Surface integrity of manufactured components has a critical impact on their functional performance. Magnesium alloys are lightweight materials used in the transportation industry and are also emerging as a potential material for biodegradable medical implants. However, the unsatisfactory corrosion performance of Mg alloys limits their application to a great extent. Surface integrity factors, such as grain size, crystallographic orientation and residual stress, have been proved to remarkably influence the functional performance of magnesium alloys, including corrosion resistance, wear resistance and fatigue life. In this dissertation, the influence of machining conditions, including dry and cryogenic cooling (liquid nitrogen was sprayed to the machined surface during machining), cutting edge radius, cutting speed and feed rate, on the surface integrity of AZ31B Mg alloy was investigated. Cryogenic machining led to the formation of a "featureless layer" on the machined surface where significant grain refinement from 12 μm to 31 nm occurred due to dynamic recrystallization (DRX), as well as increased intensity of basal plane on the surface and more compressive residual stresses. Dry and cryogenic burnishing experiments of the same material were conducted using a fixed roller setup. The thickness of the processed-influenced layer, where remarkable microstructural changes occurred, was dramatically increased from the maximum value of 20 μm during machining to 3.4 mm during burnishing. The burnishing process also produced a stronger basal texture on the surface than the machining process. Preliminary corrosion tests were conducted to evaluate the corrosion performance of selected machined and burnished AZ31B Mg samples in 5% NaCl solution and simulated body fluid (SBF). Cryogenic cooling and large edge radius tools were found to significantly improve the corrosion performance of machined samples in both solutions. The largest improvement in the material's corrosion performance was achieved by burnishing. A finite element study was conducted for machining of AZ31B Mg alloy and calibrated using the experimental data. A user subroutine was developed and incorporated to predict the grain size changes induced by machining. Good agreements between the predicted and measured grain size as well as thickness of featureless layers were achieved. Numerical studies were extended to include the influence of rake angle, feed rate and cutting speed on the featureless layer formation.

The functional performance of joint implants is largely determined by the surface layer properties in contact. Wear/debris-induced osteolysis and aseptic loosening has been identified as the major cause of failure of metal-on-metal joint implants. A crucial requirement for the long-term stability of the artificial joint is to minimize the release of debris particles. Severe plastic deformation (SPD) processes have been used to modify the surface integrity properties by generating ultrafine, or even nano-sized grains and grain size gradients in the surface region of many materials. These fine grained materials often exhibit enhanced surface integrity properties and improved functional performance (wear resistance, corrosion resistance, fatigue life, etc.) compared with their conventional coarse grained counterparts. The aim of the present work is to investigate the effect of a SPD process, cryogenic burnishing, on the surface integrity modifications of a Co-Cr-Mo alloy, and the resulting wear performance of this alloy due to the burnishing-induced surface integrity properties. A systematic experimental study was conducted to investigate the influence of different burnishing parameters on distribution of grain size, phase structure and residual stresses of the processed material. The wear performance of the processed Co-Cr-Mo alloy was tested via pin-on-disk wear tests. The results from this work show that the cryogenic burnishing can significant improve the surface integrity of the Co-Cr-Mo alloy which would finally lead to advanced wear performance due to refined microstructure, high hardness, compressive residual stresses and favorable phase structure on the surface layer. A finite element model (FEM) was developed for predicting the grain size changes during burnishing of Co-Cr-Mo alloy under both dry and cryogenic conditions. A new material model was used for incorporating flow stress softening and associated grain size refinement caused by the dynamic recrystallization (DRX). The new material model was implemented in a commercial FEM software as a customized user subroutine. Good agreement between predictions and experimental observations was achieved. Encouraging trends are revealed with great potential for application in industry.

A new approach to large-eddy simulation (LES) based on the use of explicit spatial filtering combined with backscatter forcing is presented. The forcing uses a discrete dynamical system (DDS) called the compressible ``poor man's'' Navier--Stokes (CPMNS) equations. This DDS is derived from the governing equations and is shown to exhibit good spectral and dynamical properties for use in a turbulence model. An overview and critique of existing turbulence theory and turbulence models is given. A comprehensive theoretical case is presented arguing that traditional LES equations contain unresolved scales in terms generally thought to be resolved, and that this can only be solved with explicit filtering. The CPMNS equations are then incorporated into a simple forcing in the OVERFLOW compressible flow code, and tests are done on homogeneous, isotropic, decaying turbulence, a Mach 3 compression ramp, and a Mach 0.8 open cavity. The numerical results validate the general filter-forcing approach, although they also reveal inadequacies in OVERFLOW and that the current approach is likely too simple to be universally applicable. Two new proposals for constructing better forcing models are presented at the end of the work.

