Master of Science / Department of Architectural Engineering and Construction Science / Fred Hasler / Data center space and power densities are increasing as today’s society becomes more dependent on computer systems for processing and storing data. Most existing data centers were designed with a power density between 40 and 70 watts per square foot (W/SF), while new facilities require up to 200W/SF. Because increased power loads, and consequently cooling loads, are unable to be met in existing facilities, new data centers need to be built. Building new data centers gives owners the opportunity to explore more energy efficient options in order to reduce costs. Fuel cells are such an option, opposed to the typical electric grid connection with UPS and generator for backup power. Fuel cells are able to supply primary power with backup power provided by generators and/or the electric grid. Secondary power could also be supplied to servers from rack mounted fuel cells. Another application that can benefit from fuel cells is the HVAC system. Steam or high-temperature water generated from the fuel cell can serve absorption chillers for a combined heat and power (CHP) system. Using the waste heat for a CHP system, the efficiency of a fuel cell system can reach up to 90%. Supplying power alone, a fuel cell is between 35 and 60% efficient. Data centers are an ideal candidate for a CHP application since they have constant power and cooling loads. Fuel cells are a relatively new technology to be applied to commercial buildings. They offer a number of advantages, such as low emissions, quiet operation, and high reliability. The drawbacks of a fuel cell system include high initial cost, limited lifetime of the fuel cell stacks, and a relatively unknown failure mode. Advances in engineering and materials used, as well as higher production levels, need to occur for prices to decrease. However, there are several incentive programs that can decrease the initial investment. With a prediction that nearly 75% of all 10 year old data centers will need to be replaced, it is recommended that electrical and HVAC designer engineers become knowledgeable about fuel cells and how they can be applied to these high demand facilities.

Master of Science / Department of Architectural Engineering and Construction Science / Kimberly W. Kramer / Soils conditions vary throughout the United States and effect the behavior of the foundation system for building structures. The structural engineer needs to design a foundation system for a superstructure that is compatible with the soil conditions present at the site. Foundation systems can be classified as shallow and deep, and behave differently with different soils. Shallow foundation systems are typically used on sites with stiff soils, such as compacted sands or firm silts. Deep foundation systems are typically used on sites with soft soils, such as loose sands and expansive clays. A parametric study is performed within this report analyzing tilt-up concrete structures in Dallas, Texas, Denver, Colorado, and Kansas City, Missouri to determine the most economical tilt-up wall panel and foundation support system. These three locations represent a broad region within the Midwest of low-seismic activity, enabling the use of Ordinary Precast Wall Panels for the lateral force resisting system. Tilt-up wall panels are slender load-bearing walls constructed of reinforced concrete, cast on site, and lifted into their final position. Both a 32 ft (9.75 m) and 40 ft (12 m) tilt-up wall panel height are designed on three foundation systems: spread footings, continuous footings, and drilled piers. These two wall heights are typical for single-story or two-story structures and industrial warehouse projects. Spread footings and continuous footings are shallow foundation systems and drilled piers are a deep foundation system. Dallas and Denver both have vast presence of expansive soils while Kansas City has more abundant stiff soils. The analysis procedure used for the design of the tilt-up wall panels is the Alternative Design of Slender Walls in the American Concrete Institute standard ACI 318-05 Building Code and Commentary Section 14.8. Tilt-up wall panel design is typically controlled by lateral instability as a result from lateral loads combining with the axial loads to produce secondary moments. The provisions in the Alternative Design of Slender Walls consider progressive collapse of the wall panel from the increased deflection resulting from the secondary moments. Each tilt-up wall panel type studied is designed in each of the three locations on each foundation system type and the most economical section is recommended.

