Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (leaves 141-144). / The biologically inspired method of tail articulation is investigated as a means of reducing tonal noise due to the stator wake blade interaction in underwater vehicles. This work is experimental in nature and conducted in the closed channel water tunnel at Naval Undersea Warfare Center in Newport, Rhode Island. Tail articulation is carried out with a life scale stator model with hinged flapping tail designed to (i) operate in freestream velocities corresponding to Reynolds number in the range 75,000 < Re < 300,000 and (ii) operate at frequencies up to 30 Hz in order to investigate the range of Strouhal number 0.0 < St < 0.35. Velocity measurements in the active stator wake are carried out by Laser Doppler Velocimetry, LDV, and Particle Image Velocimetry, PIV, in order to investigate the effects of tail articulation. Time averaged measurements of the stator wake by LDV show that Strouhal number of the tail articulation has a dominant effect on the time mean stator drag. Instantaneous phase averaged measurements of the stator wake by PIV show three regimes of the stator wake as Strouhal number is increased; quasi-steady wake spreading, vortex roll up, and strong vortex wake. A low order model describing the creation and convection of vorticity by tail articulation is developed which describes wake phenomena observed in experimental measurements. A two dimensional blade force simulation coupled with the reduced order tail articulation model is used to perimetrically search for a tail motion resulting in lower unsteady blade forces. / (cont.) Finally, a three dimensional unsteady propeller simulation using both experimental wake velocity data by PIV and simulated wake velocity data generated by the reduced order tail articulation model is used to predict the effect of tail articulation on radiated noise. These simulations indicate that reduction of radiated noise by 5 dB or more is possible using tail articulation. / by Daniel Lee Macumber. / S.M.

Thesis (S.B.)--Massachusetts Institute of Technology, Department of Mechanical Engineering, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (page 24). / A cam based locking mechanism was designed and fabricated to secure the joints of a continuously repositionable table capable of supporting a 11 IN load. Additionally, a frame was designed and built to test the feasibility of this joint concept as an assembly. Conventional toothed mechanisms were found to not provide a desirable smoothness of motion or resolution for implementation as an adjustable table. They also require more geometrically complex components than the proposed solution. The proposed mechanism relies on the binding of an eccentric cam and pulley, and is of interest because these key components are geometrically simple in comparison to toothed mechanisms. The reduced complexity of this solution is expected to lower the manufacturing cost of this type of joint and increase the resolution of its angular position, when compared to similar mechanisms. A model of the jamming interaction was evaluated using Matlab. This model was used to select the optimal material, eccentricity and diameter of the components. The elements were then fabricated with an Omax 2626 Precision JetMachining Center, and mechanically tested using calibrated weights. The fabricated joint is capable of holding a 56.5N*m load with a stiffness of 7.8N*m/degree. / by Phillip H. Daniel. / S.B.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2001. / Includes bibliographical references (leaves 97-98). / A machine was designed to pattern thin films of liquid by liquid embossing. 10 designs were prototyped and evaluated according to pattern transfer, alignment, and ability to emboss large area. The final design utilizes a PDMS stamp cast such that it seals an air cavity, which is then pressurized to slightly bow the stamp. The cavity is clear so alignment can be accomplished by optical feedback using a camera and microscope objective. The theory of liquid embossing is discussed. PDMS has a very high contact angle with most fluids and so it is able to clear liquid from channels approximately 5 [mu]m wide. The wettability of the substrate is modified after being in contact with PDMS so the liquid does not reflow into the channels. Sub-micron alignment between layers was achieved. Vector plots of runout between layers are given. Electrical yield was found to be 89% and was not negatively correlated by stamp age up to 1000 dry stamps. The stamps were found to wear, but due to their conformal nature this did not affect pattern transfer. Structures created by the liquid embossing machine include electrostatic actuators, test patterns with 100 nm features, vias, under-etched metal layers, and released cantilevers. / by Eric J. Wilhelm. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 215-218). / Fuel consumption reduction of more than 20% can be achieved through engine friction reduction. Piston and piston rings contribute approximately half of the total engine friction and are therefore central to friction reduction efforts. The most common method to reduce mechanical losses from piston rings has been to lower ring tension, the normal force providing sealing between the piston ring and the cylinder liner. However tension reduction can result in additional lubricant consumption. The objective of this thesis is to understand and model the physical mechanisms resulting in flow of oil to the combustion chamber in order to achieve optimal designs of piston rings. The optimal design is a compromise between friction reduction and adequate gas and lubricant sealing performance. To do so a multi-scale curved beam finite element model of piston ring is developed. It is built to couple ring deformation, dynamics and contact with the piston and the cylinder. Oil flow at the interfaces between the ring and the cylinder liner and between the ring and the piston groove can thus be simulated. The piston ring model is used to study the sealing performance of the Oil Control Ring (OCR), whose function is to limit the amount of oil supplied to the ring pack. The contributions of the three main mechanisms previously identified, to oil flow past the OCR are quantified: - Deformation of the cylinder under operating conditions can lead to a loss of contact between the ring and the liner. - Tilting of the piston around its pin can force the OCR to twist and scrape oil from the liner. - Oil accumulating below the OCR can flow to the groove and leak on the top of the OCR The OCR is found to be flexible enough to limit the impact of cylinder deformation on oil consumption. Both ring scraping and flow through the OCR groove can contribute to oil consumption in the range of engine running conditions simulated. Reduction of scraping is possible by increasing the ability of both OCR lands to maintain contact with the liner regardless of piston groove tilt. The flow of oil through the OCR groove can be reduced by designing appropriate draining of oil in the groove and an adequate oil reservoir below the OCR. The piston ring oil transport model developed in this thesis will be a valuable tool to optimize ring pack designs to achieve further ring pack friction reduction without increasing oil consumption. / by Camille Baelden. / Ph. D.

