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Thread: Parameter optimization for biphasic confined compression stress-relaxation

  1. #11
    Join Date
    Oct 2011
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    Glasgow, UK
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    Gerard,

    Thank you for the informative reply. Your thoughts are similar to my conclusions but I wanted to check that I was running the anlysis correctly. I will try to fit to the 2nd and 3rd ramps only as I believe the first ramp is revealing an experimental artefact as you suggest - the degenerate tissue was significantly depleted of PG content thus negligible swelling occurred during the initial hold phase before the onset of deformation so the tissue may not have occupied the full chamber volume.

    Kind regard,

    Mark

  2. #12
    Join Date
    Dec 2007
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    995

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    Hi Mark,

    Yes, your optimization analysis is set up properly. However, you can improve the efficiency of the computations in two ways:

    - For a stress-relaxation analysis with a ramp time of 50 s and relaxation time of ~2000 s, I don't recommend using constant time increments. You should create a must-point curve that controls the maximum time increment (dtmax), e.g., as follows: 5 s max increments from 0 to 50 s, 5 s max increments from 50 to 100 s, then 100 s max increments from 100 s to the end of the relaxation. Repeat for each stress-relaxation step. Make sure your time points correspond exactly to the beginning and end of each ramp.

    - I have found that optimizations involving the hydraulic permeability converge faster if the parameter <f_diff_scale> is set to 0.01 (instead of the default of 0.001) in the optimization input file. That's because very small changes in the permeability don't affect the solution as much.

    These are the settings I used with your files to increase computational efficiency.

    Best,

    Gerard

  3. #13
    Join Date
    Apr 2013
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    24

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    Dr. Ateshian

    I am working on a biphasic model and I want to use a "Transversely isotropic viscoelastic" solid phase.
    I know how to run the parameter optimization for the "Isotropic viscoelastic" solid phase.
    My problem is that I could not find "Transversely isotropic viscoelastic" option.
    I think I should choose orthotropic viscoelastic and make two of elastic moduli, shear moduli and Poisson's ratios equal to each other. Is this right?

    I would be grateful if you could help me how to define the transverse isotropic viscoleasticity. if what I said above it's right, how should put the moduli equal in the optimization file?

    Thanks,
    Hamed

  4. #14
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    Dec 2007
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    Hi Hamed,

    I think I should choose orthotropic viscoelastic and make two of elastic moduli, shear moduli and Poisson's ratios equal to each other. Is this right?
    Yes, that's correct.

    if what I said above it's right, how should put the moduli equal in the optimization file?
    Unfortunately it is not yet possible to constrain multiple properties to have the same value during an optimization. You can submit a feature request to add a "transversely isotropic" material in FEBio, which is easier to do than implementing constrained optimization.

    Best,

    Gerard

  5. #15
    Join Date
    Apr 2013
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    24

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    Thanks Dr. Ateshian

    Quote Originally Posted by ateshian View Post
    You can submit a feature request to add a "transversely isotropic" material in FEBio
    I did not understand this part. How can I submit a feature request to add "transversely isotropic" ?

    Regards,

    Hamed

  6. #16
    Join Date
    Mar 2011
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    17

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    Hi,

    Are these files still compatible with the latest FEBio version. I am getting the following error

    Failed importing FEBio.file
    Fatal ERROR: unrecoverable error (line 52)

    Thanks
    Michael

  7. #17
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    Dec 2007
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    Hi Michael,

    Only the model file (CCsrlxFit.feb) can be imported into PreView. The optimization file (CCsrlxOpt.feb), which is created manually, should be opened in a text editor.

    Best,

    Gerard

  8. #18
    Join Date
    Mar 2011
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    17

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    Hi Gerard,

    Thanks for the speedy response. I have tried to run the optimization file from the command line, and I am getting an error message (Error message attached). The other file is running okay. Am I doing something wrong here ? OPT_Error.jpgAre there steps I am missing or something I am not doing correctly. My aim is to run your files first and then start working on my own model and experimental data

    Thanks

    Michael

  9. #19
    Join Date
    Dec 2007
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    Hi Michael,

    To run an optimization file you need to use -s instead of -i.

    Best,

    Gerard

  10. #20
    Join Date
    Mar 2011
    Posts
    17

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    Hi Gerard,

    I am getting the following error when I try to run the optimization file (FATAL ERROR: failed openning input file CCsrlxFit.feb). I have checked the file name and its correct and the CCsrlxFit model file run okay by its self. I was wondering if its a matter of running the wrong FEBio version. As stated on my previous discussion I have viscoelastic compressive experimental data that I want to see to simulate using the bi phasic method
    Untitled.jpg

    2nd question is: Do we have an FEBio biphasic model that I can use for transversely isotropic viscoelastic tissue properties. I have experimental data obtained when the load is applied with the muscle fibres oriented at the following angles 0, 15, 30, 45, 60, 75 and 90 degrees.

    Thanks

    Michael
    Last edited by takazam; 06-04-2013 at 03:39 AM. Reason: Correcting the format

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