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Found 8 results

  1. Hello Everybody, I've been struggling with NLGEOM analysis with CNTNLSUB since yesterday and I still don't understand a few things. What I want to do is to load a steel plate for 1 s and in the next step to unload it. I load the structure with one Force in Z direction NLOAD in the subcase 310. NLOAD activates TABLED1 where the basic linear function is defined x=0, y=0; x=1, y=1. In the next subcase 311 I use CNTNLSUB = YES, the same SPC and the same NLPARM. The nonly difference is that I do not define any load, since it should be the step, where the structure is being unloaded. Below you can find the plots I got and short descriptions of respective graphs. On the Displacement - Force plot, you can see a discontinuity between the curve belonging to the SUBCASE 310 (loading) and SUBCASE 311 (unloading). What is more, the force increases in the second step despite the lack of any loading force. The force is being increased up to 8000 N, which is a doubled value of the load defined in the first step. On the Time-Displacement plot the curve is continuos. However, the displacement is being increased till the end of the simulation (as expected based on the graph Displacement - Force). The Time-Load graph shows discontinuity again. In the beginning of unloading step, the force seems to be 0 N and than in the next increment gets back immidiately to the value, as if it was being increased, according tothe linear function present in the loading step. I would be grateful for some hints / tipps / explanation, where I make a mistake and if it is possible to create a proper loading - unloading time dependent simulation in two subcases with use of CNTNLSUB. You can find my input-deck in the attachment. nlgeom_4060_H380LAD_0p6mm_1300_CNTNL_test_01.fem
  2. Hello, in my analysis of a curve-drive-part is a rotation as SPC, solids for the curve-part (red) and a rigid-spider (blue) to transfer the rotation displacement to the solids. I use an NLGEOM-analysis, because i want to simulate the contact between the other parts (not in picture) and the curve-part. In this analysis the curve-part shows a strange deformation and the contact force is going very high. There is no constraint or force, that explained the deformation. Attached filses: Topf_Start_1 - front view with a distance measure of 211.666 Topf_Start_2 - side view Topf_End_1 - front with a distance measure of 201.110 Topf_End_2 - side view It is a model in optistruct, but for the solving is radioss used, because the large sliding contact. I want to understand possibly failures in the model. greetings Pierre
  3. Hi, I tried to model the pretension for a NLGEOM analysis with enforced displacements in a local csys. If the pretension is not followed by an another loadcase, the results are OK, if there is a follower loadcase the results are not the same as before and wrong. Attached you can find a test model (with pretension with and without an additional loadstep). Nodes id. 1 and 2 are the ones with enforced displacements in the local csys id 4. Please take a look at the displacements for the pretension in both cases. Is this problem known? Is there a workaround for this problem? Thank you. Best regards, Szilard Balazs example_NLGEOM_pretens_load.zip
  4. Hello! I really need your help. whenever I implemented OPTISTRUCT, I got " Non-convergent nonlinear iterations for subcase 2" result. I set hyper-elastic material, and pshellx for 2D design. Also My load collectors are, SPC/LOAD/TABLED1/NLOAD/NLPARM, and I set load step NLGEOM I don't know why I couldn'y get nonlinear analysis result in OPTISTRUCT. My material is the example of MATX62.. I attached My entities and NLPARM screen-picture too Please give me some advices Thank you, Best Regards,
  5. Hi, I've been trying to find the force required to create an interference fit between two parts. I'm fully constraining one of them, and placing an SPCD upon the other. The contact between the parts is a sliding one (I've tried different values of friction, but nothing seems to help). I'm using a non-linear implicit analysis. The solver gets quite far down the line, but then crashes at some point because it cannot converge. One of the parts begins to deform (as it is supposed to), but then the solver doesn't get any further. Chamfering the goemetry to avoid sharp edges helped some, but not enough. Any thoughts, or a location where I can share a large .fem file? Thanks, Jai
  6. Hello, everyone ! Can anyone share some tutorials or examples on nonlinear optimization in which the analysis keyword is NLGEOM, IMPDYN or EXPDYN ? Thank you in advance !
  7. Hello Everybody, I've been struggling with NLGEOM analysis with CNTNLSUB since yesterday and I still don't understand a few things. What I want to do is to load a steel plate for 1 s and in the next step to unload it. I load the structure with one Force in Z direction NLOAD in the subcase 310. NLOAD activates TABLED1 where the basic linear function is defined x=0, y=0; x=1, y=1. In the next subcase 311 I use CNTNLSUB = YES, the same SPC and the same NLPARM. The nonly difference is that I do not define any load, since it should be the step, where the structure is being unloaded. Below you can find the plots I got and short descriptions of respective graphs. On the Displacement - Force plot, you can see a discontinuity between the curve belonging to the SUBCASE 310 (loading) and SUBCASE 311 (unloading). What is more, the force increases in the second step despite the lack of any loading force. The force is being increased up to 8000 N, which is a doubled value of the load defined in the first step. On the Time-Displacement plot the curve is continuos. However, the displacement is being increased till the end of the simulation (as expected based on the graph Displacement - Force). The Time-Load graph shows discontinuity again. In the beginning of unloading step, the force seems to be 0 N and than in the next increment gets back immidiately to the value, as if it was being increased, according tothe linear function present in the loading step. I would be grateful for some hints / tipps / explanation, where I make a mistake and if it is possible to create a proper loading - unloading time dependent simulation in two subcases with use of CNTNLSUB. You can find my input-deck in the attachment. nlgeom_4060_H380LAD_0p6mm_1300_CNTNL_test_01.fem
  8. Hello, I am trying to run a topology optimization study on a model with non-linear geometry (large displacements). I am applying my loads by imposing a force via NLOAD1 Card Image. However, whenever I run the study, I receive the following error: ERROR # 4003: Abnormal termination in NLGEOM subcases. I have no idea what this error indicates, and I can not seem to find any other online resources to help me troubleshoot. The check screen output is shown below: Additionally, here is my NLOAD1 definition: And here is my Non-Linear subcase definition: Please let me know if you can help me identify the source of this error. Thanks in advance! Branden
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