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User123

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Everything posted by User123

  1. George P Johnson, I changed the output format of the different Loadsteps to "Output2". This is working good. I think Nastran could work as well. Keep that in mind if the question comes up again.
  2. Do you mean statsub(PRETENS) or something else? Where to find this`? I am already using statsub(PRETENS)...
  3. I updated it already and it is still not working. It is not finding the results for the stresses.
  4. Hello, i need to know if it possible to use h3d result files of the latest Hypermesh/ Optistruct Version in FEMFAT? When i try to import the results it is working for the geometry only, but femfat can not find the results in the h3d file. Do i need the latest FEMFAT version or what could be the problem with this? Any ideas on this?
  5. @Prakash Pagadala i sent you one of my models, so maybe you can have a look?
  6. Hi @Prakash Pagadala, no sorry this did not help. I build a another model today and i have the same problem as before. But this time the problem also comes up when i use first order elements for the entire model. Its not about the time, the models do just not convert. After a few iterations the calculation starts again and again as shown below. Is there maybe another reason for this happening? Please help.
  7. I found this https://pveng.com/why-use-2nd-order-integration-elements-post/ According to it the error is getting very small when i reduce the element size. But still its not what i am looking for. Could i change the convergence criteria somehow?
  8. @Prakash Pagadala I avoided second order elements near contacts this time but it leaded to the same issue as before. Don't you have any other hint for me? Shouldn't it be possible to do an analysis with friction and second order elements? And by refining you mean that i should refine the mesh as much until i reach the distance between midside nodes and edge nodes? I need reliable results for the tensions.
  9. @Prakash Pagadala I will try this later and tell you if it solves the problem after. Thank you
  10. @Prakash Pagadala Okay i understand, but how i should implement this in my model? Do you mean i should use both types, first and second order, in one model? Should i transform the elements around the contact only and keep the others second order? Do i have to make a clear cut trough the solid model in a speific distance to the contact surfaces? Or just transform the elements near the contact "by hand"?
  11. Hello, I am working on an non-linear-quasi static model with pretensioned bolts and friction contacts. I set up the model with first order elements first, this model was converging fast and results were ok. in order to get the correct tensions i changed the elements to second order. After this i recreated the contacts and pretension to make sure everything is correctly linked to the second order elements. If i run this model it is taking days and doing a few iterations until it starts all over again and again. I use surface to surface contacts and a value of friction of 0,14. I am not sure why this is happening because everything is the same as in the first order elements. Could you please help? I uploaded the out. file and did a few screenshots. Thanks a lot! v4-2o.out
  12. Hello, I am still working on pretensioned bolts. I am not sure which contact types i should use for the pretensioning of bolts. In the tutorial for pretensioned bolts is nothing said about it. There is freeze contacts used everywhere, i think this is done to keep the computing time short. Definition for the Contact (Altair Help article: "Contact"): "enforces zero relative motion on the contact surface, the contact gap remains fixed at the original value and the sliding distance is forced to be zero" I think this behaviour is acceptable for the contacts 1+3, the contact of the thread and below the head of the bolt (please look at the attached drawing) but not for 2. I tried different variations (tie, stick, slide) and the results for displacement change significantly! Shouldn't it be some kind of frictional or slide contact for 2? And what is about the orientation of the contact pushout force (morient)? Leave it default? Or Norm? Thank you.
  13. I do have the same question. Yes freeze is for reducing the computation time, but which contact should be used to get correct results?
  14. @Prakash Pagadala Any update on this`? I am still not sure if the pretensioning is working correctly. Thank you.
  15. Hi, how do Í use NLOUT? Did you find out anything?
  16. Hi @Prakash Pagadala how do you see that it is not zero? Maybe its not viewed correctly. I attached 3 screenshots. First one (pretension-end) is the result of the pretension loadstep. Displayed correctly in my opinion. Second one (loadstep2-initial) is the result of the pretension together with the other loadstep (force) . Shouldn't it look like the first picture in the beginning? I can't see that the bolt is pretensioned already... Third one (loadstep2-end) shows the final state of both together. maybe this is just not visualized/displayed correctly? Please explain how i can be sure that it is realy pretensioned first and gets loaded after? Thank you!
  17. Hi, I want to analyse an engine component that is pretensioned with two bolts and I have two problems with it. In order to understand how the pretensioning is done I did the tutorial OS-1390. After doing it I applied the same concept on a simplified model with one bolt only. My goal was it to pretension the bolt first and continue with a second loadstep with pretensioned bolt. When I Iook at the result the loadcase “pretension” works fine. I can see how the bolt is pretensioned and how the structure is influenced by this behaviour. When I look at the second loadstep I can see that the calculation is not starting with the final state of the first “pretension” loadstep. Instead both loadsteps start from the initial state. Can you tell me how does this come? I build up the loadsteps like this: Loadstep 1: Pretension (non-linear quasi static) Spc -> spc Pretension -> Pretens_1 NLPARM -> NLPARM (created Loadcollector with NLPARM Card Image) Loadstep:2 Loadstep Force(non-linear quasi static) Spc -> spc NLPARM -> NLPARM (created Loadcollector with NLPARM Card Image) Load -> load (created load/ force) STATSUB(PRETENS) -> Pretension CNTNLSUB -> checked and YES (tried also SCID) Basically this is how it is done in the tutorial so I do not get why it is not working correctly. What am I doing wrong? On top of this I want to do an optimization run where I want to minimize the compliance and to reduce the weight. Therefore I would usually set up the responses “weighted compliance” and “volfrac” with the constraint “0.9” and the objective “min”. Is it possible to do this optimization run based on the already pretensioned state? If yes how to do it? Thank you. test2.fem test2.hm test2.mvw
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