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mvass

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Everything posted by mvass

  1. A few days ago I came across the following document: https://blog.altair.co.kr/wp-content/uploads/2019/09/HyperWorksSolvers_2019.1_Release_Notes.pdf If you google "optistruct delamination" or "hyperworks cohesive zone modeling" or any other similar combination of words on the same topic, chances are that you will get results on questions submitted on this forum even 8 years ago. Why? Because we had to reach version 2019.1 in order to get support within optistruct of the cohesive material definition (MCOHE) and the equivalent property card (PCOHE), still without support of 2D elements. Consider that all other big players in FEA had the method supported since 2012 (or before?). Not to mention that there is still no tutorial (Double cantilever beam is a classic one) on how to use this "newly" adopted methodology with hypermesh/optistruct and process the results with hyperview. Your constructive comments please...
  2. I managed to do it (without any assistance, thanks). In the picture attached, a correctly BL is created on the wall component surface mesh and the attached symmetry plane mesh changed to connect with the BL created. The example (which I can share with anyone interested) consists of a brick object ("wall") inside a control volume with the following faces: inlet, outlet, symmetry and farfield. In order to create the volume CFD mesh from the existing 2d surface mesh I went to CFD tetramesh-->setup BL parameters-->setup tetramesh parameters-->Boundary selection: select "wall" in with BL (fixed) menu and the rest of the surface mesh (inlet, outlet, symmetry, farfield) in the w/o BL mesh (float). Leave all other options as seen in the image attached.
  3. What was exactly the part of my question that you didn't understand and therefore need additional info? Can you provide any meaningful assistance? If not, please let someone else try. Thank you. PS: To anyone with a sincere will for support: I'll be happy to send a simple example of a similar closed mesh (body, symmetry zone, faces) for trying to create a BL on the body as per request.
  4. Dear CFD users, I am desperately trying to create a 3d cfd mesh with BL using Hypermesh. My geometry is perfectly connected with the control volume faces and the surface mesh created on the geometry (defined as "wall") and the control volume faces has passed all sanity checks (connected elements, no duplicates, no free edges) resulting to a "watertight" 2d mesh ready for 3d meshing. With these conditions a 3d mesh from the 2d boundaries is created without any problems. My problem is to create a 3d CFD mesh with a given boundary layer on the component named as "wall" (which is the body that I wish to investigate). Although the mesh is created (with the boundary layer specified), it is not connected to the symmetry plane as I want: I was expecting to see only the elements of of the symmetry plane to change their topology ("shape") in order to connect with the boundary layer created on the wall and the rest elements remaining as they were (or close). Not only this does not happen, but a BL is created both on the wall elements and all elements of the surface plane. The attached images show the control volume and describe the problem I am facing. Could you please let me know if what I want can be done in Hypermesh? How do I define my 3d meshing strategy in the CFD option? Thank you in advance for your kind assistance.
  5. (Question DELETED by author)
  6. Hi all, I would like your opinion for a quassi static analysis I am performing that includes 3d contact between a rectangular plate with a bolt hole fitted, a bushing that will be inserted with an interference fit into the plate's bolt hole and an external load. I am thinking to perform the analysis in two steps: First, calculate the stresses from the interference fit of the bushing (no external load). Second (continued from the first step) apply the external load (can be a force, or a pressure load). The question is: what kind of boundary condition will be applied on the bushing during the second step to "lock" it in place to ensure that the bushing will not move in the vertical plane or exhibit a rotation of some kind? Do we need to apply any BC to the bushing? Thank you for advance for your assistance.
  7. Hello, it has been a number of years since my last question on the ability of optistruct/radioss to tackle problems of glue failure/delamination of composite structures. Then I saw this presentation from 2016: http://mtevs.org/images/MTEVS/Projects/CAE/2016-03%20-%20Forum/Altair%20-%20RADIOSS_Moscow_160311_001a.pdf and the picture from page 22: Does anyone know if the model depicted is available? This is exactly what I was looking for. Thank you for your assistance.
  8. Sure: Optistruct 2018 (student version). I've placed the input file in your dropbox. Thank you.
  9. Hello all. I know there is a very good tutorial on the subject (https://www.youtube.com/watch?v=236ofmwz1X4) however I would like to share my latest experience when comparing stress results obtained from two different solvers i.e. MSC NASTRAN and Optistruct. By default NASTRAN calculates stress using the command: STRESS(PLOT,SORT1,REAL,VONMISES,BILIN)=ALL, meaning that (if you neglect the other terms) a bilinear extrapolation is used to get the stresses from the element's centroid to the nodes. Since optistruct/RADIOSS calculates stress at the element's centroid by default, I supposed that the equivalent command in the .fem input file for optistruct would be: STRESS(SORT1,H3D,REAL,ALL,BILIN) = YES (I have replaced "VONMISES" with "ALL" to have all stresses in my output) and performed two examples of simple static analyses: one with shell elements: the well known hole in plate and another with a bracket meshed with solid elements (4 noded tetras). In both cases the results from MSC NASTRAN and Optistruct were identical, as long as in Hyperview I activated the option "use corner data" (participation of element to the node). Without "corner data" activation the difference in VM stress between NASTRAN and Optistruct for the hole in plate problem was 175 MPa (NASTRAN) to 157 MPa (Optistruct). Now: I performed an analysis of a 3d bolted connection (two plates connected with a 3d bolt) with bolt pretension as a first step and a tensile force acting on the top plate of the connection as the second step. Obviously, this problem involved contact between the plates and the bolt. The analysis converged and the results were correct since I knew from published results (and NASTRAN) that max. stress should be approx. 80 MPa. I received the same results with optistruct, but without the "use corner data" activated, although I have used the command described before for stress. If I activate the corner data in Hyperview, then my stresses almost double in magnitude (156 MPa). So, this contradicts with what I have found with my previous tests (hole in plate and 3d bracket). Does it have to do with the "contact"? Thank you in advance for your reply.
  10. Dear PrasannaK, I had a quick look on your approach. It seems that the contact properties defined need some serious adjustments, because if you run the model as per the updated file, the lower plate performs a large rotating motion. I'll have a further look and let you know, although as mentioned before I think I can solve the problem by: a) creating a "freeze" contact between the two plates and simulating the bolt with 1D beam element connected with RBEs to the bushing and plates.
  11. Dear PrasannaK, thank you for kindly replying to my question. I'll have a look on your file later this afternoon, however I must say that I have made some progress myself yesterday: I had to define a "freeze" contact between the two plates, because the axial movement (slide contact, with friction), was causing the "hot spot" on the bushing that I mentioned in my previous post. I am not however sure if that approach is physically correct. As to the contacts, I count the following: bushing-plate 1, bushing-plate 2, plate 1 - plate 2, bolt - bushing. If you also include the bolt's head, then it is bolt head-bushing, bolt head-plate 1, so yes that makes 6 contact surfaces in total. Let me check your file and I'll contact you again. Thank you for taking the time to check my model!
  12. Dear all, Lately I am having some problems solving a problem that might seem "trivial", however I am still having problems getting some meaningful results. As seen from the files attached, the problem consists of two aluminium plates connected with a steel bolt and a bushing. There is a press fit of 0,2mm (if I remember well) between the bushing and the two plates. The upper plate has one of its sides fixed and a compressive force of 90 kN is acted on the lower plate. Although I have simulated the contact* between all components (plates, bolt, bushing) and ran a quassi static NL analysis, I keep getting extremely high stresses at the area seen on the attached picture. It is probably some mistake with the contact there but I cannot find it. Please have a look on the attached .hm file. There are no contacts defined to allow you to use your own approach to the problem. You can use any of the latest HM versions to setup the problem. Thank you in advance for your kind assistance. *: a number of approaches used: friction, no friction, slide, freeze etc. bolt_coupon.hm
  13. Thank you for your reply. As mentioned in my question, I am aware that Simsolid can show the contact forces between two bodies. Word to developers: Add this, and above all the ability to assign composite layups to parts (including post processing tools) and Simsolid will definitely become the software of choice for many-many companies... Respectfully, mvass
  14. Is it possible to see the stress results due to contact? I've seen that forces (resultant and components) between contacting surfaces can be evaluated, but I haven't seen any options for contact stresses. Thank you.
