Master of Science, The Ohio State University, 2018, Mechanical Engineering

This research advances the state-of-the-art of analytical techniques to study the steady-state nonlinear dynamics of multi-degree-of-freedom, multistable structures subjected to harmonic excitations. A recently formulated analytical methodology, validated by numerical and experimental evidence, has been shown to accurately predict the steady-state dynamics of a discrete, multistable structure. Yet, the analysis is limited to lumped-parameter systems and cannot account for multiphysics phenomena, such as thermomechanical effects. Additionally, the analysis is challenged by an inefficient solution procedure, since the completeness of the dynamic predictions is highly dependent upon the generation of initial conditions. This research develops an enhanced solution procedure and normalization scheme to rectify these limitations, providing a robust and efficient analytical tool in the process. The analytical formulation is then extended to encompass distributed-parameter structures that exhibit global nonlinear coupling among all degrees-of-freedom in a form typical of reduced order models. In the process, assumptions inherent to traditional analyses, such as considering only single-degree-of-freedom systems or systems exhibiting weak nonlinear response, are overcome. Comparisons between the analytical and computational results indicate that the generalized analysis accurately characterizes the nonlinear dynamics of such multistable structures at speeds over two orders of magnitude faster than numerical simulation. Furthermore, the analysis is extended to encompass two-way coupling between thermal and mechanical domains, overcoming limitations of previous thermomechanical analyses. The thermomechanical analysis is capable of predicting the pre- and post-buckled nonlinear dynamics of a distributed-parameter beam model, the efficacy of which is verified with experimental evidence. In the process of developing these advancements to the analytical formulation, the analysis (open full item for complete abstract)

Committee: Ryan Harne (Advisor); Jack McNamara (Committee Member) Subjects: Mechanical Engineering; Mechanics

MS, University of Cincinnati, 2010, Engineering and Applied Science: Mechanical Engineering

Hypoid and spiral bevel gears, used in the rear axles of cars, trucks and off-highway equipment, are subjected to harmful dynamic response which can be substantially affected by the structural characteristics of the shafts and bearings. This thesis research, with a focus on gear-shaft-bearing structural analysis, is aimed to develop effective mathematical models and advanced analytical approaches to achieve more accurate prediction of gear dynamic response as well as to investigate the underlying physics affecting dynamic response generation and transmissibility. Two key parts in my thesis are discussed below. Firstly, existing lumped parameter dynamic model has been shown to be an effective tool for dynamic analysis of spiral bevel geared rotor system. This model is appropriate for fast computation and convenient analysis, but due to the limited degrees of freedom used, it may not fully take into consideration the shaft-bearing structural dynamic characteristics. Thus, a dynamic finite element model is proposed to fully account for the shaft-bearing dynamic characteristics. In addition, the existing equivalent lumped parameter synthesis approach used in the lumped parameter model, which is key to representing the shaft-bearing structural dynamic characteristics, has not been completely validated yet. The proposed finite element model is used to guide the validation and improvement of the current lumped parameter synthesis method using effective mass and inertia formulations, especially for modal response that is coupled to the pinion or gear bending response. Secondly, a new shaft-bearing model has been proposed for the effective supporting stiffness calculation applied in the lumped parameter dynamic analysis of the spiral bevel geared rotor system with 3-bearing straddle-mounted pinion configuration. Also, based on 14 degrees of freedom lumped parameter dynamic model and quasi-static three-dimensional finite element tooth contact analysis program, two typical s (open full item for complete abstract)

Committee: Teik Lim PhD (Committee Chair); Ronald Huston PhD (Committee Member); David Thompson PhD (Committee Member) Subjects: Mechanical Engineering

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

Master of Science in Engineering, University of Akron, 2017, Electrical Engineering

