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Articles 1 - 30 of 54
Full-Text Articles in Mechanical Engineering
Incorporating Grain Size Effects In Taylor Crystal Plasticity, Bradley S. Fromm
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 …
Bio-Surfaces And Geometric References For A Standardized Biomechanical Design Methodology For Mass Customization, Kimberly A. Jensen
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 …
Reducing Curvature In Complex Tool Paths By Deviating From Cam-Produced Tool Paths Within A Tolerance Band, George Benjamin Naseath
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 …
One-Dimensional Radial Flow Turbomachinery Performance Modeling, Robert John Pelton
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 …
Numerical Study Of Fully Developed Laminar And Turbulent Flow Through Microchannels With Longitudinal Microstructures, Kevin B. Jeffs
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 …
Experimental Validation Of An Autonomous Control System On A Mobile Robot Platform, Timothy Mclain, Randall W. Beard, Wei Ran, J.-S. Sun
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 …
Integrated Piezoresistive Sensing For Feedback Control Of Compliant Mems, Robert K. Messenger
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 …
A Generalized Two-Dimensional Model To Reconstruct The Impact Phase In Automobile Collisions, Regis Agenor David
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 …
Principles, Functions, And Concepts For Compliant Mechanically Reactive Armor Elements, Cameron S. Andersen
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 …
Numerical Simulation Of Vortex Generating Jets In Zero And Adverse Pressure Gradients, Curtis Lynn Memory
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 …
Adaptive Quaternion Control For A Miniature Tailsitter Uav, Nathan B. Knoebel
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 …
Design And Fabrication Of Out-Of-Plane Silicon Microneedles With Integrated Hydrophobic Microchannels, Michael S. Diehl
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 …
Experiments In Cooperative Timing For Miniature Air Vehicles, Derek R. Nelson, Timothy W. Mclain, Randal W. Beard
Experiments In Cooperative Timing For Miniature Air Vehicles, Derek R. Nelson, Timothy W. Mclain, 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.
Experiments In Cooperative Timing For Miniature Air Vehicles, Timothy Mclain, Derek R. Nelson, Randal W. Beard
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.
Obstacle Avoidance Using Circular Paths, Timothy Mclain, Randal W. Beard, Jeffery Brian Saunders
Obstacle Avoidance Using Circular Paths, Timothy Mclain, Randal W. Beard, Jeffery Brian Saunders
Faculty Publications
This paper develops a method of obstacle avoidance for fixed-wing miniature air vehicles (MAV) using a series of circular oscillating paths and a single point laser ranger. The laser ranger is a low power, light-weight device used to report the distance to an object in a single direction of the body frame of a MAV. The oscillating paths allow the laser ranger to scan for obstacles and possible escape paths for the MAV in the case of obstacle detection. The circular paths are generated along waypoint paths and transition between waypoint paths without loss of scanning capabilities. Obstacle avoidance is …
Development Of A Multiple Microphone Probe Calibrator, Jonathan Reed Oldham
Development Of A Multiple Microphone Probe Calibrator, Jonathan Reed Oldham
Theses and Dissertations
This paper presents the theory, design, and validation of a microphone calibrator used to calibrate multiple microphones simultaneously. This work was done in conjunction with the development of an acoustic energy density probe, which was used to validate the calibrator. The probe uses multiple microphones to acquire the data needed to compute the acoustic energy density. The probe microphones are 0.006 m diameter electret microphones which typically do not have an ideal “flat" response over a wide range of frequencies as compared to precision condenser microphones. The probe microphone characteristics prompted the need for simultaneous, multi-microphone magnitude calibration. The idea …
Elliptical Rolling Link Toggle Mechanisms For Passive Force Closures With Self-Adjustment, Jacob Ross Montierth
Elliptical Rolling Link Toggle Mechanisms For Passive Force Closures With Self-Adjustment, Jacob Ross Montierth
Theses and Dissertations
This thesis presents elliptical rolling contact joints as an alternative to circular rolling contact and conventional revolute joints where high quality force transmission "low friction and backlash" with variable output are desired. Parameters specific to the joint and its position are developed in terms of relative link angles and elliptical surface geometry. These parameters are used to generate the basic forward kinematics for elliptical rolling link toggle mechanisms with oscillatory motion and high mechanical advantage. As large compressive loads are characteristic of such mechanisms, stress conditions are identified and principles for joint stability with variable, precision outputs are discussed. Finally, …
A Geometry-Based Motion Planner For Direct Machining And Control, Robert M. Cheatham
A Geometry-Based Motion Planner For Direct Machining And Control, Robert M. Cheatham
Theses and Dissertations
Direct Machining And Control (DMAC) is a new method of controlling machine tools directly from process planning software. A motion planning module is developed for the DMAC system that operates directly off path geometry without pre-tessellation. The motion planner is developed with the intent to process Bezier curves. The motion planning module includes a deterministic predictor-corrector-type curve interpolator, a dynamics limiting module, and a two-pass jerk-limited speed profiling algorithm. The methods are verified by machining an automotive surface in a clay medium and evaluating the resultant machine dynamics, feed rate, and chordal error throughout the machining process.
