# Under relaxation factors for pressure and velocity

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 October 12, 2005, 23:11 Under relaxation factors for pressure and velocity #1 Wasy Guest   Posts: n/a Hello, Do the under-relaxation factors for pressure and velocity always have to sum to unity? Thanks.

 October 13, 2005, 00:41 Re: Under relaxation factors for pressure and velo #2 zxaar Guest   Posts: n/a nope

 October 15, 2005, 13:01 Re: Under relaxation factors for pressure and velo #3 pUl| Guest   Posts: n/a zxaar is correct. And for some more info on URFs check out this answer given by an engineer at Fluent (the fourth comment to be precise): http://university.fluent.com/blog/in...&pb=1#comments

 October 26, 2005, 08:41 Re: Under relaxation factors for pressure and velo #4 Cyril Guest   Posts: n/a Hello, I'm a french student. i've got to fill in the Under relaxation factors box. But I don't know what is really these factors. Can somebody help me ? Thanks ! Cyril

November 19, 2012, 02:42
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Girish
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 Originally Posted by Cyril ;125527 Hello, I'm a french student. i've got to fill in the Under relaxation factors box. But I don't know what is really these factors. Can somebody help me ? Thanks ! Cyril
Because of the nonlinearity of the equation set, it is necessary to reduce the change of a variable from one iteration to the next. This is referred to as under-relaxation. For example, if the pressure under-relaxation factor is 0.3, the change in pressure value from one iteration to the next will be restricted to 30% of the difference between the initial value and the newly calculated value.

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