Recurring Meeting of Cleveland Clinic - University of Utah

Date: October 23, 2013

Time: 1:00 PM 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 FEBio feature specifications development task progress.

   • http://wiki.simtk.org/openknee/Specifications/FebioFeatures

2. Discuss infrastructure/SimulationSoftware information updates.

   • http://wiki.simtk.org/openknee/Infrastructure/SimulationSoftware

3. Decide action items for next meeting.
4. Other

Immediate action items

• Steve and Ben

• Start a Wiki page to show progress on how to implement and test the given test problem. (brief outline of algorithm and copy of relevant paper will be included).

  • Ahmet and Jason

• Provide a summary of how connector elements for joint coordinate system are implemented in Abaqus as a reference for the Utah team to incorporate the capabilities to the existing code.

Notes:

1. Discuss FEBio feature specifications development task progress.
   • Jason and Ahmet updated the team with the expected FEBio features based on their priority.
   • Features classified in groups based on conditions they are used in: constitutive modeling, pre and post processing, rigid body kinematics or surrogate modeling.
     • In situ strain
       • Test problem was discussed. This will be used to build and test the feature.
       • This feature is already being developed by the Utah team.
       • Once this feature is developed for the given test problem, it can be extended to the joint model.
       • This will be a good publication opportunity once the residual stress, in situ strain measurement feature is implemented.
       • While considering in situ strain for continuum elements, if a target strain (%) is applied to the (in case of he given test problem, for example), elements will no longer be in equilibrium, without applied force on the free end the mesh would want to retract (until zero strain), and intended strain will not be applied (will be lower).
       • Various approaches will be worked on to reach the desired conditions (e.g. feature is able to apply close enough prescribed strain, or iteratively get to the desired strain or apply a desired force, finding a reference configuration that corresponds to that in situ strain configuration having some specific strain distribution on it)
       • First step will be to consider the first two conditions.
       • A pre analysis step would be needed to equilibrate the applied strain fields. The pre analysis step would be useful in deciding the analysis (implicit static / implicit dynamic).
       • Multiple algorithms can be developed to dictate the prescribed strain conditions.
       • Ahmet created a task for wiki page development for feature development progress, assigned to Utah team.
     • Element, node and surface definition.
       • Sets will be useful to define material properties and it would be convenient to be able to define surface/ node/ element sets and assign properties instead of having to know node number / element number set.
       • Will be easier to keep track of information especially when using scripts to extract information from result files.
     • Connector elements for joint coordinate system.
       • To read and apply boundary conditions from experimental states, as a way to adopt a standard clinical coordinate frame for a joint, connector elements are used to read outputs and apply loads to instead of figuring out the transformations between the given joint bodies.
       • local coordinate system defined for the femur or tibia and define the kinematics and loads with respect to each other using the local coordinate frames.
       • The feature would be needed to take the kinematics in a given coordinate system into the rigid body coordinate system the program will use to calculate the positions of the rigid bodies. Essentially taking the local coordinate system defined for a rigid body (e.eg femur) and define kinematics and loads with respect to each other using the local coordinate frames.
       • Currently, in FEBio the rigid body kinematics are defined in terms of the center of mass coordinate system which is calculated by the program but the user can also position that coordinate system anywhere as desired. The coordinate axes are still parallel to the global system.
       • This feature will provide an ability to define coordinate axes and origin that is different than the global coordinate system.
       • An ability to define the connector elements is desirable.
     • Penetration based contact.
       • Already implemented.
       • Test problem will be created to test the existing capability.
     • Spring element and wrapping.
       • To implement ligaments wrapped around bones.
       • Spring elements can be connected together to implement this.
       • The discrete elements (springs) will need to interact (like a contact) with the surfaces underneath (contact algorithm between a line element and a surface).
     • Shell elements of cartilage.
       • Shell elements will simplify the joint model while predicting deformations in contact zone as well as contact pressures.
       • Need to find appropriate element formulation.

2. Discuss infrastructure/SimulationSoftware information updates.

• Ben updated the relevant Wiki page with simulation software infrastructure information.

3. Other

• Jeff suggested using GoToMeeting for desktop sharing for future meetings.