Department: Mechanical Engineering ![[clear]](close-x.png "Remove this limiter")
50 matches in the database.
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1.
Abuhaiba, Mohammad.
Mathematical Modeling and Analysis of a Variable Displacement Hydraulic Bent Axis Pump Linked to High Pressure and Low Pressure Accumulators.
Degree: PhD, Mechanical Engineering, 2009, University of Toledo
► Working prototypes of a Hydraulic Hybrid Vehicle (HHV) are already under testing…
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▼ Working prototypes of a Hydraulic Hybrid Vehicle (HHV) are already under testing and investigation. One of the problems reported from testing is that the noise levels emitted by the hydraulic system are not acceptable. Therefore, there is a need to perform extensive research to improve the HHV systems in terms of noise and performance. The pump is the main source of noise in HHV systems. However, the lack of space, the high pressure and the dynamics of components within the pump have prevented either direct observation or measurement of potential noise causing mechanisms within the pump structure. As a result, there are several theories as to the source of the noise from the pump units but little concrete information to further isolate and reduce the noise generation.Currently, the industry use “cut and try” methods in order to study the noise issue. This necessities the development of a theoretical tool that will enable us to avoid the costly (time and money) cut and try procedure already employed in the current efforts. This work creates a dynamic and geometric model of a bent axis pump for this purpose. Elements of the model include finding the variation of pressure, flow rate, and dynamic forces acting on the pump components and case as a function of angular rotations of both the main shaft and the yoke. The model was constructed using MathematicaTM” software and verified against test data. In turn, this study identifies and analyzes the dominant forces in both the time and frequency domains. The solution of the theoretical model using MathematicaTM is verified by a dynamic model created using ADAMS/View software. The kinematic model was able to predict the variations of the angular velocities and accelerations and the velocities and the accelerations of the center of gravity of the entire pump’s parts starting from the main shaft up to the yoke. This work presents all equations necessary to solve for the piston pressure and pump flow rate as a function of main shaft and yoke rotations. These equations were tested, and verified at a constant angular speed of the main shaft and yoke angles ranging from 5° to 40° . Results indicate that the model can predict the variations of pressure profile and flow rate as well as the forces acting on the pump’s case both in the time and frequency domains. Conclusions and recommendations are at the end of this research effort. The harmonics of the reaction forces acting on the pump case occur at frequencies of 25, 50, 100, 200, 220, 250, 350, and 450 Hz respectively.
Advisors/Committee Members: Olson, Walter.
Subjects: Engineering; Fluid dynamics; Mathematics; Mechanical engineering; Mechanics; Technology
Keywords: bent axis pump, piston pump, swash plate pump, pump noise, mathematical modeling, dynamic, flow rate, piston pressure, high pressure accumulator, low pressure accumulator, valve plate, constant velocity joint, equation of motion
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2.
Allampalli, Vasanth.
Fourth order Multi-Time-Stepping Adams-Bashforth (MTSAB) scheme for NASA Glenn Research Center’s Broadband Aeroacoustic Stator Simulation (BASS) Code.
Degree: PhD, Mechanical Engineering, 2010, University of Toledo
► By using a Multi-Time-Stepping Adams-Bashforth (MTSAB) scheme, different regions of the computational…
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▼ By using a Multi-Time-Stepping Adams-Bashforth (MTSAB) scheme, different regions of the computational grid can march with different time steps based on their local stable time steps and on local minimum length and time scales. This can save computational time for problems with large range of length and time scales. In this work, a fourth order, automated MTSAB scheme was developed for NASA Glenn Research Center’s Broadband Aeroacoustic Stator Simulation Code (BASS) code. BASS code solves the Navier-Stokes equations on structured multi-block grids. The automated MTSAB scheme, during the run assigns time steps to grid blocks, based on local stability and accuracy. The scheme automatically changes the time steps during the run as required. In this work, two automatic block cutting algorithms were also developed. The first block cutting algorithm cuts the existing grid blocks during the run, to minimize the number of points at the smallest time steps. The second block cutting algorithm cuts the grid blocks to maximize the parallel efficiency of the scheme. This scheme was tested on CAA workshop problems, highly nonlinear flows (Transonic flows) with grid motion, and viscous flow cases. Results from these cases and the speed gains from using the MTSAB scheme are presented.
Advisors/Committee Members: Hixon, Ray.
Subjects: Mechanical engineering
Keywords: Multi-Time Step, Adams-Bashforth scheme, BASS code, Fourth order
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3.
Andersen, Brett.
A Comparison of Two and Three Bladed Floating Wind Turbines.
Degree: MS, Mechanical Engineering, 2010, University of Toledo
► A possible solution to the limitations of current offshore wind technology would…
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▼ A possible solution to the limitations of current offshore wind technology would be the utilization of a floating platform. Floating platforms are not a new idea, as the oil and gas industries have been constructing and using floating platforms for a number of years. Two bladed wind turbines offer the following advantages over three bladed in a floating environment: cost savings of one blade, lower weight further reduces system costs, easier rotor lift and assembly, and greater rotor speeds reduce drivetrain stress. Additionally, two blade rotors usually feature flexible blades or a teetered hub with a pivot point. This is especially important for floating wind turbines because the teeter pin effectively decouples the motion of the rotor plane from the tower motion, reducing damaging cyclic bending moments in the drive train.
Advisors/Committee Members: Afjeh, Dr. Abdollah Aliakbarkhan.
Subjects: Mechanical engineering
Keywords: wind power floating turbines offshore
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4.
Anderson, Walter.
Parametric Investigation Toward Achieving an Optimal Magnetorheological Mount.
Degree: MS, Mechanical Engineering, 2010, University of Toledo
► Hybrid vehicles have been developed to increase the fuel economy of existing…
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▼ Hybrid vehicles have been developed to increase the fuel economy of existing vehicles. Examples include hydraulic and electric hybrid vehicles. A common issue in hybrid vehicles is the additional vibration and vibration-caused noise. This vibration is primarily caused by the switching of power modes, i.e. from the conventional gasoline engine to the electric or hydraulic motor. In certain cases, this vibration, due to the wide frequency range characteristics, cannot effectively be isolated through the use of conventional isolation technologies. In this thesis, a mixed mode magnetorheological mount has been investigated to mitigate this and similar wide-frequency vibration. In order to effectively isolate vibration, a mount should be designed for a specific application. Different engines however are required for each application; a designer therefore must alter the engine mount with the desired stiffness and damping characteristics. In this work a parametric analysis has been performed on one of the main components of the mount, the elastomeric top. The analysis and comparison to the experimental results are discussed in detail. Three different parameters were the focus of this investigation. The rubber thickness (by two means) and height were studied. It was found that varying the mount diameter (thickness) is the most influential parameter that was investigated. The initial analyses to validate the finite element model showed at most a ~5% difference. The results of this study will be instrumental for designing and optimizing different mounts including magnetorheological and hydraulic mounts.
Advisors/Committee Members: Elahinia, Mohammad.
Subjects: Mechanical engineering
Keywords: Magnetorheological; MR; engine mount; hybrid vehicle; parametric analysis
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5.
BAMIRO, OLUYINKA OLUGBENGA.
ANALYSIS OF THERMAL STRESS AND PLASTIC STRAIN IN STUDS/VIAS OF MULTILEVEL INTEGRATED CIRCUITS.
