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Crashphys

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  1. Hi, I realise this site is mostly for software help, however I am wondering if anyone can recommend any documentation on how to take characteristic sections of your model and do FEM on those? For example, imagine you are designing a plane wing iteratively. It is really hard to get convergence if you optimize each beam and panel all at once, so you take one characteristic panel and optimize that in a separate model. Now you need to generate an FEM of this characteristic panel, however this panel was part of a much more complex system of moving parts. My question is how you would constrain this panel. In the global model, the edges of this panel might have a displacement by a certain amount. Is there a specific and easy way to tell the BCs to allow for a certain amount of displacement before loads begin deforming the panel? Thanks
  2. Hi Robert, Thanks for the answer. I implemented the suggestions as you recommended. I did not constrain the center node of the RBE3 elements and have attached the undercarriage beams to the dependent node, while the independent nodes are on the shells. The issue however is still persistent. Is there anything else I may have screwed up? It seems to work fine when I perform static analysis, however it can't seem to handle modal... Looking at the statsub file, it seems the point in the simulation causing problems is from this part of the run: Total time spent in section :AMLSPRP2; CPU= 23.55; WALL= 224.67 Total time spent in section :AMLSPRP3; CPU= 12.09; WALL= 126.00 Would you be able to explain to me what this step does? Thanks again! EquivalentStaticModel_TopologyInterp.fem
  3. Hi, This is very complicated but can be done: %uploading a .fem to optistruct and reading punch file using matlab %step 0 add punch card request(s) at the top of the file % DISPLACEMENT(SORT1,PUNCH,REAL,NORMAL) = ALL % ESE(PUNCH,PEAK) = ALL %element strain energies (for compliance optimization) % GPFORCE(PUNCH,REAL) = ALL % GPSTRAIN(PUNCH,GLOBAL,ALL) = ALL % STRAIN(SORT1,PUNCH,REAL,ALL) = ALL % STRESS(SORT1,PUNCH,REAL,ALL,CENTER) = ALL %step 1 get path to fem path_new_fem = "INSERT FILEPATH TO FEM FILE HERE"; %step 2 get path to optistruct loc_opti = 'C:\Program Files\Altair\2017\hwsolvers\scripts\optistruct.bat'; %step 3 send to solver using system() or dos() command_string1 = char(strcat('"',loc_opti,'" "',path_new_fem,'" -monitor')); answer = system(command_string1); %step 4 get path of the punch file punch_path = 'INSERT FILEPATH TO PUNCH FILE'; %step 5 read the punch file PCH = reading_punch(punch_path); Using this code, matlab will run optistruct. One thing I have not included is the reading_punch code, which reads a punch file output from NASTRAN/OS. If you need this let me know, however I am certain punch file readers exist for matlab online already. If you are going to do it this way, you will need many other scripts, including one which will take your input variables calculated by matlab and write them to an FEM file. The punch reader can be used to read outputs from OS to matlab such as stress etc. What you will need is heavily dependent on what you are trying to do.
