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Zemba, Michael JSite Characterization of Phase Instability via Interferometer Measurement
Master of Science in Engineering, University of Akron, 2013, Electrical Engineering
Single-dish reflector antennas are often used for their ability to produce a highly directive (narrow beam) radiation pattern which increases in directivity as the diameter of the reflector increases. However, as reflectors grow larger in the pursuit of more directivity, they become more expensive and unwieldy to construct, maintain, and operate. A more practical solution is to employ an array of elements which are smaller individually, but which can yield similar or better gains when arrayed together. However, one trade-off associated with this approach is that antenna arrays are subject to losses introduced by atmospheric turbulence. Inhomogeneous cells of water vapor in the troposphere change the refractivity of the air along the path of the propagating wave, distorting the wavefront and introducing a phase error between the elements of the array. These losses are stochastic and site-dependent. Techniques have been developed over the past several decades to compensate for such losses on the receiving end, but uplink arraying remains challenging as it requires prediction of atmospheric conditions to effectively compensate the signal before transmitting. This is especially true at higher frequencies such as Ka-band given that atmospheric phase noise increases with frequency. Thus, a critical first step in system planning is to determine the losses a particular array configuration will experience based on the phase statistics of a given site. To this end, NASA Glenn Research Center has deployed site test interferometers to three ground-station sites with the intent to characterize their phase instability ahead of upgrades to Ka-Band operation. The sites to be studied are Goldstone, California; White Sands, New Mexico; and the island of Guam. Using three years of data collected from these campaigns, the primary goal of this thesis is to develop a thorough characterization of the phase statistics of each site which may then be used to determine the sites’ suitability for uplink arraying. In addition, a secondary goal is the development of the data analysis software suite that was used to process the data, which it is hoped will facilitate easy analysis of future sites for system designers.

Committee:

Nathan Ida, Dr. (Advisor); Igor Tsukerman, Dr. (Committee Member); Subramaniya Hariharan, Dr. (Committee Member)

Subjects:

Aerospace Engineering; Electrical Engineering; Electromagnetics; Electromagnetism; Engineering

Keywords:

Antenna Arrays; Phase Noise; Atmospheric Phase Instability; Propagation Measurements; Interferometry; NASA; Ka-Band; Radio Frequency; Electrical Engineering; Electromagnetics; Antennas; Propagation; Site Test Interferometer

Chamberlin, Kent A.Investigation and development of VHF ground-air propagation computer modeling including the attenuating effects of forested areas for within-line-of-sight propagation paths
Doctor of Philosophy (PhD), Ohio University, 1982, Electrical Engineering & Computer Science (Engineering and Technology)

Investigation and development of VHF ground-air propagation computer modeling including the attenuating effects of forested areas for within-line-of-sight propagation paths

Committee:

Richard McFarland (Advisor)

Keywords:

VHF ground-air propagation; computer modeling; propagation paths; attenuating effects

Sundaram, PreethiNew Results For Characterization Of Indoor Channels In Two Ism Bands (900-928 Mhz And 2.4-2.5 Ghz)
Master of Science (MS), Ohio University, 2006, Electrical Engineering & Computer Science (Engineering and Technology)

This work is a collection of new measurement results for indoor channel characteristics in two unlicensed bands. Part of the work is also an extension of another Ohio University student’s MS Thesis [3]. The effects of human movement on the propagation characteristics were not taken into consideration in that work, and that is one of our contributions here. The measurement and characterization of propagation path loss vs. distance on single and multiple floors with and without the movement of people in an indoor environment were performed. It has been observed that the propagation within buildings is strongly influenced by specific features such as the layout of the building, construction materials, and the building type. We have used our measurements and results from a database to estimate building material composition. A widely used propagation model is one in which there is a dominant signal arriving along with many weaker signals: this gives rise to a Ricean amplitude distribution. We have computed the Rice factor from our measurements, using the moment estimation method. We have also made a first attempt to estimate the Doppler spectrum from the signal power samples due to the time variations of the scatterers.

Committee:

David Matolak (Advisor)

Keywords:

Indoor Channel Characterization; Path Loss Measurements; Ricean K Factor; Doppler Spectrum;Indoor Propagation; Outdoor Propagation

Hassan, Mohamed K. I.Novel Elastomers, Characterization Techniques, and Improvements in the Mechanical Properties of Some Thermoplastic Biodegradable Polymers and Their Nanocomposites
PhD, University of Cincinnati, 2004, Arts and Sciences : Chemistry

This work focused in its first part on the preparation and characterization of novel elastomers based on poly(tetrahydrofuran) (PTHF) networks. Elastomers were prepared by a hydrolysis-condensation reaction which has been followed up by FTIR spectroscopic techniques. The elastomers thus obtained were studied with regard to their equilibrium swelling in toluene at 25 °C, and their stress-strain isotherms in elongation. For some of the samples, high elongations seemed to bring about highly desirable strain-induced crystallization, as evidenced by upturns in the modulus. Swelling of these samples with increasing amounts of the non-volatile diluent dibutyl phthalate caused the upturns to gradually disappear.

The second part of this work was focused on diversifying the newly developed sound wave propagation technique to characterize elastomeric polymer networks. The technique was applied to characterize polybutadiene (PBD) networks. The speed of wave propagation in PBD networks was found to be strongly dependent on the network structural parameters such as average molecular weight of chain between crosslinks and entanglement molecular weight. Also, for the swollen networks, pulse speeds decreased with increase in degree of swelling. Upturns due to strain-induced crystallization at higher elongations were clearly evidenced in the pulse speeds.

The third part of this work presented improvements in the mechanical properties of thermoplastic biodegradable poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (Nodax™) using a pre-orientation technique. This simple approach involved heating the polymer film to a temperature above its glass transition temperature, stretching it to the desired extension (%), and then quenching it to room temperature while in the stretched state. As expected, pre-orientation resulted in substantial improvements in the mechanical properties of the films. The pre-oriented films had higher values of the modulus, toughness, yield stress, and tensile strength. Attributing these changes in mechanical properties to changes in crystallinity was supported by x-ray diffraction measurements.