Degree: MS, Mechanical Engineering, 2004, University of Toledo
► The thermo-mechanical reliability of microelectronic circuitry is adversely affected by failure mechanisms…
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▼ The thermo-mechanical reliability of microelectronic circuitry is adversely affected by failure mechanisms such as void formation, interfacial delamination, cracking and electro-migration. The thermal stresses induced during typical integrated circuit fabrication aggravate these failure mechanisms. The high tensile hydrostatic stress is responsible for void nucleation while the individual stress components are responsible for failure mechanism such as void growth, delamination and cracking. The reliability of studs that connects the interconnect from one level to another have been a major source of concern in microelectronic circuitry A three dimensional elasto-plastic finite element model was used to analyze the thermal stresses and plastic strain in studs/vias. The model determined the effect of geometric parameters used to achieve higher integration on the thermal stress and plastic strain in aluminum studs. The effects of strain hardening on the thermal stresses and plastic strain of aluminum stud was determined. The implication of the trend towards copper interconnect and low –k dielectric as recommended by the National Technology Roadmap on Semiconductors on thermo-mechanical reliability of studs was explored.
Advisors/Committee Members: Pourazady, Mehdi.
Subjects: Engineering, Mechanical
Keywords: Studs/Vias, thermo-mechanical reliability ,void formation, microelectronic circuitry,finite element
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6.
BARNALA, PUKHRAJ K.
Optimization of Operating Parameters of a Material Recovery Facility using Lean Six Sigma Techniques.
Degree: MS, Mechanical Engineering, 2011, University of Toledo
► Lean six sigma is a business improvement methodology which combines tools from…
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▼ Lean six sigma is a business improvement methodology which combines tools from both lean manufacturing and six sigma. Lean manufacturing focuses on elimination of waste and thus increases overall speed of the process/operations. Six sigma focuses on quality. By combining the two, the result is better quality, cost efficient, faster and optimized process. Lean six sigma has not been used in recycling to the extent it has been in manufacturing. The objective of this research is to investigate the application and benefits of lean six sigma in the recycling industry. Specifically, the objective of the project is to improve the process for material recovery facility at Toledo, Ohio. This includes aligning and optimizing processes and the removal of process generated defects and errors. This thesis revealed the current sigma level, defects per million opportunity and performance at Material Recovery Facility (MRF), Toledo. The case study of material recovery facility at Toledo is discussed. Defects per million opportunities are calculated from the on-site data collection. Using six sigma and statistical quality tools total tons processed per year, standard processing time, current sigma level, and total tons defective and financial aspect are discussed in the thesis.
Advisors/Committee Members: Franchetti, Matthew.
Subjects: Atmosphere; Energy; Engineering; Environmental Engineering; Environmental Science; Industrial Engineering; Sustainability
Keywords: Recycling; Material Recovery Facility; Optimization; Lean Six Sigma
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7.
Boroujeni, Nariman Mansouri.
Monetite Cement Composites for Orthopedic and Dental Applications.
Degree: MS, Mechanical Engineering, 2012, University of Toledo
► Calcium Phosphate materials have been used as bone substitutes and drug delivery…
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▼ Calcium Phosphate materials have been used as bone substitutes and drug delivery systems for decades. Their scaffolds are useful tools in tissue engineering, orthopedic applications, and drug delivery. Calcium Phosphate Cement (CPC) is a bio-cement that supports loading in the absence of bone. They exhibit a remarkable biocompatibility, bioactivity, and partial biodegradability. However, their poor mechanical properties and fracture toughness in comparison to bone make them inappropriate for load bearing applications. A variety of materials and fibers have been added to CPCs as reinforcements to increase their mechanical properties. The aim of this study was to produce a new augmented CPC, monetite cement (MC), by reinforcement, and increased mechanical properties. Monetite cements were produced by mixing calcium hydroxide Ca(OH)2 powders with an aqueous setting solution. This product exhibits poor mechanical strength in comparison to cancellous bone. Carbon nanotubes (CNTs) and Chitosan, with their good mechanical properties both in tension and compression, have potential use in CPCs to further strengthen the mechanical properties. In this project, techniques and methods for synthesizing and making MC-CNT and MC-Chitosan have been compared. It was observed, the surface modification of CNT and chitosan, to enhance bonding to monetite, is necessary in order to achieve good compressive strength. Strong interfacial bonding of CNT-COOH and deposition of biomimetic calcium phosphate on chitosan powders are necessary to improve the mechanical properties of MC-CNT and MC-Chitosan composites. The mechanical and biological performance of MC-CNT and MC-Chitosan composite cements were evaluated and show potential in orthopedic and dentistry applications. The main ingredient of monetite cement is calcium hydroxide. Egg-shells have a considerable amount of calcium in their structure and provide a cheap renewable source of this mineral. If monetite cement could be produced from this natural resource it would create a new green technology saving tons of egg-shells from landfills each year. Mechanical and biological performance of monetite cement from eggshells is comparable to pure monetite cement.
Advisors/Committee Members: Bhaduri, Sarit.
Subjects: Mechanical Engineering
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8.
Cheng, Chao.
Application of Artificial Neural Networks in the Power Split Controller For a Series Hydraulic Hybrid Vehicle.
Degree: MS, Mechanical Engineering, 2010, University of Toledo
► Hybridization of vehicles has been proven a good way to reduce fuel…
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▼ Hybridization of vehicles has been proven a good way to reduce fuel consumption significantly. Working prototypes of a series hydraulic hybrid vehicle (SHHV) are already under testing. The power split strategy for those prototypes is a rule-based controller, or called a “bang-bang” controller. The controller is designed based on engineer's intuition, to keep the engine working in the region with high efficiency and low fuel consumption rate. One of the problems of that design is that it only takes one component of the hydraulic hybrid system, the internal combustion engine, into account. It is a device centered rather than system centered design. As a result, the potential of the hydraulic hybrid system is not fully realized. A more efficient power split strategy is conducted based on the Deterministic Dynamic Programming (DDP), which has been proved a powerful tool for optimal control. However, the DDP is a looking-forward tool, which means it uses the future driving conditions to split the power between the two sources for optimization. Successful applications of DDP used standard driving cycles as the known driving conditions. However, DDP is not applicable where the driving cycle is unknown. This means that the DDP could not be applied in real-time, unless the future driving conditions could be found. The driving conditions in our everyday commute are extremely different with the typical driving cycles. And different drivers have different driving habits. However, a specific driver has a certain “driving cycle” for a certain commute, although which is not a standard one. As long as the certain “driving cycle” is known, The DDP algorithm could be applied for optimization. Artificial neural network (ANN) has the ability to “learn” the “driving cycle” from a certain driver and then to “predict” the driving conditions before its happening. The “prediction” method is the “time-series forecasting” method. ANN is a good tool for time series forecasting and has also been shown a better way for long term prediction. The ANN is conducted using the software MATLAB/Simulink. A three-layer feed-forward static ANN is built up in the Simulink environment. The ANN model was able to predict the driving conditions with a twenty seconds window size which has been proven a tradeoff between the forecasting accuracy and the time consumed. The error between the predicted value and the desired value is within an accepted range. The network is tested based on three different driving cycles: federal urban driving schedule, city urban dynamometer driving schedule and highway urban dynamometer driving schedule respectively.
Advisors/Committee Members: Olson, Walter.
Subjects: Mechanical engineering
Keywords: Series Hydraulic Hybrid Vehicle Control; Artificial Neural Network; Dynamic Programming
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9.
Cioc, Carmen Ana Beatrice.
An Elastohydrodynamic Lubrication Model for Helicopter High-Speed Transmission Components.
