cylindrical BC's for rotational model

Hello Dave,

it seams that we indeed need cylinder coordinates in Code Aster .

You can reach with LIAISON_DDL what you request:

[code:1]
radial=AFFE_CHAR_MECA(MODELE=modxx,
LIAISON_DDL=(_F(NOEUD=('N1','N1',), DDL=('DX','DY'),COEF_MULT=(Y1,-X1),COEF_IMPO=0.0),
_F(NOEUD=('N2','N2',), DDL=('DX','DY'),COEF_MULT=(Y2,-X2),COEF_IMPO=0.0),
.....
[/code:1]

so there is an internal coupling of the nodes N1(X1,Y1,..), N2(X2,Y2,..) by the relation:
Y1*ux1 - X1*uy1 = 0.0 ( or <(Y1,-X1),(ux1,uy1)>=0, dotproduct zero)
Y2*ux2 - X2*uy2 = 0.0 ...

assuming that the origin (0,0,0) is on the centre of the rotation axis and the z axix is the axial direction of your rotation axis. If the origin is not on the centre the relationship can easily extended to (Y1-Yc)*ux1 - (X1-Xc)*uy1 = 0.0. A random direction of the rotation axis makes it a bit more complicated.
As far as I know the LIAISON_DDL keyword is only valid for small displacements/rotations.

To obtain the coordinates of the requested nodes see eg. zzzz189a.comm in the astest directory. This also provides an example of the LIAISON_DDL keyword.
BTW: is there a way to directly substitude the coordinates into the LIAISON_DDL command? I couldnot figure it out yet.

Solid elements have no rotational dofs, so you cannot constrain them.<br /><br />Post edited by: Kees Wouters, at: 2010/04/06 12:00

Hoi Dave

I think the restriction of the movement is not restricted to 45 degrees.

eg, the LIAISON_DDL command is:
Y1*ux1 - X1*uy1 = 0.0

nodal coord
(+1.0, 0.0,z) --&gt; uy1 = 0 --&gt; 'vertical' movement
(-1.0, 0.0,z) --&gt; uy1 = 0 --&gt; 'vertical' movement
( 0.0, +1.0,z) --&gt; ux1 = 0 --&gt; 'horizontal' movement
( 0.0, -1.0,z) --&gt; ux1 = 0 --&gt; 'horizontal' movement
( 0.7, 0.7,z) --&gt; ux1 = uy1 --&gt; -45 degree movement

so the movement should be a rotation around the z-axis with this constrains.
If you want eg no rotation but accept a radial expansion use: Y1*ux1 + X1*uy1 = 0.0.
So indeed, depending on the coordinate of the nodes, you need to define a different LIAISON_DDL command.
But maybe the suggestion on de CA forum is helpful also, using DNOR on a ''shell'' elements on the cylinder face.

kind regards - kees