Now showing items 1-20 of 72

• #### Pitorifices and small pumps in cold region water distribution systems

Most buried potable water distribution systems in colder regions of Alaska rely on pitorifices to provide circulation between the water main and service connections for freeze protection. Pitorifices are scoops which project into the main. When water is circulated in the main, they create a differential head which induces flow through dual service lines. Pitorifices have provided an inexpensive and simple alternative to installing a small pump at each service to provide circulation. However, very little information was available on the hydraulic performance of these devices. The objectives of this study were to: (i) develop techniques to measure pitorifice performance in the field; (ii) characterize performance of commonly used pitorifice shapes with different insertion depths and relative sizes in full-scale testing; (iii) develop an improved shape; (iv) research the competing technology of small pumps; and (v) present the information in a way that is useful to engineers. An inexpensive device for field checks of both differential head and flow rates at service lines was developed and the use of a low head loss meter was initiated. Methods and results of field studies in four different water systems are presented. Five commonly used pitorifice shapes and four new shapes were evaluated. The best shape was found to be one of the existing shapes, which is also one of the easiest to produce but not the most popular. It was also determined using a larger service line size can be cost effective. Test results are graphed and a theoretical framework is provided for designers. Smaller, energy efficient pumps may provide a cost effective alternative to pitorifices in some situations. Requirements for small pumps used for circulation in place of or to supplement pitorifices are given. Performance test results for different pumps are presented, most of which have not been used previously for service line circulation. Pumps with significantly lower operating costs than those in current use are identified. Several of these pumps were installed in services for long term testing.
• #### Two-dimensional analysis of natural convection and radiation in utilidors

Central heating plants are often used on large building complexes such as university campuses or military bases. Utilidors can be used to contain heat distribution lines and other utilities between a utility station and serviced buildings. Traditional thermal analysis of utilidors is one-dimensional, with heat transfer correlations used to estimate the effects of convection, radiation, and two-dimensional geometric effects. The expanding capabilities of computers and numerical methods suggest that more detailed analysis and possibly more energy-efficient designs could be obtained. This work examines current methods of estimating the convection and radiation that occur across an air space in square and rectangular enclosures and compares them with numerical and experimental data. A numerical model was developed that solves the energy, momentum, and continuity equations for the primitive variables in two dimensions; radiation between free surfaces was also included. Physical experiments were conducted with two 10-ft-long apparatuses; one had a 1-ft $\times$ 1-ft cross section, the other was 2 ft $\times$ 4 ft. Several pipe sizes and configurations were studied with the 1-ft $\times$ 1-ft apparatus. The 2-ft $\times$ 4-ft apparatus was limited to containing 4- and 8-inch insulated pipes. Corresponding numerical studies were conducted. Difficulties in modeling large enclosures or those with large temperature differences (Rayleigh numbers above 10$\sp7$) were encountered. Results showed good agreement between numerical and experimental average heat transfer rates, and for insulated pipe cases these results also compared well with rates obtained from one-dimensional analysis. A new effective conductivity correlation for air in a square enclosure was developed, and its use was demonstrated in numerical conduction solutions and compared with full numerical convection and radiation solutions and with experimental data. Reasonably good results were achieved when there was a small temperature difference across the air gap.
• #### Performance Prediction Of A Folding Fin Aircraft Rocket Using Datcom, Sens5D, And 6Dof Gem

An approach for the performance prediction of a Folding Fin Aircraft Rocket (FFAR) is presented. This prediction was compiled by calculating the gravimetrics, aerodynamics, and trajectory for a FFAR. The trajectory analysis utilized four computer codes: Rogers Aeroscience Rocket Performance Software, NASA Wallops Sens5d Trajectory and Wind-Sensitivity Calculations for Unguided Rockets, the United States Air Force (USAF) Stability and Control DATCOM, and the NASA Langley Research Center LRC-MASS program (GEM). Computations were performed for a rigid body configuration. This analysis was compared to radar data collected during the flight of a FFAR launched in February 1997 at the Poker-Flat Research Range. The comparison shows good agreement between the flight data and the predicted apogee and impact point of the vehicle. In addition, static and dynamic stability analyses were completed for the FFAR. <p>
• #### Finite element analysis of yield functions of Kelvin foams with open cells

