Doctor of Philosophy (PhD), Ohio University, 2024, Mechanical and Systems Engineering (Engineering and Technology)

This dissertation presents the design and development of a novel hydrodynamic thrust bearing test rig featuring a new (patent pending) pressure-feedback control system for maintaining static bearing alignment. This research aims to provide an enhanced understanding of how the critical operational characteristics of fixed-geometry hydrodynamic thrust bearings including minimum oil film thickness (MOFT), hydrodynamic pressure distribution, and bearing temperature are affected by variability in bearing pad taper geometry under different speed, load, and oil conditions. Further, a new (patent pending) additively manufactured (AM) thrust bearing fabricated using direct metal laser sintering (DMLS) is experimentally evaluated to determine in-service viability. To support the experimental data obtained in the variable taper experiment, a Matlab simulation code is developed using the Reynolds equation to generate numerically predicted performance data for direct comparison. The AM thrust bearing is experimentally compared to a traditionally manufactured cast alloy bearing with identical surface geometry. For the variable taper study, trends in performance established by the numerical analysis show mutually agreeable results compared to experimental data. The average percent deviation of the experimentally gathered change in MOFT as load is increased with respect to the numerically predicted values is 24%. Comparison of experimental to numerical pressure distribution data shows an overall average percent deviation of 32%. For the AM vs. traditionally manufactured bearing experiment, the AM bearing showed an average increase in minimum oil film thickness of 53%, an average increase in trailing edge hydrodynamic pressure of 116%, while exhibiting an average decrease in bearing temperature of 1%.

Committee: Muhammad Ali (Advisor); Khairul Alam (Committee Member); Arthur Smith (Committee Member); Zaki Kuruppalil (Committee Member); Jay Wilhelm (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2018, Psychology

Conditional process models are commonly used in many areas of psychology research as well as research in other academic fields (e.g., marketing, communication, and education). Conditional process models combine mediation analysis and moderation analysis. Mediation analysis, sometimes called process analysis, investigates if an independent variable influences an outcome variable through a specific intermediary variable, sometimes called a mediator. Moderation analysis investigates if the relationship between two variables depends on another. Conditional process models are very popular because they allow us to better understand how the processes we are interested in might vary depending on characteristics of different individuals, situations, and other moderating variables. Methodological developments in conditional process analysis have primarily focused on the analysis of data collected using between-subjects experimental designs or cross-sectional designs. However, another very common design is the two-instance repeated-measures design. A two-instance repeated-measures design is one where each subject is measured twice; once in each of two instances. In the analysis discussed in this dissertation, the factor that differentiates the two repeated measurements is the independent variable of interest. Research on how to statistically test mediation, moderation, and conditional process models in these designs has been minimal. Judd, Kenny, and McClelland (2001) introduced a piecewise method for testing for mediation, reminiscent of the Baron and Kenny causal steps approach for between-participant designs. Montoya and Hayes (2017) took this piecewise approach and translated it to a path-analytic approach, allowing for a quantification of the indirect effect, more sophisticated methods of inference, and the extension to multiple mediator models. Moderation analysis in these designs has been described by Judd, McClelland, and Smith (1996), Judd et al. (2001), and Montoya (open full item for complete abstract)

Committee: Andrew Hayes (Advisor); Jolynn Pek (Committee Member); Paul De Boeck (Committee Member) Subjects: Applied Mathematics; Behavioral Sciences; Biostatistics; Experimental Psychology; Psychology; Quantitative Psychology; Statistics

Doctor of Philosophy, Case Western Reserve University, 2016, EECS - Electrical Engineering

