Página 9 dos resultados de 10406 itens digitais encontrados em 0.017 segundos

‣ Mechanics of deformation of carbon nanotube-polymer nanocomposites

Akiskalos, Theodoros, 1978-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 189 leaves; 10721625 bytes; 10721430 bytes; application/pdf; application/pdf
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The goal is to develop finite element techniques to evaluate the mechanical behavior of carbon nanotube enabled composites and gain a thorough understanding of the parameters that affect the properties of the composite, both micro- and macroscopically. Micromechanical models of representative volume elements (RVEs) of unit-cell and random multi-particle distributions are used to study such parameters and their performance and accuracy in doing is compared and discussed. The microstructural parameters of interest can be loosely categorized in two groups: those related to the geometry of the composite and those associated with the matrix-nanotube interactions as well as the load transfer mechanisms along the interface and inside the nanotubes. Among the geometry-related parameters, of particular interest are the nanotube aspect ratio, the number of walls, as well as the weight and volume fraction of nanotubes, their distribution and alignment in the matrix and their curvature. In terms of the matrix-nanotube interactions, emphasis is given on the bonds developed between the matrix and the nanotube and their effect on load transfer. The amount of load transferred internally in multi-wall nanotubes is also investigated. A number of models have been created and finite element methods have been employed to analyze the macroscopic mechanical behavior of nanotube-enabled composites...

‣ Virtual environments for medical training : graphic and haptic simulation of tool-tissue interactions

Kim, Jung, 1969-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 127 leaves; 7289981 bytes; 7289787 bytes; application/pdf; application/pdf
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For more than 2,500 years, surgical teaching has been based on the so called "see one, do one, teach one" paradigm, in which the surgical trainee learns by operating on patients under close supervision of peers and superiors. However, higher demands on the quality of patient care and rising malpractice costs have made it increasingly risky to train on patients. Minimally invasive surgery, in particular, has made it more difficult for an instructor to demonstrate the required manual skills. It has been recognized that, similar to flight simulators for pilots, virtual reality (VR) based surgical simulators promise a safer and more comprehensive way to train manual skills of medical personnel in general and surgeons in particular. One of the major challenges in the development of VR-based surgical trainers is the real-time and realistic simulation of interactions between surgical instruments and biological tissues. It involves multi-disciplinary research areas including soft tissue mechanical behavior, tool-tissue contact mechanics, computer haptics, computer graphics and robotics integrated into VR-based training systems. The research described in this thesis addresses many of the problems of simulating tool-tissue interactions in medical virtual environments. First...

‣ Chondrocyte metabolism and matrix nano-electromechanics : the response to cartilage tissue shear deformation

Jin, Moonsoo, 1971-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 171 leaves; 15475249 bytes; 15475007 bytes; application/pdf; application/pdf
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Cartilage functions as a load bearing and friction reducing material in synovial joints and it is constantly exposed to in vivo loading which is coupled to electromechanical and physicochemical forces. The swelling pressure of cartilage originates from proteoglycans containing negatively charged carboxyl and sulfate groups within glycosaminoglycans. Proteoglycans are embedded within the network of collagen fibrils whose molecular structure (supercoiled helix of three alpha-chain subunits) provides resistance to tensile forces, and contributes to the overall poroviscoelastic behavior of the tissue. The dynamic balance between repulsive and tensile forces gives cartilage unique compressive and shear stiffness that varies with the rate of deformation. Chondrocytes synthesize and degrade matrix components influenced by the regulatory signals present in the extracellular matrix. The transduction mechanisms by which mechanical signals are converted to a biological response are not completely understood. Therefore, the knowledge of both biological and biophysical aspects of cartilage is important to understand the dynamic interaction between the cells and matrix. In this study, the electromechanical properties of cartilage have been studied by measuring equilibrium and dynamic shear stiffness as a function of the ionic concentration of bath solution. Measured shear properties were dependent on ionic concentration; the shear modulus increased and the phase angle between stress and strain decreased with decreasing ionic concentration.; (cont.) Theoretical models were developed to interpret the experimental results: 1) the glycosaminoglycans (GAGs) were modeled as cylindrical rods (a unit cell model) with the geometry based on the experimental measurement; 2) GAGs were embedded within collagen network which supports the repulsive forces between GAGs; 3) macroscopic shear deformation was reflected on the randomly oriented unit cell; and 4) the Poisson-Boltzmann equation was used to calculate the change in the free energy and the shear modulus as a function of ionic concentration and shear deformation. The reasonable comparison between experimental results and theoretical calculations suggests that the microstructural rearrangement of GAGs during shear deformation is an important determinant in the shear stiffness of cartilage. In vivo compression of cartilage influences chondrocyte biosynthesis through mechanical deformation...

