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Flexbody constraints

Josef K.
Hello,
 
I want to constrain a flexible body on multiple points, using rbe2 and fixed joints. When I use more than 1 joints I get a redundunt constraints message and the simulation stops due to lock errors. I tried removing some of the fixed joints, but then the flexible body just "pivoted" around the remaining last one.
 
Is there a more proper way to constrain flexible bodies on multible points?
 
Thanks,
 
Josef
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  • 0
    Hello,
     
    I double checked the flexbody's properties and eveything is fine. I also swapped the multiple RBE2+FIXED JOINT setup with a single RBE2 comprising of all the previous areas and a single FIXED JOINT and the model seems to work properly as far as the "pivoting" problem is concerned.
     
    Checking the rigid body model, there are no redundant constraints and just two degrees of freedom (just as many as they should be). When making the part flexible, the degrees of freedom increase due to the flexibility of the part and the model is still verified successfully. The flexbody's modes are also correct as I cross referenced them with a simple SOL103 I'd run beforehand.
     
    However, the model still crashes after a while and when viewing the graphics it seemd as though the forces applied to it were making it deform extremely, which is not possible considering the fact that the forces magnitude is relatively small. I also disabled them completeley, leaving only gravity and the model still crashed. Surprisingly, disabling gravity and leaving all other force allowed for the longest possible simulation duration (40 seconds, the total time needed is 100 seconds). I also tried reducing the step size to 1e-4 and 1e-5 and the model still crashed.
     
    Does the fact that even the gravity force alone deforms the flexbody beyond reason mean that my flexbody is built poorly perhaps? Or could the large simulation time be part of the problem? Could it be a matter of the stability of the model?
     
    Thanks,
     
    Josef
     
     
Reply
  • 0
    Hello,
     
    I double checked the flexbody's properties and eveything is fine. I also swapped the multiple RBE2+FIXED JOINT setup with a single RBE2 comprising of all the previous areas and a single FIXED JOINT and the model seems to work properly as far as the "pivoting" problem is concerned.
     
    Checking the rigid body model, there are no redundant constraints and just two degrees of freedom (just as many as they should be). When making the part flexible, the degrees of freedom increase due to the flexibility of the part and the model is still verified successfully. The flexbody's modes are also correct as I cross referenced them with a simple SOL103 I'd run beforehand.
     
    However, the model still crashes after a while and when viewing the graphics it seemd as though the forces applied to it were making it deform extremely, which is not possible considering the fact that the forces magnitude is relatively small. I also disabled them completeley, leaving only gravity and the model still crashed. Surprisingly, disabling gravity and leaving all other force allowed for the longest possible simulation duration (40 seconds, the total time needed is 100 seconds). I also tried reducing the step size to 1e-4 and 1e-5 and the model still crashed.
     
    Does the fact that even the gravity force alone deforms the flexbody beyond reason mean that my flexbody is built poorly perhaps? Or could the large simulation time be part of the problem? Could it be a matter of the stability of the model?
     
    Thanks,
     
    Josef
     
     
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