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How to constraint 6DOF for a surface in a Flexible body (MNF)?

Abbas Shafiee
I have generated an MNF file in Abaqus and a node of a surface is fixed and the node is MPC beam constraint to the target surface. My FEA results are correct and the surface tied to the node is fixed as expected. 
 
Now the MNF file with these BCs is generated and imported to Adams. Now I want to compare deformation from Adams and Abaqus. They are totally different even though the surface was fixed in ABAQUS and had zero displacements, it has displacement in ADAMS. Please look at the following image for more information and please help me out with what causes this issue. 
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    Hi Abbas,
     
    I am guessing this is only because where you define your zero point for the deformation output. Please try to set the datum node (you find it in the flexbody modify dbox) to the node id that is fixed to ground. Then this will be the zero point of the deformation coloring, in a similar way as it is for your FE case.
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    @Fredrik Sjogren​  Please look at the following picture. Even though I fixed the deformation spectrum, when I scaled the flexible body deformation, it did not seem right. The picture is self-descriptive.
    Picture1
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    The exaggerated deformed flex body behaves like the deformation spectrum which I had shown in the first picture (Zero deformation in the middle of part)
     
  • 0
    Hi Abbas,
     
    Nothing wrong with that. Remember that a flexible body (based on an mnf) is a linear representation of the body elasticity. When scaling the deformation you scale the modal coordinates of the flexbody. The more you scale it the more funny it may look because you scale a linear deformation base.
     
  • 0
    @Fredrik Sjogren​  OK. So you mean there is no way to fix this problem? 
     
    I have another main model where the deformation of the flexible bearing housing is in the order of microns and in order to visualize better the deformation, scaling the deformation maybe 1000 times is required. Actually scaling the deformation to visualize better the deformation is currently adding confusion instead. 
  • 0
    The scaling of the deformations of a flexbody is a powerful tool to exaggerate the deformations to better visualize how a component deforms in an animation. As long as you are aware that the scaling will have this effect there is no problem, it is part of the theory of modal flexible bodies. The simulation results are still correct, they are not affected by the scaling.
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    @Fredrik Sjogren
    ​ 
    I got you. But to make it clear, I am only exaggerating the deformation 1000 times for the post-processing in the ADAMS view. I am not sure why exaggerating the flexible body deformation in post-processing is dealing with the modal flexible bodies theory. Yes, I agree the results are not changed when exaggerating since exaggerating is for a better animation which I am seeking too. 
     
    But I will look up the theory to see how scaling in post-processing is linked to the theory. Thanks for the directions.
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    Hi Abbas,
    The deformation scaling has no real physical meaning, it is there to help you understand things better. As the name indicates this is an exageration and there is no wrong in it, please see the following in Ahelp:
     
    Adams Advanced Package > Adams Flex > Reviewing Results > Visually Investigating Results
     
    'Scaling the Deformations
    You can change the amount by which Adams Flex deforms a mode. You can exaggerate deformations so you can see deformations that might otherwise be too subtle to see, or you can limit the deformations. The default scale factor is 1.
    Note that setting the scale factor to a value other than 1 can make the joints at the flexible body appear to separate. This is because the motion of a point on a flexible body is the sum of the deformation that has been scaled and a rigid body motion that is not scaled.
    In addition, if you set the scale to 0, Adams Flex treats the flexible body as a rigid body during animations.'
  • 0
    Hello, 
     
    Thank you Alexis. Fortunately, I am modeling only a flex body and the bottom surface of flex body is fixed to the ground and a force is applied to the flex body (as shown in the pictures above). very simple model. The end goal is to scale the deformation to have a better visualization for the model where the deformation for the flex body is in order of micron and there I also see the same scaling issue. But Hopefully, your link can help me for better visualization of my results. 
     
    Appreciate it!
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