‣ Low to high strain rate deformation of amorphous polymers : experiments and modeling

Mulliken, Adam Dustin, 1979-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 212 p.; 9125498 bytes; 9155385 bytes; application/pdf; application/pdf
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A combined experimental and analytical investigation has been performed to understand the mechanical behavior of two amorphous polymers--polycarbonate and poly(methvl methacrylate)--at strain rates ranging from 10⁻⁴ to 10⁴ s⁻¹. This spectrum of strain rates was achieved in tension/compression tests using a dynamic mechanical analyzer (DMA), a servo-hydraulic testing machine and a split-Hopkinson pressure bar. Tension tests on the DMA were used to characterize the time-temperature dependence of the elastic storage moduli and the loss factors of the two polymers. The DMA data provided a quantification of the rate-dependent shift of material transitions, and led to an analytical description of the elastic moduli at all rates and temperatures. Uniaxial compression tests were performed at strain rates of 10⁻⁴ s⁻¹ to 1 s⁻¹ using a servo-hydraulic testing machine. Stress-strain behavior of the materials was found to be rate-dependent in this regime, with yield strength increasing in a linear and non-linear fashion for PC and PMMA, respectively, with the logarithm of strain rate. High strain rate tests were performed using an aluminum split-Hopkinson pressure bar system. Material strengthening as a function of strain rate was observed to be dramatically greater in this high-rate regime for both materials. A physically-based constitutive model for large strain deformation of thermoplastics...

‣ Segmented binary control of shape memory actuator systems

Selden, Brian A., 1980-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 51 p.; 2515797 bytes; 2519822 bytes; application/pdf; application/pdf
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A new approach to the design and control of shape memory alloy (SMA) actuators is presented. SMA wires are divided into many segments and their thermal states are controlled individually as a group of finite state machines. Instead of driving a current to the entire SMA wire and controlling the wire length based on the analogue strain-temperature characteristics, the new method controls the binary state (hot or cold) of individual segments and thereby the total displacement is proportional to the length of the heated segments, i.e. austenite phase. Although the thermo-mechanical properties of SMA are highly nonlinear and uncertain with a prominent hysteresis, Segmented Binary Control is robust and stable, providing characteristics similar to a stepping motor. However, the heating and cooling of each segment to its bi-stable states entail longer time and larger energy for transition. An efficient method for improving speed of response and power consumption is developed by exploiting the inherent hysteresis of SMA. Instead of keeping the extreme temperatures continuously, the temperatures return to intermediate "hold" temperatures closer to room temperature but sufficient to keep constant phase. Coordination of the multitude of segments having independent thermal states allows for faster response with little latency time even for thick SMA wires. Based on stress dependent thermo-mechanical characteristics...

‣ An integrated geometric and thermodynamic performance model of the 2.670 Stirling Engine

Sohn, Munhee, 1981-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 30 leaves; 4372860 bytes; 4371717 bytes; application/pdf; application/pdf
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2.670 is a required mechanical engineering class taught during the Independent Activities Period (IAP) at MIT in which each student constructs a Stirling Engine. For the most part, all of the engine parts are uniform, but if so desired, students are allowed to make design changes to certain parts in order to compete for the fastest engine at the end of the class. The research team in the MIT CADlab is working on an environment, called DOME, which makes it easy to link together simulations in different packages to perform integrated analysis and make them operable over the Internet. An integration environment has been created as a DOME project in which students can analyze and optimize the design of the 2.670 Stirling Engine. A thermodynamics model of the engine was created in Matlab and a parametric solid model was created in SolidWorks. Then, DOME was used to link the Matlab thermodynamic models to the Solidworks cad model so that when geometric parameters are changed one can see how this will affect engine performance. Students will be allowed to change the diameter and length of the displacer piston and see how it affects the work per cycle of the engine. In general, DOME was easy to learn how to use and the capabilities of web accessibility and the speed of design analysis and optimization was impressive. The future intention is that 2.670 students could use this integration environment to better analyze the 2.670 Stirling Engine.; by Munhee Sohn.; Thesis (S.B.)--Massachusetts Institute of Technology...

