Mechanical Engineering Commons^™

Analytical And Experimental Vibration Analysis Of Variable Update Rate Waveform Generation, Joshua F. Mark

Browse all Theses and Dissertations

Typical vibration analysis of turbine engine components incorporates the use of a function generator to produce a signal that is routed to an excitation source as the forcing function of the test specimen. These waveforms are constructed by varying the amplitude of the signal over time with a fixed update rate (time increment between samples). This research investigates generating chirp waveforms by storing only one sinusoid of points and using an external timing signal to repetitively send out these stored data points. This results in varying the amplitude of the signal over time as well as the update rate. The …

Stability Of A Strongly Anisotropic Thin Epitaxial Film In A Wetting Interaction With Elastic Substrate, Mikhail Khenner, Wondimu T. Tekalign, Margo S. Levine

Mathematics Faculty Publications

The linear dispersion relation for longwave surface perturbations, as derived by Levine et al. Phys. Rev. B 75, 205312 (2007) is extended to include a smooth surface energy anisotropy function with a variable anisotropy strength (from weak to strong, such that sharp corners and slightly curved facets occur on the corresponding Wulff shape). Through detailed parametric studies it is shown that a combination of a wetting interaction and strong anisotropy, and even a wetting interaction alone results in complicated linear stability characteristics of strained and unstrained films.

Stability Of A Strongly Anisotropic Thin Epitaxial Film In A Wetting Interaction With Elastic Substrate, Mikhail Khenner, Wondimu Tekalign, Margo Levine

Mathematics Faculty Publications

The linear dispersion relation for longwave surface perturbations, as derived by Levine et al. Phys. Rev. B 75, 205312 (2007) is extended to include a smooth surface energy anisotropy function with a variable anisotropy strength (from weak to strong, such that sharp corners and slightly curved facets occur on the corresponding Wulff shape). Through detailed parametric studies it is shown that a combination of a wetting interaction and strong anisotropy, and even a wetting interaction alone results in complicated linear stability characteristics of strained and unstrained films.

An Integrated Platform To Increase The Range/Endurance Of Unmanned Helicopters, Roy Godzdanker

Electronic Theses and Dissertations

Class I (kg) autonomous helicopters are becoming increasingly popular for a wide range of non-military applications such as, surveillance, reconnaissance, traffic monitoring, emergency response, agricultural spraying, and many other "eye in the sky" missions. However, an efficient landing/takeoff platform with refueling/recharging capabilities has not yet been developed to increase the endurance and decrease the cost for Class I helicopters.

This dissertation presents a three-prong approach for increasing the range and endurance of Class I autonomous helicopters, which will then spur demand by non-military organizations wanting to take advantage of such capabilities and, therefore, drop their price. The proposed Intelligent Self-Leveling …

Test 2012a: New Holland Workmaster 55, Nebraska Tractor Test Lab

Nebraska Tractor Tests

ABOUT THE TEST REPORT AND USE OF THE DATA The test data contained in this report are a tabulation of the results of a series of tests. Due to the restricted format of these pages, only a limited amount of data and not all of the tractor specifications are included. The full OECD report contains usually about 30 pages of data and specifications. The test data were obtained for each tractor under similar conditions and therefore, provide a means of comparison of performance based on a limited set of reported data. EXPLANATION OF THE TEST PROCEDURES Purpose The purpose of …

Probabilistic Stress Analysis Of Circular Fins Of Different Profiles, Sridhar Madhira Venkata

ETD Archive

The temperature distribution and thermal Stresses induced by a temperature difference for steady state heat transfer in silicon carbide (SiC) ceramic tube heat exchanger with circular fins was computationally simulated by a finite element method and probabilistically evaluated in view of the several uncertainties in the performance parameters. Cumulative distribution functions and sensitivity factors were computed for Hoop and Radial stresses due to the structural and thermodynamic random variables. These results are used to identify the most critical design variables in order to optimize the design and make it cost effective. The probabilistic analysis leads to the selection of the …

Computational Models Of Chemical Systems Inspired By Braess’ Paradox, Dante Lepore, Carl Barratt, Pauline Schwartz

