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Contact modeling and time dependent model(Structural mechanics module)
Posted Jun 26, 2009, 4:04 p.m. EDT Structural Mechanics 24 Replies
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Dear all.
I'm modeling a user-defined viscoelastic material which is time dependent case and I'd like to use contact
modeling also in my model. But I noticed that the contact model can not be used with time dependent solver.
Do you have any idea about how to figure out this problem?
My model has plane strain and PDE module.
Any comments would be appreciated.
Thank you.
Yoon
I'm modeling a user-defined viscoelastic material which is time dependent case and I'd like to use contact
modeling also in my model. But I noticed that the contact model can not be used with time dependent solver.
Do you have any idea about how to figure out this problem?
My model has plane strain and PDE module.
Any comments would be appreciated.
Thank you.
Yoon
24 Replies Last Post Oct 4, 2013, 5:56 a.m. EDT
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Posted:
2 decades ago
HI Yoon,
I had the same problem whit a contact simulation into a structural dynamic problem. I solved for this problem by defining the contact pairs among parts being in contact. and I disabled the augmented lagrangian solver (which works only for stationary problems). In other words you force comsol to solve the contact problem without calcutating the pressure field at contact interface. For your application, I think you have to:
1. define contact pair2.
2. assign the penalty normal pressure equal to E/h (where E is the estimated stiffness of your part and h is the mesh size). In this way you are modifing the default boundary constraint equation.
3. solve the problem with the time-dependent solver.
If any error, try to change the E value (more or less stiff).
Good luck
Pasquale
I had the same problem whit a contact simulation into a structural dynamic problem. I solved for this problem by defining the contact pairs among parts being in contact. and I disabled the augmented lagrangian solver (which works only for stationary problems). In other words you force comsol to solve the contact problem without calcutating the pressure field at contact interface. For your application, I think you have to:
1. define contact pair2.
2. assign the penalty normal pressure equal to E/h (where E is the estimated stiffness of your part and h is the mesh size). In this way you are modifing the default boundary constraint equation.
3. solve the problem with the time-dependent solver.
If any error, try to change the E value (more or less stiff).
Good luck
Pasquale
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Posted:
2 decades ago
Thank you for your reply, Pasquale.
Yoon
Yoon
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Posted:
2 decades ago
Hi Pasquale,
I was wondering if you could clarify part of the solution to this problem. If you use the time-dependent solver, there is no augmented lagrangian solver to disable. Any help would be great.
-Geoff
I was wondering if you could clarify part of the solution to this problem. If you use the time-dependent solver, there is no augmented lagrangian solver to disable. Any help would be great.
-Geoff
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Posted:
2 decades ago
Dear all.
I'm modeling a user-defined viscoelastic material which is time dependent case and I'd like to use contact
modeling also in my model. But I noticed that the contact model can not be used with time dependent solver.
Do you have any idea about how to figure out this problem?
My model has plane strain and PDE module.
Any comments would be appreciated.
Thank you.
Yoon
Hallo, Yoon,
I have a same problem as you, I am using PDE module to define the viscoelastic material, the mechanical model contains contact problem. But I have tried many times to solve the problem, never get result.
By the way, this moment I only define linear 3D viscoelastic material something like the viscoelastic material model of COMSOL.
Did you solve the problem, can you give me some help. Thank you!
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Posted:
2 decades ago
Hi, all.
I'm still having a convergence problem. The solver never find the converged solution.
I'm stuck, literally.
Sorry, guys.
Yoon
I'm still having a convergence problem. The solver never find the converged solution.
I'm stuck, literally.
Sorry, guys.
Yoon
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Posted:
2 decades ago
HI Yoon,
I had the same problem whit a contact simulation into a structural dynamic problem. I solved for this problem by defining the contact pairs among parts being in contact. and I disabled the augmented lagrangian solver (which works only for stationary problems). In other words you force comsol to solve the contact problem without calcutating the pressure field at contact interface. For your application, I think you have to:
1. define contact pair2.
2. assign the penalty normal pressure equal to E/h (where E is the estimated stiffness of your part and h is the mesh size). In this way you are modifing the default boundary constraint equation.
3. solve the problem with the time-dependent solver.
If any error, try to change the E value (more or less stiff).
Good luck
Pasquale
Hi, Pasquale,
When I change the E value, I can obtain convergent result, but the simulation results also change with different E value. Can you explain the principle of this method, how can the simulation results also change with different E value? Thank you!
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Posted:
2 decades ago
Here are some tips for contact modeling with time dependent solver.
