Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 268-289). / Meeting the ever growing global energy demand with mostly fossil fuel based energy technologies is not sustainable, pollutes the environment and is the main cause of climate change threatening our planet as we know it. Solar energy technologies are a promising, sustainable and clean alternative due to the vast abundance of sunlight. Thus far, photovoltaic solar cells and concentrated solar power are considered to be the most promising approaches. Solar cells directly convert sunlight into electricity by photon induced electron-hole pair generation. Concentrated solar power captures the sunlight in form of heat which is then converted to electricity by means of a traditional mechanical power block. In this thesis, we explore solar thermoelectric generators (STEGs) as an alternative way to convert sunlight to electricity. Similar to concentrated solar power STEGs capture the sunlight in form of heat. However, the captured heat is directly converted to electricity by means of a thermoelectric generator. This solid-state direct heat-to-electricity conversion significantly simplifies the system, reduces cost and maintenance and enables transient operation and system scalability without affecting the performance. Therefore, STEGs have the potential to be deployed as small scale solar power converters in remote areas and on rooftops and as large scale concentrated solar power plants. While the concept of solar thermoelectric power conversion has been proposed over a century ago, most successful experimental efforts reported in, the literature have been limited to below 1 % for STEGs without optical concentration and to approximately 3 - 5 % with optical concentration. Theoretical STEG performances as modeled and discussed in this thesis predict significantly higher efficiencies. A detailed STEG model is introduced to theoretically investigate various parasitic losses and how to minimize their effect to obtain highest and most realistic performance predictions. Additionally, a methodology to optimize a photovoltaic-thermoelectric hybrid system based on spectral splitting is introduced. The optimization and performance prediction of a STEG is only accurate if the relevant material properties are known with high accuracy. However, typical spectroscopy techniques to determine the optical properties, namely the solar absorptance and infrared emittance, of a solar absorber have shortcomings which can lead to significant errors. Similarly, typical commercial equipment to measure the properties of thermoelectric materials including the Seebeck coefficient, the electrical resistivity and the thermal conductivity are prone to large errors. Therefore, we introduce in this thesis novel experimental techniques to measure all relevant properties with improved accuracies in particular the techniques to measure the total hemispherical emittance of a surface and a material's thermal conductivity. A record-low total hemispherical emittance of 0.13 at 500 °C is demonstrated for an Yttria-stabilized-Zirconia-based cermet solar absorber with solar absorptance of 0.91 and thermal stability up to 600 °C. Furthermore, a method was developed to directly measure the efficiency of a thermoelectric leg. Using this method a record-high thermoelectric efficiency of 8.5 % is demonstrated at a relatively small temperature difference of 225 °C for a novel MgAgSb-based compound with hot-pressed silver contact pads. By increasing the temperature difference to a material's compatible 275 °C a thermoelectric efficiency of 10 % is achievable which, thus far, has only been achieve at almost twice the temperature difference. The third main contribution of this thesis is the experimental demonstration of solar thermoelectric power conversion. A record-high STEG efficiency of 4.6 % is demonstrated at AM1.5G (1 kW/m 2) conditions which is 7 times higher than previously reported best values. The performance improvement is achieved by using a STEG with nano-structured bulk thermoelectric materials, a spectrally-selective solar absorber and taking advantage of large thermal concentrations under a vacuum. Despite the vacuum environment and the use of a low-temperature spectrally-selective solar absorber the optimal hot-junction operating temperature is limited to approximately 200 °C due to increasing thermal radiation heat loss. In order to substantially increase the operating temperature difference and STEG efficiency, larger incident solar power densities are required. Furthermore, the STEG requires segmented thermoelectric legs and a high-temperature stable solar absorber. The optimized STEGs are fabricated and tested at moderate and high optical solar concentration. Efficiencies of close to 8 % at 38 suns and close to 10 % at 211 suns, measured based on the solar flux at the absorber, are demonstrated for a STEG with a spectrally-selective solar absorber. The maximum demonstrated solar-to-electricity CSTEG efficiency is 7.5 %. Furthermore, the performance of a STEG at moderate optical concentration with a high-temperature stable black paint solar absorber and a directionally-selective solar receiver cavity is demonstrated to be comparable to a STEG with a spectrally-selective surface at similar insolation. / by Daniel Kraemer. / Ph. D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1997. / Includes bibliographical references (p. 95-99). / by Karen E. Lawson. / M.S.