I want to converge!

[legersalazar]

Hello Forum,

I'm trying to run a non-linear analysis, but I'm having trouble getting it to converge.

I'm constantly getting this msg:

*** USER FATAL MESSAGE 4551 (NCONVG)
*** STOPPED PROBLEM DUE TO FAILED CONVERGENCE
User information:
A solution is not possible. Review NLPARM requests and modify
to select a better solution approach.

So far I've tried increasing my "convergence tolerances" but I'm still getting the same error msg.

Any suggestions?

Thank you,

Whyowhy

 

[BlasMolero]

Dear Whyowhy,
Here you are a tutorial of nonlinear static analysis using FEMAP & NX Nastran (SOL106):

http://www.iberisa.com/soporte/femap/nolineal/presion_variable_nolineal.htm

A reasonable values for nonlinear parameters are the following:

• Solution type = Static
• Number of Increments = 10
• Max. Iterations/Step = 25
• Stiffness Updates Method = 1..AUTO
• Output Control Intermediate =3..ALL
• Solution Strategy = Full Newton-Raphson

But every nonlinear problem is a world, this is the main diference between linar & nonlinear, in the second case THE CONVERGENCE IS NEVER ASURED, real like the real life. Then you must do your best to setup the nonlinear model reasonable correct from the point of view of loads, BCs, mesh quality, and also time step size, integration mthod used, convergence tolerances, etc..

Best regards,
Blas.

~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

IBERISA
48011 BILBAO (SPAIN)
WEB:

http://www.iberisa.com

Blog de FEMAP & NX Nastran:

http://iberisa.wordpress.com/

 

[rb1957]

maybe start with a linear analysis to understand how your model is working.

 

[legersalazar]

Thank you for your responses.

I'm still not converging.

Allow me to provide you with more information about my situation.

I've runned this analysis linear with no problem.

I now want to refine my analysis. I know that some components of my model have a non-linear behavior. These components are tie-rods/struts that I've modeled using SPRING/DAMPER elements.

In my linear analysis I gave an "Axial" stiffness to these elements.

In my non-linear analysis I've defined a function that I included in the "Define Nonlinear/Freq Resp Spring" card, under "Nonlinear Function Dependence" - "Force vs Displacement" under DOF 1 (I'm assuming the other DOF are for CBUSH elements).

I'm I doing this right?

Thank you,

Whyowhy