Proper design of foams requires an understanding of the response of the materials to stress. This thesis, based on finite element analysis, provides numerical solutions in modeling the yield behavior of Kelvin foams. The FEA model, representing a complicated unit cell, was calculated and meshed. C++ programs were designed and implemented to generate meshes for unit cells. Finite element analyses were performed for many cases. Multiple methods were employed for the determination of yield points which form yield surfaces. Comparisons between several results have been made. Our FEA results, Zhang's function and Gibson's theory show good agreements except some differences under hydrostatic loading. A conclusion can be made: besides the void fraction and the yield strength of the wall material, the structure of foams also has a significant effect on the yield behavior of foams. Yield surfaces normalized by the uniaxial tensile strength of foams are more reasonable.
• #### Steam reformation of diesel fuels

The Remote Area Program was created to evaluate the possible use of fuel cells and diesel reformers in residential and off-grid applications. Diesel was chose because an infrastructure already exits in rural communities. The UAF Energy Center demonstrated the use of a reformer to convert kerosene into hydrogen, which was used in a Proton Exchange Membrane fuel cell to power an AC load. In the summer of 1999, UAF hosted an Energy conference. At the conference Northwest Power (reformer manufacturer) indicated a diesel reformer efficiency of 65% while Plug Power promised a system efficiency (reformer, fuel cell and inverter) of 40%. After extensive experiments, the Energy Center found the current design reformer efficiency to be 30% and the system efficiency to be 15% at best. This efficiency does not compare favorably to the currently available diesel generator efficiency of 33%.
• #### Metal hydride storage of hydrogen for remote energy systems

As the world transitions towards more efficient and environmentally responsible energy systems there is a growing need for improved energy storage methods. For hydrogen based energy systems one method being examined involves the storage of hydrogen in a reversible metal hydride. These systems provide high storage density and low parasitic loss making them a good candidate for use in remote energy systems. In order to evaluate metal hydrides for possible use in conjuction with integrated fuel cell reformer systems a test bench was constructed and a steady state energy balance performed. This energy balance was designed to determine the heating and cooling loads associated with loading and unloading the hydride bed and give a verification of theoretical estimates. Using the test system values of 28.6 and 28.4 kJ / mol were found for the test alloys. The theoretical results were 28.6 and 28.0 kJ / mol respectively.
• #### Thermal and fluid dynamic analysis of gas-to-liquids transportation through Trans Alaska Pipeline System

Gas-to-liquids (GTL) technology involves the conversion of natural gas to liquid hydrocarbons. In this study, theoretical studies have been presented to determine the feasibility of transporting GTL products through the Trans-Alaska Pipeline System (TAPS). To successfully transport GTL through TAPS, heat loss along the route must be carefully determined. This study presents heat transfer and fluid dynamic calculations to evaluate this feasibility. Because of heat loss, the fluid temperature decreases in the direction of flow and this affects the fluid properties, which in turn influence convection coefficient and pumping power requirements. The temperature and heat loss distribution along the pipeline at different locations have been calculated. Fairly good agreement with measured oil temperatures is observed. The powers required to pump crude oil and GTL individually, against various losses have been calculated. Two GTL transportation modes have been considered; one as a pure stream of GTL and the second as a commingled mixture with crude oil. These results show that the pumping power and heat loss for GTL are less than that of the crude oil for the same volumetric flow rate. Therefore, GTL can be transported through TAPS using existing equipment at pump stations.
• #### Order reduction and eigenstructure assignment for nonsmooth vibrating systems: a nonlinear normal modes approach