The fourth part focused on the preparation and characterization of Nodax™/clay nanocomposites which were prepared by exfoliation-adsorption technique using chloroform as a solvent. X-ray diffraction measurements showed a transition in the nanocomposite structure from exfoliated to intercalated depending on organoclay content. Improved thermal stability and increased modulus were observed for the nanocomposites by increase in clay content.

Committee:

Dr. James Mark (Advisor)

Keywords:

poly(tetrahydrofuran); Elastomers; Networks; Endcapping; Sol-gel condensation; Cage-like structures; Equilibrium swelling; Stress-strain measurements; Moduli; Strain-induced crystallization; Ring-opening polymerization; Pulse speed propagation

Kilburn, KoreyA Laplace Transform/Potential-Theoretic Method for Transient Acoustic Propagation in Three-Dimensional Subsonic Flows
Doctor of Philosophy, University of Akron, 2010, Engineering-Applied Mathematics
This dissertation presents the development of a semi-analytic technique developed for the determination of far field acoustic radiation in the time domain. This method solves linear, time dependent wave propagation in an unbounded medium using a numerical Laplace transform and potential theory. The end result is a robust procedure that is accurate and computationally efficient. The Transform Potential Theoretic (TPT) method is meshless and can handle arbitrary geometries. The procedure assumes the linearity of the sound field away from a bounded region surrounding the object. The TPT method depends on the sound pressure on the boundary of this region (referred to as the Kirchhoff surface). The Euler equations are linearized about a uniform mean flow. First, the problem is transformed via the Laplace transform (with appropriate initial conditions) into a reduced wave equation. By application of a dependent variable transformation, the anisotropic terms are removed and a Helmholtz-like equation with complex wave number is obtained where both single and double layer potential theory applies. This allows the calculation of the far-field acoustic pressure in the Laplace domain. Then, an inversion of the dependent variable transform is applied. Upon application of numerical inverse Laplace transform techniques, far-field acoustic pressure is then successfully obtained as a function of space and time. Using transient monopole radiation in a uniform freestream, accuracy is analyzed with excellent results. This method shows many advantages over direct simulation, including vast savings in computational time. The freestream Mach number is only a parameter in the TPT method and has no bearing on the run time, unlike direct methods.

Committee:

Scott Sawyer, PhD (Advisor)

Subjects:

Acoustics; Engineering; Physics

Keywords:

Aeroacoustics; Potential Theory; TPT; Transient Acoustic Propagation; Three Dimensional; Subsonic Flows; Exterior Problem

Cheng, WenPropagation of Vortex Beams through a turbulent atmosphere
Master of Science (M.S.), University of Dayton, 2009, Electro-Optics

This thesis study and compare the propagation properties of both scalar and vector vortex beams through turbulent atmosphere. The irradiance pattern, degree ofpolarization, and scintillation index of radially polarized beam are computed for different propagation distance into an atmosphere with weak and strong turbulence. Corresponding properties of a fundamental Gaussian beam, a scalar vortex beam with topological charge of +1 propagating through an atmosphere under the same turbulence condition are calculated for comparison.

The results demonstrate that the existence of the vectorial vortex can be identified with longer propagation distance than the scalar vortex even with disappearing characteristic vortex structure in the irradiance images. This indicates the potential advantages of using vector vortex to mitigate atmospheric effects and enable a more robust free space communication channel with longer link distance.

Committee:

Qiwen Zhan, PhD (Advisor); Joseph Haus, PhD (Committee Member); Peter Powers, PhD (Committee Member)

Subjects:

Optics

Keywords:

Vortex Beam Propagation; Turbulence; Scintillation Index

Zhang, QianWireless Near-ground Channel Characteristics in Several Unlicensed Bands
Master of Science (MS), Ohio University, 2008, Electrical Engineering (Engineering and Technology)
This thesis presents a statistical wireless channel characterization for near-ground antennas in both indoor and outdoor environments based on narrowband and wideband measurements. We took measurements in both line of sight and non-line of sight regions. For the narrowband case, we measured indoors, in the 900 MHz and 2.4 GHz unlicensed bands. Results for the narrowband near-ground indoor channels include channel power versus frequency responses and corresponding distributions of relative received power over the measured bands. For the wideband near-ground indoor and outdoor channels, measured in the 5 GHz band, channel impulse response statistics, including delay spreads and coherence bandwidth, were obtained from power delay profiles. Wideband channel models were developed from the measurements, and these models include statistical characterizations of Markov tap persistence process parameters, tap energies, tap fading amplitudes, and correlations among taps. The wideband channel models were developed for a 10 MHz channel bandwidth. As expected, the near-ground channels yield more dispersion and deeper fading than their counterparts with elevated antennas.

Committee:

David W. Matolak, PhD (Advisor)

Subjects:

Electrical Engineering

Keywords:

wireless channel; propagation; near-ground channel characterization

Oguntade, Ayoade O.Range Estimation for Tactical Radio Waveforms using Link Budget Analysis
Master of Science in Electrical Engineering, University of Toledo, 2010, Electrical Engineering

The increasing need to design multiband tactical radio communication modems that will incorporate several waveforms has made the investigation of the performance of different tactical waveforms absolutely necessary. These different waveforms must also meet various demands in quality and nature of data. Range maximization, high data throughput, and power conservation requirements are usually not fulfilled by a single waveform. To effectively deliver tactical multimedia data including coded audio, text, video, map, and navigation information using radio, multiple choice of frequency bands exist. These include: HF, VHF and UHF. However, along with the effective delivery of quality data, the maximization of transmission range under hostile propagation environments – especially under terrain blockage in ground-to-ground (GTG) communication scenario - is of utmost importance.