The permanent magnet assisted synchronous reluctance motor (PMa-SynRM) can be defined as a hybrid motor which utilizes the advantages of both the synchronous reluctance motor (SynRM) and the interior permanent magnet motor (IPM). PMa-SynRM's ability to have a wider flux weakening range and less risk of demagnetization makes it a perfect candidate for high-speed applications. However, one of the main challenges for PMa-SynRM operating as a high-speed motor is the stress generated in the rotor. This thesis presents an optimal design procedure and rotor shape modification of a high-speed multiphase PMa-SynRM for stress reduction. In this study, a high-speed design of a five-phase PMa-SynRM has been done based on a low-speed benchmark model. An overall design procedure consisting of a lumped parameter model (LPM) and a differential evolution strategy (DES) was developed. In this study, a lumped parameter model (LPM) is used to initially design the five-phase PMa-SynRM. By using LPM and design parameters of stator and rotor with given ranges, thousands of design have been generated. From these designs, an optimal high-speed model was developed with the help of a differential evolution strategy (DES). To facilitate high-speed design, a stress function and other performance parameters are included in the objective function (OB). The optimized 25krpm five-phase PMa-SynRM is implemented in the finite element analysis (FEA) for simulation. Simulation results of the average and cogging torque high-speed model have been analyzed. Another high-speed model has been developed without considering stress function in the design. Comparison of stress has been done between the two high-speed models by doing stress analysis. Simulation results indicated that stress can be reduced by 30.14% if it is included in the design process. To reduce the stress of the high-speed PMa-SynRM more, a mini flux barrier (FB) has been added to the rotor. By using DES, the design parameters of (open full item for complete abstract)

Committee: Seungdeog Choi (Advisor); Yilmaz Sozer (Committee Member); Joan Carletta (Committee Member); Siamak Farhad (Committee Member) Subjects: Engineering

Master of Science, University of Akron, 2017, Electrical Engineering

With the advent of high power density motors in applications such as electric vehicles, the need for an effective thermal analysis of motors is further warranted to ensure their efficient and reliable operation. While existing Lumped Parameter Thermal Models (LPTMs) provide a convenient method for the thermal evaluation of motor designs, they provide a single, average temperature of the various regions of the motor without data on the temperature variation in the axial direction. LPTMs are a convenient reduced finite-element method to analyze the thermal performance of electric motors based on their design parameters and operating conditions. In this thesis the thermal analysis of a Permanent Magnet Assisted Synchronous Reluctance Motor (PMa-SynRM) is conducted by proposing two LPTMs: 1. Radial Lumped Parameter Thermal Model (R-LPTM). 2. Axial Lumped Parameter Thermal Model (A-LPTM). The R-LPTM adopts an existing approach considered for the thermal modeling of interior rotor configurations with the key contribution being the modeling of the unique rotor configuration of the PMa-SynRM under study. In this approach, the individual geometries of the motor are modeled as single nodes, the voltages of which correspond to the average temperature for the respective machine part. The A-LPTM introduces a novel thermal model by employing the Finite Volume Method (FVM). While the R-LPTM models heat flow only in the radial direction due to the lamination structure of the stator and the rotor regions, the extension of this approach to the axially thermally shorted conductor coil sides, the magnets and the shaft results in a relative oversimplication of the heat transfer in these regions. While equivalent lumped thermal resistances model axial heat flow in these regions in the R-LPTM, by employing the FVM in the A-LPTM a higher resolution of axial temperature data is determined by providing a more accurate method of radial and axial heat flow modeling in these re (open full item for complete abstract)

Committee: Seungdeog Choi (Advisor); Guo-Xiang Wang (Committee Member); Malik Elbuluk (Committee Member); Jin Kocsis (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy, The Ohio State University, 2015, Electrical and Computer Engineering

