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-   -   dynamic wall (http://www.cfd-online.com/Forums/fluent/104908-dynamic-wall.html)

Mohammed Al-Azawy July 18, 2012 10:05

dynamic wall
 
Hi everybody,
I'm using FLUENT and i want to check if I can use the dynamic mesh to move the base of cylinder(piston) without UDF or should I use the UDF to move the wall.
Thanks in advance

Marion July 19, 2012 04:16

Hi,
You can use a profile file (with a table displ or velo vs. time) or the "In-Cylinder" option in Fluent.
These 2 methods are shown in the tutorials if I remember correctly.
Marion.

Mohammed Al-Azawy July 19, 2012 06:14

Quote:

Originally Posted by Marion (Post 372303)
Hi,
You can use a profile file (with a table displ or velo vs. time) or the "In-Cylinder" option in Fluent.
These 2 methods are shown in the tutorials if I remember correctly.
Marion.

Thanks Marion,
You mean I can use profile file with UDF or In-cylinder without UDF please can remember the number of tutorial in FLUENT. I want to check to use UDFD on no.
Best regards
Mohammed

Mohammed Al-Azawy July 19, 2012 06:17

Thanks Marion,
You mean I can use profile file with UDF or In-cylinder without UDF please can remember the number of tutorial in FLUENT. I want to check to use UDFD on no.
Best regards
Mohammed

Marion July 19, 2012 07:09

Hi Mohammed,
These 2 options are without udf. the in-cylinder option was designed for IC engines, and with the profile it's just points that define a curve (there is a special format for these files though).
I do not have time right now to search throught the tutorials, I'll try later.
Marion.

Mohammed Al-Azawy July 19, 2012 07:48

Thanks so much for fast reply, oki I'll try to find tutorials about these options. My geometry is Artificial heart pump ( positive displacement) like the design of pistion (pusher plate and two valves) therefore I need to move the base of cylinder as pusher plate. Please when be free help me with some tutorials about it.
Thanks again,
Regards
Mohammed

Marion July 19, 2012 08:38

tutorials
 
Unfortunately there aren't any tutorials on these particular topics on the fluent website, but there is one on a ball valve with a udf ("Using dynamic meshes"in the tutorials guide).

I don't think you need a udf when the displacement of the piston is an input (but it is useful when it is a flow driven displacement).

For the profile:
you have to write it like this and save it as filename.prof:
disp_needle 2 10 0
time x
0.00000E+00 0.00000E+00
1.00000E-06 -1.20000E-07
2.00000E-06 -2.40000E-07
3.00000E-06 -3.60000E-07
4.00000E-06 -4.80000E-07
5.00000E-06 -6.00000E-07
6.00000E-06 -7.20000E-07
7.00000E-06 -8.40000E-07
8.00000E-06 -9.60000E-07
9.00000E-06 -1.08000E-06

where
*disp_needle--> name of the profile
*2 --> number of columns
*10 --> number of points
*0 --> not sure what that is - I always leave it at 0 :p

once you've created this file, within Fluent you type
file
rtt
filename.prof
(make sure everything is in your working directory)

and then in the fluent dynamic mesh panel, choose disp_needle in the drop down list under "profile/udf".

As it is displacement vs. time the 1st column has to be time. the 2nd column can be displacement (x,y,z) velocity (v_x, v_y, v_z) , etc... There is a chapter about profiles in the Fluent user's guide.


For in cylinder feature:

As I said, this was designed for IC engine pistons. therefore you have to put in a crank angle and other parameters linked to a piston displacement. I've never used it, but it may be appropriate for your problem.

Mohammed Al-Azawy July 19, 2012 08:59

Thanks Marion,
I thind u undestood my geometry there are two valves one for the inlet and the other for the outlet, when the blood enter the chamber from the inlet valve the pusher plate will back and then the outlet valve will open the pusher plate will push the blood to it, therefore i need periodic motion for the pusher plate.
What do u think can I do it without UDF?
Regards

Marion July 19, 2012 09:18

Your question "What do u think can I do it without UDF?" isn't clear to me.

You use either option without udf: create a profile file as I described above (with displacement vs. time, 1 period and then it is repeated by Fluent automatically) or use the in cylinder parameters (crank speed / crank angle etc).

If you already have the curve displ. vs time then I would use the profile option.

Marion.

Mohammed Al-Azawy July 19, 2012 10:34

Thanks for valuable information,
let us take simple case for example just cylinder, can I use the option in-cylinder to move the base of the cylinder periodically. I will check tutorials about profile file with displacement vs. time because I don't know about it.
Regards

Marion July 20, 2012 01:47

Yes, I believe you can use the in-cylinder option to move the piston head up and down.
Marion.

Mohammed Al-Azawy July 24, 2012 09:35

Hi Mrion,
Hope u r fine, Do you have this file(cyl3d.msh), because I found the tutorial (3D Adiabatic compression) and it is good to use the option in-cylinder to move the base of the cylinder.
Regards
Mohammed

Marion July 24, 2012 10:08

No I don't have the file, I remember the tutorial but it was a while back and I didn't keep the files, sorry!
Marion.


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