non linear buckling analysis " boundary condition problem" 1

[aniket79]

hello everyone,
Currently, I am working on Plain channel section having dimensions 180 mm length, 60 mm web x 30 mm flange and 1.1 mm thickness. I have generated codes for axis symmetrical section for analysis but whenever I am running those codes, ANSYS gives me warning message (Non-linear buckling analysis) “Both solid model and finite element model boundary conditions have been applied to this model. As solid loads are transferred to the nodes or elements, they can overwrite directly applied loads”. After few minutes solution gets converged. But results obtained are different from my theoretically calculated results. results differ by 50% in ANSYS and calculated.

it would be great if any on help me out...

thanks a lot

aniket

 

[Drej]

The message means that you have applied loads (constraints) to both the solid model (the geometry - keypoints, lines, areas...) and the finite element model (directly to nodes or elements). It may be that in one part of the model you've applied these to geometry and another directly to the FE model. This is fine, but check these to make sure you have applied the loads as you expect.


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[btrueblood]

"I have generated codes for axis symmetrical section for analysis ..."

Do you mean you are using a quarter-section model for the analysis, and applying symmetry boundary conditions across the "cut" faces? If so, then you are artificially constraining the mode shapes available, since no deformation is allowed on the lines of symmetry, and thus artifically constraining the part to higher order buckling modes.

 

[aniket79]

thanks both of you

but still i am struggling with same problem.

 

[ESPcomposites]

Have you made a model without symmetry? If that model does not correlate with the hand calculation, then may be looking in the wrong direction (i.e. assuming the problem is with the symmetry application). How do you know that the problem is not something else?





Brian

http://www.espcomposites.com

 

[hacksaw]

you know the applied moment including the any weight contributions, and the dimensions of the base, than thus the stresses at any cross-section, almost any hand book will do- Marks, Roark, and so on

 

[chris9]

I think the problem is probably due to the way you have applied your constraints. For a pinned joint you need to apply constraints to allow rotation only in the plane of buckling. The FEA results should be almost identical to textbook formulas from Roark.

Chris

http://www.value-design-consulting.co.uk

 

[btrueblood]

"thanks both of you

but still i am struggling with same problem. "

Umm, maybe we have answered the wrong question. Can you post a sketch or jpg of your model, with boundary conditions (including lines/planes of symmetry if they exist) noted?