This thesis discusses the results of Link Budget Analysis (LBA) performed for the estimation of maximum delivery range of tactical radio waveforms using variety of data rates for three typically different waveforms – High Frequency Waveform (HFW), Very High Frequency Waveform (VHFW) and OFDM based Wideband Network Waveform (WNW). Center frequencies of 27 MHz, 60 MHz, and 500 MHz respectively were used for the simulations.

Results show that HFW produces the longest range, followed by VHFW and the WNW – which delivered the highest data rate. Also, the amount of variation in propagation range that was noticed while parameters like center frequency, antenna height, antenna gain, transmitter power were varied were also computed.

Committee:

Junghwan Kim, PhD (Committee Chair); Lawrence Miller, PhD (Committee Member); Ezzatollah Salari, PhD (Committee Member)

Subjects:

Electrical Engineering

Keywords:

Link Budget Analysis; OFDM; Orthogonal Frequency Division Multiplexing; Propagation Modeling; Wideband Network Waveform; WNW;

Li, JiaUltrasonic Characterization of Polycrystals with Texture and Microtexture: Theory and Experiment
Doctor of Philosophy, The Ohio State University, 2015, Welding Engineering
When an ultrasonic wave propagates in polycrystalline materials, the wave is scattered on grain boundaries and the scattered waves carry important information on material microstructure, e.g. grain size and texture. Using grain scattering information for nondestructive testing purposes can be useful as quality control in many manufacturing processes. In particular, measurement and interpretation of ultrasonic scattering can be very useful in the development of practical methods for nondestructive ultrasonic characterization of microtextured regions in titanium alloys that are widely used for aeroengine components. Ultrasonic scattering and scattering-induced ultrasonic attenuation are two measurable ultrasonic characteristics that can be employed for material microstructures characterization. Most past studies address ultrasonic attenuation and scattering in polycrystals with macroscopic isotropy or simple artificial textures and equiaxed grains of high crystallographic symmetry (cubic or hexagonal). However, most manmade materials, as a result of thermomechanical processing, exhibit nonequiaxed grains and complex forms of macroscopic texture. One objective of this dissertation is to provide a better understanding of ultrasonic propagation and scattering in textured polycrystyals. In this dissertation, general attenuation and scattering models are developed for polycrystals with arbitrary macrotexture and ellipsoidal grain shape with triclinic symmetry. The attenuation coefficients were derived in the Born approximation by generalizing previous theoretical models that were suitable for equiaxed grains and uniaxial hexagonal textures. The general scattering coefficients were obtained from the integrand of the attenuation coefficients. The second major objective is to ultrasonically characterize the microtextured regions (MTRs) in Ti alloys which is a result of orientation clustering of crystallites and leads to a reduction of dwell fatigue properties of the material. The models developed are extended to titanium alloys with those dual-scale microstructures. The third objective of this dissertation is to establish an inversion methodology to robustly reconstruct material characteristics from ultrasonic attenuation and backscattering measurements. By using a combination of the attenuation-to-backscattering ratios and directional backscattering ratios, an inversion procedure is developed for a complete reconstruction of MTR sizes and its effective elastic parameters. The experimental methodology and the system calibration method are described for the near field of the ultrasonic transducer measurements. Examples of measurements and application of inversion models to typical titanium alloy samples are given. It is shown that in general, the MTR sizes and the microtexture parameters determined by ultrasonic inversion models are in reasonable agreement with those measured by others on the same samples by destructive electron backscatter diffraction (EBSD) characterization methods.

Committee:

Stanislav Rokhlin (Advisor); Dave Farson (Committee Member); Daniel Mendelsohn (Committee Member); Adam Pilchak (Committee Member)

Subjects:

Acoustics; Materials Science

Keywords:

ultrasound propagation and scattering; material characterization; macrotexture and microtexture

Hashtroodi, SeyedowjanCrack Propagation Analysis of a Pre-stressed L-shaped Spandrel Parking Garage Beam
Master of Science, University of Toledo, 2014, Civil Engineering
Recently, a pre-stressed spandrel L beam of a parking garage at Northwest Ohio failed. Upon visiting the site and inspecting the beam, it was illustrated that the beam had experienced a sudden, brittle failure. This was concluded due to the fact that there was only one dominant crack which had propagated through the depth of the beam at the mid-span. There was no sign of any other equivalently distributed micro-cracks, which would normally form in ductile structures prior to failure. In order to further investigate and understand the sudden failure of the pre-stressed spandrel L-shaped parking garage beam, it was decided to perform analytical and numerical analysis of the beam. Primary, hand calculations was performed by use of MathCAD to compute ultimate moment capacity and the cracking moment of the beam based on PCI and ACI 318 codes. According to ACI 318-11, if the ratio of ultimate moment capacity over cracking moment exceeds 1.2, then the structure should be ductile enough to undergo considerable deflection before failure. Moreover, in a ductile member, equivalently distributed cracks visible to naked eye would warn when the member’s nominal strength is approached, so that immediate occupancy and safety regulations could be applied. Secondly, RESPONSE2000 was used for cross-sectional analysis of the beam and validation of hand calculation results by MathCAD in order to conduct the rest of the study in a more efficient, less time consuming manner. Moreover, a few damage scenarios have been proposed for the beam; in which, a number of strands have been considered fully corroded by removing them from the model. For each scenario, using RESPONSE2000, the ultimate moment capacity over cracking moment ratio have been calculated to figure out the exact number of corroded strands needed for the beam to experience brittle failure. Crack patterns throughout the length of the beam and the existence of a dominant macro-crack was also studied and validated. Finally, after conducting extensive literature review, Abaqus software was chosen for simulation purposes of the crack propagation along the depth of the beam. A three-dimensional finite element model of the pre-stressed parking garage beam was created by use of SolidWorks and Abaqus software. One initial crack was defined at mid-span of the beam by modelling a cohesive segment surface which would allow the crack to open up and propagate through the depth of the beam when the stress exceeds the corresponding limit.

