This research is to investigate the performance of mini and micro devices driven magnetically through simulations and experiments. Micro-Electro-Mechanical Systems (MEMS) invoking magnetic coupling were designed and tested. Scaled up models and numerical simulation of the micro spiral channel flow were also presented. Magnetic devices can generate larger forces for larger distance than their electrostatic counterparts; the energy density between the magnetic plates is usually larger than that between the electric plates. Properly designed, magnetic actuators can be made to hold high torques with no intervening wires. Magnetic actuation may be considered a feasible method to drive the MEMS with advantages. Pulsed laser deposition method is used for growing magnetic material to the surface of micro device. Magnetic material properties are investigated. A permanent magnet made of NdFeB is used as a target for pulsed laser deposition to produce the thin film on a micro device which may induce magnetic coupling with external magnet sources. The properties of the thin film formed at different substrate temperatures and effects of external magnetic field to the thin magnetic film are presented. A mini screw pump invoking the magnetic driven system is demonstrated and its working performance is verified experimentally. The experiment on mini screw pump is to demonstrate the advantages of magnetic coupling and to verify the feasibility of magnetic coupling concept in a real device. The mathematical modeling and numerical simulations for magnetic coupling are also carried out. Further, the design and microfabrication technologies are introduced for a magnetically driven micro gear and micro viscous pump. Through the study of several experiments, improvements for designs are made. Due to the challenge in testing the actual microdevices, scaled-up experiments for magnetically driven viscous pumps are made. These studies simulate the performance of the micro size counterpart. In addition, the analyses of flow in micro size channels are made. Boundary conditions required for a proper simulation are discussed. Numerical simulations required for a pump performance are given. The factors to affect the pump performance are discussed based on the theoretical model, experiment and numerical simulation results. / A Dissertation submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Degree Awarded: Summer Semester, 2004. / Date of Defense: July 6, 2004. / MEMS, Micropump, Magnetic / Includes bibliographical references. / Ching-Jen Chen, Professor Co-Directing Dissertation; Yousef Haik, Professor Co-Directing Dissertation; Jim P. Zheng, Outside Committee Member; Namas Chandra, Committee Member; Peter Kalu, Committee Member.

Superconducting magnet systems are the enabling technology for several research fields, e.g., experimental high-energy physics and fusion. Advanced superconducting magnet systems are strongly needed to achieve ever-higher beam energy in particle accelerators. They are also extensively used in plasma confinement for fusion. The energy stored in a magnet converts to heat when the magnet is quenching, i.e., a state change from superconducting to normal. The temperature increase and the high turn-to-turn voltage developed in a quench may degrade or damage the magnet. Thus, one of the key issues for the successful operation of superconducting magnets is the quench detection and protection. This thesis discusses the self-field quench behavior of Bi2Sr2CaCu2O8+x (Bi2212) short samples and coils with the purpose of discovering key critical quench conditions that cause loss in critical current (Ic) of the conductor. Bi2212 tapes and round wires are investigated in short sample quench experiments. The experiments are conducted by means of heater induced quenching, and V(t) and T(t) data during a quench is recorded. The minimum quench energy (MQE) and normal zone propagation velocity (NZPV) are determined for both conductors. Using the collected data, and measuring the Ic of samples after quenching, critical values for energy deposited into the conductor via Joule heating (E), maximum temporal temperature gradient (dT/dt|max), maximum spatial temperature gradient (dT/dx|max) and maximum temperature (Tmax) that cause loss in Ic are determined. These quench conditions are varied in order to determine specifically what the critical values for each are. It was determined that while the tape short samples exhibited higher stability than the round wires, their NZPV was excessively slower and critical quench conditions significantly smaller. Coil quench experiments where conducted on round wires due to their proven resilience to quench induced degradation during short sample experimentation. In similar fashion to short samples, MQE and NZPV were determined for coils, as operating conditions and conductor batch varied. Coil quench experiments where also conducted via means of "hot-spot" generation using a heater. It was concluded that the coils exhibited larger stability, yet slower NZPV than short sample round wires. The critical quench conditions that do not cause loss in Ic to the conductor agreed with those determined in the short sample round wire experiments. This allows for the conclusion that critical quench conditions are intrinsic to the conductor and not dependant on operating conditions. The dependence of quench behavior on sample Ic and current sharing temperature (Tcs) is also observed. It is noticed that with smaller Tcs, NZPV increases and stability decreases. Furthermore, inhomogeneous Ic and Tcs along the length of the conductor allow for inhomogeneous quench behavior. In turn quench conditions are difficult to predict, and vary between samples. / A Thesis submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Degree Awarded: Summer Semester, 2008. / Date of Defense: June 3, 2008. / 2212, Bi2212, Quench / Includes bibliographical references. / Justin Schwartz, Professor Directing Thesis; Simone Peterson Hruda, Committee Member; Juan Ordonez, Committee Member.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1999. / Includes bibliographical references (leaves 157-160). / by Jun Beom Kim. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1999. / Includes bibliographical references (leaf 104). / by Hyoseok D. Yang. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1999. / Includes bibliographical references (p. 85-88). / by Sandra Rugonyi. / S.M.

