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Found 10 results

  1. Hello there, I've been trying to optimize a simple aluminium structure, using Optistruct. After defining all needed steps, I start up the optimization and the solver asks for 15GB of RAM to solve the problem. This seems to be a little too much, since it is an easy optimization. The first iteration takes a long time to run and after that, the solver just freezes. How can I solve this? I will add the .fem file. Thank you, JRego DV_EBS_05_01.hm
  2. Guest

    Nonlinear continuation

    Hi sir, I am very new to Optistruct and tried doing multistep analysis -like carrying the 1st step result to next consecutive steps, but results does't seem to carry forward the previous step results. solver type used - generic type, and also tried doing in NLstatic. can you suggest some useful tips, Thanks in advance.
  3. Hello everyone, I would like to ask for an advice in solving a modal problem on a preloaded structure. I know that this is easily attainable with linear statics using STATSUB card, but I would like to find normal modes of a structure after non-linear static analysis (with contacts). Is it possible to run this sequence of analyses in OptiStruct: nonlinear statics --> normal modes? If not, would you have any suggestions how to do this? Best regards, Jakub
  4. Hello, i've modelled a frame with beam elements, beam sections were set with hyperbeam and attached to the right properties. The properties are added to the right components. Now i have noticed, that in one of my two loadsteps (both static, both with only one force and a few constraints) the displacement won't change, if i change the beam sections affected by the load. The other loadstep is affected by a change of loaded beam sections. Can't figure out my mistake, analysis runs fine without errors. Is there something i'm missing? BR mechengstud
  5. Hello, I am trying to do a linear buckling analysis on a telescopic mast of 12m. The assembly has a blend of 1D, 2D & 3D elements followed by contacts. Anyways i have taken care of all the parameters like element quality, free edges, T connections etc. As usual, I carried out a FREE-FREE Analysis first followed by MODAL & then a STATIC Analysis (Gravity Loading). All the rigid body modes have been eliminated and my modal frequency are as follows 0.676, 0.677, 6.75, 6.78, 19.53, 19.70, 39.55, 39.71, 45.30, 59.39. I don't know why the modal frequency fetched such initial low values and how to interpret the intermediate frequencies occurring in pairs? The Static Analysis results are also satisfactory with a max displacement of 0.235 mm (Mag) and stress of 11.34 MPa.The stress flow pattern is also satisfactory. Now when I simulate a linear buckling analysis I get this error: ERROR 165- Gram-Schmidt reorthogonalization did not converge. This is caused by ill-conditioning of the shifted matrix in Lanczos run. I have gone through a few other posts in this forum which said to remove rigid body modes, but i don't have any rigid body modes as such. And it is quite evident from the static analysis that my model is well connected and contacts are acting. Could you please let me know how to resolve this issue? Thank you.
  6. Hello everybody, my question is, what yields more stress static or dynamic (transient) analysis? According to what I could know up til now, it is dynamic analysis in which the stress values are expected to be higher in case of the static analysis. It it always likely to happen that stress values will be higher in case of the transient analysis if I perform both analyses for the same structure? Please guide.
  7. Hello all, How to set up a displacement load for a static analysis in HyperMesh with OptiStruct solver? I used the constraints panel with SPCD card (pictured show below), however it doesn't work. Anyone can help this? A simple example will be more appreciated.
  8. Hi all, I want to compare the result of shell and solid element for a thin plate bending analysis. So I select a thin plate with dimension 100*100*2mm, the four edge of the plate are all clamped, and a uniform pressure is applied on the top surface. However, I got a different result from OptiStruct and Ansys with the same solid model. Both the material and the mesh are the same. The in-plane element size is 1.25*1.25mm, and there are two elements through its thickness. The maximum stress in X direction from OptiStruct and Ansys is 74.4MPa and 158.7MPa. It's so different. What's more, according to the theory, the maximum stress may be 154MPa, which makes me suspect the optistruct result. The maximum stress theory for four clamped thin plate under uniform pressure loading is given in following link http://www.roymech.co.uk/Useful_Tables/Mechanics/Plates.html What's the reason for this strange result? I have attached my HM file. In addition, is there any document which explain the different options meaning of stress result type and average method? See figure below Thank you Roy Shell_Solid.zip ShellSolidCompare.hm ShellSolidCompare.fem
  9. For Modal and Stiffness(torsional and bending) of ladder frame chassis, is there any significant difference in results when I use stick contact between frame and cross-members or when I use shell/rigid weld elements to connect cross-members and long members?
  10. Dear community, I am wondering if it is possible to print the responses defined for optistruct (as per optimization) to output file even if optimization is not performed (-optskip). This could be very useful to verify a model, in terms of constraints fulfilment, without performing an optimization. I know that it is possible to print all unretained responses to output file with "RESPRINT = option", but this is not working if optimization is not running. Any suggestion? Thanks in advance, Alessandro
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