Now showing items 1-20 of 72

• #### Aerodynamic heating of the student rocket project-5 sounding rocket

This thesis deals with the calculation of the flow properties and heat transfer around the rocket nose cone for Student Rocket Project-5 (SRP-5). Governing differential equations are presented for this purpose, giving the fundamental relations between the skin temperature and flight history. The determination of all the required parameters in the equations is discussed, and the Runge-Kutta numerical method of integration is used to obtain the solution. A model to implement the above equations to predict skin temperature for the given trajectory was built in SIMULINK®. Individual sub-systems of the SIMULINK® model are used to calculate local tree-stream values, Reynolds number, heat absorption capacity and skin friction coefficient. The SIMULINK® model was used to predict the variation of the skin temperature for the SRP-5 flight trajectory. The simulation results also show comparisons of the different subsystem outputs with data provided by the contractor for the NASA Sounding Rocket Contract (NSROC).
• #### Analysis and control of time-periodic systems with time delay via chebyshev polynomials

A technique for studying the transient response and the stability properties of dynamic systems modeled by delay-differential equations (DDEs) with time-periodic parameters is presented in this thesis. The approach is based on an orthogonal polynomial expansion (shifted Chebyshev approximation). In each time interval with length equal to the delay period, the dynamic system can be reduced to a set of linear difference equations for the Chebyshev expansion coefficients of the state vector in the previous and current intervals. In this way, the transient response of the dynamic system can be directly obtained and the stability properties are found to be determined by a linear map which is the "infinite-dimensional Floquet transition matrix". The technique is then used to study the stability of an elastic system subjected to periodically-varying retarded follower forces, solve a finite horizon optimal control problem via quadratic cost function, and design a delayed feedback controller by using both numerical and symbolic approaches to control the chaotic behavior of a nonlinear delay differential equation.
• #### Analysis of a generic flip chip under shock and vibration

A flip chip package, underfilled or non-underfilled, was analyzed under mechanical shock and/or vibration at the device and board levels, respectively. For the tests at the device level, the maximum stress developed at the corner-most solder joint. The horizontal drop orientation, with the chip facing up, produced the worst scenario for solder joint lifetime prediction. The underfilled package is better than non-underfilled under the excitation of mechanical shock and vibration. Parametric studies of the underfill material strength suggested that the higher the elastic modulus, the better it carried the mechanical shock. However, practically the upper bound of the elastic modulus is limited to avoid die cracking due to thermal mismatch of material expansion. The combined loading of thermal residual stress and mechanical shock was also conducted to study their influence on the solder lifetime prediction. It was found that the thermal pre-stressed condition plays a key role for the von Mises stress excursion, but has almost no influence on the shock-induced normal stress. The phenomenon appears similarly in the board level testing, but with worse reliability in solders due to the higher stresses induced.
• #### Analysis of an oscillating plate coupled with fluid

The mechanical vibration of an oscillating cantilever plate is studied to determine the interaction of a plate coupled with air and with water. Experimental data was collected and analyzed using multiple methods including Fast Fourier Transform, wavelet analysis, and the Hilbert-Huang Transform (HHT) to characterize the behavior of the plate. The HHT is able to process nonlinear and nonstationary signals and provides more meaningful information compared to the traditionally used Fourier transform for similar applications. The HHT was found to be appropriate and more descriptive for the analysis of coupled fluid-structure systems. Digital Particle Image Velocimetry (DPIV) was also used to analyze the circulation and energy transferred to the fluid.
• #### Analysis of ground source heat pumps in sub-Arctic conditions

The Purpose of this project is to investigate the factors involved in the application of a ground source heat pump in subarctic conditions. This project originated with the construction of a ground source heat pump (GSHP) built at Cold Climate Housing Research Center's (CCHRC) Research Testing Facility. The GSHP built by CCHRC is an experiment to test the viability of a GSHP with different surface coverings. Specifically, this project will focus on different soil and atmospheric properties to gauge their effect on a GSHP in sub-arctic conditions. The project is primarily broken into 3 main sections which test in simulation: the effects of soil and atmospheric properties on heat flow into soil, the effects of these properties on a hypothetical GSHP and applying this to a simulation of CCHRC's GSHP. Additionally, some mitigation efforts were attem pted in simulation to improve the viability of the GSHP built by CCHRC.
• #### Analytical and numerical studies on macro and micro scale heat sinks for electronics applications