A thorough investigation on the existing hydrodynamic lubrication theories and the reverse pumping theories for the conventional lip seal is conducted. On that basis, the algorithms and the methods used in the numerical modeling of the conventional lip seal are modified and applied to the study of the lip seal running against surface textured shafts. For each step of the study, the numerical model is benchmarked against the experimental results. Important physical mechanisms which explain the reverse pumping ability of the triangular surface structures are revealed. Meanwhile, the accuracy of the numerical model is tested. In general, the numerical simulation results match the experimental observation well. However, there are several important discrepancies. For each discrepancy the possible causes are discussed, which benefits the further attempts of the modeling work on the lip seal running against surface textured shafts. The conclusions of this study themselves can be used as a guidance to the design of the surface textured shafts for the lip seal applications. Finally the limitation of the current theories and the modeling methods are discussed and reasonable improvements which can be done are proposed for the future work.

Brazing and soldering, as advanced manufacturing processes, are of significant importance to industrial applications. It is widely accepted that joining by brazing or soldering is possible if a liquid metal wets the solids to be joined. Wetting, hence spreading and capillary action of liquid metal (often called filler) is of significant importance. Good wetting is required to distribute liquid metal over/between the substrate materials for a successful bonding. Topographically altered surfaces have been used to exploit novel wetting phenomena and associated capillary actions, such as imbibitions (a penetration of a liquid front over/through a rough, patterned surface). Modification of surface roughness may be considered as a venue to tune and control the spreading behavior of the liquids. Modeling of spreading of liquids on rough surface, in particular liquid metals is to a large extent unexplored and constitutes a cutting edge research topic. In this dissertation the imbibitions of liquid metal has been considered as pertained to the metal bonding processes involving brazing and soldering fillers. First, a detailed review of fundamentals and the recent progress in studies of non-reactive and reactive wetting/capillary phenomena has been provided. An imbibition phenomenon has been experimentally achieved for organic liquids and molten metals during spreading over topographically modified intermetallic surfaces. It is demonstrated that the kinetics of such an imbibition over rough surfaces follows the Washburn-type law during the main spreading stage. The Washburn-type theoretical modeling framework has been established for both isotropic and anisotropic non-reactive imbibition of liquid systems over rough surfaces. The rough surface domain is considered as a porous-like medium and the associated surface topographical features have been characterized either theoretically or experimentally through corresponding permeability, porosity and tortuosity. Phenomenological records and empirical data have been utilized to verify the constructed model. The agreement between predictions and empirical evidence appears to be good. Moreover, a reactive wetting in a high temperature brazing process has been studied for both polished and rough surfaces. A linear relation between the propagating triple line and the time has been established, with spreading dominated by a strong chemical reaction.

This dissertation examines the assessment and mitigation of airborne noise from power generation equipment. The first half of the dissertation investigates the diagnosis and treatment of combustion oscillations in boilers. Sound is produced by the flame and is reflected downstream from the combustion chamber. The reflected sound waves perturb the mixture flow or equivalence ratio increasing the heat release pulsations and the accompanying sound produced by the flame. A feedback loop model for determining the likelihood of and diagnosing combustion oscillations was reviewed, enhanced, and then validated. The current work applies the feedback loop stability model to two boilers, which exhibited combustion oscillations. Additionally, a feedback loop model was developed for equivalence ratio fluctuations and validated. For the first boiler, the combustion oscillation problem is primarily related to the geometry of the burner and the intake system. For the second boiler, the model indicated that the combustion oscillations were due to equivalence ratio fluctuations. Principles for both measuring and simulating the acoustic impedance are summarized. An approach for including the effect of structural-acoustic coupling was developed. Additionally, a method for determining the impedance above the plane wave cut-off frequency, using the acoustic FEM, of the boiler was proposed. The second half of the dissertation examines the modeling of bar silencers. Bar silencers are used to mitigate the airborne noise from large power generation equipment (especially gas turbines). Due to the large dimensions of the full cross section, a small representative cell is isolated from the entire array for analysis purposes. To predict the acoustical performance of the isolated cell for different geometric configurations, a numerical method based on the direct mixed-body boundary element method (BEM) was used. An analytical solution for a simplified circular geometry was also derived to serve as a comparison tool for the BEM. Additionally, a parametric study focusing on the effects of flow resistivity, perforate porosity, length of bars, and cross-sectional area ratio was performed. A new approach was proposed to evaluate the transmission loss based on a reciprocal work identity. Moreover, extension of the transmission loss computation above the plane wave cut-off frequency was demonstrated.