Thesis: M. Eng. in Manufacturing, Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 78-80). / Inspection is the formal examination of a product manufactured by any manufacturing process. Inspection process is critical to all the industries as it ensures that a good quality product reach at the end customers. In order to ensure minimum variation in the quality of inspection of a product, industries rely on advanced equipment or gauge to measure the quality parameters of the product. The accuracy of inspection depends a lot on the method and equipments used to inspect a product. However, at AvCarb material solutions, a product called pyrolytic graphite sheet (PGS) is manufactured and at present the types of defects that occur during their manufacturing process can only be identified visually. The problem with using human senses as a tool to perform an inspection is that the accuracy and speed of the inspection vary from person to person based on their experience, their state of mind and other human factors. Automating a visual inspection system ensures minimum variation in the accuracy and speed of an inspection process. This thesis proposes the use of the automatic vision system to perform visual inspection of PGS. The document presents how some software tools can be used to identify and quantify the defects generated on PGS and gives a comparison of the accuracy of identifying a defect through the automatic vision system and accuracy achieved through human inspection. / by Yugank Chawla. / M. Eng. in Manufacturing

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 43-46). / The Atlantic razor clam, Ensis directus, burrows underwater by expanding and contracting its valves to fluidize the surrounding soil. Its digging method uses an order of magnitude less energy than would be needed to push the clam directly into soil, which could be useful in engineering applications such as anchoring and sensor placement. The first chapter of this thesis presents the theoretical basis for the timescales necessary to achieve such efficient digging and gives design parameters for a device to validate the timescales. It then uses RoboClam, a robot designed to imitate the razor clam's movements, to test the design rules. It was found that the minimum contraction time is the most critical timescale for efficient digging, and that efficient expansion times vary more widely. The results of this chapter can be used as design rules for other robot architectures for efficient digging, optimized for the size scale and soil type of the specific application. The second chapter of this thesis examines whether it would be theoretically possible to use the same E. directus-inspired method to dig into dry soil, for applications such as sensor placement. The stress state of the soil around the robot was analyzed, and a target stress state for dry soil digging was found. Then, the two possible modes of soil collapse were investigated and used to determine how quickly the robot would have to contract to achieve the target stress state. It was found that for most dry soils, a RoboClam-like device would have to contract in 0.02 seconds, a speed slightly faster than the current robot is capable of, but still within the realm of possibility for a similar machine. These results suggest that the biomimetic approach successfully used by RoboClam to dig into submerged soil could feasibly be used to dig into dry soil as well. / by Monica Isava. / S.M.

Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (page 19). / Using male, varsity, division 3 collegiate track and field results from the past decade, critical coaching decisions such as optimizing meet scheduling, targeting efficient training programs to mimic, and identifying potential performance-influencing factors on athletes can be made more easily. To come to these conclusions, 200-meter race times were normalized using seasonal athlete improvement factors and wind data to identify at which facilities athletes tended to run faster times and what factors make those facilities fast. It can be concluded that the variation in banked track and field facilities makes the banked-to-flat track conversion factor implemented by the NCAA in 2012 is potentially too harsh for athletes to compete on some banked indoor tracks compared to others. The data also has the potential for many other applications such as identifying the highest quality training programs, analyzing conversion factors and facility speed for races other than the 200-meter dash, and applying similar principals to variations in swimming facilities. / by Brandon Corts. / S.B.

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018. / 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 (pages 103-110). / In time-sensitive and dynamic missions, autonomous vehicles must respond quickly to new information and objectives. In the case of dynamic task allocation, a team of agents are presented with a new, unknown task that must be allocated with their original allocations. This is exacerbated further in decentralized settings where agents are limited to utilizing local information during the allocation process. This thesis presents a fully decentralized, dynamic task allocation algorithm that extends the Consensus-Based Bundle Algorithm (CBBA) to allow for allocating new tasks. Whereas static CBBA requires a full resetting of previous allocations, CBBA with Partial Replanning (CBBA-PR) enables the agents to only partially reset their allocations to efficiently and quickly allocate a new task. By varying the number of existing tasks that are reset during replan, the team can trade-off convergence speed with amount of coordination. By specifically choosing the lowest bid tasks for resetting, CBBA-PR is shown to converge linearly with the number of tasks reset and the network diameter of the team. In addition, limited replanning methods are presented for scenarios without sufficient replanning time. These include a single reset bidding procedure for agents at capacity, a no-replanning heuristic that can identify scenarios that does not require replanning, and a subteam formation algorithm for reducing the network diameter. Finally, this thesis describes hardware and simulation experiments used to explore the effects of ad-hoc, decentralized communication on consensus algorithms and to validate the performance of CBBA-PR. / by Noam Buckman. / S.M.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 39). / The prevalence of diesel particulate filters (DPF) is increasing as emissions standards worldwide evolve to match current technologies. Since the first application of DPFs in the 1980's, PM trapping effectiveness has increased by orders of magnitude. During the filter's use phase, it is subject to multiple cycles of particulate matter trapping and regeneration. The soot particles are combusted in the high temperatures; however, metal additives referred to as ash, primarily from lubricants, remain behind and restrict exhaust flow. Further ash accumulation causes a pressure drop across the filter and necessitates replacement in order to maintain fuel economy and engine performance. Research into more efficient DPF designs and geometries examines current limitations with the goal of emitting cleaning emissions and extending DPF use. In order to gain a better understanding of PM trapping and regeneration and acquire real-time feedback, an improved visualization method of DPF is required. For that method, powder glass frit was applied between the filter and glass window and heated to form a bond. After the heating process, the bond strength was measured to determine optimal heating cycles and surface conditions for the glass seal. The experimental results were examined to measure the success of the bonding method relative to previous research using alternative methods. The ability to test and observe ash accumulation in different DPF designs will contribute to the understanding of PM trapping. / by Kevin Boehm. / S.B.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1997. / Includes bibliographical references (leaf 32). / by Jonathan D. Albert. / B.S.