Conventional thermoelectric modules (TEMs) are composed of n-type and p-type thermoelectric (TE) legs connected electrically in series and thermally in parallel. The development of TE technology based on the traditional TEM structure has been limited by its low efficiency and high cost. Most of ongoing research nowadays focuses on developing new TE materials that have higher intrinsic efficiency. This research analyzes the TE problem from an electrical engineering angle. The conventional electrically serial structure considers TE legs as voltage power sources. In contrast, this research takes advantage of TE legs as current power sources, leading to an alternative TEM structure, where all TE legs are made from single type of TE material and connected in parallel both electrically and thermally. Experimental, analytical and numerical analysis have been carried out to evaluate the performance of unit modules with the newly proposed electrically parallel structure. It indicates that the modules' figure-of-merit and energy conversion efficiency can be increased within a certain device area limit, the fabrication cost can be decreased, the power density and mechanical durability can be increased, while the temperature gradient is kept in the cross-plane direction. It can also increase the device lifetime, because on the one hand, there is no mismatch between the thermal expansion rate among TE legs. On the other hand, for serial structure, even a single break of the connection can lead to the failure of the device. However, for the electrically parallel structure, a small break of the junction will not affect the performance significantly. Meanwhile, the proposed electrically parallel structure can also benefit the back-end step-up DC-DC converter design. It can produce a higher output voltage (so a higher output power and efficiency) to the load, and possibly work under a slower switching frequency to decrease the switching energy loss. In addition, th (open full item for complete abstract)

Committee: Xiong Yu (Advisor); Christian Zorman (Committee Member); Philip Feng (Committee Member); Hongping Zhao (Committee Member); Chung-Chiun Liu (Committee Member); Alp Sehirlioglu (Committee Member) Subjects: Electrical Engineering; Energy

MS, University of Cincinnati, 2016, Engineering and Applied Science: Mechanical Engineering

Viscoelastic coatings are currently being used in a variety of industries to provide shock absorption, energy absorption, noise reduction, and vibration isolation. They are commonly used through aerospace, automotive, and electronic industries. These materials have a complex behavior that causes their mechanical properties to vary with both temperature and frequency. Testing historically has been done on a composite material due to the inability of the coatings to support themselves at high temperatures. One common method is the vibrating beam technique, which examines two cantilever beam specimen, an uncoated beam and a coated beam. The change in modal properties is used to determine the properties of the viscoelastic material by itself. However, when the environment is harsh or space is restricted, measurements and excitations cannot be made in a traditional contacting manor. This paper examines methods of non-contact excitation and measurements and explores the effects from these methods. Specifically, magnetic excitation was examined as a source of non-contact excitation on a non-ferrous material. This requires that a magnetic material be attached to the beams in order for the magnetic excitation to be successful. The mass loading effects were examined for the two beam specimen to most accurately define the modal parameters of the beams. This excitation source was also used to test the specimen at a range of temperatures to determine the effect temperature had on the modal parameters of the specimen as well. Finite element models were subsequently created to see if the results from the experimental modal analysis could be confirmed with the FEA results.

Committee: Randall Allemang Ph.D. (Committee Chair); Jay Kim Ph.D. (Committee Member); Allyn Phillips Ph.D. (Committee Member) Subjects: Mechanics

Doctor of Philosophy, Case Western Reserve University, 2015, EMC - Mechanical Engineering

Analyses and experiments demonstrate the potential benefits of optimizing piston and displacer motion in a free piston Stirling Engine. Isothermal analysis shows the theoretical limits of power density improvement due to ideal motion in ideal Stirling engines. More realistic models based on nodal analysis show that ideal piston and displacer waveforms are not optimal, often producing less power than engines that use sinusoidal piston and displacer motion. Constrained optimization using nodal analysis predicts that Stirling engine power density can be increased by as much as 58% using optimized higher harmonic piston and displacer motion. An experiment is conducted in which an engine designed for sinusoidal motion is forced to operate with both second and third harmonics, resulting in a maximum piston power increase of 14%. Analytical predictions are compared to experimental data showing close agreement with indirect thermodynamic power calculations, but poor agreement with direct electrical power measurements.

Committee: Joseph Prahl (Advisor) Subjects: Aerospace Engineering; Alternative Energy; Applied Mathematics; Conservation; Design; Electrical Engineering; Energy; Engineering; Mechanical Engineering; Mechanics; Naval Engineering; Nuclear Engineering; Technology

MS, University of Cincinnati, 2014, Engineering and Applied Science: Mechanical Engineering

The vast field of rotational systems – including measurement capabilities, analytical tools and observability – is still evolving. Spectral maps and order tracks are the most popular tools for analyzing the behavior of various components subject to a rotational characteristic. Although various forms of these tools are well researched and implemented, they are still susceptible to improper sensor location on the structure and to measurement noise. This thesis attempts to bridge the gap between properly located sensors and effective analysis based on their measurements. The concept of singular value decomposition (SVD), which is already well used in modal analysis, forms the basis of observability improvement. By using response data acquired from multiple sensors on a structure, it is possible to calculate and plot the singular values obtained from the entire frequency domain response data at each point in the spectral map graph. The resulting singular value plots will depict the magnitude of contribution of the sensor assembly which can form a noise-free and reliable basis for further analytical tools.

