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Thread: Prestrain on local axes

  1. #1
    Join Date
    Dec 2014
    Posts
    6

    Unhappy Prestrain on local axes

    Hello oh wise and beneficent FEBio developers,
    I have successfully implemented the prestrain plugin on a simple cylindrical geometry, but when I apply the same formulation to a complex geometry (tet4), I get the following error message:
    ************************************************** ***********************
    * ERROR *
    * *
    * NAN Detected. *
    ************************************************** ***********************

    The formulation I am using sets the local axes using "mat_axis" like this:
    <ElementData>
    <element id="1">
    <mat_axis>
    <a>-0.96593,0.25882,1.6273e-19</a>
    <d>6.6617e-16,-1.6663e-16,1</d>
    </mat_axis>
    </element>

    And the in situ prestrain is defined thus:
    <material id="1" name="Material1" type="prestrain elastic">
    <density>1</density>
    <prestrain type="in-situ stretch">
    <stretch>3</stretch>
    <isochoric>1</isochoric>
    </prestrain>
    <elastic type="neo-Hookean">
    <density>1</density>
    <E>1</E>
    <v>0.3</v>
    </elastic>
    </material>

    Why am I getting NAN only for the complex geometry and not the simple one? I have attached the simple and complex geometries. Oops, the complex is 2.4 MB and can't be attached to the forum. -David
    Attached Files Attached Files

  2. #2
    Join Date
    Nov 2007
    Location
    Salt Lake City, UTAH
    Posts
    2,064

    Default

    Hi David,

    In your file "Prestrain_lig_PS.feb" (which Dr. Ateshian forwarded to me), on line 11879 the value for "d" is NAN. This is the mat_axis definition for element 22:

    Code:
    			<element id="22">
    				<mat_axis>
    					<a>-0.96534,0.15514,-0.20988</a>
    					<d>nan,nan,nan</d>
    				</mat_axis>
    			</element>
    In fact, it looks like there are quite a few nans in the input file. How did you generate this data? Was this PreView, FEBioStudio, or a custom code?

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

  3. #3
    Join Date
    Dec 2014
    Posts
    6

    Default

    Steve,

    Hello and thanks for the speedy reply. The local axes were generated with a custom code. Somewhere I divided by zero, and failed to send the code without the nans. I have some code without the nans, but it still generates an "error nan detected". Where could I send it?

    David

  4. #4
    Join Date
    Nov 2007
    Location
    Salt Lake City, UTAH
    Posts
    2,064

    Default

    Hi David,

    You can send it to steve dot maas at Utah dot edu.

    Cheers,

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

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