Chemistry and Chemical Engineering Faculty Publications

Systems chemistry is a new discipline which investigates the interactions within a network of chemical reactions. We have studied several computational models of chemical systems inspired by mathematical paradoxes and have found that even simple systems may behave in a counterintuitive, non-linear manner depending upon various conditions. In the present study, we modeled a set of reactions inspired by one such paradox, Braess’ paradox, an interesting phenomenon whereby the introduction of additional capacity (e.g. pathways) in some simple network systems can lead to an unexpected reduction in the overall flow rate of “traffic” through the system. We devised several chemical …

Nitric Oxide-Generating Silicone As A Blood-Contacting Biomaterial, Kagya Amoako

Mechanical and Industrial Engineering Faculty Publications

Coagulation upon blood-contacting biomaterials remains a problem for short and long-term clinical applications. This study examined the ability of copper(II)-doped silicone surfaces to generate nitric oxide (NO) and locally inhibit coagulation. Silicone was doped with 3-micron copper (Cu(0)) particles yielding 3 to 10 weight percent (wt%) Cu in 70-μm thick Cu/Silicone polymeric matrix composites (Cu/Si PMCs). At 3, 5, 8 and 10 wt% Cu doping, the surface expression of Cu was 12.1 ± 2.8%, 19.7 ± 5.4%, 29.0 ± 3.8%, and 33.8 ± 6.5% respectively. After oxidizing Cu(0) to Cu(II) by spontaneous corrosion, NO flux, JNO (mol*cm−2*min−1), as measured by …

Development Of A Friction Testing Apparatus For Demoulding Force Prediction, Kevin Delaney, David Kennedy, G. Bissacco

Conference Papers

Friction between replication tools and replicated parts determines the force required to demould the part and also the stresses which develop in both the tool and the part during the demoulding process. Standardized equipment and procedures have been developed which strive to improve the repeatability and reproducibility of friction tests. Specific test standards, describing sled-type tests, include JIS K 7125, ISO 8295 and ASTM D1894. However these tests do not produce results which are representative of the conditions typically found within replication tools such as injection moulds or embossing tools. This paper reviews how this challenge has been addressed by …

Toward Increasing Performance And Efficiency In Gas Turbines For Power Generation And Aero-Propulsion Unsteady Simulation Of Angled Discrete-Injection Coolant In A Hot Gas Path Crossflow, Perry L. Johnson

HIM 1990-2015

This thesis describes the numerical predictions of turbine film cooling interactions using Large Eddy Simulations. In most engineering industrial applications, the Reynolds-Averaged Navier-Stokes equations, usually paired with two-equation models such as k-Greek lowercase letter epsilon] or k-Greek lowercase letter omega], are utilized as an inexpensive method for modeling complex turbulent flows. By resolving the larger, more influential scale of turbulent eddies, the Large Eddy Simulation has been shown to yield a significant increase in accuracy over traditional two-equation RANS models for many engineering flows. In addition, Large Eddy Simulations provide insight into the unsteady characteristics and coherent vortex structures of …

High Frequency Thermally Actuated Single Crystalline Silicon Micromechanical Resonators With Piezoresistive Readout, Amir Rahafrooz

Electronic Theses and Dissertations

Over the past decades there has been a great deal of research on developing high frequency micromechanical resonators. As the two most common and conventional MEMS resonators, piezoelectric and electrostatic resonators have been at the center of attention despite having some drawbacks. Piezoelectric resonators provide low impedances that make them compatible with other low impedance electronic components, however they have low quality factors and complicated fabrication processes. In case of electrostatic resonators, they have higher quality factors but the need for smaller transductions gaps complicates their fabrication process and causes squeezed film damping in Air. In addition, the operation of …

Nebraska Summary: S806 New Holland T7.250, Nebraska Tractor Test Lab

Nebraska Tractor Tests

ABOUT THE TEST REPORT AND USE OF THE DATA The test data contained in this report are a tabulation of the results of a series of tests. Due to the restricted format of these pages, only a limited amount of data and not all of the tractor specifications are included. The full OECD report contains usually about 30 pages of data and specifications. The test data were obtained for each tractor under similar conditions and therefore, provide a means of comparison of performance based on a limited set of reported data. EXPLANATION OF THE TEST PROCEDURES Purpose The purpose of …

Development Of Optimal Bubble-Seeding Microheaters To Study Nucleate Boiling Heat Transfer In Microgravity, Ryan Martineau

Reports and Proposals

No abstract provided.

