Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005. / Includes bibliographical references (p. 38). / Planar magnet-coil actuators are used in many different MEMS devices. This report describes one way to improve the actuator range per current input of planar coil actuators. This is accomplished by adding a flux channel around and beneath the actuator's magnet. The Lorentz force is created by putting a current carrying planar coil over a magnet in an actuator assembly. The Lorentz force depends on the current vector and the magnetic field vector. In this thesis the Lorentz force is altered by changing the direction and concentration of the magnetic field. Magnetic fields may be modeled as flux lines traveling from the north face of the magnet to the south face along the least resistant path. Iron is a magnetic material with 4000 times the magnetic permeability of air, so when iron is placed in a magnetic field, the majority of the magnetic flux will travel from North to South through the iron. This "channel" alters the way the magnetic field would normally travel given the bare magnet. The magnetic flux that travels through the channel depends in part upon the channel geometry. The result of varying the width of this channel is modeled and tested in this work. The physical principle was examined in simulations by varying channel width and then extracting the corresponding actuator output. A relationship was fit to the simulated results. / (cont.) The actuator output augmentation was maximized at a critical width and remained steady thereafter. Beyond the critical width, the addition of the flux channel was able to produce more than 45% increase in the actuator force. Experimental results showed less than a 5% difference from the simulated results. / by Jacob Bourgeois. / S.B.

Thesis (S.M. and Nav. E.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008. / Includes bibliographical references (leaves 98-106). / Composite materials are gaining popularity in U.S. Naval applications because of their unparalleled strength, stiffness, and manufacturing simplicity. A better understanding of the structural integrity of these materials has the potential to reduce overdesign, decrease manufacturing cost, and simplify repairs. Though underwater nondestructive evaluation of composites has not been well documented, this thesis illustrates the available technologies for underwater evaluation and repair of laminated composite structures, similar to those currently used in marine applications. Dependent on accuracy and reliability of underwater evaluation, the decision to pursue temporary or permanent repairs may be made based on available information regarding the structural integrity of the effected repairs. Discussion of the environmental effects on composite laminates and their repairs is included to provide insight into the detrimental effects of contaminates such as saltwater and petroleum products. The effect of the environment has a profound impact on the quality of composite repairs using currently available repair materials. Underwater repairs, whether permanent or temporary, are suggested for future U.S. Navy components such as the DDG-1000 composite twisted rudder. Furthermore, a suggestion is made to eliminate the use of cofferdams on U.S. Navy shaft covering repairs in order to reduce both cost and the risk of injury associated with a cofferdam. / by William L. Hagan III. / S.M.and Nav.E.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 55-56). / Various states of hydrophobic wetting and hysteresis are observed when water droplets are deposited on micro-post surfaces of different post densities. Hysteresis is commonly defined as the difference between the advancing and receding contact angle and after many decades of research, the mechanisms governing hysteresis are still not fully understood. Particularly, stick-slip behavior of the three-phase contact line has been observed and qualitatively attributed to surface or chemical heterogeneities, but the behavior has yet to be quantified. In this thesis, contact line motion particularly focused on stick-slip behavior and its influence on drop width and contact angle was examined as a new approach to understanding hysteresis as pertaining to micro-textured surfaces. This work focuses on developing a fundamental understanding and physical model of the stick-slip behavior of the contact line and preliminarily explores the influence of contact line velocity on this stick-slip behavior and contact angle. By characterizing stick-slip behavior and hysteresis on micro-post surfaces, models can be developed that in the future can aid in surface design for optimal wetting behavior in industrial and power plant applications. Additionally, the pinning parameter has been used to predict roll off angle on micro-post surfaces for a variety of post densities and these predictions have been experimentally verified. With further definition of the pinning parameter to include surface roughness and impact phenomena, the pinning parameter can be used in surface design for droplet shedding in industrial applications. / S.B.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 289-290). / The propagation of surface waves over a flat muddy seabed are studied. Mud is first considered as a Newtonian fluid. Water and mud equations are derived in order to obtain governing equation for surface and interface waves. By the method of multiple scales. nonlinear evolution equations are derived for the harmonic amplitudes. These equations are numerically solved for a finite number of harmonics to show the behavior of surface and interface motions. A drift current in mud is found at the second order., meaning that surface waves induce mud motion. Equation governing the total wave energy variation is derived and used to verify the accuracy of numerical solutions. The model is extended to viscoelastic mud, using the results of four experiments carried on different types of muds. These muds range from very elastic to rather viscous, allowing us to compare hie differences in behavior. Surface and interface variations. mud drift current and energy variations are plotted and compared to the results with Newtonian muds. A sloping muddy seabed is then considered. Mud is modeled as viscoelastic to avoid a constant static current that would happen with Newtonian mud. By the method of multiple scales and by introducing a space-dependent wavenumber, mud drift current and energy variation equations are derived again, taking into account the effect of the slope. An analytic stud v of the surface variations demonstrates that surface and interface waves, as well as drift current, exponentially decay to reach a zero value at the shore. / by Erell-Isis Garnier. / S.M.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2003. / Includes bibliographical references (leaf 24). / by William James Fienup. / S.B.