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Strange behaviour when solving stick slip problem
Posted 24 nov 2015, 07:26 GMT-5 Structural Mechanics Version 5.1 2 Replies
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Hi,
I'm modeling a simple stick slip problem using a block on a beam. The beam has a prescribed sawtooth displacement which results in the block sticking to the beam at low accelerations and slipping at high accelerations.
I'm trying to solve the problem in two steps:
1) I use a stationary solver to calculate the initial position of the block on the beam (in this way i also check if the contact between the two bodies works correctly).
2) By using a time dependant solver i calculate the displacement of the block over time caused by the displacement of the beam.
My problem:
The results of the time dependant solver are not the same as what you would expect. The block jumps up from the beam, while it should move with or slip along the beam. I added a gif which shows the strange behaviour.
I tried numerous things, but I'm not getting any closer to the solution.
I hope someone can give me some more information on how to solve this problem.
The model can be found here:
drive.google.com/a/avistotech.com/file/d/0B5cJ2RDJaaYJNHRILUNaS2pwbWc/view?usp=sharing
Thanks in advance,
Janeau
I'm modeling a simple stick slip problem using a block on a beam. The beam has a prescribed sawtooth displacement which results in the block sticking to the beam at low accelerations and slipping at high accelerations.
I'm trying to solve the problem in two steps:
1) I use a stationary solver to calculate the initial position of the block on the beam (in this way i also check if the contact between the two bodies works correctly).
2) By using a time dependant solver i calculate the displacement of the block over time caused by the displacement of the beam.
My problem:
The results of the time dependant solver are not the same as what you would expect. The block jumps up from the beam, while it should move with or slip along the beam. I added a gif which shows the strange behaviour.
I tried numerous things, but I'm not getting any closer to the solution.
I hope someone can give me some more information on how to solve this problem.
The model can be found here:
drive.google.com/a/avistotech.com/file/d/0B5cJ2RDJaaYJNHRILUNaS2pwbWc/view?usp=sharing
Thanks in advance,
Janeau
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2 Replies Last Post 26 nov 2015, 11:24 GMT-5
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Posted:
9 years ago
Hi Janeau,
There are many files in your Google Drive so I could find the right model. Basically the contact formulation in COMSOL is strictly for stationary contact problems, and transient problems where inertia effects are not significant in the contact region (that is well described in the Documentation). What you are solving is an impact problem. That is not to say that it cannot be solved in COMSOL.
We do that frequently by switching to a penalty contact formulation (and friction as well) and selecting the penalty stiffness and the time step size “judiciously”. The penalty stiffness suitable for transient analysis is typically smaller than that required for stationary analyses in my opinion. That way we avoid unphysical oscillations resulting in impact problems.
Nagi Elabbasi
Veryst Engineering
There are many files in your Google Drive so I could find the right model. Basically the contact formulation in COMSOL is strictly for stationary contact problems, and transient problems where inertia effects are not significant in the contact region (that is well described in the Documentation). What you are solving is an impact problem. That is not to say that it cannot be solved in COMSOL.
We do that frequently by switching to a penalty contact formulation (and friction as well) and selecting the penalty stiffness and the time step size “judiciously”. The penalty stiffness suitable for transient analysis is typically smaller than that required for stationary analyses in my opinion. That way we avoid unphysical oscillations resulting in impact problems.
Nagi Elabbasi
Veryst Engineering
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Posted:
9 years ago
Thank you for your response.
I attached the COMSOL file.
What do you mean by "selecting the penalty stiffness and time step size judiciously" and how can i implement this in COMSOL? I've searched in other impact and contact problems but i can't seem to find more information about it.
Janeau
I attached the COMSOL file.
What do you mean by "selecting the penalty stiffness and time step size judiciously" and how can i implement this in COMSOL? I've searched in other impact and contact problems but i can't seem to find more information about it.
Janeau
Attachments: