Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 101-104). / The humidification dehumidification (HDH) desalination system can be advantageous in small-scale, off-grid applications. This system is very robust and can tolerate a wide range of feed salinities, making it a good candidate for treating produced water from hydraulically fractured natural gas wells. The main drawback of this technology has been its low energy efficiency, which results in high water production costs. This work focuses on the thermodynamic balancing of HDH. The first part uses a fixed-effectiveness approach to model the use of multiple air extractions and injections to thermodynamically balance the HDH system, so as to make it more energy efficient. The effect of the number of extractions on several performance parameters is studied. In addition, we study the effect of the enthalpy pinch, which is a measure of performance for a heat and mass exchanger, on these performance parameters. Further, we present results that can be used as guidelines in designing HDH systems. These results include the identification of appropriate temperatures for the extracted/injected air streams, the division of the heat duty between stages, and the value of the mass flow rate ratio in each stage at various values of enthalpy pinch. Fixing the effectiveness of the heat and mass exchangers allows them to be modeled without explicitly sizing the components and gives insight on how the cycle design can be improved. However, linking the findings of fixed-effectiveness models to actual systems can be challenging, as the performance of the components depends mainly on the available surface areas and the flow rates of the air and water streams. In the second part of this study, we present a robust numerical solution algorithm for a heat and mass transfer model of a complete humidification-dehumidification system consisting of a packed-bed humidifier and a multi-tray bubble column dehumidifier. We look at the effect of varying the water-to-air mass flow rate ratio on the energy efficiency of the system. In addition, we study the effect of the top and bottom temperatures on the performance of the system. We recommended the implementation a control system that varies the mass flow rate ratio in order to keep the system balanced in off-design conditions, especially with varying top temperature. Finally we consider a single air extraction, and look at the effect of the location of extraction, and its direction. We define the criteria for achieving a completely balanced system. / by Karim Malek Chehayeb. / S.M.

Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 29-30). / A path-planning methodology that takes into account sea state fields, specifically wind forcing, is discussed and exemplified in this thesis. This general methodology has been explored by the Multidisciplinary Simulation, Estimation, and Assimilation Systems group (MSEAS) at MIT, however this is the first instance of wind effects being taken into account. Previous research explored vessels and isotropy, where the nominal speed of the vessel is uniform in all directions. This thesis explores the non-isotropic case, where the maximum speed of the vessel varies with direction, such as a sailboat. Our goal in this work is to predict the time-optimal path between a set of coordinates, taking into account flow currents and wind speeds. This thesis reviews the literature on a modified level set method that governs the path in any continuous flow to minimize travel time. This new level set method, pioneered by MSEAS, evolves a front from the starting coordinate until any point on that front reaches the destination. The vehicles optimal path is then gained by solving a particle back tracking equation. This methodology is general and applicable to any vehicle, ranging from underwater vessels to aircraft, as it rigorously takes into account the advection effects due to any type of environmental flow fields such as time-dependent currents and dynamic wind fields. / by Benjamin D. Hessels. / S.B.

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 77-79). / The ultimate objective of this research is to develop an innovative underwater pipe inspection robot with both swimming and crawling capabilities as opposed to conventional in-pipe robots with wheeled designs or driven by propellers. The contents of this thesis include two different parts: a propulsion mechanism using a passive compliant tail and a reversible underwater adhesion mechanism. The propulsion mechanism is the primary concern of this research. The hypothesis of this part of research is that a continuous passive compliant tail structure with an optimized stiffness profile in its longitudinal direction along with the proper control of a single actuator can allow the undulatory motion of this mechanism to resemble real fish swimming locomotion. This approach is in contrast to conventional approaches where multiple joints are actuated to create traveling waves to emulate propulsion mechanisms of fish. Four iterations of experiments are developed in total to verify the hypothesis, take measurements and improve the performance of the propulsion mechanism. It is proven that a continuous passive compliant structure driven by a DC motor through a four bar linkage can generate sufficient propulsion to drive a moving unit forward along a guide rail. The experiments with a simple prototype demonstrate that the propulsion mechanism is promising to drive a robot forward along a prescribed path without a guide rail. It is demonstrated that the stiffness profile in the longitudinal direction is one of the critical factors that affects the performance of the propulsion mechanism. A simulation model is developed to guide the design process of the passive compliant structure, mainly to optimize its stiffness profile along the tail structure. Special measures are implemented into the experiments to extract data to compare with simulated results. The reversible underwater adhesion mechanism is another critical component of the underwater pipe inspection robot that is under development. The goal of developing a reversible underwater adhesion mechanism is to provide adequate traction to various surfaces while the robot operates in water. This reversible underwater adhesion mechanism allows a robot to stick and crawl in water pipes even across the stream. This mechanism may enable recharging capability extracting energy from kinetic energy of the pipe flow. Two generations of robot prototypes are developed to demonstrate the crawling and propulsion mechanisms. / by Yichao Pan. / S.M.