The unique spectroscopic utility and high spatial resolution of terahertz (THz) waves offer a new and vastly unexplored paradigm for novel sensing, imaging, and communication applications, varying from deep-space spectroscopy to security screening, from biomedical imaging to remote non-destructive inspection, and from material characterization to multi-gigabit wireless indoor and outdoor communication networks. To date, the THz frequency range, lying between microwave and infrared bands, has been the last underexploited part of the electromagnetic (EM) spectrum due to technical and economical limitations of classical electronics- and optics-based system implementations. However, thanks to recent advancements in nano-fabrication and epitaxial growth techniques, sources and sensors with cutoff frequencies reaching the submillimeter-wave (sub-mmW) band are now realizable. Such remarkable improvement in electronic device speeds has been achieved mainly through aggressive scaling of critical device features, such as the junction area for Schottky barrier diodes (SBDs), and the gate length in high electron mobility transistors (HEMTs). Such aggressively-scaled and refined device topologies can significantly enhance the intrinsic device capabilities, however, the overall device performance is still limited by the parasitic couplings associated with device interconnect metallization. Consequently, geometry- and material-dependent parasitic couplings, induced by EM field interactions within the device structure, exacerbate the performance and diminish the gains achieved by the improved intrinsic device behavior. In particular, as the operation frequency approaches the THz barrier, device dimensions become comparable to signal wavelength. The main objective of this dissertation is to develop accurate lumped- and distributed-element equivalent circuits, and full-wave EM simulation-based iterative parameter extraction algorithms, (open full item for complete abstract)

Committee: Kubilay Sertel (Advisor); Fernando Teixeira L. (Committee Member); Patrick Roblin (Committee Member); Gary Kennedy (Committee Member) Subjects: Electrical Engineering

Master of Science, The Ohio State University, 2014, Mechanical Engineering

Elastomeric joints are utilized in many automotive applications, and exhibit frequency and excitation amplitude dependent properties. Commercial methods identify only cross-point joint property using displacement excitation at stepped single frequencies. This process is often time consuming and is limited to measuring a single dynamic stiffness term of the joint stiffness matrix. This study focuses on developing tractable laboratory inverse experiments to identify frequency dependent stiffness matrices up to 1000 Hz. Direct measurements are performed on a commercial elastomer test system and an inverse experiment consisting of an elastic beam (with a square cross section) attached to a cylindrical elastomeric joint. The experimental methods are applied to two different elastomeric materials of the same geometry. Sources of error in the inverse methodology are thoroughly examined and explained through simulation which include ill-conditioning of matrices and the sensitivity to modeling error. The identified translational dynamic stiffness and loss factor values show good agreement between the two identification methods, though challenges remain for the rotational and coupling stiffness terms.

Committee: Rajendra Singh (Advisor); Scott Noll (Committee Member); Brian Harper (Committee Member) Subjects: Mechanical Engineering

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

Hand-Arm Vibration Syndrome (HAVS) collectively refers to diseases associated with prolonged, intensive exposure to hand-transmitted vibrations. Millions of construction workers who use hand-held power tools are affected by HAVS in the United States. Numerous dynamic models of the hand-arm system were developed to better understand the injury mechanism. One of the problems in dynamic response analysis of the hand-arm system has been difficulty in finding the excitation forces generated by the operation of hand-held tools. Especially, the force transmitted to the hands from the tool and the force interacting between the tool and work-piece are very useful information in hand-arm vibration study; however, they cannot be measured directly. Methods to estimate these forces are developed in this work by utilizing a hand-arm model, the acceleration measured at the hand, and two measured transfer functions of the tool. Experimental validation procedures of the methods are devised, which show the estimated forces are accurate enough to be used for practical applications. The method developed in this work enables estimation of the force acting between the tool and workpiece in a hand-held power tool in operation for the first time. There are many potential applications of the method developed in this work. For example, the methods can be used to make design changes in the handle bar of a grinder to reduce vibration transmission to the hands, ultimately leading to a lower frequency of HAVS.

