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Everything posted by Hyperman

  1. Hi, glad to help. In the explicit quasistatic analysis it is recommended: The loading should be gradually ramped up from zero over a reasonable period (at least 0.3 s). Instantaneous loading (non-zero loading at time zero) causes propagation of a stress wave through the model similar to impact load. The kinetic energy should be bellow 5% internal strain energy throughout the simulation to ensure a quasistatic process without inertial effects. Vibrations should be damped using for instance /DAMP Rayleigh damping. The implicit quasistatic analysis with instantaneous loading has convergence difficulties as the equilibrium solution at initial load is far from the initial position. As a workaround try: create two engine files with the first engine ending after the preload is applied using the ramping function and the second simulation starts in the equilibrium condition perform pretension analysis and export deformed shape and stress fields using STATE file. Then initialize the stresses and deformed position in the original solver deck. However, this approach is not tested as I am away from my Hyperworkstation. Implicit and explicit solutions can be compared only if the explicit solution satisfies above recommendations regarding slower loading and damping- both will increase explicit solution CPU time. The implicit solution could be further optimized for better convergence. Note also that Radioss implicit is only meant to complement explicit (capability to switch during simulation)- otherwise use NLSTAT non-linear quasi-static analysis in Optistruct.
  2. Hi, to minimize compliance use minimize internal strain energy response (RTYPE=8). Unfortunately, not all responses are available for Radioss optimization. When the desired response is not directly available from Radioss, it may be calculated using /DRESP2. Or the model could be converted to Optistruct and run explicit dynamic analysis (Radioss simulation in the background). _DRESP1.pdf _DRESP2.pdf
  3. Hi, the loading function should be ramped up from zero use Tools>Engine file assistant to define simulation parameters ctrl+F find IMPL/QSTAT = implicit quasistatic second_order_0000.rad
  4. Hi, given the impacting object's high kinetic energy (KE = 71940 J or 430x the energy of a .22 rifle bullet) fragmentation on impact is expected. However, From Radioss help: As a workaround, define FAIL/TENSSTRAIN card to get a more realistic fracture behavior. Collision_edit_0000.rad
  5. Hi, that is correct- you can use TYPE2 tied contact to set no relative motion (Kinematic Constraint); except Spotflag=25 which is Penalty formulation with constant stiffness calculated using Istf and Stfac.
  6. Hi, since version 12 Radioss Bulk is named Optistruct.
  7. Hi, the energy error is coming from the bird component as hourglass energy. One major difference is the bird in your example weighs 11 grams, while in the tutorial it weighs 1.93kg. Unfortunately, I am not familiar with SPH theory to figure this one out
  8. Hi, as mentioned before, this positive energy is somehow due to the too high minimum gap. Reducing the gap to 4e-5 will make the model able to solve without positive energy. Test8_edit_0000.rad
  9. @harshitpuri actually, also in the HTC paper the total energy does increase slightly at 50 and 325ms. Like mentioned before, additional external energy is due to gravity body loads. If gravity is turned off there will be no total energy increase.
  10. Hi, the reason for total energy rising is due to the external work (Total Energy = Internal Energy + Kinetic energy + External Work). External work is any external loading applied in the simulation. This can include Imposed movement (displacement, velocity or acceleration), force (/CLOAD or /GRAV), and pressure to name a few. Work done by an external force on a system is always a transfer of energy to some other form of energy and this negative work represents the transfer of energy during the simulation and this is fine. The work being done by gravity is gradually increasing, which can be plotted in HG as External forces work. A similar query was already posted: Check the following research papers on bus rollover, where energy balance graphs show total energy increasing. https://pdfs.semanticscholar.org/0a6b/90b7129a175f0d2279fdcd144341d8b4356e.pdf?_ga=2.241711170.1350978322.1564233254-407258112.1557865095 https://advancedstructures.in/blogs/bus-rollover-simulation-analysis/ http://ijsetr.org/wp-content/uploads/2016/05/IJSETR-VOL-5-ISSUE-5-1815-1820.pdf
  11. Hi, the penetration is detected after assigning property with thickness value defined. This is due to the way the Minimum gap for impact activation (Gapmin) is computed if not specified. If no thickness is provided the penetration checker will fail to detect penetrations as tm is not available. This isn't a real issue anyway since the model will not be able to run without material and property properly defined. For more details refer to the attached document from Radioss Help. _INTER_TYPE7.pdf
  12. Hi, The ACELL requires an additional table. A minimum of two pairs of (LOCi and VALi) should be specified. Refer to the attached documentation for more info. Card edit the load to access continuation lines. accel.wmv ACCEL.pdf
