I have a problem with realising rotation on a rigid body around a remote point.
Am I right that I can set up a center(and a coordinate system) to the rigid body using a local coordinate system (lco1 in mat_rigid keyword)? I use boundary_prescribed_motion_rigid to the part but it seems like it recalculates a center of mass and always wants to apply rotation etc. to that center, not the one I defined with lco1.
(I attached 2 videos, showing that instead of using the orangeish/green point as center of rotation (where I defined lco1), it uses one that looks to be the center of mass of the part)
Hi @kilipeti,
I looked at the videos. It was a little difficult to see the point that you want it to rotate around. Could you attach an image that highlights where it is rotating and where you want it to rotate?
Try adding "_local" to your motion card: *boundary_prescribed_motion_rigid_local
Thanks for the answer/hint!
I have found the corresponding remark in the manual:
When the RIGID option is used to prescribe rotation of a rigid body, the axis of rotation
will always be shifted such that it passes through the center-of-mass of the rigid body. By
using *PART_INERTIA or *CONSTRAINED_NODAL_RIGID_BODY_INERTIA, one can
override the internally-calculated location of the center-of-mass.
My fear was proven, setting up an lco1 in *MAT_RIGID is not enough, I had to define *PART_INERTIA for the rigid body and now it works perfectly!
@kilipeti Hello,
I am having similar issue. I did what you did;
1-Defined rigid material for the part and defined lco1 for the part where I want to be the rotation axis
2-Defined *PART_INERTIA and there I assigned cog node of the part
3- Lastly used rigid_Local option for prescribed motion
Yet, none of these worked , every time the part rotates about its original cog. What am I missing here? Thanks in advance for your reply.
Regards
Emirhan
@emirhan-dyna I'm believe you need to fill in the NODEID in the *Part_inertia to be the node id of that grey node in your image where you want the rotation center to be.
@negativevolume Unfortunately it is not about that. I had/have tried that too. Didn't work. I am starting to be skeptic about a bug in the solver. Could you take a look at the key file in the attachments. Thanks
Looks like It does not allow me to add anything to attachments. Can you see any file?
Regards
@emirhan-dyna I have been able to get a hold on this (see attached video).
Little help with *PART_INERTIA:
*C:=*-coordinate of center of mass. If nodal point, NODEID, is defined XC, YC, and ZC are ignored and the corrdinates of the nodal point, NODID, are taken as the center of mass.
So I guess XC, YC and ZC are important and it is also important that NODEID=0 and there is no nodal point (whatever that means, maybe it cannot be a *constrained_nodal_rigid_body?)...
See an example keyword snippet in my case (tm and i** values are hypothetical I guess):
*PART_INERTIA
$# title
.
$# pid secid mid eosid hgid grav adpopt tmid
7 7 7 0 0 0 0 0
$# xc yc zc tm ircs nodeid
18.71017 26.60626 15.27 4.535 0 0
$# ixx ixy ixz iyy iyz izz
0.0159222-4.2334E-41.42205E-4 0.02397787.45264E-6 0.0221
$# vtx vty vtz vrx vry vrz
14.77972-0.7745721 0.0 0.0 0.0 0.0
*MAT_RIGID
$ ID ro E pr n couple m alias
$# mid ro e pr n couple m alias
77.85000E-9 200000.0 0.3 0.0 0.0 0.00
$ cmo con1 con2 unused1
$# cmo con1 con2
1.0 0 0
$ lco A2 A3 V1 V2 V3 unused2
$#lco or a1 a2 a3 v1 v2 v3
0.0 0.0 0.0 0.0 0.0 0.0
*SECTION_SOLID
$ ID elform aet unused1
$# secid elform aet
7 13 0
*BOUNDARY_PRESCRIBED_MOTION_RIGID
$ sid dof vad lcid sf vid death birth
$# pid dof vad lcid sf vid death birth
7 3 2 2 1.0 0 0.0 0.0
...
In your *PART_INERTIA is OPTION row 6 really needed? Isn't it that local CS that causes trouble?
Hi @negativevolume I tried to upload key file. changed extension to .k it worked.
Hi @kilipeti. Thanks for your reply. In your case it seems to be working just fine.
So I guess XC, YC and ZC are important and it is also important that NODEID=0 and there is no nodal point (whatever that means, maybe it cannot be a *constrained_nodal_rigid_body?)...
As for your comment on xc,yc, zc and nodeid I tried all possible combinations. with just nodeid and without nodeid. Still rotates about its original COG.
In your *PART_INERTIA is OPTION row 6 really needed? Isn't it that local CS that causes trouble?
I also tried with/without option 6 did not work.
I attached my model named Main.k Please take a look at it and if possible please run the model. I want to make sure the problem is not specific to solver version I am using.
By the way your prescribed motion parameters confused me even more:) Is it just an example?
you did not use _LOCAL option for Prescribed motion
dof=3 (z translational motion)
