MEGN 536 Computational Biomechanics

1. MEGN 536Computational Biomechanics Rotations for Rigid Body Kinematics Prof. Anthony Petrella

2. Knee (or any joint) Biomechanics • You are all MATLAB ninja or sous-ninja now • So, let’s start thinking about knee biomechanics… • Joint motion (kinematics) and forces (kinetics) are the foundation for defining design requirements • How do we express these quantities? • Let’s consider an example…

3. Run Abaqus Knee Model • Download Abaqus knee model from project page, unzip (on hard drive!) • Follow PDF instructions to run solution • View an animation of a gait cycle… • Color Code  by Part instances • Options  Common…  Feature edges • Result  Active Steps/Frames…  deactivate “compress” • Options  Animation…  make Frame Rate about 75% • Use Ctrl+Shift+Left mouse to rotate view • Question: What’s the best way to express 6 DOF kinematics and forces for this knee?

4. Rigid Body Motion • It is standard to describe rigid body motion by rotationsand translationsof a reference frame fixed in body – relative to a fixed global frame • For the knee, we will measure motion of the tibia relative to the femur • Femur will act like fixed global and tibia will be moving Right Leg X Y Z x z y (Frey et al., 2006)

5. Rigid Body Rotations • We will begin to consider rigid body motion with rotations only (translations are easy) • We’ll define the global fixed frame with capital letters and the moving local frame with lowercase letters • See PDF notes andws4 for more details…