Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1986. / Bibliography: leaf 78. / by Eric B. Ratts. / M.S.

A primary focus of research in the field of integrated optics is the reduction of coupling losses into and out of waveguide structures. Grating couplers, taper couplers, and prism couplers each have limitations that restrict their viability for certain designs. This thesis presents a reflective optical coupler as an alternative means of coupling between a silicon-on-oxide waveguide and a target structure. Based on simulation results, the reflective coupler is found to have several advantages over standard grating and prism couplers. The reflective coupler has high coupling efficiency over a broad range of wavelengths, with a large drop in efficiency only occurring when the waveguide mode changes due to the wavelength variation. The reflective coupler is also able to couple at nearly any arbitrary angle with minimal additional coupling loss. Manufacture of the reflective coupler remains difficult, however. A specialized dicing saw was used to attempt to manufacture the coupler in a waveguide structure. However, the waveguide was damaged in an unexpected way during this manufacture process. As such, the experimental results indicate low coupling efficiency. In spite of this damage and other issues, the coupler still achieved coupling efficiency approaching 20dB, indicating that the coupler could be a valid structure should a more reliable manufacturing method be identified.

A RANS simulation of flow through a pipe is performed and validated against experimental data and previous DNS results. A mesh refinement study is performed to illustrate the near wall mesh size needed to correctly predict mean flow characteristics. In addition, aspects of the model are changed to study their impact on the results as well as the computational requirements. Comparisons are made between a two-dimensional analysis with axisymmetric boundary conditions, a one-eighth axisymmetric model, a one-fourth axisymmetric model, and a full three-dimensional pipe. The two-dimensional model provides the best match to past data; however, it is noted that the model may not be well tuned for a three-dimensional mesh. The simulation is also performed using three different turbulence models and the results of each model are compared. The purpose of the model is to create a tool that can be used for design iterations. While the model does not fully capture the complexities of turbulent flow, it is able to predict the mean flow accurately enough to be useful in a design setting. The goal of this work is to create a foundation upon which further studies of pipe flow with internal obstructions can build. The overall results show the model is able to predict the mean flow well for the validation case. However, the model does not perform well when certain aspects are changed. Increasing the robustness of the model and the determination of more usable boundary conditions remains a subject for future studies.

Under the proper conditions, bubbles formed near a solid surface can collapse, creating a high-velocity liquid jet as the bubble implodes. These jets have the potential to damage the surfaces on which they collapse, often after only brief exposure to cavitating flow. Since cavitation damage has been observed on propellers, hydrofoils, hydro power machinery, and bubble chambers used in high energy nuclear particle detection, the concept of bubble collapse has piqued the interest of researchers across multiple industries. Most laboratory experimental attempts to create the jetting collapse rely on transient events, and measurements are hampered by the short time scale associated with the collapse, the often unpredictable position and time of the event, the small size of the cavity during the final stages of the collapse, and the self-destructiveness of the event. The purpose of this work is to develop a method to generate repetitive jet collapse and rebound at temporal and spatial scales that render measurement and observation easy. The goal is also to expand on the previously detailed experimental methods by identifying and tolerancing the key dependent variables to define a robust and repeatable procedure. The experimental set up uses an acrylic test chamber mounted on an electromagnetic shaker with variable driving frequency near 60 Hz and amplitude of up to 2 mm peak. The atmospheric pressure in the test chamber is reduced between -26 and -30 in.-hg with a vacuum pump to decouple shape and volume oscillations of the bubbles. An analog camera is positioned to record bubbles formed at the bottom surface of the containers, and the driving amplitude and frequency of the shaker is controlled by a waveform generator. A key outcome of this study was the identification of a region in the parameter space of shaker amplitude and ambient pressure where stable volumetric or ‘breathing’ oscillations could be maintained. The maximum ambient pressure with observable breathing was 27.5 in Hg of vacuum at a range of 0.2 mm to 1.2 mm of peak vertical shaker amplitude. Near -30.5 in Hg breathing was observed at smaller shaker amplitudes. The parameter space was bounded by the threshold for the rapid onset of clouds of cavitation bubbles filling large volumes of the test chamber. Repetitive jetting was observed within this region for a bubble approximately 3 mm in diameter, at 0.5 in Hg above the vapor pressure being driven at 0.3 mm amplitude at 60.1 Hz. The jetting occurred near the bottom corner and the jet angle was approximately 50 degrees from the horizontal surface. The knowledge gained from this study points the way towards achieving a more robust process to generate repetitive bubble collapse. Suggestions for improvements to the experimental setup are presented in the concluding section.

