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Articles 121 - 130 of 130

Full-Text Articles in Mechanical Engineering

Structuring Emperical Methods For Reuse And Efficiency In Product Development Processes, Marshall Edwin Bare Dec 2006

Structuring Emperical Methods For Reuse And Efficiency In Product Development Processes, Marshall Edwin Bare

Theses and Dissertations

Product development requires that engineers have the ability to predict product performance. When product performance involves complex physics and natural phenomena, mathematical models are often insufficient to provide accurate predictions. Engineering companies compensate for this deficiency by testing prototypes to obtain empirical data that can be used in place of predictive models. The purpose of this work is to provide techniques and methods for efficient use of empirical methods in product development processes. Empirical methods involve the design and creation of prototype hardware and the testing of that hardware in controlled environments. Empirical methods represent a complete product development sub-cycle …

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Constitutive Modeling Of The Thermo-Mechanics Associated With Crystallizable Shape Memory Polymers, Gautam Barot Aug 2006

Constitutive Modeling Of The Thermo-Mechanics Associated With Crystallizable Shape Memory Polymers, Gautam Barot

Dissertations

This research addresses issues central to material modeling and process simulations. Here, issues related for developing constitutive model for crystallizable shape memory polymers are addressed in details. Shape memory polymers are novel material that can be easily formed into complex shapes, retaining memory of their original shape even after undergoing large deformations. The temporary shape is stable and return to the original shape is triggered by a suitable mechanism such heating the polymer above a transition temperature. Crystallizable shape memory polymers are called crystallizable because the temporary shape is fixed by a crystalline phase, while return to the original shape …

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Preliminary Modeling, Control, And Trajectory Design For Miniature Autonomous Tailsitters, Nathan B. Knoebel, Stephen R. Osborne, Deryl Snyder, Timothy W. Mclain, Randal W. Beard, Andrew Mark Eldredge Aug 2006

Preliminary Modeling, Control, And Trajectory Design For Miniature Autonomous Tailsitters, Nathan B. Knoebel, Stephen R. Osborne, Deryl Snyder, Timothy W. Mclain, Randal W. Beard, Andrew Mark Eldredge

Faculty Publications

A tailsitter UAV has unique advantages over typical fixed wing aircraft or hovercraft. This paper highlights topics of interest in our preliminary research in developing a tailsitter UAV. An aerodynamic model and quaternion-based attitude and position control scheme is presented for controlling a tailsitter through hover maneuvers, with simulation results. Desired trajectories are also developed through feedback linearization of the dynamic equations, intended for quaternion-based attitude control. Finally, a hardware platform is proposed.

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Performance Modeling Of Explosively Actuated Devices, Adam M. Braud Jan 2006

Performance Modeling Of Explosively Actuated Devices, Adam M. Braud

LSU Master's Theses

Explosively actuated devices (pin pullers, cable cutters, valves, etc) are used extensively to perform critical functions for aerospace, industrial, and defense related applications. The failure of these devices have led to a greater effort to quantify device design and performance. This thesis describes the actuation process of an explosively actuated valve, including: 1) the burning of the solid explosive HMX (C4H8N8O8) and production of its high pressure gas products, 2) the mass transfer of gas products through an actuator to an expansion volume including choked flow effects, 3) the resulting piston motion …

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Techniques In The Design Of Thermomechanical Microactuators, Larry L. Howell, Timothy W. Mclain, Michael S. Baker, Christian D. Lott Jan 2006

Techniques In The Design Of Thermomechanical Microactuators, Larry L. Howell, Timothy W. Mclain, Michael S. Baker, Christian D. Lott

Faculty Publications

The purpose of this chapter is to provide fundamental background for the design of thermomechanical microactuators. Actuation has been a particularly challenging aspect of microsystem development. Many actuation approaches used at the macro level, such as hydraulics, pneumatics, electric motors, internal combustion engines and turbines, are either too difficult to fabricate at the micro level or do not work well at that scale. Electrostatic attraction is one approach that has been widely used for actuation of microsystems; however, electrostatic actuators tend to have high voltage requirements and low output force capabilities. While electrostatic actuation is suitable for many applications, some …

