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Description
The friction condition is an important factor in controlling the compressing process in metalforming. The friction calibration maps (FCM) are widely used in estimating friction factors between the workpiece and die. However, in standard FEA, the friction condition is defined by friction coefficient factor (µ), while the FCM is used

The friction condition is an important factor in controlling the compressing process in metalforming. The friction calibration maps (FCM) are widely used in estimating friction factors between the workpiece and die. However, in standard FEA, the friction condition is defined by friction coefficient factor (µ), while the FCM is used to a constant shear friction factors (m) to describe the friction condition. The purpose of this research is to find a method to convert the m factor to u factor, so that FEA can be used to simulate ring tests with µ. The research is carried out with FEA and Design of Experiment (DOE). FEA is used to simulate the ring compression test. A 2D quarter model is adopted as geometry model. A bilinear material model is used in nonlinear FEA. After the model is established, validation tests are conducted via the influence of Poisson's ratio on the ring compression test. It is shown that the established FEA model is valid especially if the Poisson's ratio is close to 0.5 in the setting of FEA. Material folding phenomena is present in this model, and µ factors are applied at all surfaces of the ring respectively. It is also found that the reduction ratio of the ring and the slopes of the FCM can be used to describe the deformation of the ring specimen. With the baseline FEA model, some formulas between the deformation parameters, material mechanical properties and µ factors are generated through the statistical analysis to the simulating results of the ring compression test. A method to substitute the m factor with µ factors for particular material by selecting and applying the µ factor in time sequence is found based on these formulas. By converting the m factor into µ factor, the cold forging can be simulated.
ContributorsKexiang (Author) / Shah, Jami (Thesis advisor) / Davidson, Joseph (Committee member) / Trimble, Steve (Committee member) / Arizona State University (Publisher)
Created2013
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Description
Due to great challenges from aggressive environmental regulations, increased demand due to new technologies and the integration of renewable energy sources, the energy industry may radically change the way the power system is operated and designed. With the motivation of studying and planning the future power system under these new

Due to great challenges from aggressive environmental regulations, increased demand due to new technologies and the integration of renewable energy sources, the energy industry may radically change the way the power system is operated and designed. With the motivation of studying and planning the future power system under these new challenges, the development of the new tools is required. A network equivalent that can be used in such planning tools needs to be generated based on an accurate power flow model and an equivalencing procedure that preserves the key characteristics of the original system. Considering the pervasive use of the dc power flow models, their accuracy is of great concern. The industry seems to be sanguine about the performance of dc power flow models, but recent research has shown that the performance of different formulations is highly variable. In this thesis, several dc power-flow models are analyzed theoretically and evaluated numerically in IEEE 118-bus system and Eastern Interconnection 62,000-bus system. As shown in the numerical example, the alpha-matching dc power flow model performs best in matching the original ac power flow solution. Also, the possibility of applying these dc models in the various applications has been explored and demonstrated. Furthermore, a novel hot-start optimal dc power-flow model based on ac power transfer distribution factors (PTDFs) is proposed, implemented and tested. This optimal-reactance-only dc model not only matches the original ac PF solution well, but also preserves the congestion pattern obtain from the OPF results of the original ac model. Three improved strategies were proposed for applying the bus-aggregation technique to the large-scale systems, like EI and ERCOT, to improve the execution time, and memory requirements when building a reduced equivalent model. Speed improvements of up to a factor of 200 were observed.
ContributorsQi, Yingying (Author) / Tylavsky, Daniel J (Thesis advisor) / Hedman, Kory W (Committee member) / Sankar, Lalitha (Committee member) / Arizona State University (Publisher)
Created2013
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Description
Today, more and more substations are created and reconstructed to satisfy the growing electricity demands for both industry and residence. It is always a big concern that the designed substation must guarantee the safety of persons who are in the area of the substation. As a result, the safety metrics

Today, more and more substations are created and reconstructed to satisfy the growing electricity demands for both industry and residence. It is always a big concern that the designed substation must guarantee the safety of persons who are in the area of the substation. As a result, the safety metrics (touch voltage, step voltage and grounding resistance), which should be considered at worst case, are supposed to be under the allowable values. To improve the accuracy of calculating safety metrics, at first, it is necessary to have a relatively accurate soil model instead of uniform soil model. Hence, the two-layer soil model is employed in this thesis. The new approximate finite equations with soil parameters (upper-layer resistivity, lower-layer resistivity and upper-layer thickness) are used, which are developed based on traditional infinite expression. The weighted- least-squares regression with new bad data detection method (adaptive weighted function) is applied to fit the measurement data from the Wenner-method. At the end, a developed error analysis method is used to obtain the error (variance) of each parameter. Once the soil parameters are obtained, it is possible to use a developed complex images method to calculate the mutual (self) resistance, which is the induced voltage of a conductor/rod by unit current form another conductor/rod. The basis of the calculation is Green's function between two point current sources, thus, it can be expanded to either the functions between point and line current sources, or the functions between line and line current sources. Finally, the grounding system optimization is implemented with developed three-step optimization strategy using MATLAB solvers. The first step is using "fmincon" solver to optimize the cost function with differentiable constraint equations from IEEE standard. The result of the first step is set as the initial values to the second step, which is using "patternsearch" solver, thus, the non-differentiable and more accurate constraint calculation can be employed. The final step is a backup step using "ga" solver, which is more robust but lager time cost.
ContributorsWu, Xuan (Author) / Tylavsky, Daniel (Thesis advisor) / Undrill, John (Committee member) / Ayyanar, Raja (Committee member) / Arizona State University (Publisher)
Created2013
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Description
Underground cables have been widely used in big cities. This is because underground cables offer the benefits of reducing visual impact and the disturbance caused by bad weather (wind, ice, snow, and the lightning strikes). Additionally, when placing power lines underground, the maintenance costs can also be reduced as a

