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large rotation of hinged rigid beam

large rotation of hinged rigid beam

large rotation of hinged rigid beam

(OP)
Hello,
My new workplace just has linear FEA software (for now), so can anyone help me out by running VM40 (www.kxcad.net/ansys/ANSYS/ansyshelp/Hlp_V_VM40.html) with and without NLGEOM,ON to determine the minimum rotation for which the nonlinear and linear solutions significantly differ?  Thanks for any assistance with this urgent matter!
 

RE: large rotation of hinged rigid beam

Hi,
just a small premise: "small displacements" hypothesis is the hypothesis under which the sinus of a dimension can be approximated by the dimension itsels: sin(alfa) = alfa.
So, for example: is your rigid beam rotating of more than some tenths of degrees (some thousandths of radians)? If NO, then small displacements is OK; if YES, large displacements is necessary OR you know you will use small-displacements hypothesis with larger and larger error... It's up to you.

Regards

RE: large rotation of hinged rigid beam

(OP)
Thanks, cbrn.

The large deflection solution for cantilever beams (http://users.cybercity.dk/~bcc25154/Webpage/largedeflection.htm) differs from elementary theory when delta/L > ~0.3.  For small delta, delta/L = sin(phi_0).  sin(phi_0) = phi_0 for phi_0 < ~0.3 rad (~17.5 deg).  Yes, this solution then differs when sin(phi_0) <> phi_0.

I would think, though, the condition for a difference between nonlinear and linear solutions is problem specific.  That is, the sine approximation indicates no large deflection of a cantilever beam but maybe isn't an indicator of no large rotation of a hinged rigid beam.  This would be easy to check if someone can run VM40 with and without NLGEOM,ON for 17.5 deg rotation...

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