CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > FLUENT

stress free boundary condition

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

Like Tree1Likes
  • 1 Post By LuckyTran

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   September 22, 2015, 18:49
Default stress free boundary condition
  #1
Ari
New Member
 
Arianna
Join Date: Sep 2015
Posts: 9
Rep Power: 10
Ari is on a distinguished road
Hi everyone, does anyone know what is a "stress free" boundary condition? and how do you set that in FLUENT? I'm going to simulate the blood flow in a model of thoracic aorta. I've read some papers in which they talk about this stress free outflow BC to impose at the outlet. I've searched around but could't figure out what stress free boundary condition exactly is and how to impose it on fluent.
Any help would be really appreciated! thanks!
Ari is offline   Reply With Quote

Old   September 23, 2015, 04:23
Default
  #2
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,760
Rep Power: 71
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
Quote:
Originally Posted by Ari View Post
Hi everyone, does anyone know what is a "stress free" boundary condition? and how do you set that in FLUENT? I'm going to simulate the blood flow in a model of thoracic aorta. I've read some papers in which they talk about this stress free outflow BC to impose at the outlet. I've searched around but could't figure out what stress free boundary condition exactly is and how to impose it on fluent.
Any help would be really appreciated! thanks!

it is often equivalent to set to zero the normal derivative of the velocity components
FMDenaro is offline   Reply With Quote

Old   September 23, 2015, 17:32
Default
  #3
Ari
New Member
 
Arianna
Join Date: Sep 2015
Posts: 9
Rep Power: 10
Ari is on a distinguished road
Quote:
Originally Posted by FMDenaro View Post
it is often equivalent to set to zero the normal derivative of the velocity components
Thanks for your reply!
I also found this kind of explanation, but it still not clear to me how I'm supposed to impose this boundary condition at the outlet of my domain. I found some people talking about the use of symmetry condition in fluent but this is not clear to me since it seems to be more related to the no-slip condition at the wall and not at the outlet...
Ari is offline   Reply With Quote

Old   December 19, 2023, 13:26
Default
  #4
Senior Member
 
Matthew
Join Date: Mar 2022
Location: United Kingdom
Posts: 175
Rep Power: 4
hunt_mat is on a distinguished road
Quote:
Originally Posted by FMDenaro View Post
it is often equivalent to set to zero the normal derivative of the velocity components
from a mathematical perspective, does this come from:
[LaTeX Error: Syntax error]
I have a sheet of compressible elastic material that is resting on one edge, and the others are free to move.

I know that there is going to be no stress on the boundary and no shear. Would the above BC cover the conditions?
hunt_mat is offline   Reply With Quote

Old   December 19, 2023, 13:46
Default
  #5
Senior Member
 
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,654
Rep Power: 65
LuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura about
Latex formula showing but,

Normal derivative equal to zero is the impenetrable BC for a slip-wall. If you have a free surface of an elastic solid (which I suspect you do from your bajillion other posts) then you need the entire stress tensor going to zero. For the butted end, normal derivative of velocity going to zero is okay because that is also the impenetrable BC.
hunt_mat likes this.
LuckyTran is offline   Reply With Quote

Old   December 19, 2023, 14:12
Default
  #6
Senior Member
 
Matthew
Join Date: Mar 2022
Location: United Kingdom
Posts: 175
Rep Power: 4
hunt_mat is on a distinguished road
Quote:
Originally Posted by LuckyTran View Post
Latex formula showing but,

Normal derivative equal to zero is the impenetrable BC for a slip-wall. If you have a free surface of an elastic solid (which I suspect you do from your bajillion other posts) then you need the entire stress tensor going to zero. For the butted end, normal derivative of velocity going to zero is okay because that is also the impenetrable BC.
So set the ENTIRE tensor to be zero at the boundary? I need to think about how I derive the stress condition for the part resting on the floor.

Cheers.
hunt_mat is offline   Reply With Quote

Old   December 19, 2023, 21:12
Default
  #7
Senior Member
 
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,654
Rep Power: 65
LuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura about
Your case is 1D, your "entire" stress tensor is only one derivative
LuckyTran is offline   Reply With Quote

Old   December 20, 2023, 07:00
Default
  #8
Senior Member
 
Matthew
Join Date: Mar 2022
Location: United Kingdom
Posts: 175
Rep Power: 4
hunt_mat is on a distinguished road
Quote:
Originally Posted by LuckyTran View Post
Your case is 1D, your "entire" stress tensor is only one derivative
The 1D case is done, and I'm looking to 2D and 3D. I have seen that stress-free should really mean "traction free"? That is the vector \boldsymbol{\sigma}\cdot\hat{\mathbf{n}}=\mathbf{0}. I've seen this around the internet, and it makes sense, as it can be thought of as a force.

I'm thinking about a 2D compressible sheet with a free surface. I know that on that free surface there is no stress(or traction?) and I have the usual free surface equation derived by saying that particles on the free surface remain on the free surface.
hunt_mat is offline   Reply With Quote

Reply

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
Free Flow Boundary Condition Shabirmean OpenFOAM Running, Solving & CFD 0 December 1, 2014 13:00
Error finding variable "THERMX" sunilpatil CFX 8 April 26, 2013 08:00
No-slip condition for non-resolved boundary layer in open channel banks Lupocci Main CFD Forum 1 January 17, 2013 04:11
Defined Wall Shear Stress Boundary Condition mart.hein OpenFOAM Programming & Development 1 April 14, 2011 13:44
External Radiation Boundary Condition for Grid Interface CFD XUE FLUENT 0 July 9, 2010 03:53


All times are GMT -4. The time now is 05:59.