‣ An improved fingernail trimmer

Allen, Alexander Lawrence, 1982-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 22 leaves; 2552791 bytes; 2550874 bytes; application/pdf; application/pdf
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The purpose of this undergraduate thesis project was to design and develop a first iteration prototype fingernail trimming device. The device was designed to make nail trimming easier, especially for people with poor eyesight, limited hand coordination or problems with hand steadiness. As such the device was designed to meet several design requirements such as improved nail trimming over conventional mechanical devices, simple mechanical design, safety, ease of use and a marketable construction.; by Alexander Lawrence Allen.; Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.; Includes bibliographical references.

‣ Macro scale physical model of nanoindentation on vertically aligned carbon nanotube forests

Ebeling, Geoffrey F. (Geoffrey Foster), 1981-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 56 p.; 3303590 bytes; 3304646 bytes; application/pdf; application/pdf
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Currently the process of nanoindentation is being explored as a reliable means of determining the mechanical properties of carbon nanotubes (CNTs) and the constituent tubes of vertically aligned carbon nanotube (VACNT) forests. Under indentation, each CNT can be modeled as a cantilevered beam subjected to deflection from the penetration of the indenter. The resistance to indentation is the result of the cumulative bending of the VACNTs. Using beam theory, the effective bending stiffness is determined by fitting the mechanical model to the indentation force-penetration curves. In order to validate the process of nanoindentation as a means of determining the elastic modulus of CNTs, a macro scale physical model was built using cylindrical rods of a known material and used to help explain some of the interactions of the tubes and indenter. Two models and two indenters were built to explore these effects and how they changed between models and indenters. The models demonstrated that for the indenter with a low face angle, the process was rather accurate with corresponding errors of 7% and 15%. When using a flatter indenter on both models, particularly the model with the higher areal density of tubes, demonstrated the inaccuracy of the process as a means for determining the elastic modulus of the material. Such a result was due to abnormal spikes in the data that were observable and attributed to tube interaction with the edge of the indenter. The process of indentation is reliable when the aberrations are minimal or are identifiable in the indentation force versus indentation depth curves and thus can be easily discounted. The process of scratching was also explored. For scratching the indenter is fixed at a certain indentation height and the tube forest; (cont.) is then horizontally displaced and thus further deflects the tubes. The tubes enter three phases of contact...

‣ Conducting polymer actuators : temperature effects

Del Zio, Michael R. (Michael Robert), 1982-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 77 leaves; 3974441 bytes; 3974250 bytes; application/pdf; application/pdf
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In order to utilize conducting polymer actuators as a viable engineering solution, it is necessary to produce usable levels of force with a reasonable bandwidth. Polypyrrole actuated at temperatures as high as 100 °C increases stress magnitudes by as much as 4x and stress rates by 5x. The effect is caused by a combination of decreased solution resistance and increased ion diffusion within the polymer. However, these temperatures cause accelerated degradation due to the time-temperature correlation common to viscoelastic polymers. Actuation at these temperatures can decrease cycle life by as much as 20x. Excessive heating without actuation can also result in poor actuator performance. Impedance spectroscopy coupled with electro-mechanical analysis highlighted previous results and also showed an improved frequency response from actuation at high temperatures.; by Michael R. Del Zio.; Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.; Includes bibliographical references.

