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Structural Mechanics Module
Posted Jun 15, 2016, 12:43 p.m. EDT Modeling Tools & Definitions, Parameters, Variables, & Functions, Structural Mechanics Version 5.2 2 Replies
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Dear all,
What is the difference between roller and prescribed displacement in the solid mechanics tab? I would like to model a simple rectangular film being stretched on both sides. Hence, the top and bottom face is allowed to experience stretch so should i use roller?
if anyone can help me that will be great.
What is the difference between roller and prescribed displacement in the solid mechanics tab? I would like to model a simple rectangular film being stretched on both sides. Hence, the top and bottom face is allowed to experience stretch so should i use roller?
if anyone can help me that will be great.
2 Replies Last Post Jun 17, 2016, 12:09 p.m. EDT
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Posted:
8 years ago
Hi
Turn on the Equation section and check the equations, and check the help and Doc, everything is in there ;)
Basically a roller condition says n*u=0 where n=(nx,ny,nz) the local normal vector to the surface and here u=(u,v,w) is the deformation vector.
While prescribed displacement means local boundary u-ux_value=0 and/or v-vy_value=0 and/or w-wz_value=0 that is each of the displacement are set to the desired value or expression.
These two conditions are mostly quite different in terms of boundary behavior, all depends on the surface normal orientation. A pure horizontal (X-Y) surface with normal nz=1 says n*u=nz*w=0 => w=0 and is the same condition as prescribed Displacement w=0 or wz_value=0 in my way of writing it above. In this case the are the same.
Just as a "Fixed" boundary condition is the same as a prescribed Displacement with u=0, v=0, w=0
so sometimes the BC overlap and you can get the same effect in different ways.
But now think of a sphere, the normal vector n varies for all point X,Y,Z in space hence the identity "Roller" BC = "Prescribed Displacement" BC is a bit trickier to write out, but possible.
--
Good luck
Ivar
Turn on the Equation section and check the equations, and check the help and Doc, everything is in there ;)
Basically a roller condition says n*u=0 where n=(nx,ny,nz) the local normal vector to the surface and here u=(u,v,w) is the deformation vector.
While prescribed displacement means local boundary u-ux_value=0 and/or v-vy_value=0 and/or w-wz_value=0 that is each of the displacement are set to the desired value or expression.
These two conditions are mostly quite different in terms of boundary behavior, all depends on the surface normal orientation. A pure horizontal (X-Y) surface with normal nz=1 says n*u=nz*w=0 => w=0 and is the same condition as prescribed Displacement w=0 or wz_value=0 in my way of writing it above. In this case the are the same.
Just as a "Fixed" boundary condition is the same as a prescribed Displacement with u=0, v=0, w=0
so sometimes the BC overlap and you can get the same effect in different ways.
But now think of a sphere, the normal vector n varies for all point X,Y,Z in space hence the identity "Roller" BC = "Prescribed Displacement" BC is a bit trickier to write out, but possible.
--
Good luck
Ivar
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Posted:
8 years ago
Thanks. I found the solution. Instead of using stationary study, I used time dependent and it worked. i was able to observe the film experiencing stress tensile on both ends