Committee:

Douglas K. Nims (Committee Chair); Mark A. Pickett (Committee Member); Liangbo Hu (Committee Member)

Subjects:

Engineering

Keywords:

Crack Propagation; pre-stressed concrete; prestressed concrete; Finite Element; Abaqus; RESPONSE2000; MathCAD; Parking Garage; Spandrel Beam;

Deogekar, Sai SharadA Computational Study of Dynamic Brittle Fracture Using the Phase-Field Method
MS, University of Cincinnati, 2015, Engineering and Applied Science: Mechanical Engineering
This thesis describes the use of the phase-field method to model and simulate dynamic crack propagation in brittle materials. In this method, the discrete crack is modeled as a smeared or diffuse interface using a continuous phase-field. In the solid phase, the phase-field takes on the value one, while it is zero in the crack phase. A length parameter is introduced into the problem to model the thickness of the transition region between the solid and crack phases. To capture the weakening of the material in the crack phase, the constitutive response is modified to depend on the local value of the phase-field. The evolution of the phase-field is described by a partial differential equation derived using variational arguments. This leads to a coupled system of two partial differential equations for the displacement field and the phase-field, which is solved using a staggered nonlinear finite element method. The phase-field approach does not require numerical tracking of the discontinuities in a domain and is able to capture complex crack behavior such as branching and merging/interaction of cracks without any ad hoc criteria for crack nucleation. In this work, we implement the phase-field formulation for two-dimensional domains under plane strain conditions. We use this implementation to study various cases of dynamic brittle fracture, namely the interaction between two cracks and the crack propagation in composite materials. We simulate the interaction between two cracks, under both static and dynamic loading, for various distances between the crack tips. The results from our dynamic simulations indicate that, unlike crack interaction under quasi-static or fatigue loading, the presence of another crack does not accelerate crack propagation when dynamic loads are applied. However, some similarities in the crack topologies are observed between the quasi-static and dynamic loading. We also use this method to model dynamic crack propagation in laminated and fibrous composites successfully. We observe that the crack branches and the crack path changes so as to evade the tougher material

Committee:

Kumar Vemaganti, Ph.D. (Committee Chair); Woo Kyun Kim, Ph.D. (Committee Member); Yijun Liu, Ph.D. (Committee Member)

Subjects:

Mechanics

Keywords:

Phase-field method;Dynamic brittle fracture;Crack interaction;Crack propagation in composites;Multiple cracks

Bricker, David A.Analysis of Joint Effects of Refraction and Turbulence on Laser Beam Propagation in the Atmosphere
Master of Science (M.S.), University of Dayton, 2013, Electro-Optics
Experimental data obtained from recently conducted long-range laser beam propagation experiments has revealed inconsistencies with analytic and numeric simulations results based on classical Kolmogorov turbulence theory. This inconsistency may be related with not accounting for refraction effects caused by refractive index variation with elevation and presence of large-scale atmospheric structures which introduce refractive index gradients and can alter the trajectory of optical wave energy flux. In this thesis, atmospheric refraction effects are studied using a ray tracing technique. Due to refraction a ray propagating in the atmosphere doesn't follow a straight line and may not arrive to a desired location. In this thesis the ray tracing technique was applied for analysis of optical propagation over a 150 km propagation path. It was shown that due to refraction the ray trajectory may deviate from the geometric straight line by 60m in the middle of the path. We also considered the impact of refraction on atmospheric propagation of laser beams with different wavelengths (λ=0.532µm, λ=1.064µm, and λ=1.550µm) which were launched at the same angle. Due to the difference in refractive index of air for different wavelengths, the ray's paths follow different trajectories. It was shown that at the end of the propagation path, the distance between ray trajectories can be as long as ~4.1m for the 0.532µm and the 1.064µm rays, and ~4.3m for 0.532µm and 1.550µm rays. Besides traditional ray tracing technique we also introduced a new computational method that allows analysis of combined refraction and turbulence effects on laser beam propagation. In this method, traditional beam propagation using the well-known split step operator method is combined with ray tracing. In this technique the atmospheric volume is represented as a set of thin phase screens that obey Kolmogorov turbulence statistics. The ray tracing technique is applied to describe optical wave propagation between phase screens. At each screen, the turbulence-induced random tip and tilt wave-front phase component is added to the ray angle. In this way, the ray trajectory is no longer deterministic, but it has a turbulence induced uncertainty. It was shown that at the end of a 150km propagation path, the turbulence induced deviation on ray trajectory can be on the order of 5m. These results show that for correct analysis of laser beam propagation over long distances in the atmosphere, refraction and turbulence effects should be considered jointly. The proposed numerical simulation technique allows this joint analysis.

Committee:

Mikhail Vorontsov, Ph.D (Advisor); Partha Banerjee, Ph.D (Committee Member); Paul McManamon, Ph.D (Committee Member)

Subjects:

Optics

Keywords:

Atmospheric Turbulence, Ray Tracing, Numerical Simulation, Laser Beam Propagation

Vural, SerdarInformation propagation in wireless sensor networks using directional antennas
Doctor of Philosophy, The Ohio State University, 2007, Electrical Engineering
The information propagation capability of Wireless Sensor Networks (WSN) is directly related with the properties of multihop paths. Two main measures of the multihop data propagation capability are the maximum Euclidean distance that can be covered in a multihop path and the effectiveness of the medium access control (MAC) protocol. To achieve high propagation capacity, MAC protocols should enhance the channel use by maximizing simultaneous traffics and reducing end-to-end delay in high data load scenarios often encountered in WSN data collection applications. In this regards, directional antennas offer various benefits such as the extended communication ranges, spatial reuse capability, and reduced interference patterns that enable higher network performance compared to omnidirectional antennas. In this thesis, the maximum multihop Euclidean distance covered by directional packet transmissions is evaluated for both linear and planar WSNs using analytical modeling of distance distributions. Expressions for calculating the distribution parameters are derived and provided. Comparison of experimental and analytical results demonstrate the high accuracy of the proposed models in estimating distance distributions. Furthermore, a WSN security application which utilizes the derived models for verifying sensor locations is presented. The second contribution of this thesis is the Smart Antenna-Based MAC (SAMAC) protocol designed for multihop data collection applications for WSNs with sectored antennas. A detailed protocol description as well as performance evaluation results are provided. Simulation results demonstrate that SAMAC with sectored antennas improves end-to-end delay, data throughput, and data delivery ratio under high data generation rates and highly loaded traffic conditions compared to IEEE 802.11 with omnidirectional antennas.