Degree: PhD, Mechanical Engineering, 2004, University of Toledo
► This thesis describes a deterministic approach to analyze elastohydrodynamic lubrication (EHL) of…
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▼ This thesis describes a deterministic approach to analyze elastohydrodynamic lubrication (EHL) of helicopter transmission gear surfaces with asperities. Thermal, Newtonian or non-Newtonian models are used to study the mechanisms of film generation, pressure distribution and temperature distributions within the fluid and on the surface, for an EHL line contact. A two-slope viscosity-pressure model is used to avoid overestimation of the viscosity of the lubricant under heavy loads. The three-dimensional roughness description of an actual gear tooth surface is measured using a non-contact surface profilometer. Detailed analysis of the fluid parameters and the surface roughness influences are presented. Five different types of lubricants are studied in order to determine which one best corresponds to the operating conditions. The pressure distribution, fluid film thickness distribution and the temperature rise at the contact surface are predicted as a function of the gear operating conditions including normal load, lubricant temperature and rolling/sliding speed. A new numerical method, used to solve the Reynolds equation, is employed in order to maximize the computational speed. The numerical developments described for EHL lubrication are extended then to incorporate metal-to-metal contact. A mixed-elastohydrodynamic lubrication model is presented in order to analyze helicopter transmission gears. A parametric analysis is performed in order to determine explicitly the metal-to-metal contact effects on the viscosity, and implicitly on the pressure, fluid film generation, and temperatures for both fluid and surfaces.
Advisors/Committee Members: Keith, Theo G.
Keywords: tribology; elastohydrodynamic lubrication; Newtonian and non-Newtonian fluids; surface roughness effects; thermal effects; transient effects
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10.
Cioc, Sorin.
Application of the Space – Time Conservation Element and Solution Element Numerical Method to Flows in Fluid Films.
Degree: PhD, Mechanical Engineering, 2004, University of Toledo
► This work, situated at the confluence between CFD and tribology, is the…
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▼ This work, situated at the confluence between CFD and tribology, is the first application of a relatively new numerical method, the space-time conservation element and solution element (CE/SE) method, to flows in thin films. The general features of the numerical method are highlighted, and also the concept of fluid film bearings is presented. The formulations of the governing equations and boundary conditions for four main cases are shown: 1-D and 2-D cavitated bearings using Elrod’s formulation, hybrid gas bearings, and gas bearings including inertial effects. The numerical formulations applied on both uniform and non-uniform grids are presented, with emphasis on the important features of the method when used to solve these specific problems, including the formulation of the boundary conditions. Based on the described formulations, numerical codes have been developed. The results obtained are compared with experimental values, theoretical results, and numerical results obtained by using other algorithms. In the case of cavitated bearings, because the algorithm developed is capable of capturing potential discontinuities, the differences between the results obtained with the CE/SE method and with previous methods are significant when the position of the full film reformation point is not imposed through the supply system (boundary conditions). Important differences have also been noted in the case of gas bearings including inertia effects. Results demonstrate that the inclusion of inertial effects becomes necessary when the bearing speed is very high and/or the film clearance is large. Flow discontinuities are shown to occur in a manner similar to that of shock waves in supersonic flows. Comparisons prove that the CE/SE method, when contrasted to previous algorithms, can successfully predict the pressure distribution within bearings, including cases with discontinuities in the lubricant film. Moreover, the method accomplishes this without any special treatment and without introducing distortion and/or excessive dissipation into the solution. The method is thus a strong candidate in applications that require more precise results, such as accurate, robust computation of the cavitation boundaries, as well as for transient problems. The method is also a perfect candidate in more complex problems, such as flows at very high speeds with inertia effects.
Advisors/Committee Members: Keith, Theo G.
Subjects: Engineering, Mechanical
Keywords: CFD; fluid film; lubrication; discontinuities; inertial effects; cavitation; gas bearings
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11.
Colin, Julie Anne.
Deformation History and Load Sequence Effects on Cumulative Fatigue Damage and Life Predictions.
Degree: PhD, Mechanical Engineering, 2009, University of Toledo
► Fatigue loading seldom involves constant amplitude loading. This is especially true in…
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▼ Fatigue loading seldom involves constant amplitude loading. This is especially true in the cooling systems of nuclear power plants, typically made of stainless steel, where thermal fluctuations and water turbulent flow create variable amplitude loads, with presence of mean stresses and overloads. These complex loading sequences lead to the formation of networks of microcracks (crazing) that can propagate. As stainless steel is a material with strong deformation history effects and phase transformation resulting from plastic straining, such load sequence and variable amplitude loading effects are significant to its fatigue behavior and life predictions.The goal of this study was to investigate the effects of cyclic deformation on fatigue behavior of stainless steel 304L as a deformation history sensitive material and determine how to quantify and accumulate fatigue damage to enable life predictions under variable amplitude loading conditions for such materials. A comprehensive experimental program including testing under fully-reversed, as well as mean stress and/or mean strain conditions, with initial or periodic overloads, along with step testing and random loading histories was conducted on two grades of stainless steel 304L, under both strain-controlled and load-controlled conditions. To facilitate comparisons with a material without deformation history effects, similar tests were also carried out on aluminum 7075-T6. Experimental results are discussed, including peculiarities observed with stainless steel behavior, such as a phenomenon, referred to as secondary hardening characterized by a continuous increase in the stress response in a strain-controlled test and often leading to runout fatigue life. Possible mechanisms for secondary hardening observed in some tests are also discussed. The behavior of aluminum is shown not to be affected by preloading, whereas the behavior of stainless steel is greatly influenced by prior loading. Mean stress relaxation in strain control and ratcheting in load control and their influence on fatigue life are discussed. Some unusual mean strain test results are presented for stainless steel 304L, where in spite of mean stress relaxation fatigue lives were significantly longer than fully-reversed tests. Prestraining indicated no effect on either deformation or fatigue behavior of aluminum, while it induced considerable hardening in stainless steel 304L and led to different results on fatigue life, depending on the test control mode. In step tests for stainless steel 304L, strong hardening induced by the first step of a high-low sequence significantly affects the fatigue behavior, depending on the test control mode used. For periodic overload tests of stainless steel 340L, hardening due to the overloads was progressive throughout life and more significant than in high-low step tests. For aluminum, no effect on deformation behavior was observed due to periodic overloads. However, the direction of the overloads was found to affect fatigue life, as tensile overloads led to longer lives, while compressive overloads led to shorter lives. Deformation and fatigue behaviors under random loading conditions are also presented and discussed for the two materials. The applicability of a common cumulative damage rule, the linear damage rule, is assessed for the two types of material, and for various loading conditions. While the linear damage rule associated with a strain-life or stress-life curve is shown to be fairly accurate for life predictions for aluminum, it is shown to poorly represent the behavior of stainless steel, especially in prestrained and high-low step tests, in load control. In order to account for prior deformation effects and achieve accurate fatigue life predictions for stainless steel, parameters including both stress and strain terms are required. The Smith-Watson-Topper and Fatemi-Socie approaches, as such parameters, are shown to correlate most test data fairly accurately. For damage accumulation under variable amplitude loading, the linear damage rule associated with strain-life or stress-life curves can lead to inaccurate fatigue life predictions, especially for materials presenting strong deformation memory effect, such as stainless steel 304L. The inadequacy of this method is typically attributed to the linear damage rule itself. On the contrary, this study demonstrates that damage accumulation using the linear damage rule can be accurate, provided that the linear damage rule is used in conjunction with parameters including both stress and strain terms. By including both loading history and response of the material in damage quantification, shortcomings of the commonly used linear damage rule approach can be circumvented in an effective manner. In addition, cracking behavior was also analyzed under various loading conditions. Results on microcrack initiation and propagation are presented in relation to deformation and fatigue behaviors of the materials. Microcracks were observed to form during the first few percent of life, indicating that most of the fatigue life of smooth specimens is spent in microcrack formation and growth. Analyses of fractured specimens showed that microcrack formation and growth is dependent on the loading history, and less important in aluminum than stainless steel 304L, due to the higher toughness of this latter material.
