CFD Online Logo CFD Online URL
Home > Forums > Software User Forums > ANSYS > FLUENT

UDS DIffusivity...

Register Blogs Members List Search Today's Posts Mark Forums Read

LinkBack Thread Tools Search this Thread Display Modes
Old   July 6, 2001, 16:18
Default UDS DIffusivity...
Posts: n/a

I'm a having a difficulty with UDS modeling. I'm trying to define the UDS Diffusivity with a UDF, and it gives me the following error.

Error: UDS_Diffusivity: unrecognized diffusivity method for UDS-0: 198172680. Error Object: ()

I've changed the UDS Diffusivity to a constant value and defined it from materials panel, but i'm still getting the same error. Since manual does not cover anything in detail about UDS modeling, can you please help me?

I'd appreciate your help...

  Reply With Quote

Old   July 8, 2001, 21:05
Default Re: UDS DIffusivity...
Greg Perkins
Posts: n/a
I suspect that you must return a value for each index that fluent calls in your UDS. From memory:

DEFINE_DIFFUSIVITY(my_uds,cell,thread,k) {

if (k==my_uds) return my_uds_value;

else return 0.0; }

this will return the value for uds k with diffusivity defined by you. All others will be zero. When you use this fucntion you will need to return the diffusivity for all uds's by checking k as above. Sometimes you may need to return a small non-zero value 1e-9 instead of 0.0 - depedning upon what other models are activated etc.
  Reply With Quote

Old   July 15, 2001, 02:58
Default Re: UDS DIffusivity...
Posts: n/a
Thanks Greg for your reply;

But the thing is I think I have a different problem, even if I try to use a constant diffusivity it's giving the same error to me.

Is there anything i'm missing? I just define one uds from uds panel, then i set the bc's and diffusivity from materials panel.

But whether i select a udf to define the diffusivity or a constant it's giving me the same error.

By the way, do i need to define uds before any iterations?

Thanks a lot...
  Reply With Quote

Old   July 15, 2001, 23:25
Default Re: UDS DIffusivity...
Greg Perkins
Posts: n/a

stick with a constant for the moment. As you pointed out if you can't get this to go, its not likely to be your user code.

Check bc in the bc panel. Pick somthing simple.

Also what have you chosen for your mass flux?? Usually its either none or the fuid phase mass flux.

I assume its steady too.

Can you perform any its. If not, it must be in your setup - so keep checking those - and maybe trying different options.

If you get some iterations, then in my experience, you can run into problems if convection is very large compared to diffusion and you have strong 'shock' like gradients in the solution. If this is the case try increasing the diffusion, at least until you start getting solutions.

Generally I found user scalars work pretty well - and are very flixble, but they do take a bit of effort.


  Reply With Quote

Old   July 16, 2001, 08:11
Default Re: UDS DIffusivity...
Posts: n/a
Thanks for you response Greg;

However, the funny thing it's not working with a constant either. I really wonder is there anything I'm missing, because I tried the same thing several times, it's not working at all...
  Reply With Quote


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On

Similar Threads
Thread Thread Starter Forum Replies Last Post
Question about UDS diffusivity zhaohui FLUENT 1 March 7, 2018 01:39
PEM modeling UDS diffusivity in mixture gemini FLUENT 6 August 7, 2012 07:37
What is UDS diffusivity of a self-defined material? aleisia FLUENT 0 March 5, 2011 22:08
Fluent 6.3 pemfc module, UDS diffusivity yerem3 FLUENT 0 January 19, 2010 03:10
Directional Diffusivity of UDS Source Greg Perkins FLUENT 2 September 4, 2003 03:02

All times are GMT -4. The time now is 17:43.