http://hdl.handle.net/1721.1/7758 http://hdl.handle.net/1721.1/49685 Safety-driven system engineering process Stringfellow, Margaret Virgina As the demand for high-performing complex systems has increased, the ability of engineers to meet that demand has not kept pace. The creators of the traditional system engineering processes did not anticipate modern complex systems, and the application of traditional processes to complex systems such as spacecraft has repeatedly led to disastrous results. Too often, system safety is considered late in the design process, after much of the design is set. This thesis presents an iterative safety-driven system engineering process to address this problem. The process integrates safety into the design process, ensuring that safety is designed into the system, rather than added on. The techniques used in this process are: I) Intent Specifications, a framework for organizing system development and operational information in a hierarchical structure; 2) the System-Theoretic Accident Modeling and Processes (STAMP) model of accident causation, a framework upon which to base powerful safety engineering techniques; 3) STAMP-based Hazard Analysis (STPA) a novel hazard analysis technique; and 4) SpecTRM-Requirements Language (SpecTRM-RL), a formal modeling language. Intent Specification is used to document the design with complete traceability from system goals, requirements, and constraints to the operational design and software code. The STAMP framework is used to apply concepts from control theory to system engineering. STPA is used to identify hazards and eliminate them or mitigate their effects to ensure a safe system design. Finally, SpecTRM-RL is used to create the blackbox behavior models. An example of this process applied to an outer moon exploration mission is presented (in the form of an intent specification) and discussed. The specification focuses on the design of the control system and functionality of the scientific instruments, while also including a high-level design of the entire spacecraft. The application of the process described in this thesis demonstrates that design decisions are safety-driven, and that the results of the hazard analysis are integrated into all aspects of the design. Thesis (S. M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2008. MIT Barker Library copy: leaves 82 to 106 bound upside-down. Includes bibliographical references (leaves 56-59). Mon, 29 Oct 2007 22:58:59 GMT http://hdl.handle.net/1721.1/49684 Design, manufacturing, and testing of an active twist rotor Shin, SangJoon, 1967- Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1999. Includes bibliographical references (p. 153-156). Thu, 29 Oct 1998 22:58:59 GMT http://hdl.handle.net/1721.1/49682 Motion at low Reynolds number Tam, Daniel See Wai, 1980- The work described in this thesis centers on inertialess motion at low Reynolds numbers at the crossroad between biofluids and microfluids. Here we address questions regarding locomotion of micro-swimmers, transport of nutrient around micro-organisms as well as mixing and heat exchange inside micro-droplets of water. A general framework for the investigation of optimal locomotion strategies for slender swimmers has been developed and applied to different systems. Here we exclusively study the hydrodynamical aspects of locomotion without further consideration for the swimmers internal dynamics. The first system studied is the "three-link" swimmer, first introduced and discussed by Nobel prize laureate E.M. Purcell in his famous lecture "Life at low Reynolds number" [121]. For this simple swimmer, we find and later discuss optimal stroke kinematics and swimmer geometries. We then further investigate flagellated swimmers and verify the convergence of the optimization procedure in the case of a single flagellum, for which the optimal stroke kinematics are known analytically. Optimal stroke kinematics and geometries for unifiagellates are also computed and found to be relevant in the context of biological microorganisms. (cont.) We then turn our attention to stroke kinematics of biflagellates and demonstrate that all the different strokes, which are experimentally observed to be performed by biflagellated organisms such as green algae chlamydomonas, are found to be local hydrodynamical optima. These observations strongly suggest the central role of hydrodynamics in the internal dynamical organization of the stroke patterns. Finally, we present experimental results on convective transport and mixing inside small droplets of water sitting on superhydrophobic substrates. We demonstrate by a scaling analysis, that the regular convection pattern is due to a thermocapillary driven Marangoni flow at the surface of the droplet. We develop an analytical solution for the temperature and flow field inside the droplet, which is found to be in agreement with our experimentally recorded data. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2008. Includes bibliographical references (p. 181-192). Mon, 29 Oct 2007 22:58:59 GMT http://hdl.handle.net/1721.1/49678 Design of an active compressor blade for aeroelastic studies Maahs, Gordon Lewis, 1974- Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1999. Includes bibliographical references (p. 137-140). Thu, 29 Oct 1998 22:58:59 GMT