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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
    There's a few thoughts:
    1. Make sure you flexible body is all one "part". No hinges, connections, CBUSH, etc within the flexbody.
    2. It's strange that the flexbody is "pivoting" about the final fixed joint. If it's really "fixed" to the fixed joint, you would see no relative moment between the flexbody and the fixed joint.
    3. If you are getting messages about redundant constraints after adding a flexible body, I think the issue lies elsewhere in the model, and not the flexible body. Flexbodies ADD degress of freedom to your model, and is a common way of eliminating redundant constraints in your model
    4. Typically, you don't use fixed joints to attach a flexbody to the rest of your model. Normally, you are replacing a rigid body that's already connected to the rest of the model with joints and bushings with a flexible body. In that case, there is no need to introduce fixed joints into the model.
    5. finally, and honestly this is the first thing to look at: make sure the model runs correctly first without the part in question being flexible. You may have redundant constraints, but it should at least have the correct kinematic behavior.
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  • 0
    There's a few thoughts:
    1. Make sure you flexible body is all one "part". No hinges, connections, CBUSH, etc within the flexbody.
    2. It's strange that the flexbody is "pivoting" about the final fixed joint. If it's really "fixed" to the fixed joint, you would see no relative moment between the flexbody and the fixed joint.
    3. If you are getting messages about redundant constraints after adding a flexible body, I think the issue lies elsewhere in the model, and not the flexible body. Flexbodies ADD degress of freedom to your model, and is a common way of eliminating redundant constraints in your model
    4. Typically, you don't use fixed joints to attach a flexbody to the rest of your model. Normally, you are replacing a rigid body that's already connected to the rest of the model with joints and bushings with a flexible body. In that case, there is no need to introduce fixed joints into the model.
    5. finally, and honestly this is the first thing to look at: make sure the model runs correctly first without the part in question being flexible. You may have redundant constraints, but it should at least have the correct kinematic behavior.
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