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Articles 931 - 960 of 1342

Full-Text Articles in Mechanical Engineering

Material Flow Behavior In Friction Stir Welding, Brian C. Liechty Jun 2008

Material Flow Behavior In Friction Stir Welding, Brian C. Liechty

Theses and Dissertations

Material flow in friction stir welding is largely uncharacterized due to the difficulty in material flow measurement and visualization in metals. This study investigates plasticine for use as an analog for modeling material flow in friction stir welding (FSW) of metals. Qualitative comparisons between welded plasticine and metal sections exhibit many similarities. The transient temperature response of the plasticine also shows the same qualitative behavior as welds conducted in metal. To quantify its similarity to metal, the plasticine is further analyzed through compression tests to characterize its strain, strain-rate, and temperature sensitivities. A detailed analysis is presented which defines the …

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Adaptive Quaternion Control Of A Miniature Tailsitter Uav, Nathan B. Knoebel, Timothy W. Mclain Jun 2008

Adaptive Quaternion Control Of A Miniature Tailsitter Uav, Nathan B. Knoebel, Timothy W. Mclain

Faculty Publications

The miniature tailsitter is a unique aircraft with inherent advantages over typical unmanned aerial vehicles. With the capabilities of both hover and level flight, these small, portable systems can produce efficient maneuvers for enhanced surveillance and autonomy with little threat to surroundings and the system itself. Such vehicles create control challenges due to the two different flight regimes. These challenges are addressed with a computationally efficient adaptive quaternion control algorithm. A backstepping method for model cancellation and consistent tracking of reference model attitude dynamics is derived. This is used in conjunction with a regularized data-weighting recursive least-squares algorithm for the …

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An Investigation Of Positive Engagement, Continuously Variable Transmissions, Ryan R. Dalling May 2008

An Investigation Of Positive Engagement, Continuously Variable Transmissions, Ryan R. Dalling

Theses and Dissertations

A Positive Engagement, Continuously Variable Transmission (PECVT) allows for a continuously variable transmission ratio over a given range using positively engaged members, such as gear teeth, to transmit torque. This research is an investigation of PECVTs to establish a classification system and governing principles that must be satisfied for an embodiment to overcome the non-integer tooth problem. Results of an external patent search are given as examples of different concepts and PECVT embodiments that have been employed to negate the effects of the non-integer tooth problem. To classify all published and unpublished PECVT embodiments, a classification system is developed, based …

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Measurements And Modeling Of Coal Ash Deposition In An Entrained-Flow Reactor, Ryan P. Blanchard Apr 2008

Measurements And Modeling Of Coal Ash Deposition In An Entrained-Flow Reactor, Ryan P. Blanchard

Theses and Dissertations

Coal plays a significant role in meeting the world's need for energy and will continue to do so for many years to come. Economic, environmental, and public opinion are requiring coal derived energy to be cleaner and operate in a more narrow window of operating conditions. Fouling and slagging of heat transfer surfaces continues to be a challenge for maintaining boiler availability and expanding the use of available fuels and operating conditions. The work incorporates existing information in the literature on ash deposition into a User-Defined Function (UDF) for a commercial comprehensive combustion and CFD code. Results from the new …

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Parametric Optimization Design System For A Fluid Domain Assembly, Matthew Jackson Fisher Apr 2008

Parametric Optimization Design System For A Fluid Domain Assembly, Matthew Jackson Fisher

Theses and Dissertations

Automated solid modeling, integrated with computational fluid dynamics (CFD) and optimization of a 3D jet turbine engine has never been accomplished. This is due mainly to the computational power required, and the lack of associative parametric modeling tools and techniques necessary to adjust and optimize the design. As an example, the fluid domain of a simple household fan with three blades may contain 500,000 elements per blade passage. Therefore, a complete turbine engine that includes many stages, with sets of thirty or more blades each, will have hundreds of millions of elements. The fluid domains associated with each blade creates …

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Development Of A Miniature Vtol Tail-Sitter Unmanned Aerial Vehicle, Jeffrey V. Hogge Apr 2008

