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Matteo

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Everything posted by Matteo

  1. Hello. Has anybody got any suggestions? I have tried to use the rbe2 in a simpler case (using shell elements) and it works perfectly fine. Unfortunately the same cannot be said about this case...
  2. Hi pratik, Thank you for your reply. Do you mean that in LGDISP analysis contacts might not work properly if you do not use SPCD? I've read in the manual that prescribing motion using SPC or SPCD is pretty much equivalent as a matter of fact.
  3. Hi everyone, I am writing here hoping someone can help me with the following problem. I have a plate which is connected to one end of a flexural spring (0.8mm thick) through FREEZE contact (please see picture below). The other spring end is fixed. I have used 2 loadsteps to perform this analysis: The plate has to translate downwards of about 1.4 mm. LGDISP non linear static analysis activated. From the position reached in the previous point, the plate must rotate about the X axis of an angle 0.25° (DOF4).LGDISP non linear static analysis activated. All displacements have been enforced through SPC. Picture of the model: I have used CNTNLSUB in order to make one subcase follow the other. Unfortunately, from other threads in this forum, I seem to have guessed the 1st loadstep loads (SPC enforced displacements in this case) must be enforced in 2nd loadstep as well. This proves to be impractical, since my final goal is to simulate bending+torsion in the flexural spring. In fact, I cannot impose the desired rotation in the 2nd loadstep because the plate has to be forced to translate downwards like it is in the 1st loastep. I am attaching my file in order to get the matter as clear as possible. Thank you in advance for any help you will wish to provide. Best Regards Matteo Spring_Plate.fem
  4. Dear Rahul Thank you for your reply. I have tried using fixlen some days ago and it worked! Thank you very much!
  5. Dear Rahul, Thank you for your kind reply. What is this error due to? A further update: I have seen that if I run only the non linear analysis part only, the analysis starts smoothly. So, apparently, only if I impose a pretensioned modal analysis, the error comes out. I have one question: how do I disable memory allocation? Do I have to use fixlen or is there another command I should type in?
  6. Hi everyone, I am currently running a pre-stressed modal analysis using Altair Optistruct. The first loadcase is a LGDISP non linear quasi static analysis and the second loadcase is a normal modes analysis which is PRETENS with loadcase#1. The model comprises of friction, freeze and slide contacts, 2nd order tetrahedral elements, CBEAM elements and RBE2 elements. Everything has been checked but something strange happens when I run it into Optistruct: If I change the order of the tetrahedral elements from 2nd to 1st, I get the following error: OptiStruct error termination report printed to file "def_linear2.stat". PROGRAM STOPPED DUE TO ERROR. NOTE # 1422 There were 1 automatic memory expansion(s). (The result is not affected by this.) ************************************************************************ A fatal error has occurred during computations: *** ERROR # 292 *** Available working storage insufficient. The strange thing is that if I run the 2nd order the simulation proceeds and starts as it should. At first I corrected all RBE2 free-nodes and deleted any duplicate elements. Unfortunately, this keeps happening. Please, I COULD USE some feedback asap. If there is any need to share something, I would consider using file transfer. I am attaching the .out file. Thank you in advance for your consideration. Matteo def_linear2.out
  7. Hi Prakash, Sorry for the late reply. In short, I have a problem during non linear analysis of the structure contained in the file below. As you can see, there are 2 subcases. For the first one (1.2mm of imposed displacement) there are seemingly contradictory (and wrong) results with what happens in subcase number 2 (2 mm of imposed diplacement). This happens when the model is made of second order elements. Not big problems are encontered when I use only first elements instead. I need to use second order elements for this analysis, so it is my priority to make it run. Find attached my file below. Best Regards Matteo Analysis.fem
  8. Hi @User123 I am having the same problem too. I know your post is dated almost 1 year ago but...did you happened to find something? If you don't maybe we can try to get a solution...
  9. Thank you! How did I end up not noticing it! Thank you very much :)
  10. Hi everybody, I was running a test with optistruct using two simple cubes. They are both fixed at opposite ends. Their faces are separated by 0.1 mm and can, if pushed, become engaged in a contact (type SLIDE). Type of analysis: nonlinear quasistatic. Issue: Even if I fixed both cubes at their bases and there is no applied force and no contact is engaged (shcdist=0.001 and the solver warns me that no contact elements have been defined during the analysis), the cubes translate of 2 mm as if they are moving like rigid bodies. I have already tried to constrain some more nodes, to no avail. Any explanation for this thing by anyone? Thank you in advance. Find attached my .fem file to check SHRCTOL001.fem
  11. Hi Prakash, Can I upload it without the GRID cards attached? Unfortunately it would be better if the geometry of the model doesn't get shared.