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 169-175). / Despite remarkable recent advances in robotic research, legged machines are still far from robustly executing physical actions with comparable performance to humans. Yet, the potential applications for robots with such unique capabilities range from disaster response all the way to elderly care and further. Hence, an intuitive short-term answer for this issue lies on harnessing human motor control abilities and transferring them to the remote robot via whole-body teleoperation while providing the operator with real-time physical feedback from his/her actions. Motivated by such a promising solution, this Thesis presents an introductory study to achieve human and bipedal robot dynamic synchronization via whole-body teleoperation and bilateral feedback. This work describes how we can utilize powerful simple models to explore the interplay between human Center of Mass motion and the contact forces with the environment in order to transmit to the robot the underlying balancing and stepping strategy. All the necessary fundamental equations for the coupled dynamics in the Frontal Plane are presented along with the human feedback law and motion data mapping derived from the imposition of dynamic similarity. We take a closer look on how the natural frequency of each system influences the resulting motion and analyze how the coupled system responds to various robot scales. We present experiments in which a human operator controls a bipedal robot to show how the feedback from the Human-Machine Interface varies according to the robot's characteristic time response and the perturbations from its surrounding environment. Finally, we describe the implementation of the presented strategy on a small-scale dynamic robot, Little HERMES, to allow it to balance, jump and take steps in place simultaneously with the human operator. We expect that the results presented in this Thesis will eventually allow robots to achieve motor dexterity and coordination that can rival their biological counterparts. / by João Luiz Almeida de Souza Ramos. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1993. / Includes bibliographical references (leaves 176-184). / by Kenneth E. Goodson. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004. / Includes bibliographical references (leaf 40). / An apparatus of the classical ball-on-beam problem was designed and constructed to be used as a pedagogical instrument in feedback courses. The aesthetic and mechanical design incorporated economical materials to make kits of this apparatus attractive and cost effective. This thesis describes the design of the apparatus and the design of the two control loops to control the angle of the motor and the position of the ball along the beam. A lead compensator was used in each loop and an additional integrator was used in the motor loop to ensure the beam level when supporting the ball. The motor closed loop was designed for a bandwidth of 25 Hz and the ball loop was designed for 1 Hz. The closed loop control was implemented using a Matlab Simulink model and a dSPACE digital signal processor controller board. The feedback sensor of the motor angle was an encoder mounted to the back of the motor, and the sensor for the ball position was a linear potentiometer resistive element. After multiple iterations and debugging of the ball position sensor, the ball-on-beam system performed successfully, responding well to step commands and disturbances. / by Evencio A. Rosales. / S.B.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005. / Includes bibliographical references (leaf 25). / Working with Gillette Corporation, an automated mechanical testing tool that bent a small flat piece of steel was designed. The design of the tool was an effort to improve upon previous generations of the same tool. It consisted of three main elements; a servomotor, connected to a torque transducer, which was connected to a break device. A thin piece of steel was loaded into the break device and the motor was activated, moving a flipper arm on the device which bent the steel. While bending this piece of steel, the torque transducer would relay torque and angle information to a computer. This information was collected and displayed in Excel as torque versus angle plots, which would show the moment at which the piece of steel was broken. This entire process was automated so that after loading the steel, one click of a button would run one test. Razorblades were primarily bent with the device until they would break, and for this reason, the measuring tool was called the 'blade break test.' The work consisted of designing a robust mechanical system coupling the three devices mentioned above in series. Code was written in Visual Basic that managed all the individual devices in the measuring tool, getting them to work together and linking them with a computer. / (cont.) A user interface was designed with engineers in mind, imbedding automated data collection and representation through Excel. Finally, a manual was created accompanying the device so other engineers could use, troubleshoot, and modify the 'break test.' The result of this project was the creation of a successful measuring instrument with full documentation and functionality. / by Stephen Weiner. / S.B.