Master of Science / Department of Architectural Engineering and Construction Science / Rhonda Wilkinson / Until recently sunlight was the primary source of illumination indoors, making perimeter fenestration essential and impacting the layout of buildings. Improvements in electric fixtures, light sources, control systems, electronic ballasts and dimming technology have influenced standard design practices to such a degree that allowing natural sunlight into a room is often seen as a liability. In the current climate of increasing energy prices and rising environmental awareness, energy conservation and resource preservation issues are a topic of governmental policy discussions for every nation on the planet. Governmental, institutional, social and economic incentives have emerged guiding the development and adoption of advanced daylighting techniques to reduce electric lighting loads in buildings used primarily during the day. A growing body of research demonstrates numerous health, occupant satisfaction, worker productivity and product sales benefits associated with natural lighting and exposure to sunlight. However, incorporating natural light into a lighting strategy is still complicated and risky as the intensity, variability and thermal load associated with sunlight can significantly impact mechanical systems and lead to serious occupant comfort issues if additional steps aren’t taken to attenuate or control direct sunlight. Fiber optic daylighting systems represent a new and innovative means of bringing direct sunlight into a building while maintaining the control ability and ease of application usually reserved for electric lighting by collecting natural light and channeling it through optical fibers to luminairies within the space. This technology has the ability to bring sunlight much deeper into buildings without impacting space layout or inviting the glare, lighting variability and heat gain issues that complicate most daylighting strategies. As products become commercially available and increasingly economically viable, these systems have the potential to conserve significant amounts of energy and improve indoor environmental quality across a variety of common applications.

Master of Science / Department of Electrical and Computer Engineering / Balasubramaniam Natarajan / In this thesis, we present an automated system for detection and classification of cracks, based on the new standard proposed by `American Association of State Highway and Transportation Officials (AASHTO)'. The AASHTO standard is a draft standard, that attempts to overcome the limitations of current crack quantifying and classification methods. In the current standard, the crack classification relies heavily on the judgment of the expert. Thus the results are susceptible to human error. The effect of human error is especially severe when the amount of data collected is large. This lead to inconsistencies even if a single standard is being followed. The new AASHTO guidelines attempt to develop a method for consistent measurement of pavement condition. Gray scale images of the road are captured by an image capture vehicle and stored on a database. Through steps of thresholding, line detect and scanning, the gray scale image is converted to binary image, with 'zeros' representing cracked pixels. PCA analysis, followed by closing and filtering operation, are carried out on the gray scale image to identify cracked sub-images. The output from the filtering operation, is then replaced with its binary counterpart. In the final step the crack parameters are calculated. The region around the crack is divided into blocks of 32x32 to approximate and calculate the crack parameters with ease. The width of the crack is approximated by the average width of crack in each block. The orientation of the crack is calculated from the angle between direction of travel and the line joining the ends of the crack. Length of the crack is the displacement between the ends of the crack, and the position of the crack is calculated from the midpoint of the line joining the end points.

Master of Science / Department of Chemical Engineering / Larry E. Erickson / The impact of human activities on the atmosphere and the accompanying risks of long-term global climate change are by now familiar topics to many people. Although most of the increase in greenhouse gas (GHG) concentrations is due to carbon dioxide (CO2) emissions from fossil fuels, globally about one-third of the total human-induced warming effect due to GHGs comes from agriculture and land-use. This report provides a brief review of greenhouse effects and impacts on climate, human health and environment. The sources of emissions of greenhouse gases due to human activities, both current estimates and future projections, have been included. The report further discusses possible options for mitigation of greenhouse gases. The report also discusses the role agriculture can play towards mitigation of greenhouse gases as many agricultural processes such as anaerobic digestion, manure gasification; carbon sequestration etc. can help reduce or offset greenhouse gas emissions. Capture and sequestration of CO2 released as a result of burning fossil fuel in power plants, energy and other industries is gaining widespread interest as a potential method of controlling greenhouse gas emissions. Various technologies such as amine (MEA)-based CO2 absorption system for post-combustion flue gas applications have been developed, and can be integrated with existing plant operations. Removal of SO2 by using amine-based carbon capture system offers additional benefit. Efforts are underway to develop a broader suite of carbon capture and sequestration technologies for more comprehensive assessments in the context of multi-pollutant environmental management. Geologic formations and/ or possibly oceans can be used as sinks to store recovered CO2. In oil and gas exploration industry CO2 may be injected in producing or abandoned reservoirs which will not only help in maintaining the reservoir pressure (which improves overall field exploitation) but in some cases even leads to enhanced oil recovery.

