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Simulate 2D steady flow in a collapsible tube, need big help! Thank you very much!
Posted Mar 8, 2011, 1:03 a.m. EST Fluid & Heat, Mesh, Structural Mechanics Version 4.1 5 Replies
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Dear Sir/Madam,
I am really a new beginner for Comsol 4.1, and it really drive me to die!
My project is about simulating the 2D steady flow in a collapsible tube which envolves the Navier-Stokes Equation for incompressible Newtonian Fluid; Structure Mechanics and ALE moving mesh!
I don't know how to decouple these three models and how to use the moving mesh, like material frame and surface frame, I spend lots of time to read the papers, but it still sucks!
And also I was confusing about how to set the solid mechanics, because in the membrane will be the surface tension and pressure difference across the membrane
P inside-P exteranl+2*H*T=0
And I don't know how to draw the geometry to display the external pressure! In the structure mechanics modle, I cannot find the place for me to choice the membrane, all are domains! No boundary!
If somebody can give me some instructions or some similar models for me to learn, I will be so appreciate!
Waiting for some nice person to help me !
I am really a new beginner for Comsol 4.1, and it really drive me to die!
My project is about simulating the 2D steady flow in a collapsible tube which envolves the Navier-Stokes Equation for incompressible Newtonian Fluid; Structure Mechanics and ALE moving mesh!
I don't know how to decouple these three models and how to use the moving mesh, like material frame and surface frame, I spend lots of time to read the papers, but it still sucks!
And also I was confusing about how to set the solid mechanics, because in the membrane will be the surface tension and pressure difference across the membrane
P inside-P exteranl+2*H*T=0
And I don't know how to draw the geometry to display the external pressure! In the structure mechanics modle, I cannot find the place for me to choice the membrane, all are domains! No boundary!
If somebody can give me some instructions or some similar models for me to learn, I will be so appreciate!
Waiting for some nice person to help me !
5 Replies Last Post Mar 9, 2011, 1:43 a.m. EST
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Posted:
1 decade ago
Can someone give me some suggestions? Please:)
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Posted:
1 decade ago
I attached my file, I know it is not right, but I don't know how to fix it!
Attachments:
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Posted:
1 decade ago
Hi
first of all you should start 1 physics at the time, then later, once you master each, you can start to couple them.
Some remarks:
if you do not use some physics at least disable them (if not deleting them) as otherwise COMSOL will attempt to add the dependent variables to the solver
with your fluid flow, you have defined an inlet, but no outlet, the fluid entering must be allowed to excit somewere, otherwise its not a collaps but a blow-out that you will observe
To get a fluid flow to run quickly in a model, you shoudl add some initial conditions on the velocity (an approximate v^2 profile across the tube section is OK, then add some pressure drop (i.e. simple analytical Poiseille value is OK) This will strongly improve your convergence.
For the ALE (later you will need it if you want to collaps your stube) you could define it only in the collapsing region, not really required to fill the full tube length with ALE (for that you need two limiting borders on each side of the collaps.
With 1 domain full of fluid, you cannot add any "solid" physics without adding some new domain (area in 2D)
Finally you are in 2D and not 2D axi, sou you are in fact modelling a slab of default 1[m] depth, but as your collapsing tube destroys the symmetry you cannot really work in 2D-axi aou you should just consider 2D with a given depth (not to forget for flux extraction
--
Good luck
Ivar
first of all you should start 1 physics at the time, then later, once you master each, you can start to couple them.
Some remarks:
if you do not use some physics at least disable them (if not deleting them) as otherwise COMSOL will attempt to add the dependent variables to the solver
with your fluid flow, you have defined an inlet, but no outlet, the fluid entering must be allowed to excit somewere, otherwise its not a collaps but a blow-out that you will observe
To get a fluid flow to run quickly in a model, you shoudl add some initial conditions on the velocity (an approximate v^2 profile across the tube section is OK, then add some pressure drop (i.e. simple analytical Poiseille value is OK) This will strongly improve your convergence.
For the ALE (later you will need it if you want to collaps your stube) you could define it only in the collapsing region, not really required to fill the full tube length with ALE (for that you need two limiting borders on each side of the collaps.
With 1 domain full of fluid, you cannot add any "solid" physics without adding some new domain (area in 2D)
Finally you are in 2D and not 2D axi, sou you are in fact modelling a slab of default 1[m] depth, but as your collapsing tube destroys the symmetry you cannot really work in 2D-axi aou you should just consider 2D with a given depth (not to forget for flux extraction
--
Good luck
Ivar
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Posted:
1 decade ago
Dear Mr. ivar,
Thank you so so much! You are so nice to me! I will try to do it again as you said! My background is biology, so this engineering software really drives me to get depression!
Your remark really encourage me a lot!
Thank you!
Thank you so so much! You are so nice to me! I will try to do it again as you said! My background is biology, so this engineering software really drives me to get depression!
Your remark really encourage me a lot!
Thank you!
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Posted:
1 decade ago
Hi, sir
I try to did what you said, I am so sorry I still feel so confused! Would you please can give me more suggestions!
1.the Geometry
I add the membrane part. Is it still a slab? can you check it for me? Because if the geometry is not right, next work would be sucks!
2. I try to do the physics 'laminar flow' first. As to what you said
"To get a fluid flow to run quickly in a model, you shoudl add some initial conditions on the velocity (an approximate v^2 profile across the tube section is OK, then add some pressure drop (i.e. simple analytical Poiseille value is OK) This will strongly improve your convergence."
I do not know how to do this. Is it in 'Initial Value'---Velocity Field'---when I type V^2 in the X window, it turns to be orange color.
3. In the solid mechanics physics, my equation would be
P-Pe(external pressure)+2*H*T(tension)=0
2*H=dh^2/dx^2/(1+dh^2/dx^2)^(3/2) curvature equation
But in the model the equation is
rho*du^2/dt^2-delt stress=Fv
How can I write this into the model?
Thank you so much, sir! I am so appreciate your big help!
Thank you !
I try to did what you said, I am so sorry I still feel so confused! Would you please can give me more suggestions!
1.the Geometry
I add the membrane part. Is it still a slab? can you check it for me? Because if the geometry is not right, next work would be sucks!
2. I try to do the physics 'laminar flow' first. As to what you said
"To get a fluid flow to run quickly in a model, you shoudl add some initial conditions on the velocity (an approximate v^2 profile across the tube section is OK, then add some pressure drop (i.e. simple analytical Poiseille value is OK) This will strongly improve your convergence."
I do not know how to do this. Is it in 'Initial Value'---Velocity Field'---when I type V^2 in the X window, it turns to be orange color.
3. In the solid mechanics physics, my equation would be
P-Pe(external pressure)+2*H*T(tension)=0
2*H=dh^2/dx^2/(1+dh^2/dx^2)^(3/2) curvature equation
But in the model the equation is
rho*du^2/dt^2-delt stress=Fv
How can I write this into the model?
Thank you so much, sir! I am so appreciate your big help!
Thank you !