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 71). / High inventory holding costs, strain on warehouse capacity and the competition of lead time are concerns of a food packaging manufacturer. In this work, causes of high WIP were identified and three approaches were developed to reduce and control better the WIP. We propose to split the production line into dedicated lines, to change the push production system to a pull production system, and to align the process times to the takt time. A simulation model of the proposed production line was analyzed and was verified by a simulation model of the current production line. Three configurations were tested for production line A and production line B. We found that the proposed production line reduced the WIP by 70% and saved $990,000 annually in inventory holding costs. In addition, the lead time was reduced from 6.4 days to 1.9 days and the strain on the warehouse capacity was eliminated. / by Kevan Yong Cai Chim. / M.Eng.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student submitted PDF version of thesis. / Includes bibliographical references (p. 105). / The mechanisms that lead to bulk flow within a ferrofluid-filled container subjected to a rotating uniform magnetic field are experimentally studied. There are two prevailing theories: spin diffusion theory and flow due to non-uniformities in magnetic field within the ferrofluid due to nonuniform demagnetizing factors. This research sought to confirm previous measurements that indicated demagnetizing factors are the primary cause of bulk ferrofluid flow. Flattened spherical containers of various volumes, and thus different demagnetizing factors, were filled with EFH1 oil-based ferrofluid and subjected to a uniform rotating magnetic field of varying conditions (rotation direction and field strength). The shapes and magnitudes of the velocity profiles measured by an ultrasound velocimeter system differed between containers, indicating that demagnetizing factors did affect flow. The complicated flows within the flattened spheres that affected both the shape and magnitude of the flow velocity prevented a direct magnitude comparison between profiles but the flows differed enough to safely conclude that spatial non-uniformities within the fluid likely caused the bulk flow of fluid in the uniform rotating magnetic field. / by Michael John Snively. / S.B.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 57-59). / This thesis presents the design, analysis and testing of a bone plate for mandibular fracture fixation. Conventional bone plates are commonly used to set fractures of the mandible in a surgical setting. If proper alignment between the two bone segments is not achieved, then a malocclusion can result; this condition often causes significant discomfort to the patient, and may require costly and risky revision surgery to repair. Current methods of bone plate fixation require a surgeon to visually align the segments of bone, and once the plate has been affixed to the bone, there is little that can be done to adjust alignment of the fracture. The modified bone plate presented here has a deformable mid-section, with the purpose of allowing a surgeon to compensate for mis-alignment observed after the plate has been affixed to the fractured bone. The mechanics of deformation associated with various adjustment mechanisms was explored analytically, numerically, and experimentally. It was found that in order to plastically deform the adjustable section, a force of 358.8 N is required, compared with a predicted value of 351 N obtained using numerical simulations and 487 N using a fixed-fixed beam model with a concentrated central load. In addition to static tests, a dynamic testing jig has been designed with the intent of evaluating in vitro performance of the modified bone plate. Current ASTM and ISO standards for bone plate testing require forces to be applied to the faces of the bone plate, orthogonal to the direction of loading experienced in vivo. This condition is applicable to long bones such as the humerus or femur, however loading conditions of the mandible are significantly different. The testing jig allows for any bone plate of any shape to be fixed such that a force can be applied in order to simulate the normal in vivo loading conditions. This system could be used to further optimize the design of current and future deformable bone plates before they are incorporated into invasive animal or clinical trials. / by Thomas Michael Cervantes. / S.B.

Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (page 20). / The first step out of the lecture hall and into the machine shop is an eye opening period for engineering students. This exciting yet sometime intimidating experience happens for undergraduate mechanical engineers in 2.007 at MIT, Manufacturing and Design I. This experience holds an essential place in the curriculum as a class to build familiarity using the machine shop and creating self-confidence in the young students as engineers. As friendly and open as the mentors are, communication gaps are still found when students nod their heads, too embarrassed to ask another question in this completely foreign environment. Therefore, an interactive learning tool was developed to supplement 2.007 curriculum and provide another confidence building resource. The website design was chosen to give students a learning outlet in the comfort of their typical study space. Using this medium also allowed the opportunity to learn website design including, but not limited to, setting up a server, and coding html and php. With time, this project could be expanded to cover the majority of resources available in the Pappalardo Lab. / by Alexandra Taylor. / S.B.