Modelling Compression of Material at a Rate

Topics: Compression, 4.2a

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Adrian Li

Adrian Li

January 17, 2013 1:03am UTC

Modelling Compression of Material at a Rate

Hello,

I am a beginner to COMSOL 4.2a and I would like to build a simple model where a material (a cylindrical block of polymer) is compressed at a rate of 10 mm/min.

Using Solid Mechanics, I was able to construct the cylinder and apply a boundary load. However, this is just an instantaneous load.

My question is how do I go about implementing a compression of the material at a rate of 10mm/min?

Thanks for your help!

-Adrian

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Ivar Kjelberg

Ivar Kjelberg

January 17, 2013 6:40am UTC in response to Adrian Li

Re: Modelling Compression of Material at a Rate

Hi

you can work in th time domain, and say the displacement is 10[mm/s]*t, but try to smoothen the displacement velocity as you will get many transient at the beginning around t=0, one way to improve is to remove the inertial terms (2nd order derivatives) but then you remove all wave propagations. But you can also, if the time behaviour is not the essential use a stationary parametric sweep and increase either the force load with a parameter or impose a displacement with a parameter. You loose the time response but you see the displacement force response, interesting in particular if your material is nonlinear, or for large deformations

--
Good luck
Ivar

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Adrian Li

Adrian Li

January 17, 2013 5:41pm UTC in response to Ivar Kjelberg

Re: Modelling Compression of Material at a Rate


Hi

you can work in th time domain, and say the displacement is 10[mm/s]*t, but try to smoothen the displacement velocity as you will get many transient at the beginning around t=0, one way to improve is to remove the inertial terms (2nd order derivatives) but then you remove all wave propagations. But you can also, if the time behaviour is not the essential use a stationary parametric sweep and increase either the force load with a parameter or impose a displacement with a parameter. You loose the time response but you see the displacement force response, interesting in particular if your material is nonlinear, or for large deformations

--
Good luck
Ivar


Thank you Ivar. I will try your suggestions and see where I can get.

Thanks,
-Adrian

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Adrian Li

Adrian Li

January 17, 2013 10:17pm UTC in response to Adrian Li

Re: Modelling Compression of Material at a Rate

Update:

I tried to apply a prescribed velocity and conducted a time-dependent study. However, I am getting a

"Failed to find a solution" error message.

It says that there are void equations (empty rows in matrix) and returned solution is not converged.

Looking up previous discussions, it seems that this error could be tied to the size of the mesh. However, I have tried different mesh sizes with no avail.

Any suggestions would be great!

Thanks!
-Adrian

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Ivar Kjelberg

Ivar Kjelberg

January 18, 2013 6:53am UTC in response to Adrian Li

Re: Modelling Compression of Material at a Rate

Hi

are you using a segregated iterative solver or a direct one, perhaps the direct one would work (if you have enough RAM)

--
Good luck
Ivar

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Nagi Elabbasi

Nagi Elabbasi
Certified Consultant
Veryst Engineering

January 18, 2013 3:17pm UTC in response to Ivar Kjelberg

Re: Modelling Compression of Material at a Rate

Hi Adrian,

Are you getting this error message right at the start of the analysis or do you get a partial solution? If at the start then try ramping up the velocity gradually starting at zero as Ivar suggested earlier. Getting an initial solution should be easy since there are no applied loads. Consider also changing the time stepping setting in the transient solver from Generalized Alpha to BDF. I found the BDF to be easier to converge for some problems.

Nagi Elabbasi
Veryst Engineering

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