Committee:

Eylem Ekici (Advisor)

Keywords:

wireless sensor networks; directional antennas; information propagation

Srikasem, SuthumWave reflection in uniaxially anisotropic media
Master of Science (MS), Ohio University, 1987, Electrical Engineering & Computer Science (Engineering and Technology)

The science of optics is very old, but now there have been a number of new and far reaching developments. The most notable among these is the laser and its applications. The field of fiber optic communications has also been a rapidly changing one. These, and other innovations have resulted in a remarkable upsurge in the importance of optics in both pure science and in technology. The technological improvement in the fabrication of optical fibers, interconnection devices, cables, source and detectors has moved from the early stage into a major industry in the 1980s[7].

The theory of propagation and excitation of electromagnetic waves have been studied for a long period of time. Most of the previous studies on these subjects considered in solving the problem of wave reflection from the surface of an anisotropic medium and propagation in an anisotropic medium by the incident wave in isotropic medium. [3,4,5].

The object of this thesis is to present a study of the reflection in a uniaxially anisotropic medium from the surface of an isotropic medium. These media are considered source - free and homogeneous. We adopt the coordinate - free approach, introduced by Chen [6], as a mathematical means that greatly facilitates the solutions of our problems. This method is based on the direct manipulation of vectors, dyadics, and their invariants, eliminates the use of coordinate systems since the coordinate method renders not only the computation extremely tedious and complicated, but also the final results are difficult to interpret.[8]

Committee:

Hollis Chen (Advisor)

Keywords:

Wave Reflection; Uniaxially Anisotropic Media; Propagation; Excitation of Electromagnetic Waves

Zheng, HuiApplication of the hybrid finite element procedure to crack band propagation
Master of Science (MS), Ohio University, 1987, Civil Engineering (Engineering)

The crack band modeling of the fracture of concrete has so far been numerically studied only for the displacement finite element procedure. In this thesis, a hybrid stress model is applied to problems in the fracture of concrete. The results of this model are compared with those obtained from the displacement method, experimental data and exact solutions. It is shown that the hybrid stress model can provide results closer to the experimental data and less bias in the mesh direction than those obtained from the displacement finite element method.

The propagation of a crack for a concrete beam on an elastic foundation is also studied. A thin-layer interface element is used to simulate the interaction between the beam and elastic foundation.

Committee:

Shad Sargand (Advisor)

Subjects:

Engineering, Civil

Keywords:

Hybrid Finite Element Procedure; Crack Band Propagation; Hybrid Stress Model

Lewicki, David G.Crack propagation studies to determine benign or catastrophic failure modes for aerospace thin-rim gears
Doctor of Philosophy, Case Western Reserve University, 1995, Mechanical Engineering
Analytical and experimental studies were performed to investigate the effect of rim thickness on gear tooth crack propagation. The goal was to determine whether cracks grew through gear teeth (benign failure mode) or through gear rims (catastrophic failure mode) for various rim thicknesses. Gear tooth crack propagation was simulated using a finite element based computer program. Principles of linear elastic fracture mechanics were used. Quarter-point, triangular elements were used at the crack tip to represent the stress singularity. Crack tip stress intensity factors were estimated and used to determine crack propagation direction and fatigue crack growth rate. The computer program used had an automated crack propagation option in which cracks were grown numerically using an automated re-meshing scheme. In addition, experimental studies were performed in the NASA Lewis Spur Gear Fatigue Rig. Gears with various backup ratios were tested to validate crack path predictions. Also, specialized crack propagation gages were installed on the test gears to measure gear tooth crack growth rate. From both predictions and tests, gears with backup ratios (rim thickness divided by tooth height) of 3.3 and 1.0 produced tooth fractures while a backup ratio of 0.3 produced rim fractures. For a backup ratio of 0.5 , the experiments produced rim fractures and the predictions produced both rim and tooth fractures, depending on the initial crack conditions. Good correlation between the predicted number of crack propagation cycles and measured number of cycles was achieved using both the Paris fatigue crack growth method and the Collipriest crack growth equation when fatigue crack closure was considered

Committee:

Roberto Ballarini (Advisor)

Subjects:

Engineering, Mechanical

Keywords:

Crack propagation; Failure mode, benign/catastrophic; Gears

Kapadia, SharvariCramer Rao Lower Bound and Maximum Likelihood Estimation for Multipath Propagation of GPS Signals
MS, University of Cincinnati, 2013, Engineering and Applied Science: Electrical Engineering
Multipath propagation refers to a phenomenon wherein a radio signal winds up taking two or more paths because the signal is reflected off buildings or other obstructions near the receiver, resulting in one or more secondary propagation paths. In a GPS receiver, multipath effect can cause a stationary receiver's output to indicate as if it were randomly jumping about or creeping. The presence of multipath generally causes errors in the phase or delay measurements, thereby degrading the navigation accuracy. The main attention of this thesis is on computation of Cramer Rao Lower Bound that expresses a lower bound on the variance of estimated signal parameters. Cramer Rao Bound is computed for amplitude, phase and time delay signal parameters by taking the diagonal components of the Fisher Information Matrix, which is a 66 matrix for a 2-path multipath model. The Fisher Information Matrix entries are computed by taking the expected value of the product of the partial derivatives of log-likelihood function with respect to the signal parameters. The next part of the thesis is estimation of the signal parameters from distorted received signal of the same 2-path model using Maximum Likelihood estimation theory. The values of estimated parameter variance computed from estimated signal parameters, are compared with the Cramer Rao Lower bound.