Development Of A Miniature Vtol Tail-Sitter Unmanned Aerial Vehicle, Jeffrey V. Hogge

Theses and Dissertations

The design, analysis, construction and flight testing of a miniature Vertical Take-Off and Landing (VTOL) tail-sitter Unmanned Aerial Vehicle (UAV) prototype is presented in detail. Classic aircraft design methods were combined with numerical analysis to estimate the aircraft performance and flight characteristics. The numerical analysis employed a propeller blade-element theory coupled with momentum equations to predict the influence of a propeller slipstream on the freestream flow field, then the aircraft was analyzed using 3-D vortex lifting-line theory to model finite wings immersed in the flow field. Four prototypes were designed, built, and tested and the evolution of these prototypes is …

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Exploring The Common Design Space Of Dissimilar Assembly Parameterizations For Interdisciplinary Design, Brady M. Larson Apr 2008

Exploring The Common Design Space Of Dissimilar Assembly Parameterizations For Interdisciplinary Design, Brady M. Larson

Theses and Dissertations

The use of parametric CAD models in engineering, analysis, and optimization has greatly enhanced the effectiveness and efficiency of the product development process. Parametric models provide an attractive avenue for expansive design exploration. There still exists, however, a great challenge for products requiring design input from multiple disciplines. The collaboration of engineering disciplines can be hampered by many factors including: competing design objectives, communication of design changes, the use of different design and analysis software, and different geometry definitions. These obstacles become compounded when developing products at the assembly level. The use of solid parametric assembly models is not readily …

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Generating Cad Parametric Features Based On Topology Optimization Results, William R. Blattman Apr 2008

Generating Cad Parametric Features Based On Topology Optimization Results, William R. Blattman

Theses and Dissertations

Shape optimization has become an important tool in industry to minimize weight and generate new designs. At the same time, companies are turning to CAD-centric design strategies where robust parametric CAD models are used to generate new designs and part-families of current designs, as well as the tooling and manufacturing procedures. However, due to its complexity, the optimal topology results are often discarded or recreated by hand into a CAD model. From a design stand point, the results can be improved with the use of manufacturing constraints on the shape optimization process. These constraints improve the manufacturability based on common …

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Characterization Of Synthetic, Self-Oscillating Vocal Fold Models, James S. Drechsel Mar 2008

Characterization Of Synthetic, Self-Oscillating Vocal Fold Models, James S. Drechsel

Theses and Dissertations

The vocal folds are essential for speech production, and a better understanding of vocal fold vibration characteristics may help improve treatments of voice disorders. However, studying real vocal folds presents significant challenges. In-vivo studies are limited by access and safety issues. Excised larynges have a short useable lifetime (on the order of minutes) and are difficult to parameterize. In contrast, synthetic vocal fold models have long useable lifetimes and can be easily parameterized. In this thesis, a series of tests performed on recently developed synthetic, self-oscillating models of the human vocal folds are discussed. These tests include measurements of vibration …

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Development Of A Quality Improvement Method For International Manufacturing, Andrew J. Strong Mar 2008

Development Of A Quality Improvement Method For International Manufacturing, Andrew J. Strong

Theses and Dissertations

Many companies are entering the international manufacturing arena. The continued expansion of the global market suggests that international manufacturing will grow. Among other concerns, the difficulty of producing high quality in some countries suggests that it is critical that companies using international locations for manufacturing find methods to better monitor and improve quality. The purpose of this research was to develop and test a method for quality improvement in an offshore environment. This method would be specifically applicable to a third-party logistics company (3PL), where the 3PL is a United States company that brokers manufacturing in China, networks to multiple …

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Robust Parameterization Schema For Cax Master Models, Courtney L. Berglund Mar 2008

Robust Parameterization Schema For Cax Master Models, Courtney L. Berglund

Theses and Dissertations

Today's engineering companies rely heavily on an engineer's ability to use computers to analyze and optimize designs. With this use of computers in the design process, products undergo multiple design iterations between preliminary concept and final form. This in turn results in Computer Aided Design (CAD) models being passed from one discipline to the next. In attempts to keep consistency within the design process, an industry wide shift towards the use of CAD master models is taking place. With this change to master models, manufacturing and engineering development companies are attempting to more fully employ the use of parametrics in …

