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S. Ferraris July 8, 2002 14:46

UDF's experts !!
Hi everybody :

I am working with UDF. I am trying to get the matrix (AMG) coefficient for each equation (Vx,Vy and Pressure correction). I could set the solver in such a way that it does not remove all the information of the matrix (i.e. Ap,reconstruccion vectors,residuals,sources,etc) , but I could not find how to get the offdiagonal elements of the matrix. (I have saw the UDF manual, but nothing appeared). I want to calculated the discretization error, and for that I need the eigenvalues of the inverse matrix, Any there knwons how to do it ?

PD: What this the reconstruction vectors ?

Thank ...a lot.

PD2 : this is a good question. Dont you think ?


Greg Perkins July 8, 2002 22:44

Re: UDF's experts !!
The best people to ask are Fluent.

But, this may or may not help.

There appears to be some macro called F_COEFF_01(f,t) and F_COEFF_10(f,t) defined in sg.h. This in turn seems to get its values directly from the AMG matrix via their definition in the sg_mem.h header file. I suggest you have a look at these variables in the .h header files.

Now these may give you something like you want - but to be honest I don't fully know these internal details. These internal details are not documented by Fluent in any manual. You'd have to request this information from them to be certain I think.


S. Ferraris July 10, 2002 08:37

Re: UDF's experts !!
Yes , you are right. These are the macro and , also , in the manuals did not appear nothing about this. Also I saw in the .h files a lot of DEFINE macro (some very interesting) . but these dont appear in the manuals (I dont know why).

I am not so sure if with this macro I could get the AMG macro coefficients , I put the option in the solver in such a way it does not delete the matrixs (Vx,Vy,P, etc) but I am not sure if it is doing the right thing.

Anyway, thank you and I am seening you are one of more experimented user in FLUENT . Arent you ?

Best regards.

And if you find something about this matter please write me.I ll do the same , if you are interesting in this.


Greg Perkins July 10, 2002 19:15

Re: UDF's experts !!
I suggest you talk to Fluent to be sure on these matters. They generally provide very good support.

These aspects aren't in the manual because what your asking is a very specific aspect of the code internal data structures etc. For the most part, users aren't concerned with this and I don't think we can expect Fluent to document everything. But I'm sure they will provide you with an answer if you request technical support on the matter.

Yes please let me know how you go.

Regards Greg

Allan July 11, 2002 15:11

Re: UDF's experts !!

You must have had good success with Fluent support. My experience has been not so good. When we pose a direct question to our support engineer on a UDF variable, we can expect at least a week with follow-up phone calls and e-mails to get an answer. Part of the problem is that our support engineer has to check with a development engineer who has to get back to him, and maybe get some clarification.

From my experience, it is faster (and more illuminating) to try and hack through the code to try and find out what the variables are.

I guess I can see why Fluent doesn't provide more documention to their users, but they could provide more comments in the header files. How do they do their own internal documentation of variables?

One response we have gotten back from Fluent is that the user-defined functions were not really intended for what we need to do with them.

I have used Fluent quite a bit since the mid-80's and have customized versions 2 and 4, but after spending some time on V6, we are looking at CFD packages from other vendors.


Greg Perkins July 11, 2002 19:15

Re: UDF's experts !!
Well, I admit it can depend on your support engineer/distributor a bit. Fluent has recently changed the one here is Australia and I've noticed a marked improvement in the service.

I did have a frustrating time in 2000/2001 and pretty well had to hack through the code in the manner you describe. Its also true that for detaield udf questins you need to get answers from the developers - most of the support engineers don't know much about the internal workings of the code. Most of my questions need to be forwarded back to the US. The bottleneck (if there's one) often resides in how this forwarding process is handled by your support engineer etc.


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