No Linear Buckling analysis using Ryks algorithm
Vložit
- čas přidán 10. 09. 2024
- In this tutorial I will show you how to perform a simple buckle analysis and how to introduce into the model imperfections.
1st Tutorial, Linear Buckle analysis
• Abaqus Buckle Analysis...
The LPF is a factor proportional to the load applied. Usually you calculate the linear buckling load, than you apply that load to the structure and perform the riks analysis. When LPF=1 mean that the load is the same of the one imposed. Usually buckling occur at lower load respect the linear obtained with the linear buckling analysis that does not take into account many non linearities.
In few days I will try to show you all how to introduce plasticity, I hope to do this soon as possible, thanks again for the comment.
Thanks a lot for the comment, I will try to redo the video in a better resolution, but if you are able to watch it on full screen it is better ;).
Dear Julius, your if your problem is, what type of analysis to use , the answer is depend by your task. In concept and new design project, where many expert work in the initial stage they need NUMBERS. So they need results faster as possible. Euler analysis is simple and can give some starting points. Anyway if your geometry is simple and there are no local stress concentrator and you need a quick results a linear buckling analysis is perfect. Just refine the mesh and perform a mesh sensitivity.
Hi,
can you tell more about Riks Method, how to determine perfect arc-length I am doing crack simulation using cohesive elements and abaqus stops after reaching peak value and exits even after I use riks method.
please help
This is possible, you can impose imperfection directly on a NODE SET using the option NSET= nodesetname. With this option you will apply the imperfection only to the nodes selected in the set. If you open the manual on the KEYWORD section you will find a lot of other command to use deeper it.
Thank you for these videos. The have been very helpful
Is there any way to do such buckling analysis using static riks on a column without imperfections? It gives a linear behavior of load-displacement curve without any buckling (for no imperfections) and column fails in squashing rather than buckling. Although I'm getting accurate results for imperfect columns. Someone please help..
Hi, ask your question.
Why don't change to results material plasticity on buckling analysis?
To add a particular mode is simple, after *IMPERFECTION, file=filename, STEP=1 you have to write the mode number, magnitude. I make an example
*IMPERFECTION, FILE=test, STEP=1
1, 0.5
2, 0.5
In this case Abaqus will take from the buckling analysis results (test.fil) all the modes, and will combine mode 1 and mode 2 scaling the displacement of each mode by 0.5. So depend by you which mode will be considered in the analysis. I hope to have answered to your question.
Best
For example when it discover a negative stiffness matrix. Sometime is a problem of the model, badly constrained or loaded other time is an issue of the problem and you need to lower the minimum step increment.
PLEASE WHAT COULD BE THE CAUSE CAUSE ERROR SAYING 'TIME INCREMENT REQUIRED IS LESS THAN MINIMUM SPECIFIED' many thanks for response in advance
How can we find the ultimate load from this analysis?
Hello everyone!
I would like to ask regarding the REGION TYPE (6:15) in RIGID BODY CONSTRAINT, why did you use TIE instead of PIN? Would there be a great difference in he results? Thank you and have a day!
hi, thanks for your useful videos, go on with this work, it's really helpful.
I have one technical question, why does my model show a maximum LPF value of about 9.5? The beam shouldn't collapse before or at LPF=1 (lowest critical load)? The other interesting thing is that after 9.5 the curve falls down a bit and then it starts increasing again, now is above 15... is that normal?
Check the load you applied.
many thanks for this video, is any way we can model this so that the effects of discrete support will be studied, for instance introducing columns so that the cylinder rests on definite number of rigid support as in case of elevated silos
Ok many times what happen is that the BCs are not setted properly, try to understand if your condition are consistent with your model. What is happening is that the solver start to integrate your equation solving them numerically. The solver apply the load at each increment, if this increment is too big you are not able to see the response of the structure. Sometime when there are high non linearity the solver try to reduce the increment step to understand what is happening...
Dear expert,i am doing the buckling analysis for the tubular column and i am being confused that which one i have to go:,whether Euler buckling or Non -linear buckling...and in euler i will get Eigen value..wat ll i get in non-linear buckling and how to conclude???...hope u understand my problem..thanks in advance..