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Achieving Complex Motion With Fundamental Components For Lamina Emergent Mechanisms, Brian Geoffrey Winder Mar 2008

Achieving Complex Motion With Fundamental Components For Lamina Emergent Mechanisms, Brian Geoffrey Winder

Theses and Dissertations

Designing mechanical products in a competitive environment can present unique challenges, and designers constantly search for innovative ways to increase efficiency. One way to save space and reduce cost is to use ortho-planar compliant mechanisms which can be made from sheets of material, or lamina emergent mechanisms (LEMs). This thesis presents principles which can be used for designing LEMs. Pop-up paper mechanisms use topologies similar to LEMs, so it is advantageous to study their kinematics. This thesis outlines the use of planar and spherical kinematics to model commonly used pop-up paper mechanisms. A survey of common joint types is given, …

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Fundamental Components For Lamina Emergent Mechanisms, Joseph O. Jacobsen Feb 2008

Fundamental Components For Lamina Emergent Mechanisms, Joseph O. Jacobsen

Theses and Dissertations

This thesis introduces lamina emergent mechanisms (LEMs) and presents components that can be used as building blocks to create LEMs capable of more complex motion. As the name suggests, lamina emergent mechanisms are fabricated out of planar materials (the lamina) but their motion is out of that plane (emergent). Lamina emergent mechanisms can provide benefits that include reduced manufacturing costs and minimal volume when in the planar state. The compact initial state of LEMs is beneficial in reducing shipping costs, especially in volume critical applications. LEMs also exhibit the potential benefits of compliant mechanisms, namely increased precision, reduced weight, reduced …

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Observations Of Piezoresistivity For Polysilicon In Bending That Are Unexplained By Linear Models, Tyler L. Waterfall, Gary K. Johns, Robert K. Messenger, Brian D. Jensen, Timothy W. Mclain, Larry L. Howell Feb 2008

Observations Of Piezoresistivity For Polysilicon In Bending That Are Unexplained By Linear Models, Tyler L. Waterfall, Gary K. Johns, Robert K. Messenger, Brian D. Jensen, Timothy W. Mclain, Larry L. Howell

Faculty Publications

Compliant piezoresistive MEMS sensors exhibit great promise for improved on-chip sensing. As compliant sensors may experience complex loads, their design and implementation require a greater understanding of the piezoresistive effect of polysilicon in bending and combined loads. This paper presents experimental results showing the piezoresistive effect for these complex loads. Several n-type polysilicon test structures, fabricated in MUMPs and SUMMiT processes, were tested. Results show that, while tensile stresses cause a linear decrease in resistance, bending stresses induce a nonlinear rise in resistance, contrary to the effect predicted by linear models. In addition, tensile, compressive, and bending loads combine in …

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Characterizing The Three-Dimensional Behavior Of Bistable Micromechanisms, Brian B. Cherry Feb 2008

Characterizing The Three-Dimensional Behavior Of Bistable Micromechanisms, Brian B. Cherry

Theses and Dissertations

Compliant bistable micromechanisms have been proposed for use in applications such as switches, relays, shutters, and sensing arrays. Unpublished laboratory testing suggests that off-axis forces may affect the bistable nature of fully compliant bistable micromechanisms (FCBMs). The actuation forces required to snap the FCBM from one stable equilibrium position to another can be altered if the off-axis forces are applied to the mechanism during transition between stable positions. Understanding the three-dimensional characteristics of these mechanisms and the effect of eccentric loading conditions would be helpful in design and analysis of FCBMs. Two 3-D FEA models were developed for analysis and …

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A Model For Predicting The Piezoresistive Effect In Microflexures Experiencing Bending And Tension Loads, Gary K. Johns, Larry L. Howell, Brian D. Jensen, Timothy W. Mclain Feb 2008