Committee: Randall Allemang Ph.D. (Committee Chair); David L. Brown Ph.D. (Committee Member); Allyn Phillips Ph.D. (Committee Member) Subjects: Engineering

MS, University of Cincinnati, 2010, Engineering : Mechanical Engineering

Modal analysis is a critical part of the automotive development process. Identification of the vehicle's modal signature, especially in the low-frequency end of the spectrum, is essential for tuning the dynamic performance of the vehicle structure for optimal ride and handling comfort. Traditional methods to characterize the system - in terms of its natural frequencies, associated damping values and mode shapes - have typically employed conventional impact and shaker tests. While these tests are able to accurately study the modal behavior of the vehicle under static conditions, they are not truly reflective of the real-world operating conditions of the vehicle A four-post road simulator is used in automotive development to simulate on-road conditions in the laboratory primarily for durability, transmissibility, noise and vibration studies, etc. Some of these studies often involve a similar setup of response sensors across the automotive structure as conventional modal tests. Utilization of the road-simulator for modal analysis can potentially reduce the duration of the automotive development cycle in the testing phase, allowing for a faster time-to-market, in addition to improved accuracy of estimation of the vehicle's dynamic performance under simulated operating conditions. This thesis work explores the feasibility of using a four-post road simulator for experimental modal analysis (EMA) of automotive structures. The MTS 320 Road Simulator in the Structural Dynamics Research Laboratory, University of Cincinnati, is employed for the study, with a truck frame being the test structure. Frequency response functions (FRFs) are estimated with displacement and pressure measurements at the hydraulic excitation posts of the simulator, provided by transducers built into the four-poster, replacing force measurements as inputs. The applicability of these non-conventional FRF formulations for modal parameter identification using existing parameter estimation algorithms is st (open full item for complete abstract)

Committee: Randall Allemang PhD (Committee Chair); Allyn Phillips PhD (Committee Member); David Brown PhD (Committee Member) Subjects: Mechanical Engineering

PhD, University of Cincinnati, 2024, Engineering and Applied Science: Aerospace Engineering

The move towards renewable energy has highlighted the need for large-scale, environmentally friendly energy storage solutions. Among these, the Supercritical Carbon Dioxide (sCO2) power cycle is emerging as a promising technology for advanced energy conversion. The effectiveness of such systems depends heavily on the compressor's performance. Using optimization-based methods, a multistage axial compressor has been designed, and its first stage has been built and tested experimentally. Through a series of detailed design iterations and optimization strategies, 3D CFD analyses, the compressor's geometric and operational parameters were fine-tuned to address the unique challenges posed by operation using CO2. Key findings highlight the successful implementation of design optimization that significantly reduces aerodynamic losses and improves the overall efficiency of the compressor stages. The optimized compressor demonstrates robust performance across a range of operating conditions, particularly focusing on improved stall margin, which emphasizes the potential of sCO2 technology in contributing to efficient and sustainable energy systems. Further detailed studies using CFD to analyze cavity effects in shrouded configurations, tip clearance effects, real gas effects, and Reynolds number effects were performed. Experimental validations, conducted at the University of Notre Dame Turbomachinery Laboratory, confirm the CFD predictions and showcase the practical viability of the compressor design and the approach used. This work not only advances the state-of-the-art in turbomachinery design for supercritical fluids but also lays a foundation for future research into the integration of sCO2 and real gas based compressors in renewable energy systems and industrial applications. The insights gained from this study underscore the critical importance of tailored design and optimization strategies in overcoming the thermophysical challenges associated (open full item for complete abstract)

Committee: Mark Turner Sc.D. (Committee Chair); Daniel Cuppoletti Ph.D. (Committee Member); Kelly Cohen Ph.D. (Committee Member); Jeong-Seek Kang Ph.D. (Committee Member); Shaaban Abdallah Ph.D. (Committee Member) Subjects: Aerospace Engineering

PhD, University of Cincinnati, 2024, Engineering and Applied Science: Mechanical Engineering