From the practice in computer industry the standard approach for electronics cooling is fan-cooled heat sinks. We developed thermal models for forced convection heat sinks. An Intel Pentium ill chip has been adopted as a preliminary design case to develop necessary equations. We found the heat dissipated from the aluminum heat sink, based upon different modes of airflow over the fins. We also considered radiation heat transfer. We performed transient heat transfer analysis to determine the time to attain the steady state temperature for the whole system for macro and micro scale also. Next, we refined our one-dimensional analytical convection analysis using the numerical analysis. This was done using the computational fluid dynamics code Fluent to obtain accurate velocity fields over the fins. Using these improved velocities, convective heat transfer coefficients were computed. Next, we have miniaturized the processor chip size to the micrometer scale and have designed a heat sink based upon the models we have developed. Calculations of mean free path and Knudsen number shows the continuum theory for air still holds for our designed micro-channels. Equations for natural convection heat sinks are also explored as a part of this study. In the microscale study, we did forced and natural convection analysis.
• #### Axisymmetric numerical heat transfer analysis of natural gas hydrates reservoir

Gas hydrates are crystalline substances, occurring in nature under high pressure and low temperature. Numerical studies were conducted on dissociation of gas hydrate to recover natural gas. The model is a cylindrical geometry with a wellbore at the center through which hot water is injected. Through this thermal stimulation technique frozen hydrate reservoir is melted and natural gas is released. The computational fluid dynamics software FLUENT was adopted to generate the model. The initial model was solely comprised of a hydrate layer. This model was refined by adding the overburden and the underburden to the hydrate and exploring the thermal regime of the entire composite medium. Unsteady state results showing the dissociation front propagation with respect to time were calculated. In the first part, the hydrate medium is dissociated by the conduction phenomenon only. In the second part, due to the porous nature of the hydrate medium, both conduction and convection phenomena are considered. This thesis presents the following results obtained from simulations using Fluent. They are: temperature rise within the reservoir with time, temperature profiles in the radial direction, and steady and transient state solutions of the dissociation of gas hydrate with the liquid fraction in the reservoir. Comparison of our results with a finite difference model and a finite element model is also included. Volumes of gas released with respect to time and thermal efficiency ratios are also determined.
• #### Building a toolset for fuel cell turbine hybrid modeling

Fuel cell/gas turbine hybrids show promise of high efficiency power generation, with electrical efficiencies of 70% or better shown by modeling, although these efficiency levels have not yet been demonstrated in hardware. Modeling of such systems is important to optimize and control these complex systems. This work describes a modeling tool developed to examine steady-state operation of different hybrid configurations. This model focuses on the area of compressor-turbine modeling, which is a key component of properly controlling fuel cell/gas turbine hybrids. Through side-by-side comparisons, this model has been tested and verified by Dr. Wolf of Brayton Energy [1]. This modeling tool will be used in further work to evaluate various configurations of turbines and fuel cells in hybrid configurations, focusing on both the performance and cost of such systems.
• #### Buoyancy Effects On Building Pressurization In Extreme Cold Climates

This research investigates building pressurization due to buoyancy effect. The American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) presents an idealized equation to calculate the buoyancy effect. This dissertation compares differential pressure measurements from an actual building exposed to extremely cold temperatures to this idealized model. It also presents new statistical models based on the collected data. These new models should provide engineers with improved tools to properly account for building pressurization for designs in extreme cold climates. Building pressurization, the differential pressure between the interior of a building and its exterior surroundings, is an important design consideration. Pressurization is the driving force in building infiltration/exfiltration. It also affects air flow within building zones. Improper calculation of pressurization can result in under-sizing the building's heating and cooling systems, improper operation of air distribution systems, improper operation of elevators, and freezing and failure of water distribution and circulation systems. Building pressurization is affected by: wind (speed and direction), exterior-to-interior temperature difference, and mechanical equipment operation. In extreme cold climates, the predominant effect is air buoyancy due to temperature differences across the building envelope. The larger the temperature difference, the larger the buoyancy effect. In extreme cold climates, the largest temperature differences often occur at times when wind speed is negligible. This dissertation also demonstrates the use of existing data sources such as building automation systems to collect data for basic research. Modern systems automation provides a tremendous amount of data that, in the past, had to be collected through separate instrumentation and data acquisition systems. Taking advantage of existing automation systems can provide the required data at greatly reduced costs when compared to previous industry practices. The statistical analysis approach taken in this research expands the tools for engineering design. Actual interactions of real world variables are analyzed and used to produce prediction models. These techniques allow the model to incorporate relationships which may not be fully understood at the underlying principle level but are evidenced in the data collected from actual installations.* *This dissertation includes a CD that is compound (contains both a paper copy and CD as part of the dissertation). The CD requires the following applications: Internet Browser; Adobe Acrobat; Microsoft Office; Image Viewer.
• #### A case/control analysis and comparison of indoor air quality in Alaskan homes