Investigation Of Particle Velocity And Drag With Spherical And Non-Spherical Particles Through A Backward Facing Step, Kyle Frederick Larsen
Investigation Of Particle Velocity And Drag With Spherical And Non-Spherical Particles Through A Backward Facing Step, Kyle Frederick Larsen
Theses and Dissertations
Numerous practical applications exist where dispersed solid particles are transported within a turbulent accelerating or decelerating gaseous flow. The large density variation between phases creates the potential for significant differences in velocity known as velocity slip. Flow over a backward facing step provides a well characterized, turbulent, decelerating flow useful for measuring the relative velocities of the solid and gaseous phases in order to determine velocity slip and particle drag. Numerous investigations have been conducted to determine the gas phase velocity in a backward facing step for both laminar and turbulent flows and therefore the gas phase flow is well …
Autonomic Product Development Process Automation, John E. Daley
Autonomic Product Development Process Automation, John E. Daley
Theses and Dissertations
Market globalization and mass customization requirements are forcing companies towards automation of their product development processes. Many task-specific software solutions provide localized automation. Coordinating these local solutions to automate higher-level processes requires significant software maintenance costs due to the incompatibility of the software tools and the dynamic nature of the product development environment. Current automation methods do not provide the required level of flexibility to operate in this dynamic environment. An autonomic product development process automation strategy is proposed in order to provide a flexible, standardized approach to product development process automation and to significantly reduce the software maintenance costs …
Comparing The Feasibility Of Cutting Thin-Walled Sections From Five Commonly Used Metals Utilizing Wire Electric Discharge Machining, Richard C. Stephenson
Comparing The Feasibility Of Cutting Thin-Walled Sections From Five Commonly Used Metals Utilizing Wire Electric Discharge Machining, Richard C. Stephenson
Theses and Dissertations
Wire Electric Discharge Machining (wire-EDM) is a non-traditional machining process. Controlled electric sparks are successively used to vaporize part of a workpiece along a programmed path in order to machine a desired part. Because there is no tool that comes in direct contact with the workpiece, it is possible to machine thin, delicate parts. This thesis was designed to observe and analyze the differences in cutting capabilities for a conventional wire-EDM machine when cutting thin-walled sections from five commonly used metals utilizing a variation of roughing and finishing passes. The five metals that were used in this study are: Aluminum …
Development Of Deployable Wings For Small Unmanned Aerial Vehicles Using Compliant Mechanisms, Steven D. Landon
Development Of Deployable Wings For Small Unmanned Aerial Vehicles Using Compliant Mechanisms, Steven D. Landon
Theses and Dissertations
Unmanned Air Vehicles (UAVs) have recently gained attention due to their increased ability to perform sophisticated missions with less cost and/or risk than their manned counterparts. This thesis develops approaches to the use of compliant mechanisms in the design of deployable wings for small UAVs. Although deployable wings with rigid-link mechanisms have been used in the past to maintain flight endurance while minimizing required storage volume, compliant mechanisms offer many advantages in manufacturability and potential space savings due to function sharing of components. A number of compliant, deployable wing concepts are generated and a classification system for them is formed. …
Friction Stir Welding Of High-Strength Automotive Steel, Eric Michael Olsen
Friction Stir Welding Of High-Strength Automotive Steel, Eric Michael Olsen
Theses and Dissertations
The following thesis is a study on the ability to create acceptable welds in thin-plate, ultra-high-strength steels (UHSS) by way of friction stir welding (FSW). Steels are welded together to create tailor-welded blanks (TWB) for use in the automotive industry. Dual Phase (DP) 590, 780, and 980 steel as well as Transformation-Induced Plasticity (TRIP) 590 steel with thicknesses ranging from 1.2 mm to 1.8 mm were welded using friction stir welding under a variety of processing conditions, including experiments with dissimilar thicknesses. Samples were tested under tensile loads for initial determination if an acceptable weld had been created. Acceptable welds …
Vector Field Path Following For Miniature Air Vehicles, Timothy Mclain, Derek R. Nelson, D. Blake Barber, Randall W. Beard
Vector Field Path Following For Miniature Air Vehicles, Timothy Mclain, Derek R. Nelson, D. Blake Barber, Randall W. Beard
Faculty Publications
