.012 /\r\n\r\n***\r\nObstruction, 0.1 m * 0.2 m * 0.1 m (one grid cell) = 0.002 m3\r\nDensity = 100 kg/m3 (unless BULK DENSITY is set)\r\nHeat of combustion = 30000 kJ/kg\r\nIntegrated heat output obtained from the HRR file sum of (dt * HRR)\r\nResults from several tests at the end of this file\r\n***\r\n\r\n&OBST XB=0.8,0.9,0.2,0.4,0.4,0.5,SURF_ID='UPHOLSTERY',BULK_DENSITY=5.0 /\r\n\r\n***\r\nThis is the ignition particle, coordinates are:\r\nSide: XYZ=0.85,0.19,0.45\r\nTop:  XYZ=0.85,0.30,0.51\r\n***\r\n\r\n&SURF ID='ignitor',TMP_FRONT=1000.0,GEOMETRY='CYLINDRICAL',LENGTH=0.1,RADIUS=0.01 /\r\n&PART ID='ignitor particle',SURF_ID='ignitor',STATIC=.TRUE.,AGE=10000 /\r\n&INIT XYZ=0.85,0.30,0.51,DX=0.1,PART_ID='ignitor particle',N_PARTICLES=1 /\r\n\r\n&BNDF QUANTITY='BURNING RATE' /\r\n\r\n&TAIL /\r\n\r\n\r\n\r\n***\r\nRESULTS\r\n\r\nIf the particle ignites the side of the obstacle and bulk density is not set:\r\nHeat = 0.1 * 0.1 * 0.02 * 100 * 30000 = 600 kJ (594 kJ - ok)\r\n\r\nIf the particle ignites the top of the obstacle and bulk density is not set:\r\nHeat = 0.1 * 0.2 * 0.02 * 100 * 30000 = 1200 kJ (1179 kJ - ok)\r\n\r\nIf the particle ignites the top of the obstacle and bulk density is set to 100 kg/m3:\r\nHeat should equal = 0.1 * 0.2 * 0.1 * 100 * 30000 = 6000 kJ\r\nHeat actually is = 1174 kJ\r\n\r\nIf the particle ignites the top of the obstacle and bulk density is set to 20 kg/m3:\r\nHeat should equal = 0.1 * 0.2 * 0.1 * 20 * 30000 = 1200 kJ (1179 kJ - ok)\r\n\r\nIf the particle ignites the top of the obstacle and bulk density is set to 15 kg/m3:\r\nHeat should equal = 0.1 * 0.2 * 0.1 * 15 * 30000 = 900 kJ (893 kJ - ok)\r\n\r\nIf the particle ignites the side of the obstacle and bulk density is set to 15 kg/m3:\r\nHeat should equal = 0.1 * 0.2 * 0.1 * 15 * 30000 = 900 kJ\r\nHeat actually is = 594 kJ\r\n\r\nIf the particle ignites the side of the obstacle and bulk density is set to 5 kg/m3:\r\nHeat should equal = 0.1 * 0.2 * 0.1 * 5 * 30000 = 300 kJ (300 kJ - ok)\r\n\r\nIf the particle ignites the top of the obstacle and bulk density is set to 5 kg/m3:\r\nHeat should equal = 0.1 * 0.2 * 0.1 * 5 * 30000 = 300 kJ (300 kJ - ok)\r\n***\r\n\r\n\r\n\r\n"},"comment":{"url":"https://api.github.com/repos/firemodels/fds-smv/issues/comments/148823723","html_url":"https://github.com/firemodels/fds-smv/issues/2949#issuecomment-148823723","issue_url":"https://api.github.com/repos/firemodels/fds-smv/issues/2949","id":148823723,"user":{"login":"mcgratta","id":11333911,"avatar_url":"https://avatars.githubusercontent.com/u/11333911?v=3","gravatar_id":"","url":"https://api.github.com/users/mcgratta","html_url":"https://github.com/mcgratta","followers_url":"https://api.github.com/users/mcgratta/followers","following_url":"https://api.github.com/users/mcgratta/following{/other_user}","gists_url":"https://api.github.com/users/mcgratta/gists{/gist_id}","starred_url":"https://api.github.com/users/mcgratta/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/mcgratta/subscriptions","organizations_url":"https://api.github.com/users/mcgratta/orgs","repos_url":"https://api.github.com/users/mcgratta/repos","events_url":"https://api.github.com/users/mcgratta/events{/privacy}","received_events_url":"https://api.github.com/users/mcgratta/received_events","type":"User","site_admin":false},"created_at":"2015-10-16T20:20:00Z","updated_at":"2015-10-16T20:20:00Z","body":"Did this advice help?"}}