{"action":"created","issue":{"url":"https://api.github.com/repos/firemodels/fds-smv/issues/3112","labels_url":"https://api.github.com/repos/firemodels/fds-smv/issues/3112/labels{/name}","comments_url":"https://api.github.com/repos/firemodels/fds-smv/issues/3112/comments","events_url":"https://api.github.com/repos/firemodels/fds-smv/issues/3112/events","html_url":"https://github.com/firemodels/fds-smv/issues/3112","id":116595686,"number":3112,"title":"v5 and v6 visibility comparison","user":{"login":"bcasterline","id":15819697,"avatar_url":"https://avatars.githubusercontent.com/u/15819697?v=3","gravatar_id":"","url":"https://api.github.com/users/bcasterline","html_url":"https://github.com/bcasterline","followers_url":"https://api.github.com/users/bcasterline/followers","following_url":"https://api.github.com/users/bcasterline/following{/other_user}","gists_url":"https://api.github.com/users/bcasterline/gists{/gist_id}","starred_url":"https://api.github.com/users/bcasterline/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/bcasterline/subscriptions","organizations_url":"https://api.github.com/users/bcasterline/orgs","repos_url":"https://api.github.com/users/bcasterline/repos","events_url":"https://api.github.com/users/bcasterline/events{/privacy}","received_events_url":"https://api.github.com/users/bcasterline/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":2,"created_at":"2015-11-12T17:13:47Z","updated_at":"2015-11-12T20:49:35Z","closed_at":null,"body":"We have made quite a few visibility comparisons between v5 and v6 and wonder why the visibility is consistently lower with v6.\r\nKevin, a co-worker asked you about this at the recent Conference and you said post it to the issue tracker. \r\n\r\nthanks,\r\n\r\nBrad\r\n\r\n\r\n\r\n[mk-032-v5.txt](https://github.com/firemodels/fds-smv/files/33101/mk-032-v5.txt)\r\n[mk-032-v6-smag.txt](https://github.com/firemodels/fds-smv/files/33102/mk-032-v6-smag.txt)\r\n\r\n"},"comment":{"url":"https://api.github.com/repos/firemodels/fds-smv/issues/comments/156229765","html_url":"https://github.com/firemodels/fds-smv/issues/3112#issuecomment-156229765","issue_url":"https://api.github.com/repos/firemodels/fds-smv/issues/3112","id":156229765,"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":"2015-11-12T20:49:34Z","updated_at":"2015-11-12T20:49:34Z","body":"I'm not sure that this case indicates that there is a significant difference between 5 and 6. It is a very coarse grid which might lead to spurious conclusions. Take, for example, the following images:\r\n\r\n![mk-032-v5_1000](https://cloud.githubusercontent.com/assets/11333911/11130265/1e128fc8-8952-11e5-9ffa-74edebef5cf2.png)\r\n\r\n![mk-032-v6-smag_1000](https://cloud.githubusercontent.com/assets/11333911/11130269/265f3b5e-8952-11e5-83c3-f0670a0f8b4b.png)\r\n\r\nGoing from FDS 5 to 6, we made improvements to the velocity boundary conditions. Notice in the FDS 5 figure that the left most velocity component is more or less zero, whereas it is positive in the FDS 6 figure. That is due to subtle changes in how we handle the boundary layer, especially near OPEN boundaries and edges. \r\n![vdot](https://cloud.githubusercontent.com/assets/11333911/11130575/bd75c0ca-8953-11e5-8170-bfe9c2a8b8fa.png)\r\nI added a printout of 'VOLUME FLOW' through the ceiling vent, and noticed that in FDS 5 you are a losing a bit more smoke to the outside. Not a huge difference, but your hole is only covered by 4 grid cells, so it's hard to say if FDS 5 or 6 is more accurate. In any case, your VISIBILITY is based on the exponential of smoke concentration, and your smoke concentration is different in FDS 5 and 6 for various reasons. In this case, those reasons appear to be due more to the crude grid than any substantial change in physics. \r\n\r\nLooking over the entire case, there are a number of places where subtle changes in BCs can affect things. The connections of multiple meshes, for example. We improved that functionality going into FDS 6. \r\n\r\nCan you run this case at higher resolution and record VOLUME FLOW through the various openings. It could be that a big more smoke is escaping in the FDS 5 case which would explain the increased visibility at the end of the hall. Focus your attention more on MASS FRACTION than VISIBILITY, and try to figure out where the smoke is going. \r\n\r\n"}}