The switching noise in a hard-switched point-of-load (POL) converter may result in false turn on, electromagnetic interference issues, or even device breakdown. A resonant cross-commutated buck (rccBuck) converter operates with low noise since all MOSFETs are turned on with zero voltage within a wide load range. A state-space model was developed to calculate the voltage gain, voltage stresses, and current stresses. Design guidelines for the rccBuck converter operating at continuous voltage mode or discontinuous voltage mode are provided. The design methodology of a one-turn inductor with significant ac and dc fluxes is given. Four fabricated one-turn inductors achieved 2.1% higher efficiency and 50% smaller total magnetic volume than the commercial inductors in the same rccBuck converter. The Omni-coupled inductors (OCI), composed of a twisted E-E core and PCB windings, further improve power density and efficiency. The core loss and inductances were modeled from a complex reluctance network. According to the loss-volume Pareto fronts, the total inductor loss was minimized within a smaller volume than that of discrete inductors. The expectations were validated by an OCI-based rccBuck converter switched at 2 MHz with 12 V input, 3.3 V at 20 A output, and peak efficiency of 96.2%. The small-signal model with a good accuracy up to half switching frequency was developed based on the averaged equivalent circuit. The transient performance of an rccBuck regulator is comparable to that of a second-order buck regulator with the same switching frequency, output capacitance, and closed-loop bandwidth. / Ph. D. / The switching noise in a hard-switched point-of-load (POL) converter may result in false turn on, electromagnetic interference issues, or even device breakdown. A resonant cross-commutated buck (rccBuck) converter operates with low noise since all MOSFETs are turned on with zero voltage within a wide load range. A state-space model was developed to calculate the voltage gain, voltage stresses, and current stresses. Design guidelines for the rccBuck converter operating at continuous voltage mode or discontinuous voltage mode are provided. The design methodology of a one-turn inductor with significant ac and dc fluxes is given. Four fabricated one-turn inductors achieved 2.1% higher efficiency and 50% smaller total magnetic volume than the commercial inductors in the same rccBuck converter. The Omni-coupled inductors (OCI), composed of a twisted E-E core and PCB windings, further improve power density and efficiency. The core loss and inductances were modeled from a complex reluctance network. According to the loss-volume Pareto fronts, the total inductor loss was minimized within a smaller volume than that of discrete inductors. The expectations were validated by an OCI-based rccBuck converter switched at 2 MHz with 12 V input, 3.3 V at 20 A output, and peak efficiency of 96.2%. The small-signal model with a good accuracy up to half switching frequency was developed based on the averaged equivalent circuit. The transient performance of an rccBuck regulator is comparable to that of a second-order buck regulator with the same switching frequency, output capacitance, and closed-loop bandwidth.

The United States Air Force is in the process of developing a more electric aircraft. The development of an aircraft Integrated Power Unit and an Internal Starter/Generator will be instrumental in producing sufficient electrical power to run all non propulsive systems. Iron-cobalt alloys, such as Hiperco alloy 50HS, are high temperature, high strength magnetic materials ideal for these power applications. Design requirements and previous studies indicate that these materials need to survive in temperatures up to 1000F (810K), rotation speeds of about 55,000 rpm, and have strengths in excess of 80 ksi. Research conducted by Fingers provided the material and creep properties used in the analysis presented in this report. The finite element method was used to analyze a spinning rotor mounted to a circular shaft via an interference fit subjected to various operating environments. The power law creep model defined by Fingers was used to analyze three distinct rotor configurations. The first configuration was a constant temperature single lamina, mounted to a shaft of equal thickness, subject to temperatures between 727K and 780K, rotation speeds between 35,000 rpm and 60,000 rpm, and two different interference fits: 0.0015 inches and 0.003 inches. The results yield conservative predictions that indicate that these models could not survive the required operating conditions. The second configuration was a linear radial variation in temperature single lamina, mounted to a shaft of equal thickness, subjected to three temperature ranges, rotation speeds between 30,000 rpm and 55,000 rpm, and two different interference fits; 0.0015 inches and 0.003 inches. These results represent a more realistic model, which indicate that the "cooler" inner portions of the rotor restrict the creep deformations of the "hotter" outer portions resulting in higher possible operating temperatures and rotation speeds very near the required operating conditions. The third configuration was a lamina stack comprised of two rotor lamina, with a Coulomb friction surface interaction, and held together by a compressive axial force. These models represent a first step towards understanding the behavior of the entire rotor stack. / Master of Science