Thesis (S.B. and S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1999. / Includes bibliographical references (p. 188). / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / by Robert D. White. / S.B.and S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005. / Includes bibliographical references. / Conducting polymers are a subset of materials within the electroactive polymer class that exhibit active mechanical deformations. These deformations induce stresses and strains that allow for conducting polymers to be used as an actuator for mechanical devices. Incorporation of conducting polymer actuators into mechanical devices requires electrochemical and mechanical characterization of varying polymer sample sizes and their active properties. Of particular interest, is the characterization of macro-length polymer samples, which have yet to be investigated. An understanding of conducting polymer films and their feasibility as an actuator in a mechanical device are required for the development of a conducting polymer based rotary motor. The conducting polymer, polypyrrole, was studied for its feasibility as an actuator for control surfaces on autonomous underwater vehicles. Enhancements to the actuator's performance were addressed following the feasibility study. The development of an electrochemical dynamic mechanical analyzer provides an instrument for characterization of the polymer's properties over a variety of sample sizes and actuation conditions. Finally, the application of polypyrrole as an actuator and possible enhancements combined with the characterization of macro-length polymers provides the necessary tools to develop a rotary motor. Enhancements to polypyrrole actuators in this study account for an increase in tip force of 350% and a seven fold increase in achievable strain. / (cont.) Completion of a novel electrochemical dynamic mechanical analyzer, construction of a finite rotary motor able to subtend angular displacements, and the developed embodiment of a polymer based rotary eccentric motor are accomplished in this study. / by Bryan D. Schmid. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005. / Includes bibliographical references (leaves 72-78). / Prostate cancer has become the most commonly diagnosed cancer in men in the United States. Clinical diagnostic procedures currently include prostate-specific antigen (PSA) screening, digital rectal exam, and prostatic needle biopsy. However, these methods lack the sensitivity to detect small lesions that occur in the early stages of cancer and metastasis. I propose a molecular imaging modality that provides a biochemical characterization of localized regions of prostate tissue. Using fluorescence resonance energy transfer (FRET), several peptide substrates have been designed to respond to varying concentrations of PSA with a concomitant increase in fluorescence. In the near-infrared wavelength range, these fluorescent substrates can be imaged through thin sections of tissue to allow surface volume imaging of biochemical function, and thus, to provide additional insight into prostate cancer localization and progression. The goal of this study was to develop novel fluorescent substrates for prostate-specific antigen to serve as indicators of prostate cancer progression. PSA is a biomolecular marker that has gained widespread clinical use in prostate cancer detection. Produced primarily by prostate epithelium, PSA is an androgen-regulated serine protease that acts to cleave semenogelins. Several peptide substrates for PSA have been identified and optimized for specific and efficient hydrolysis. Two of these substrates, QFYSSN and SSIYSQTEEQ were modified with fluorescent dye and quencher molecules to suppress fluorescence in the inactivated form. Light absorbed by the fluorescent molecule is dissipated via nonradiative interaction with the quencher molecule. / (cont.) Disruption of dye and quencher interaction, as in substrate proteolysis, results in an increase in fluorescence. I report several promising substrates that generate significant increases in fluorescence upon cleavage by PSA in purified systems as well as with human prostate cancer cell lines. Selected FRET substrates can distinguish between PSA- producing and non-PSA-producing human prostate cancer cells. / by Chunyao Jenny Mu. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1995. / Includes bibliographical references (p. 144-147). / by Scott D. Wright. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1984. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by Pyung-Hun Chang. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 67-69). / Multi-scale surface interaction methods have been studied to achieve optimal locomotion over surface features of differing length scales. It has been shown that anisotropy is a convenient way of transferring an undirected force to a preferred direction or movement. In this thesis, the fundamentals of friction were studied to achieve a better understanding of how to design multi-scaled robotic feet that use anisotropy for terrestrial locomotion. Static and kinetic friction coefficients were found for novel test geometries under varying load conditions. The test geometries were manufactured with materials of variable durometer and were tested using unconventional rheometry methodology. Test results were then compared to standard friction laws. As predicted, the effects of contact area were shown to have an effect on the friction forces experienced by the softer materials. The contact area effects were then modeled as Hertzian contacts for a given material. Verification of the area dependencies for the materials with adhesive effects was performed for the samples used in the friction tests. The samples were subjected to varying compressive force and images of the corresponding contact areas were obtained using an inverted microscope. The microscope images were then processed using MATLAB's image processing toolbox to find the actual contact area for the samples. The contact area results were shown to be in accordance with Herztian contact principles. The effects of varying surface roughness were also studied for a given anisotropic arrangement of bristles. The array of bristles was used to provide propulsion to a controllable robot called BristleBot. The untethered nature of the robot allowed for unhindered velocity and force measurements that were used to analyze the effects of surface roughness. The force input for the robot was provided by two vibration motors that created an excitation which was then translated to horizontal movement by the anisotropic formation of the bristles. It was found that the BristleBot was able to achieve optimal locomotion when roughness conditions were minimized. Results of the anisotropic friction and adhesion tests were used to improve footpad development for soft robotic platforms. / by Jeffrey W. Morin. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 46-48). / Pulsed sonoelectrochemical synthesis is a widely used technique for producing nanoparticles. In this technique, alternating pulses of electric current and power ultrasound are applied to an electrochemical cell to create and suspend particles in the electrolyte. The pulsed technique largely separates the particle morphology defining physical action of electrochemistry and ultrasound. Despite the large body of work characterizing the pulsed method, surprisingly little is written about the behavior of particles in the continuous case, where electric current and ultrasound are simultaneously present. In this thesis, continuous ultrasound assisted electrochemical synthesis of nanoparticles is established. Potentially useful mechanisms for particle size and shape control in continuous reactors are discussed. A continuous sonoelectrochemical reactor was designed and demonstrated to produce submicron copper powders. Improvements to the batch reactor design are proposed to extend the technique to a flow reactor useful for commercial production of submicron metal powders. / by Joseph Reneker. / S.M.