Advisors/Committee Members: Fatemi, Ali.
Subjects: Engineering; Mechanical engineering
Keywords: Aluminum 7075-T6; Stainless Steel 304L; Cyclic Hardening; Deformation History Effect; Pre-hardening; Mean Stress; Fatigue Life Prediction; Load Sequence Effect; Overload Effect; Variable Amplitude Loading
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12.
Cyril, Nisha S.
Anisotropy and Sulfide Inclusion Effects on Tensile Properties and Fatigue Behavior of Steels.
Degree: MS, Mechanical Engineering, 2007, University of Toledo
► During metal forming processes such as rolling and forging, deformable sulfide inclusions…
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▼ During metal forming processes such as rolling and forging, deformable sulfide inclusions become elongated. Such elongated inclusions can have considerable adverse effects on mechanical properties, if the inclusions are not aligned with the loading direction. The objectives of this study were to evaluate and compare fatigue, monotonic tensile and CVN impact behavior of SAE 4140 steel with high (0.077%S), low (0.012% S) and ultra low (0.004% S) sulfur contents at two hardness levels approximately 43 HRC and 52 HRC). The longitudinally oriented samples at 40 HRC, where sulfide inclusions were oriented along the loading direction, did not exhibit any significant sensitivity of tensile or fatigue properties to the sulfur content. For the transversely oriented samples, however, the tensile ductility and the impact toughness of the high sulfur material was very low at either hardness level while the yield strength of the materials did not differ significantly with the sulfur content at either hardness level. Based on strain-life curves at 52 HRC, there was about a factor of 8 difference in fatigue life in the low cycle fatigue regime and more than an order of magnitude difference in the high cycle regime between the high S and the low S transverse materials. This difference was about a factor of 30 in the low cycle regime and about two orders of magnitude in the high cycle regime between the high S and the ultra low S materials. At 43 HRC, there was about a factor of 40 difference in short life and about one order of magnitude difference at long life between the high S and the ultra low S materials in the transverse direction. At 43 HRC, for which case longitudinal direction data were also available, little difference was noted between the low S, the ultra low S and the longitudinal materials. At 52 HRC, the high S material had a 27% lower fatigue limit than the ultra low S material under transverse loading. At 43 HRC, this reduction was 18%. SEM inspection of failed fatigue test specimens revealed that the fracture surfaces of the high S material were very rough and jagged, indicating several cracks originating from MnS inclusions at either hardness level. For the higher amplitude strain-controlled fatigue tests at both hardness levels, surface cracks that did not result in failure were found for all transverse materials indicating that the cracks initiated very early in the fatigue life. The ratios of predicted fatigue limit values using the parea parameter model proposed by Murakami et al based on inclusion inspection, to the experimental values, ranged between 0.84 and 1.29. The variations of the fatigue and tensile properties were plotted against the sulfur content and relations were obtained for the fatigue constants as functions of sulfur. The relations for the fatigue strength and ductility coefficients and exponents were expressed as functions of sulfur in the Roessle-Fatemi equation which is used to predict the strain-life curve of a steel based on only the hardness, in order to incorporate the effects of sulfur under transverse loading.
Advisors/Committee Members: Fatemi, Ali.
Subjects: Engineering, Mechanical
Keywords: Fatigue, Anisotropy, steels
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13.
Dasari, Praveen K.
Investigation of Micro Channel Fabrication by Electroforming.
Degree: MS, Mechanical Engineering, 2010, University of Toledo
► Nanotechnology has the potential to create many new materials and devices with…
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▼ Nanotechnology has the potential to create many new materials and devices with wide range of applications. Nanofabrication is the design and manufacture of devices with dimensions measured in nanometers. Development of an economic and reliable technique for the fabrication of reproducible micro channels has been an important challenge in this field. Feasibility of fabricating reproducible electrode gaps based on electroforming is investigated in this study. The proposed technique is investigated by both theoretical modeling and experimental methods. Finite Element Analysis (FEA) technique is implemented to investigate the proposed hypothesis of fabrication of micro channels on thin films coated on insulator substrate. The gap formation for aluminum, gold, and tungsten oxide is attempted. The influence of various parameters on the heat transfer phenomenon during the electroforming is studied. Micro channel formation for gold is also investigated experimentally. Surface measurements were conducted to investigate the electroforming process and the current-voltage characteristics are collected during the electroforming process. The experimental results obtained are compared with the Finite Element Analysis based modeling data. The simulation and experimental results confirm the feasibility of the fabrication of micro gaps by the proposed electroforming technique. It is found that proposed method can be employed to produce micro channels using a wide range of materials such as metals, metal oxides and compound semiconductors.
Advisors/Committee Members: Jayatissa, Ahalapitiya.
Subjects: Materials Science; Mechanical Engineering
Keywords: micro, electroforming,fabrication, comsol, simulation, finite element analysis
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14.
Dauster, Andrew J.
Development of University of Toledo Knee Simulator: First Generation.
Degree: MS, Mechanical Engineering, 2011, University of Toledo
► The objective of this thesis is to describe the design, development, and…
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▼ The objective of this thesis is to describe the design, development, and initial testing of the first generation of the UT Knee Simulator. The simulator was designed to simulate normal, weight bearing, daily living activities such as squatting or rowing and therefore allowed in-vitro testing with the lower limb in a vertical or horizontal position. Design and development included muscle simulation, correct movement of hip and ankle, data acquisition, and muscle simulation control. For better physiologic conditions of movement, the foot was considered fixed in space, the ankle free to rotate in each axis, to a limited degree, and the hip was limited to planar rotation. The hip rotation point was attached to a linearly sliding plate constrained to only move in an axial motion. Two servomotors, in conjunction with planetary gear systems, were used to simulate the loadings of the quadriceps and hamstring muscles. Each of the load straps were instrumented with load gauges. A flexible driveshaft was utilized with a hanging weight to drive the internal and external loaded rotation of the tibia. A programmable logic controller was used to communicate with both of the motors and all of the instrumentation. Of particular interest to this examination was the capability and interaction of antagonist muscles to limit and control motion of the knee. Horizontal and vertical orientations of the construct were used for the testing, as well as internally, externally, and neutral loadings of the tibia. Results obtained utilizing the UT Knee Simulator were repeatable and show that the UT Knee Simulator functions well when compared to other data sources, indicating it is a reliable starting point from which an advanced version may be created to better mimic the physiologic loading in the knee. Data developed from this simulator may be used to better understand the motions and loading in the knee, and design better orthopedic implants as well as physical therapy regimens.
Advisors/Committee Members: Hefzy, Mohamed.
Subjects: Biomechanics; Biomedical Research; Kinesiology
Keywords: Knee; Simulator; Deep Flexion
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15.
Eshghinejad, Ahmadreza.
Finite element study of a shape memory alloy bone implant.