A Model For Predicting The Piezoresistive Effect In Microflexures Experiencing Bending And Tension Loads, Gary K. Johns, Larry L. Howell, Brian D. Jensen, Timothy W. Mclain

Faculty Publications

This paper proposes a model for predicting the piezoresistive effect in microflexures experiencing bending stresses. Linear models have long existed for describing piezoresistivity for members in pure tension and compression. However, extensions of linear models to more complex loading conditions do not match with experimental results. A second-order model to predict piezoresistive effects in tension, compression, and more complex loading conditions is proposed. A reduced form of the general second-order model is presented for thin flexures in bending. A three-step approach is used to determine the piezoresistive coefficients for this reduced-form model. The approach is demonstrated for two sets of …

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Reduced Order Modeling Of Time-Dependent Reflectance Profiles From Purely Scattering Media, R. Scott Larson, Matthew R. Jones Jan 2008

Reduced Order Modeling Of Time-Dependent Reflectance Profiles From Purely Scattering Media, R. Scott Larson, Matthew R. Jones

Faculty Publications

Due to the widespread existence and importance of foam, inverse techniques for characterizing industrial foams are of interest. An essential element in an inverse method used to characterize a foam layer is a model of the time-dependent reflectance of a laser pulse. Monte Carlo methods may be used to accurately model reflectance, but these methods are computationally expensive. Computationally efficient methods based on the diffusion approximation have been developed, but this approach is not sufficiently accurate in many cases of interest. Therefore, a computationally efficient and robust method is desirable. This paper presents a computationally efficient method for modeling the …

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Incorporating Grain Size Effects In Taylor Crystal Plasticity, Bradley S. Fromm Dec 2007

Incorporating Grain Size Effects In Taylor Crystal Plasticity, Bradley S. Fromm

Theses and Dissertations

A method to incorporate grain size effects into crystal plasticity is presented. The classical Hall-Petch equation inaccurately predicts the macroscopic yield strength for materials with non-equiaxed grains or materials that contain unequal grain size distributions. These deficiencies can be overcome by incorporating both grain size and orientation characteristics into crystal plasticity theory. Homogenization relationships based on a viscoplastic Taylor-like approach are introduced along with a new function, the grain size and orientation distribution function (GSODF). Estimates of the GSODF for high purity α-titanium are recovered through orientation imaging microscopy coupled with the chord length distribution. A comparison between the new …

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Bio-Surfaces And Geometric References For A Standardized Biomechanical Design Methodology For Mass Customization, Kimberly A. Jensen Dec 2007

Bio-Surfaces And Geometric References For A Standardized Biomechanical Design Methodology For Mass Customization, Kimberly A. Jensen

Theses and Dissertations

This dissertation presents a method for the design of customizable products that interface with the human body. The method presented involves first, a consistent method of capturing and representing the human model so that the model can be used with CAx tools and solid modeling techniques. Second, it provides a design methodology based on feature structure planning and assembly modeling that provides a consistent structure to the design process so that it can be reused and parameterized. Third, a strategy for identifying parametric variables that are referenced to the human body is introduced. The core of this method is the …

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Reducing Curvature In Complex Tool Paths By Deviating From Cam-Produced Tool Paths Within A Tolerance Band, George Benjamin Naseath Dec 2007

Reducing Curvature In Complex Tool Paths By Deviating From Cam-Produced Tool Paths Within A Tolerance Band, George Benjamin Naseath

Theses and Dissertations

This thesis develops an algorithm to decrease high-curvature sections in tool paths for complex parts to achieve shorter machining times resulting in higher production rates. In the research sample cases, the algorithm decreased machining times by 1% to 9% for design-induced sections of high curvature and by 16% to 75% for CAM induced ripples using high path tolerances. High-curvature sections in tool paths are caused by complex part geometry, noise, and discontinuities in the model. The curvature is decreased by deviating the tool path within an allowable path tolerance. The feedrate along the tool path is directly related to the …

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One-Dimensional Radial Flow Turbomachinery Performance Modeling, Robert John Pelton Dec 2007

