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IvanCFD February 8, 2010 11:24

simulation of a vibrating surface

I have come across with a problem I have to solve and I don't really know how to start.

I have to simulate in Fluent 2D a vibrating surface (vibrating line).

Imagine a box (a square), the bottom edge of the square has to move up and down, not like a piston, but like a snare. That is, the ends of the edge are clamped (fixed) and the line deforms like half period of a sine wave, i.e. with its maximum deformation at the middle of the edge.

I have got a script in Matlab which simulates the up-and-down motion of each node of that edge over time, and I was wondering how I can implement it into Fluent.

Plus, I don't know if the mesh of the model has to include nodes below that bottom edge in order for Fluent to simulate those instants at which the nodes of the vibrating edge are below their rest position.

I'd really appreciate any hint about this problem.

Many thanks beforehand,


Trev February 8, 2010 14:47


I suggest you look at the Fluent tutorial with the oscillating membrane as it describes exactly what you are trying to attempt and you can easily adapt the UDF. With regards to the mesh you will need a tri mesh scheme so that the spring analogy dynamic mesh option can be activated.


IvanCFD February 8, 2010 14:52

Hi Neil,

thanks a lot for your rapid reply (that was really quick!).

I don't have the Fluent tutorial. Would you mind to give some hint about where to find it? At the moment I am looking through the Fluent 6.3 UDF Manual. It;s the only thing I've got.



IvanCFD February 8, 2010 15:02

Hi again Neil,

do you mean the Wave Tank tutorial from the following link?


Trev February 8, 2010 15:39

Its a different one to that, post your email address then I can send you the files.


IvanCFD February 8, 2010 15:47


Trev February 8, 2010 16:04

I tried emailing several times but it never got through so here is a download link instead. Hope this helps.


IvanCFD February 13, 2010 19:03

Hello Neil,

first of all, thanks a lot, because that tutorial you sent me about, amongst other things, a membrane oscillating sinusoidally is simply great. Actually that case is even more complicated than mine.

Therefore, I started to replicate that tutorial. Everything was alright until I get the moment of building the UDF...

I'm going through a nightmare trying to make the UDF work:

When I loaded the UDF for the first time I got the following message:

- "nmake" not recognized as an internal or external command, operable program or batch file.

I saw out there that it is an issue related to the interaction between Fluent and Visual Studio To solve it, during the installation process, one needs to select the "register environment variables" option. However, I didn't saw such option during the Fluent installation. This is what I did step by step:

1) Install full Microsoft Visual Studio 2008.

2) Install Windows-based Fluent.

3) Go to "Start" --> "All Programs" --> "Fluent Inc Products" --> "Fluent 6.3.26" --> "Set Environment"

After doing all that, I still couldn't load my UDF. Same error message.

Then, I downloaded nmake.exe and installed at \Fluent.Inc\fluent6.3.26\ntx86 and also at WINDOWS\system32, I opened a command prompt and executed nmake. After doing all this, back on Fluent I was able to get rid of the nmake error message.

However I now get another error message:

Opening library "libudf"...
Error: open_udf_library: (...)

I installed Visual Studio 2008 and I didn't see at any step whether path to be set or not. But after doing the "Set Enviroment" thing mentioned above I checked that PATH is at ntx86 indeed.

Would you know what I'm missing?

Many thanks beforehand,


Trev February 15, 2010 15:24

You need to open Fluent through the visual studio command prompt.


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