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| = Priority List = | = Target Outcome = |
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| 1. ''in situ'' strain | Implementation of analysis and pre- & post-processing related features in FEBio to accommodate simulations conducted using Open Knee(s) = Priority List for Implementation = 1. ''In situ'' strain |
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| == Constitutive == | = Features Related to Constitutive Modeling= |
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| === ''In Situ'' Strain === | == ''In Situ'' Strain == |
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| ==== Description ==== | === Description === |
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| ==== Test Problem ==== | === Test Problem === |
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| ==== Estimated Completion ==== | === Estimated Completion === |
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| == Pre- and Post-Processing == | = Features Related to Pre-/Post-Processing = |
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| === Set Definitions for Elements, Nodes, and Surfaces === | == Set Definitions for Elements, Nodes, and Surfaces == |
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| ==== Description ==== | === Description === |
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| ==== Test Problem ==== | === Test Problem === |
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| ==== Estimated Completion ==== | === Estimated Completion === |
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| == Rigid Body Related Features == | = Features Related to Rigid Body Kinematics Representations == |
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| === Local Coordinate Systems === | == Local Coordinate Systems == |
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| === Connector Elements for Joint Coordinate Systems === | == Connector Elements for Joint Coordinate Systems == |
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| ==== Description ==== | === Description === |
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| ==== Test Problem ==== | === Test Problem === |
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| ==== Estimated Completion ==== | === Estimated Completion === |
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| == Surrogate Modeling == | = Features Related to Surrogate Modeling = |
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| === Penetration Based Contact === | == Penetration Based Contact == |
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| === Spring Elements with Wrapping === | == Spring Elements with Wrapping == |
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| === Shell Elements for Contact Problems === | == Shell Elements for Contact Problems == |
Page to describe all feature requests and associated specification for FEBio
Target Outcome
Implementation of analysis and pre- & post-processing related features in FEBio to accommodate simulations conducted using Open Knee(s)
Priority List for Implementation
In situ strain
- Element, node, and surface set definitions
- Connector elements for joint coordinate system
- Penetration based contact
- Spring elements with wrapping
- Shell elements for cartilage
= Features Related to Constitutive Modeling=
''In Situ'' Strain
Description
The zero force reference lengths (or "slack length") of the ligamentous knee structures have been shown to be important contributors to overall joint mechanics. As they are difficult to measure, ligament slack lengths are a commonly targeted parameter during optimization of specimen-specific joint level kinetic-kinematic response. Regardless of the level of refinement in the modeling approach, whether continuum or spring based, a parameter based representation facilitates these iterative studies.
Ideally, this behavior could be defined either along the ligament line of action or locally within a given element. While the local mesh coordinate frames could be used to approximate a ligament's line of action (if hexahedral elements are used), it would also be convenient to incorporate ligament wrapping, without needing to remesh to reflect this behavior (if possible).
Test Problem
The test problem will be developed using the following:
- Geometry/Mesh: a 1 by 1 by 10 mm mesh with fiber direction defined along the 10 mm length
- Boundary Conditions: a ramp displacement profile (+/- 2.5 mm load-unload) applied to one end of the mesh along the fiber direction (see figure below). The other end is fixed.
- Material Model: a fiber based model, e.g. transversely isotropic Mooney-Rivlin
Sensitivity: fiber direction in situ strain values ranging -0.2 to +0.2, in 0.1 increments.
- Output: force-displacement response of the loaded end of the mesh
For application in current OpenKnee simulations, implementation in both implicit static and implicit dynamic analyses
ImageLink(FEBio_insitu_test.png, width=600, alt=Experimentation Workflow)
Estimated Completion
April, 2014
Features Related to Pre-/Post-Processing
Set Definitions for Elements, Nodes, and Surfaces
Description
The ability to define node, element, or surface sets could add convenience to both the pre- as well as post-processing of FEBio analyses. Often, models are made up of multiple components while the output(s) of interest may be limited to a specific component, or an even smaller region of interest. In terms of pre-processing, element sets could be used to assign material properties or request specific types of output for a given region. For post-processing, instead of searching across all elements (or nodes) in a model, and cross-referencing for specific element numbers, one could simply extract the region of interest by name.
Test Problem
Estimated Completion
September, 2014
= Features Related to Rigid Body Kinematics Representations ==
Local Coordinate Systems
Connector Elements for Joint Coordinate Systems
Description
Joint level simulations, especially in the knee, often rely on application and/or description of kinetic-kinematic response in commonly accepted joint coordinate systems <REF Grood, Fujie, etc.>. This requires adoption of moving local coordinate systems that are assigned to a given body, e.g. the femur and tibia, to track overall rigid body motions as well as a means to "connect" two coordinate frames. In the case of Abaqus, we often use what's called "connector" elements to set these frames up. Their convenience is evident during both model setup, during prescription of relevant boundary conditions, as well as post-processing of the model results, where the connector outputs can be directly translated into clinically accepted descriptions of motion and/or loading.
To accomplish this feature request, we anticipate setting up a test problem with a known input-output relationship. This test problem could act as a surrogate for joint level simulations.
Test Problem
Estimated Completion
Late 2014
Features Related to Surrogate Modeling
Penetration Based Contact
Spring Elements with Wrapping
Shell Elements for Contact Problems