COMSOL Forums: Contact modeling and time dependent model(Structural mechanics module)

Re: Contact modeling and time dependent model(Structural mechanics module)

Tue, 17 May 2011 15:34:19 +0000

What do you mean by Quasi-static contact?

Re: Contact modeling and time dependent model(Structural mechanics module)

Tue, 05 Apr 2011 14:36:31 +0000

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 However, could you post a newer version of the file?, or could you just break it down for me step by step, cause I've already followed what says in the forum, but it ain't working.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

Re: Contact modeling and time dependent model(Structural mechanics module)

Tue, 23 Nov 2010 21:43:15 +0000

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

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.

Re: Contact modeling and time dependent model(Structural mechanics module)

Mon, 15 Mar 2010 03:43:31 +0000

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!

Re: Contact modeling and time dependent model(Structural mechanics module)

Mon, 15 Mar 2010 03:40:01 +0000

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

Re: Contact modeling and time dependent model(Structural mechanics module)

Fri, 12 Mar 2010 10:24:10 +0000

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 .....

Re: Contact modeling and time dependent model(Structural mechanics module)

Fri, 12 Mar 2010 09:04:17 +0000

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.

Re: Contact modeling and time dependent model(Structural mechanics module)

Fri, 12 Mar 2010 09:02:23 +0000

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.

Re: Contact modeling and time dependent model(Structural mechanics module)

Thu, 11 Mar 2010 19:33:37 +0000

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

Re: Contact modeling and time dependent model(Structural mechanics module)

Thu, 11 Mar 2010 19:15:56 +0000

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

Re: Contact modeling and time dependent model(Structural mechanics module)

Thu, 11 Mar 2010 19:13:36 +0000

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

Re: Contact modeling and time dependent model(Structural mechanics module)

Thu, 11 Mar 2010 15:06:30 +0000

Hi, Louvet

Thank you for your model. I think this is really good.

Wonseok

Re: Contact modeling and time dependent model(Structural mechanics module)

Thu, 11 Mar 2010 15:06:25 +0000

Hi, Louvet

Thank you for your model. I think this is really good.

Wonseok

Re: Contact modeling and time dependent model(Structural mechanics module)

Thu, 11 Mar 2010 10:52:44 +0000

Re: Contact modeling and time dependent model(Structural mechanics module)

Thu, 11 Mar 2010 09:49:19 +0000

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?

Re: Contact modeling and time dependent model(Structural mechanics module)

Thu, 11 Mar 2010 09:43:54 +0000

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

Re: Contact modeling and time dependent model(Structural mechanics module)

Thu, 13 Aug 2009 11:52:08 +0000

Re: Contact modeling and time dependent model(Structural mechanics module)

Wed, 12 Aug 2009 18:10:00 +0000

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!

Re: Contact modeling and time dependent model(Structural mechanics module)

Tue, 04 Aug 2009 18:11:18 +0000

Hi, all.

I'm still having a convergence problem. The solver never find the converged solution.
I'm stuck, literally.

Sorry, guys.

Yoon

Re: Contact modeling and time dependent model(Structural mechanics module)

Tue, 04 Aug 2009 17:44:25 +0000

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!