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Type: Posts; User: ateshian

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  1. Hi Eng, I was the developer who originally...

    Hi Eng,

    I was the developer who originally created the class for 4th-order tensors with major and minor symmetries (tens4ds, 21 distinct entries). This was primarily intended to facilitate the...
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    Hi Margot, The problem you are trying to solve...

    Hi Margot,

    The problem you are trying to solve is exceptionally stiff, which is the reason that the analysis has difficulty converging. You can reduce the stiffness in a variety of ways:

    1)...
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    Hi Lance, These types of norms typically occur...

    Hi Lance,

    These types of norms typically occur when there isn't any significant loading taking place in the analysis. (In a contact problem under displacement control, this could occur when the...
  4. Hi Doug, I have attached a sample problem,...

    Hi Doug,

    I have attached a sample problem, 1543, which connects a single muscle element to a single elastic element. The activation curve contracts the muscle and elongates the elastic element. ...
  5. Hi, This could mean several things: (a) The...

    Hi,

    This could mean several things: (a) The range of parameters you picked does not include the optimal set of properties for your analysis. (b) The model does not reproduce the experimental...
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    Hi Jerry, Thanks, the User Manual has been...

    Hi Jerry,

    Thanks, the User Manual has been updated.

    Best,

    Gerard
  7. The negative permeability occurs probably because...

    The negative permeability occurs probably because you are also performing an optimization on other material parameters, such as the modulus of the tissue. Since modulus is typically of order 1 and...
  8. Hi, If the model file runs without error but...

    Hi,

    If the model file runs without error but the optimization produces a negative jacobian, it means that some of the material properties in the trial space of the optimization are responsible for...
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    Hi Jerry, Turn off and reset...

    Hi Jerry,

    Turn off <auto_penalty> and reset the <penalty> parameter manually to a suitable value (a value that produces no negative jacobians, while converging reasonably fast). For example you...
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    Hi Jerry, Instead of , try...

    Hi Jerry,

    Instead of <active_contraction>, try <activation>. Please let me know if you recover the same response as FEBio1.8, and we'll update the User's Manual accordingly.

    Best,

    Gerard
  11. Hi Geoffrey, Phi represents the osmotic...

    Hi Geoffrey,

    Phi represents the osmotic coefficient. Its default value is Phi=1 (so, if you don't include <Phi> in your material definition, you should recover the behavior from v1.2). I have...
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    Hi Julian, Creating a joint model in a finite...

    Hi Julian,

    Creating a joint model in a finite element analysis usually poses some challenges due to the fact that the model typically under-represents the real structure, which often means that...
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    Hi Julian, For multi-step analyses, you should...

    Hi Julian,

    For multi-step analyses, you should not use fixed constraints in individual steps, because this removes the corresponding degrees of freedom from the global system of equations. So, if...
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    Hi Julian, The short answer to your question...

    Hi Julian,

    The short answer to your question is no, that is not a common problem, though there is always a possibility of a code bug. Would you please attach a sample file that reproduces this...
  15. Hi Stuart, The model you attached uses the...

    Hi Stuart,

    The model you attached uses the linear pressure boundary condition, which means that the applied pressure does not account for the change in area as the pressure expands the inner tube...
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    Hi Oliver, My email is ateshian at...

    Hi Oliver,

    My email is ateshian at columbia.edu

    Best,

    Gerard
  17. Hi Jerry, I am glad it worked out. I have...

    Hi Jerry,

    I am glad it worked out. I have updated the User's Manual to revise the large penalty parameters suggested in the examples and to provide more guidelines on how to select those...
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    Hi Oliver, Would you mind attaching a small...

    Hi Oliver,

    Would you mind attaching a small example file that illustrates this issue? It would be easier for us to debug it with an example.

    Thanks,

    Gerard
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    Hi Scott, Yes, currently the...

    Hi Scott,

    Yes, currently the tension-compression contact only models frictionless contact (whether deformable-on-deformable or deformable-on-rigid). We have recently implemented a robust...
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    Hi Oliver, In my experience, using...

    Hi Oliver,

    In my experience, using tension-only springs (or tension-only fiber models) can cause instabilities in a model, so I would suspect that this is the issue with your model.

    Best,
    ...
  21. Hi Jerry, Here are the changes I made to get...

    Hi Jerry,

    Here are the changes I made to get your model (trr3.feb) to run:

    1) Since the two bodies are connected by a revolute joint, I deleted the rigid body constraints you placed on body 2. ...
  22. Hi Alessandro, As per my email message to you,...

    Hi Alessandro,

    As per my email message to you, I was able to resolve this issue by setting the stiffness matrix to non-symmetric (<symmetric_stiffness>0</symmetric_stiffness> in the Control...
  23. Hi Sanaz, Are you using the 2.0 format or 2.5?...

    Hi Sanaz,

    Are you using the 2.0 format or 2.5? The element data specification is different for these two formats.

    Best,

    Gerard
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    Hi Oliver, Tied contact interfaces should work...

    Hi Oliver,

    Tied contact interfaces should work equally well with curved or planar surfaces. Have you turned the auto-penalty on? This will make it easier to calculate a valid penalty parameter. ...
  25. Hi Alessandro, Yes, I'll take a look and see...

    Hi Alessandro,

    Yes, I'll take a look and see if I can resolve the issue.

    Best,

    Gerard
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