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 demaram March 17, 2010 15:07

Put "calculated" boundary condition

Hi everyone,

I'm new user in OpenFoam and I need to solve a problem where I have to use a "calculated" boundary condition and I would like to know how I do this. Could somebody help me?

 sega March 17, 2010 16:15

Quote:
 Originally Posted by demaram (Post 250469) Hi everyone, I'm new user in OpenFoam and I need to solve a problem where I have to use a "calculated" boundary condition and I would like to know how I do this. Could somebody help me? Thank your kind attention.
What is a "calculated" boundary condition to you?
A function depending on coordinates and/or time, or some kind of data (from a file for examle)?

 demaram March 17, 2010 21:01

Put "calculated" boundary condition

Hi Sega,

Let me explain what I want. I made a code to calculate the velocity field in an extrusion process with the following geometry:

I want to put, on the indicate surfaces, a manner to calculate the tangential velocity. I already put the boundary conditions like “fixedValue”, “fixedGradient”, “zeroGradient”, “symmetryPlane”, “empty” and all the conditions failed because the profile solution gets different mainly on the face number 1 when I do a comparison with the literature solution. Then, I want to put a “calculated” boundary condition and I hope it is work. This boundary condition is a friction boundary and it will be calculated by equation that it is being described on the paper that I put a part of the paper where this equation is being described.

In the indicated surface, on the above figure, I want to calculate the tangential velocity where the used equation is inside the red rectangle described in the part of the paper above. This is, I have to implement this equation in my solver to calculate the tangential velocity on the boundary surfaces. I don’t know how I can make the implementation in the OpenFoam because I don’t know the commands and I don’t know which the place I have to put this comands.

Could you help me?

Thank so much!!!

 sega March 18, 2010 05:05

Well, I can't see your images, but I have learned that you have some kind of algebraic function which describes your boundary condition?!

In this case there is a tool called groovyBC, which can apply functional boundary conditions.

 demaram March 18, 2010 08:25

Put "calculated" boundary condition

Hi Sega,

I’m sorry for the last post. Let me explain what I want. I made a code to calculate the velocity field in an extrusion process. I want to put, on the contact surface, a manner to calculate the tangential velocity in function of the internal velocity close the contact surface. How I said I tried all default boundary condition in OpenFoam but all failed. This boundary condition is a friction boundary and it will be calculated by following equation:

vt = vtp <Φ[1 – f(ε)]>

Where, vt is the tangential velocity on the contact surface, vtp is the internal velocity close on the contact surface, the terms McCauley’s < > brackets are “active” only for Φ>0. The function f(ε) is calculated by:

{ m · (pb/μb) · (hb/|vtp|) for Coulomb’s friction law
f(ε) ={
{ f · (ks/μb) · (hb/|vtp|) for constant friction law

Where, m and f are friction coefficient and friction factor, respectively, ks is the yield shear stress, and μb is the viscosity and pb is the pressure at the boundary node, hb is the distance from the internal point close of the contact surface to the boundary.

This is, I have to implement this equation in my solver to calculate the tangential velocity on the boundary surfaces. I don’t know how I can make the implementation in the OpenFoam because I don’t know the commands and I don’t know which the place I have to put this comands.

Could you help me?

I’m sorry again and thanks so much.

 sega March 18, 2010 08:50

Quote:
 Originally Posted by demaram (Post 250604) Could you help me?

Sorry, I'm a little bit confused.
You are talking about contact and boundary surfaces.
What is that?

 demaram March 18, 2010 10:12

Put "calculated" boundary condition

Hi Sega,

My work has aim to calculate the velocity field in the extrusion process. My code solve the momentuum equation for all geometry, but I wanted that the my code solve the momentuum equation for the internal field and giving me the internal velocity and the tangential velocity, that is, the velocity on the surface should be calculated by the equation that I quoted in last post.

Do you understand? If not ask me again.

Thank you so much for your kind attention.

 sega March 18, 2010 10:41

I'm still not getting it, sorry.
If you want to simulate an extrusion process you are dealing with multiphase simulation?! The multiphase solver will be capable of dealing with the whole velocity field (internal or external - whatever that is to you?? Can you explain?).

Would you be so kind to repost your images from above?
(You can't use pictures from your hard-drive)
Maybe this will help.

 demaram March 18, 2010 14:09

Put "calculated" boundary condition

1 Attachment(s)
Hi Sega

Let me try to explain again.

I made some modification in the icoFoam solver to work with extrusion process in aluminium. I am working with the geometry showed in the first figure on the attached.

I am getting to obtain the internal velocity field right when I compare with literature value. However, on the Face 1 in the first figure on the attached the velocity profile is giving different how you can see in the second figure on the attached that show the velocity contours for a central slice.

I would like to become the solutions more closely each other. How I tried all default boundary condition available in the OpeFoam I want to put a calculated boundary condition, that is, I want to calculate the tangential velocity from this before equation.

 sega March 18, 2010 14:14

Quote:
 Originally Posted by demaram (Post 250680) I want to calculate the tangential velocity from this before equation.
Ok. I think I'm finally getting what you want.
But still sounds like groovyBC to me. This tool can apply boundary conditions from functions.

 demaram March 18, 2010 14:26

Put "calculated" boundary condition

Ok, Sega

I'm going to see how this groovybc works.

If I have doubt I can write you again.

Thank you so much.

 xiaoma November 26, 2014 02:58

Quote:
 Originally Posted by demaram (Post 250497) Hi Sega, Thank your attention. Let me explain what I want. I made a code to calculate the velocity field in an extrusion process with the following geometry: [IMG]file:///C:/DOCUME~1/ADMINI~1/CONFIG~1/Temp/msohtml1/01/clip_image002.gif[/IMG] I want to put, on the indicate surfaces, a manner to calculate the tangential velocity. I already put the boundary conditions like “fixedValue”, “fixedGradient”, “zeroGradient”, “symmetryPlane”, “empty” and all the conditions failed because the profile solution gets different mainly on the face number 1 when I do a comparison with the literature solution. Then, I want to put a “calculated” boundary condition and I hope it is work. This boundary condition is a friction boundary and it will be calculated by equation that it is being described on the paper that I put a part of the paper where this equation is being described. [IMG]file:///C:/DOCUME~1/ADMINI~1/CONFIG~1/Temp/msohtml1/01/clip_image002.gif[/IMG] [IMG]file:///C:/DOCUME~1/ADMINI~1/CONFIG~1/Temp/msohtml1/01/clip_image002.gif[/IMG] In the indicated surface, on the above figure, I want to calculate the tangential velocity where the used equation is inside the red rectangle described in the part of the paper above. This is, I have to implement this equation in my solver to calculate the tangential velocity on the boundary surfaces. I don’t know how I can make the implementation in the OpenFoam because I don’t know the commands and I don’t know which the place I have to put this comands. Could you help me? Thank so much!!!
hi,
recently ,I am simulating an extrusion process too .I meet the same problem .I do not know how to set up the friction boundary condition .Have you solved the problem now?

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