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Old   May 14, 2003, 02:52
Default UDS
  #1
sebeci
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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

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Old   May 14, 2003, 08:15
Default Re: UDS
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jeroen
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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.
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Old   May 14, 2003, 08:31
Default Re: UDS
  #3
sebeci
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Thanks for your reply But,If I set apu and su to zero, It takes an error and gives AMG error.

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Old   May 14, 2003, 11:26
Default Re: UDS
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jeroen
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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.
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Old   May 15, 2003, 00:33
Default Re: UDS
  #5
sebeci
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Thanks

But,how could I define time derivative.

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Old   May 15, 2003, 05:45
Default Re: UDS
  #6
jeroen
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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.
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Old   May 17, 2003, 05:20
Default Re: UDS
  #7
sebeci
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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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