Four potential new monomers were prepared, all of which were structural analogues of BisGMA (2,2-bis(4-(2-hydroxy-3-methacryloxyprop-1-oxy) phenyl)propane). The synthesis of these tetrafunctional dimethacrylate monomers was based on structural modifications of Bis-GMA in the core and the side chain and required a two-step reaction. The first step was propoxylation or ethoxylation of the bisphenols and the second step was the methacrylation of the resulting products. The core structures are designated by Bis-A for isopropylidene and 6F for hexafluoropropyl. The side chain structures were designated on the basis of the pendant side chains in the glycidyl moiety as -OH, -H, and -CH3 from the epichlorohydrin, ethyleneoxide, and propyleneoxide reaction products with the bisphenols, respectively. Bis-GMA was commercially obtained and used as a standard for comparison of the experimental monomers. All the monomers were prepared by the following general procedure of propoxylation or ethoxylation of the biphenols followed by methacrylation. They were characterized by NMR, FTIR, DSC and Cone and Plate Viscometry. All the experimental monomers exhibited lower viscosities and glass transition temperatures than the control, which was attributed to the elimination of the hydrogen bonding. The monomers were photopolymerized in a differential scanning calorimetry modified with an optics assembly (DPA 7; Double Beam Photocalorimetric Accessory) to study the photo-induced crosslinking reactions. The influence of monomer structure, temperature, light intensity, and initiator concentration on the photopolymerization kinetics of ethoxylated and propoxylated dimethacrylates was investigated by isothermal DSC. The DSC curves showed a rapid increase in rate due to the Trommsdorff effect, and then a decline due to the decrease of monomer concentration and the autodeceleration effect. The monomers with lower viscosities and glass transition temperatures exhibited higher conversions of the double bonds. The final extent of conversion increased with curing temperature, light intensity and initiator concentration. The radiation intensity exponent varied from 0.68 (BisGMA) to 0.74 for the ethoxylated 6F system. The initiator exponent were varied from 0.34 (for BisGMA) to 0.44 for the propoxylated BisA system. The ratio of the reaction rate constant (kt/kp) was calculated for PropBisAdm from both steady-state and non steady-state conditions. The effect of dilution on photopolymerization kinetics of BisGMA/triethyleneglycoldimethacrylate (TEGDMA) mixtures was also studied by isothermal photo-DSC. Dilution with TEGDMA significantly reduced the viscosity and glass transition temperatures of the mixtures due to the increase in the flexibility. The extent of polymerization increased with increasing TEGDMA and curing temperature. The calculation of ratio of rate constants (kt/kp) was also determined and the significance was discussed herein. / Master of Science

The centrifugal compressor is a central part of the turbocharger on a truck. It compresses the air which allows for a larger intake of gas into the cylinders. This raises the amount of oxygen available for combustion which increases the efficiency of the engine. However, the operating range of a compressor is limited. If the mass flow through the compressor gets too low, it can start to surge. The surging phenomenon for centrifugal compressors is characterized by axial oscillations in the mass flow which can cause a backflow of air through the compressor. This can result in structural damage on the compressor. It is therefore important to understand under which conditions surge occurs. When it comes to the development and design of compressors, Computational Fluid Dynamics (CFD) is a valuable tool. It enables us to simulate the performance of compressors without the costly process of building a prototype and testing it. Even simpler steady-state simulations can give valuable insight on the performance. However, since surge is a dynamic phenomenon, it is not readily accessible through one of these steady-state simulations, where the sought solution is a flow field constant in time. The aim of this thesis is to capture the surge phenomenon in a steady-state simulation and develop a method for predicting when the compressor surges. This is done by looking at oscillations in the solver for the total pressure at a cross-sectional plane upstream of the compressor wheel. We find that the amplitude of these oscillations increases when the compressor is approaching surge. From this we define a surge criterion and fit the model parameters to an experimentally determined surge line. We then predict the location of the surge line for the same compressor, now equipped with a ported shroud (a geometry feature with the intention of mitigating surge). With this ported shroud, we expect the compressor’s operating range to be widened, which is also what the model predicts. However, this prediction needs to be compared with real data in order to see if the method accurately captures the location of the surge line.