‣ Upgrading the SplinterBot; Upgrading the Splinter Bot

Martinez, Nicholas
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 14 leaves
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Today, we are seeing the beginning of the robotics revolution. In the United States, the company iRobot has developed robots to vacuum the house and scrub the floors. In Japan, Mitsubishi has designed an autonomous robot to live with families, with the ability to take the initiative as well as take commands.2 One of the allures of robotics is the fusion of many academic areas, from mechanical engineering to artificial intelligence. However, this combination of academic fields also leads to the difficulty in teaching robotics. Noticing the future demand for robotics, MIT and other top universities have started teaching undergraduate robotics courses to educate new roboticists. In the fall of 2005, the MIT Computer Science and Artificial Intelligence Lab launched the second part in a two term class, Robotics: Systems and Science II (RSSII). The main goal of this class was to have the students apply all the principles learned over the previous semester on solving a complicated problem. The challenge for the term was to have the robot for the course, SplinterBot, autonomously navigate around the MIT campus and retrieve the plastic bricks scattered around. Once SplinterBot returned to base, it would build a simple structure with the bricks it collected.; by Nicholas Martinez.; Thesis (S.B.)--Massachusetts Institute of Technology...

‣ Design of a tree moving and planting device

Nabar, Sean J; Pallante, Salvatore B
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 67 leaves
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Planting trees that weigh over 200 pounds normally requires three or more able persons. Therefore, a device that allows a single person to easily and efficiently plant such trees possible by one person is highly desirable. During a Product Design class in the Mechanical Engineering Department at the Massachusetts Institute of Technology, a group of 14 students developed a series of four concept models which culminated in a Final Prototype of such a product that can successfully lift, move and plant trees of over 200 pounds. This paper is aimed at documenting this series of designs and analyzing, testing and further developing the Final Prototype built in the course in order to make it marketable. Based on customer feedback, testing results, and user interaction, revisions to the next prototype of this device are proposed. Testing with trees of 170 and 370 lbs determined that the current outrigger stabilizing mechanism needs modification. The current outriggers, which are stored inside the frame, sustained maximum loads of 29 lbs for the 170 lbs tree, and 46 lbs for the 370 lbs tree. A sketch model built to simulate the outrigger mechanism suggests that the outriggers should be attached outside the base frame of the device rather than stored inside.; (cont.) The revised device is also to include two stacked pipe clamps for securing the vertical member members of the outriggers. The upper and lower frames are to be reduced in width from 42 to 36 inches...

‣ Statistics of amplitude and fluid velocity of large and rare waves in the ocean

Suh, Il Ho
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 137 leaves
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The understanding of large and rare waves in the ocean is becoming more important as these rare events are turning into more common observances. In order to design a marine structure or vehicle to withstand such a potentially devastating phenomenon, the designer must have knowledge of extreme waves with return periods of 50 and 100 years. Based on satellite radar altimeter data, researchers have successfully predicted extreme significant wave heights with the return periods of 50 and 100 years. This thesis extends their research further by estimating the most probable extreme wave heights and other wave statistics based on spectral analysis. The same technique used for extreme significant wave height prediction is applied to extrapolation of corresponding mean wave periods, and they are used to construct two parameter spectra representing storm sea conditions. The prediction of the most probable extreme wave heights as well as other statistical data is based on linear theory and short term order statistics. There exists sufficient knowledge of second order effects on wave generation, and it could be applied to a logical progression of the simulation approach in this thesis.; (cont.) However, because this greatly increases computation time...

‣ 2.672 experiment design : heat sink fin configurations; Heat sink fin configurations

Reynolds, Zachary W. (Zachary William)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 61 leaves
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2.672 is an undergraduate mechanical engineering laboratory course which requires students to solve real-world problems using both theoretical calculations and laboratory experiments. Many of the experiments currently in the laboratory have aged and their replacement presents an opportunity for the introduction of a new experiment. In this proposed experiment, students will optimize a heat sink for a certain type of rack-mount server. For a correct execution of the experiment, students will test the power dissipation of several different heat sinks against a model for how they should behave using principles of incompressible flow, extended surfaces and heat exchangers. An apparatus has been designed and constructed to simulate the air duct inside one possible server, and allow for measurements to be taken of power dissipation, temperature, and pressure in the duct. Seven different heat sink configurations were chosen to provide students with insight into how each parameter alters the effectiveness of the heat sink. Students are then asked to choose the parameters which give the optimal configuration.; by Zachary W. Reynolds.; Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.; Includes bibliographical references (leaf 61).