One-Dimensional Radial Flow Turbomachinery Performance Modeling, Robert John Pelton

Theses and Dissertations

The Two-Element In Series (TEIS) and Two-Zone models have been used successfully for over twenty years to model test data for radial flow compressors and pumps. The models can also be used to predict the performance of new machines provided that the model inputs can be accurately specified. Unfortunately, use of the TEIS and Two-Zone models as a predictive tool has been limited because an accurate and broadly applicable method of predicting the modeling parameters, etaA, etaB, chi and d2p does not exist. Empirical models have been developed to predict the TEIS and Two-Zone modeling parameters based on a large …

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Numerical Study Of Fully Developed Laminar And Turbulent Flow Through Microchannels With Longitudinal Microstructures, Kevin B. Jeffs Nov 2007

Numerical Study Of Fully Developed Laminar And Turbulent Flow Through Microchannels With Longitudinal Microstructures, Kevin B. Jeffs

Theses and Dissertations

Due to the increase of application in a number of emerging technologies, a growing amount of research has focused on the reduction of drag in microfluidic transport. A novel approach reported in the recent literature is to fabricate micro-ribs and cavities in the channel wall that are then treated with a hydrophobic coating. Such surfaces have been termed super- or ultrahydrophobic and the contact area between the flowing liquid and the solid wall is greatly reduced. Further, due to the scale of the micropatterned structures, the liquid is unable to wet the cavity and a liquid meniscus is formed between …

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Experimental Validation Of An Autonomous Control System On A Mobile Robot Platform, Timothy Mclain, Randall W. Beard, Wei Ran, J.-S. Sun Nov 2007

Experimental Validation Of An Autonomous Control System On A Mobile Robot Platform, Timothy Mclain, Randall W. Beard, Wei Ran, J.-S. Sun

Faculty Publications

An autonomous control system designed for a non-holonomic wheeled mobile robot that is programmed to emulate a fixed-wing unmanned air vehicle (UAV) flying at constant altitude is experimentally validated. The overall system is capable of waypoint navigation, threat avoidance, real-time trajectory generation and trajectory tracking. Both the wheeled mobile robot experimental platform and the hierarchical autonomous control software architecture are introduced. Programmed to emulate a fixed-wing UAV flying at constant altitude, a non-holonomic mobile robot is assigned to follow a desired time-parameterised trajectory generated by a real-time trajectory generator to transition through a sequence of targets in the presence of …

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Integrated Piezoresistive Sensing For Feedback Control Of Compliant Mems, Robert K. Messenger Oct 2007

Integrated Piezoresistive Sensing For Feedback Control Of Compliant Mems, Robert K. Messenger

Theses and Dissertations

Feedback control of MEMS devices has the potential to significantly improve device performance and reliability. One of the main obstacles to its broader use is the small number of on-chip sensing options available to MEMS designers. A method of using integrated piezoresistive sensing is proposed and demonstrated as another option. Integrated piezoresistive sensing utilizes the inherent piezoresistive property of polycrystalline silicon from which many MEMS devices are fabricated. As compliant MEMS structures flex to perform their functions, their resistance changes. That resistance change can be used to transduce the structures' deflection into an electrical signal. This dissertation addresses three topics …

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A Generalized Two-Dimensional Model To Reconstruct The Impact Phase In Automobile Collisions, Regis Agenor David Oct 2007

A Generalized Two-Dimensional Model To Reconstruct The Impact Phase In Automobile Collisions, Regis Agenor David

Theses and Dissertations

Automobile accident reconstruction has been facilitated by the development of computer based modules to allow evaluation of evidence gathered at the accident scenes. Although the computer modules are based in fundamental physical laws, an understanding of these laws by the user is required for proper application of the computer model in a given accident scenario. Vehicle collision analysis techniques generally separate the collision into three phases: pre-impact, impact, and post impact. The intent of the research is to provide a generalized model to reconstruct two dimensional impact problems in the area of accident reconstruction. There are currently two modeling techniques …

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Principles, Functions, And Concepts For Compliant Mechanically Reactive Armor Elements, Cameron S. Andersen Sep 2007