The objective of this research is to provide an in-depth analysis of the contact patch behavior of a specific passenger car tire. A Michelin P205/60R15 tire was used for this study. Understanding the way the tire interacts with the road at various loads, inflation pressures and driving conditions is essential to optimizing tire and vehicle performance. The footprint shape and stress distribution pattern are very important factors that go into assessing the tire's rate of wear, the vehicle's fuel economy and has a major effect on the vehicle stability and control, especially under severe maneuvers. In order to study the contact patch phenomena and analyze these stresses more closely, a finite element (FE) tire model which includes detailed tread pattern geometry has been developed, using a novel reverse engineering process. In order to validate this model, an experimental process has been developed to obtain the footprint shape and contact pressure distribution. The differences between the experimental and the simulation results are discussed and compared. The validated finite element model is then used for predicting the 3D stress distribution fields at the contact patch. The predictive capabilities of the finite element tire model are also explored in order to predict the handling characteristics of the test tire under different maneuvers such as pure cornering and pure braking. / Master of Science / The objective of this research is to study how the tire interacts with the road and how this “interaction” affects vehicle and tire performance. When the tire is in contact with the ground, the region of the tire that is in contact with the surface is referred to as the “tire contact patch” or the “tire footprint”. A Michelin tire was used in order to study this “footprint phenomena”. The effects of weight, tire pressure and different driving conditions (such as braking and cornering) have a very significant impact on the footprint phenomena. The footprint shape, size and pressure distribution pattern are very important factors that go into assessing the tire’s rate of wear, the vehicle’s fuel economy and has a major effect on the vehicle stability, especially under severe maneuvers. As conducting large scale experiments to study this phenomenon is expensive and difficult, simulation methods (such as the finite element method) are used to create tire simulation models as it is provides a way for tire engineers to study the contact patch and make design changes much more quickly and efficiently. In order to check the veracity of the simulation results, a simple and cost effective experimental process has been developed to obtain the footprint shape and contact pressure distribution. The differences between the experimental and the simulation results are discussed and compared. The validated finite element tire model is then explored to see how well it predicts this “footprint phenomena’ at different driving conditions such as cornering and braking.

Yes / Reverse osmosis (RO)is one of the most important technologies used in wastewater treatment plants due to high contaminant rejection and low utilization of energy in comparison to other treatment procedures. For single-component spiral-wound reverse osmosis membrane process, one dimensional steady state and dynamic mathematical models have been developed based on the solution-diffusion model coupled with the concentration polarization mechanism. The model has been validated against reported data for wastewater treatment from literature at steady state conditions. Detailed simulation using the dynamic model has been carried out in order to gain deeper insight of the process. The effect of feed flow rate, pressure, temperature and concentration of pollutants on the performance of the process measured in terms of salt rejection, recovery ratio and permeate flux has been investigated.

Lubricated friction issues are central to all hydraulic actuation systems undergoing motion and any in-depth understanding of the nature of lubricated friction will advance future component design. The classic friction models of hydraulic actuation systems under steady state conditions and their dependency on velocity and temperature have been studied extensively over the past years. A model which is commonly employed to represent the characteristics of friction is that of Stribeck in which the dependency of the friction force is based on velocity alone. However, experimentally, it has been found that lubricated friction is dependent on acceleration. Thus, the Stribeck model can be considered as a subset of a dynamic friction model in which acceleration is zero. Thus, it can be concluded that the Stribeck model is best applied to cases when the change rate of the velocities is very small. This thesis considers the dependency of lubricated friction on acceleration when pressure and temperature changes are relatively constant. As such, the basic hypothesis for this study was proposed as follows: “Lubricated friction in hydraulic actuation systems is not only a function of velocity, but is also a function of both velocity and acceleration”. In this thesis several terms are defined which facilitate the description under which friction models are developed. For example, the term non-steady state friction is used to account for the effect of acceleration on lubricated friction force while in motion. Further, the lubricated friction models are divided into two groups: steady state friction models and non-steady state friction models. Nonlinear friction modeling and measuring methods are reviewed in this dissertation. This review also includes nonlinear lubricated friction modeling in hydraulic actuation systems. A conclusion from this review was that limited research has been done in documenting and explicitly demonstrating the role of acceleration on lubricated friction. The research first introduced a methodology to experimentally measure friction as a function of acceleration and to demonstrate this dependency in the form of a three dimensional graph. A novel technique to experimentally obtain data for the lubricated friction model was introduced. This allowed the lubricated friction forces to be measured as a function of velocity in a continuous manner, but with acceleration being held constant as a family parameter. Two different valve controlled hydraulic actuation systems (VCHAS) were studied under a wide variety of accelerations at constant temperature and pressure. To enable repeatable data collection for the different friction conditions and to accommodate for the effect of hysteresis, a periodic parabolic displacement waveform was chosen which enabled the acceleration to be a family parameter. The second phase of the research introduced a method of representing the data (lubricated friction model) in a lookup table form. The relationship of lubricated friction (in this work, pressure differential, ΔP across the actuator) as a function of velocity and acceleration was presented in a unique semi-empirical 2D lookup table (2D LUT). Limitations of this experimental approach were identified, but the dependency on acceleration was clearly established. The last phase of the study implemented this 2D LUT model into a practical software model of an actuator and demonstrated its accuracy when compared to its experimental counterpart. The semi-empirical model (2D LUT) was experimentally verified by implementing the semi-empirical and Stribeck models into a real time simulation of an actuator and by comparing the experimental outputs against simulated outputs for a common sinusoidal input. A sinusoidal actuator displacement input was chosen to test the simulations as it was not used in the collection of the original data. The output of the simulation was compared to the experimental results and it was evident that for the range in which data could be collected in developing the model, the proposed 2D LUT model predicted an output that was superior to a model which used a standard Stribeck model. It was concluded that the semi-empirical model could be integrated into a simulation environment and predict outputs in a superior fashion when compared to the Stribeck friction model. Thus it was concluded that the stated hypothesis is consistent with the experimental evidence shown by all hydraulic actuators considered. Further, it was also observed that the traditional Stribeck form (steady state dynamic friction) does change with increasing acceleration to the point that the standard breakaway friction almost disappears. It is evident that the 2D LUT is a viable tool for modeling the non-steady state friction of hydraulic actuation systems. The semi-empirical 2D LUT model so developed is a more global representation of hydraulic actuator lubricated friction. In this research, only linear hydraulic actuators were considered; however, the novel nonlinear semi-empirical 2D LUT lubricated friction model can be applied to any actuator (linear and rotary) and provides a new way in which the dynamic friction can be viewed and modeled.

