published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

Thesis (Ph. D.)--University of Hawaii at Manoa, 2004. / Includes bibliographical references (leaves 145-149).

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Shape Memory Alloys (SMAs) are metal alloys which are capable of changing their crystallographic structure as a result of externally applied mechanical or thermal loading. This work is a systematic effort to develop a robust, thermodynamics based, 3-D constitutive model for SMAs with special features, dictated by new experimental observations. The new rate independent model accounts in a unified manner for the stress/thermally induced austenite to oriented martensite phase transformation, the thermally induced austenite to self-accommodated martensite phase transformation as well as the reorientation of self-accommodated martensite under applied stress. The model is implemented numerically in 3-D with the help of return-mapping algorithms. Numerical examples, demonstrating the capabilities of the model are also presented. Further, the stationary Fluid-Structure Interaction (FSI) problem is formulated in terms of incompressible Newtonian fluid and a deformable solid. A numerical method is presented for its solution and a numerical implementation is developed. It is used to verify an existing asymptotic solution to the FSI problem in a simple channel geometry. The SMA model is also used in conjunction with the fluid-structure solver to simulate the behavior of SMA based filtering and flow regulating devices. The work also includes a numerical study of wave propagation in SMA rods. An SMA body subjected to external dynamic loading will experience large inelastic deformations that will propagate through the body as phase transformation and/or detwinning shock waves. The wave propagation problem in a cylindrical SMA is studied numerically by an adaptive Finite Element Method. The energy dissipation capabilities of SMA rods are estimated based on the numerical simulations. Comparisons with experimental data are also performed.

Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, December 2009. / Thesis Advisor: Kwon, Young W. Second Reader: Didoszak, Jarema M. "December 2009." Description based on title screen as viewed on January 26, 2010. Author(s) subject terms: Composite, Carbon, Low Velocity Impact, Fluid Structure Interaction. Includes bibliographical references (p. 49-50). Also available in print.

Thesis (M.S.)--Brigham Young University. Dept. of Mechanical Engineering, 2003. / Includes bibliographical references (103-106).

In SCUBA diving, the propulsive efficiency of a diver regulates, in part, his autonomy. An inefficient method of propulsion will increase the power output required and, therefore, the intake of oxygen and increase fatigue. Since the development of the SCUBA apparatus, fins have evolved based on the designer's intuition and knowledge of hydrodynamics. Some experimental work has been performed, but it is usually limited to studying the diver as whole and does not focus on the fin design. In this dissertation, a state-of-the-art fluid-structure interaction framework is developed and then used to study fin propulsion. This framework couples the structural dynamics of the fin with the fluid dynamics surrounding it using a modular framework. This way, mature state-of-the-art solvers can be used in each domain (structural and fluid). The flow field is solved using a computational fluid dynamics solver which resolves the Navier-Stokes equations. Coupled with these equations are a variety of turbulence models which can be used to resolve the turbulence in the flow. The CFD method is validated using a two-dimensional circular cylinder and a pitching and heaving airfoil, both immersed in a turbulent flow field. A commercial structural dynamics solver, is used to resolve the structural dynamics. The coupling of the two solvers is also described in detail. The basic design of a fin (a simple flat plate) is studied and modified in order to test the effect that altering key structural parameters has on the thrust, power and efficiency of the fin. The end result is a set of design recommendations which can be used to enhance the performance of a SCUBA fin. These recommendations are based on both quantitative and qualitative analysis of the performance characteristics of the fin.

While most propulsion systems which drive aquatic and aerial vehicles today are based on rotating blades or foils, there has recently been renewed interest in the use of oscillating foils for this purpose, similar to the fins or wings of biological swimmers and flyers. These propulsion systems offer the potential to achieve a much higher degree of manoeuvrability than what is possible with current man-made propulsion systems. There has been extensive research both on the theoretical aspects of oscillating-foil propulsion and the implementation of oscillating foils in practical vehicles, but the current understanding of the physics of oscillating foils is incomplete. In particular, questions remain about the selection of the appropriate structural properties for the use of flexible oscillating foils which, under suitable conditions, have been demonstrated to achieve better propulsive performance than rigid foils. This thesis investigates the effect of the foil inertia, stiffness, resonant frequency and oscillation kinematics on the thrust generation and efficiency of a flexible oscillating-foil propulsion system. The study is based on experimental measurements made by recording the applied forces while driving foil models submerged in a water tunnel in an oscillating motion using servo-motors. The design of the models allowed for the construction of foils with various levels of stiffness and inertia. High-speed photography was also used to observe the dynamic deformation of the flexible foils. The results show that the frequency ratio, or ratio of oscillation frequency to resonant frequency, is one of the main parameters which determines the propulsive efficiency since the phase of the deformation and overall amplitude of the motion of the bending foil depend on this ratio. When comparing foils of equivalent resonant frequency, heavier and stiffer foils were found to achieve greater thrust production than lighter and more flexible foils but the efficiency of each design was comparable. Through the development of a semi-empirical model of the foil structure, it was shown that the heavier foils have a lower damping ratio which allows for greater amplification of the input motion by the foil deformation. It is expected that the greater motion amplitude in turn leads to the improved propulsive performance. Changing the Reynolds number of the flow over the foils was found to have little effect on the relation between structural properties and propulsive performance. Conversely, increasing the amplitude of the driven oscillating motion was found to reduce the differences in performance between the various structural designs and also caused the peak efficiency to be achieved at lower frequency ratios. The semi-empirical model predicted a corresponding shift in the frequency ratio which results in the maximum amplification of the input motion and also predicted more rapid development of a phase lag between the deformation and the actuating motion at low frequency ratios. The shift in the location of the peak efficiency was attributed to these changes in the structural dynamics. When considering the form of the oscillating motion, foils driven in combined active rotation and translation motions were found to achieve greater efficiency but lower thrust production than foils which were driven in translation only. The peak efficiencies achieved by the different structural designs relative to each other also changed considerably when comparing the results of the combined motion trials to the translation-only cases. To complete the discussion of the results, the implications of all of these findings for the design of practical propulsion systems are examined. / Graduate / 0548

Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, September 2009. / Thesis Advisor(s): Kwon, Young W. "September 2009." Description based on title screen as viewed on 6 November 2009. Author(s) subject terms: Fluid-structure interaction, composite, carbon fiber composite, dynamic response, finite element. Includes bibliographical references (p. 95-96). Also available in print.

Thesis (M.S.)--University of Wyoming, 2008. / Title from PDF title page (viewed on Apr. 1, 2010). Includes bibliographical references (p. 48-51).