  15. Answer: The use of "R-trias" elements of the right size does the trick...
  16. Hello all, I would like your expert opinion about the surface mesh I am trying to perform on the curved areas of a simple wing (leading edge). Since I would like to export the mesh for a CFD analysis, I am trying to mesh the surfaces with "trias" elements. However I am not happy with the mesh on the leading edges which exhibit a high curvature. I know the result will be better with "quad" elements, however as I mentioned before I would like "tria" elements on my surfaces. The "surface deviation" option meshed the surface (as per attached example) but with too many elements. Can you please have a look on the attached model (note: HM version 10)? Thank you in advance for your assistance. surface_deviation.bmp elevator.hm
  17. Thank you for your reply. In my study, I am not looking for post buckling and my solution scheme does not include a velocity BC like the example shown. Besides the obvious constraints, the load is exerted on the model via an enforced displacement. In addition, I am not looking on a transient NL analysis. But I guess it wouldn't hurt if I'll try to solve the problem with NLPARM and TSTEP card, provided that it is possible. Should I get something worth to write about, I'll post it here.
  18. Hi, any views on my updates about the problem? Thank you in advance
  19. Second update: I managed to solve the afore-mentioned problem, by specifying a value of 1.0 (instead of the default 1.1) to the DTSCI entry of the NLPARMX card (see the attached picture). However the question still remains: Why the solution is different when the default values are used? How come there is no warning/error in the previous situation? nlparmx.bmp
  20. OK, here is my update to the problem. Unfortunately I cannot share the model with you, however, please find attached the .out file and the solution scheme from the .fem (input file). As mentioned before, the solution converges normally but the results are not correct. It is a NL buckling problem (compression of a panel) and I am supposed to have a max displacement (magnitude) on the panel of 20mm. This doesn't happen and the max. displ. magnitude I get is 10mm. My solution was a NL geometric (impl) that I set up in Optistruct and automatically translated to Radioss (version 2017.2). I tried to run the problem as quasi-static NL with large displacement activated in optistruct but it didn't converge. Thank you in advance for your assistance. CCCC_v2_rad_s1_0001.out problem_fem_extraction.txt
  21. I agree with you. That's why I was surprised to see different results when NINC was 50. Maybe I couldn't see where the mistake was, however there was no error shown in both runs (NINC=50, NINC=25). Thanks for the advice about the param option.
  22. Thanks for your reply and sorry for my late feedback. I cannot remember what I did with the latest version, however I'll give it a go with NLSTAT and large displacement option and contact you again. However I still cannot understand why when you specify that you want a NL analysis with fixed number of increments (constant DT), the problem converges with less increments completed (and the result doesn't capture the phenomenon as it should).
  23. OK, here is an update, after solving my .fem file on two different versions (thanks to my friends): HW version 13.0 completes the solution in 50 increments as requested, and the analysis is complete and correct. HW version 2017.2 (student version) completes the (same) solution in 25 increments the analysis says that it is completed but the results are not comparable to the previous ones. Any ideas why this happens?
  24. Hello. I am working on the NL buckling of a composite panel (geometric NL implicit) and I successfully setup the model and ran the analysis within radioss after automatic conversion from the optistruct input. The problem is that although I specify I need 50 increments (NINC) with PW convergence criteria, the solution ALWAYS converges at 25 increments and of course the total buckling is not captured. Below is my NLPARM card from the .fem file. I am not specifying anything else in the NLPARM card or in any other cards. Can you please help? NLPARM 6 50 0.0 6 50 PW + 0.01 0.01 20 + 1.0 Thank you
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