I have put the imperfections into my model, but when I try to run the job to obtain my .odb, I have an error like this and the job is aborted:
A ZERO DISPLACEMENT SOLUTION WAS FOUND IN THE FIRST ITERATION OF A RIKS STEP. THE ANALYSIS CANNOT PROCEED. THE MOST LIKELY CAUSE IS THAT ALL DISPLACEMENT DEGREES-OF-FREEDOM ARE CONSTRAINED TO BE ZERO.
Do you now what happens and what can I do to solve it? Thanks.
Dear mark the most possible reason of that message is the model load or boundaries condition. In the first case you applied no load or not a force for example if. You impose a thermal field this is not considered a "load" by the solver also if a thermal load can cause a buckling. In the second case is possible that with out BCs or proper BCs the model is ill conditioned and the equation bring a singularity. Hope this can bring you to the solution
I always get an error message saying there is conflict in keywords. Can anyone help me?
Yes, but what does that mean an LPF>1? The "imperfect" beam with non linearities collapse at an higher load than the one predicted by the linear elastic analysis? Do you think that this is possible?
While I enter mode number and magnitude as in your example it gives syntax error "the syntax of following keyword is not correct" what can be the reason for that? Thank you.
+Mans celeb Yes, I had the same error with you at first. But I closed and opened it again, and tried many times, using non-capital letters, finally, it did work.
hello.
What are common errors in the procedure of following your example if you receive the following error message after 222 increments
"Time increment required is less than the minimum specified"
Ryan Cudo Could it possibly be that I have not yet defined the plastic properties? And, when defining the plastic properties, How many must I enter? I know the more I enter the more accurate the results, but from where can I receive the plastic Properties. Is it from matweb.com as you suggested?
When I enter the yield stress and strain (under plasticity) I get errors stating: the strain increment is so large that the program will not attempt the plasticity calculation at xxx points" this is repeated. and also:
"The strain increment has exceeded fifty times the strain to cause first yield at XX points"
are these warnings allowed to be ignored? Why / why not?
HELLO, I am student. I try to follow your tutorial but when try to edit the keyword.
Then I when I do analysis I see that error massage like this "The following results file(s) could not be located: Buckle_load.fil".
Could you show me what the problem is?
Chan Dara Koem Hello - I believe what you should try is to first run the "buckle_load" file, then run your other model which uses your first. This seemed to work for me. Hope this helps!
Im modeling a submarine, aplying pressure to the outside of a hull. I found the buckling load (doesnt cause yeld) and then i aplyed the Riks alg. to calculate the post buckle deformations until yeld was reached. i wanted to know how can get the pressure aplyed in each on the Riks iteration, until the yeld is reached.
Dear Garcia, in the history output, for the Riks analysis you will find the LPF, Load Product Factor. If you multiply that for the applied pressure you will see the pressure wich cause you the buckling. :) Sorrie for delay
Astro Abaqus
Hi Astro, thanks for the reply but i did some reading and figured that out :).
Thank you sir..
Sir i wanted to mention that Imperfection directly specifying the NODE no..??
I wat to give imperfection to the Flange of a I section beam with one side of flange upward n the other downward..
Waiting for your reply..
Thank u very much ...:)
Thanks for the very useful video. I am modeling a composite joist and have successfully carried out the eigenvalue buckling analysis, however, trying to do the non-linear analysis using the Riks method, I kept getting this error message " A zero displacement solution was found in the first iteration of the Rik's step. The Analysis cannot proceed. the most likely cause is that all displacement degrees of freedom are constrained to be zero" Please, how can I solve this problem.
i m having same problem.how did u solved it then?
Thank you sir for your tutorial.
Sir i want to give imperfection directly by specifying the mode no..How to do that??
waiting for your reply
I am wanting to put the imperfections into my model. I ran the buckling and inputted my eigenvalue like you showed. However, I want to scale my eigenvalues to a particular value. How can I find my multipliers to give me that particular magnitude?
have you find the answer for your question? if yes then kindly share it.
Thanks for your work, it's really helpfull! I have a question. I read in Abaqus documentation that we can also use the mode shapes from a *FREQUENCY Analysis. When I run the Risk analysis abaqus says that can't find *.fil file. How can I create that?
Hi, do you get the answer?
thank you very much keep in progress could you please repeat tutorail 1 with high resolution
Thank you for this tutorial. I made the same model but I get the following
error: TOO MANY ATTEMPTS MADE FOR THIS INCREMENT.