Committee:

H. Howard Fan, Ph.D. (Committee Chair); Eric T. Vinande, Ph.D. (Committee Member); Xuefu Zhou, Ph.D. (Committee Member)

Subjects:

Electrical Engineering

Keywords:

Cramer Rao bound;GPS signals;Multipath Propagation;Maximum Likelihood Estimation;Parameter Estimation;;

Cheng, JiqiA Study of Wave Propagation and Limited-Diffraction Beams for Medical Imaging
Doctor of Philosophy in Engineering, University of Toledo, 2005, Bioengineering
In this dissertation, wave propagation and limited-diffraction beams are further studied to gain a deep understanding of their principles and applications in ultrasonic imaging. With the concept of angular spectrum, the ultrasound fields generated by array transducers are mapped as the summation of limited-diffraction beams. A new method of spatial impulse response based on simple algebraic operations instead of complex geometrical considerations for rectangular arrays is derived. Numerical and experimental results show that the method developed has a high accuracy and efficiency. Based on the knowledge of previous studies, a general theory of Fourier based imaging method is developed from the diffraction tomography theory that solves the inhomogeneous Helmoholtz equation under the Born approximation. The object function defined in this theory is more naturally linked to the physical properties of the object, such as the relative change of local compressibility and density. With this treatment, limited-diffraction array beam and broad-band steered plane wave transmissions studied previously are included, in addition to other previously studied imaging methods. A relationship between the Fourier transform of the echo data and that of the object function is established. The theory is developed directly in 3D. Computer simulations, imaging experiments for wire targets, tissue-mimicking phantoms, and in vivo kidney and heart are carried out to verify the theory using the high frame rate imaging system. To study various methods on wave propagations, limited diffraction beams, and high frame rate imaging, logics and programs are designed and implemented for a general-purpose high-frame-rate ultrasound imaging system. The system has 128 independent transmit and receive channels, each has a high-speed, high-precision A/D, D/A, and a large storage. The system is flexible for various ultrasound experiments.

Committee:

Jian-yu Lu (Advisor)

Subjects:

Engineering, Biomedical

Keywords:

ultrasound imaging; optical imaging; Fourier analysis; wave propagation; limited diffraction beam; angular spectrum; spatial impulse response; optical coherence tomography; coded excitation; high frame rate imaging; 3D imaging; image formation

Zhang, MingmingSEPTO-TEMPORAL PATTERNS AND MECHANISMS OF NEURAL PROPAGATION
Doctor of Philosophy, Case Western Reserve University, 2015, Biomedical Engineering
Understanding how neural signal conduction is important for learning normal brain functions and delivering neuromodulation therapy. However, it is not clear how in many cases neural activity propagates in the brain. For instance, seizure activity starts in the temporal lobe and propagates to the rest of other brain areas in epilepsy patients. Furthermore, the propagation of theta waves responsible for memory consolation in the hippocampus has not been elucidated. To study neural propagation, we adopted the unfolded hippocampus in-vitro preparation from rodent animals. Not only is the hippocampus one of the most important functional subunits in the brain, but also it is an ideal model for analyzing propagation through an intact neural network within a flat tissue preparation. Finally, the combination of the unfolded hippocampus with penetrating microelectrode array (PMEA) is a powerful tool to monitor neural signal propagation in a large area of the hippocampal network. Previous studies in the unfolded hippocampus using PMEA show that 4-AP-induced spontaneous activity could propagate in both transverse and longitudinal directions, generating a diagonal wave front across the entire hippocampal area at a speed of 0.12 ± 14 0.03 m/s. Further experiments showed that propagation is independent of either synaptic transmission or gap junction conductions, but is consistent with an electrical field effect. In addition, in a train of activity with various firing spikes. This could be interpreted by a change in the propagating direction. However, it was determined that the source of the spikes moved within the hippocampus. This particular pattern is consistent over a large number of experiments in different hippocampal preparation from both sides of the brain hemisphere. Overall, this study shows spiking activity in the hippocampus can take place in the absence of synaptic transmission, electric gap junction or diffusion at a speed of about 0.1 m/s. The prevalence of non-synaptic propagation across several experimental approaches suggests that there exists a common mechanism mediating the neural signal travelling in the brain associated with the change of extracellular electrical field. Moreover, further analysis shows that source of these spikes is itself moving by a slower speed of about 0.016 m/s. Therefore, these results indicate a novel type of neural activity propagation mechanisms in the hippocampus. This could be important to explain how neural activity can be synchronized across neural tissue in both normal and abnormal conditions such as epilepsy.

Committee:

Dominique Durand (Advisor); Andrew Rollins (Committee Member); Erin Lavik (Committee Member); David Friel (Committee Member)

Subjects:

Biomedical Engineering; Neurosciences

Keywords:

Neural propagation

Nessel, James AaronEstimation of Atmospheric Phase Scintillation Via Decorrelation of Water Vapor Radiometer Signals
Doctor of Philosophy, University of Akron, 2015, Electrical Engineering
The coherent arraying of antenna elements by widely distributed ground-based antenna systems has proven to be a valuable technological approach for high precision astrometric measurements and imaging via Very Long Baseline Interferometry (VLBI) and has been performed with considerable success by radio astronomers for several decades. The fundamental factor limiting the precision in which these measurements can be conducted, however, is due to the turbulence-induced refractivity changes of the atmospheric medium (troposphere) through which the propagating waves must traverse. For radio science applications, this problem can be significantly reduced via three well-demonstrated means: (1) proper choice of ground site location (i.e., dry, high altitude climates), (2) conducting observations during non-turbulent times (i.e., nights vs. days, winter vs. summer), and (3) employing relatively long integration time (on the order of minutes) compensation through the use of water vapor radiometers in data post-processing. For communications applications, however, this may not necessarily be the case, and a means to accurately estimate the water vapor variability of the troposphere at short time scales will be required to efficiently combine signals from ground-based antenna elements in an array environment, particularly for transmit arraying. It is thus the goal of this research effort to identify and validate a means in which phase fluctuations induced by the atmosphere can be accurately measured which could be employed to ultimately improve the coherent combining of several spatially separated signals transmitted from ground to space without the use of an active source (i.e., receive signal). The method in which this will be accomplished is through the use of a passive radiometric technique capable of accurately determining phase fluctuations on the necessary time scales to provide real-time phase compensation to realize transmit arraying at Ka-band frequencies and higher. To improve the accuracy over the state of the art in radiometric water vapor retrieval techniques, a novel blind source separation technique has been developed and demonstrated. Utilizing experimental data using a water vapor radiometer and a two-element interferometer, it is statistically shown that the approach described herein improves water vapor retrieval accuracy, particularly during cloudy conditions, over the state of the art.

