Mechanical Engineering Commons^™

The Search For An Optimal Means Of Determining The Minmax Control Parameter Using Sensitivity Analysis, John Teye Brown

Doctoral Dissertations

The use of computational methods for design and simulation of control systems allows for a cost-effective trial and error approach. In this work, we are concerned with the robust, real-time control of physical systems whose state space is infinite-dimensional. Such systems are known as Distributed Parameter Systems (DPS). A body whose state is heterogeneous is a distributed parameter. In particular, this work focuses on DPS systems that are governed by linear Partial Differential Equations, such as the heat equation. We specifically focus on the MinMax controller, which is regarded as being a very robust controller. The mathematical formulation of the …

Manufacturing And Characterization Of Soy-Based Polyurethane Composites, Rama Bhadra Raju Vuppalapati

Doctoral Dissertations

"The major cost drivers for composites are raw materials and manufacturing process. Automated manufacturing processes like pultrusion and low cost bio-based raw materials can significantly lower the cost of composites. Polyurethane (PU) resin systems are being introduced in the pultrusion industry as they have higher performance characteristics and manufacturing feasibility when compared to conventional resin systems such as polyester and vinyl ester. PU resin systems are generally characterized as aromatic and aliphatic. Aliphatic PU has lower mechanical properties than the aromatic resin system due to its chemical structure. Nano materials can be used to increase the mechanical properties of aliphatic …

The Risk Mitigation Strategy Taxonomy And Generated Risk Event Effect Neutralization Method, Daniel A. Krus

Doctoral Dissertations

"In the design of new products and systems, the mitigation of potential failures is very important. The sooner in a product's design mitigation can be performed, the lower the cost and easier to implement those mitigations become. However, currently, most mitigations strategies rely on the expertise of the engineers designing a product, and while models and for failure modes do exist to help, there are no guidelines for performing product changes to reduce risk. To help alleviate this, the risk mitigation strategy taxonomy is created from an empirical collection of mitigation strategies used in industry for failure mitigation, creating a …

Advanced Thermal Models For Improved Design Of Counter Flow Microchannel Heat Exchangers, Bobby Mathew

Doctoral Dissertations

Theoretical models of counter flow microchannel heat exchangers subjected to scaling and secondary effects are developed in this dissertation. The scaling effects studied include axial heat conduction and viscous dissipation, while the secondary effects considered in this dissertation is that of external heat transfer via heat flux and temperature. The theoretical models developed are one-dimensional and consist primarily of ordinary governing equations that describe the axial variation of hot and cold fluid. For the case of axial heat conduction, the axial variation of wall temperature is also modeled. The models are dependent on various factors, such as Reynolds number, Prandtl …

Development Of A Simple Vibration Model For Predicting The Structural Dynamics Of An Hcci Engine, Jeffery A. Massey

Doctoral Dissertations

"The hypothesis tested in this work is that the surface vibration and radiated sound of an engine operating under HCCI combustion is dominated by the free vibration response of the engine's structural components to an impulsive loading brought about by the rapid energy release of the HCCI combustion process. Recent work by the author has shown that classical vibration theory describing the dynamic response of a single-degree-of-freedom (SDOF) oscillator may capture the major characteristics of the engine surface vibrations. Through an experimental investigation of HCCI combustion engine dynamics this model has been developed further.

A band level analysis of measured …

Nonlinear Modeling And Simulation Of Radial Forging Process, Jian Chen

Doctoral Dissertations

"Radial forging is an important manufacturing process to produce large cannon barrels. It is used to improve the material properties and reduce the porosity of the billet. The objective of this study is to develop finite element models to investigate the behavior of the workpiece and predict the elimination of void defects in the radial forging process. A nonlinear coupled finite element model has been developed to study the behavior of a large-diameter tube subjected to mechanical and thermal loadings in hot radial forging. The model is formulated in a three-dimensional frame, accounting for both axial and circumferential effects. A …

Advanced Composites Using Non-Autoclave Processes: Manufacturing And Characterization, V. G. K. Menta

