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Mechanical Engineering Commons™

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2007

Series

Faculty Publications

Articles 1 - 16 of 16

Full-Text Articles in Mechanical Engineering

). Size Dependency Of The Elastic Modulus Of Zno Nanowires: Surface Stress Effect, Guofeng Wang, Xiaodong Li Dec 2007

). Size Dependency Of The Elastic Modulus Of Zno Nanowires: Surface Stress Effect, Guofeng Wang, Xiaodong Li

Faculty Publications

Relation between the elastic modulus and the diameter (D) of ZnOnanowires was elucidated using a model with the calculated ZnOsurface stresses as input. We predict for ZnOnanowires due to surface stress effect: (1) when D>20nm, the elastic modulus would be lower than the bulk modulus and decrease with the decreasing diameter, (2) when 20nm>D>2nm, the nanowires with a longer length and a wurtzite crystal structure could be mechanically unstable, and (3) when D<2nm, the elastic modulus would be higher than that of the bulk value and increase with a decrease in nanowire diameter.

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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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Nanoindentation Of The A And C Domains In A Tetragonal Batio3 Single Crystal, Young-Bae Park, Matthew J. Dicken, Zhi-Hui Xu, Xiaodong Li Oct 2007

Nanoindentation Of The A And C Domains In A Tetragonal Batio3 Single Crystal, Young-Bae Park, Matthew J. Dicken, Zhi-Hui Xu, Xiaodong Li

Faculty Publications

Nanoindentation in conjunction with piezoresponse force microscopy was used to study domain switching and to measure the mechanical properties of individual ferroelectric domains in a tetragonal BaTiO3 single crystal. It was found that nanoindentation has induced local domain switching; the a and c domains of BaTiO3 have different elastic moduli but similar hardness.Nanoindentationmodulus mapping on the a and c domains further confirmed such difference in elasticity. Finite element modeling was used to simulate the von Mises stress and plastic strain profiles of the indentations on both a and c domains, which introduces a much higher stress level than …

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

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.

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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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Obstacle Avoidance Using Circular Paths, Timothy Mclain, Randal W. Beard, Jeffery Brian Saunders Aug 2007

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 …

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Vector Field Path Following For Miniature Air Vehicles, Timothy Mclain, Derek R. Nelson, D. Blake Barber, Randall W. Beard Jun 2007

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 …

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Vision-Based Landing Of Fixed-Wing Miniature Air Vehicles, Blake Barber, Timothy Mclain, Barrett Edwards May 2007

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.

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An Overview Of Mav Research At Brigham Young University, Timothy W. Mclain, Randal W. Beard, D. Blake Barber, Nathan B. Knoebel May 2007

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.

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Probabilistic Searching Using A Small Unmanned Aerial Vehicle, Steven R. Hansen, Timothy W. Mclain, Michael A. Goodrich May 2007

Probabilistic Searching Using A Small Unmanned Aerial Vehicle, Steven R. Hansen, Timothy W. Mclain, Michael A. Goodrich

Faculty Publications

Ground breaking concepts in optimal search theory were developed during World War II by the U.S. Navy. These concepts use an assumed detection model to calculate a detection probability rate and an optimal search allocation. Although this theory is useful in determining when and where search effort should be applied, it offers little guidance for the planning of search paths. This paper explains how search theory can be applied to path planning for an SUAV with a fixed CCD camera. Three search strategies are developed: greedy search, contour search, and composite search. In addition, the concepts of search efficiency and …

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Autonomous Landing Of Miniature Aerial Vehicles, D. Blake Barber, Stephen R. Griffiths, Timothy W. Mclain, Randal W. Beard May 2007

Autonomous Landing Of Miniature Aerial Vehicles, D. Blake Barber, Stephen R. Griffiths, Timothy W. Mclain, Randal W. Beard

Faculty Publications

This paper outlines an approach for automated landing of miniature aerial vehicles (MAVs). A landing algorithm defining the landing flight path as a function of height above ground, and the control strategies for following the path, are described. Two methods are presented for estimating height above ground, one based on barometric pressure measurements and the other utilizing optic-flow measurements. The development of an optic-flow sensor and associated sampling strategies are described. Utilizing estimates of height above ground from barometric pressure and optic-flow measurements, repeated landings were performed with a 1.5 m wingspan MAV. With height above ground estimated from barometric …

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In-Situ Optimized Pwas Phased Arrays For Lamb Wave Structural Health Monitoring, Lingyu Yu, Victor Giurgiutiu Jan 2007

In-Situ Optimized Pwas Phased Arrays For Lamb Wave Structural Health Monitoring, Lingyu Yu, Victor Giurgiutiu

Faculty Publications

No abstract provided.

