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Found 4 results

  1. Hello everyone, I'm trying to set up a direct transient analysis of the beam you see in the picture below (simplified geometry): The beam is meshed with tetra elements. On top the beam is constrained in all dof. In the middle of the beam is a hump and the mass of it has an influence on the eigenfrequency of the beam. At the lower end of the beam a periodically enforced displacement in the range of the eigenfrequency (3 kHz < f < 4 kHz) of the beam is applied. With the FE analysis I want to get information about the following questions: What is the stress at the top of the beam? Later I would like to get information about fatigue. What is the eigefrequency of the beam? What is the exact displacement of the hump in the middle of the beam when a certain displacement is applied at the lower end with its eigenfrequency? So far I've tried to adapt the tutorial "OS-T: 1310 Direct Transient Dynamic Analysis of a BracketOS" to my purposes but I have problems with applying the periodically enforced displacement. Can someone tell me what the best way is to realize this problem with optistruct? Thank you in advance Felix Link to the tutorial: https://altairhyperworks.com/hwhelp/Altair/2017/help/os/topics/solvers/direct_transient_dynamic_anlaysis_bracket_r.htm#direct_transient_dynamic_anlaysis_bracket_r
  2. Hello, I want to transfer Displacements from a model to a submodel. I used "fields" to Import the .op2 file and then Realization to create SPCD's (one for the Displacement(x,y,z) and one for the Rotation(x,y,z)). I used the Card Image SPCADD to combine both. Then i created SPC load collector for all six DOF at the nodes where the SPCD's are. Then i created a load Step and put at subcase Definition SPC to SPC and SPCD to LOAD. If i start calculation i get the error: "* ERROR # 1908 *** Case Control data LOAD=4 is not referenced by any bulk data relevant for used subcase type." (LOAD 4 is the SPCADD load collector) So is it not possible to Combine SPCD's with SPCADD? How can I do it instead? If it helps i can upload the file?
  3. Hello all, I have a question about the equations behind the difference between loadcases that use forces vs loadcases that use enforced displacements. I am aware that these two loadcases lead to different results on Optistruct, but have found very few info in the help about it. I did a simple test watching the behaviour of a part under torsion and bending when I try to optimize it on Optistruct (minimize mass, Von Mises static constraints, gauge optimization). -When "enforced displacements" are used, we obtain a lighter part ( decrease of the thickness ) but the stresses decrease as well ! This is totally illogical since a decrease of the thickness should necessarily lead to an
  4. Hello all, I have a question about the equations behind the difference between loadcases that use forces vs loadcases that use prescribed displacements. I am aware that these two loadcases lead to different results on Optistruct, but have found very few info in the help about it. I did a simple test watching the behaviour of a part under torsion and bending when I try to optimize it on Optistruct (minimize mass, Von Mises static constraints, gauge optimization). -When "enforced displacements" are used, we obtain a lighter part ( decrease of the thickness ) but the stresses decrease as well ! This is totally illogical since a decrease of the thickness should necessarily lead to an increase of the stresses. -When "forces" are used, we obtain a logical behaviour ( lighter final part with lower thickness but higher stresses ). Could anyone explain why the second model is right in this case ? And also is there a way to still use enforced displacements and get logical results. Thank you very much, P.S : the only help I found on Optistruct documentation about the matter is the following paragraph What is the difference between using forces and prescribed displacements? In order to increase stiffness, minimize compliance should be used with forces and maximize compliance with prescribed displacements. The compliance is defined as: Compliance ~ Force · Displacement When prescribed displacements are used, the reaction force must be increased to increase the stiffness. This means that the compliance has to be maximized. In case the forces are given, a stiffer structure means having lower displacements. To achieve this goal, the compliance needs to be minimized.
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