Two related problems are addressed in this thesis. The first one is for order reduction of conservative vibrating systems with piecewise linear nonsmooth nonlinearities of arbitrary dimension. Linear-based, PMM-based and LELSM-based order reduction transformations are applied. The technique is applied to multi-degree-of-freedom systems with nonsmooth clearance, deadzone, bang-bang, and saturation nonlinearities. The resulting approximate frequencies are compared with those obtained from numerical simulations. The second technique is eigenstructure assignment of n-degree-of-freedom conservative vibrating systems with nonsmooth nonlinearities. Three distinct control strategies which utilize methods for approximating the NNM frequencies and mode shapes are employed. First, PMM for approximating NNM frequencies is used to determine n constant actuator gains for eigenvalue placement. Second, an approximate single-degree-of-freedom reduced model is found with one actuator gain for the mode to be controlled. The third strategy allows the frequencies and mode shapes (eigenstructure) to be placed by using a full n x n matrix of actuator gains and employing LELSM for approximating NNM frequencies and mode shapes.
• #### 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.
• #### 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.
• #### 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.
• #### Fluid flow in oscillating cavities

Oscillatory flows have gained considerable research attention in the recent decades following an interest in transport enhancement in micro-electronic devices. Heat transfer enhancement due to flow modulation has an inherent advantage over conventional mechanical heat transfer components in terms of reduction in weight and space. The present work is aimed at studying fluid flow in oscillating square cavities as a first step towards heat transfer enhancement. A commercial CFD code, Fluent, was used to model a test case consisting of Stokes' second problem, with a source code written in the C programming language. The simulated results were in good agreement with the analytical results found in the literature. Since the description of an oscillatory boundary condition in complex geometries would prove to be a difficult exercise because of the presence of spanwise walls, Newton's second law of motion for accelerating reference frames was used. This method proved to be an effective one computationally and the results agreed well with the analytical results. The cavity problem was analyzed using Fluent with the Non-Newtonian formulation described above. Fluid dynamic characteristics were studied with respect to dimensionless parameters and they exhibited an explicit dependence on these parameters.
• #### Synthesis and investigation of properties of barium titanate doped with ferromagnetic materials for use in spin field effect transistors

The fundamental aspect of this research was to synthesize nano particles of certain materials and to investigate their properties related to potential use in spin-field effect transistor (Spin-FET). Barium titanate was doped with ferromagnetic material and nano particles of this material were synthesized using a sol-gel process. Sol-gels were characterized for their size and shape using an atomic force microscope and a scanning electron microscope. Composition of these compounds and the distribution of dopents were investigated using x-ray fluorescence and the scanning electron microscope. Dielectric properties were measured using high precision impedance, capacitance, and resistance (LCR) meter. Barium titanate, when doped with ferromagnetic materials, becomes ferroelectric material. Ferroelectric materials have finite polarization even in the absence of an applied electric field, which can be exploited for their use as source/drain in spin-FET. The sintering temperature and pH of the sol-gel solution play important roles in determining the dielectric constants, particle size and distribution of dopent in barium titanate. It was found that iron has advantage over nickel and cobalt as a dopent, as it has high electrical susceptibility.
• #### Stability of milling using Chebyshev collocation method

The dynamic stability of the milling process is investigated through single and two degree-of-freedom mechanical models by determining the regions where chatter (unstable) vibrations occur in the two-parameter space of spindle speed and depth of cut. Dynamic systems like milling are modeled by linear delay-differential equations (DDEs) with time-periodic coefficients. A new approximation technique for studying the stability properties of such systems is presented in this thesis. The approach is based on the properties of Chebyshev polynomials and a collocation expansion of the solution at their extremum points, the Chebyshev collocation points. The stability properties are determined by the eigenvalues of the monodromy matrix which maps collocation points from one interval to the next and which is a finite dimensional approximation to which the exact infinite dimensional Floquet transition matrix (monodromy operator). We check the results for convergence by varying the number of Chebyshev collocation points and by simulation of the transient response via the DDE23 MATLAB routine. Stability charts and chatter frequency diagrams are produced for up-milling and down-milling cases of 1, 2, 4 and 8 cutting teeth and 0 to 100 % immersion levels. The unstable regions due to both secondary Hopf and flip (period-doubling) bifurcations are found which agree with the results found by other techniques in the previous literature. An in-depth investigation in the vicinity of the critical immersion ratio for down-milling (where the average cutting force changes from negative to positive) and its implication for stability is presented.
• #### Effects of electromigration on the reliability of radio frequency microelectro mechanical switches

