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Thread: Converged to huge displacement for a model of rigid bodies

  1. #1
    Join Date
    Sep 2019
    Posts
    3

    Default Converged to huge displacement for a model of rigid bodies

    My model converged to very large displacement (1e18 mm) after normal convergence of a few steps at mm scale. I listed the log at here:
    20
    Nonlinear solution status: time= 0.288935
    stiffness updates = 8
    right hand side evaluations = 25
    stiffness matrix reformations = 3
    step from line search = 1.000000
    convergence norms : INITIAL CURRENT REQUIRED
    residual 4.002869e+012 3.824931e-003 0.000000e+000
    energy 1.719156e+004 5.515403e-008 1.719156e+002
    displacement 1.865357e-003 5.073303e-006 2.370165e-005

    convergence summary
    number of iterations : 20
    number of reformations : 3
    ------- converged at time : 0.288935

    AUTO STEPPER: decreasing time step, dt = 0.0658156

    ===== beginning time step 4 : 0.354751 =====
    Reforming stiffness matrix: reformation #1

    ===== reforming stiffness matrix:
    Nr of equations ........................... : 7
    Nr of nonzeroes in stiffness matrix ....... : 28

    1
    Nonlinear solution status: time= 0.354751
    stiffness updates = 0
    right hand side evaluations = 4
    stiffness matrix reformations = 1
    step from line search = 0.500000
    convergence norms : INITIAL CURRENT REQUIRED
    residual 1.562653e+003 1.536755e+011 0.000000e+000
    energy 1.169239e+000 5.700300e+003 1.169239e-002
    displacement 4.036265e-003 1.009066e-003 1.009066e-009
    .........

    29
    Nonlinear solution status: time= 0.354751
    stiffness updates = 0
    right hand side evaluations = 65
    stiffness matrix reformations = 9
    step from line search = 1.000000
    convergence norms : INITIAL CURRENT REQUIRED
    residual 3.730757e+048 3.730757e+048 0.000000e+000
    energy 1.346692e+040 3.825714e+005 1.346692e+038
    displacement 4.036265e-003 2.071642e-016 3.837805e+030

    convergence summary
    number of iterations : 29
    number of reformations : 9

    ------- converged at time : 0.354751

    I have no clue why this happened and how to avoid? Please help.
    Thanks
    Sam

  2. #2
    Join Date
    Nov 2007
    Location
    Salt Lake City, UTAH
    Posts
    2,329

    Default

    Hi Sam,

    Can you please attach this model? There are indeed some odd things going on here, but it's difficult to say what could be causing this, without seeing the actual model.

    Thanks,

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

  3. #3
    Join Date
    Sep 2019
    Posts
    3

    Default

    Hi Steve,

    Thank you. the geometry part of my model is grater than 2 MB. so I used google drive to share. Let me know if you cannot download it.
    https://drive.google.com/drive/folde...Np?usp=sharing

    Note: version2_control_resected.feb is the main file which includes other two feb files.
    Sam

    Quote Originally Posted by maas View Post
    Hi Sam,

    Can you please attach this model? There are indeed some odd things going on here, but it's difficult to say what could be causing this, without seeing the actual model.

    Thanks,

    Steve
    Attached Files Attached Files

  4. #4
    Join Date
    Nov 2007
    Location
    Salt Lake City, UTAH
    Posts
    2,329

    Default

    Hi Sam,

    I cannot access the google page. Can you please allow me access it? Otherwise, you may email it to me as well (steve dot maas at utah dot edu).

    Thanks,

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

  5. #5
    Join Date
    Sep 2019
    Posts
    3

    Default

    Hi Steve,

    Sorry. Now I updated the permission and you should access from the below link:
    https://drive.google.com/drive/folde...Np?usp=sharing

    Thanks
    Sam

  6. #6
    Join Date
    Nov 2007
    Location
    Salt Lake City, UTAH
    Posts
    2,329

    Default

    Hi Sam,

    When I run the model (either in febio2 or febio3), I get NANs, so I'm not getting the exact results as you are getting, but nevertheless I think I found the problem. I tracked the issue down to the load curves that define 4 points, where each point is repeated. The load curves are defined as smooth, and the repeated points are causing a division by zero. I'll see if I can fix this (by either throwing an error, or ignoring repeated points), but I think if you fix these load curves by removing the duplicate points, the problem will be fixed. Please give that a try and let me know what you find.

    Cheers,

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

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