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Electrothermomechanical Modeling Of A Surface-Micromachined Linear Displacement Microactuator, Christian D. Lott Mar 2005

Electrothermomechanical Modeling Of A Surface-Micromachined Linear Displacement Microactuator, Christian D. Lott

Theses and Dissertations

The electrothermomechanical characteristics of an electrically-heated polycrystallinesilicon microactuator are explored. Using finite-difference techniques, an electrothermal model based on the balance of heat dissipation and heat losses is developed. For accurate simulation, the relevant temperature dependent properties from the microactuator material are included in the model. The electrothermal model accurately predicts the steady-state power required to hold position, and the energy consumed during the thermal transient. Thermomechanical models use the predictions of temperature from the electrothermal solution to calculate displacement and force from pseudo-rigid-body approximations and commercial finite-element code. The models are verified by comparing experimental data to simulation results of …

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Percolation Paths Of Three-Dimensions In Sensitized Stainless Steel, Alisa J. Millar Henrie Aug 2004

Percolation Paths Of Three-Dimensions In Sensitized Stainless Steel, Alisa J. Millar Henrie

Faculty Publications

The study of three-dimensional percolation paths through materials is important in its contribution to understanding defect sensitive properties of materials. This work shows the importance of grain boundary character in modeling defect sensitive boundaries. Also presented are trends of percolation of sensitized grain boundaries in 304 stainless steel (304SS). Of particular interest is how open paths form in a three-dimensional model created through serial sectioning. Evidence is presented that triple or quadruple points that contain typically two boundaries with special character that intersect the percolation path break up the path. Some boundaries with no known special qualities; they are not …

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Numerical Modeling Of Friction Stir Welding: A Comparison Of Alegra And Forge3, Alma H. Oliphant Apr 2004

Numerical Modeling Of Friction Stir Welding: A Comparison Of Alegra And Forge3, Alma H. Oliphant

Theses and Dissertations

The objective of this research was to evaluate the capabilities of ALEGRA, a Sandia National Labs hydrocode, and Forge3, a Transvalor S.A. product, to accurately model the Friction Stir Welding Process. ALEGRA and Forge3 are discussed in light of the inherent challenges of modeling Friction Stir Welding, and a rotational boundary condition is added to ALEGRA. Results are presented from Friction Stir Welding modeling outputs from both ALEGRA and Forge3. ALEGRA is shown to be incapable of modeling the Friction Stir Welding process, in large part due to its focus on shock propagation, which causes extremely small time steps. Forge3 …

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Dynamic Modeling Of Compliant Constant-Force Compression Mechanisms, Cameron Boyle, Larry L. Howell, Spencer P. Magleby, Mark S. Evans Dec 2003

Dynamic Modeling Of Compliant Constant-Force Compression Mechanisms, Cameron Boyle, Larry L. Howell, Spencer P. Magleby, Mark S. Evans

Faculty Publications

A mathematical dynamic model is derived for compliant, constant-force compression-mechanisms, based on the pseudo-rigid-body model simplification of the device. The compliant constant-force compression mechanism (CFCM) is a slider mechanism incorporating large-deflection beams, which outputs near-constant-force across the range of its designed deflection. The equation of motion is successfully calibrated with empirical data from five separate mechanisms, comprising two basic configurations of CFCMs. The dynamic equation is derived from a generalized pseudo-rigid-body model. This allows every configuration to be represented by the same model, so a separate treatment is not required for each configuration. An unexpected dynamic trait of the constant-force …

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Task Specific Uncertainty In Coordinate Measurement, R. G. Wilhelm, R. Hocken, H. Schwenke Jan 2001

Task Specific Uncertainty In Coordinate Measurement, R. G. Wilhelm, R. Hocken, H. Schwenke

Department of Mechanical and Materials Engineering: Faculty Publications

Task specific uncertainty is the measurement uncertainty associated with the measurement of a specific feature using a specific measurement plan. This paper surveys techniques developed to model and estimate task specific uncertainty for coordinate measuring systems, primarily coordinate measuring machines using contacting probes. Sources of uncertainty are also reviewed.

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