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Thread: Importing from Abaqus: Spring and Connector elements

  1. #1
    Join Date
    Jul 2017
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    11

    Default Importing from Abaqus: Spring and Connector elements

    Good day

    I am attempting to import a number of files from ABAQUS. Specifically the Natural Knee Data from the University of Denver (The finite element model for knee extension testing: http://digitalcommons.du.edu/natural_knee_data/1/).

    I does not allow me to import spring and connector elements (ELEMENT TYPE=MASS, TYPE=CONN3D2, TYPE=SPRINGA). Is there any way around this?

    Kind regards,
    Julian

  2. #2
    Join Date
    Nov 2007
    Location
    Salt Lake City, UTAH
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    1,690

    Default

    Hi Julian,

    I'll take a closer look at those model files and the issues you are reporting, but I'm afraid there is currently no way around it. PreView should read in the SPRINGA elements, though, so if that's not working there might be a bug in PreView. If you have a small example file with SPRINGA elements that is not read in, that would be helpful. The MASS and CONN3D2 are not supported. I'll need to see what these elements really are. If we have something equivalent in FEBio I might be able to add support for them.

    Cheers,

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

  3. #3
    Join Date
    Jul 2017
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    11

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    Hi Steve

    Thank you for the response.

    I am struggling to recreate a few things from this knee set. Currently, I am able to input the bone and cartilage structures with their mesh. I have then assigned material properties and done a basic simulation with a sliding contact (I locked the femur and pushed the tibia up into it).

    I am then having difficulty recreating the following:

    Unsupported elements - I need to recreate the parts that I am not able to import. This includes the patella tendon, rectus femoris tendon, mpl and lpl which were created using 2D fiber reinforces membranes and nonlinear spring elements. I then need to recreate muscles (1 quadricep muscle and 2 hamstring muscles) which were created using the above mentioned connector element. I suppose my alternatives are either a group of 1D elements, or a 3D element?

    Recreating the motion - Tibiofemoral flexion extension is driven using quadriceps excursion (This is shown in the amp_quad_disp file). All of the other TF DOFs were kinematically prescribed to match the experiment (As I understand it these are described in the amps_gs_2660). I am not sure if I am able to recreate this combination of prescribed rotation, prescribed displacement and prescribed force in one model. I also noticed that the the kinematics file are relative displacements, and as I understand it is only possible to describe displacements in a global coordinate system, correct?

    Thank you for your help!

    Kind regards,
    Julian

  4. #4
    Join Date
    Jul 2017
    Posts
    11

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    Update:

    I am now able to apply the motions to the tibia, and I am modelling the patella tendon as just a rigid element. Now I need to apply the quadriceps force to the patella. I have the force in an input file, however I don't have the direction the force is applied in (in abaqus they apply the quad force to a rectus femoris tendon that wraps over the bone). I then either need to recreate wrapping over the bone which I don't know is possible in febio, or I need to figure out a way to break up the force in an x,y,z component.

    Also, will my model be under constrained if my patella is essentially only constrained on either end (by the patella tendon and the force pulling it)?

    Kind regards,
    Julian

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