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Simon Križnik

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Everything posted by Simon Križnik

  1. Hi, the time step should not vary significantly during the run and could be a sign of some modeling error. Use timestep control CST mass scaling or AdvancedMassScaling to impose a constant time step. Or use the smallest timestep from the moment when the failure is expected.
  2. Hi, the stress-strain slope should be positive (the data points must be in ascending order). Convert the engineering stress-strain to true stress-strain. The first point of yield stress functions (plastic strain vs stress) should have a plastic strain value of zero. The curve should be nearly flat (slightly increasing) after the ultimate strength. To model failure use εt,εm, and εf parameters or dedicated failure models. Materials.pdf
  3. I can help you learn, but do not expect me to do your work. First try yourself and ask for help only if you fail.
  4. Attached is the model file and result for a simply supported plate on all four sides. multiBC2.hm multiBC2.h3d multiBC2.op2 multiBC2.out multiBC2.pch multiBC2.fem
  5. The solver deck you shared is a Nastran bdf file and that error was reported by a Nastran solver. Nastran issues should be posted on Nastran forums (this is Altair forum). Optistruct can import bdf files and I was I able to run your model without issues- see attachments. multiBC.out multiBC.pch multiBC.h3d multiBC.fem multiBC.hm multiBC.op2
  6. Hi @Sony Dhotre create a separate load collector for each set of boundary conditions. For example, create a load collector with all DegreesOfFreeedom fixed and a second load collector fixing only translational DOFs. Create only one load collector if you need to constrain only one set of DOFs.
  7. Glad to help. There are free nodes in your model. Either apply autocorrect in model checker or remove by Analysis>preserve node>clear all preserved. The 1662 warning is due to PARAM>AUTOSPC>YES (by default) Automatically constrains degrees-of-freedom with no stiffness- in your case it applied to free nodes: GRID 1417172 DOF 6 GRID 1549910 DOF 4 Use Tools>Model Checker>Optistruct to find & correct modeling errors and warnings. https://insider.altairhyperworks.com/wp-content/uploads/2017/09/T-T-1248-HyperMesh-Model-Checker.pdf
  8. Hi, The model can be downloaded by copy-pasting the link in the browser's address bar. It is easier to debug a smaller, coarsely meshed model. Element Quality Check reports a warning that 56 elements exceeded the recommended range. Use the following tools to obtain a better quality mesh: Geom>autocleanup to clean up the geometry 2D>automesh (F12)>QI optimize>edit criteria to define element quality criteria 2D>elem cleanup can be used to clean up a group of elements 2D>qualityindex where element quality can be checked visually and edited using cleanup tools one at a time. The failing elements can be saved to later be retrieved in elem cleanup or automesh again tool>check elems>2D (F10) to check elements The warning 5628 is due to large compliance. The "t8" tub is so thin and unsupported it sags excessively (710mm). The analysis results are invalid because large displacements and rotations violate the linear static assumptions. The "vincoli" constrains the Z translational degree of freedom at the bottom, but the "carichi2" has a force acting in the same DOF so it does not have an effect.
  9. PBEAML allows selecting from a library of standard cross-section shapes such as BAR, BOX, BOX1, CHAN, CHAN1, CHAN2, CROSS, H, HAT, HEXA, I, I1, L, ROD, T, T1, T2, TUBE, or Z. PBEAML.pdf
  10. Hi, there are several issues in your model: the payload is modeled with shell elements, but solid element would be more appropriate. The upper surface shell would sag under gravity and its weight would be transferred only by side shell surfaces. Solid elements would equally distribute the weight over the floor. the "lc6" load collector referenced in linear static load step is empty, which is invalid (the solver will error out). Reference a gravity load collector "0.1_z negi" instead. the master component is usually stiffer or in case of equal stiffness the one with the coarser mesh. In your case, the cargo has the same stiffness and mesh size as a steel cargo box, but I would still choose the cargo as a slave. Sliding contact might not work using linear static analysis. In linear static analysis, the contact status does not change, does not slide and the contact stiffness is constant. Freeze Contact enforces zero relative motion on the contact surface, the contact gap opening remains fixed at the original value and the sliding distance is forced to be zero. Additionally, rotations at the slave node are matched to the rotations of the master patch. The FREEZE condition applies to all respective contact elements, regardless of whether they are open or closed. Freeze Contact can be activated using TYPE=FREEZE on the CONTACT, MU1=FREEZE on the PCONT entry or by using the Penalty-based Tied Contact. Penalty-based tied contact is activated by using the TIE entry for the contact interface (with CONTPRM,TIE,PENALTY, the default).