Degree: MS, Mechanical Engineering, 2012, University of Toledo
► Shape memory alloys have been used in several biomedical devices in recent…
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▼ Shape memory alloys have been used in several biomedical devices in recent years. Their special thermo-mechanical behavior in recovering a certain shape upon heating and being able to tolerate large deformations without undergoing the plastic transformations make them a good choice for different applications. Biocompatibility of nitinol as a widely used shape memory alloy material is the other main property for biomedical devices. Osteoporosis is a common bone disease especially in elderly people. Bone degradation as the result of osteoporosis causes loosing of screws implanted in the bone during or after surgery. A new nitinol-based device which is designed to mitigate this adverse effect has been studied. This thesis analyzes the functionality of this novel nitinol-based expandable-retractable pedicle screw. The unique feature of this screw is that it is removable as needed. The functionality of the screw is verified by experiment and compared to the results of the numerical simulation in Abaqus. This simulation tool is the combination of the numerical implementation of shape memory alloy constitutive thermo-mechanical modeling into the Abaqus UMAT Fortran subroutine and the Abaqus finite element solver. The verification of this tool in several experiments has been carried out to establish validity of the numerical approach. The effect of the designed pedicle screw in mitigating the loosing effect has also been studied. Pullout test is a common way of evaluating a bone implant. The pullout force of a normal screw out of a normal bone was simulated with finite element in Abaqus. Consequently, performance of the new design in improving pull-out strength in osteoporosis bones has been studied. This thesis presents the design of the novel pedicle screw and paves the way of evaluating various medical devices with enhanced functionality.
Advisors/Committee Members: Elahinia, Mohammad.
Subjects: Mechanical Engineering
Keywords: Shape memory alloy; nitinol; pedicle screw; osteoporosis
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16.
Han, Peidong.
A Study on Electrolytic In-Process Dressing (ELID) Grinding of Sapphire with Acoustic Emission Monitoring.
Degree: MS, Mechanical Engineering, 2009, University of Toledo
► Single crystal sapphire is of significant interest due to its combination of…
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▼ Single crystal sapphire is of significant interest due to its combination of excellent physical, optical, electrical, chemical and mechanical properties. However, fine grinding of sapphire is quite challenging because of its high hardness and low fracture toughness, making it sensitive to cracking. Furthermore, wheel loading is another common problem in conventional grinding of hard and brittle materials. A new technique, Electrolytic In-process Dressing (ELID) grinding, shows great promise in overcoming the problems of conventional grinding of hard and brittle materials. This technology provides continuous dressing of metal-bonded wheels during the grinding process, while maintaining sharp abrasives from the superabrasive wheels. In this research, ELID technique was applied in the grinding of sapphire in order to obtain super surface finish and to minimize the problems in conventional grinding of sapphire. The research was focused on the pre-dressing oxide layer thickness, surface finish quality, and acoustic emission monitoring of the ELID grinding process. The effects of processing parameters on the oxide layer thickness, surface finish, and acoustic emission signals were evaluated. Correlations were found among the dressing current intensity, oxide layer thickness, surface finish and acoustic emission signals. A smoother surface was obtained using a higher dressing current at the cost of a higher wheel wear rate. The wheel wear mechanism in ELID grinding of sapphire is dominated by bond fracture because the bond strength is reduced by electrolysis. Results indicate that the acoustic emission technique has the potential to be used for monitoring the ELID grinding process, detecting the condition of the grinding wheel, and investigating the mechanisms of ELID grinding.
Advisors/Committee Members: Marinescu, Ioan.
Subjects: Engineering
Keywords: ELID Grinding, Acoustic Emission, Sapphire
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17.
Heminger, Michael Alan.
Dynamic Grid Motion in a High-Order Computational Aeroacoustic Solver.
Degree: MS, Mechanical Engineering, 2010, University of Toledo
► In this work, moving meshes will be employed to solve unsteady computational…
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▼ In this work, moving meshes will be employed to solve unsteady computational problems, while maintaining high-order, and high-accuracy. The main problem of interest is that of a plunging piston. The plunging piston problem, first presented in the First Workshop for Computational Aeroacoustics. Typically, computational aeroacoustics is seperate from aeroelasticity, a field where moving surfaces is integral. This project will join the two field, attempting to resolve propagating waves from a moving boundary. While this particiular problem has been attempted before, it was done using boundary conditions. This project’s main goal is to bridge the gap between computation fluid dynamic disciplines, creating a general standalone mesh morpher, enabling a new breed of acoustic problems to be solved. To do this, a highly efficient method of moving the mesh will need to be developed. Since the code uses high-order schemes to resolve the small sound waves, the mesh mover must be methods which keep the grid metrics continuous and smooth.
Advisors/Committee Members: Hixon, Ray.
Subjects: Acoustics; Engineering; Fluid dynamics; Mechanical engineering
Keywords: cfd; caa; computational fluid dynamics; aeroacoutics; mesh; grid; deformation; morphing; fluid structure interaction; piston
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18.
Herron, Joshua R.
Application of ALE contact to Composite Shell Finite Element model for Pneumatic Tires.
Degree: MS, Mechanical Engineering, 2005, University of Toledo
► To predict the spindle reaction forces and moments of a tire during…
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▼ To predict the spindle reaction forces and moments of a tire during rolling, engineers require a computationally efficient model. This thesis describes an efficient model for use in tire prototyping to generate force and moment curves for a rolling tire. Since the intent of this model is use in tire prototyping, it must be able to be built from tire engineering parameters and material properties. Furthermore, the model must be able to predict the forces and moments under several boundary conditions; including normal loads, inflation pressures, slip angles, and camber angles. To be practical, the model must also be able to solve for all these conditions under a day of CPU time. Darnell [6] proposed a tire model for vehicle impact simulations that used a Galilean Transformation to predict the rolling contact. The Darnell model required the generation of a sidewall look-up table, and composite properties of the tread region. The contact model was implemented in the commercial finite element software ABAQUS as a user element.
Advisors/Committee Members: Mousseau, Cedric.
Subjects: Engineering, Automotive
Keywords: Tire; Finite Element; Galiliean; Lagrangian; Arbitrary Lagrangian Eularian; Rolling; Contact; Force and Moments; Composite Shells
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19.
Jayanty, Sharmila.
Negative Poisson’s Ratio Composites - Finite Element Modeling and Experiments.
Degree: MS, Mechanical Engineering, 2010, University of Toledo
► Auxetic or negative Poisson’s ratio materials are of great research interest as…
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▼ Auxetic or negative Poisson’s ratio materials are of great research interest as they exhibit improved mechanical properties such as impact resistance, fracture toughness, hardness and shear modulus over conventional materials with a positive Poisson’s ratio and same stiffness. Most auxetic materials manufactured to date are porous, and the major hindrance of using these materials in structural applications is their low strength. In this research a new approach for manufacturing auxetic fiber-reinforced composites by embedding an auxetic fibrous network in a conventional polymer matrix is investigated using numerical and experimental methods. In this project, a finite element model was developed to investigate the proposed hypothesis of manufacturing an auxetic composite. Compressed mats of sintered stainless steel fibers are known to have negative Poisson’s ratio out-of-plane. It is hypothesized that their auxetic behavior is from the arrangement of fibers within the matrix, relative stiffness of the matrix and network of reinforcement. First, tension tests were performed on the compressed sintered mats and the experimental results have shown that Poisson’s ratio for all metal mat specimens is negative in transverse direction. Next, mechanical tests were performed and microscopic images were taken of the composite samples made by embedding the stainless steel mats with silanol terminated polydimethoxysiloxane (PDMS) polymer. Finally, polymer nanocomposites were made through the inclusion of high loading carbon nanofibers in the polymer matrix (PDMS). The experimental results of both the composite mats and nanocomposites confirm the feasibility of manufacturing an auxetic composite by embedding an auxetic network in a conventional polymer. The auxetic behavior in the composite mats is due to the arrangement of fibers in the network and compression of stainless steel mats during fabrication process. It was assumed that the auxetic behavior of the nanocomposites is due to effective network formation of nanofibers and the compression of the sample during preparation process.
Advisors/Committee Members: Berhan, Lesley M.
Subjects: Materials Science; Mechanical Engineering
Keywords: auxetic; nanofibers; polymer; nanocomposite; negative Poisson's ratio
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20.