‣ Nano-materials for novel magneto-rheological liquids and nano-fluids

Samouhos, Stephen V. (Stephen Vincent), 1982-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 60 p.
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Introduction: Nanotechnology, in its many forms, has evolved as a forefront of the global scientific and technological frontier. Materials once disregarded as very small dust or particulate impurities twenty years ago, are today, the focus of intensely popularized investigation. New materials have been synthesized via nanometer precision engineering, and their resulting properties continue to defy the thermal, electrical, and mechanical limitations of conventional materials [1]. Even liquid suspensions of nano-particles yield tremendous enhancements in thermal and transport rates that still remain unexplained. Analogously, forty years ago the machining and synthesis of object features with nanometer dimensions and accuracy was a mere scientific interest. Today, that capability forms the core technical competency of the leading manufacturers of micro-processor electronics. The purpose of this thesis is to contribute to the field of nanotechnology through the synthesis of a novel nano-material, and to examine its utility in areas such as directed self-assembly and nanofluid enhanced mass transport.; by Stephen V. Samouhos.; Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.; Includes bibliographical references (p. 56-60).

‣ Design of a tabletop lathe educational kit

Lopez, Marcus, S.B. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 47 p.
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The purpose of this research is to create and characterize an educational kit for the mechanical engineering courses, 2.75: Precision Machine Design and 2.72: Elements of Machine Design. This kit is intended to provide instructors with a means to create a positive learning experience by (1) providing an opportunity for students to be innovative, (2) allowing students to better understand the limitations and strengths of their designs, and (3) optimizing the benefit of the learning experience. Engaging students with a project that motivates and inspires them ultimately produces a more capable engineer. The redesign and analysis of a table-top lathe is covered in this thesis. The efforts entailed herein revolve around the design of modular lathe that best suits the needs of students and instructors in 2.75 and 2. 72. Additionally, this thesis reviews the fabrication and testing of a prototype used to identify any problems with the manufacturing and assembly.; by Marcus Lopez.; Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.; Includes bibliographical references.

‣ Design of a minimalist autonomous robotic vehicle

Spadafora, Mark (Mark A.)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 20 leaves
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The purpose of this thesis is to investigate design alternatives for the creation of a minimalist autonomous robotic vehicle, based on the Ford Escape. The work builds on prior work performed by the MIT DARPA Urban Challenge team, which competed in the national DARPA Urban Challenge NQE and UCE events in October and November 2007. The MIT team pursued an ambitious design that was rich in both sensors and computation. The excessive amount of equipment and computing power throughout the current vehicle make it too expensive and unreasonable to go into actual production. The goal for this work is to revisit the design approach of the MIT team, and from a Mechanical Engineering perspective, to perform a new conceptual design that would bridge the gap between the current vehicle and present in production technologies. By developing a minimalist sensor/processor configuration, the Ford Escape can more closely reflect a present day vehicle, in both appearance and cost, and be more viable for future production. Using the Ford Escape rapid prototype vehicle, the previous installation was stripped out in order to design, re-engineer, and implement a configuration that will allow new research in affordable autonomy and active safety for in-production vehicles.; by Mark Spadafora.; Thesis (S.B.)--Massachusetts Institute of Technology...

‣ Lorentz force actuator and carbon fiber co-winding design, construction and characterization

Chen, Yi, S. B. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 76 p.
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Carbon fiber composites are materials that present many benefits to engineering applications, ranging from aerospace to medicine. This thesis provides background on carbon fiber properties and manufacturing techniques, and outlines the methodology for manufacturing a co-wound carbon fiber and copper coil for use in linear Lorentz force actuators. A conventionally-wound, plastic-bobbin actuator coil and the new, co-wound coil were then tested to compare their electrical, thermal, and mechanical performance. In a needle-free injection application, the cowound coil demonstrated improved performance over the conventional coil configuration. The carbon fiber coil is lighter by 3.75 ± 0.155 grams, increases the transient heat transfer by 15.7 %, is 2.18 ± 0.13 times stiffer, and can survive a higher compressive force than the conventional plastic bobbin.; by Yi Chen.; Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.; Includes bibliographical references (p. 66-67).