Radio Frequency (RF) Micro-Electro-Mechanical System (MEMS) switches have many advantages over semiconductor switches. Despite these advantages they are not implemented in reliability demanding space, defense and commercial applications because of reliability concerns. Although some failure modes have been identified so far, other failure modes are still under research. Electromigration, a well-known failure mechanism in interconnects, was recently recognized as a possible cause of failure in micro-switches. However, there have been no instances of electromigration studies in the literature. This thesis presents a preliminary study on the electromigration failure and its impact on the lifetime of MEMS switches. A simulation program that emulates the electromigration process was developed. Parametric studies were performed to study the impact of impact certain parameters on electromigration process. The combined effects of Joule heating and electromigration were analyzed. Unlike passivated interconnects, the micro-switch is cantilevered and suspended in an inert medium without encapsulation. The electromigration lifetime estimation program developed in this thesis is applicable to all such free structures. Joule heating has been demonstrated to be a key factor in the electromigration failure of micro-switches. Results showed that the electromigration process is very slow at the beginning. After a certain time, the resistance is found to increase exponentially, increasing the temperature of the strip drastically toward failure. The same trend is also observed in a gold micro-switch, but with much slower rate of electromigration degradation, indicating a longer lifetime.
• #### Predictive semi-empirical analysis for tire/snow interaction

A semi-analytical method is presented to predict the shear stress and motion resistance at the tire/snow interaction. The shear stress model is a function of normal pressure and slip. The main goal was to develop a simplified model by reducing the number of parameters in the model, so that the computational time could be reduced towards real time simulations. Motion resistance is calculated by integrating the horizontal component of normal pressure along the tire/terrain contact surface. The motion resistance obtained is slip dependent because the sinkage is a function of slip. The calculations of motion resistance and sinkage were done using the presented model and an existing model. Also the calculated results were compared with the FEA (Finite Element Analysis) data, which matched reasonably well. In the second part of the thesis shear force is expressed as a function of normal load, slip and slip angle. Shear force parameters tire stiffness, friction coefficients, and contact pressure constants were assumed as the functions of normal load and the coefficients of parameters were found through curve fitting using FEA data. These functions were used to calculate tire stiffness, friction coefficient and contact pressure constant. The calculated results matched well with FEA simulation results for the same tire and snow conditions. Pure shear force and the combined shear force were compared, and the pure shear force is always greater than the combined shear force for the same slip and slip angle.
• #### 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.
• #### 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.
• #### Nanotribological Characterization Of Dynamic Surfaces

This dissertation research includes three fundamental areas: utilizing an atomic force microscope (AFM) to study the nanomechanical and tribological properties, to understand friction and wear at nanometer length, and to study wear mechanisms of boride coatings for biological applications. This was the first time that an AFM was used to study the nanomechanical and tribological properties and the performance of the materials. The AFM enables detailed investigation of the wear modes at multi-length scales as well as the surface mechanical properties. Surface analysis using an AFM included the surface texture, profile of indents, wear tracks, and wear scars. The friction force microscope (FFM) revealed the relationship between surface texture and frictional properties, thus contributing to the fundamental understanding of nanotribology. A new wear model was proposed. Also, hardening was discovered under the indents. The multi-scale wear study was focused on fundamental wear mechanisms. New wear modes, different than the traditional ones, were proposed. In this research, nanocracks and other damage (hardening and plastic flow) were found at different scales. Boride coatings on refractory metals were investigated for biological applications. Tribological performance of these coatings was studied in dry and wet (biofluid) conditions. It was found that boron plays an important role in forming amorphous and crystalline wear debris.
• #### 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).