Principles, Functions, And Concepts For Compliant Mechanically Reactive Armor Elements, Cameron S. Andersen

Theses and Dissertations

There exists a great need for armor systems with greater mass efficiencies and ballistic limits. This thesis explores the development of a new field of armor capable of satisfying the increased demand for modern armor: Mechanically Reactive Armor or MRA. More specifically, the thesis focuses on Compliant MRA or CMRA. From the physics governing projectile-armor interactions, principles governing successful design of MRA are identified and presented. These principles or design approaches focus primarily on rejecting, minimizing, or absorbing the incoming projectile's kinetic energy. After identifying these principles, the specific mechanical functions required by the principles are isolated. These functions represent …

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Numerical Simulation Of Vortex Generating Jets In Zero And Adverse Pressure Gradients, Curtis Lynn Memory Sep 2007

Numerical Simulation Of Vortex Generating Jets In Zero And Adverse Pressure Gradients, Curtis Lynn Memory

Theses and Dissertations

Numerical simulations of particle image velocimetry (PIV) experiments conducted with vortex generating jets (VGJs) on a flat plate, at a Reynolds number based on plate length of 50,000, were performed for three flow conditions using a time-accurate hybrid Navier-Stokes solver. Time-averaged steady blowing of angled jets, subjected to a zero pressure gradient, yielded excellent agreement with the PIV data in terms of vortex formation and strength. Observed flow features include primary and secondary vortices, where the primary vortex eventually dominates the downstream region. A shell wall structure, created by smaller vortical structures surrounding the developing vortices, was also observed. A …

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Adaptive Quaternion Control For A Miniature Tailsitter Uav, Nathan B. Knoebel Aug 2007

Adaptive Quaternion Control For A Miniature Tailsitter Uav, Nathan B. Knoebel

Theses and Dissertations

The miniature tailsitter is a unique aircraft with inherent advantages over typical unmanned aerial vehicles. With the capabilities of both hover and level flight, these small, portable systems can produce efficient maneuvers for enhanced surveillance and autonomy with little threat to surroundings and the system itself. Such vehicles are accompanied with control challenges due to the two different flight regimes. Problems with the conventional attitude representation arise in estimation and control as the system departs from level flight conditions. Furthermore, changing dynamics and limitations in modeling and sensing give rise to significant attitude control design challenges. Restrictions in computation also …

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Design And Fabrication Of Out-Of-Plane Silicon Microneedles With Integrated Hydrophobic Microchannels, Michael S. Diehl Aug 2007

Design And Fabrication Of Out-Of-Plane Silicon Microneedles With Integrated Hydrophobic Microchannels, Michael S. Diehl

Theses and Dissertations

Microfabricated needles have the potential for inexpensive drug delivery without pain. The ability to deliver medication painlessly to patients will someday be not just hoped for but expected by the general public. The commercialization of this technology will also lead to other valuable technologies, such as systems that continually monitor and control insulin or other drugs in diabetic patients. This research presents fabrication procedures developed to produce pyramidal-shaped microneedles with microchannels that will allow for fluid delivery. The microchannels are etched into the substrate surface of a [100] silicon wafer using inductively coupled plasma etching. After the channel etch a …

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Experiments In Cooperative Timing For Miniature Air Vehicles, Timothy Mclain, Derek R. Nelson, Randal W. Beard Aug 2007

Experiments In Cooperative Timing For Miniature Air Vehicles, Timothy Mclain, Derek R. Nelson, Randal W. Beard

Faculty Publications

This paper presents experimental results for two cooperative timing missions carried out using a team of three miniature air vehicles (MAVs). Using a cooperative timing algorithm based on coordination functions and coordination variables, the MAV team executed a series of simultaneous arrival and cooperative fly-by missions. In the presence of significant wind disturbances, the average time difference between the first and last vehicle in the simultaneous arrival experiments was 1.6 s. For the cooperative fly-by experiments, the average timing error between vehicle arrivals was 0.6 s. These results demonstrate the practical feasibility of the cooperative timing approach.

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