
Re: The rod does not want to fit.
Jared Conway Feb 9, 2014 4:07 PM (in response to Afran Menu)why not cut it down the middle and leverage symmetry to simplify your problem further?
what is the error that you're getting when you try to solve it?
i'd suggest to start a bit simpler
run your analysis without contact to make sure you can get things to move the way you want.
then you can move to adding the contact.

Re: The rod does not want to fit.
Afran Menu Feb 10, 2014 6:04 AM (in response to Jared Conway)Hello Jared, Thanks for responding.
The problem get solved quickly enough with the 2D simplification. I know that he problem moves as I want because I already solved it by imposing the lowest point of the rod to move 22 mm down. Please, click the attached gif to see the full movement.
Now, would like to to solve it again by applying a force.
If I remove the contact restrictions, problem won't to be solved because the rod will move as a free body.
The solution process progresses without mayor problems, but only till it reaches a point, and no matter what modifications I do: the nonlinear solution process progresses stops always at the same point, the point where, in the linear solution, the sheet opens too much and loses contact with the rod.
I hope my description is understandable...

Re: The rod does not want to fit.
Jared Conway Feb 10, 2014 1:11 PM (in response to Afran Menu)If I remove the contact restrictions, problem won't to be solved because the rod will move as a free body.
>correct, this is a troubleshooting method. to make sure that the full "throw" is acheived.
Now, would like to to solve it again by applying a force.
>this isn't necessary. just read the reaction force on the displacement. that will tell you how much force it took to create the motion.

Re: The rod does not want to fit.
Afran Menu Feb 10, 2014 2:24 PM (in response to Jared Conway)Hi Jared, thanks again for your time,
this isn't necessary. just read the reaction force on the displacement. that will tell you how much force it took to create the motion.
I am interested in the force and the problem is that I cannot plot force vs time, so I have to review every solution step in order to find the max reaction force in the lowest support (what I find very tedious). Besides, I did it and the results do not convince me (the thickness of the sheet = 1 mm AISI 304; rod = 25 mm): max force applied = 3.11 N... about 300 grams seems too little for me.
Anyway, even if the result is correct, I do not consider it unnecessary, just because I want to solve it. Let's say it's now an exercise: something doesn't work and I want to find out what it is. For me that is the best way to learn.
Thus: any idea what can I do to achieve the convergence of the problem applying a force??
Thanks!!

Re: The rod does not want to fit.
Jared Conway Feb 10, 2014 5:33 PM (in response to Afran Menu)use the force output from your displacement study as the input. see if you can get it to run with an "unassumed" force.

Re: The rod does not want to fit.
Afran Menu Feb 11, 2014 4:19 AM (in response to Jared Conway)Jared, thanks again for your aswer,
use the force output from your displacement study as the input
Of course, that is the first thing I did. Applying this force wasn't able to move the rod down.


Re: The rod does not want to fit.
Jerry Steiger Feb 10, 2014 6:37 PM (in response to Afran Menu)Afran,
The way that the clip separates from the rod may be due to scaling of the display being greater than 1.
What is the assumed length of the rod and the clip in the analysis? Perhaps your 300 grams of force is correct for that length.
Have you included friction? If not, I would not trust any answer that you get.
Jerry S.

Re: The rod does not want to fit.
Afran Menu Feb 11, 2014 4:31 AM (in response to Jerry Steiger)Jerry, thanks for your answer,
The way that the clip separates from the rod may be due to scaling of the display being greater than 1.
No. I have such details under control, but rightly pointed out. :)
Have you included friction? If not, I would not trust any answer that you get.
Uhmmm... may be... I'll come back when I have tried.
Thanks!!

Re: The rod does not want to fit.
Jared Conway Feb 11, 2014 11:26 AM (in response to Afran Menu)probably worth posting the file at this point
it would also be helpful to know what version/service pack you're using and exactly what error you get when you run the analysis
you may also want to try this in 3d

Re: The rod does not want to fit.
Afran Menu Feb 11, 2014 1:12 PM (in response to Jared Conway)Jared: SW2011. It isn't ideal, I know. I'll say my boss again.
Once solved in 2D I will try it in 3D.
Thanks for following the thread with so much interest.








Re: The rod does not want to fit.
Shaun Densberger Feb 11, 2014 12:30 PM (in response to Afran Menu)After reading all the posts I have a few comments.
 Solving this with an enforced displacement is the ideal way to do this. Enforced displacement nonlinear problems are always more stable when compared to applied force. This is especially true for you model, where you have a "snapthrough" effect occurring, which is partly defined by a negative stiffness. This effect can causes serious convergence issues, even if you have an arclength method being applied in your code. I'm not too familiar with SW nonlinear side, but a potential resolution to your model with an applied force could be to increase the number of pseudo time steps, especially around the point that the stiffness goes from positive to zero and negative.
 Can you clarify what you mean by, "try to solve this as a linear problem"? If you're still including contact in your "linear" problem, then did you disable large strain and displacement formulation?
 Even though the problem runs quick enough, it's still probably a good ideal to apply symmetry. If you want to try to get your applied load model to work (by increasing the number of pseudo time steps), then it's worth modifying the model for symmetry. It will also help if your going to try and capture friction in your model.

Re: The rod does not want to fit.
Afran Menu Feb 11, 2014 1:24 PM (in response to Shaun Densberger)Shaun, thank you very much for your great input.
I'll try to solve the problem with friction over the night. I'll try it first with enforced displacement: I think it's the best approach because, by applying a force, once exceeded the "midpoint" (let us say, it is the point when the force turns from positive to negative) I think the problem won't to converge no way.
Can you clarify what you mean by, "try to solve this as a linear problem"? If you're still including contact in your "linear" problem, then did you disable large strain and displacement formulation?
>I tried to solve with the linear solver, maintaining contact and with the large displacement flag up. Contact and large displacement problems are nonlinear by definition, but I just did the test, and it gave me a clue what was happening.
Even though the problem runs quick enough, it's still probably a good ideal to apply symmetry. If you want to try to get your applied load model to work (by increasing the number of pseudo time steps), then it's worth modifying the model for symmetry. It will also help if your going to try and capture friction in your model.
Absolutely. With friction the problem will be totally different and every saved resources will be worth.
Anyway, It's silly that you can not plot force vs time: In nonlinear problems that goes over 500 steps it is a nonsense to have to examine all solution steps to find what is the max reaction force...
Thanks.

Re: The rod does not want to fit.
Jared Conway Feb 11, 2014 8:12 PM (in response to Afran Menu)You can plot force vs time in 2014.
Have you tried list selected? Plot reaction force and then go to list selected.

Re: The rod does not want to fit.
Afran Menu Feb 13, 2014 4:01 AM (in response to Jared Conway)I tried it, but can´t be done. You can plot only stress and displacement.
Thanks again.



Re: The rod does not want to fit.
Afran Menu Feb 13, 2014 4:11 AM (in response to Afran Menu)Ok. Solved. I was able to solve the problem by applying a force. Anyway, the solution's convergences seems a little erratic... I must to increase the convergente tolerance from the default value = 0.001 till 0.05, and the solution doesn´t "moves" toward the convergence... I mean with this, that in step X the rod still didn't move and in step X+1 the rod has moved full down.
Anyway, it seems like the friction was the key.
The solution with an enforced displacement and friction now seems much more coherent also.
Thanks to you all.