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 33). / Professor Steven Leeb teaches Power Electronics Lab, which teaches the fundamentals of power electronic systems and has students build their own motor controllers. As a fun way to test these student built motor controllers, Professor Leeb has been using large go-karts built specifically for the class. However, these go-karts are large, heavy, and difficult to maintain. Professor Leeb recently acquired a number of production stand-up electric scooters with the intention of replacing the aging gokarts. To enhance the educational value of the scooters, Professor Leeb wanted them heavily modified to allow students to explore the effect of gearing on electromechanical systems. Furthermore, the scooters were modified to incorporate a modular motor mounting system, allowing students to easily switch out different motor models, including brushed and BLDC motors. This thesis details the design and construction of the scooter transmission and motor mount. / by Andrew T. Carlson. / S.B.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Accurate non-contact temperature measurements of objects using thermal radiation is often limited by low emission of IR radiation because of low temperatures and/or emissivities, or by the unknown or changing emissivity of the material being measured. This thesis covers an effort to build a practical, inexpensive, and widely applicable non-contact system for accurately measuring the temperatures of materials of low, unknown, and/or variable emissivity. The method to be used is intended specifically for those objects at low temperatures (below 100 degrees Celsius), which are conventionally the most difficult to accurately measure. / by Jason Neal Jarboe. / S.B.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 103-113). / This thesis presents highly parallelized control programming methodologies developed for multi-degrees of freedom (DoF) robots capable of highly dynamic movements. In robotic applications that require rapid physical interactions with the environment, it is critical for the robot to achieve a high-frequency synchronization of data processing from a large number of high-bandwidth actuators and sensors. To solve this important problem in robotics, I developed parallelized control programming methodologies that effectively utilize the advantages of modern parallel real-time computing technologies: multicore CPU, the Field Programmable Gate Array (FPGA), and distributed local processors. This approach was implemented in the fast running experiments of the MIT Cheetah. In such a highly dynamic robot, the required control bandwidth is particularly high since the MIT Cheetah's leg actuation system is designed to generate high force (output torque up to 100Nm) with high bandwidth (closed loop bandwidth up to 120Hz) with minimal mechanical impedance for fast locomotive capability. On the integrated control system, a multi-layered architecture is programmed. Inspired by data parallelism, task parallelism, and the pipelining method, more than 50 processes are operated in parallel, and major processes among them are optimized to achieve the maximum throughput.The proposed methodologies enable the high-level control sampling frequency 4 kHz. With this control system platform, I achieved a high-force proprioceptive impedance control [1], and a trot-running up to 6 m/s with a locomotion efficiency rivaling animals [2].. / by Sangok Seok. / Ph. D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1999. / Includes bibliographical references (p. 89-91). / Driven in part by concerns regarding global wanning, there is a clear trend towards increased usage of compression ignition vehicles running on diesel fuel. Use of diesel fuel has a downside, namely relatively high oxides of nitrogen (NOx) and particulate matter (PM) emissions. Emulsified fuel is a mixture of water and diesel fuel. Quantum Energy Technologies Corporation (QET) have developed nanoemulsified fuels that contain water clusters in the nanometer size range. The main benefits claimed for these fuels are reduced emissions of PM and NOx without any decrease in engine performance levels compared to conventional diesel fuels. This work investigates these benefits by running different base diesels and nanoemulsions with varying water content in a single cylinder direct injection Ricardo Hydra engine. The effect of water addition on the base diesel is modeled using a previously verified model of the test engine. The experimental and modeling results are compared to published results for conventional microemulsions. There is no decrease in indicated fuel conversion efficiency for the nanoemulsions. Fer a 9% water nanoemulsion specific NOx emissions are reduced by l 3 - 20% and specific PM emissions are reduced by 15 - 20% compared to the base diesel. However, these fuels do not exhibit any significant emissions improvement over conventional microemulsions. / by Cornelius O'Sullivan. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005. / Includes bibliographical references (p. 106-108). / Lithium cobalt dioxide is the most commonly used material for positive electrodes in lithium rechargeable batteries. During lithium de-intercalation from this material, ... undergoes a number of phase transitions, which have been studied by bulk techniques and first-principles calculations. The objective of this work was to examine the effect of charge and discharge on individual LiC₀O₂ crystals. Atomic Force Microscopy and Transmission Electron Microscopy were used to observe the effects of lithium ion de-intercalation from ... in individual crystals. This work was the first study to use in-situ Atomic Force Microscopy to probe the dynamic evolution of ... crystal morphology as lithium ions are de-intercalated from the material. The overall crystal morphology did not seem to evolve very much during the first charge and discharge cycle however evidence was found for expansion and contraction of crystal steps during cycling. The evolution of layer spacing was quantified from AFM data and was found to be in agreement with X-ray diffraction studies by other researchers. Furthermore, rounded bumps were observed on the surface of most of the crystals, and it is speculated that these bumps are Li₂CO₃ impurities, formed on the surface of LiC₀O₂ after storage in air. Lastly, the formation of a surface layer on ... crystals and the gold foil substrate was observed when the cell was over-discharged to approximately 2.5V. Transmission Electron Microscopy was used to image individual LixCoO2 crystals for different values of lithium concentration in the range corresponding to the insulator-metal phase transition. / (cont.) Electron diffraction patterns revealed the presence of lithium-vacancy ordering in charged ... samples. In parallel, Electrochemical Impedance Spectroscopy and X-ray Diffraction were used to characterize the evolution of the electronic and structural properties of ... during the phase transition. EIS data showed that the electronic resistivity of ... decreased by three orders of magnitude at the onset of charge, in agreement with literature. XRD data from charged ... samples showed an increase in layer spacing, also in good agreement with previous studies done by other researchers. / by Anne Clémençon. / S.M.