Doctor of Philosophy / Department of Biological & Agricultural Engineering / Naiqian Zhang / Soil surface roughness is a major factor influencing soil erosion by wind and water. Studying surface roughness requires accurate Digital Elevation Model (DEM) data. A vehicle-based laser measurement system was developed to generate high-resolution DEM data. The system consisted of five units: a laser line scanner to measure the surface elevation, a gyroscope sensor to monitor the attitude of the vehicle, a real-time kinematic GPS to provide the geographic positioning, a frame-rail mechanism to support the sensors, and a data-acquisition and control unit. A user interface program was developed to control the laser system and to collect the sensors data through a field laptop. Laboratory experiments were conducted to evaluate the performance of the laser sensor on different type of targets. The results indicated that the laser measurement on a white paper had the least variability than that on other targets. The laser distance measurement was calibrated using the data acquired on the white paper. Static accuracy tests of the gyroscope sensor on a platform that allowed two-axis rotations showed that angle measurement errors observed in combined pitch/roll rotations were larger than those in single rotations. Within ±30° of single rotations, the measurement errors for pitch and roll angles were within 0.8° and 0.4°, respectively. A model to study the effect of attitude measurement error on elevation measurement was also developed. DEM models were created by interpolating the raw laser data using a two-dimensional, three-nearest neighbor, distance-weighted algorithm. The DEM models can be used to identify shapes of different objects. The accuracy of the laser system in elevation measurement was evaluated by comparing the DEM data generated by the laser system for an unknown surface with that generated by a more accurate laser system for the same surface. Within four replications, the highest correlation coefficient between the measured and reference DEMs was 0.9371. The correlation coefficients among the four replications were greater than 0.948. After a median threshold filter and a median filter were applied to the raw laser data before and after the interpolation, respectively, the correlation coefficient between the measured and reference DEMs was improved to 0.954. Correlation coefficients of greater than 0.988 were achieved among the four replications. Grayscale images, which were created from the intensity data provided by the laser scanner, showed the potential to identify crop residues on soil surfaces. Results of an ambient light test indicated that neither sunlight nor fluorescent light affected the elevation measurement of the laser system. A rail vibration test showed that the linear rail slightly titled towards the laser scanner, which caused small variations in the pitch angle. A preliminary test on a bare soil surface was conducted to evaluate the capability of the laser system in measuring the DEM of geo-referenced surfaces. A cross-validation algorithm was developed to remove outliers. The results indicated that the system was capable of providing geo-referenced DEM data.

Master of Science / Department of Architectural Engineering and Construction Science / Sutton F. Stephens / Cold-formed steel has become a preferred building material for structural farming in many different types of structures, commonly for repetitive members such as floor joists, roof rafters, roof trusses and wall studs. For wood framed structures with repetitive members, a repetitive member factor increases the allowable bending stress from 1.00 to 1.50 times the reference design value, depending on both the type of material and the type of load. Currently, however, the bending strength of cold-formed steel repetitive members is not permitted to be increased, even though the method of framing is quite similar to that of wood except for the material properties. Typical light-frame wood construction consists of floor, roof, and wall systems, each with repetitive members connected by sheathing. A repetitive system is one of at least three members that are spaced not farther apart than 24-inches. These members must also be joined by a load distributing element adequate to support the design load. The behavior of the individual members, then, is affected by inclusion into this system. Additionally, the connected sheathing increases the bending capacity of bending members due to both composite action and load sharing. Composite action is a result of T-beam-like action between the repetitive member and connected sheathing, but is limited by nail slippage in the connection. Secondly, due to differential deflection between the members, sheathing is also able to distribute loads from weaker, more flexible members to the more rigid and stronger members. This effect is known as load-sharing. The same general principles of repetitive use should apply to cold-formed steel due to its similarity to wood construction. Accordingly, this paper conducts a preliminary study of the effects of both composite action and load-sharing in cold-formed steel assemblies and subsequently recommends using a repetitive member factor for cold-formed steel members.

In the last 10-15 years, large-eddy simulation (LES) has become well established for non-reacting flows, and several successful models have been developed for the transfer of momentum and kinetic energy to the subfilter-scales (SFS). However, for reacting flows, LES is still undergoing significant development. In particular, for many premixed combustion applications, the chemical reactions are confined to propagating surfaces that are significantly thinner than the computational grids used in practical LES. In these situations, the chemical kinetics and its interaction with the turbulence are not resolved and must be entirely modelled. There is, therefore, a need for accurate and robust physical modelling of combustion at the subfilter-scales. In this thesis, modelled transport equations for progress variable and flame surface density (FSD) were implemented and coupled to the Favre-filtered Navier-Stokes equations for a compressible reactive thermally perfect mixture. In order to reduce the computational costs and increase the resolution of simulating combusting flows, a parallel adaptive mesh (AMR) refinement finite-volume algorithm was extended and used for the prediction of turbulent premixed flames. The proposed LES methodology was applied to the numerical solution of freely propagating flames in decaying isotropic turbulent flow and Bunsen-type flames. Results for both stoichiometric and lean flames are presented. Comparisons are made between turbulent flame structure predictions for methane, propane, hydrogen fuels, and other available numerical results and experimental data. Details of subfilter-scale modelling, numerical solution scheme, computational results, and capabilities of the methodology for predicting premixed combustion processes are included in the discussions. The current study represents the first application of a full transport equation model for the FSD to LES of a laboratory-scale turbulent premixed flame. The comparisons of the LES results of this thesis to the experimental data provide strong support for the validity of the modelled transport equation for the FSD. While the LES predictions of turbulent burning rate are seemingly correct for flames lying within the wrinkled and corrugated flamelet regimes and for lower turbulence intensities, the findings cast doubt on the validity of the flamelet approximation for flames within the thin reaction zones regime.

