• RecurringMeetings
• 2016-09-14

Recurring Meeting of Cleveland Clinic - University of Utah

Date: September 14, 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)
4. Ben Ellis (University of Utah)

Agenda:

1. Ongoing and planned activities at Cleveland Clinic.
2. Ongoing and planned activities at University of Utah.
3. Other.

Immediate Action Items:

• Cleveland Clinic (Ahmet)
  • Work with Steve on sample cloud computing problem to evaluate convergence performance and connector feature.
• University of Utah (Steve)
  • Continue generalization of wrapping spring elements feature for nonlinearity and for model setup.
  • Follow up with Gerard Ateshian about formulations for shell elements on solid elements.
  • Explore the possibility to implement dampers in FEBio.

Notes:

1. Ongoing and planned activities at Cleveland Clinic.
   • Ahmet informed the University of Utah team that he has slowed down the project. Ongoing activities are mostly tedious and include tissue testing and geometry generation.
   • Ahmet also noted that he prepared a simple femur-acl-tibia model as a sample problem for cloud computing. While doing so, he tried convergence settings and explored the possibility to use rigid body kinematic constraints to prescribe joint movements. He mentioned that the convergence when using constraints was not possible all the time. Prescribing movements using traditional rotation axis - angle based strategy converged all times at faster rates.
2. Ongoing and planned activities at University of Utah.
   • Steve has worked on what he calls deformable springs, which are serial piece-wise arrangement of springs to allow wrapping. His updated formulation calculates forces based on total length of the springs. Convergence has not been good, possibly caused my singularities in determining displacements of intermediate nodes. To resolve the problem, he has been using artificial bending stiffness and relying on penalty formulation to enforce the constraints.
3. Other.
   • Ahmet and Jeff discussed providing letters of support for a grant application by Simbios. This was requested recently by Joy Ku.
   • Ahmet asked the possibility to define dampers in FEBio. Steve thought that this would be easy to implement. Ahmet intends to use these to stabilize rigid body movements that may cause convergence issues.
   • The group also discussed implementation of Lagrange multipliers to enforce constraints. Steve noted that this may require major rewrite of the code but it may need to happen to alleviate numerical issues.