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Found 3 results

  1. 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
  2. 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.
  3. Hallo, I am having a model of bicycle pedal crank in which I want to apply loads on the pedal ( on the created node). If we take the pedal goes 360degree I want to split the 360 into some lets take 18 steps so I have to create 20 load cases. I considered when the pedal is at top as Top dead center ( TDC) and when it is at bottom Bottom dead center (BDC). The load which i apply on the tdc is high and when it goes bdc it gets reduce and again to complete one cycle the load goes load just like the real case of pedaling the cycle. I can manually calculate each load case Fx,Fy and Fz component and give accordingly for 20 steps. My question : Is there any other way that giving initial load that is load at TDC Fx,Fy and Fz value and the next consecutive load cases for the next 20 degree, then 40 degree and so on the value has to decrease ? , Because for 20 steps we can calculate what if there is a component with 1000 loadsteps. the values of Fx,Fy and Fz cant be calculated manually it will make the person frustrated. So there has to be a way as a factor ( with this initial factor the consecutive load has to change either decrese or increase). Is there a way to give a initial factor or way to implement all other corresponding loads ? It would be much appreiciated if I get any positive response . I have attached a sample pic of my model with just 4 load cases with certain angle apart. It was easy to do by calcualting Fx,Fy and Fz values. But if i want to implement more loads by dividing 360 by so and so ... Thanks in advance for the response. Kind Regards, Muthu,.
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