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# Nonlinear static analysis with LGDISP

Hey everyone,

I've been trying to simulate a stent model in Femap and after a several try outs and with your help I've been able to go a little further in my model. Although, now I'd like to ask what influence does the use of LGDISP in a nonlinear static analysis (#10) has?

In the first steps in femap I simulated the same model with a linear elastic material and I was able to use this type of analysis, with LGSTRN and LGDISP both activated. But now that I'm using a shape memory alloy as a material, I'm not able to run the analysis with LGDISP on. Does anybody know why?

The fatal error I get says that there's no convergence.

I'd be grateful to have any responses at all every one of them is worth a try!

Solution
Solution
Accepted by topic author AndreiaSantos
2 weeks ago

## Re: Nonlinear static analysis with LGDISP

[ Edited ]

Dear Andrea,
With Linear Static analysis in NX NASTRAN (SOL101) not matter if you activate LGDISP or not, is useless because in linear static analysis is not supported, we run small displacements always.

In nonlinear static analysis (SOL106) the parameter LGDISP activate the large displacement effects, this takes account the geometric nonlinearity.

The geometric nonlinearity is characterized by large rotations which usually cause large displacements. Its effects should be significant if the deformed shape of the structure appears distinctive from the original geometry without amplifying the displacements.

If you activate large displacements effects and material nonlinearity and the solution do not converge, then you need to reduce the solution time increment (o increase the number of steps). You need to identify the reason of the solution divergence: mesh too much distorted, high load level, etc... The mesh quality need to be as better as possible. The best advice is to start with a simplest model as possible, with reduced size.

Nonlinear analysis is complex, and each problem is a world, patience!.

Best regards,
Blas.

Blas Molero Hidalgo, Ingeniero Industrial, Director
IBERISA • 48004 BILBAO (SPAIN)
WEB: http://www.iberisa.com
Blog Femap-NX Nastran: http://iberisa.wordpress.com/