Skid-steered robots are commonly used in outdoor applications due to their mechanical simplicity, high maneuverability, and robustness. The maneuverability of these robots allows them to perform turning maneuvers ranging from point turns to straight line motion under ideal conditions (e.g., flat terrain and powerful actuators). However, sloped terrain, terrain with high friction, or actuator torque and power limitations can limit the achievable turning radii. The aim of this research is to analyze and experimentally verify the dynamic and power models for skid-steered autonomous ground vehicles equipped with non-ideal (i.e., torque and power limited) actuators and moving on sloped terrains. In particular it investigates the ability of the proposed models to predict motor torques (including motor saturation), power requirement, and minimum turn radius as a function of terrain slope, vehicle heading, payload, terrain parameters and actuator characteristics. The experimental results show that the model is able to predict motor torques for the full range of turning radii on flat ground, i.e., from point turns to straight line motion. In addition, it is shown that the proposed model is able to predict motor torques (including motor saturation) and minimum turn radius as a function of terrain slope, vehicle heading, payload, terrain parameters and actuator characteristics. This makes the model usable for curvilinear motion planning tasks on sloped surfaces. The research uses these results along with Sampling Based Model Predictive Optimization to develop an effective methodology for generating dynamically feasible, energy efficient trajectories for skid-steered autonomous ground vehicles (AGVs) and compares the resultant trajectories with those based on the standard distance optimal trajectories. The simulated and experimental results consider an AGV moving at a constant forward velocity on both wood and asphalt surfaces under various loads. They show that a small increase in the distance of a trajectory over the distance optimal trajectory can result in a dramatic savings in the AGV's energy consumption. They also show that it is not difficult for distance optimal planning to produce trajectories that violate the motor torque constraints for skid-steered AGVs, which can result in poor navigation performance. In addition, the research motivates and provides a methodology that integrates the robot's dynamic model and actuator limitations, and the terrain models with SBMPO to exploit the vehicle momentum as a way to successfully traverse the difficult terrains such as steep hills, mud, or stiff vegetation patches. These scenarios are particularly critical for smaller robots with torque and power limited actuators, which as experimentally shown in this research can easily fail to accomplish their tasks in these environments. In particular, the experimental results showing the efficacy of the proposed methodology are presented for a vegetation patch and a steep hill. Finally, a discussion of the necessary perception work to fully automate the process is included. Further, for walking and running robots, analysis of the power consumption is particularly important for trajectory planning tasks as it enables motion plans that minimize energy consumption and do not violate power limitations of the robot actuators. The research here is motivated by the hypothesis that for certain regimes of operation (i.e., certain gait parameters), legged robots from the RHex family behave in a similar fashion to skid-steered robots while in general curvilinear motion. Hence, using the experience gained from skid-steered wheeled vehicles, presents models of the inner and outer side torques and power requirements for the XRL hexapedal robot. In addition, the applicability of the power model to energy efficient motion planning is illustrated for a walking gait on a vinyl surface. / A Dissertation submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Summer Semester, 2014. / July 8, 2014. / Dynamic Modeling, Energy Efficient, Motion Planning, Power Modeling, Skid-Steered Vehicles / Includes bibliographical references. / Emmanuel G. Collins, Jr., Professor Directing Dissertation; Chris S. Edrington, University Representative; Jonathan Clark, Committee Member; William S. Oates, Committee Member.

It has been documented that heat is generated during friction stir processing. The amount of heat generated between the shoulder and the work piece during friction stir processing dictates the quality of the processed zone. Hence understanding the distribution of heat and obtaining the temperature contours will assist in understanding the general process of friction stir processing. In this thesis a three dimensional heat transfer model has been developed to obtain the temperature distribution in the work piece. An example problem was solved to understand the method of solving a transient heat transfer problem using ANSYS. The developed finite element model was validated by comparing the simulation results with experimental data from five different papers. A parametric study was carried out to understand the variation in temperature for different rotational and translational speeds. The variation of temperature with respect to thermal conductivity, specific heat and density was developed. A trend line equation which predicts the peak temperature attained during friction stir processing was also developed. The predicted peak temperature is used to obtain the temperature contours through out the work piece. / A Thesis submitted to the Department of Mechanical Engineering In partial fulfillment of the requirements for the degree of Master of Science. / Spring Semester, 2006. / March 17, 2006. / Includes bibliographical references. / Peter Kalu, Professor Co-Directing Thesis; Namas Chandra, Professor Co-Directing Thesis; Juan Carlos Ordonez, Committe Member.