A aplicação de uma sequência de pulsos com tempo de repetição muito menor que os tempos de relaxação Tp << T2; T1, faz com que a magnetização atinja um estado estacionário descrito por H.Y. Carr como Estado Estacionário em Precessão Livre, Steady State Free Precession (SSFP). Nessa condição, o sinal é composto pela complexa sobreposição das componentes FID e eco. Sequências tipo SSFP são utilizadas na aquisição rápida de sinais, resultando em uma boa razão sinal ruído (s/r) em curto intervalo de tempo, porém introduzem fortes anomalias de fase e amplitude devido a complexa interação das componentes que formam o estado estacionário. Neste trabalho, desenvolvemos sequências de pulsos tipo SSFP para RMN em alta e baixa resolução com alternância e incremento de fase. Em alta resolução desenvolvemos as sequências SSFPdx e SSFPdxdt com incremento de fase linear e quadrático respectivamente. Os resultados mostram que espectros de núcleos com baixa sensibilidade podem ser obtidos com mesma razão s/r em menor tempo experimental e as sequências desenvolvidas removem as anomalias espectrais. Em baixa resolução, os resultados mostram que a introdução de alternâncias de fase na Continuous Wave Free Precession (CWFP) possibilita a remoção da dependência da sequência com o offset de frequência e com o tempo entre pulsos. Além disso, mostramos que a sequência CP-CWFPx-x com ângulo de refocalização pequeno (5&deg; a 10&deg;) possibilita a estimativa rápida do tempos de relaxação longitudinal. Apresentamos também resultados dos estudos e desenvolvidos no estágio de pesquisa no exterior, onde as sequências de pulsos no estado estacionário &ndash; DECPMG e Split 180&deg; &ndash; foram estudas numericamente e implementadas nos sistemas magnéticos compactos: mini-Halbach e MOUSE-NMR. Por fim, são apresentados resultados com os métodos de processamento de dados Krylov Basis Diagonalization Method (KBDM) e a Transformada Inversa de Laplace aplicados na análise de sinais SSFP. Resultados mostram que KBDM é uma ferramenta útil no processamento de dados em alta e baixa resolução, tanto na obtenção de espectros como na determinação da distribuição dos tempos de relaxação. / The application of a pulse sequence with repetition time much smaller than the relaxation times, Tp << T2; T1, causes the magnetization to reach a steady state, described by H. Y. Carr as a Steady State Free Precession (SSFP). In this condition, the signal is composed of the complex overlapping of the FID and eco components. SSFP type sequences are used in fast acquisition of NMR signals, resulting in a good signal to noise ratio (s/r) in a short time interval, however, they introduce phase and amplitude anomalies due to the complex interaction between the components of the steady state. In this work, we develop SSFP type pulse sequences for NMR in high and low resolution, with alternation and increment of phase. In high resolution, we develop SSFPdx and SSFPdxdt sequences, with linear and quadratic phase increment respectively. Results show that the low sensitivity nuclei spectra can be obtained with the same s/r ratio in smaller experimental time, about an order of magnitude, and the developed sequences can remove the spectral anomalies. In low resolution, the results show that the introduction of a phase alternation in the Continuous Wave Free Precession (CWFP) allows the elimination of the dependence of the sequence with the offset frequency and the time between pulses. Besides, we show that the CP-CWFPx-x sequence with a small refocalization angle (5° to 10°) allows the fast estimative of the longitudinal relaxation time in a single experiment. The results of the studies conducted during an international research internship are also presented. Steady state pulse sequences &ndash; DECPMG and Split 180° &ndash; were studied and implemented in compact magnetic systems: mini-Halbach and MOUSE-NMR. Finally, the results of the application of the Krylov Basis Diagonalization Method (KBDM) and the Inverse Laplace Transform for the analysis of SSFP signals are presented. The results show that KBDM is a useful tool in data processing for low and high resolution, both for obtaining spectra and determining the relaxation times distribution.