1. Modify the contact pairs definition in order to use a penalty method instead of the default augmented lagrangian technique. To use a penalty contact method you just need to change the normal penalty
factor expression to E/h*n where E is the Young modulus of the material h
the element size and n a parameter that you will play with in order to improve the convergence and the accuracy of the model. Typically, the higher of n, the better. However, too high value of n leads to convergence problem. Need some trade-off.
On the other hand, the expression can be treated as a constant if your model is not linear isotropic material.
Instead of E/h*n, use constant and adjust the constant to get converged solution.
Also, I found the initial contact pressure affects the convergency too. Adjust the pressure if you need.
Sometimes, weak constraints on or off does as well if your model is highly nonlinear.
I don't know why.
2. You need to go to the solve menu > solver manager > solve for page and remove (deselect) the contact pressure variable from the list. With this method you are no longer computing for the contact pressure.
I hope this helps.
Yoon.
1. Modify the contact pairs definition in order to use a penalty method instead of the default augmented lagrangian technique. To use a penalty contact method you just need to change the normal penalty
factor expression to E/h*n where E is the Young modulus of the material h
the element size and n a parameter that you will play with in order to improve the convergence and the accuracy of the model. Typically, the higher of n, the better. However, too high value of n leads to convergence problem. Need some trade-off.
On the other hand, the expression can be treated as a constant if your model is not linear isotropic material.
Instead of E/h*n, use constant and adjust the constant to get converged solution.
Also, I found the initial contact pressure affects the convergency too. Adjust the pressure if you need.
Sometimes, weak constraints on or off does as well if your model is highly nonlinear.
I don't know why.
2. You need to go to the solve menu > solver manager > solve for page and remove (deselect) the contact pressure variable from the list. With this method you are no longer computing for the contact pressure.
I hope this helps.
Yoon.
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Posted:
1 decade ago
I've been having a lot of trouble trying to complete a similar contact analysis. I cannot seem to be able to remove the Tn_cp1 from solve for menu.. I feel like this should be a really trivial task, but I don't see a way to remove it.
John
John
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Posted:
1 decade ago
Also.. if I'm modeling an articulating surface, such as a ball and joint, do these boundaries have to be defined as contact pairs and identity pairs? or just contact pairs?
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Posted:
1 decade ago
hi, everybody i post a transient contact model which could give some hint about how to cope with this difficult problem within comsol.
the trick is here to use the segragated solver to enable convergence
the trick is here to use the segragated solver to enable convergence
Attachments:
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Posted:
1 decade ago
Hi, Louvet
Thank you for your model. I think this is really good.
Wonseok
Thank you for your model. I think this is really good.
Wonseok
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Posted:
1 decade ago
Hi, Louvet
Thank you for your model. I think this is really good.
Wonseok
Thank you for your model. I think this is really good.
Wonseok
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Posted:
1 decade ago
Hey,
The recommendation is sort of helping. The problem is converging to a solution, but I'm also workin in 3d. I seem to run the simulation and the answer isn't harmonic and the video isl ike a 1 second clip of a slight deformation. Do the setting in the solve parameters have to be BDF?
John
The recommendation is sort of helping. The problem is converging to a solution, but I'm also workin in 3d. I seem to run the simulation and the answer isn't harmonic and the video isl ike a 1 second clip of a slight deformation. Do the setting in the solve parameters have to be BDF?
John
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Posted:
1 decade ago
Also, I can't seem to appply the loading over a period of time. It seems the loading is applied instantaneously and then teh simulation runs for a few seconds with no further deformations. How can I apply the loading over a specified time?
John
John
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Posted:
1 decade ago
I'm sorry about the previous posts. Apparently, I only set the contact to be identity pairs and not contact pairs. When I set them to contact pairs, I am still getting an error..
Step Time Stepsize Res Jac Sol Order Tfail NLfail
0 0 out 100 12 100 0
Group #1: 50 6 50
Group #2: 50 6 50
Error:
Failed to find consistent initial values.
Last time step is not converged.
In the actual boundary conditions of the pair, I copied and pasted the same expression as your model. However, i replaced the E with the modulus, and the bottom portion with a mesh size of 1, and I ran the analysis. I also created a second group in the solve parameters.
John
Step Time Stepsize Res Jac Sol Order Tfail NLfail
0 0 out 100 12 100 0
Group #1: 50 6 50
Group #2: 50 6 50
Error:
Failed to find consistent initial values.
Last time step is not converged.
In the actual boundary conditions of the pair, I copied and pasted the same expression as your model. However, i replaced the E with the modulus, and the bottom portion with a mesh size of 1, and I ran the analysis. I also created a second group in the solve parameters.
John
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Posted:
1 decade ago
hi, everybody i post a transient contact model which could give some hint about how to cope with this difficult problem within comsol.
the trick is here to use the segragated solver to enable convergence
First of all, thx for your file.