Indoor Air Quality (IAQ) parameters such as CO, CO₂, relative humidity, temperature, radon, particulate matter, formaldehyde, benzene, toluene, hexane, Total Volatile Organic Compounds (TVOC) and microbial matter were monitored before and after remediation in 36 low-income homes in Alaska (Hooper Bay and Fairbanks). The objective was to see if there was any improvement in IAQ with remediation. Hooper Bay homes had significantly higher levels of CO₂ and relative humidity compared to Fairbanks homes both before and after remediation. There was a general reduction in CO₂ with remediation, although it was not statistically significant. When IAQ in two moderate-income homes in Fairbanks was compared with that in the remediated low-income homes, it was observed that indoor CO₂ levels were affected by ventilation rates and per capita floor area. A single zone model to predict concentration of indoor pollutants was constructed, using steady state and transient mass conservation, to predict, metabolically produced CO₂, and particulate matter when no indoor sources were present. The cost of energy to reduce indoor CO₂ levels in one of the homes by increasing ventilation by either using an exhaust-only system or a Heat Recovery Ventilator (HRV) is discussed.
• #### Cofiring coal and biomass at Aurora Power Plant in Fairbanks, Alaska

Biomass energy has been a topic of great interest over the previous few years in Alaska; especially when various fuel sources were priced at a record high. Interior Alaska has the potential to utilize woody biomass to offset the use of coal in many of its power generating facilities. In this study, woody biomass in the form of clean aspen (Populus tremuloides) chips was cofired with Usibelli coal at the Aurora Power Plant facility in downtown Fairbanks, Alaska. Biomass was successfully cofired at low average rates of 2.4% and 4.81% of total energy value. Combustion gasses were analyzed using measuring probes in the exhaust stack. The 2.4% biomass test saw, on average, an increase in CO and CO₂ by 95ppm and 2%, respectively. A decrease in NOx of 1ppm was observed. During the 4.81% biomass test, CO increased by 83ppm, NOx decreased by 18ppm, and CO decreased by 1%. Opacity increased by 0.1% during the 2.4% biomass test and 0.17% during the 4.81% biomass test. The challenges facing a small scale facility in Interior Alaska are also presented. The testing exemplified that the use of biomass in stoker/grate boilers in Alaska is technically feasible with relative ease. No technical barriers to cofiring at low levels on an on-going basis were found at the Aurora Power Plant and this conclusion would likely hold true at similar facilities in interior Alaska.

• #### Corrosion behavior and residual stress of microarc oxidation coated AZ31 magnesium alloy for biomedical applications

