# UDS

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 May 14, 2003, 02:52 UDS #1 sebeci Guest   Posts: n/a Sponsored Links Hello to all I want to solve two coupled equations in the form bellow by UDS but for introducing the time derivative we have three options in Fluent: Default,none and UDF. If I choose Default, both of time derivative will remain. so we have d(fi1)/dt-D.(gama1.D(fi1))=Source1 d(fi2)/dt-D.(gama2.D(fi2))=Source2 If I choose None ,both of time derivative will omit. 0 -D.(gama1.D(fi1))=Source1 0 -D.(gama1.D(fi1))=Source1 In UDF I couldn't do that. So,how do I define this two equations? d(fi1)/dt-D.(gama1.D(fi1))=Source1 0 -D.(gama2.D(fi2))=Source2 Thanks in addvance

 May 14, 2003, 08:15 Re: UDS #2 jeroen Guest   Posts: n/a In the UDF DEFINE_UDS_UNSTEADY(name, c, t, i, apu, su) the i is the counter of the UDS's. So with an if statement you can define two different time derivatives for your two UDS's. More information on fluent 6.1 UDF-manual chapter 4.3.20.

 May 14, 2003, 08:31 Re: UDS #3 sebeci Guest   Posts: n/a Thanks for your reply But,If I set apu and su to zero, It takes an error and gives AMG error.

 May 14, 2003, 11:26 Re: UDS #4 jeroen Guest   Posts: n/a Take for the option time derivative for UDS none and incorporate the time derivative of one UDS in a define_source because the two terms A and B of a source term are equal to su and apu.

 May 15, 2003, 00:33 Re: UDS #5 sebeci Guest   Posts: n/a Thanks But,how could I define time derivative.

 May 15, 2003, 05:45 Re: UDS #6 jeroen Guest   Posts: n/a The example in the udf manual for DEFINE_UDS_UNSTEADY is nothing more than the time derivative rewritten to use it in that UDF. So you can just copy that.

 May 17, 2003, 05:20 Re: UDS #7 sebeci Guest   Posts: n/a Thanks again But,If you can please explain about it more. If you have any example please write it down. sebeci,

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