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Iii Finishing, Lapping, Honing And Polishing: Processes, Characterisation And Novel Techniques-Experimental Research On Ultra-Smooth Surface Polishing Based On Two-Dimensional Vibration Of Liquid, Zhong Ning Guo, X. Z. Huang, Z. G. Huang, Z. Q. Yu, T. M. Yue, Wing Bun Lee Jan 2007

Iii Finishing, Lapping, Honing And Polishing: Processes, Characterisation And Novel Techniques-Experimental Research On Ultra-Smooth Surface Polishing Based On Two-Dimensional Vibration Of Liquid, Zhong Ning Guo, X. Z. Huang, Z. G. Huang, Z. Q. Yu, T. M. Yue, Wing Bun Lee

Faculty Publications

No abstract provided.

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Accelerated Testing Method For Pem Fuel Cell Based Uninterrupted Power Supply Systems, Xinyu Huang, Xiaofeng Wang Jan 2007

Accelerated Testing Method For Pem Fuel Cell Based Uninterrupted Power Supply Systems, Xinyu Huang, Xiaofeng Wang

Faculty Publications

Proton exchange membrane fuel cell based power systems are on the verge of commercialization for a number of niche applications where batteries are traditionally used. Uninterrupted power supply (UPS) for wireless communication towers and broadband network relay utilities is one of the targeted application of fuel cell power systems with capacity ranging from one to serveral kilowatts. It is believed that fuel cell based UPS systems can offer considerable advantage when extended backup time is desirable. In order to replace the well-known battery based UPS systems, the reliability and perofrmance of fuel cell based UPS system need to be thoroughly …

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Compliant High-Precision E-Quintet Ratcheting (Cheqr) Mechanism For Safety And Arming Devices, John A. Kennedy, Larry L. Howell, William Greenwood Jan 2007

Compliant High-Precision E-Quintet Ratcheting (Cheqr) Mechanism For Safety And Arming Devices, John A. Kennedy, Larry L. Howell, William Greenwood

Faculty Publications

Ratchet and pawl mechanisms are used in safety applications to provide mechanical isolation between inputs and an output to insure that extreme environmental conditions do not inadvertently allow an unexpected output. These devices have become smaller and are approaching a size regime where traditional precision components, such as precision bearings and springs, are not available. This paper introduces the Compliant High-precision E-Quintet Ratcheting (CHEQR) mechanism as a means of exploiting the advantages of compliant mechanisms to create safety devices that eliminate the need for bearings and springs. The pseudo-rigid-body model was used to design a mechanism with the desired force-deflection …

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Obstacle And Terrain Avoidance For Miniature Aerial Vehicles, Timothy Mclain, Jeff Saunders, Blake Barber, Randall W. Beard, Stephen R. Griffiths Jan 2007

Obstacle And Terrain Avoidance For Miniature Aerial Vehicles, Timothy Mclain, Jeff Saunders, Blake Barber, Randall W. Beard, Stephen R. Griffiths

Faculty Publications

Unmanned aerial vehicles (UAVs) are playing increasingly prominent roles in defense programs and strategy around the world. Technology advancements have enabled the development of large UAVs (e.g., Global Hawk, Predator) and the creation of smaller, increasingly capable UAVs. The focus of this Chapter is on smaller fixed-wing miniature aerial vehicles (MAVs), which range in size from % to 2 m in wingspan. As recent conflicts have demonstrated, there are numerous military applications for MAVs including reconnaissance, surveillance, battle damage assessment, and communications relays.

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