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Crashphys

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Everything posted by Crashphys

  1. Hi, I am trying to perform a simple 3D beam non-linear bending analysis and get the following error int he attached .out file. I have attached the .fem for reference. Can anyone help me out? *** INTERNAL PROGRAMMING ERROR *** in file "hexa8_bb_ls.F", at location # 158. ioerr(1) = 995 **** ABORTING RUN DUE TO AN INTERNAL ERROR **** Bottom_Lead_PunchSim_Implicit_NoJig.fem Bottom_Lead_PunchSim_Implicit_NoJig.out Bottom_Lead_PunchSim_Implicit_NoJig_001_nl.out
  2. In case anyone is ever wondering, I finally got around to trying this and Robert's answer works. Thanks Robert!
  3. Hi Simon, I guess this is not so much a software problem but a theoretical one but: Considering there are both loads and displacements applied here, if I wanted to optimize this is there a way to address this if I wanted to run OS optimization with stress constraints?
  4. Hi Simon, Thanks again for the help. In this case, loads are applied and not displacements. That's what makes it all the more confusing... Worth mentioning also: For all load cases, compliance appears to increase with increased core thickness.
  5. Hi, I am modelling sandwich panels applied to a wall with loading in various cases. In sandwich theory, the stress should decrease with core thickness. However when the core is thick here, the minimum principal stress is much higher than when the core is thin. I am aware there is a high load specifically at this point in specific so stress is high, however stress should still decrease with increased thickness. I am wondering if anyone has an explanation to help me understand? Thin Composite: Thick Composite: forum.zip
  6. Thank you for letting me know. There goes 7 days of my life :'(
  7. I think there are a few issues in your model you need to fix. At a glance, your INTER/TYPE7 has a set gapmin of 0.1. This implies that anything within 10 cm of your impactor is in contact with it. Meanwhile, your impactor starts only ~1 mm away from the foam, which implies your impactor is penetrating 10 cm into the foam from T=0 seconds. Unfortunately my solver is currently bogged down with some other work, so I can't play around with your model. Make sure you read up on TYPE7 Interfaces in the reference manual. I recommend gapmin to be 0.1*(smallest 3d elem edge length) as per recommendations in the manual.
  8. Time until a solution is attained is variable and depends on your time step heavily. If your elements keep distorting, your simulation may start at a 3 hour solve time, then when it calculates the next stage it will estimate 3.5 hours due to the deformation. You can achieve reduction in sim times with DT/NODA/CST or AMS (see video). You might also consider the multi-domain method.
  9. The model you are working with would help in finding you a solution. Which composite? How did you model the bird? Just like how no one can correct your code without seeing what your program is line-by-line, no one can guess what your simulation is doing. I have attached a bird strike simulation I performed on a GLARE plate from a while back. Let me know if it works for you. GLARE2_0000.rad GLARE2_0001.rad
  10. There's a few kinematic issue in your model. I think the fact you are working on a skew is resulting in lots of pain, so if you can remake the model not in a skew, I would. I don't have much experience with rigid walls, but from what I can tell: - You did not set any skew for your velocity. I went ahead and change it so it moves in line with your created system. - You were constraining the whole model in the up/down direction while also applying gravity. I applied gravity on your model and constrained only the floor in the up/down direction. - I cannot figure out why the rigid wall has incompatible kinematic BCs. Perhaps someone else will be able to chime in on this. Make sure to review rigid walls and ensure you have implemented it correctly. Try running a tutorial with one first. Incompatible kinematic conditions means you have done something like apply motion and restrict it at the same time on a node or something. test_0001.rad test_0000.rad
  11. Crashphys

    H3D

    Cannot tell you why without knowing which tutorial or model, however if you would like to view your simulation results, you can just open the animation (_A00X) files in Hyperview instead and all your results will be there.
  12. Hi, In the attached video, the instructor mentions that BC's and initial velocities can be changed mid-simulation using a restart procedure. Since he specifically mentions BC's and Initial velocities, I am wondering if this also extends to other BC's like accelerations. I am currently running a costly simulation and really do not want to restart it just to change a load case that I have not used yet. I want to change a /GRAV card to an /IMPACC card. The acceleration does not begin before the point which I want to restart, so changing it will not change results prior. If I want to change accel types, will the solver read my modified starter file, or will I have to rerun my starter file for it to read it thereby erasing all my progress? I tested to see if I can change the /GRAV card by purposefully sabotaging by inputting values which should break the simulation, then ran my _0002.rad engine file. The solver carried on like normal, which implies to me that I have to re-run my starter file to change the acceleration type. If a procedure exists so that I can change accel type mid simulation, please let me know. Thanks
  13. Thank you for the help. So you think it is worth a try? If possible, would you kindly elaborate what you mean (I'm not super great with computers, not sure what you mean by scratch folder and how to set it up)? Thanks again!
