Study To Determine Methods Of Simulating G Effects

Author : Wenwu Xiu
Publisher :
ISBN 13 :
Total Pages : 246 pages
Book Rating : 4.:/5 (922 download)

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Download or read book Study of Human Dynamics in Simulated Reduced-G Environment and Its Applications written by Wenwu Xiu and published by . This book was released on 2015 with total page 246 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation describes the experiment and model-based research on one important topic of human dynamics, namely, the legged locomotion under varying gravity environment generated by a passive statically-balanced reduced-gravity simulator. The requirements of human space exploration have raised interest about the legged locomotion in a hyper/hypo gravity environment. The main questions concern how a legged locomotor system, evolved to cope with the Earth terrestrial gravity, could move in an environment with different gravity acceleration magnitude. Will the well-established locomotion relevant criterion still be applicable to reduced-gravity conditions? The objective of this research is to study and investigate the possible effects of reduced gravity on human bipedal locomotion kinematics and dynamics. To simulate reduced gravity conditions in a laboratory environment, a high-fidelity, low-cost, easy-to-operate reduced-G facility is developed based on the static balancing technique. The dynamic similarity hypothesis (DSH) is tested and explored for human walking and running under the simulated reduced gravity environments. The dissertation contents eight chapters. In Chapter 1, a brief background research approach and the objective of the work is given. The background contents the importance of dynamic similarity hypothesis in governing the locomotion dynamics by providing a potential unifying theory for combing the effects of speed, size and gravity. The Froude number, which is widely accepted as the criteria for defining dynamic similarity, is also introduced. The most prominent mechanical paradigms of walking and running, namely the stiff inverted pendulum and the compliant spring-mass model, are introduced by demonstrating their importance in analyzing legged locomotion. With the limitations of current methods in simulating zero- or reduced- gravity stated, the need of using the statically balanced technique to develop an innovative reduced gravity simulator are shown. In Chapter 2, the methods of using inverted pendulum and spring loaded inverted pendulum (SLIP) models are reviewed to represent the two distinct human locomotion strategies, i.e. walking and running respectively. The dynamic similarity hypothesis is key issue in understanding and predicting legged system dynamics. The limitations of using Froude number to determine the dynamically similar locomotion under reduced-G environment are also addressed. In chapter 3, the need of simulating a reduced-G environment emerges in order to better explore the dynamic similarity hypothesis with varying gravity conditions. The design and development of one passive, multiple degrees of freedom reduced gravity simulator using the underlying static balancing technology is included. The conditions of realizing the gravity compensation to simulate reduced gravity environment by appropriate design parameter choice are addressed. It is showed that, by properly selecting the springs in the system, the total potential energy of the human and mechanism combined system can remain constant, such that a desired level of gravity will be compensated. In Chapter 4, the end-effector dynamic effects of the developed reduced gravity simulator are analyzed in terms of impedance between the robotic system and the test subject. It is addressed to what extent the system inertia and friction forces could affect the gravity compensation. In Chapter 5, the reduced gravity simulator prototype is demonstrated with the design and the lab equipment setup included. The fidelity of the development reduced gravity facility in simulating one reliable reduced gravity environment is tested and validated using static and dynamic experiments. The performance of the human legged locomotion with the system is also reported in terms of the gait kinematics with different simulated gravity conditions. In Chapter 6, the test of dynamic similarity hypothesis is conducted for walking and running gaits with reduced gravity environment generated by the reduced gravity simulator. The results show that Froude number fails to define dynamic similarity for both the walking and running gaits under the reduced gravity conditions. This raises one important question: why does the Froude number predict dynamic similarity in Earth gravity, but no in simulated reduced gravity? In Chapter 7, a general criteria is identified that must be met in order to ensure dynamically similar locomotion in different gravity conditions. Our study is based on the analysis of the bipedal locomotion with the spring loaded inverted pendulum (SLIP) model. This provides a theoretical framework for defining the correct dynamic similarity hypothesis, and therefore allows us to address the above questions. In the final part of this dissertation, in Chapter 8, the results of the preceding chapters are summarized to a more coherent picture of human legged dynamics. The complete sufficient criterion for dynamic similarity utilizing the effects of speed, size, gravity and leg elasticity are built for the bipedal gaits under varying gravity environment.