  13. You're welcome. If the structure is only supported by contact at both ends of the girder, then the towers will undergo rigid body motion (rotation) after 70% load increment causing convergence difficulties for implicit method. This can be observed in the *_nl.h3d bellow (activated by PARAM>NLMON>DISP). You mentioned the girder is supposed to move up, but in the shared models there are only downward forces acting on the top of both towers. Also, if the structure is initially on the ground, the outermost edge of the towers baseplate will slide on the ground during rotation, as indicated by the undeformed plot. I have converted the Optistruct model to Radioss, because the explicit method does not fail due to rigid body motion. Note that the "dummy" material was assigned a density of steel due to the timestep issue, therefore the model is heavier (77 instead of 38 tonnes). The same rotation could be observed indicating the towers are not properly constrained, so boundary condition assumptions should probably be revised. JDN_Loading_Beam_Rev_A1_Radioss_0000.rad JDN_Loading_Beam_Rev_A1_Radioss_0001.rad JDN_Loading_Beam_Rev_A1_Radioss.hm
  14. Glad to help. Yes, usually models experience convergence difficulties if they are not properly constrained. This is especially problematic with models constrained only by contact. The following changes were made to make the model converge: -the main issue was that the girder was split at the midpoint. Shift+F3 to equivalence nodes along the plane of symmetry -I assume the "Bottom plate" is attached to the ground so it was constrained with SPC in all DOF. -contact is set as surface to surface (DISCRET=S2S) -contact stabilization CNTSTB were defined and referenced in the subcase -nonlinear expert system was activated PARAM>EXPERTNL>YES -Nonlinear Monitoring was activated PARAM>NLMON>DISP -the number of increments was increased to 3 in the NLPARM>NINC=3 JDN_Loading_Beam_Rev_A1_edit.hm JDN_Loading_Beam_Rev_A1_edit.fem
  15. Hyperman


    Hi @hyperlove, 1. Skew in CLOAD definition is used to define a different coordinate system than the global system. Therefore the orientation (direction) of the skew axis is important, not its relative position. 2. RBE3 elements are used to distribute loads without inducing unwanted stiffness. It is not an element to be used to model a connection, but rather an element to induce motion in a node as a function of the weighted average of other nodes.
  16. Hi, The SOUT field on the PCOMP or PCOMPG Bulk Data Entry must be set to YES to activate stress results calculation for the corresponding ply. For PCOMPP, the SOUT field on the corresponding PLY entries should be set to YES.
  17. Hi, the "Undefined SET SSID on CONTACT" error was due to contact surfaces having inappropriate card image- SURF should be used instead of ELIST. The compression-only boundary condition can be created by duplicating, offsetting and constraining a set of elements in the region where contact is expected to model the upper support surface of the SPMT truck. Define a contact interface between support and the bottom plate. Contacts should also have friction to prevent slipping, which could result in rigid body motion. 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. Therefore, a nonlinear quasistatic analysis (NLSTAT) should be used. If no liftoff is expected then linear static analysis can be used. There were some other modeling issues: -the symmetry boundary conditions were inappropriate. To constrain in the YZ plane, only X translation and Y & Z rotations should be constrained. -"dummy" material has no density -single point constraints and forces were in the same load collector "400 ton Weight", but they should be separated. Also, forces were applied to the same nodes as constraints, which cancels the effect of forces. -the pyramids of contact surfaces should be pointing in the direction of contact with MORIENT=NORM JDN_Loading_Beam_Rev_A_edit.hm JDN_Loading_Beam_Rev_A_edit.fem
  18. Hi, check the resource library Virtual Durability Process: Bringing Together MBD, FE and Fatigue is the most relevant to your query. You can request more e-learning material from nCode
  19. Hi, try /DYREL (dynamic relaxation) where Period to be damped and Relaxation factor can be specified. /DYREL/1 can be applied to a group of nodes.
  20. Hi, looks like an issue with the interface. Check the interface for initial penetrations and if any are found depenetrate them all. In HyperMesh, go to Tools>Penetration and manually or automatically fix them. Please refer HM-3320 tutorial.
  21. Hi, most spring properties support some failure criteria. Spring beam supports deformation, force and energy-based failure criteria.
  22. Hi, the nonlinear force-displacement graph is consistent with geometric (buckling) or material (plasticity) non-linearity. Can you share the model or the engine out file? WARNING ID : 343 (INITIAL PENETRATIONS IN INTERFACE) should be removed. In HyperMesh, go to Tools>Penetration and check the model for any penetrations. You can manually or automatically fix them. Please refer HM-3320 tutorial in Help Menu which shows the steps.
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