Recurring Meeting of Cleveland Clinic - University of Utah

Date: November 25, 2013

Time: 11:00 AM EST

Means: Conference call

Attendees:

  1. Ahmet Erdemir (Cleveland Clinic)
  2. Jason Halloran (Cleveland Clinic)
  3. Snehal Chokhandre (Cleveland Clinic)
  4. Jeff Weiss (University of Utah)
  5. Steve Maas (University of Utah)
  6. Ben Ellis (University of Utah)

Agenda:

  1. Discuss assigned task progress.
  2. Discuss FEBio feature request and test problems.
  3. Decide tasks for next meeting.
  4. Other.

Immediate Action Items:

Notes:

  1. Discuss assigned task progress.

    • Ahmet had assigned two tasks to the Utah team: to implement in situ strain feature in FEBio and to document the progress in Wiki.

    • In situ strain.

      • Steve implemented the algorithm which allows to prescribe a fiber stretch for transversely isotropic Mooney-Rivlin material model. User specifies the fiber stretch, the algorithm makes sure the stresses are equilibriated while applying the stretch. Implementation in a general 3D framework with different materials needs to be evaluated.

      • For illustration, an example was provided showing constant in situ fiber stretch of 50% enforced on a cubical block. A similar implementation was also done to replicate an arterial opening experiment: 3% fiber stretch, fibers oriented along the circumference, outer ring in tension, inner ring in compression, radial cut relieves the stresses. This implementation required a multi-step analysis: first a tied interface was active and the in situ stretch was applied. Then, in the second step the tied interface was removed.

      • The algorithm enforces the desired fiber stretch by adjusting the overall deformation gradient using an iterative process (Lagrangian framework). The framework works when the reference configuration is not known but the in situ strain is known. A framework needs to be developed to accommodate cases where reference configuration is known and a pre-tension value is desired etc. A solution that works regardless of the analysis type (dynamic or quasi-static) would be ideal.

      • In terms of pre-tensioning ligaments in the Open Knee model, the current feature should work and the next step would be to take femur-ligament-tibia from the model to confirm the implementation of the algorithm and therefore the feature. Nonetheless, the test problem provided by Jason needs to be implemented first.
  2. Discuss FEBio feature request and test problems.
    • Rigid body kinematics representation.
      • We need to be able to prescribe kinematics and kinetics of the joint in a clinically based coordinate frame. Details of a joint coordinate system wer added to the FEBio feature specifications page.
      • A figure was created by Ahmet to illustrate the coordinate frames. This illustrates embedded axes in each of the bones (femur and tibia). The flexion axis is defined in a femur fixed coordinate frame. The internal-external rotation axis is defined in a tibia fixed coordinate frame. Another cylindrical joint on a floating axis (common perpendicular between the femur and tibia fixed rotation axes) is used for varus-valgus. In FEBio, user friendly means to set these up and be able to apply kinematics or loads about each of these axes are necessary.
      • With current release of FEBio, center of mass location of a body (therefore origin of a local coordinate system) can be changed. The user can specify joint motions by a transformation matrix, and the kinematic output can be accessed using quaternions. Prescription of moments in local coordinate systems may be challenging.
      • Abaqus has implementation of local coordinate systems and connectors. Jason will provide relevant documentation to the University of Utah team in this regard.
  3. Decide tasks for next meeting.
    • See immediate action items above.
  4. Other.
    • None noted.

RecurringMeetings/2013-11-25 (last edited 2016-05-04 22:09:49 by localhost)