Combining strain FRF data and acoustic pressure FRF data with displacement FRF data for modal parameter estimation is the focus of this research. While these measurements have been shown to work standalone for modal analysis, it has not been shown experimentally that different physical measurements can be combined to get the same modal results. Recent work by Coppolino [1], showing that at least in theory this combination should be possible and should yield the same modal results as when only accelerometer FRF data is used, was important to the following work. This dissertation attempts to experimentally obtain data for strain, pressure and displacement FRF data and combine these three datasets in different ways to explore if some displacement information can be replaced without changing the modal parameter results. The data acquired is from several impact hammer tests carried out on a flat rectangular plate. Two different ways of combining this data have been discussed with all the possible combinations explored. Modal frequencies and damping have been compared and modal assurance criterion used to compare modeshapes. Intuitively speaking, strain and displacement can seem to have ‘inversed' behavior as in the simple case of a cantilever beam. To evaluate this concern, finite element based analytical work has been presented to check which locations on the structure are best to measure strain FRFs to be able to replicate modal parameters obtained from an only displacement FRF analysis. A new criterion, local scale factor consistency, has been developed to be able to compare shapes degree of freedom by degree of freedom as well as mode by mode.

Committee: Randall Allemang Ph.D. (Committee Chair); Allyn Phillips Ph.D. (Committee Member); Robert N. Coppolino Ph.D. (Committee Member); Aimee Frame Ph.D. (Committee Member); David Thompson Ph.D. (Committee Member) Subjects: Mechanical Engineering

PhD, University of Cincinnati, 2023, Engineering and Applied Science: Civil Engineering

The constant growth of population and urbanization in conjunction with the demand for enhanced building services and comfort have led to a substantial increase in energy consumption in the building sector accounting for up to 40% in developed countries. Among the several end uses in buildings, heating, ventilation, and air conditioning (HVAC) systems consume the largest quantity of energy. Therefore, energy efficiency in these systems has become a prime objective for building standards and energy policies. The variable air volume (VAV) systems that are the most commonly used HVAC systems in the USA offer some advantages to achieve energy efficiency in buildings but also have some inherent limitations that can increase the energy consumption and cost of the systems. In response, this dissertation proposes an optimal design and control of the VAV systems that aims to achieve both energy and cost benefits in buildings, taking the existing systems' attributes into account. In this research, (i) a new configuration of dual duct systems named the ‘Dual VAV' system is proposed that has the characteristics of existing single and dual duct VAV systems to utilize their benefits while eliminating the shortcomings, (ii) a new sequence of control is designed for the dual VAV system after several iterations that largely varies from the standard control sequence of the VAV systems for the effective control and operation of the proposed system, (iii) a modeling strategy is developed for dual VAV and three other existing systems for the building simulation purposes as the specific AHU arrangement is not available in any simulation platforms, (iv) a small multizone office building is simulated with the model and control sequence at first and later a large four story multizone office building is simulated for the evaluation of annual heating, cooling and fan power consumption for the proposed system, (v) two optimization strategies for supply air temperature reset and outdoor (open full item for complete abstract)

Committee: Nabil Nassif (Committee Chair); Munir Nazzal Ph.D. (Committee Member); Hazem Elzarka Ph.D. (Committee Member); Pravin Bhiwapurkar Ph.D. (Committee Member) Subjects: Civil Engineering

Doctor of Philosophy, The Ohio State University, 2023, Mechanical Engineering

As emission standards of passenger vehicles become more and more strict, automotive manufacturers are seeking lightweight solutions to increase vehicle's fuel economy. Fibrous reinforced polymers (FRPs) are known to have high strength to weight ratios, and thus, made them good candidates for the application in the automotive industry. FRP is a composite material made of a polymer matrix reinforced with fibers. The inhomogeneity, anisotropy, visco-elasticity/plasticity, mechanical degradation due to temperature/damage, brittleness characteristics of the unidirectional FRP composites bring challenges to determine mechanical responses both experimentally and numerically. In this dissertation, mechanical behavior of unidirectional carbon fiber reinforced polymer (CFRP) made of Toray T700S carbon fiber and G83-CM prepreg system is studied. Specimens are fabricated from 8-ply and 16-ply CFRP plates. An experimental series is performed including tension, compression, and shear coupon tests at various strain rates ranging from 0.001 to 1000 s-1. Anisotropy is studied by conducting tension, compression, and shear coupon tests in different fiber orientations. Thermal dependence of the material is investigated by performing coupon tests under temperatures ranging from 25 °C to 120 °C. CFRP has been found that loading in one direction can potentially lead to damage in other directions. Thus, coupled, and uncoupled damage testing is performed to characterize such behavior. Digital image correlation (DIC) is applied for deformation and strain measurement on the surface of the specimens. The coupon test data and damage test data are used to calibrate the deformation and damage sub-models of the constitutive material model, *MAT_COMPOSITE_TABULATED_PLASTICITY_DAMAGE, also called *MAT_213, in LS-DYNA. The deformation sub-model predicts elasto-plastic behavior, and it uses a strain-hardening-based orthotropic yield function with a non-associated flow rule extended from Tsai-Wu fail (open full item for complete abstract)