Committee:

Nathan Ida, Dr. (Advisor); Igor Tsukerman, Dr. (Committee Member); Arjuna Madanayake, Dr. (Committee Member); Kevin Kreider, Dr. (Committee Member); Ernian Pan, Dr. (Committee Member)

Subjects:

Communication; Electrical Engineering; Electromagnetics

Keywords:

propagation; atmosphere; microwave; antenna array; Ka-band; water vapor radiometer; phase scintillation; interferometer; blind source separation

Lowe, Robert LindseyFinite-Deformation Modeling of Elastodynamics and Smart Materials with Nonlinear Electro-Magneto-Elastic Coupling
Doctor of Philosophy, The Ohio State University, 2015, Mechanical Engineering
Eulerian formulations of the equations of finite-deformation solid dynamics are ideal for numerical implementation in modern high-resolution shock-capturing schemes. These powerful numerical techniques -- traditionally employed in unsteady compressible flow applications -- are becoming increasingly popular in the computational solid mechanics community. Their primary appeal is an exceptional ability to capture the evolution and interaction of nonlinear traveling waves. Currently, however, Eulerian models for the nonlinear dynamics of rods, beams, plates, membranes, and other elastic structures are currently unavailable in the literature. The need for these reduced-order (1-D and 2-D) Eulerian structural models motivates the first part of this dissertation, where a comprehensive perturbation theory is used to develop a 1-D Eulerian model for nonlinear waves in elastic rods. The leading-order equations in the perturbation formalism are (i) verified using a control-volume analysis, (ii) linearized to recover a classical model for longitudinal waves in ultrasonic horns, and (iii) solved numerically using the novel space-time Conservation Element and Solution Element (CESE) method for first-order hyperbolic systems. Numerical simulations of several benchmark problems demonstrate that the CESE method effectively captures shocks, rarefactions, and contact discontinuities. The second part of this dissertation focuses on another emerging area of finite-deformation mechanics: magnetoelectric polymer composites (MEPCs). A distinguishing feature of MEPCs is the tantalizing ability to electrically control their magnetization, or, conversely, magnetically control their polarization. Leveraging this magnetoelectric coupling could potentially impact numerous technologies, including information storage, spintronics, sensing, actuation, and energy harvesting. Most of the research on MEPCs to date, however, has focused on optimizing the magnitude of the magnetoelectric coupling through iterative design. Substantially less activity has occurred in the way of mathematical modeling and experimental characterization at finite strains, which are needed to advance fundamental understanding of MEPCs and encourage their technological implementation. The aforementioned needs motivate the second part of this dissertation, where a finite-strain theoretical framework is developed for modeling soft magnetoelectric composites. Finite deformations, electro-magneto-elastic coupling, and material nonlinearities are incorporated into the model. A particular emphasis is placed on the development of tractable constitutive equations to facilitate material characterization in the laboratory. Accordingly, a catalogue of free energies and constitutive equations is presented, each employing a different set of independent variables. The ramifications of invariance, angular momentum, incompressibility, and material symmetry are explored, and a representative (neo-Hookean-type) free energy with full electro-magneto-elastic coupling is posed.

Committee:

Sheng-Tao John Yu (Advisor); Marcelo J. Dapino (Committee Member); Daniel A. Mendelsohn (Committee Member); Amos Gilat (Committee Member); Kelly S. Carney (Committee Member)

Subjects:

Engineering; Mechanical Engineering; Polymers

Keywords:

Eulerian; rod; elastic; nonlinear wave; CESE method; first-order hyperbolic; wave propagation; method of characteristics; magnetoelectric polymer; magnetoelectric composite; finite deformation; electro-magneto-elastic; free energy; constitutive equation

Almanee, Mohammad S.Intense, Ultrashort Pulse, Vector Wave Propagation in Optical Fibers
Doctor of Philosophy (Ph.D.), University of Dayton, 2017, Electro-Optics
The planned research is initially motivated by experiments on twisted fiber to examine the polarization of the output pulses. The initial polarization launched into the fiber evolves to a new final state that asymptotically moves to one of two opposite circular polarizations. The initial research was to program the vector wave equations of one and coupled solitons in a twisted fiber including the additional nonlinear terms stimulated Raman scattering and self-steepening. The high-twist fiber eliminates small linear birefringence at the expense of introducing circular birefringence manifested in the group velocities. The vector equations are naturally written in the circular polarization basis. To verify the numerical results, I made a sojourn to INAOE in Puebla, Mexico to run an experiment and compare the results. The numerical compare extremely well with the experimental results. For one soliton, the output polarization of the twisted fiber follows the input with high fluctuations. However, for the coupled soliton input, when the input polarization is close to linear, we observe a very abrupt polarization switch from nearly negative circular, -45° to nearly positive circular, 45° over a very narrow range of the input ellipticities. The literature is full of simulations of super-continuum generation using scalar wave equations, but we have not seen any report on the polarization of the output Supercontinuum light. Again, motivated by the experiments on polarization evolution in optical fibers we wanted to study the vector wave equations at higher incident powers to discover what the polarization state of the output waves are in an extreme nonlinear situation.