A primary purpose of elasticity imaging, commonly known as elastography, is to extract the viscoelastic properties of a medium (including soft tissue) from the displacement caused by a stress field. Dynamic elastography methods that use the acoustic radiation force of ultrasound have several advantages, such as, non-invasiveness, low cost, and ability to produce a highly localized force field. A method for remotely generating localized low frequency shear waves in soft tissue is investigated, by using the modulated radiation force resulting from two intersecting quasi-CW confocal ultrasound beams of slightly different frequencies. In contrast to most radiation force-based methods previously presented, such shear waves are narrowband rather than broadband. As they propagate within a viscoelastic medium, different frequency-dependent effects will not significantly affect their spectrum, thereby providing a means for measuring the shear attenuation and speed as a function of frequency. Furthermore, to improve the detection signal-to-noise-ratio (SNR), increased acoustic pressure conditions may be needed, causing higher harmonics to be generated due to nonlinear propagation effects. Shear-wave propagation at harmonic modulation frequencies does not appear to have been previously discussed in the elastography literature. The properties of the narrowband shear wave propagation in soft tissue are studied by using the Voigt viscoelastic model and Green’s functions. In particular, the manner in which the characteristics of the viscoelastic medium affect their evolution under both low-amplitude (linear) and high-amplitude (nonlinear) source excitation and conditions that conform to human safety standards. It is shown that an exact solution of the viscoelastic Green’s function is needed to properly represent the propagation in higher-viscosity media, such as soft tissue, at frequencies much beyond a few hundred hertz. Methods for estimating the shear modulus and viscosity in viscoelastic media are developed based on both the fundamental and harmonic shear components.

Master of Science / Department of Biological and Agricultural Engineering / Donghai Wang / Acid catalysts have been successfully used for pretreatment of cellulosic biomass to improve sugar recovery and its later conversion to ethanol. However, use of acid requires a considerable equipment investment as well as disposal of residues. Acid-functionalized nanoparticles were synthesized for pretreatment and hydrolysis of lignocellulosic biomass to increase conversion efficiency at mild conditions. Advantages of using acid-functionalized metal nanoparticles are not only the acidic properties to catalyze hydrolysis and being small enough to penetrate into the lignocellulosic structure, but also being easily separable from hydrolysis residues by using a strong magnetic field. Cobalt spinel ferrite magnetic nanoparticles were synthesized using a microemulsion method and then covered with a layer of silica to protect them from oxidation. The silanol groups of the silica serve as the support of the sulfonic acid groups that were later attached to the surface of the nanoparticles. TEM images and FTIR methods were used to characterize the properties of acid-functionalized nanoparticles in terms of nanoparticle size, presence of sulfonic acid functional groups, and pH as an indicator of acid sites present. Citric acid-functionalized magnetite nanoparticles were also synthesized and evaluated. Wheat straw and wood fiber samples were treated with the acid supported nanoparticles at 80°C for 24 h to hydrolyze their hemicellulose fraction to sugars. Further hydrolysis of the liquid fraction was carried out to account for the amount of total solubilized sugars. HPLC was used to determine the total amount of sugars obtained in the aqueous solution. The perfluroalkyl-sulfonic acid functional groups from the magnetic nanoparticles yielded significantly higher amounts of oligosaccharides from wood and wheat straw samples than the alkyl-sulfonic acid functional groups did. More stable fluorosulfonic acid functionalized nanoparticles can potentially work as an effective heterogeneous catalyst for pretreatment of lignocellulosic materials.