  11. It is possible the restart file is corrupt- try deleting (or just moving to another folder) the last restart file and restarting from the second to last. Restart file without a model file is useless. Unfortunately, I can not provide further help with the given information. Check FAQ on restart: Restart.pdf
  12. Hi, the von Mises stress will be output by default when using PBARL or PBEAML with standard cross section. beam.fem
  13. @tranty these parameters require strain value input: EPS_p_max is Failure plastic strain EPS_m is Maximum tensile failure strain at which the stress in element is set to zero.
  14. Hi, choose the Optistruct user profile. Here is a video on how to import geometry: I recommend you go through FREE eBooks: Practical Aspects of Finite Element Analysis Introduction to Practical Aspects of Composites with Altair OptiStruct Check the following webinar: Alo search for other videos related to composites: https://www.google.com/search?q=composite+optistruct&sxsrf=ACYBGNSfNx5x1oRFY-AfexZKWyQXsUDT-w:1574068736682&source=lnms&tbm=vid&sa=X&ved=0ahUKEwj3n5v_tvPlAhWvlosKHTfYBU8Q_AUIEygC&biw=1858&bih=977
  15. Hi, the file you shared is empty. Either the restart file is not compatible with the version you are using or there is some problem with the restart file. Can you share the model? This error was already posted:
  16. Hi, To fix free edges of the holes use Geom>surfaces>Spline/filler or quick geometry edit (F11)>filler surf Use the following tools to obtain a better quality mesh: Geom>autocleanup to clean up the geometry 2D>automesh (F12)>QI optimize>edit criteria to define element quality criteria such as min size 2D>elem cleanup can be used to clean up a group of elements 2D>qualityindex where element quality can be checked visually and edited using cleanup tools one at a time. The failing elements can be saved to later be retrieved in elem cleanup or automesh again tool>check elems>2D (F10) to check elements retrovisor_esfuerzos_NO_edit.hm
  17. Hi, such abrupt termination is unusual. The run is usually prematurely terminated either with an error message or by user intervention. I was able to run the model to the 7th frame, after which I manually stopped the simulation (see attached out file). In your run the Radioss calculation process was probably terminated. You can try restarting: There is no engine file because the engine file was merged with starter on export. Since you have checked "Merge starter and engine file" option, the engine control cards defined will be in the starter file (_0000.rad) itself and that's why the engine file was not created separately. Open the _0000.rad file in Textpad or Notepad and ensure that engine control cards are present. 11_11_2edit_0001.out
  18. You're welcome. Actually, tie contact can not be automatically converted with tools>convert>Optistruct>to Radioss while connectors elements like CWELD can be converted. Type 2 tied contact is tie contact equivalent in Radioss and can be easily recreated. I am not sure how to export version 2017 compatible model but here is the solver deck: TopologyReconstruction-edit.fem
  19. Hi, the optimization problem is not well-posed: the weight is constrained to be the same as the initial weight. Laminate thickness can not increase in free-size optimization. Therefore the optimization result is the same as the initial configuration. Try lower mass constraint than the initial mass or use volume/mass fraction constraint. The 3.6 mm thickness is actually the result of the 1st iteration that starts with 0.6 material fraction by default with mass constraint . CompositeOptimization2-edit.hm CompositeOptimization2-edit.fem
  20. Hi, tie contact can be used in Linear Static Analysis (STATICS) and Small Displacement Nonlinear Analysis (NLSTAT). Penalty-based and MPC-based TIE contacts are available and can be selected using CONTPRM, TIE. TopologyReconstruction-edit.hm Connectors can be used alternatively. Refer to tutorial HM-3400: Create Connectors.
  21. Hi, in the quick geometry edit panel (F11) multiple lines can be selected with a cursor-drawn rectangle. Alternatively, use the Autocleanup panel to perform automatic geometry cleanup and prepare your model for meshing based on the parameters set in the BatchMesher criteria file.
  22. Glad to help. The topology stress constraint acts as a global stress control. It will filter out only the artificial local stresses caused by point loading or boundary conditions so artificial stresses will not be removed. Refer to Topology Optimization of a Hook with Stress Constraints. Those stress concentrations can be removed in the subsequent design fine-tuning stage such as size, shape and free shape optimization with DRESP1 stress constraint. The artificial stress concentrations are stress singularities due to a point load or constraint, sharp re-entrant corners, corners of bodies in contact,... For more information refer to: http://www.acin.net/2015/06/02/stress-singularities-stress-concentrations-and-mesh-convergence/ https://www.comsol.com/blogs/singularities-in-finite-element-models-dealing-with-red-spots/ https://www.digitalengineering247.com/article/dealing-stress-concentrations-singularities
  23. Hi, check the units used for added masses. Their magnitudes are consistent with kg, not with tonnes which are units used for material laws. Therefore the weight of the added masses is 1000x too high.
  24. I prefer Utility>Radioss Tools>RBODY manager where all rigid elements are listed with their related master nodes. There are other ways to get master node ID:
  25. Hi, I was able to make the law 42 work law2_finer_edit.hm
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