Jiang, Hao.
Numerical Modeling and Analysis of Micro-structuring on Silicon on Insulator (SOI) Film under Localized Single Pulse Laser Irradiation.
Degree: MS, Mechanical Engineering, 2011, University of Toledo
► For micro- and nano-structuring, localized single-pulse laser irradiation based techniques have proven…
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▼ For micro- and nano-structuring, localized single-pulse laser irradiation based techniques have proven less complex and expensive compared to traditional lithography based techniques. The formation process has been shown controllable and repeatable. However, because of the small size (micro- or nano-meters) and processing time period (nano-seconds) of the formation, the mechanism behind the formation by localized single-pulse laser irradiation, in many aspects, is still not fully understood. A numerical model was built in ANSYS-FLUENT to simulate and explain the structure formation and show the effect of surface tension. The model was validated numerically by comparing to the experimental data for three different laser spot sizes; in addition, the grid study was performed to check the feasibility of the model. The simulations show that there is no deformation during the heating process and the deformation happens solely when the silicon is cooling. The Marangoni stress and flow, induced by temperature gradient, is the main cause of the structure formation. The surface tension between silicon and surrounding air influences the size and shape of the micro-tip to some extend. In addition, the absorption coefficients are shown as an important factor, and they are calculated numerically for three different spot sizes.
Advisors/Committee Members: Cioc, Sorin.
Subjects: Mechanical Engineering
Keywords: micro tip; surface tension; numerical simulation
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21.
Jones, Matthew.
Ignition and Combustion Characteristics of Nanoscale Metal and Metal Oxide Additives in Biofuel (Ethanol) and Hydrocarbons.
Degree: MS, Mechanical Engineering, 2011, University of Toledo
► Metal energetic additives are added to propellants and explosives to improve ignition…
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▼ Metal energetic additives are added to propellants and explosives to improve ignition and combustion performance. In particular, aluminum has been used as an energetic material in solid-based propellant rockets and explosives for many years due to its high combustion enthalpy and low cost. Recently, the introduction of nanotechnology has led to significant developments in the field of energetic materials. Nanoscale energetic materials, due to their surface area and unique thermal properties, are known to exhibit many advantages over conventional micron sized particles. However, the current mechanisms of nanoaluminum ignition and combustion are not fully understood. Furthermore, studies involving suspensions of energetic nanomaterials in a liquid medium (nanofluids) are very limited. A fundamental understanding of micron and nanoscale aluminum combustion is critical to the design and implementation of practical propulsion systems that use aluminum additives. Therefore, a comprehensive review on the ignition and combustion of energetic nanoparticles was performed, with a primary focus on aluminum, and two novel experimental studies were performed to investigate the combustion characteristics of nanoscale aluminum (n-Al) and aluminum oxide (n-Al2O3) in liquid fuels, namely, ethanol (C2H5OH). The first experimental study examined the heating values of several nanofluid suspensions of n-Al (50 nm) and n-Al2O3 (36 nm) in ethanol. The primary objective of this experimental study was to characterize the combustion reaction and gain a better understanding of nanoaluminum oxidation in a multi-component heterogeneous system. The heat of combustion was studied using a modified static bomb calorimeter system. Combustion experiments were performed with volume fractions of 1%, 3%, 5%, 7%, and 10% for n-Al, and 0.5 %, 1%, 3%, and 5% for n-Al2O3. Combustion element composition and surface morphology were evaluated using a scanning electron microscope and energy dispersive spectroscopy system. The results indicate that the amount of heat released volumetrically from ethanol combustion increases almost linearly with n-Al concentration. Nanoaluminum volume fractions of 1% and 3% did not show enhancement in the average volumetric heat of combustion, however, higher volume fractions of 5%, 7%, and 10% increased the volumetric heat of combustion by 5.82%, 8.65%, and 15.31%, respectively. Aluminum oxide and heavily passivated n-Al additives did not participate in combustion reactively, and there was no contribution from Al2O3 to the combustion enthalpy in the tests. A combustion model that utilized Chemical Equilibrium with Applications (CEA) was conducted as well and was shown to be in good agreement with the experimental results. Along with energy density enhancement, achieving precise control over the reactivity of nanofluids is an opportunity for future nanoenergetic fuel applications. A second experimental study involved the study in ignition probability of n-Al (50 nm) and n-Al2O3 (36 nm) in ethanol and the commonly used No. 2 fuel oil (diesel). The primary aims in this study were to study the effect of nanoenergetic additives on the ignition probability of ethanol with a hot-plate setup, and to explore the underlying mechanisms of ignition. Aluminum and Al2O3 were suspended in ethanol and diesel fuels from 0.1% to 3% volume fractions, and dropped onto a hot plate at temperatures varying from approximately 300 °C to 600 °C. The experimental probability was calculated and a logistic regression approach was used to determine the 50% ignition threshold. Nanoaluminum in ethanol was found to significantly increase the ignition probability: ethanol suspensions with 1%, 2%, and 3% aluminum volume fractions ignited as much as 100 °C lower than pure ethanol, and exhibited burning regimes similar to disruptive combustion in slurry droplets, while ethanol suspensions with n-Al2O3 volume fractions ignited at higher temperatures than pure ethanol. In addition, diesel mixtures with n-Al and n-Al2O3 additives demonstrated relatively the same hot plate ignition probability as pure diesel. Therefore, the likelihood of nanofluid ignition was strongly correlated with volume fraction concentration, metal additive material, and surface tension (contact angle).
Advisors/Committee Members: Li, Calvin.
Subjects: Mechanical Engineering
Keywords: Biofuel; Calorimetry; Combustion; Energetics; Ethanol; Fuels; Fuel additives; Heat of combustion; Ignition; Ignition probability; Nanoaluminum; Nanoenergetics; Nanofluids; Nanoparticles; Nanotechnology
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22.
Kenney, Peter Martin.
An Initial Study to Determine a Friction-Factor Model for Ground Vegetation.
Degree: PhD, Mechanical Engineering, 2009, University of Toledo
► Fluid drag data for flows through ground vegetation is needed by those…
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▼ Fluid drag data for flows through ground vegetation is needed by those studying the atmospheric boundary layer near the earth in wind turbine design, by those performing drainage calculations for fields awash from a great river, by CFD modelers of the lowest levels of a forest fire, and by agriculturalists investigating the wind overturning of crops. All of these researchers lament that there is little plant-drag data available. This work presents an initial study into a plant friction-factor model for a forest-fire simulation CFD program; but hopefully will be useful to the other professionals mentioned. The model develops a friction factor as a function of Reynolds number for various percentage cover of plants. Artificial plant arrangements were mounted in a clear acrylic frame, backlit from underneath, and, using a mirror, are photographed from sixty feet away. From the photographic data, fractal dimension and an average gap diameter can be determined as a function of percentage coverage. Then the arrangement is placed in a wind tunnel and drag forces on the system measured for upstream velocities ranging up to thirty-eight miles an hour. Most arrangements had axes of greatest and least flow resistance. Averaging the friction-factor values computed for these extremes a friction-factor model is developed for three different artificial plants. These individual models are, in turn, combined into a single model using the fractal dimension data for the plants. Vorticity and flow through the plant canopy causing plant oscillation are not considered.
Advisors/Committee Members: Keith, Theo G., Jr.
Subjects: Mechanical engineering
Keywords: ground vegetation, drag, percentage cover, fractal dimension, grass, friction factor
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23.
Kilaru, Prabhu Kiran.
Estimation of carbon emissions from municipal solid waste and determination of the impact of recycling on emissions.
