Recurring Meeting of Cleveland Clinic - University of Utah

Date: January 13, 2016

Time: 2:00 PM EST

Means: Conference call

Attendees:

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

Agenda:

1. Discuss immediate action items from the last meeting.
2. Practical use of in situ strain feature.
3. Decide action items for next meeting.
4. Other.

Immediate Action Items:

• University of Utah (Jeff)
  • E-mail Ben to reschedule conference calls if desired.
• University of Utah (Steve)
  • Work on a sample contact problem to compare shell-based surface on foundation model against hexahedral representation.
  • Provide example problem illustrating node/element numbering discontinuity.

  • Ask Dave Rawlins to compile a newer version of PostView compatible to visualize simulation results with in situ strains.

  • Provide documentation on the use of in situ strain feature.

Notes:

1. Discuss immediate action items from the last meeting.
   • Ahmet followed up with Joy. She will joint the conference call on February 10, 2016.
   • Jeff has been looking at shell formulations for modeling of cartilage. From what he has read, he did no see any inherent problems for FEBio shell formulations that will preclude their use. He asked Steve to work on a problem. Ahmet noted that the cartilage problem is essentially a thin layer on a foundation. Jeff requested Steve to compare existing shell formulations (shell with a constant thickness on a rigid body) against hexahedral representation of the layer (with the prescribed thickness). It will be useful to compare predictive response, e.g. contact pressures, and computational cost. Steve asked for more information about the sample model. Jeff noted that it can be as simple as a 20 x 20 mm square layer compressed by a 40 mm diameter half cylinder, all with shell thickness of 2mm on both sides. Ahmet mentioned that existing verification problems related to contact can also be used. To start with the model, Mooney-Rivlin material can be used. Steve will work on this for the next meeting.
   • Steve did not have a chance to work on contact with springs and surfaces allowing wrapping of springs. He implemented the flexibility to start node and element numbering at any desired number. This feature also allows discontinuous numbering for nodes and elements. Steve will provide an example problem.
   • Ben was not able to attend the meeting. Jeff will follow up with him to see if there is a need to change the conference call schedule.
2. Practical use of in situ strain feature.
   • Ahmet ran the Open Knee(s) - Generation 1 model with in situ strains. The model for valgus loading converged. Ahmet confirmed the constraints on rigid body degrees of freedom (translations free, rotations except for varus/valgus fixed). The model solved in about 40 minutes on his laptop. He also tried to run a passive flexion model with in situ strains (translations and rotations free except flexion as prescribed). The simulation converged up to about 50 degrees.

   • Ahmet was not able to visualize the results using PostView. The latest version he utilized was version 1.9, which he downloaded from the FEBio site. Steve told him that he would need a new version. He will ask Dave to compile.

   • Ahmet was also wondering how to set in situ stretch prescription level, i.e. strong (geometry changes) vs weak (geometry fixed, in situ stretch relaxed). Steve mentioned that in the Open Knee(s) - Generation 1 model he utilized the default setting. He will provide documentation on representing in situ strain feature parameters in the model file.
3. Decide action items for next meeting.
   • See Immediate Action Items above.
4. Other.
   • None noted.