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Can I prevent prescribed displacements
Posted Mar 9, 2012, 10:03 a.m. EST Modeling Tools & Definitions, Parameters, Variables, & Functions Version 4.2a 1 Reply
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Hi,
When I apply forces (in my case by boundary loads) I have add things that keep the object in place. Currently I tried to use prescribed displacement for this. However it seems that an object that is under prescribed displacement cannot be deformed (correct me if I am wrong) even in directions that aren't fixed. Now from the additional options (Symetry, Roller,... I didn't understand that much from the description). In the simple case of a cube under shear forces, what can I add that will keep it in place (solver find a solution) without impacting it's deformation in any way.
When I apply forces (in my case by boundary loads) I have add things that keep the object in place. Currently I tried to use prescribed displacement for this. However it seems that an object that is under prescribed displacement cannot be deformed (correct me if I am wrong) even in directions that aren't fixed. Now from the additional options (Symetry, Roller,... I didn't understand that much from the description). In the simple case of a cube under shear forces, what can I add that will keep it in place (solver find a solution) without impacting it's deformation in any way.
1 Reply Last Post Mar 9, 2012, 3:06 p.m. EST
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Posted:
1 decade ago
Hi
you should think "how do I hold an object in place ?
Mostly you would "fix" it by welding or gluing one face of your cube to something "very rigid".
In fact "fixed" = prescribed displacement => (0,0,0)= (u,v,w), where u,v,w are the displacment along x,y,z
So either you should fix one face or set it to prescribed displacement "0".
Another way is to model only 1/2, 1/4, or 1/8 th of the full model by applying 1,2 resp. 3 symmetry planes. this corresponds to fixng the vertex at the 3 sym. planes intersection and blocking all other 6 dof's along these sides by pairs. But such a design assumes you apply 1:2, 1:4 or 1:8 symmetric loads to your device, which might not e your desire.
A last way, is to fix one vertex=Point in prescribed dislacement all 3 direction to 0, then two other vertex of the same plane, each along 2 directions i.e. x,z and y,z + adding a "roller" condition on the boundary belonging to these 3 vertex's.
But "point loads" might give you singularities and excessively high stress concentrations, so I recommend to stay, as far as possible, with only boundary loads, and fixing
--
Good luck
Ivar
you should think "how do I hold an object in place ?
Mostly you would "fix" it by welding or gluing one face of your cube to something "very rigid".
In fact "fixed" = prescribed displacement => (0,0,0)= (u,v,w), where u,v,w are the displacment along x,y,z
So either you should fix one face or set it to prescribed displacement "0".
Another way is to model only 1/2, 1/4, or 1/8 th of the full model by applying 1,2 resp. 3 symmetry planes. this corresponds to fixng the vertex at the 3 sym. planes intersection and blocking all other 6 dof's along these sides by pairs. But such a design assumes you apply 1:2, 1:4 or 1:8 symmetric loads to your device, which might not e your desire.
A last way, is to fix one vertex=Point in prescribed dislacement all 3 direction to 0, then two other vertex of the same plane, each along 2 directions i.e. x,z and y,z + adding a "roller" condition on the boundary belonging to these 3 vertex's.
But "point loads" might give you singularities and excessively high stress concentrations, so I recommend to stay, as far as possible, with only boundary loads, and fixing
--
Good luck
Ivar