Degree: MS, Mechanical Engineering, 2010, University of Toledo
► The objective of this thesis is to develop and apply a model…
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▼ The objective of this thesis is to develop and apply a model to systematically analyze the impact of recycling in reducing green house gas emissions and estimate the revenue generated from recycling at a facilities. The analysis is focused on both environmental and economical performance of a facility. Increasing global importance of carbon emissions has resulted in numerous studies on estimation of emissions from various processes. The estimation of emissions from processes like electricity usage, fuel usage etc. by a random calculation procedure yields almost similar results. The case is not the same for recycling. Some calculators totally ignore the impact of recycling while others use odd ball approach to estimate the reduction in emissions from recycling. There is a great necessity for accurate estimation of emissions not only to understand the impact on environment but also help an organization to take proper measures to minimize these emissions. This thesis will address that need. Initially a model was developed using Microsoft Excel to estimate the waste generated at a facility. Emissions from waste were calculated using US EPA conversion factors and revenue was estimated based on recycling market prices. This model was applied to a facility in Lucas county OH. Total municipal solid waste generated was calculated. Emissions were estimated and recycling opportunities were studied at the facility. This study revealed that the estimation of emissions from waste and recycling can be done to an acceptable level by applying the recommended model. The application of the model to the facility in Lucas County (OH) predicted that if all the recyclables that are generated at the facility can be captured and recycled, the emissions from waste can be compensated and in most cases the reduction in emissions would exceed the emissions generated at the facility from waste. Revenue generated from the recycling makes the model more attractive because, the decision makers at the facility can really understand the financial benefits of recycling. The case study of a facility discussed in Chapter 4 reveals that waste management, which is presently a liability to the facility, can be a source of revenue by recycling solid waste. The results shows that just by recycling mixed office paper generated at the facility, roughly $1500 can be obtained annually. The comparison between emissions under present conditions and suggested conditions helps the facility to focus on its major sources of emissions. The results from case study also predict that current carbon emissions from waste at the facility around 7 MTCE and that would have gone down to -11 MTCE if all the possible solid waste had been recycled. The major sources of emissions identified from the study are food waste and mixed office paper. Only a little can be done to reduce emissions from food waste, where as recycling mixed office paper can reduce emissions from 1.4 MTCE to -11.3 MTCE. This methodology can be applied to any facility in the United States with minor modifications based on the materials recycled in the region.
Advisors/Committee Members: Franchetti, Matthew J.
Subjects: Mechanical Engineering
Keywords: MSW; Recycling; carbon emissions; green house gases
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24.
Koosukuntla, Narender Reddy.
Towards Development of a Multiphase Simulation Model Using Lattice Boltzmann Method (LBM).
Degree: MS, Mechanical Engineering, 2011, University of Toledo
► Lattice Boltzmann Method is evolving as a substitute to the prevalent and…
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▼ Lattice Boltzmann Method is evolving as a substitute to the prevalent and predominant CFD modeling especially in cases such as multiphase flows, porous media flows and micro flows. This study is aimed at developing simulation model for multiphase flows for practical applications such as cavitation in a journal bearing or lubrication of micro contact. The code is first validated against benchmark single phase flows like Poiseulle flow and flow over a cylinder. In the process, various boundary conditions like velocity, pressure, out-flow, no-slip and periodic boundary conditions are tested. Finally, the Shan-Chen model for multiphase physics, which is based on the interaction force between the fluid particles, is incorporated into the code and is validated.
Advisors/Committee Members: Cioc, Sorin.
Subjects: Mechanical Engineering
Keywords: LBM; Lattice Boltzmann Method; CFD
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25.
Kuznetov, Alexandru Marius.
An Investigation of the Steady-State Performance of a Pressurized Air Wave Journal Bearing.
Degree: MS, Mechanical Engineering, 2010, University of Toledo
► The purpose of this thesis is to investigate the steady-state behavior of…
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▼ The purpose of this thesis is to investigate the steady-state behavior of a pressurized wave bearing. The pressurized air wave journal bearing was analyzed using a commercial CFD software, Fluent. The 3D Navier Stokes compressible equations were integrated to simulate the flow. Turbulence effects were included in the computation. The real geometry of the wave bearing and of the supply holes were simulated by using a structured grid. The steps performed during the numerical simulation and the set-up of Fluent used in the thesis are presented in detail. The model was validated by comparing the flow rate obtained at different supply pressures for zero eccentricity and zero rotational speed to values of the flow rate obtained experimentally. The steady-state behavior of the bearing for eccentric positions is simulated using the “moving reference frame” method. The load capacity for different eccentricities and velocities at a constant supply pressure of 50 PSI were calculated. The advantage of the method used in this thesis is that it does not require a correction of the flow rate with an empirical discharge coefficient. Moreover, the method allows the calculation of the discharge coefficient based on the results of the simulation. In the present thesis, the discharge coefficients are calculated for different eccentricities and rotational speeds and supply pressures
Advisors/Committee Members: Afjeh, Abdollah.
Subjects: Engineering
Keywords: bearings, steady-state, eccentricity ratio, Fluent
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26.
Kwasniak, Peter James.
Construction and Testing of an Ultrasonic Transducer for Biofilm Removal.
Degree: MS, Mechanical Engineering, 2011, University of Toledo
► A serious problem with total joint replacement procedures is the risk of…
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▼ A serious problem with total joint replacement procedures is the risk of infection. Bacterial biofilm colonies can attach to the surface of the implant, and usually require the removal and replacement of the entire joint. Through acoustical cavitation, it could be possible to remove the biofilm colonies from the implant, thus eliminating the need to remove and replace the implant. Ideally, this would involve constructing a device that could be incorporated into and existing medical device, in this case a pulsed lavage. In this thesis, biofilm was simulated by painting the back of mirrors with acrylic paint. These mirrors were then exposed to ultrasonic cavitation for a period of time ranging from 2 to 20 minutes and the sonicated slides were scanned and read through an image processor to determine cleaning effectiveness. Using a commercial sonicator, proof of concept tests, as well as tests to find the effects of distance, position, and use with a water jet on cleaning effectiveness were run. However, because of its size, it is impractical to use the large sonicator on biofilm removal. The original ultrasonic transducer ring was constructed and tested. Once proof that the device removed the paint from the test slides was achieved, the device was tested under a several conditions including distance and temperature. Water flow tests and rotation and orientation tests were performed to determine how these factors influenced cleaning efficiency. The results were very encouraging in showing that an ultrasonic transducer could be constructed and be effective in removing biofilm from a surface. Further work will test the device on biofilm colonies to validate the usefulness of the device.
Advisors/Committee Members: Cioc, Sorin.
Subjects: Biomedical Engineering; Engineering; Mechanical Engineering
Keywords: Sonication; cavitation; ultrasonic transducer; biofilm
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27.
Lindsey, Justin.
Fatigue Behavior in the Presence of Periodic Overloads Including the Effects of Mean Stress and Inclusions.
