Dynamic Modeling
Dynamic Biomechanical Model
A dynamic biomechanical model relates the motion of specified body segments (e.g. limb leg segments) to the resulting forces and torques acting at the joints of those segments. With such models, computer-based simulations can be performed to evaluate the mechanical response of the system (e.g. ground reaction forces at the feet) to system inputs (e.g., joint angle trajectories).
Space Cycle Model Development
A model for the Space Cycle must include, not only the body segments of the subject and the joint angle trajectories produced during a squat, but also the rotational forces imposed on the subject from riding the Space Cycle. The subject has been modeled using 12 rigid bodies with specified length and mass properties representing the different segments of the body (forearm, upper-arm, foot, shank, thigh, trunk and head) along with kinematic constraints prescribing the joints motion. Joint angle trajectories will be specified (input) using measured joint angles from Penny and Giles goniometers at the hip, knee, and ankle of the subjects’ right leg.
The dynamic model of the space cycle is being developed in SimMechanics, a software package which combines Simulink® and MATLAB® to simulate mechanical systems. Forces and torques are numerically calculated from differential equations representing the Newtonian dynamics of the rigid body motions.
Space Cycle Model Implementation
The model will be able to simulate the ground reaction forces (GRF) that results from experimentally measured joint angle trajectories. To validate the model, GRFs from simulated squats will be compared to those measured form squats performed during typical squats (in 1G). The model will then be used as an investigative tool, examining the altered subjects’ biomechanics due to imposed forces from the rotational spin of the Space Cycle. For instance, the model which contains only Newtonian dynamics will simulate GRFs that do not contain additional forces that may be imposed by subject cocontraction for stabilization. The model will also be used as a predictive tool simulating the GRF that a crewmember would experience when riding the Space Cycle in microgravity, an experiment that would be impossible to replicate on-earth.