‣ An analysis of Pre-Columbian balsa raft design to determine the suitability of such rafts for ancient maritime trade between Ecuador and Mexico

Dewan, Leslie
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 28 leaves
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By approximately 100 BCE Ecuadorian traders had established extensive maritime commercial routes reaching from Chile to Colombia. Historical sources indicate that they transported their merchandise in large, ocean-going sailing rafts made of balsa logs. By about 700 CE the data show that Ecuadorian metalworking technology had reached the west coast of Mexico but remained absent in the intermediate region of Central America. Archaeologists have argued that this technology was most plausibly transmitted via maritime routes. However, no remains of pre-columbian rafts have been found in West Mexico. This thesis uses mechanical and materials engineering analysis to determine whether these craft could have sailed from Ecuador to Mexico. Using historical accounts of the rafts as a data set, this thesis models their aerodynamic and hydrodynamic properties, their buoyancy and cargo capacity, their functional lifetime, and the load-bearing capacities of their components. The analysis shows that these prehistoric rafts were fully functional sailing vessels and could have been sailed between Ecuador and Mexico. This study greatly strengthens the argument that maritime trade transmitted Ecuadorian metallurgical technology from South America to Western Mexico.; by Leslie Dewan.; Thesis (S.B.)--Massachusetts Institute of Technology...

‣ Design, dynamic modeling, simulation and feedback control of hydrostatic bearing

Rothenhöfer, Gerald S. (Gerald Sven)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 113 p.
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A hydrostatic bearing carriage (Hydrocline) that uses an open face linear motor to drive the carriage as well as to preload the hydrostatic bearings has been developed by Professor Alexander Slocum and Gerald Rothenhöfer of the Massachusetts Institute of Technology's Mechanical Engineering Department. The Hydrocline is made to cope with the increasing requirements for accuracy in silicon wafer grinding machines. The prototype was built of aluminum oxide ceramic due to its high stiffness-to-weight ratio, low thermal expansion and corrosion resistance. In order to keep the cost of manufacturing as low as possible, a modular design that uses micron-level precision ceramic beams was chosen. Initial testing of the prototype carriage indicates that it has the following performance specifications: a vertical load capacity exceeding 5000N (theoretical limit at 12000N, max. pressure of pumps); a carriage pitch error of 0.7arc seconds; a yaw error of 0.7arc seconds; a roll error of +/- 0.6arcsec a vertical straightness at the center of the carriage of +/-0.75microns; and a vertical stiffness of the carriage of 900N per micron (load range from 0 to 1000N).; (cont.) A dynamic model of the hydrostatic bearing and fluid supply system has been developed and accurately predicts the performance of the Hydrocline. The model has been used to simulate a feedback control loop that adjusts the bearing supply flow such that changes in load can be compensated and theoretically infinite stiffness can be reached. In first experiments on a specially designed test setup the measured static stiffness of the single pocket test bearing could be increased by a factor 8 (load range 45 to 270N). The dynamic stiffness of the bearing could be increased by a factor of 2.5.; by Gerald S. Rothenhöfer.; Thesis (S.M.)--Massachusetts Institute of Technology...

‣ Large contraction conducting polymer molecular actuators

Anquetil, Patrick A. T. (Patrick Armand T.), 1973-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 239 leaves
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The development of powerful and efficient artificial muscles that mimic Nature will profoundly affect engineering sciences including robotics and prosthetics, propulsion systems, and microelectromechanical systems (MEMS). Biological systems driven by muscle out-perform human-engineered systems in many key aspects. For example, muscle endows animals with a level of dexterity and speed that has yet to be emulated by even the most complex robotic system to date. Conducting polymers were chosen for research as actuators, based on a review of the relevant properties of all known actuators and active materials. Key features of conducting polymer actuators include low drive voltages (1 - 2 V) and high active strength (10 - 40 MPa) but moderate active strains (2 %). Active strains of 20 %, which human skeletal muscle is capable of, are desirable for applications in life-like robotics, artificial prostheses or medical devices. This thesis focuses on two approaches to create large contraction in conducting polymer actuators. The first strategy utilizes polypyrrole (PPy), a conducting polymer actuator material that contracts and expands based on a bulk ion swelling mechanism. Optimization of the polymer activation environment via room temperature ionic liquids enables PPy actuators to generate large contractions (16.3 % recoverable strain at 2.5 MPa...