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A contact problem with transient solution

Posted 7 mag 2012, 08:39 GMT-4 Modeling Tools & Definitions, Structural Mechanics Version 4.4 3 Replies

Rowling
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Hi ,

I am trying to model a contact problem which is that rectangle 1 presses rectangle 2 to a prescribed displacement. I use a contact pair between the two rectangles. And I use both stationary solution and time-dependent solution for this question. As the results show, the stationary solution was successed, but the transient solution was failed. And the error is :
Failed to find consistent initial values.
Segregated group X2
Size of vector and sparse matrix disagree.
Last time step is not converged.

Any help will be appreciated.
models are attached.
3 Replies Last Post 8 mag 2012, 01:21 GMT-4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 7 mag 2012, 11:05 GMT-4
Hi

contact in the time domain means often collisions and bouncing, that is delicate to get the solver to converge for, but if you use small enough steps and intermediate or strict time stepping (often gen alpha is more stable as the BDF, but not always) then it mostly works out. To improve your solver tweaking start by turning off the inertial terms (main physics node)

--
Good luck
Ivar
Hi contact in the time domain means often collisions and bouncing, that is delicate to get the solver to converge for, but if you use small enough steps and intermediate or strict time stepping (often gen alpha is more stable as the BDF, but not always) then it mostly works out. To improve your solver tweaking start by turning off the inertial terms (main physics node) -- Good luck Ivar
Rowling
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Posted: 1 decade ago 7 mag 2012, 22:36 GMT-4
Hi,
Ivar, thanks a lot for your reply!

I cannot fix the problem by using smaller steps(0, 0.001,1), and intermediate or strict time stepping (and gen alpha). It still have the same error.

And I don't know the mean of "to improve your solver tweaking start by turning off the inertial terms (main physics node)", I could not find the inertial terms in my model (I use only solid mechanics here).

Hi, Ivar, thanks a lot for your reply! I cannot fix the problem by using smaller steps(0, 0.001,1), and intermediate or strict time stepping (and gen alpha). It still have the same error. And I don't know the mean of "to improve your solver tweaking start by turning off the inertial terms (main physics node)", I could not find the inertial terms in my model (I use only solid mechanics here).
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 8 mag 2012, 01:21 GMT-4
Hi

take a closer look at this tab (v4.2a), and the related doc (use Quasi static and check what happends to the equations). try an easy example beam and a fixed block, in 2D run the contact with and via an increasing loading with an without the inertial terms you will quickly understand

--
Good luck
Ivar
Hi take a closer look at this tab (v4.2a), and the related doc (use Quasi static and check what happends to the equations). try an easy example beam and a fixed block, in 2D run the contact with and via an increasing loading with an without the inertial terms you will quickly understand -- Good luck Ivar

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