Committee:

Joseph Haus (Advisor); Partha Banerjee (Committee Member); Andy Chong (Committee Member); Youssef Raffoul (Committee Member)

Subjects:

Engineering; Optics

Keywords:

Nonlinear optics; soliton pulse; twisted fiber; vector wave propagation; supercontinuum generation

Doty, AustinNonlinear Uncertainty Quantification, Sensitivity Analysis, and Uncertainty Propagation of a Dynamic Electrical Circuit
Master of Science (M.S.), University of Dayton, 2012, Engineering
The development of a statistically-based process for verification and validation of computational experiments is presented in this study. The process can be used to identify sources of uncertainty, quantify magnitudes of uncertainty, and propagate uncertainty through a model. Model form error was identified through prototype experiments with the system and subsystem, and methods for reducing model form error are presented. Existing validation metrics are applied to the system in this analysis, and a new statistical validation metric is introduced. The methodology for performing Uncertainty Analysis (UA), nonlinear Sensitivity Analysis (SA), and nonlinear Uncertainty Propagation (UP) is presented in this investigation as part of the validation process. The results of this portion of the methodology guided the development of the experimental design and evaluation. Experimental validation experiments were developed for a simple electrical system in order to demonstrate the computational-to-experimental validation process. The process is applicable to any system, but a simple example was chosen so that any interested person can follow the implementation. Despite the simplicity of the system selected, the analysis proved to be complicated and tedious, while also identifying many avenues for future work. A numerical example is presented along with the relevant data in sufficient detail to demonstrate how the analysis was performed. By applying this new process, the electrical system is studied from a statistical perspective, with an emphasis on uncertainty quantification and propagation. The sensitivity analysis discovered that the behavior of each component varied significantly, and several critical parameters were identified. By identifying and quantifying the uncertainty in each parameter, the quality of the computational model can be improved, and decisions can be made with quantifiable confidence.

Committee:

Jose Camberos (Advisor); John Doty (Committee Member); Markus Rumpfkeil (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

verification; validation; uncertainty propagation; uncertainty quantification; sensitivity analysis

Jain, Jayesh R.Homogenization Based Damage Models for Monotonic and Cyclic Loading in 3D Composite Materials
Doctor of Philosophy, The Ohio State University, 2009, Mechanical Engineering

This dissertation develops a three dimensional homogenization based continuum damage mechanics (HCDM) model for fiber reinforced composites undergoing micromechanical damage under monotonic and cyclic loading. Micromechanical damage in a representative volume element (RVE) of the material occurs by fiber-matrix interfacial debonding, which is simulated using a hysteretic bilinear cohesive zone model. The proposed HCDM model expresses a damage evolution surface in the strain space in the principal damage coordinate system (PDCS). PDCS enables the model to account for the effect of non-proportional load history. The material constitutive law involves a fourth order orthotropic tensor with stiffness characterized as a macroscopic internal variable. Three dimensional damage in composites is accounted for through functional forms of the fourth order damage tensor in terms of components of macroscopic strain and elastic stiffness tensor. The HCDM model parameters are calibrated from homogenized micromechanical solutions of the RVE for a few representative strain histories. The proposed model is validated by comparing the CDM results with homogenized micromechanical response of single and multiple fiber RVEs subjected to arbitrary loading history. Finally the HCDM model is incorporated in a macroscopic finite element code to conduct damage analysis in structures. The effect of different microstructures on the macroscopic damage progression is examined through this study.

To efficiently simulate the dynamic response of heterogeneous microstructures, an assumed stress hybrid Voronoi Cell Finite Element Method (VCFEM) for stress wave propagation is developed. In the proposed formulation, stresses in the domain and compatible displacements at the element boundary are approximated independently. The inertia field is approximated in terms of stresses so as to satisfy the equilibrium a-priori. The weak forms of kinematics and traction reciprocity are obtained by minimization of the complementary variational principle. As stress wave is a local disturbance, localization and multi-resolution properties of the wavelet functions are exploited to adaptively enrich the stress functions locally near the wave front. At the outset, a stable, accurate, and computationally efficient adaptive computational framework is developed for micromechanical response of composites under impact loading. The effectiveness of the proposed method is demonstrated through comparison with conventional FEM packages.

Committee:

Somnath Ghosh, Prof. (Advisor); Gregory Washington, Prof. (Committee Member); Stephen Bechtel, Prof. (Committee Member); Mark Walter, Prof. (Committee Member)

Subjects:

Aerospace Materials; Design; Materials Science; Mechanical Engineering; Mechanics

Keywords:

Composite materials; continuum damage mechanics; homogenization; interfacial debonding; fatigue; finite element method; stress wave propagation

Mutha, Chetan V.Software fault failure and error analysis at the early design phase with UML
Master of Science, The Ohio State University, 2011, Mechanical Engineering
A framework for fault-failure and error propagation through different UML diagrams is introduced. The method is formalized by defining rules for fault propagation across different UML diagrams and also within a particular diagram. A study of the propagation of faults through each diagram highlights various structural and behavioral aspects of the software failure. This method will allow the designers to proactively analyze the functionality of the systems early in the design process, understand functional and other failures and their propagation paths, overall impact on the system, and redundancies and safeguards that should be added. The main advantage of the method is that it permits the analysis of the failure and fault propagation at a highly abstract level before any potentially high-cost design commitments are made thereby supporting decision making early in the design process, providing guidance to the designers to allow elimination of failures through exploration of system components and their functionality, and facilitating the development of more reliable system configurations. This method is discussed using an example and results are given for the Helium tank sub-system of the Space Shuttle's Reaction Control System (RCS). The work is further extended to automate the FPSA and build an executable model of FPSA

Committee:

Prof. Carol Smidts (Advisor); Prof. Aldemir Tunc (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

Software fault propagation; Software design

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