Recurring Meeting of Cleveland Clinic - University of Utah

Date: April 23, 2014

Time: 3:00 PM EST

Means: Conference call

Attendees:

1. Ahmet Erdemir (Cleveland Clinic)
2. Jason Halloran (Cleveland Clinic)
3. Jeff Weiss (University of Utah)
4. Steve Maas (University of Utah)

Agenda:

1. Progress on in situ strain test problem.

   • http://wiki.simtk.org/openknee/Febio/InSituStrain

2. Update on local coordinate systems and connector elements.

   • http://wiki.simtk.org/openknee/Febio/RigidBodyMotions

3. Update on set definitions in FEBio input and output.

   • http://wiki.simtk.org/openknee/Febio/SetDefinitions

4. FEBio solution repeatability.
5. Decide action items for next meeting.
6. Other.

Immediate Action Items:

• University of Utah (Jeff)
  • Follow up with Ben to provide results from previous FEBio repeatability studies.
  • Provide a copy of CMBBE 2014 abstract.
• University of Utah (Steve)
  • Provide a summary of recent results, issues, and planned strategies on in situ strain wiki page.

Notes:

1. Progress on in situ strain test problem.
   • Steve extended the capability for multidirectional prescription of in situ strain. The feature now works with any number of fiber directions. He submitted an abstract to CMBBE 2014, with Jeff, Ahmet, and Jason as co-authors. A copy of the abstract will be sent to the Cleveland Clinic team.
   • Steve noted that current formulation is uncoupled and accommodates residual strains in the deviatoric components not in the volumetric components. As a result when pre-strain is applied a deformation of the structure is observed. Ideally, when material, geometry and boundary conditions are compatible, no deformation should be observed. To address this issue, Steve will reimplement this feature for coupled constitutive formulation, test, and then move on to the uncoupled formulation with the an updated approach. Adaption of the iterative correction of the applied in situ strain is a novel feature when compared to previous literature. Steve will update the wiki to reflect these discussions.
2. Update on local coordinate systems and connector elements.
   • Gerard Ateshian has been implementing features relevant to local coordinate systems and dynamics. The dynamics formulation causes issues, in relation to integration approaches currently adapted in FEBio. Gerard will be working on these issues in time and with progress the team can explore specific implementation of local coordinate systems and connectors for rigid body kinematics-kinetics.
3. Update on set definitions in FEBio input and output.

   • Steve has started to incorporate set definitions in PreView. Currently, PreView supports surface definitions. Sets will be part of the FEBio 2.0 input file format; Steve noted that the team can take a look at the FEBio user manual for version 2.0. The Utah group is getting closer to releasing FEBio version 2.

   • Implementation of sets in output file (xplt file) is still a question. Incorporating the capacity to have sets in the output file is one thing, interacting with the file and/or data structures another. Ideally, a Python scripting interface to FEBio input/output and data structures provides a robust mechanism. Nonetheless, if input/output file specifications are known, the Cleveland Clinic team can still utilize Python to change models and extract important results. This way of thinking may result in plug-ins, i.e. an Open Knee(s) specific post-processing gui, or allow unsupervised (scripted) simulations.
4. FEBio solution repeatability.
   • Ben has been on vacation. He will return back in the upcoming week. Jeff will follow up with Ben to explore this issue and find results from previous studies.
5. Decide action items for next meeting.
   • See Immediate Action Items above.
6. Other.

   • Jeff noted that registration deadline for summer course on FEBio, see http://ibbm.sci.utah.edu/, is approaching.