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Variable length of the boundary load

Posted 25 avr. 2013, 12:35 UTC−4 Structural Mechanics Version 4.3a 4 Replies

Fabio Greco
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Dear all,

I have a simple 2D model, that is a cantilever beam. I would apply on this beam a boundary load, but the LENGTH of the boundary load should change over time (increasing or decreasing).
Just to be more clear, I have the length of the cantilever beam equal to 100 mm. At time t=0, the length upon which the boundary load should be =0 mm, and then it should increase with time increasing, for instance at t=40 the length it's 40 mm etc. Of course, the load per unit length remains constant.

I hope I've been clear
Thank you for any suggestions

Fabio
4 Replies Last Post 26 avr. 2013, 07:37 UTC−4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 26 avr. 2013, 02:15 UTC−4
Hi

you can define a Gaussian pulse (or a rect) in Model Definition Functions, and have that modulating it's central position with time, then check the normalisation and adapt it to give you a pressure or load on your boundary, with the desired time "t" dependence

--
Good luck
Ivar
Hi you can define a Gaussian pulse (or a rect) in Model Definition Functions, and have that modulating it's central position with time, then check the normalisation and adapt it to give you a pressure or load on your boundary, with the desired time "t" dependence -- Good luck Ivar
Henrik Sönnerlind COMSOL Employee

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Posted: 1 decade ago 26 avr. 2013, 03:57 UTC−4
Hi,

I think Fabio is looking for something simpler than that. Just writing an expression in the text field for the load like

load_intensity*(x<t*0.001)

With more careful unit handling, the same expression could be written as

load_intensity*(x<t*1[mm]/1[s])

If the problem is not truly dynamic, then the parametric solver should be used, and the parameter itself could be the load extension (including units). This would give

load_intensity*(x<my_parameter)

Regards,
Henrik
Hi, I think Fabio is looking for something simpler than that. Just writing an expression in the text field for the load like load_intensity*(x
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 26 avr. 2013, 04:00 UTC−4
Hi Henrik

True it depends if you read "Length" as "extent" or "position along the boundary",
and I tend to use as far as possible continuous functions, but indeed that can also be an overkill

--
Good luck
Ivar
Hi Henrik True it depends if you read "Length" as "extent" or "position along the boundary", and I tend to use as far as possible continuous functions, but indeed that can also be an overkill -- Good luck Ivar
Fabio Greco
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Posted: 1 decade ago 26 avr. 2013, 07:37 UTC−4
Hi Henrik,

yes exactly what I needed! Thank you very much! I am simulating this simple example to try, step-by-step, dealing with modelling of a welding in Comsol (I am interested in residual stresses after the process). The boundary load that increases (the extension) over time represents the thermal stress due to the cooling of the joint. As I have also to introduce a thermal effect that "moves" along the joint (the torch), also the solution proposed by Ivar it's useful.

I don't know if I am approaching correctly or not with welding, and I have not found any Comsol tutorials on residual stress due to welding, so I should start from scratch...

Thank you if you have any other suggestion!

Fabio
Hi Henrik, yes exactly what I needed! Thank you very much! I am simulating this simple example to try, step-by-step, dealing with modelling of a welding in Comsol (I am interested in residual stresses after the process). The boundary load that increases (the extension) over time represents the thermal stress due to the cooling of the joint. As I have also to introduce a thermal effect that "moves" along the joint (the torch), also the solution proposed by Ivar it's useful. I don't know if I am approaching correctly or not with welding, and I have not found any Comsol tutorials on residual stress due to welding, so I should start from scratch... Thank you if you have any other suggestion! Fabio

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