Doctoral Dissertations

"The objective of the present study is to develop non-autoclave processes to manufacture high performance composites for aerospace applications. In Paper 1, vacuum assisted resin transfer molding (VARTM) process was developed for elevated temperature composites. Use of VARTM process for fabricating high temperature resins presents unique challenges such as high porosity and low fiber volume contents. Two different vacuum bagging methods: Seeman Composite Resin Infusion Molding Process (SCRIMP) and Double Vacuum Bagging Infusion (DVBI) process were evaluated. Flow simulation tool was used to predict key flow parameters needed for the successful infusion. In Paper 2, honeycomb sandwich panels were manufactured …

Femtosecond Laser Micromachining Of Microstructures For Sensing And Detection, Yukun Han

Doctoral Dissertations

"This thesis focuses on the fabrication and analysis of miniature functional devices that can be used for different sensing and detection applications. As the first step, the surface characteristics and morphology of the micro/nano structures on substrates (fused silica and silicon) fabricated in water and in air by femtosecond laser were investigated. Based on this study, three micro devices have been designed and fabricated by femtosecond laser, and they were analyzed for optical and chemical sensing and detections. The three micro devices are: 1) an optical Fabry-Perot interferometer in optical fiber (made from fused silica) with smooth cavity surfaces. The …

Approximate Dynamic Programming Solutions With A Single Network Adaptive Critic For A Class Of Nonlinear Systems, Jie Ding

Doctoral Dissertations

"Approximate dynamic programming formulation implemented with an Adaptive Critic (AC) based neural network (NN) structure has evolved as a powerful technique for solving the Hamilton-Jacobi-Bellman (HJB) equations. As interest in ADP and the AC solutions are escalating with time, there is a dire need to consider possible enabling factors for their implementations. A typical AC structure consists of two interacting NNs which is computationally expensive. In this work, a new architecture, called the "Cost Function Based Single Network Adaptive Critic (J-SNAC)" is presented that eliminates one of the networks in a typical AC structure. This approach is applicable to a …

Dynamic Ergonomic Analysis And Simulation Of Fastening Operation, Akul Joshi

Doctoral Dissertations

"Operator performing fastening operation with powered hand-tools at awkward postures is subjected to external forces that may pose a risk of developing ergonomic injuries. For design of safe workplaces and selection of tools it is necessary to identify the probable causes of discomfort by simulating the work conditions and quantifying the risk factors. An ergonomic simulator is developed to simulate the fastening operation and quantify the effects of posture and force in fastening operation. The effect of dynamic forces is analyzed using two approaches. The first approach analyzes the effect of tool vibration while the second analyzes the hand-arm system …

Sandwich Structures With Advanced Facings, Cody H. Nguyen

Doctoral Dissertations

"The purpose of this research is to investigate potential advantages of two innovative designs of sandwich panels. The first design involves sandwich panels with a piece-wise thickness of the facings aiming at two possible outcomes: (I) improved the structural response, i.e. strength and stiffness, without increasing the weight of the structure or (2) reduction in the weight of the structure without a detriment to its structural response. The analysis is conducted analytically using the first-order shear deformation theory and numerically by the finite element analysis of conventional and stepped-wise sandwich panels. The applicability of the first-order shear deformation theory to …

Elimination Of Deck Joints Using A Corrosion Resistant Frp Approach, Ashok Reddy Aleti

Doctoral Dissertations

The research presented herein describes the development of durable link slabs for jointless bridge decks based on using FRP grid for reinforcement. Specifically, the ductility of the FRP material was utilized to accommodate bridge deck deformations imposed by girder deflection, temperature variations, and concrete shrinkage. It would also provide a solution to a number of deterioration problems associated with bridge deck joints.