Committee: J. Kim Ph.D. (Committee Chair); Thomas Richard Huston Ph.D. (Committee Member); David Thompson Ph.D. (Committee Member) Subjects: Engineering

MS, University of Cincinnati, 2004, Engineering : Mechanical Engineering

Friction has been a complicated subject to understand for many years. Much can be attributed to the complex, non-linear nature of friction and its implicit influence on the system parameters. Besides research pointed at understanding the fundamental principles and characters of friction, the interaction of friction dynamics and system dynamics has been a study of much interest. This work covers the interaction of friction and system dynamics. Two different models involving dry friction, distinguished by the number of DOF have been studied: - Single-DOF model with external excitation (Den Hartog's model) - Two-DOF model with external excitation (Extension of Pratt & William's model). The first model is studied to understand the general response characteristics like stick-slipbecause of friction and external forces. The latter part of this work is an extension to the second model. The results obtained have been validated with earlier works to show more confidence in the observations made thereafter. The difference in the system parameters on the masses brings asymmetry in the system. This is studied in the joint problem. Two resonant peaks are observed in the FRF plot for an unsymmetrical system; the resonant frequency peaks shift farther from each other with increasing unsymmetry in the system. Also, the influences of normal load and excitation frequency on the percentage stick, energy dissipation and frequency shifts are studied. Better understanding of the joint dynamics with friction interfaces provides necessary insight into the uses and effects of friction damping so as to increase the energy dissipation and minimize unwanted response.

Committee: Dr. Edward Berger (Advisor) Subjects:

PhD, University of Cincinnati, 1999, Engineering : Environmental Engineering

Increasing regulatory pressure for VOC emissions reduction has accelerated the development of more cost effective VOC air pollution control (APC) technologies. Biofiltration is a viable technology to fill this role, for the purification of air streams polluted with biodegradable VOCs. In the biofilter, these pollutants diffuse from the air stream into a stationary mass of moist biological film, where they are oxidized by enzymatic catalysis at ambient pressures and temperatures. Properly operated, this natural, biological mineralization process will produce only benign by-products, such as inorganic salts, carbon dioxide, and water, with some additional biomass. Although research into the science and development of the technology of biofiltration has been performed for over fifteen years, biofiltration remains not widely accepted as a proven technology for VOC APC. This perception is especially true for applications treating high influent VOC concentrations and requiring high VOC removal efficiencies. This research was undertaken to develop a new, cost effective biofiltration technology which can reliably treat air streams polluted with high VOC concentrations and achieve very high removal (elimination) efficiencies. Investigations were made to evaluate different biological attachment media, in order to identify the medium most suited to such an application. Using this medium, a reliable biofiltration technology was developed and extensively tested, which can achieve the goal of reliably treating high concentrations of VOCs at high loadings with high removal efficiency. Techniques for the management and control of the accumulating by-product biomass were developed. Procedures are presented for the calculation of VOC solubility and biological kinetic parameters, at the biofiltration operating temperature. A procedure for estimating the upper limit for biofiltration for the influent air VOC concentrations is presented. A simple, explicit biofilter design equation was (open full item for complete abstract)

Committee: Makram Suidan (Advisor) Subjects:

MS, University of Cincinnati, 2002, Engineering : Mechanical Engineering

Friction is one of the oldest problems that has been studied intensively for several hundred years by many researchers. The underlying reason for this is the complex nature of friction and its strong influence on the behavior of various physical systems. Vast amount of research work can be found in literature that primarily aims at understanding the underlying mechanism of these kinds of system behavior. This thesis work is a step in the same direction. It investigates the effect of variation of system parameters on the stick-slip response of the following three models that are widely used for modeling various physical systems with dry sliding friction: • Self-excited friction oscillator without external excitation • Friction oscillator with external excitation (Den Hartog's model) • Friction interface modeling using bilinear hysteresis elements Simple, low order, lumped, macroslip mathematical models used in these studies do not accurately predict the actual system behavior. However these studies give insight into the similarities and differences between the three models and aid designers and researchers to select appropriate model for analyzing the behavior of actual physical system with dry friction. A new approach based on continuous microslip model for analyzing the response of frictionally damped turbine blades is also discussed in this work with emphasis on the need to integrate the model based on this more accurate approach with existing industrial computational tools for the system response predictions.

Committee: Edward Berger (Advisor) Subjects: Engineering, Mechanical