  12. Hi Prakash, Tried as you said, it runs smoothly! I took a look at the .fem file. It had a huge number of ACCEL1 cards. I think that Optistruct might experience problems dealing with them all. Is this correct? One last thing...what is the SPASMB section? Thank you for the fast and accurate reply Matteo
  13. Hi, I happened to run a linear static analysis on a model. Everything worked fine. After that I had to rerun the same analysis on the same model BUT I had to add on EVERY NODE of the model an acceleration of about 10g using the card ACCEL1. The analysis got stucked after few minutes on the same screen. It has been like that since several hours. I don't know what it is...it's just as the solver got...stucked. Does anyone has an idea of why this is happening? I will now upload the .stat and the .out files, should there be some more informations, let me know. Best Regards Matteo ASFEL18004.out ASFEL18004.stat
  14. Hi Prakash, Thank you very much!
  15. Prakash I have a question on this issue too. The SPC card whose D field is to be changed is the one in the CNTLSUB subcase (Subcase2) or the one in the first Subcase? I suppose the second. Correct?
  16. Hi everyone, I am currently trying to perform a modal analysis of a component AFTER it has been loaded with a force. During the loading step, some parts of the component engage in SLIDE type contact. I use OPTISTRUCT. I currently plan to make two loadsteps for the analysis: 1.A non-linear quasistatic step during which I load my model and contacts are engaged 2.A normal modes analysis which should compute the modes for the deformed structure obtained after step1 Is this possible in Optistruct? Thanks in advance for any answer. Regards Matteo
  17. Dear Prakash, thank you for your reply. I will rearrange the model accordigly!
  18. Hi! Yeah, I noticed it and tried to fix it by increasing the searchdist length. However, nothing happened. Do you have any suggestion about a way to take care of this issue?
  19. Unfortunately I can't share too much. But the .out file should do. If you need more information please just ask. test.out
  20. Hi everybody, I am running a non-linear quasi static analysis in Optistruct. This analysis features a partial fan structure, with several components kept in place only by mutual contact with other elements. and various bolts wich keep together the parts via preload. In particular: -ALL COMPONENTS ARE MODELLED VIA 3D ELEMENTS (FIRST ORDER TETRA) -ALL BOLTS HAVE FREEZE CONTACT. OTHER PARTS ARE MODELED WITH CONTACT CARDS USING MU=0.1. ALL Contact surfaces match node by node. -The gap between every contact surface is zero. There is NO GAP between one surface and another. -MY INPUT ENTRIES ARE (AS LISTED IN MY .FEM FILE): PARAM,AUTOSPC,YES PARAM,CONTFEL,YES PARAM,EXPERTNL,CNTSTB PARAM,PRGPST,ALL That being said, I obtain the following warnings at the end of the run: *** WARNING # 312 In static load case 2 the compliance is negative or large -2.49893e+010. Optimization/buckling analysis cannot be performed. due to possible rigid body mode. *** INFORMATION # 942 Apparently some contributions to negative compliance come from gap/contact elements. This can happen in case of initial interference (U0<0) or significant attractive force (KB>0). To ignore gap/contact contributions to compliance, set GAPCMPL to NO on the GAPPRM card. My question is: Since all displacements seem ok and stresses seem to be consistent with the applied loads and preload seem to work properly, should I ignore contact contributions or they might be invalidating all my results? Thank you in advance for any reply.
  21. Hi Alex and Frehab, You both posted quite "a while ago" but, thanks to your posts, I came up with a workaround of sorts, which isn't very straightforward but helps me as long as there are not tons of rigids to clean. So I would recommend to use it as soon as you start making the first group of rigids in your model. To put it simple: INITIAL ASSUMPTION: you have FREE 1D NODES in A NUMBER OF RIGIDS PROCEDURE 0.SAVE A COPY OF YOUR FILE BEFORE DOING THIS. CAUTION IS ALWAYS THE BEST WAY IN THIS KIND OF THINGS. 1.Visualize with F10 your free 1d nodes-->save them in the user mark (save found) 2.create a dummy component. In this component create a rigid retrieving ALL THE NODES SAVED IN 1. This will automatically make HM see them as no more free nodes. 3.Now go to 2D/3D-->Detach. Detach your rigids (the ones you have created and you WANT TO KEEP) from their components. This will make all the "correct" nodes of the rigids free nodes. 4.F10-->recheck 1D free nodes-->you should be able to visualize your correct nodes as free now. Save them in the user mark 5.Go to Analysis-->Preserve Nodes-->Retrieve your correct nodes from the user mark (stored in 4) ad click make preserve. 6.Go to Analysis-->entity sets-->create a set-grid of nodes with these nodes (the ones saved in 4 retrieve them from the user mark as they still should be there). Now you have saved and you can retrieve all the nodes you wish to keep. 7.Delete the rigid created in point 2. This will delete all the free nodes (the ones you wished to DELETE IN THE BEGINNING) as well. 8. Delete your original rigids too. Switch to your actual rigid component and make new rigids. All the dependent nodes are placed in the entity set created at point 6. So you just have to recreate them. I know it can be bothersome but it should get the job done by click and not by looking for all the nodes in the solver exported file. Let me know if this helps. And more importantly, let me know if you managed to find a better workaround.
  22. Hi Enrico, I am experiencing an almost identical problem on a structure of mine. If there has been any improvement on the matter, please let me know, lost tons of time on it too.
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