The design concept of the link slabs was then examined to form the basis of design for FRP grid link slabs. Improved design of FRP grid link slab/concrete deck slab interface was confirmed in the numerical analysis. The …

Mitigation Of Chloride And Sulfate Based Corrosion In Reinforced Concrete Via Electrokinetic Nanoparticle Treatment, Kunal Kupwade-Patil

Doctoral Dissertations

Concrete is a porous material which is susceptible to the migration of highly deleterious species such as chlorides and sulfates. Various external sources, including sea salt spray, direct seawater wetting, deicing salts and chlorides can contaminate reinforced concrete. Chlorides diffuse into the capillary pores of concrete and come into contact with the reinforcement. When chloride concentration at the reinforcement exceeds a threshold level it breaks down the passive oxide layer, leading to chloride induced corrosion. The application of electrokinetics using positively charged nanoparticles for corrosion protection in reinforced concrete structures is an emerging technology. This technique involves the principle of …

Experimental Investigation Of Flow And Heat Transfer Characteristics Of R -134a In Microchannels, Abdullahel Bari

Doctoral Dissertations

The purpose of this study was to investigate the flow and heat transfer characteristics of liquid refrigerant R-134a in rectangular microchannels. The research concentrated mostly upon single-phase experiments with limited investigation of boiling phenomenon in microchannels. Tests were performed using rectangular microchannels with hydraulic diameters ranging from 112 μm to 210 μm and aspect ratios varying approximately from 1.0 to 1.5. The Reynolds number in the experiments ranged from 1,200 to 13,000 although most data were collected in the transition and turbulent flow regimes.

The experimental data for friction factor measurement had a similar trend as predicted by macroscale theory …

Solid Oxide Fuel Cell Electrode Characterization And Improvement For Fuel Flexibility And Supplemental Power Production, Isaiah D. Kellogg

Doctoral Dissertations

"Solid oxide fuel cells (SOFC) were fabricated and the electrodes tested for their individual catalytic effectiveness in various fuels by exposing each electrode to mixed gas while the opposite electrode was exposed to its respective pure gas. Mixed hydrogen and oxygen gas was successfully utilized as fuel in a single chamber SOFC (SC-SOFC). The conditions at which the porous nickel-yttria-stabilized zirconia (Ni-YSZ) cermet anode performed well did not significantly overlap the conditions at which the La₀.₈Sr₀.₂Fe₀.₈Co₀.₂ oxide (LSCF) cathode performed well, but there was significant catalytic activity at both electrodes which increased the open circuit voltage (OCV) beyond that predicted …

Molecular Simulation Of The Infrared Absorption Cross Section And Thermophysical Properties Of A Polyatomic Fluid, Zhi Liang

Doctoral Dissertations

"The work presented in this dissertation aims at ab initio calculations of the infrared absorption cross section, heat capacity, self-diffusion coefficient, shear viscosity and thermal conductivity of a polyatomic fluid with the aid of statistical mechanics. The simulation is firstly focused on calculating single-molecule properties such as molecular structure, vibrational energy eigen values and transition dipole moments using an efficient method based on the density functional theory. Based on these ab initio results, the infrared absorption cross sections are determined by the Fermi's Golden rule, and the thermophysical properties are determined from molecular dynamics simulations. Using carbon dioxide as an …

Analysis Of Laminated Architectural Glazing Subjected To Combined Wind And Debris Impact Loading, Mahesh Shibarooru Shetty

Doctoral Dissertations

"Laminated glazing has been a popular form of window glazing in recent years and is found to be effective during extreme weather conditions like hurricane. Laminated glass is composed of two glass layers with a polymer as an interlayer. The main objective of this work involves studying the stress response, failure and damage analysis of rectangular laminated architectural glazing against combined wind and windborne debris impact. Here both small-hard (like roof gravel) and large-soft (like timber) windborne debris are considered. The stress response of the rectangular laminated architectural glazing was modeled using the finite element code ABAQUS. The effect of …

Effects Of Optimized And Sub-Optimum Two Degree Of Freedom Lining Tolerances On Modeled Inlet Acoustic Attenuation And Normal Incidence Impedance Measurement At Elevated Temperatures, David R. Burd