  14. Hi, I noticed I have very high wall time from OptiStruct. I currently run OptiStruct on a server through my school. I am wondering: if I install an external SSD and run my .fem files off of it, will this reduce wall time? The thing is, OptiStruct itself cannot be installed on the SSD - I can only have my own files on it. So my process would be running OptiStruct on the server but using files in my SSD instead of from a local HDD. Can I expect any benefit for this? Thanks in advance.
  15. Hi, I want to model the forming procedure for a part similar to what is shown in the picture below. It is not a flat plate element but more like a square rod which is bent in a Z shape. As I understand it, the best way to do this will be with solid elements but there doesn't seem to be a way to do this other than with a pipe forming simulation. Can anyone advise me on similar tutorials? It is important I model the stresses due to forming very accurately. Thanks
  16. Hi Simon, This is a very interesting and clever observation. I could not have come to this conclusion alone for sure. I suppose this could very well happen in a realistic situation, however the vibration amplitude is crazy high +/- 1.5 cm or so... The thing is, if the cargo sticks to the wall, my intuition tells me it should be absorbing the vibration energy, so it shouldn't be possible that this fluctuation is so high. Do you know of any documentation dealing with how the total interface force is calculated? Is it some sort of sum of all the loads? I was thinking it is possible that the load may also be fluctuating because as the particles are lifted by lateral acceleration they lose some contact with the wall (for ex the particles near the bottom of the car), but then they make contact with the rest of the SPH further driving them in? While the acceleration profile makes sense, I just can't see how total interface force can fluctuate as much as 200,000 N which is approximately 10% the weight of the cargo. Either way, thank you for the observation. PS, Not able to message you privately, so I am posting here: I do not know if you are comfortable with it or if you are interested, however I am currently writing up my thesis and you have helped me greatly with my work over its course. If you are interested, I would like to add you to my acknowledgements. I can use your name tag here if you like, or I can temporarily put up contact information if you want to associate your name/work with the acknowledgement. Thanks again
  17. Hi Simon, Thank you for your continued help despite technical issues. Please see the link below for the whole model: https://drive.google.com/file/d/1wK9cGuk0CiQ_WDQM9eyLtPDtatouQig1/view?usp=sharing I went ahead and ran it without any mass scaling (took forever) and the results are agreeable with AMS, so I do not think it is possible the AMS is the issue. See image below, light pink and green is the AMS run, others are from no mass scaling at all. I also plotted on a logarithmic scale. I do not know if this is valid, but if so, then it may indicate that the force interface is behaving as expexted... Thanks in advance.
  18. Was not able to upload across two posts unfortunately. I tried to compress with a higher error but it completely scrambles the mesh. Here are my TH files. Test1T02 Test1T01
  19. Hi, Thank you for your time. This is my mass error time-history plot with only CST: The energy plot with AMS is: /KEREL is applied in the first 0.9 seconds without AMS, which is why you see those peaks at first. Energy error is -0.2% total by end of simulation and stays near zero for most of it. I plotted the F-t diagram logarithmically on the Y-axis and is does seem to show somewhat of a constant load, but I do not know if this actually is accurate. I am including my H3D file from 0.9 seconds to 1.75 seconds here. The relevant simulation time is 0.9 seconds to 2.5 seconds. I will include the second part from 1.75 seconds to 2.5 seconds in the next post. ComrpessedResults.h3d
  20. Hi, I am trying to interpret my results for a sloshing simulation using interface loads. Unfortunately, I cannot attach all my results due to the size of the model, however I am running it in two parts: One using KEREL and one using AMS. The KEREL is used only to settle the SPH, before the sloshing begins in the AMS portion of the simulation. To my understanding, sloshing simulations should show a single peak for interface forces at the point where slosh is at a peak, however my T01 file has various up and down peaks, while the T02 file shows a linear increase in interace force until the end of the simulation. I am not sure which interface force graph to trust (if either, because it does not seem consistent with reality either way). Furthermore, based on observations in the model stresses, it seems the interface load is on the order of 8e5 only in very specific spots, even though the elements are highly refined. Would appreciate any suggestion. Thanks in advance. Test1_0000.rad Test1_0001.rad Test1_0002.rad Test1T01 Test1T02
  21. For question 1, you will need to upload both your MATLAB code and your model, at the very least your model. Implementation is likely the difference in the results. Make sure you validate both your code and model according to some kind of baseline. For question 2, OptiStruct (the solver), uses the SIMP method to perform Topology Optimization. The SIMP method is costly when performing topology optimization if you use a discrete approach (that is, either 1 or 0 for element density). To overcome the issue, OS uses a relative density between 0 and 1. Given these relative densities, you as the designer will have to determine what elements you will remove and which will remain. Usually you assign a cut-off of something like anything <0.67 relative density is zero volume. The ISO slider allows you to quickly view which elements are under a certain relative density so that you can determine which is which.