Committee: Amos Gilat (Advisor); Prasad Mokashi (Committee Member); Kelly Carney (Committee Member); Jeremy Seidt (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy in Materials Science and Engineering, Youngstown State University, 2023, Materials Science

This work discusses the relevance of Metal Additive Manufacturing (MAM) and focuses on one method: Direct Energy Deposition (DED). Different types of DED processes are discussed, including their main parameters and issues. A general procedure to simulate DED processes is presented and founded on the finite element analysis (FEA) workflow. Based on this, two initial case studies are analyzed, which were selected from the literature and reproduced via a commercially available FEA software. Their results provided evidence of the feasibility of the software in simulating a DED process. Two experiments were carried out, called single bead and rectangular prism, for the purpose of this research. These were built with a hot wire and laser DED system, where experimental thermal data was obtained. Geometric information was obtained later via a 3D scan. Limitations of the equipment used as well as observed defects in the material deposition are discussed based on the experimental data. FEA models were developed to duplicate the experiments, which included a detailed geometry of the single bead. Two modifications to the bead geometry are presented and evaluated, where it was concluded that a semicircular bead approximation provides better results than if a rectangular one is assumed. This led to the definition of a thermal and structural equivalent model of the single bead, which was the basis for the numerical work of the rectangular prism. The results obtained for the latter show good agreement with the thermal results, although differences in the structural results are perceptible.

Committee: Kyosung Choo PhD (Advisor); Pedro Cortes PhD (Committee Member); Timothy Wagner PhD (Committee Member); Jae Joong Ryu PhD (Committee Member); Holly Martin PhD (Committee Member) Subjects: Experiments; Materials Science; Mechanical Engineering; Mechanics

Doctor of Philosophy, The Ohio State University, 2022, Mechanical Engineering

Materials experiencing impact loading deform under complex three dimensional states of stress and at high strain rates. Accurately simulating impact events using finite element modeling requires material models capable of depicting the material behavior under these same conditions. In order to create accurate material models, this material behavior must first be determined experimentally. It is of particular interest to determine the equivalent plastic fracture strain at stress states consisting of in-plane biaxial tension and out-of-plane compression, and the plastic stress-strain response at strain rates on the order of 104 s-1. Both of these conditions are found during impact loading, and are outside the scope of current testing techniques. A new test technique is used to investigate Aluminum 2024, Titanium 6Al-4V, and Inconel 718 under in-plane biaxial tension and out-of-plane compression. The test consists of a small spherical or elliptical punch that is advanced into a thin specimen plate to induce in-plane biaxial tension on the back surface of the specimen. A second plate of an appropriate material is placed against the back surface of the specimen plate during loading in order to create out-of-plane compression. The equivalent plastic fracture strain at these stress states is determined from the experimental data and simulations using the commercial finite element software LS-DYNA. The same materials mentioned above are also tested using a modified, direct impact split-Hopkinson bar testing technique to induce strain rates greater than 104 s-1. For these tests, a small cylindrical specimen is placed in contact with the end of a larger cylindrical bar. The specimen is then impacted with a free flying cylindrical projectile to compress the specimen at a high rate of deformation. The stress-strain response of the material at these high strain rates is then investigated from the experimental data and in conjunction with LS-DYNA finite element simulati (open full item for complete abstract)

Committee: Amos Gilat (Advisor); Prasad Mokashi (Committee Member); Jeremy Seidt (Committee Member) Subjects: Aerospace Materials; Engineering; Experiments; Mechanical Engineering; Mechanics

