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Thread: Parameter optimization for biphasic confined compression stress-relaxation

  1. #21
    Join Date
    Apr 2013
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    24

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    Quote Originally Posted by ateshian View Post
    You can submit a feature request to add a "transversely isotropic" material in FEBio.
    How can I do that?

    Hamed

  2. #22
    Join Date
    Dec 2007
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    995

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    Hi Michael,

    If you run the optimization file from a folder other than where it resides you must include the full path to the model filename in the optimization file.

    Best,

    Gerard

  3. #23
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    Dec 2007
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    On the main MRL forum page click on "Send bug reports and request new features for FEBio."

    Gerard

  4. #24
    Join Date
    Mar 2011
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    17

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    Dear Gerard

    Thanks, optimization file is now running

    Best Regards

    Michael

  5. #25
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    Apr 2013
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    Dr. Ateshian,

    I am trying to run optimization for a tension test using a biphasic model. Neo-Hookean viscoelastic was chosen for the solid phase.
    The first 10 points in the load curve are related to constant strain rate ramp and proceeding points are showing relaxation. While the optimization is running, in all iterations, when I compared the current column with required column, I saw that the load in the current column is increasing in the first 12 points. It seems that there is an inconsistency between the FEBio file and loadcurve in terms of time. I checked FEBio file and the time for prescribed displacement is the same as ramp time in the load curve data.

    I would like to know if there is an explanation for it.
    To help you understand the problem better, I have attached the FEBio file and Optimization file. Tension.febOp.feb

    Regards,
    Hamed

  6. #26
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    Dec 2007
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    995

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    Hi Hamed,

    You did not use must points in your Tension.feb file. This means that FEBio will not necessarily pass through the time point corresponding to the end of the ramp displacement (t=18 s according to your Op.feb file). That's why you are getting this problem.

    Best,

    Gerard

  7. #27
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    Dec 2007
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    To run this example in FEBio2, use CCsrlxFit2.feb for the model file and CCsrlxOpt2.feb for the optimization file. Use the following command to run the optimization:
    Code:
    febio2 -i CCsrlxFit2.feb -s CCsrlxOpt2.feb
    Gerard

  8. #28
    Join Date
    Aug 2015
    Posts
    27

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    Hi Gerard,

    Thanks for example.

    I am doing Optimisation on viscoelastic and hyperelastic material coefficients by simulating indentation test. By doing the optimisation, I got some coefficients, but the force-deformation graph using optimised values, have some positive loads which means tension. These positive values have effects on objective function and may change my final results.

    I thought may be not a bad idea to change these positive values to zero, however I couldn't find any way to do it. Do you have any suggestion about this problem?

    Opt-Sara-70%-all-param.febSara-70%.zip

    Many thanks
    Sara

  9. #29
    Join Date
    Dec 2014
    Posts
    27

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    Hi Gerard,

    I found parameters in the "solid mixture" cannot be optimized. Is it possible to fix that? Correct me if I am wrong.

    For example
    <material id="1" name="Material1" type="solid mixture">
    <solid type="fiber-pow-linear">
    <E>20</E>
    <beta>6</beta>
    <lam0>1.05</lam0>
    <fiber type="vector">0,0,1</fiber>
    </solid>
    <solid type="Mooney-Rivlin">
    <density>1</density>
    <c1>0.2</c1>
    <c2>0.01</c2>
    <k>6</k>
    </solid>
    </material>

  10. #30
    Join Date
    Dec 2007
    Posts
    995

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    Hi Bo,

    When using solid mixtures, you need to assign a name to each mixture component, then use that name in the optimization file. For example, in the model file,
    Code:
    		<material id="1" name="Cartilage" type="biphasic">
    			<phi0>0.2</phi0>
    			<solid type="solid mixture">
    				<solid name="fibers" type="spherical fiber distribution">
    					<beta>2</beta>
    					<ksi>3</ksi>
    				</solid>
    				<solid name="ground" type="neo-Hookean">
    					<density>1</density>
    					<E>0.92</E>
    					<v>0</v>
    				</solid>
    			</solid>
    			<permeability type="perm-const-iso">
    				<perm>0.002</perm>
    			</permeability>
    		</material>
    Then, in the optimization file,
    Code:
      <Parameters>
        <param name="Cartilage.solid.ground.E">0.92, 0.2, 2.0,1</param>
        <param name="Cartilage.solid.fibers.ksi">2, 0.2, 10,1</param>
        <param name="Cartilage.permeability.perm">0.002, 0.0005, 0.01,0.005</param>
      </Parameters>
    Best,

    Gerard

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