Doctoral Dissertations

"This work first investigates the effect of manufacturing tolerances on realized attenuation for two degree-of-freedom linings with the use of lining models and finite element duct propagation codes. Acoustic linings were created for two turbofan engines that optimize attenuation at takeoff/sideline and approach conditions. Lining physical and geometric parameters were set, which best meet the optimum impedance requirements at two target frequencies. Similar linings were created to investigate sub-optimum designs. Variations of these parameters representing realistic manufacturing tolerances were used to systematically examine the effect on installed impedance and predicted attenuation. Attenuation at sideline and approach conditions was found to …

Experimental And Computational Investigations Of Hydrogen Safety, Dispersion And Combustion For Transportation Applications, Shravan K. Vudumu

Doctoral Dissertations

"Hydrogen is an energy carrier that can be produced from a variety of sources, offering one of the viable solutions to the increasing demands for clean and sustainable energy. Compared to the conventional fuels, hydrogen has distinct properties that need to be properly accounted for during its safer storage and delivery as well as more efficient and cleaner utilization. The broader objective of this study is to contribute to the scientific knowledge necessary to overcome key technical barriers to the widespread implementation of hydrogen in transportation applications. Specifically, lower flammability limit of hydrogen is first measured with an enhanced experimental …

Systematic Functional And Object-Oriented Product Design Frameworks, Jen-Chi Wu

Doctoral Dissertations

"The existing co-design methods of mechatronic products focus on co-design of mechanical and electronic components or co-design of computer hardware and software components. There exist no effective co-design methods for mechanical, electronic and software components at the concept design stage. The research objective of this dissertation work is to develop more effective systematic product design approaches for co-design of mechatronic products. Three innovative functional and object-oriented integrated design frameworks and one virtual prototyping application, which leverages on these three design frameworks, have been developed for co-design of mechatronic products. The three frameworks are: I) Hierarchical Object-Oriented Functional Modeling Framework, 2) …

Modeling And Simulation Of High Pressure Composite Cylinders For Hydrogen Storage, Jianbing Hu

Doctoral Dissertations

"Composite hydrogen cylinders provide an efficient means of storage of hydrogen gas for modern hydrogen vehicles. Safety issues arising from the high gas pressure, temperature variation, fire attack, and fracture failures are the main concerns. The focus of this study is to develop a Finite Element (FE) model to predict the performance of composite cylinders subjected to extreme mechanical/thermal loadings and provide guidance for design optimization"--Abstract, page iv.

Fundamentals Of Friction Stir Spot Welding, Harsha Badarinarayan

Doctoral Dissertations

"The recent spike in energy costs has been a major contributor to propel the use of light weight alloys in the transportation industry. In particular, the automotive industry sees benefit in using light weight alloys to increase fuel efficiency and enhance performance. In this context, light weight design by replacing steel with Al and/or Mg alloys have been considered as promising initiatives. The joining of structures made of light weight alloys is therefore very important and calls for more attention. Friction Stir Spot Welding (FSSW) is an evolving technique that offers several advantages over conventional joining processes.

The fundamentals aspects …

Information Archival And Reuse: Drawing Conclusions From The Past, Matt R. Bohm

Doctoral Dissertations

"Over the last few decades design researchers have put forward theories and proposed methodologies that increase the chance that a design team will reliably arrive at the optimal solution to a given design problem. Studies, however, bear out that theories and methodologies alone will not guarantee an optimal or even good design solution. Instead, a breadth of knowledge across multiple engineering domains and the time and tools to thoroughly evaluate the design space are as important as any prescriptive design method. This work presents a set of underlying engineering technologies to define, archive and reuse product design knowledge to provide …

A Finite Difference Method For Studying Thermal Deformation In Three-Dimensional Thin Films Exposed To Ultrashort Pulsed Lasers, Suyang Zhang

Doctoral Dissertations

Thermal analysis related to ultrashort-pulsed lasers has been intensely studied in science and engineering communities in recent years, because the pulse duration of ultrashort-pulsed lasers is only the order of sub-picoseconds to femtoseconds, and the lasers have exclusive capabilities in limiting the undesirable spread of the thermal process zone in the heated sample. Studying the thermal deformation induced by ultrashort-pulsed lasers is essential for preventing thermal damage. For the ultrashort-pulsed laser, the thermal damage is different from that caused by the long pulsed lasers and cracks occur after heating.