How can I fix this problem?
Thank you!
Increase the number of increments in the step
sir,can you help me?
I addded imperfection in input file as
*imperfection,File=L48F3000-1,Step=2
3,2.9997
39,0.4998
53,1.3818
and inserted it via job->create->source=input file->continue->submit
but the abaqus cae result not showing any imperfection in shape.
anybody know how can i rectify it? :(
Try to use the keyword in the cae and try the same. I think the way the imperfection is applied in the input file is different from that of the keyword.
Hi
can you tell how to calculate these imperfections.
Thank you
In ABAQUS, you can do buckling analysis [linear], and then use the first buckling mode to update the geometry [simple command to implement] prior to applying other loads. Has anyone does that before? Any tips? Any tutorials?
Do you refer to *IMPERFECTION command? Using it you can update the structure using the output from linear buckling analysis, and you will decide the ammount of % "imperfection" introduced.
Check the manual on the keyword manual!
Cheers
Hello Sir,thank you for this tutorial.I am currently working on postbuckling of composite laminates, is it ok to use same method as above or some Changes needed?
Its is ok, but you will need to model in a different way your composite. Infact in this case the material is Isotropic. In your case you have to use the composite layup to define the material lamination.
modelling is ok.i have done it.i was just looking for how to perform postbuckling. Now i know how to. Thank you sir for the tutorial and your reply once again
sir how can i use imperfections on a membrane so as to get it wrinkled and then perform my analysis
Hi I worked a lot on thin membrane wrinkling, for space application. Your aim is to model the wrinking or to analyze wrikled structure? In the first case depend on the shape of your membrane. I suggest you this paper, made by Sergio Pellegrino one of the most briliant scientist on this topic.
www.pellegrino.caltech.edu/PUBLICATIONS/Wrinkled%20membranes.%20Part%20I%202006.pdf
www.pellegrino.caltech.edu/PUBLICATIONS/Wrinkled%20membranes.%20Part%20II%202006.pdf
www.pellegrino.caltech.edu/PUBLICATIONS/Wrinkled%20membranes.%20Part%20III%202006.pdf
Hope this help you!
Astro Abaqus sir i m getting the eigen mode shape....but i m unable to save them as my wrinkled pattern...please tell me the steps to get a model which is wrinkled so that i can perform my analysis ...it will be a grt help sir
Astro Abaqus sir my aim is to first model a membrane structure which is wrinkled.....and then doing analysis on that wrinkled model
hi. so the only way to get the load vs displacement is using risk analysis..
?????
Jonathan Carrera
Dear Jonathan, the load displacement curve can be obtained in anycase. But depend what you would like to study. In this case I was interested in studing the structural instability of this model. Riks analysis is stricly useful to study the instability and collaspe of structure and obiviuosly you can obtain the stress strain curve to see the stability and instability behaviour. Hope to have answered to your question.
Regards
Astro Abaqus Hi, I want to get the load vs max displacement of a simply-supported plate using (thin plate element S4R). The linear perturbation will only give me eigenvalue and buckling mode shape. I want to get a curve that has the load vs displacement and this load should approach the first critical load given by Ncr (compressive force) or not?
The eigenvalue is the predicted imperfection by the software but using the riks method as in this tutorial, You can find the compressive force by the load proportionality factor.
i am the 1k subscriber :)
I still confused how ABAQUS calculate "scale factor" IMPERFECTION in model. I think ABAQUS will do the following formula to calculate IMPERFECTION:
Example Node i:
- Original coordinate : (a ; b ; c)
- 1st eigenvalue coordinate : (a’ ;b’; c’) New coordinate of model(imperfection) :
Case 1: If a’ > a --> [ a+k|a-a’| ; b+k|b-b’| ; c+k|c-c’| ]
Case 2: If a’ < a --> [ a-k|a-a’| ; b-k|b-b’| ; c-k|c-c’| ]
Is it right, everyone? And if we enter 3 "scale factor" according 3 eigenvalue mode,,, what is the formula?
Can I have your email please I have some questions about this topic?
you have an email address I would like to know some kind of information?
You may message me here or in private using youtube messages.
best regards
No, thank you!!!!
very useful video, Thank you my friend. May I have your email? In this way, its very hard to communicate with you.