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| * To illustrate that an example was also provided a showing constant in-situ fiber stretch of 50% enforced on a cubical block. A similar implementation was also done to replicate an open angle experiment done on arteries (3% fiber stretch, fibers oriented along the circumference, outer ring in tension, inner ring in compression, radial cut relieves the stresses). | * To illustrate that an example was also provided showing constant in-situ fiber stretch of 50% enforced on a cubical block. A similar implementation was also done to replicate an open angle experiment done on arteries (3% fiber stretch, fibers oriented along the circumference, outer ring in tension, inner ring in compression, radial cut relieves the stresses). |
Recurring Meeting of Cleveland Clinic - University of Utah
Date: November 25, 2013
Time: 11:00 AM EST
Means: Conference call
Attendees:
- Ahmet Erdemir (Cleveland Clinic)
- Jason Halloran (Cleveland Clinic)
- Snehal Chokhandre (Cleveland Clinic)
- Jeff Weiss (University of Utah)
- Steve Maas (University of Utah)
- Ben Ellis (University of Utah)
Agenda:
- Discuss assigned task progress.
- Discuss FEBio feature request and test problems.
- Decide tasks for next meeting.
- Other
Immediate action items:
Utah team
- Implement In-situ strain test problem.
Jason
- Send connector element documentation in Abaqus to the Utah team.
Notes:
1 and 2. Discuss assigned task progress and FEBio feature request.
- In-situ strain
- Ahmet had assigned two tasks to the Utah team: 1. Implement in situ strain feature in FEBio and, 2. document the progress in Wiki.
- Steve implemented the algorithm which allows to prescribe a fiber stretch (transversely isotropic material) and strain is generated entirely by the fiber stretch. User specifies the fiber stretch, the algorithm makes sure the stresses are equilibrated while applying the stretch.
- To illustrate that an example was also provided showing constant in-situ fiber stretch of 50% enforced on a cubical block. A similar implementation was also done to replicate an open angle experiment done on arteries (3% fiber stretch, fibers oriented along the circumference, outer ring in tension, inner ring in compression, radial cut relieves the stresses).
- This is a multi-step analysis (tied interface is active, stretch is applied, in the second step tied interface is removed). The goal here is to explore both quasi-static and dynamic analyses.
- A solution that works regardless of the analysis (dynamic vs quasi-static), would be ideal.
- This algorithm enforces the desired fiber stretch by adjusting the overall deformation gradient using an iterative process (Lagrangian framework).
- 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/ feature.
- The test problem (provided by Jason) needs to be implemented before an actual Open knee model application.
- This 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, a pre-tension value is desired etc.
- This feature applies to transversely isotropic Mooney-Rivlin materials, the implementation in a general 3D framework needs to be evaluated.
- Rigid-body kinematics representation
- Need to be able to prescribe kinetics at the joint based on a clinical coordinate frame
- Details about the coordinate frames were added.
- The figure was created by Ahmet to illustrate the coordinate frames. This illustrates embedded axes in each of the bones (femur and tibia). In the femur frame, a fixed flexion axis is defined and in the tibia a fixed internal-external frame.So there is a cylindrical joint and a floating frame that is a common perpendicular between those two (as per Grood- Suntay). An efficient way to set up these and be able to apply kinematics or loads about each of these joints.
- Effectively, the two embedded coordinate systems can be currently defined. Prescribing the motion of one relative to the other can be accomplished by different ways of representing the transformation matrix ( e.g Quaternions ).
- Implementing a way to prescribe these will entail providing a user interface to specify these angles and converting them in FEBio to a standard transformation matrix and delivering to the user the kinematic parameters which are derived directly from the transformation matrix.
- Prescribing moments in the local coordinate systems may be challenging.
- Abaqus has this implementation and Jason will provide the Utah team with the relevant documentation.
3. Decide tasks for next meeting
- See immediate action items above.
4. Other
- None noted.