{"action":"opened","issue":{"url":"https://api.github.com/repos/schmie/hemeMove/issues/492","labels_url":"https://api.github.com/repos/schmie/hemeMove/issues/492/labels{/name}","comments_url":"https://api.github.com/repos/schmie/hemeMove/issues/492/comments","events_url":"https://api.github.com/repos/schmie/hemeMove/issues/492/events","html_url":"https://github.com/schmie/hemeMove/issues/492","id":96333751,"number":492,"title":"Wall normal direction convention in HemeLB","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":[],"state":"open","locked":false,"assignee":null,"milestone":null,"comments":0,"created_at":"2015-07-21T14:39:27Z","updated_at":"2015-07-21T14:39:27Z","closed_at":null,"body":"**Reported by miguel on 6 May 2014 12:29 UTC**\nWhile working on the retinal blood flow paper rebuttal I think I found a bit of an inconsistency in HemeLB's treatment of wall normals.\r\n\r\nIf I understood correctly, the setup tool generates outwards pointing wall normals. This becomes a bit of an issue if one wants to compute traction with the typical formula t = Tn, where t is traction, T the stress tensor, and n is the inwards pointing normal (isn't it?).\r\n\r\nTo correct for this, HemeLB computes -T as the stress tensor, so that t will point in the right direction. At some point we made -T accessible through the property extraction framework as the stress tensor. This is misleading if not plain wrong.\r\n\r\nI propose:\r\n * Computing T instead of -T as the stress tensor.\r\n * Change the direction of the wall normal before computing traction, i.e. t= T * -n\r\n * Update documentation (NewGeometryFiles) to make it explicit that the normals in a .gmy file are outward pointing.\r\n\r\nRupert, your views please?"}}