Heat Transfer And Friction Augmentation In A Narrow Rectangular Duct With Symmetrical And Non-Symmetrical Wedge-Shaped Turbulators, Michelle Valentino

Electronic Theses and Dissertations

The need for cleaner and more fuel efficient means to produce electricity is growing steadily. Advancements in cooling technologies contribute to the improvements in turbine efficiency and are used for gas turbines and for power generation in automotive, aviation, as well as in naval applications, and many more. Studies introducing turbulators on walls of internal cooling channels, which can be applied to hot gas components and in recuperative heat exchangers, have been reviewed for their ability to promote heat transfer in the channel while observing pressure loss caused by adding the features. Several types of turbulators have been studied; ribs, …

Model Identification, Updating, And Validation Of An Active Magnetic Bearing High-Speed Machining Spindle For Precision Machining Operation, Adam C. Wroblewski

ETD Archive

High-Speed Machining (HSM) spindles equipped with Active Magnetic Bearings (AMBs) are envisioned to be capable of autonomous self-identification and performance self-optimization for stable high-speed and high quality machining operation. High-speed machining requires carefully selected parameters for reliable and optimal machining performance. For this reason, the accuracy of the spindle model in terms of physical and dynamic properties is essential to substantiate confidence in its predictive aptitude for subsequent analyses.This dissertation addresses system identification, open-loop model development and updating, and closed-loop model validation. System identification was performed in situ utilizing the existing AMB hardware. A simplified, nominal open-loop rotor model was …

A Cfd Model Of Mixing In A Microfludic Device For Space Medicine Technology, Terri Lynn Mckay

ETD Archive

The DNA Medicine Institute (DMI) is currently developing a device to be used for blood analysis to satisfy the unique requirements of space medicine applications. A key component of that device is the micromixer, which will ensure mixing and dilution of reagents utilized for detection assays. As part of the device design process, the micromixer was modeled, and the mixing characteristics were analyzed and compared to experimental data. The experimental data was based on a top-view of the system and, lacking data throughout the fluid domain, could not provide the insight into the mixing process that modeling could readily provide. …

Cfd Simulations For The Effect Of Unsteady Wakes On The Boundary Layer Of A Highly Loaded Low Pressure Turbine Airfoil (L1a), Samuel J. Vinci

ETD Archive

The study of a very high lift, low-pressure turbine airfoil in the presence of unsteady wakes was performed computationally and compared against experimental results. The experimental data were collected in a low speed wind tunnel under high (4.9 ) and then low (0.6 ) freestream turbulence intensity conditions on a linear cascade with wakes that were produced from moving rods upstream of the cascade. The flow coefficient was kept at 0.7 while the rod to blade spacing was changed from 1 to 1.6 to 2 blade spacings. These cases were conducted for Reynolds number equal to 25,000 and 50,000, based …

Evaluation Of Lean Systems In Rail Maintenance Operations, Mert Baykut

ETD Archive

The recognized strength of lean systems is its broad applicability to every process industry even though they include some complicated and time-intensive processes. However, this conception is based on the tools and philosophy of Lean systems and the nature of the industry. The required craftsmanship and repetitive processes in rail maintenance define the uniqueness of this research The objective of this thesis was to research the opportunities and applicability for lean systems in rail maintenance. During the research a unique system, consisting of Lean systems and systems engineering tools, is realized and tried to integrate instead of a pure Lean …

A Systems Engineering Reference Model For Fuel Cell Power Systems Development, T. L. Blanchard

ETD Archive

This research was done because today the Fuel Cell (FC) Industry is still in its infancy in spite over one-hundred years of development has transpired. Although hundreds of fuel cell developers, globally have been spawned, in the last ten to twenty years, only a very few are left struggling with their New Product Development (NPD). The entrepreneurs of this type of disruptive technology, as a whole, do not have a systems engineering 'roadmap", or template, which could guide FC technology based power system development efforts to address a more environmentally friendly power generation. Hence their probability of achieving successful commercialization …

Fea Analysis Of Novel Design Of Cylindrical Roller Bearing, Prasanna Subbarao Bhamidipati

ETD Archive

This work presents a finite element stress analysis of a novel design of cylindrical roller. The focus of this study is to create a uniform contact-stress distribution along the length of the roller and to recommend a roller bearing design which is easier to fabricate. The new design relies on creating symmetric cylindrical cavities at both ends of a roller. The cavity is concentric with the main body of the roller. The new roller design reduces overall mass of the typical assembly with helps to improve bearing life and its overall performance. The FEA results published herein shows that new …