{"action":"created","issue":{"url":"https://api.github.com/repos/schmie/test/issues/58","labels_url":"https://api.github.com/repos/schmie/test/issues/58/labels{/name}","comments_url":"https://api.github.com/repos/schmie/test/issues/58/comments","events_url":"https://api.github.com/repos/schmie/test/issues/58/events","html_url":"https://github.com/schmie/test/issues/58","id":90432846,"number":58,"title":"Consider implementing a maximum density difference report","user":{"login":"schmie","id":6473158,"avatar_url":"https://avatars.githubusercontent.com/u/6473158?v=3","gravatar_id":"","url":"https://api.github.com/users/schmie","html_url":"https://github.com/schmie","followers_url":"https://api.github.com/users/schmie/followers","following_url":"https://api.github.com/users/schmie/following{/other_user}","gists_url":"https://api.github.com/users/schmie/gists{/gist_id}","starred_url":"https://api.github.com/users/schmie/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/schmie/subscriptions","organizations_url":"https://api.github.com/users/schmie/orgs","repos_url":"https://api.github.com/users/schmie/repos","events_url":"https://api.github.com/users/schmie/events{/privacy}","received_events_url":"https://api.github.com/users/schmie/received_events","type":"User","site_admin":false},"labels":[{"url":"https://api.github.com/repos/schmie/test/labels/enhancement","name":"enhancement","color":"84b6eb"},{"url":"https://api.github.com/repos/schmie/test/labels/P:%20minor","name":"P: minor","color":"dcffff"}],"state":"open","locked":false,"assignee":{"login":"schmie","id":6473158,"avatar_url":"https://avatars.githubusercontent.com/u/6473158?v=3","gravatar_id":"","url":"https://api.github.com/users/schmie","html_url":"https://github.com/schmie","followers_url":"https://api.github.com/users/schmie/followers","following_url":"https://api.github.com/users/schmie/following{/other_user}","gists_url":"https://api.github.com/users/schmie/gists{/gist_id}","starred_url":"https://api.github.com/users/schmie/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/schmie/subscriptions","organizations_url":"https://api.github.com/users/schmie/orgs","repos_url":"https://api.github.com/users/schmie/repos","events_url":"https://api.github.com/users/schmie/events{/privacy}","received_events_url":"https://api.github.com/users/schmie/received_events","type":"User","site_admin":false},"milestone":{"url":"https://api.github.com/repos/schmie/test/milestones/18","html_url":"https://github.com/schmie/test/milestones/0.2","labels_url":"https://api.github.com/repos/schmie/test/milestones/18/labels","id":1177583,"number":18,"title":"0.2","description":"None","creator":{"login":"schmie","id":6473158,"avatar_url":"https://avatars.githubusercontent.com/u/6473158?v=3","gravatar_id":"","url":"https://api.github.com/users/schmie","html_url":"https://github.com/schmie","followers_url":"https://api.github.com/users/schmie/followers","following_url":"https://api.github.com/users/schmie/following{/other_user}","gists_url":"https://api.github.com/users/schmie/gists{/gist_id}","starred_url":"https://api.github.com/users/schmie/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/schmie/subscriptions","organizations_url":"https://api.github.com/users/schmie/orgs","repos_url":"https://api.github.com/users/schmie/repos","events_url":"https://api.github.com/users/schmie/events{/privacy}","received_events_url":"https://api.github.com/users/schmie/received_events","type":"User","site_admin":false},"open_issues":2,"closed_issues":10,"state":"closed","created_at":"2015-06-23T15:13:10Z","updated_at":"2015-06-23T16:29:47Z","due_on":"2011-12-16T16:59:59Z","closed_at":"2015-06-23T15:13:10Z"},"comments":5,"created_at":"2015-06-23T16:29:47Z","updated_at":"2015-06-23T16:30:08Z","closed_at":null,"body":"**Reported by miguel on 14 Oct 2011 13:11 UTC**\nI'm currently developing a set of tests against analytic solutions of Poiseuille flow in 3D. I've noticed that in order to get good match, you need to make sure that the system remains in the quasi-incompressible regime (i.e. moderate density gradients).\r\n\r\nThis is nothing new and I assume it has to do with the error of order squared Mach number that appears in the derivation of NS from LB. For a fixed maximum velocity and space step, reducing the time step reduces Mach number and therefore your error.\r\n\r\nA good example of this is the current configuration of difftest which does not give a good match with an analytic solution due to differences of density of up to 17%. Reducing time step by a factor of 4 reduces this difference down to 1.5% and gives pretty decent matches (modulo the non-zero velocity at the boundary due to bounce-back being use). See plot attached.\r\n\r\nI would therefore suggest implementing a small check for maximum density difference at the end of the simulation that gives a hint to the user about how trustworthy the results generated are.\r\n\r\n"},"comment":{"url":"https://api.github.com/repos/schmie/test/issues/comments/114563856","html_url":"https://github.com/schmie/test/issues/58#issuecomment-114563856","issue_url":"https://api.github.com/repos/schmie/test/issues/58","id":114563856,"user":{"login":"schmie","id":6473158,"avatar_url":"https://avatars.githubusercontent.com/u/6473158?v=3","gravatar_id":"","url":"https://api.github.com/users/schmie","html_url":"https://github.com/schmie","followers_url":"https://api.github.com/users/schmie/followers","following_url":"https://api.github.com/users/schmie/following{/other_user}","gists_url":"https://api.github.com/users/schmie/gists{/gist_id}","starred_url":"https://api.github.com/users/schmie/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/schmie/subscriptions","organizations_url":"https://api.github.com/users/schmie/orgs","repos_url":"https://api.github.com/users/schmie/repos","events_url":"https://api.github.com/users/schmie/events{/privacy}","received_events_url":"https://api.github.com/users/schmie/received_events","type":"User","site_admin":false},"created_at":"2015-06-23T16:30:08Z","updated_at":"2015-06-23T16:30:08Z","body":"**Modified by miguel on 15 Nov 2011 16:43 UTC**"}}