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Hyperman

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Hyperman last won the day on November 10

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  1. 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.
  2. 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
  3. 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.
  4. 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:
  5. Hi, I was able to make the law 42 work law2_finer_edit.hm
  6. Hi initial velocity and gravity should include all slave nodes of a rigid body as well as its master node. Other boundary conditions require only the master node.
  7. Hi, Stress constraint is not recommended in the design concept stage: topology, topography and free-size optimization.  The stress constraint definition in a topology optimization is a global constraint and does not target local stress concentrations. These areas can be addressed subsequently through size, shape, and free shape optimization or a combination thereof. Artificial stress concentrations are filtered out during topology optimization with stress constraints. These include regions around rigid connections, concentrations due to hard geometric features such as corners, etc. Stress constraints for a partial domain of the structure are not allowed because they often create an ill-posed optimization problem since the elimination of the partial domain would remove all stress constraints. Consequently, global stress constraint applies to the entire model when active, including both design and non-design regions. Stress constraints may not work well in a model where there is a large differential in response values between design and non-design spaces. In these cases, it is recommended to modify the problem formulation to say, compliance based for example. It is not recommended to use the global stress constraint along with a mass/volume constraint. The constrained mass/volume may not allow the stress constraint to be satisfied. DRESP1-card stress constraint is used in subsequent design fine-tuning stage such as size, shape and free shape optimization.
  8. Hi, the model you shared still has too low timestep for me to run. Try to run the attached model with imposed displacement, which should induce crashbox deformation- unless the impactor plate loses contact. imposed_displacement2.hm
  9. Hi, while the mesh in this model is of good quality, the mesh size is not appropriate for explicit- remember the timestep issue! A 100ms run would take 22 hours on my end. The 300kg mass added to the impactor should give sufficient kinetic energy. The only issue I can think of is initial velocity should include all the nodes of a rigid body.
  10. Hi, while you have increased the mass of the impactor the initial kinetic energy is still not enough to plastically deform the crash box. You can load the model with imposed displacement and obtain the energy required to deform the crashbox by plotting the total energy in Hypergraph and observing the corresponding deformation in Hyperview. Then you can use this energy as the initial kinetic energy to calculate the required velocity and mass of the impactor. There are modeling errors: the base plate of crashbox is not attached to the fixed supporting structure so it will slide sideways when loaded. the impactor has a relatively small contact area and it can lose contact during deformation. Provide some friction or use larger impactor plate the mesh quality is bad. Use F10 Check elements>3D to check the solid element quality and remesh accordingly. the impactor and some other components are meshed inappropriately by double walls, effectively halving the stresses. You have to mesh a single mid surface instead. imposed_displacement_0000.rad
  11. Hi, It looks like it is not supported in HM. Keywords and parameters can still be manually inserted with text editor.
  12. Hi, open the run_name.mvw session file in the run directory. Alternatively, open the run_name_s1.h3d file which contains only stress and displacement data. Note that by default only the first and last optimization iteration results are output by default. All iterations can be output with Analysis>control cards>Results>toggle RES_VI to ALL.
  13. Glad to help. Damping can not be defined in the material properties (like in Optistruct). Rayleigh damping /DAMP and dynamic relaxation /DYREL/1 can be applied to a group of nodes to avoid damping the whole model. Use the damping type that achieves primarily a better correlation to the experiments and secondarily better computational efficiency.
  14. Hi, when the shell element size is small compared to thickness it loses validity. https://www.linkedin.com/pulse/shells-vs-solids-finite-element-analysis-quick-review-kuusisto-p-e- Solid elements are more appropriate and the simulations runs fine. law2_solid_edit_0000.rad
  15. Hi, the initial kinetic energy is not enough to deform the crashbox. The impactor weighs 0.6 kg which is far less than the 100 kg structure so the impactor simply bounces off. Increase the kinetic energy by increasing mass, initial velocity or both. Negative energy error represents energy dissipated from the system and this can be from many sources like plastic deformation, hourglass energy, contact with friction, damping,... Review the energy balance to identify the source of this error.
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