Zu den wichtigsten Werkzeugen in der medizinischen Diagnostik gehören bildgebende Verfahren, wie die Magnetresonanztomographie. Ein weiteres diagnostisches Hilfsmittel ist die Palpation, die es erlaubt, Veränderungen oberflächennaher Organe qualitativ zu erfassen. Die Magnetresonanzelastographie (MRE) stellt eine Kombination dieser Techniken dar. Das Prinzip der MRE besteht darin Gewebedeformationen aufgrund extern induzierter Scherwellen mittels bewegungssensitiver MR-Bildgebung darzustellen und über die Art der Deformation auf die Elastizität des Gewebes zu schließen. Einen großen Anteil schwerwiegender Erkrankungen bilden Störungen des Herz-Kreislaufsystems. Das Ziel dieser Arbeit war es, eine Methode zu entwickeln, die in-vivo MRE am menschlichen Herzen ermöglicht. Die Weiterentwicklung der mechanischen Anregungseinheit ergab mit Einführung eines Audio-Lautsprechers das nötige Instrument, Vibrationen in innere Organe zu übertragen. Der entscheidende Faktor bei der Herz-MRE war die Geschwindigkeit der Aufnahme, die zur Entwicklung der ''fraktionierten MRE'' führte. Die Basis waren schnelle Herzbildgebungstechniken, wie die balancierte Steady-State- (bSSFP) und Spoiled Steady-State-Technik (SPGRE). Die Einführung eines unbalancierten Phasenpräparationsgradienten in der bSSFP-Aufnahmetechnik lieferte ein verbessertes SNR und zusammen mit der SPGRE-MRE-Aufnahmetechnik ließen sich damit MRE-Studien auch am menschlichen Herzen durchführen. Es gelang erstmals, extern induzierte mechanische Schwingungen in das Herz zu koppeln und mittels fraktionierter MRE mit hoher zeitlicher Auflösung zu detektieren. Die in 6 gesunden Probanden beobachtete Modulation der Scherwellenamplituden innerhalb des Myokards korrelierte sehr gut mit den Kontraktionszuständen des Herzens. Die entwickelten Techniken und Methoden sind ein Schritt hin zur routinemäßigen klinischen Anwendung der MRE am Herzen und deuten auf ein hohes Potential im Bereich der Diagnostik kardialer Erkrankungen hin. / Imaging techniques, including magnetic resonance imaging, belong to the most important tools in modern medical diagnostics. Another diagnostic aid is palpation, which is suitable for the qualitative characterization of pathological changes in organs near the surface. Magnetic resonance elastography (MRE) is a combination of these techniques. In principle, MRE uses motion-sensitive MR-imaging to depict tissue deformation caused by externally induced shear waves. The type of deformation supply useful information about the elasticity of the tissue. Cardiac disorders are among the most common diseases. The goal of this study was to develop a method of applying in-vivo MRE to the human heart. The development of the mechanical stimulus, ultimately resulting in the introduction of an audio speaker as the source of vibration, provided the necessary means to introduce vibrations into inner organs. A crucial factor in applying MRE to the heart is the speed of the recording, which led to the development of "fractional MRE". The currently conventional fast heart imaging techniques were used as a starting point. The use of an unbalanced phase preparation gradient in the balanced steady-state imaging technique resulted in an improved phase-to-noise ratio. Along with the spoiled steady-state MRE imaging technique, initial MRE-studies on the human heart were performed. For the first time, externally induced mechanical vibrations were successfully introduced into the heart and were detected using fractional MRE with a high temporal resolution. The modulation of the shear wave amplitudes observed in the myocard of 6 healthy subjects correlated with the phases of the cardiac cycle. The techniques and methods developed here are a step toward routine clinical application of MRE of the heart and indicate high potential in the area of early diagnosis of cardiac disease.

No description available.