Heart failure (HF) is one of the leading causes of death and impacts millions of people throughout the world. Recently, injectable hydrogels have been developed as a potential new therapy to treat myocardium infarction (MI). This dissertation is focused on two main topics: 1) to gain a better understanding the transmural contractility in the healthy left ventricle (LV) wall and 2) investigate the efficacy of the hydrogel injection treatment on LV wall stress and function. The results indicate that a non-uniform distribution of myocardial contractility in the LV wall provide a better representation of normal LV function. The other important study explored the influence altering the stiffness of the biomaterial hydrogel injections. These results show that a larger volume and higher stiffness injection reduce myofiber stress the most and maintaining the wall thickness during loading. The computational approach developed in this dissertation could be used in the future to evaluate the optimal properties of the hydrogel. The last study used a combination of MRI, catheterization, finite element (FE) modeling to investigate the effects of hydrogel injection on borderzone (BZ) contractility after MI. The results indicate that the treatment with hydrogel injection significantly improved BZ function and reduce LV remodeling, via altered MI properties. Additionally, the wall thickness in the infarct and BZ regions were significantly higher in the treated case. Conclusion: hydrogel injection could be a valuable clinical therapy for treating MI.

Time series forecasting and modeling are challenging problems during the past decades, because of its plenty of properties and underlying correlated relationships. As a result, researchers proposed a lot of models to deal with the time series. However, the proposed models such as Autoregressive integrated moving average (ARIMA) and artificial neural networks (ANNs) only describe part of the properties of time series. In this thesis, we introduce a new hybrid model integrated filter structure to improve the prediction accuracy. Case studies with real data from University of Kentucky HealthCare are carried out to examine the superiority of our model. Also, we applied our model to operating room (OR) to reduce the inefficiency cost. The experiment results indicate that our model always outperforms compared with other models in different conditions.

The process, structure, and property relationship of PAN fiber as a precursor to carbon fiber was studied. The limitations of stable spinning and property improvement associated with hot draw in solution spinning were found and quantified. Conditions were varied to generated precursor fiber up to the limit of draw, from which actual samples were collected for thermal conversion to carbon fiber. Samples of PAN and subsequent carbon fiber were characterized using tensile testing and x-ray analysis. The effects of draw on modulus and break stress, as well as the orientation of the crystalline structure of both parent precursor and resultant carbon fiber were found and related back to the quantified draw limit.

Selective Laser Melting (SLM) of Additive Manufacturing is an attractive fabrication method that employs CAD data to selectively melt the metal powder layer by layer via a laser beam and produce a 3D part. This method not only opens a new window in overcoming traditional NiTi fabrication problems but also for producing porous or complex shaped structures. The combination of SLM fabrication advantages with the unique properties of NiTi alloys, such as shape memory effect, superelasticity, high ductility, work output, corrosion, biocompatibility, etc. makes SLM NiTi alloys extremely promising for numerous applications. The SLM process parameters such as laser power, scanning speed, spacing, and strategy used during the fabrication are determinant factors in composition, microstructural features and functional properties of the SLM NiTi alloy. Therefore, a comprehensive and systematic study has been conducted over Ni50.8 Ti49.2 (at%) alloy to understand the influence of each parameter individually. It was found that a sharp [001] texture is formed as a result of SLM fabrication which leads to improvements in the superelastic response of the alloy. It was perceived that transformation temperatures, microstructure, hardness, the intensity of formed texture and the correlated thermo-mechanical response are changed substantially with alteration of each parameter. The provided knowledge will allow choosing optimized parameters for tailoring the functional features of SLM fabricated NiTi alloys. Without going through any heat treatments, 5.77% superelasticity with more than 95% recovery ratio was obtained in as-fabricated condition only with the selection of right process parameters. Additionally, thermal treatments can be utilized to form precipitates in Ni-rich SLM NiTi alloys fabricated by low energy density. Precipitation could significantly alter the matrix composition, transformation temperatures and strain, critical stress for transformation, and shape memory response of the alloy. Therefore, a systematic aging study has been performed to reveal the effects of aging time and temperature. It was found that although SLM fabricated samples show lower strength than the initial ingot, heat treatments can be employed to make significant improvements in shape memory response of SLM NiTi. Up to 5.5% superelastic response and perfect shape memory effect at stress levels up to 500 MPa was observed in solutionized Ni-rich SLM NiTi after 18h aging at 350ºC. For practical application, transformation temperatures were even adjusted without solution annealing and superelastic response of 5.5% was achieved at room temperature for 600C-1.5hr aged Ni-rich SLM NiTi. The effect of porosity on strength and cyclic response of porous SLM Ni50.1 Ti49.9 (at%) were investigated for potential bone implant applications. It is shown that mechanical properties of samples such as elastic modulus, yield strength, and ductility of samples are highly porosity level and pore structure dependent. It is shown that it is feasible to decrease Young’s modulus of the SLM NiTi up to 86% by adding porosity to reduce the mismatch with that of a bone and still retain the shape memory response of SLM fabricated NiTi. The shape memory effect, as well as superelastic response of porous SLM Ni50.8Ti49.2,were also investigated at body temperature. 32 and 45% porous samples with similar behaviors, recovered 3.5% of 4% deformation at first cycle. The stabilized superelastic response was obtained after clicking experiments.