axisymmetric problem

[katherine2011]

hi
i would like to modelize an axissymetric model i don't know what to impose in the boundary conditions ?
in the load module i choose :
1-symm/antisymm/encast
2-XSYMM
that is true what i am doing or not
thanks a lot

 

[rstupplebeen]

On the symmetry line, assuming you do not have a hole, constrain X and rotation in Z. From there it depends on your geometry and desired loading. I hope this helps.

Rob Stupplebeen

https://sites.google.com/site/robertkstupplebeen/

 

[corus]

On the symmetry line, where R=0, you don't really need to impose any restraints at all, other than perhaps a Z restraint, as these nodes will be effectively restrained anyway. Somewhere on the model you must have at least one Z restraint to prevent the thing moving off (where RZ is equivalent to XY in the view). In general I'd try to avoid using the simplistic methods of XSYMM, encastre etc. as these stop you from thinking of what the real restraints mean.

Tara

http://tinyurl.com/4ydjg7m

 

[katherine2011]

hi
thanks for your response but i did not really understand what do you mean that i must not use constraint his is my example to more understand it
In the line whre i have R=0 Iapplied XSYM
In the other lines i imposed encastre
thanks for your hellp

 

[katherine2011]

this is the file

 

[corus]

Ok. You may find a few warnings though as 2D solid axisymmetric elements don't have rotational degrees of freedom, which encastre and xsymm restraints automatically impose. You can ingnore the warnings if they appear.

Tara

http://tinyurl.com/4ydjg7m

 

[katherine2011]

yeah i have this warnings but my analysis converge without errors
thanks a lot for help

 

[rstupplebeen]

corus,
I used to not add those constraints then I believe I saw it somewhere in the manual and started adding them. I can not find it now and never saw a difference. My only guess is for imported geometry if the nodes are slightly in +X space that the constraints would not automatically be added.


Rob Stupplebeen

https://sites.google.com/site/robertkstupplebeen/

 

[katherine2011]

but normally they should be added (these conditions of axisymmetry) because it is a problem of axisymmetry also for the choice of type of elements must be chosen with axisymmetric stress.

 

[corus]

Rob, I don't think constraints are automatically added, it's just that the maths (or math) ensures the restraint at R=0. You make a good point though as imported geometry can sometimes be 'off' and a hole, even though tiny, can make a difference, so I'm told. Maybe a stress concentration appears with such a hole? It's just laziness on my part not to add restraints as I've never noticed any difference, though I usually build geometry from scratch.

Tara

http://tinyurl.com/4ydjg7m