Degree: MS, Mechanical Engineering, 2011, University of Toledo
► Variable amplitude loading of components or structures can result in failures which…
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▼ Variable amplitude loading of components or structures can result in failures which occur much sooner than would be predicted by commonly used life prediction models, utilizing constant amplitude loading. The goal of this study was to investigate the effect of periodic overloads on fatigue behavior of smooth specimens made from five grades of steel and one grade of aluminum. This history included a periodic fully-reversed overload cycle followed by smaller cycles in the presence of a mean stress. Life predictions were performed for each test by implementing the Linear Damage Rule along with the strain-life equation or Smith-Watson-Topper (SWT) mean stress parameter. Life predictions were then compared to experimental results. Life predictions with the SWT parameter showed an increase in accuracy versus the strain-life method but there still remained predictions that were unaffected by the use of this parameter. Presence of periodic overloads in a load history resulted in increased damage for small cycles not only at strain levels above the fatigue limit, but also in damage for cycles below the fatigue limit. Additional tests were performed in order to identify the amount of damage resulting from individual aspects of the load history. These aspects included small cycles in the presence of mean stress without overloads, fully-reversed small cycles with overloads, as well as variations in the number of small cycles per load block. Comparison of these different aspects showed that in some cases the application of mean stress in the periodic overload history resulted in little to no additional small cycle damage. Anisotropy resulting from sulfide inclusions was examined by applying the periodic overload history to three sets of steel 4140 containing three different levels of sulfur content (0.004%, 0.012%, and 0.077%). The specimens were machined so that the axis of the specimen was transverse to the rolling direction of the material. Results of the testing showed that, although the sulfur content has a drastic effect on fully-reversed constant amplitude fatigue lives, there is little noticeable different between the materials with different levels of sulfur in the presence of periodic overloads.
Advisors/Committee Members: Fatemi, Ali.
Subjects: Mechanical Engineering
Keywords: Periodic Overloads; Life Prediction; Inclusion; Sulfur Effect
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28.
Lopera, Javier.
Aerodynamic Control of Slender Bodies from Low to High Angles of Attack through Flow Manipulation.
Degree: PhD, Mechanical Engineering, 2007, University of Toledo
► This dissertation presents experimental investigations of several novel active flow control methodologies…
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▼ This dissertation presents experimental investigations of several novel active flow control methodologies that have been implemented for aerodynamic control and maneuvering of slender bodies at low and high angles of attack through flow manipulation. For low angles of attack, a U.S. Army Smart Cargo projectile was examined. For high angles of attack a U.S. Air Force countermeasure concept projectile termed DEX (Destructive Expendable) was examined. Low angle of attack control was attempted using two novel separation control techniques: reconfigurable porosity and miniature deployable spoilers. Results show that significant aerodynamic forces are generated by implementing reconfigurable porosity and can be effectively used to steer and maneuver air vehicles. Porous patterns with a “saw-tooth” configuration seem to be the most effective in generating consistent control forces over a wide range of angles of attack. Miniature deployable spoilers successfully demonstrated their ability in producing both positive and negative pitch and yaw controls by modulating the spoiler height and length when used on the boattail and Aero Control Fins (ACFs) of a projectile. The effect of aftbody strake parameters such as shape, locations (axial and azimuthal), deployment height, and number of strakes implemented was examined on a short blunt-nose projectile. Large yaw control authority was attained for á > 40 deg. The largest yaw control authority was produced by a rectangular-shaped strake. A robust closed-loop feedback controller was successfully tested using dynamic wind tunnel experiments to control the coning motion of a projectile. The controller showed good control authority and was capable of attaining and maintaining the commanded roll angle with a tolerance of ± 10 deg. A study was conducted to gain some insights into the fluid mechanics of short blunt-nose bodies of revolution at high angles of attack. Off- and on-surface flow visualization records are collected to study the effects of two blunt noses: a hemispherical nose and an elliptical nose with 33% ellipticity. It was found that the elliptical-nose results in flow behaviors typical of a blunt-nose, while the hemispheric-nose results in behaviors that are akin to a pointed-nose. An explanation for the contrasting behaviors is provided.
Advisors/Committee Members: Ng, T. Terry.
Keywords: active flow control, aerodynamic control, slender bodies, blunt bodies, high angle of attack, forebody vortex control, coning motion, strakes, flowfield
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29.
McKelvey, Sean Ambrose.
Influence of Surface Finish on Bending Fatigue of Forged Steel Including Heating Method, Hardness, and Shot Cleaning Effects.
Degree: MS, Mechanical Engineering, 2011, University of Toledo
► The overall objective of this study was to conduct a systematic and…
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▼ The overall objective of this study was to conduct a systematic and comprehensive experimental investigation to evaluate and quantify forged surface finish effect at several hardness levels (19 HRC, 25 HRC, 35 HRC, and 45 HRC) on bending fatigue specimens of a commonly used forged steel (10B40 steel). Specimens were subjected to reverse cantilever bending and rotating bending fatigue. Two surface conditions were evaluated, a smooth-polished surface finish to be used as the reference surface, and a hot-forged surface finish. The heating methods used for forging were gas furnace heating as well as induction heating, to allow comparison of the two heating methods, as decarburization depth differs between the two methods. Since shot blasting is commonly used as a forged surface cleaning process with the additional benefit of inducing compressive residual stress, the hot-forged surface finish was evaluated with and without shot blasting. Some testing was also conducted to investigate the effect of the flash left by the forging process. In addition, the effect of grain flow resulting from the forging process was evaluated by testing smooth specimens machined from the same rolled bar used for forging. Fatigue test results in this investigation confirm that the old data commonly used for the as-forged surface condition are too conservative. New forged surface finish factors and curves as a function of hardness or tensile strength and fatigue life were developed based on experimental data. A fracture mechanics-based approach was also used to predict fatigue life for the as-forged fatigue specimens.
Advisors/Committee Members: Fatemi, Dr. Ali.
Subjects: Engineering
Keywords: Fatigue; Surface Finish Effects; Forged Steel; Bending Fatigue
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30.
Medida, Shivaji.
Curvilinear Extension to the Giles Non-reflecting Boundary Conditions for Wall-bounded Flows.
Degree: MS, Mechanical Engineering, 2007, University of Toledo
► In the present work, the Giles non-reflecting boundary conditions have been extended…
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▼ In the present work, the Giles non-reflecting boundary conditions have been extended to Curvilinear co-ordinates for wall-bounded flows. In addition to the non-reflecting boundary conditions, wall boundary conditions have been derived and implemented for inflow/outflow-wall corners (grid points common to the inflow/outflow and wall boundaries) so that the flow solution at the corner points satisfies both the inflow/outflow boundary conditions and the wall boundary conditions. Two-dimensional, wall-bounded, Ringleb flow configurations (with non-orthogonal grids and curved boundary geometries) were used as test cases to validate the non-reflecting boundary conditions and the wall corner conditions. The wall corner conditions for the Cartesian Giles boundary conditions were sufficient to eliminate the flow through wall at inflow and outflow corners. However, the Cartesian Giles boundary conditions along with the wall corner conditions could not solve the corner problem in the Ringleb flow test cases and eventually caused the flow solution to diverge. Two-dimensional Curvilinear Giles boundary conditions derived from the Curvilinear form of the linearized Euler equations resulted in additional terms that were not present in the chain rule form of Cartesian Giles boundary conditions. These additional terms contained the factor (xx + yy) which becomes zero for an orthogonal grid. The Curvilinear Giles boundary conditions, when implemented without the additional terms, displayed the same corner problem that was encountered with the chain rule form of Cartesian Giles boundary conditions, proving the significance of the additional orthogonal terms. In order to completely eliminate flow through the wall and obtain the correct solution at the corners, the Curvilinear boundary conditions with the additional terms and the wall corner conditions were required. The Curvilinear Giles boundary conditions along with the wall corner conditions were successfully tested on various Ringleb flow geometries and grid densities. However, a long-term instability was noticed for all the Ringleb flow configurations beyond a certain number of grid points. This was eliminated by stretching the grid towards the inflow and outflow boundaries. Converged solutions were obtained for all the test cases with acceptable L2 errors.
Advisors/Committee Members: Hixon, Duane Ray.
Keywords: non-reflecting; boundary conditions; wall-bounded; corner condition; Giles; characteristic
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