Hello everyone,
I am trying to model and analyze a Chiral Graphene Nanosheet in ANSYS MAPDL. I am done with the modeling and boundary conditions part. But when I go for solution, I am stuck with this error message which says "Degree of freedom limit exceeded. Then value of ROTZ at a particular node has exceeded the limit". I checked for all constraints and loading conditions, but everyting seems to be ok. Any kind of clue that might rectify the problem would be of great help. Thanks in advance.
I think the model is not properly constrained
If possible can you explain what boundary conditions you applied and what element you taken and weather it 2d or 3d model, than I can help you
Dear Rayudu Nithin manohar,
Thanks for your concern. I have considered BEAM4 element for modeling the 2-D sheet. E considered = 5.49e-6 (according to concept of molecular dynamics for Carbon Nanotubes), and m=0.33. Boundary conditions:
The lowermost row of nodes of the sheet are fixed (Displ=0)
The uppermost row of nodes are applied with a vertical load (Fy) of 200N.
I am attaching a picture of the sheet herewith (in case required for reference).
i think you want to do 2d analysis and you used 3d element element (6 dof) do one thing constrain Z (displacement, rotation)dof on all nodes
or take beam 3 which is 2d element and solve
if you want to do 3d analysis then try to decrease the load/poissons ratio or increase the modulus value. I think due to poisson's effect the structure may be bending more than allowable
Dear Rayudu Nithin manohar,
Thanks for your suggestions. I tried with beam 3 and applying constraints(z displ and rot) on all nodes, but it didn't work out. However increasing value of E solves the problem, but that won't give me the correct results. I am clueless again! :-P
dont worry
can you tell me what error came when you used beam3 element
degrees of freedom exceeded means ,it is due to over constraints or fix in xy translation,in roatation, apply the force in only z direction and use 2d elements to solve
Dear Rayudu Nithin Manohar,
Sorry for the delay in reply. I am attaching a screenshot of the error message. Please check.
Dear Emon barua
i am also getting same error message.did you find any solution?
Thank you
Dear Vijay,
This kind of error message usually appears when there is an error in defining the material properties or error in defining the constraints. In my case, I was committing a mistake in defining the young's modulus of the structure. There was a mistake in conversion of the units due to which the stiffness of the structure was too less than required. Hope you can sort it out.
Regards,
Emon
the last error message indicates that there are nodes that are not constrained = when u apply the load on unconstrained model the displacement value go to infinite.
I was the same problem when I was changed the thickness of shells in my model and re-meshing it. Although I apply displacement constraint again (BCs of my model), but the error appeared when I execute the solve command.
After reading some weblogs I simply try this in GUI:
Main Menu>Preprocessor>Numbering Ctrls>Merge Items
Then in appeared window I select "all" items.
This solved the problem and error was disappeared.
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