Engineering Commons^™

Robust Multichannel Functional-Data-Analysis Methods For Data Recovery In Complex Systems, Jian Sun

Doctoral Dissertations

In recent years, Condition Monitoring (CM), which can be performed via several sensor channels, has been recognized as an effective paradigm for failure prevention of operational equipment or processes. However, the complexity caused by asynchronous data collection with different and/or time-varying sampling/transmission rates has long been a hindrance in the effective use of multichannel data in constructing empirical models. The problem becomes more challenging when sensor readings are incomplete. Traditional sensor data recovery techniques are often prohibited in asynchronous CM environments, not to mention sparse datasets. The proposed Functional Principal Component Analysis (FPCA) methodologies, e.g., nonparametric FPC model and semi-parametric …

Micromechanical Studies Of Intergranular Strain And Lattice Misorientation Fields And Comparisons To Advanced Diffraction Measurements, Lili Zheng

Doctoral Dissertations

Inhomogeneous deformation fields arising from the grain-grain interactions in polycrystalline materials have been evaluated using a crystal plasticity finite element method and extensively compared to neutron diffraction measurements under fatigue crack growth conditions. The roles of intergranular deformation anisotropy, grain boundary damage, and non-common deformation mechanisms (such as twinning for hexagonal close packed crystals) are systematically evaluated. The lattice misorientation field can be used to determine the intragranular deformation behavior in polycrystals or to describe the deformation inhomogeneity due to dislocation plasticity in single crystals. The study of indentation-induced lattice misorientation fields in single crystals sheds lights on the understanding …

Dynamics, Electromyography And Vibroarthrography As Non-Invasive Diagnostic Tools: Investigation Of The Patellofemoral Joint, Filip Leszko

Doctoral Dissertations

The knee joint plays an essential role in the human musculoskeletal system. It has evolved to withstand extreme loading conditions, while providing almost frictionless joint movement. However, its performance may be disrupted by disease, anatomical deformities, soft tissue imbalance or injury. Knee disorders are often puzzling, and accurate diagnosis may be challenging. Current evaluation approach is usually limited to a detailed interview with the patient, careful physical examination and radiographic imaging. The X-ray screening may reveal bone degeneration, but does not carry sufficient information of the soft tissue conditions. More advanced imaging tools such as MRI or CT are available, …

In Situ Preconcentration By Ac Electrokinetics For Rapid And Sensitive Nanoparticle Detection, Kai Yang

Doctoral Dissertations

Reducing cost and time is a major concern in clinical diagnostics. Current molecular diagnostics are multi-step processes that usually take at least several hours or even days to complete multiple reagents delivery, incubations and several washing processes. This highly labor-intensive work and lack of automation could result in reduced reliability and low efficiency. The Laboratory-on-a-chip (LOC), taking advantage of the merger and development of microfluidics and biosensor technology, has shown promise towards a solution for performing analytical tests in a self-contained and compact unit, enabling earlier and decentralized testing. However, challenges are to integrate the fluid regulatory elements on a …

The Biglobal Instability Of The Bidirectional Vortex, Joshua Will Batterson

Doctoral Dissertations

State of the art research in hydrodynamic stability analysis has moved from classic one-dimensional methods such as the local nonparallel approach and the parabolized stability equations to two-dimensional, biglobal, methods. The paradigm shift toward two dimensional techniques with the ability to accommodate fully three-dimensional base flows is a necessary step toward modeling complex, multidimensional flowfields in modern propulsive applications. Here, we employ a two-dimensional spatial waveform with sinusoidal temporal dependence to reduce the three-dimensional linearized Navier-Stokes equations to their biglobal form. Addressing hydrodynamic stability in this way circumvents the restrictive parallel-flow assumption and admits boundary conditions in the streamwise direction. …

Development Of A Rigid Body Forward Solution Physiological Model Of The Lower Leg To Predict Non Implanted And Implanted Knee Kinematics And Kinetics, John Kyle Patrick Mueller

Doctoral Dissertations

This dissertation describes the development and results of a physiological rigid body forward solution mathematical model that can be used to predict normal knee and total knee arthroplasty (TKA) kinematics and kinetics. The simulated activities include active extension and weight-bearing deep knee bend. The model includes both the patellofemoral and tibiofemoral joints. Geometry of the normal or implanted knee is represented by multivariate polynomials and modeled by constraining the velocity of lateral and medial tibiofemoral and patellofemoral contact points in a direction normal to the geometry surface.

Center of mass, ligament and muscle attachment points and normal knee geometry were …

Effect Of Unsteady Combustion On The Stability Of Rocket Engines, Tina Morina Rice

Doctoral Dissertations

Combustion instability is a problem that has plagued the development of rocket-propelled devices since their conception. It is characterized by the occurrence of high-frequency nonlinear gas oscillations inside the combustion chamber. This phenomenon degrades system performance and can result in damage to both structure and instrumentation.

The goal of this dissertation is to clarify the role of unsteady combustion in the combustor instability problem by providing the first quantified estimates of its effect upon the stability of liquid rocket engines. The combination of this research with a new system energy balance method, accounting for all dynamic interactions within a system, …

Telerobotic Sensor-Based Tool Control Derived From Behavior-Based Robotics Concepts, Mark William Noakes

Doctoral Dissertations

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Teleoperated task execution for hazardous environments is slow and requires highly skilled operators. Attempts to implement telerobotic assists to improve efficiency have been demonstrated in constrained laboratory environments but are not being used in the field because they are not appropriate for use on actual remote systems operating in complex unstructured environments using typical operators. This work describes a methodology for combining select concepts from behavior-based systems with telerobotic tool control in a way that is compatible …

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 …

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 …

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 …

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 …

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 …

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 …

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 …