This dissertation presents a new finite difference method for studying thermal …

Addressing Nonlinear Combustion Instabilities In Highly Dilute Spark Ignition Engine Operation, Brian C. Kaul

Doctoral Dissertations

"Dilute operation is a promising approach for increasing spark-ignition engine efficiency, in the form of either lean burn (air dilution) or EGR (inert dilution). High levels of charge dilution, however, lead to cyclic variability that is largely deterministic in nature. The determinism and nonlinear nature of the system indicate that it should be possible to reduce the cycle-to-cycle variations by implementing an electronic controller. Several needs arise when considering the development of such a controller. Three topics of interest are covered herein. First, a method of analysis for nonlinear dynamical systems is applied to engine data in order to estimate …

Unsteady Flow And Heat Transfer In Periodic Complex Geometries For The Transitional Flow Regime, Li-Kwen Chen

Doctoral Dissertations

"Diesel engines are facing significant challenges with upcoming changes in emissions standards. In general, meeting the increased emission standards will require a larger fraction of the engine heat rejection to occur in the vehicle cooling system. For certain applications, the surface geometry must also be such that it resists particulate fouling, precluding common interrupted surfaces such as louvered fins. Although acceptable continuous surface geometries such as bumped fin geometries are in use, the impacts of changing the parameters of this geometry are unknown. This study investigates the transport characteristics of bumped fins in the transitional flow regime using unsteady multi-dimensional …

Integrated Process Planning For A Hybrid Manufacturing System, Lan Ren

Doctoral Dissertations

"A hybrid manufacturing system integrated CNC machining and laser-aided layered deposition and achieves the benefits of both processes. In this dissertation, an integrated process planning framework which aims to automate the hybrid manufacturing process is investigated. Critical components of the process planning, including 3D spatial decomposition of the CAD model, improvement of the toolpath generation pattern, repairing strategies using a hybrid manufacturing system, etc., are discussed"--Abstract, page iv.

Modeling And Rendering For Development Of A Virtual Bone Surgery System, Qiang Niu

Doctoral Dissertations

"A virtual bone surgery system is developed to provide the potential of a realistic, safe, and controllable environment for surgical education. It can be used for training in orthopedic surgery, as well as for planning and rehearsal of bone surgery procedures...Using the developed system, the user can perform virtual bone surgery by simultaneously "seeing" bone material removal through a graphic display device, "feeling" the force via a haptic deice, and "hearing" the sound of tool-bone interaction"--Abstract, page iii.

Modeling, Analysis And Experimentation For Building Ice Parts With Supports Using Rapid Freeze Prototyping, Frances D. Bryant

Doctoral Dissertations

"Rapid Freeze Prototyping (RFP) is a freeform fabrication method that freezes water droplets into ice in a layer-by-layer manner to additively create a 3-dimensional part. Each layer of a geometry is deposited and allowed to freeze before the next layer is added. Ice parts produced by RFP can be used in investment casting to replace wax patterns and in other applications which may benefit from the unconventional method of using ice as a pattern or mold. More recently, a sacrificial support material has been incorporated into RFP so that over-hung areas and complex geometries can be fabricated. The research presented …

Virtual Prototyping With Surface Reconstruction And Freeform Geometric Modeling Using Level-Set Method, Weihan Zhang

Doctoral Dissertations

"More and more products with complex geometries are being designed and manufactured by computer aided design (CAD) and rapid prototyping (RP) technologies. Freeform surface is a geometrical feature widely used in modern products like car bodies, airfoils and turbine blades as well as in aesthetic artifacts. How to efficiently design and generate digital prototypes with freeform surfaces is an important issue in CAD. This paper presents the development of a Virtual Sculpting system and addresses the issues of surface reconstruction from dexel data structures and freeform geometric modeling using the level-set method from distance field structure. Our virtual sculpting method …