An experimental study was conducted to examine the aeroacoustic characteristics of supersonic twin jets and compare them to a single jet of equivalent area. Axisymmetric converging diverging nozzles having a fully expanded Mach number of 1.76 were operated at overexpanded and ideally expanded conditions. Planar velocity field measurements were made using Particle Image Velocimetry (PIV) at cold operating conditions. The results obtained show a decrease in potential core length for the twin jets. The twin jets were found to merge earlier when they were canted. Lower turbulence levels were observed for the twin jets compared to a single jet. The turbulence in the inter nozzle region of the canted twin jets was significantly reduced due to increased jet interaction. Far-field noise measurements for the twin jets were made at two azimuthal angles and compared to a single jet of equivalent diameter. Noise measurements showed a reduction in OASPL for the twin jets at most of the polar angles measured, with a 2 dB reduction in peak radiation direction. The OASPL levels of the twin jets showed a strong dependence on the azimuthal angle. Broadband shock noise was observed to have shifted to higher frequencies. Acoustic shielding was observed at some sideline angles, which caused significant reduction in high frequency noise. / A Thesis submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Degree Awarded: Fall Semester, 2005. / Date of Defense: September 16, 2005. / Twin Jets / Includes bibliographical references. / Krothapalli Anjaneyulu, Professor Directing Thesis; Farukh Alvi, Committee Member; Robert van Engelen, Committee Member.

The present work attempts to investigate the effect of magnetic annealing on texture and microstructure of grain non-oriented (GNO) cold rolled Fe-0.75%Si steel samples. The cold rolled specimens were annealed at constant magnitude of magnetic field, 17T, for different annealing times and at different magnitudes of magnetic field at a constant annealing time, 10 minutes. In order to evaluate the effect of the magnetic field, the cold rolled specimens were also annealed at the same conditions (temperature, time and inert atmosphere) as for the magnetic annealing but without any magnetic field. EBSD/OIM, X-ray measurements and optical micrograph have being used to characterize the texture and microstructure of the samples after each annealing treatment. Magnetic annealing at high magnetic fields has shown to influence the final texture of the samples through changes in the ç, ã and á fibers. Magnetic field has not had a significant effect on the volume fraction of Goss-oriented grains but has affected the GBCD of these grains. High magnetic have shown to be a key factor for the improvement of texture and microstructure of Fe-0.75%Si steel. / A Dissertation submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Degree Awarded: Spring Semester, 2005. / Date of Defense: December 17, 2004. / Magnetic Annealing, Silicon Steel, Texture / Includes bibliographical references. / Hamid Garmestani, Professor Directing Dissertation; Anthony D. Rollett, Committee Member; Chuck Zhang, Outside Committee Member; Peter Gielisse, Committee Member; Chiang Shih, Committee Member.

An earlier work on reactant delivery in a Proton Exchange Membrane Fuel Cell using supersonic microjet impingement showed enhanced distribution of reactant and active cooling effect during operation. By comparative analysis with a commercial single cell unit, the microjet fuel cell offered significant cooling effect without sacrificing performance. Nonetheless, the microjet fuel cell was limited by its water management ability as it was susceptible to flooding and consequent degradation in performance. By using a combination of independent microjets and serpentine flow channels, flooding of the fuel cell was significantly reduced. Electrode Impedance Spectroscopy, a non invasive and in-situ method, was utilized as a diagnostic tool to detect the onset of flooding as well as provide a qualitative assessment on the extent of flooding within the fuel cell. Polarization and Impedance spectroscopy measurements are used to characterize the performance of the fuel cell. To obtain useful power for most domestic applications, unit cells are stacked together. A prototype two-cell microjet based fuel cell has been designed and built. As the conventional bipolar configuration cannot be used in a microjet based fuel cell, connection between the cells is achieved externally. The characterization is done for different flow rates and relative humidity and temperature / A Thesis submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Degree Awarded: Spring Semester, 2010. / Date of Defense: January 14, 2010. / Fuel Cell, Proton Exchange Membrane, Flooding, Mitigation, Microjet, Water Management, Impedance Spectroscopy, Stacking / Includes bibliographical references. / Anjaneyulu Krothapalli, Professor Directing Thesis; Brenton Greska, Committee Member; Juan Ordonez, Committee Member; William Oates, Committee Member.