Urgent help: Arc-length method in ANSYS

[RJKhan]

Hi,

I am performing large deformation non-linear static analysis of a
shell pressurised radially from outside.

To account for possible "Snap-through" or Snap-back" I have activated
"Arclength method".

It simply keeps on bisecting and never stops where it needs a smaller
arc-length.
It stops when "Min arclength" is reached without convergance.

What to do? Please help.

Also, kindly help me on how to "see" the Typical "Nonlinear Force
dispplacement plot" of this analysis. I want to see the "Snap-thorugh/
back" in the plot.

Thanks

RJKhan

[Krzysztof Patralski]

Which Ansys version do you use ??

nasdak

[RJKhan]

ANSYS 8

RJ Khan

[Angel Alberich-Bayarri]

I use ANSYS 11.

Angel

-----Mensaje original-----
De: An...@googlegroups.com [mailto:An...@googlegroups.com] En nombre de
RJKhan
Enviado el: sábado, 29 de noviembre de 2008 18:01
Para: Ansys
Asunto: Re: Urgent help: Arc-length method in ANSYS

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10:59

[RJKhan]

Kindly suggest me something for the problem if u can help. I needed
the help urgently.

On Nov 28, 1:49 pm, Krzysztof Patralski <badzpie...@gmail.com> wrote:

[Krzysztof Patralski]

I suggest you to use version 5.7.1. In this version of ansys Arc-
length method is well developed. There is no workbench in this version
but the geometry is simple to include. In help you will find the
proper example of arc-length method. I did same projects with shell
buckling.

best regards

[RJKhan]

The main issue is only what values are appropriate for the "Max
Arclength radius" and Min Arclength radius" ; so I dont think I need
to give more parameters for using arclength option. Therefore I need
just to know how to decide the above Two paramters only.

At this stage (in this short time) I cant afford to revert to an older
version (i.e. 5.7)
Please give me some more specific solution.

Best regards,

RJ Khan

[Krzysztof Patralski]

Ok you're right. Do you have posibility to monitor the displacement of
the structure?? in v.5.7.1 the command is MONITOR with the parameters
exp. node number ?

[RJKhan]

Yes I can go to "Time history Post Processor". There I can select a
node and Monitor its "Nodal displacement" over "another varying
parameter"

> > > > > nasdak- Hide quoted text -
>
> - Show quoted text -

[Krzysztof Patralski]

In my opinion on the begining (before you start the ansys) you should
know the expected value of the displacement of your structure. I mean
the maximum displacement. than try to turn on the solution control
(SOLCONTROL,ON).
Min and max radius is calculated from the displacement or load I don't
know what load you introduced, but I suggest you introduce to your
solution the number of the substeps NSUBST,100 and

Reference Arc-Length Radius = Total Load (or Displacement) / NSBSTP
and

lower limit = MINARC * (Reference Arc-Length Radius)
upper limit = MAXARC * (Reference Arc-Length Radius)

If "It stops when "Min arclength" is reached without convergance." Try
to decrease the MINARC or increase the NSUBST.
During the analysis monitor the displacment of your structure. I think
you have some instability, and the buckling effect can appear

If it is possible print here your solution procedure.

good luck

[Ali Zare]

hello
what arc lenght method codes for ansysy version 15???

[dante hermoza]

You have to modify mesh size: maybe your mesh does not have a good Quality,

you can also modfify the substep number for arclen method with command: NSUBST, 100

Try with several values, 100, 200, 500

You can Change the value of the pressure, maybe it is too high: first I recommend to use a linear Eigenvalue Analysis 

them the imput pressure for arclen method can be 150% the value of eigen value method.

Those are some strategies to get a convergent Solutions

Regards

[Venu Barathan]

Good morning sir!

I am working with nonlinear buckling analysis, newton raphson method is not sufficient to converge the solution for nonlinear analysis. Arclength method is best to predict behaviour of material beyond yield point. 

My query is how to add ARCLEN ON command to workbench.

I believe that you will help for me in this case.

Thank you sir

[Rahul Rajeev]

Hello @RJKhan,

If you were able to solve the issue of convergence, please do let me know. I am facing the exact issue.

[P.M.Deshmukh]

Good Afternoon !!!

I also don't know how to run command arc length on work bench.

Regards,

Shri Praveen Deshmukh

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[Sebastian Vega]

I've used apdl command to activate the Riks method directly in workbench. It has its pros and cons, because mechanical can not interpret negative values of time (a.k.a. load multipliers) for postbuckling response, but it gets the job done. You can check this tutorial with english cc https://youtu.be/LzcjjY_Xevo

Regards,

Sebastian