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Thread: Importing data

  1. #1

    Default Importing data

    Dear sir,
    I am a new user for Preview and Postview packages, and i want to know if it is possible to import a data file (Excel sheet) to define a displacement constraint for a specific element?
    Also i want to know how to add a node in a specific position.

    Best regards
    Shady

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

    Default

    Hi Shady,

    Unfortunately, both of these operations would be difficult, if not impossible to do within PreView. For the first, it's probably easier to write a little script (Matlab, Python, c/c++) that modifies the .feb input file directly and apply the displacement constraint. The best way to do this is to set the displacement scale value for each node.

    Code:
    <prescribe>
      <node id="1" bc="x" lc="1">1.0</node>
      ...
    </prescribe>
    You would change the 1.0 value to whatever you want to apply for that particular node.

    The second problem, inserting a node at a specific location, will be more challenging since you would also have to modify the local mesh connectivity so that elements and faces connect to that inserted node. This is currently not possible within PreView. (We are working on a improved tetmesher that in principle can do this very thing, but won't be available for a while).

    Sorry I don't have any better answers, but I hope this is helpful.

    Cheers,

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

  3. #3

    Default

    Thanks steve for your reply, but what if my displacement is changing in each time step, do i have to add a step for each change of displacement constraint?
    also my displacement constraint is identifiying X, Y, Z, Rx, Ry & Rz, how would be the formatting of this modification in .feb input file? (in your reply you mentioned only how to update the displacement constraint in x direction)

    shady

  4. #4
    Join Date
    Nov 2007
    Location
    Salt Lake City, UTAH
    Posts
    1,690

    Default

    Hi Shady,

    You mention rotational degrees of freedom. Are you trying to prescribe a rigid transformation? If so, you can actually do that much easier in FEBio by creating a rigid body and then prescribing the kinematics on to the rigid body. That way, you can prescribe your displacement using a load curve, so that you can specify a time-dependent displacement. Check out the section on rigid body constraints (section 3.9.1 in the user's manual) and see if this is what you are looking for. Let me know if you need any additional information.

    Cheers,

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

  5. #5

    Default

    See here http://www.gibboncode.org/ for a MATLAB toolbox that links with FEBio. You can also specify nodal displacements for each node or element separately as you which. See the demos for that.

    Perhaps what you want is to specify your total displacement as a function of a specific load curve. If the load curve is just the linear curve [0 0; 0 1] then the variation in time is linear like that for a single step. To make it vary in time in a more complicated fashion you could either have multiple load curves and steps as suggested before or you could specify a single load curve (e.g. smooth or multi-linear) whereby you specify each point on the curve as you wish like [0 0; 0.25 0.5; 0.5 0.6; 0.6 0.7; 1 1] would be a different history. So if you can formulate your desired displacement history as a function of the total displacement for each component then this is possible. I'm not sure if that is enough though, for instance if your motion is so complex that you need negative entries in the load curve I am not sure if that is allowed/valid (is it Steve?) otherwise you would probably need multiple load curves and steps.

    All the best,

    Kevin

  6. #6

    Default

    Thanks Kevin for your kindly reply, it was really useful.

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