  22. Hi, When I run optistruct static through Hypermesh and am using /ACCEL cards, I get the following error. I edit the card and assign a direction, however, it instead exports the 0.0 I have highlighted and bolded. Is there a reason for this? Seems like a bug. If I go into the .fem file and change the 0.0 to a Z myself, it works but I do not want to have to do this every time I run. Also, when I run my edited .fem, I am not able to see composite stresses by layer. Did I miss something? *** See next message about line 25808 from file: H:/Hopper Car FINAL/Optimization Scheme 4 - New Plan 01-22-2020/6 Characteristic Panel Optimization/Panel 4 FEM Creation/HopperCarPanel4.fem "ACCEL* 4 0 0.0 0.0 -12.30.0" *** ERROR # 4950 *** Components direction can only be 1/2/3 or X/Y/Z in bulk card ACCEL. *** Run terminated because of error(s) in the input data. Attached is my .hm file and my personally edited .fem file. HopperCarPanel4_HC.fem HopperCarPanel4_HC.hm HopperCarMatrix_AX.pch
  23. Hello Mr. Alb, I had to take some time to consider what you're saying. The problem with optimizing my whole model all at once is that it is infeasible. I would end up with hundreds of design variables which are highly non-linear and convergence would be unlikely. The only way I can think of is to create a submodel. In another post I made: I found out how to create a break-out model in linear static FEM. What I want to do is take those equivalent forces and apply them on my submodel. The problem is I don't see how I can constrain it. For example, see my two models attached. One is my local and one is my global model. The local model has the resultant forces on each node from the global model applied through linear interpolation. The thing is, the edges of the local panel model I have are not stationary, they should be able to move a certain amount, but unconstraining them too much also results in disagreement in results. What I am wondering is the best methodology to constrain the panel. How should the edges of my local panel be constrained such that the model is at least close to reality as possible? To my understanding, there must be some kind of way, otherwise how could such huge and complex systems such as aircraft be optimized? Edit: As an example, see this outside link: https://structures.aero/blog/submodels-breakout-models-fea/ In this article, they mention one use of submodelling/breakout models is to iteratively design local component so that you don't need to run your full model. Quoting: "When should I use submodels? In what circumstances might you use a submodel? When a small design change requires analysis. When a small portion of a large design needs to be iteratively designed You don’t want to have to run your large analysis model over and over again. Instead, you can iterate the submodel and save computation time on the solution. When a feature is added to an existing part. In our first example, we will look at a scenario where avionics wants to add a pass-through to a wing-rib. It will be computationally expensive to run the entire model just to analyze the new mesh on the rib, so a breakout model would be useful." EquivalentStaticModel_Global.fem EquivalentStaticModel_Panel4l.fem
  24. Hello, I was following the tutorial HM 9010 up until step 8. When I get to the highlighted step, no loadcases are found. I did skip the first part because I am not interested in creating shear moment/potato plots and started from step 7. The tutorial said I could start from this point. If anyone has suggestions on what I might have missed please let me know. I would also like to know: When performing analysis on a cross section, how can I also enforce the displacements correctly? See the last two pictures attached: The first is a panel in my global model. The second is my panel in the DFEM (.fem files attached). I used the FBD->Forces tool to extract the loads on the section I want, however when I import those forces to my model via BC->Create->Forces->Interpolation, I end up with a ridiculous stress concentration in one part of my model. I'm not sure why this happens, but as far as I can tell there is no way to constrain the model correctly according to the global model. In the global model, all nodes are displaced a certain amount, but in the DFEM the nodes along the edge are forced to be constrained. Is there a way to ensure agreement between the two models? EquivalentStaticModel_Panel4l.fem EquivalentStaticModel_Global.fem
  25. Hi, I am trying to connect the beam modelled as 3D elements to the composite plate. Is there a faster way to do this? I tried using spot connectors and it did not work... It turns out that the reason connectors are not working well is because I am running a modal analysis. Can anyone explain why rigids cause problems in modal analysis? .
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