BA, Kent State University, 2021, College of Arts and Sciences / Department of Sociology and Criminology

"Dazed and Confused and Triumphant" is often the experience of both readers and writers of ergodic literature, whose struggle to understand it becomes a meaningful accomplishment after they do. Ergodic literature, as defined by its founder Espen Aarseth in his book 'Cybertext: Perspectives on Ergodic Literature', is literature in which "nontrivial effort is required to allow the reader to traverse the text". "Nontrivial effort" encompasses anything beyond reading a text from front to back, such as nonlinearity, space subversion, and multiple endings to choose from. In this thesis, I use the syllabus of a Fall 2012 NEOMFA Craft & Theory course to design the hypothetical 16 week class "Dazed and Confused and Triumphant" as a way to teach myself ergodic literature and grow as an experimental writer. The syllabus requires students to read and experience a comprehensive list of ergodic literature all throughout time (ex: the 'I Ching', the 'Choose Your Own Adventure' series, and the video game 'Undertale'), write weekly essays analyzing ergodic techniques in these readings, and create original ergodic literature based on what they've learned. All of these assignments and more are completed and included in this thesis. The thesis itself is arguably ergodic in its creation, format, and puzzle for its readers to solve.

Committee: Lauren Vachon MFA (Advisor); Carol Robinson Ph.D. (Committee Member); Molly Merryman Ph.D. (Committee Member); Suzy D'Enbeau Ph.D. (Committee Member) Subjects: Curriculum Development; Fine Arts; Language Arts; Literature; Web Studies

Bachelor of Fine Arts (BFA), Ohio University, 2021, Film

Barbara Hammer, a trailblazing figure of queer and feminist experimental filmmaking, exemplifies the alternative cinema proposed by Laura Mulvey in her seminal essay, 'Visual Pleasure and Narrative Cinema.' By breaking down the formal techniques used in Hammer's 1975 film 'Superdyke Meets Madame X,' this paper seeks to emphasize how Hammer's deliberate inclusion of her own queer body calls out and subverts the conventions established by a mainstream cinema dominated by the patriarchy's male gaze.

Committee: Steven Ross (Advisor); Lindsey Martin (Committee Chair); Erin Schlumpf (Committee Member); David Colagiovanni (Committee Member) Subjects: Film Studies; Gender

PhD, University of Cincinnati, 2020, Education, Criminal Justice, and Human Services: School Psychology

The current study is an exploratory evaluation of brief experimental analysis of reading comprehension interventions designed to develop a functional hypothesis of comprehension difficulties and inform intervention selection for parent implementation over time. Three students in Grades 6, 10, and 11 with significant weaknesses in reading comprehension were provided four different interventions specifically targeting each stage in the instructional hierarchy during the first BEA session. During the second BEA session, the interventions producing the greatest gains in reading comprehension rate were reevaluated in isolation and in combination. Using a brief multi-element design with mini reversals, a most effective intervention was identified by visually discriminable changes in level of responding across conditions. A parent-validation trial was also included. Differential effects were apparent for two of the three participants. Results are discussed in terms of future research.

Committee: Julie Morrison Ph.D. (Committee Chair); Renee Hawkins Ph.D. (Committee Member); Quintino Mano Ph.D. (Committee Member) Subjects: Psychology

Master of Science, The Ohio State University, 2020, Mechanical Engineering

The topic of this research is motivated by the practical needs in the automotive industry to design bolted connections at the interface between an attachment and a locally compliant thin-walled, sheet metal structure. Bolted connections introduce local stiffness and damping nonlinearities resulting in excitation dependent properties. This study focuses on developing a tractable laboratory experiment that includes a rigid box tube attachment bolted to a nut which is projection welded to thin-walled hat section. Dynamic linear and quasi-static nonlinear finite element models of the laboratory experiment are developed to gain insight of the modal properties and the nature of the bilinear stiffness of the experiment. Controlled uniaxial dynamic experiments are then carried out to capture the excitation level where the transition between linear and the amplitude dependent contact phenomena occur that results in normal vibroimpacts. Three types of excitation profiles - burst random, periodic chirp and narrow band sinusoidal sweep excitation are investigated with the use of an electrodynamic shaker. The measured experimental results are used as benchmark data to evaluate a model formulation and identify model parameters. The proposed nonlinear stiffness formulation accurately captures observed changes in the system natural frequency and the contact damping formulation reasonably captures the excitation amplitude damping properties. Such analytical models and benchmark experiments serve to aid in modeling bolted joints for use in virtual product development.