I was wondering how you determined the tolerance values for u v and Tn_cp1.
Is this done by trial & error or did you realy have an idea of all this values.
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Posted:
1 decade ago
hi, everybody i post a transient contact model which could give some hint about how to cope with this difficult problem within comsol.
the trick is here to use the segragated solver to enable convergence
First of all, thx for your file.
I was wondering how you determined the tolerance values for u v and Tn_cp1.
Is this done by trial & error or did you realy have an idea of all this values.
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Posted:
1 decade ago
this file was send me by the comsol support,i have worked on a similar problem in 3D with the dimension and velocity near from this example. I didn't have to twist my mind on the tolerance because my model converge with these values. try to adapt the tolerance regarding to the dimensions,displacements and velocity in your model. Probably the tolerance on the traction unknown is more drived by the velocity. If you won't succed, try the comsol support .....
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Posted:
1 decade ago
In the boundary contact pn..
your model has the following:
E_smps/hmin_cp1_smps*min(1e-3*5^segiter,1)
where is E_smps and hmin_cp1_smps stored? When I enter this line into my 3d simulation, it can't find the values and can't run the simulation.
When I put my own values in, the simulation still will not converge.
John
your model has the following:
E_smps/hmin_cp1_smps*min(1e-3*5^segiter,1)
where is E_smps and hmin_cp1_smps stored? When I enter this line into my 3d simulation, it can't find the values and can't run the simulation.
When I put my own values in, the simulation still will not converge.
John
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Posted:
1 decade ago
Attached is my comsol file. If someone can go through it and debug it, that would be great.
I am trying to simulate a joint and cup.
Every subdomain is free.
The only boundary constraints are on the back of the cup which is constrained fixed.
As for the ball.. its stem has a force being applied on the stem boundary.
I am trying to simulate its motion given this force.
Thanks!
I am trying to simulate a joint and cup.
Every subdomain is free.
The only boundary constraints are on the back of the cup which is constrained fixed.
As for the ball.. its stem has a force being applied on the stem boundary.
I am trying to simulate its motion given this force.
Thanks!
Attachments:
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Posted:
1 decade ago
Hi, all,
I'm doing transient contact modeling. I tried to adjust the penalty factor and it works in some case. But it didn't work when finer mesh was used. I thought this may be due to smaller mesh size and I adjust the penalty factor to E/n (where n is a constant number), it still worked when coarse mesh was used and didn't work when finer mesh was used. Do you have any idea why this happened?
Any suggestion will be appreciated.
Hongqiang
I'm doing transient contact modeling. I tried to adjust the penalty factor and it works in some case. But it didn't work when finer mesh was used. I thought this may be due to smaller mesh size and I adjust the penalty factor to E/n (where n is a constant number), it still worked when coarse mesh was used and didn't work when finer mesh was used. Do you have any idea why this happened?
Any suggestion will be appreciated.
Hongqiang
Here are some tips for contact modeling with time dependent solver.
1. Modify the contact pairs definition in order to use a penalty method instead of the default augmented lagrangian technique. To use a penalty contact method you just need to change the normal penalty
factor expression to E/h*n where E is the Young modulus of the material h
the element size and n a parameter that you will play with in order to improve the convergence and the accuracy of the model. Typically, the higher of n, the better. However, too high value of n leads to convergence problem. Need some trade-off.
On the other hand, the expression can be treated as a constant if your model is not linear isotropic material.
Instead of E/h*n, use constant and adjust the constant to get converged solution.
Also, I found the initial contact pressure affects the convergency too. Adjust the pressure if you need.
Sometimes, weak constraints on or off does as well if your model is highly nonlinear.
I don't know why.
2. You need to go to the solve menu > solver manager > solve for page and remove (deselect) the contact pressure variable from the list. With this method you are no longer computing for the contact pressure.
I hope this helps.
Yoon.
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Posted:
1 decade ago
Hi there,
Which version of Comsol are you using? It must be older than 3.5, cause It isn't letting me open it. However, could you post a newer version of the file?, or could you just break it down for me step by step, cause I've already followed what says in the forum, but it ain't working.
Thank you
Which version of Comsol are you using? It must be older than 3.5, cause It isn't letting me open it. However, could you post a newer version of the file?, or could you just break it down for me step by step, cause I've already followed what says in the forum, but it ain't working.
Thank you
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Posted:
1 decade ago
What do you mean by Quasi-static contact?
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Posted:
1 decade ago
There is an error and file is not getting opened can you please run the same problem in new COMSOL version and can you please attach that model again :)
It will be a great help from your side if you do it:)
It will be a great help from your side if you do it:)