In this paper, a method for accurate path following for miniature air vehicles is developed. The method is based on the notion of vector fields, which are used to generate desired course inputs to inner-loop attitude control laws. Vector-field path-following control laws are developed for straight-line paths and circular arcs and orbits. Lyapunov stability arguments are used to demonstrate asymptotic decay of path-following errors in the presence of constant wind disturbances. Experimental flight tests have demonstrated mean path-following errors on less than one wingspan for straight-line and orbit paths and less than three wingspans for paths with frequent changes in …
An Investigation Of A Positive Engagement, Continuously Variable Transmission, Brian S. Andersen
An Investigation Of A Positive Engagement, Continuously Variable Transmission, Brian S. Andersen
Theses and Dissertations
A continuously variable transmission (CVT) is a type of transmission that allows an infinitely variable ratio change within a finite range, allowing the engine to continuously operate in an efficient or high performance range. A brief history of CVTs is presented, including the families under which they can be categorized. A new family of CVTs, with the classification of positive engagement, is presented. Three different published embodiments of CVTs of the positive engagement type are presented describing a meshing problem that exists apparently regardless of the embodiment in this family. The problem is called the non-integer tooth problem and its …
Computationally Efficient Modeling Of Transient Radiation In A Purely Scattering Foam Layer, Rudolph Scott Larson
Computationally Efficient Modeling Of Transient Radiation In A Purely Scattering Foam Layer, Rudolph Scott Larson
Theses and Dissertations
An efficient solution method for evaluating radiative transport in a foam layer is a valuable tool for predicting the properties of the layer. Two different solution methods have been investigated. First, a reverse Monte Carlo (RMC) simulation has been developed. In the RMC simulation photon bundles are traced backwards from a detector to the source where they were emitted. The RMC method takes advantage of time reflection symmetry, allowing the photons to be traced backwards in the same manner they are tracked in a standard forward Monte Carlo scheme. Second, a reduced order model based on the singular value decomposition …
Large-Displacement Linear-Motion Compliant Mechanisms, Allen B. Mackay
Large-Displacement Linear-Motion Compliant Mechanisms, Allen B. Mackay
Theses and Dissertations
Linear-motion compliant mechanisms have generally been developed for small displacement applications. The objective of the thesis is to provide a basis for improved large-displacement linear-motion compliant mechanisms (LLCMs). One of the challenges in developing large-displacement compliant mechanisms is the apparent performance tradeoff between displacement and off-axis stiffness. In order to facilitate the evaluation, comparison, and optimization of the performance of LLCMs, this work formulates and presents a set of metrics that evaluates displacement and off-axis stiffness. The metrics are non-dimensionalized and consist of the relevant characteristics that describe mechanism displacement, off-axis stiffness, actuation force, and size. Displacement is normalized by …
Multi-Stable Compliant Rolling-Contact Elements, Peter Andrew Halverson
Multi-Stable Compliant Rolling-Contact Elements, Peter Andrew Halverson
Theses and Dissertations
The purpose of this research is the development of design concepts and models of large-angle, compliant, multistable, revolute joints. This research presents evidence of the capability of these models and concepts by presenting a case study in which the miniaturization of revolute joints are examined. Previous attempts at multistable revolute joints can be categorized into two categories: compliant and non-compliant mechanisms. Non-compliant multistable revolute joints are typified by a combination of pin-in-slot joints, springs, and detents. Due to factors inherit in design, noncompliant joints often succumb to friction, wear, and undesirable motion, that leads to a decline in performance. Compliant …
Vision-Based Landing Of Fixed-Wing Miniature Air Vehicles, Blake Barber, Timothy Mclain, Barrett Edwards
Vision-Based Landing Of Fixed-Wing Miniature Air Vehicles, Blake Barber, Timothy Mclain, Barrett Edwards
Faculty Publications
This paper outlines a method for using vision-based feedback to accurately land a MAV on a visually identifiable target of approximately known location. The method presented is robust to wind, capable of handling both stationary and moving targets, and capable of cor- recting for camera misalignment, state estimation biases, and parameter estimation biases. Landing results from actual flight tests are presented which demonstrate the effectiveness of the proposed method.
An Overview Of Mav Research At Brigham Young University, Timothy W. Mclain, Randal W. Beard, D. Blake Barber, Nathan B. Knoebel
An Overview Of Mav Research At Brigham Young University, Timothy W. Mclain, Randal W. Beard, D. Blake Barber, Nathan B. Knoebel
Faculty Publications
This paper summarizes research efforts at Brigham Young University related to the control of miniature aerial vehicles (MAVs). Recent results in the areas of vector field path following, precision landing and target prosecution, target localization, obstacle detection and avoidance, tailsitter aircraft control, and cooperative control are presented.