Committee: Scott Noll (Advisor); Shaun Midlam-Mohler (Committee Member); Luke Fredette (Committee Member) Subjects: Mechanical Engineering

MS, University of Cincinnati, 2019, Engineering and Applied Science: Mechanical Engineering

Riveted connections are widely used to join basic components, such as beams and panels, for engineering structures. However, accurately modeling joined structures with riveted connections can be a challenging task due to the riveting process of the connections. Solid rivets are ones of the most commonly used riveted connections. In the riveting process of a solid rivet, the rivet is inserted into matching holes of structural components to be joined, and a rivet setter and a bucking block are placed onto the rivet head and protruding end of the rivet shank, respectively. By simultaneously applying continuous loads to the rivet setter and holding the bucking block, the protruding end of the shank will be compressed and undergo plastic deformation. The riveting process of the rivet is concluded when the rivet shank is formed into a driven head. The riveting process is considered to be complex for two reasons. One reason is that the diameter of the shank increases due to its plastic deformation. The other reason is that surface contacts occur between the rivet and joined components and also between the joined components. In this work, an accurate linear finite element modeling method is proposed for joined structures with riveted connections. The proposed finite element modeling technique for a joined structure with riveted connections consists of two steps. The first step is to develop intensive finite element models that simulate the riveting process of solid rivets, where plastic deformations and surface contacts occurring to the rivets and components to be joined are considered. The second step is to develop a linear finite element model of the joined structure with the riveted connections simulated in the first step. The riveted connections are modeled using solid elements with dimensions and material properties obtained from the intensive finite element models in the first step. An experimental investigation was conducted to study the accuracy of the proposed fini (open full item for complete abstract)

Committee: Yongfeng Xu Ph.D. (Committee Chair); Jay Kim Ph.D. (Committee Member); Allyn Phillips Ph.D. (Committee Member) Subjects: Mechanical Engineering

MA, Kent State University, 2018, College of Arts and Sciences / Department of Sociology and Criminology

Sociologists have been unable to determine whether online communication supports the development of communities, or perhaps ironically, encourages increased isolation. The important question arises: can solidarity be established and maintained electronically (i.e., online). To address this question, I conducted an experiment that utilizes Fast Fourier Transform (FFT) methods to determine whether individuals can experience interpersonal synchronization and solidarity while interacting through different mediums. Results from this study show that face-to-face interaction produces greater feelings of solidarity than audio-only and audio/video forms of mediated communication, that audio/video produces less solidarity than audio-only interaction, and that the impact of communication medium on solidarity grows stronger over time. Further research is needed to fully understand the problems of solidarity in modern society, including the examination of other solidarity-producing forms of distance media.

Committee: Will Kalkhoff (Advisor) Subjects: Sociology

MA, Kent State University, 2016, College of Arts and Sciences / Department of Anthropology

This research elucidates the complex nature of pottery tempers used in the Scioto River Valley of south central Ohio. The data suggest that during the Late Prehistoric Period indigenous potters began using composite temper types with concretionary hematite as a secondary temper — most often found alongside shell as the primary temper. This project involved two phases 1) petrographic research and 2) mechanical properties testing. The initial research phase involved a detailed analysis of the clay matrix using polarized light microscopy. Precise temper densities were determined using point counting procedures. The second phase involved the production of test samples based on the petrographic data, followed by compressive bend testing of the experimental samples. The test samples were evaluated for mechanical strength, fracture toughness, and rate of thermal expansion. It was shown that hematite tempered samples exhibited significantly higher strength values—however, these samples fractured in a catastrophic manner signaling low post-peak toughness. The shell tempered samples exhibited the weakest strength values—however, they exhibited the most elasticity and most resistance to post-peak fracture. Based on the data, it is suggested that these two distinct temper types were being used in complement.

Committee: Linda Spurlock Ph.D. (Advisor); Richard Meindl Ph.D. (Committee Member); Metin Eren Ph.D. (Committee Member); Timothy Matney Ph.D. (Committee Member) Subjects: Ancient Civilizations; Archaeology; Materials Science