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Thread: Biphasic Unconfined Compression Relaxation

  1. #1
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    Default Biphasic Unconfined Compression Relaxation

    This example extends the previous classical confined compression problem to that of an unconfined compression and relaxation for a biological tissue modeled with the biphasic theory. A comparison is provided between the output from FEBio and the analytical solution for this problem. This tutorial was written by Manuel Rausch and edited by David Rawlins.
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    Last edited by maas; 05-15-2013 at 10:44 AM. Reason: Updated tutorial for PreView 1.12 and FEBio 1.6

  2. #2
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    Default How to set the zero pressure?

    Hi,
    I would like to ask how do I set the pressure = 0? More specifically – which nodes/faces do I have to choose? Because when I choose whichever node or set of nodes it alerts me (in the Physics/Pressure loads) that „You must make a valid selection before you can define a boundary condition.“ The only chance, how I am able to set the prescribed zero pressure is to choose the whole face/faces, but than I don´t get the same results (as in Biphasic Unconfined Compression Relaxation tutorial). Actually, nothing happens.

    Thanks for your reply

    Michala

  3. #3
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    Default

    Hi Michala,

    This tutorial is apparently created using an older version of PreView, so I apologize for the confusion. I'll see if I can update the tutorial to a more recent version of PreView.

    Regarding your question, please keep in mind that the "pressure" is not the same as the "fluid pressure". The pressure load is a mechanical pressure (for example, an expanding balloon), but if I understand you correctly, you want to apply a fluid pressure. In that case, you can select your nodes and then select Physics/fixed constraint and then select the fluid pressure as the variable you wish to fix.

    Let me know if that answers you question.

    Cheers,

    Steve.
    Department of Bioengineering, University of Utah
    Scientific Computing and Imaging institute, University of Utah

  4. #4
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    Default

    Hi Steve,
    yes this helps. Thanks
    Michala

  5. #5
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    Mar 2010
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    Default

    Hi,

    I was wondering if the biphasic unconfined compression relaxation tutorial has been updated to the most recent version of preview?

    Thanks,

    Catherine

  6. #6
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    Default

    Unfortunately, I have not had the time to update the tutorial. Are you having problems with it?

    Steve.
    Department of Bioengineering, University of Utah
    Scientific Computing and Imaging institute, University of Utah

  7. #7
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    Mar 2010
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    Default

    I just have a few questions related to the preview portion.
    First of all, I am unsure how to select parts of the cylinder to delete in order to have a quarter cylinder.
    When I enter the parameters under material editor the units are not specified. Are the default units MPa and 10^-3 mm^4/Ns?
    There are no "nodal constraints" or "nodal displacement" options under the physics tabs. Are these equivalent to "fixed constraints" and "prescribed constraints"?
    How do I create the mustpoint file in excel?

    Sorry for all the confusion. I really appreciate your help!

    Thanks,

    Catherine

  8. #8
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    Default

    To delete part of the cylinder, you first need to convert it to an editable mesh. You can do this by activating the Modify panel, click on Modifier Stack, click the Convert button and select editable mesh. If you now go into the Mesh panel, you can select and delete the individual elements of the mesh. It is important to do this before you apply any boundary conditions.

    PreView does not support any units. Basically, it is assumed that whatever numbers are input by the users are consistent.

    Yes, the "nodal constraint" is now "fixed constraints" and the "nodal displacement" is now "prescribed constraint".

    Why do you want to create the must-point file in Excel? You can create it easily in PreView. If you open the curve editor, select the Project icon. Double click the must-point parameter to activate it. Finally, place your must points on the curve.

    Let me know if this answers your questions.

    Cheers,

    Steve.
    Department of Bioengineering, University of Utah
    Scientific Computing and Imaging institute, University of Utah

  9. #9
    Join Date
    Mar 2010
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    Default

    Hey Steve,

    Yes, I was using the editable mesh. However, it only seems to let me select one square in the mesh or the entire thing.

    The tutorial says to "select nodal displacement and double click on z-displacement to apply a displacement of 0.01 in the axial direction". Then, there should be a graph that allows you to input time and displacement. When I select "prescribed constraint" these options are not the same. Can this option be used to apply a set displacement in the negative z direction?

    The tutorial also says to create a mustpoint input file with excel to get apply an exponential distribution. This can be done in the preview program?

    Thanks again,

    Catherine

  10. #10
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    Default

    Hi Catherine,

    To select multiple elements, you have to hold down your shift button while you click and drag with your left mouse button.

    All the graphs are now collected in the Curve editor. After you apply your boundary condition, you can set the load curve in the Curve editor which can be opened from the "View/Curve editor" menu or from the main toolbar.

    You can indeed create the mustpoint curve in PreView. I imagine that whoever wrote that tutorial found it easier to create the graph in excel and then import the data into PreView. You can do that from the Curve Editor as well by clicking the "load" button (or "load" menu in the most recent version).

    Hope this helps.

    Cheers,

    Steve.
    Department of Bioengineering, University of Utah
    Scientific Computing and Imaging institute, University of Utah

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