Mg alloys are potentially new biomaterials for bone repair or replacement. Appropriate coating is, however, needed to make the Mg alloy more resistant to corrosion. In this research, protective microarc oxidation (MAO) coatings were produced on AZ31 Mg alloys in sodium phosphate electrolyte. The coatings were produced under varying pulse frequency, applied voltage, oxidation time and electrolyte concentrations. This research analyzed the effects of the above four MAO process control parameters on the residual stresses and the corrosion behavior. Optimization of the MAO control parameters would allow production of AZ31 Mg alloy with high corrosion resistance. It is well accepted that residual stress and corrosion behavior are two significant factors in the development of AZ31 Mg alloys. The residual stresses in the MAO coatings were evaluated by the X-ray diffraction (XRD)-sin²ψ method. A predictive model of the residual stresses is proposed and a principal components analysis (PCA) was conducted to determine the contribution of the MAO control parameter on the residual stresses. Long-term corrosion behavior of MAO-coated Mg alloys was evaluated by the potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests. The porosity of the samples after various immersion durations was evaluated by the potentiodynamic polarization method. The pre- and post- corrosion microstructures and the phase composition of MAO-coated samples were studied. Post-corrosion phase identification showed that hydroxyapatite (HA) was formed on the surface of the samples. The ratio of Ca/P in HA was determined by the X-Ray Fluorescence (XRF) technique. The degradation of the MAO-coated AZ31 alloys is reduced due to the MAO coating and the formation of a corrosion product layer. A predictive model of the corrosion current density is proposed and a PCA was conducted to determine the contributions of the individual MAO control parameter on the corrosion rate. The corrosion process and mechanism of MAO-coated AZ31 alloys in SBF were modeled based on the electrochemical corrosion results and the pre- and post-corrosion surface analysis. It is believed that under optimized control parameters, the MAO-coated AZ31 Mg alloy is superior implant material for biomedical applications.
• #### Corrosion behavior of microarc oxidation and polycaprolactone coatings applied to AZ31 magnesium alloy evaluated in simulated body fluid and balanced salt solution

Recent research in orthopedic implant materials has focused on the use of magnesium alloys as a base material due to its mechanical properties similar to that of human bone. Rapid corrosion of magnesium materials in aqueous environments poses a significant hurdle to their application as a biomedical implant. A variety of coatings have been shown to improve the corrosion resistance of magnesium based materials in simulated body fluid environments including microarc oxidation and polymer coatings. However, formulation and corrosion rates vary significantly between solution types. Furthermore, in vivo results have shown that many common in vitro solutions over estimate corrosion rates. In addition to variations between solutions needing to be resolved, there has been little work performed to characterize large sample corrosion under stress. This is an essential step in evaluating concept performance at a macro scale, for application as a human implant. The experiments performed and presented in this thesis primarily involve the comparison of conventional simulated body fluid (c-SBF) and Earle's balanced salt solution (EBSS). Samples evaluated in these environments are microarc oxidation (MAO) coated AZ31 magnesium alloy and polycaprolactone dip-coated AZ31. MAO coated samples were created for a range of process settings to observe the effect of processing on corrosion performance. A dependence of MAO coating thickness on process voltage was found which augmented the initial corrosion resistance values observed via electrochemical testing. Both MAO and PCL coatings were found to improve the corrosion resistance of the samples as compared to uncoated AZ31. It was found that all variations (MAO, PCL, and uncoated) showed a reduced corrosion rate in EBSS as compared to c-SBF. This corrosion reduction was apparent through potentiodynamic scanning, electrochemical impedance spectroscopy, and visual inspection. Preliminary mechanical corrosion results, in the form of constant extension testing, showed no dependence of corrosion on stress level. Future work may be aimed towards expanding modes of mechanical testing and further refining simulated body fluids to fit with in vivo test results.
• #### Corrosion behavior of titanium dioxide (TiO₂)-coated Al alloy in saline environment

Al alloys have been used in many applications, however, they are susceptible to corrosion when exposed in saline environment. In this work, TiO₂ nanoellipsoids with aspect ratios (AR) of 1, 2, 4 and 6 were synthesized, TiO₂ coatings of AR 1, AR2, AR4, and AR6 were fabricated on AA2024-T3 Al alloy substrate, and their corrosion behaviors in the saline environment were investigated by analyzing the scanning electron microscope (SEM) imaging, potentiodynamic polarization scans and electrochemical impedance spectroscopy. TiO₂-coated Al samples showed better corrosion performance compared to the bare Al sample. Among the coated samples, TiO₂ AR6 coated samples showed lower corrosion rate compared to other samples. Although TiO₂ nanoellipsoids coatings show good corrosion resistance, it is noted that TiO₂ coatings are porous, which allows the penetration of corrosive media through the pores to reach the surface of the substrate. A polystyrene (PS)-TiO₂ AR6 nanocomposite coating was fabricated, where the pores of the coatings were sealed by polystyrene, which is expected to further improve the corrosion resistance of TiO₂ coatings.