  4. Hi, I am running the following model in OS. Due to issues with artificial stress concentrations, I applied RBE3 to distribute the loads more realistically. At the same time, I am also running a modal analysis as subcase 5. When I run, I get the following information message: *** INFORMATION # 3454 MPC constraints for subcase 5 will be enforced with elimination of dependent dofs. The simulation is stuck at 3% for a very long time before finishing. Is there something theoretical I am missing here about RBE3 and its validity in modal analysis? Thanks EquivalentStaticModel_TopologyInterp.fem
  5. Hi, When I run OptiStruct I get xxxx.out, then when I run I get xxxx_1.out, then xxxx_2.out on the next run and so one. I am having matlab read my .out file and running OptiStruct through it as I go, so I need it to keep overwriting the file as it goes. How can I make it so I get only one output file that keeps getting overwritten? Thanks in advance Edit: Sorry, immediately after I posted this I found a solution. In case anyone happens to be looking for it ever, here it is: https://insider.altairhyperworks.com/syssettings-save-file/
  6. Hi, I got my sysadmin to update me to OS 2019. It currently runs slower than it did on 2017, please advise what the issue could be. The one labelled with _013 was run on OS2017 2 days ago. Without the label was run this morning with OS2019. I also have attached a run where I used one core and -np 4. It appears that CPU time is not improved, however wall time increases. Is there a reason for this on my end? Something which did not occur to me: is SPMD or SMP recommended for a single Linear Static analysis? I have four load cases. Is this something which can be effectively parallelized? Thanks HopperModel.stat HopperModel_013.stat HopperModel_onecore.stat HopperModelnp4.stat
  7. Hi, I am using SPMD on the attached model with: -optskip -mpi i -ldm -np 4 Without using LDM, I get a simulation time of 19 seconds. With it, I get 18 seconds. Is there anything else I can do to speed up the simulation? Am I perhaps using it incorrectly? I used the attached guide to start the SPMD run. I also tried SMP and it did not give any noticeable advantages. HopperModel.fem OptiStruct SPMD.docx
  8. Hi, In the pictures shown, I am using the mesh refinement toolbox as instructed by the guide, however instead of a refined mesh, it is also shrinking my elements: Result: Can anyone explain? Thanks Edit: With a more refined mesh:
  9. Hi, To clarify, I am not really worried about seeing the results in hyperview. What I want to do is read the data from the PCH file. I have already developped my methodology to read it, but I need to interpret it. $ELEMENT TYPE = 95 (CQUAD4 COMP) 318922 12 -8.670271E+07 -3.871894E+07-CONT- -2.489154E+05 9.592118E+02 -2.192493E+04-CONT- -8.970279E+01 -3.871765E+07 -8.670400E+07-CONT- 7.523074E+07 Above are the stresses in the ply. Which value corresponds to which stress? Which of these values is principal, von mises, shear etc? Thanks
  10. Hi, What is the file format for ply stresses? Here is what I have: $TITLE = (OS 2017.2) $SUBTITLE= $LABEL = Slosh $ELEMENT STRESSES $REAL OUTPUT $SUBCASE ID = 1 $ELEMENT TYPE = 95 (CQUAD4 COMP) 318922 12 -8.670271E+07 -3.871894E+07 -CONT- -2.489154E+05 9.592118E+02 -2.192493E+04 -CONT- -8.970279E+01 -3.871765E+07 -8.670400E+07 -CONT- 7.523074E+07 This does not appear to be consistent with what is in the help manual. I need the maj. and min. principal stresses, von mises and shear for each ply. Any suggestions on where I can find the format? Thanks in advance.
  11. Thank you for the suggestion. I'll give it a try, but my solution was eventually to just convert to a NASTRAN model (very easy) and use that. Most open source code that exists to interpret it follows NASTRAN format anyway...
  12. Hi, I ran DMIGPCH to extract the mass and stiffness matrix for the attached file. The result only extracted a stiffness matrix. There does not seem to be in input to request a mass matrix, so I assume it should be outputted automatically. Can anyone explain why I might not be getting one? Unable to attach the .pch due to huge size (350 mb). Thanks ExtractMKMatrices_NOSPC.fem
  13. Thank you very much for the suggestion. I will try it an report back for future users.
  14. Hi Rahul, Can you please clarify? Each structural element I have has its own property. I have 7 properties I am optimizing for, each with their own stress constraints. The thing is, for 5 of them my stress constraint is equal to some multiple of their thickness, so their stress constraint changes with the design variables. Is it possible to relate a design variable to the stress cosntraints?
  15. Hi, I am doing a size optimization of a sandwich composite for thickness. The thing is, every time you change the thickness the stress constraints change with the design variables. Is there any way to address this issue in the software? For example, my stress constraint in a ply might be 423 MPa, but that stress constraint may drop if the thickness is changed to 300 MPa, so the stress constraint cannot be fixed. Edit2: Also, if possible, how can you adjust stress constraints based on element size/area? Thanks in advance!
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