Elastin provides many tissues with remarkable resilience and longevity. In elastic arteries such as aorta, elasticity is crucial for energy storage and transmission of the pulsatile blood flow. Human aorta is comprised of approximately 47% elastic fibers and undergoes several billion stretch cycles in the course of one's lifetime. Elastin is remarkably long lived, and it can suffer from cumulative effects of exposure to biochemical damages. Non-enzymatic glycation is one of the main mechanisms of aging and its effect is magnified in diabetic patients. The overall goal of this research is to advance the current understanding of the structural and mechanical roles of elastin in arterial mechanics with the effects of immediate biochemical environments using a coupled experimental and modeling approach. Such knowledge is integral to understanding the performance of elastin in living biological systems. Our study shows that there exists an intrinsic mechanical interaction among extracellular matrix (ECM) constituents that determines the mechanics of arteries and carries important implications to vascular mechanobiology. Considering the organization and engagement behavior of different ECM constituents in the arterial wall, we proposed a new constitutive model of ECM mechanics that considers the distinct structural and mechanical contributions of medial elastin, medial collagen, and adventitial collagen, to incorporate the constituent-specific fiber orientation and the sequential fiber engagement in arterial mechanics. Our study also reveals several interesting and important changes associated with non-enzymatic elastin glycation. Specifically, with in vitro glucose treatment, the stiffness of elastin increases significantly, and elastin exhibits a large hysteresis in the stress-stretch curves and an increase stress relaxation. Analysis of the relaxation time distribution spectra suggests that hydrogen bonding plays a major role in the relaxation behavior after glucose exposure. A multi-exponential model was developed to describe the relaxation behavior with material parameters obtained directly from continuous relaxation time distribution spectra. Elastin at different hydration levels was also studied to further understand the effects of immediate biochemical environments on the biomechanical behavior of elastin, and the close association of extra- and intrafibrillar water with the mechanical behavior of elastin.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2001. / Includes bibliographical references (p. 206-220). / Electrophoresis of DNA has become particularly attractive in today's age of bio-technology. The goal of the present research is to optimize the the gel-loading and sample-loading protocols used prior to electrophoresis within microfabricated devices. During gel-loading, electrophoretic channels are filled with a polymer matrix prior to their use in DNA separations. The injection rate is constrained by the desire to minimize shear-induced degradation of the polymer molecules. In this study, measurements of the zero shear-rate viscosity of linear polyacrylamide (LPA) solutions are used to determine the LPA molecular weight before and after gel-loading protocols. The results demonstrate induced molecular degradation of polymer molecules even when matrixes are injected at minimal flow rates of 1 microliter per minute. Next, digital images are used to analyze the electrophoretic migration of DNA samples during conventional sample-loading and injection protocols. Experimental data illustrate that the 'stacked' DNA sample plug is comprised of distinct concentrated populations of DNA molecules that migrate with the same mechanism of transport. This study produced a detailed exploration of the injection process as well as a standardized method to measure the level of 'stacking' exhibited by a system. Additionally, a novel high voltage injection protocol correlates increases in resolution and separation with higher levels of sample stacking during injection. Developments realized through these experiments demonstrate great promise for upgraded electrophoretic protocols and future microdevices. / by Maribel Vazquez. / Sc.D.

Thesis (Mech. E.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1994. / Includes bibliographical references (leaves 56-57). / by Pierre E. Jalkh. / Mech.E.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1995. / Includes bibliographical references (leaves 125-130). / by Sang-Joo Kim. / Ph.D.

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 75-77). / Aluminum fuel has become an attractive form of energy storage in recent years as it is both a highly abundant and extremely energy dense material. Research has discovered methods of treating aluminum with liquid metal, enabling the aluminum to produce large amounts of hydrogen when oxidized by liquid water. When this fuel reacts with water, it produces hydrogen, heat, and aluminum hydroxide (Al(OH) 3 ). Although this aluminum fuel has already been integrated into an effective mobile hydrogen production source for hydrogen fuel cells, the system size and weight is restricted by the amount of water that is required to react the aluminum. The less water that needs to be carried on board, the better, and the only way to decrease the amount of water that is required to produce hydrogen through aluminum-water reactions is to alter the chemistry of the reaction. This thesis investigates the possibility of manipulating the chemistry of these reactions at high pressures and temperatures to produce aluminum oxyhydroxide (AlOOH) or aluminum oxide (Al203 ), both of which are byproducts of aluminum-water reactions which consume less water than the Al(OH) 3 reaction for the amount of hydrogen produced. A MATLAB simulation was constructed to predict the favorability of each byproduct by analyzing the Gibbs free energy of the reactions as a function of pressure and temperature. This simulation revealed that A100H becomes favorable over Al(OH) 3 at 142.38°C and 387kPa and A120 3 becomes favorable over A100H at 174.21°C and 889kPa in a system with a 200ml volume in which 5g of fuel is reacted. Pressurized tests were also carried out and the experiment results showed that A1OOH was produced from these aluminum-water reactions at 181°C and 1035kPa, proving that it is possible to manipulate these reactions to improve the performance of aluminum fuel as a hydrogen source. / by Kelsey Carolyn Seto. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 71-74). / This thesis presents the work accomplished in the design, experimental characterization and control of a soft batoid robot. The shape of the robot is based on the body of the common stingray, Dasyatidae, and is made of soft silicone polymers. Although soft batoid robots have been previously studied, the novelty brought by the present work centers around autonomy and scale, making it suitable for field operations. The design of the robot relies on the organismic consideration that the stingray body is rigid at its center and flexible towards its fins. Indeed, all mechanical and electrical parts are inside a rigid shell embedded at the center of the robot's flexible body. The silicone forms a continuum which encases the shell and constitutes the two pectoral fins of the robot. The core idea of this design is to make use of the natural modes of vibration of the soft silicone to recreate the fin kinematics of an actual stingray. By only actuating periodically the front of the fins, a wave propagating downstream the soft fins is created, producing a net forward thrust. Experiments are conducted to quantify the robot's swimming capabilities at different regimes of actuation. The forward velocity, the stall forces produced by the robot when it is flapping its fins while being clamped, and the power consumption of the actuation are all measured. The peak velocity of the robot is 0.35 body-length per second and is obtained for a flapping frequency of 1.4 Hz and a flapping amplitude of 30°. At a flapping frequency of 2 Hz, and an amplitude of 30°, the maximum stall forward force of the robot averages at 45 Newtons and peaks at 150 Newtons. Other data collected is used to better understand the hydrodynamics of the robot. / by Audren Damien Prigent Cloitre. / S.M.