Underground cables have been widely used in big cities. This is because underground cables offer the benefits of reducing visual impact and the disturbance caused by bad weather (wind, ice, snow, and the lightning strikes). Additionally, when placing power lines underground, the maintenance costs can also be reduced as a result. The underground cable rating calculation is the most critical part of designing the cable construction and cable installation. In this thesis, three contributions regarding the cable ampacity study have been made. First, an analytical method for rating of underground cables has been presented. Second, this research also develops the steady state and transient ratings for Salt River Project (SRP) 69 kV underground system using the commercial software CYMCAP for several typical substations. Third, to find an alternative way to predict the cable ratings, three regression models have been built. The residual plot and mean square error for the three methods have been analyzed. The conclusion is dawn that the nonlinear regression model provides the sufficient accuracy of the cable rating prediction for SRP's typical installation.
ContributorsWang, Tong (Author) / Tylavsky, Daniel (Thesis advisor) / Karady, George G. (Committee member) / Holbert, Keith E. (Committee member) / Arizona State University (Publisher)
Created2013
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Description
Synchronous buck converters have become the obvious choice of design for high efficiency voltage down-conversion applications and find wide scale usage in today's IC industry. The use of digital control in synchronous buck converters is becoming increasingly popular because of its associated advantages over traditional analog counterparts in terms of

Synchronous buck converters have become the obvious choice of design for high efficiency voltage down-conversion applications and find wide scale usage in today's IC industry. The use of digital control in synchronous buck converters is becoming increasingly popular because of its associated advantages over traditional analog counterparts in terms of design flexibility, reduced use of off-chip components, and better programmability to enable advanced controls. They also demonstrate better immunity to noise, enhances tolerance to the process, voltage and temperature (PVT) variations, low chip area and as a result low cost. It enables processing in digital domain requiring a need of analog-digital interfacing circuit viz. Analog to Digital Converter (ADC) and Digital to Analog Converter (DAC). A Digital to Pulse Width Modulator (DPWM) acts as time domain DAC required in the control loop to modulate the ON time of the Power-MOSFETs. The accuracy and efficiency of the DPWM creates the upper limit to the steady state voltage ripple of the DC - DC converter and efficiency in low load conditions. This thesis discusses the prevalent architectures for DPWM in switched mode DC - DC converters. The design of a Hybrid DPWM is presented. The DPWM is 9-bit accurate and is targeted for a Synchronous Buck Converter with a switching frequency of 1.0 MHz. The design supports low power mode(s) for the buck converter in the Pulse Frequency Modulation (PFM) mode as well as other fail-safe features. The design implementation is digital centric making it robust across PVT variations and portable to lower technology nodes. Key target of the design is to reduce design time. The design is tested across large Process (+/- 3σ), Voltage (1.8V +/- 10%) and Temperature (-55.0 °C to 125 °C) and is in the process of tape-out.
ContributorsKumar, Amit (Author) / Bakkaloglu, Bertan (Thesis advisor) / Song, Hongjiang (Committee member) / Kitchen, Jennifer (Committee member) / Arizona State University (Publisher)
Created2013
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Description
Autonomous vehicle control systems utilize real-time kinematic Global Navigation Satellite Systems (GNSS) receivers to provide a position within two-centimeter of truth. GNSS receivers utilize the satellite signal time of arrival estimates to solve for position; and multipath corrupts the time of arrival estimates with a time-varying bias. Time of arrival

Autonomous vehicle control systems utilize real-time kinematic Global Navigation Satellite Systems (GNSS) receivers to provide a position within two-centimeter of truth. GNSS receivers utilize the satellite signal time of arrival estimates to solve for position; and multipath corrupts the time of arrival estimates with a time-varying bias. Time of arrival estimates are based upon accurate direct sequence spread spectrum (DSSS) code and carrier phase tracking. Current multipath mitigating GNSS solutions include fixed radiation pattern antennas and windowed delay-lock loop code phase discriminators. A new multipath mitigating code tracking algorithm is introduced that utilizes a non-symmetric correlation kernel to reject multipath. Independent parameters provide a means to trade-off code tracking discriminant gain against multipath mitigation performance. The algorithm performance is characterized in terms of multipath phase error bias, phase error estimation variance, tracking range, tracking ambiguity and implementation complexity. The algorithm is suitable for modernized GNSS signals including Binary Phase Shift Keyed (BPSK) and a variety of Binary Offset Keyed (BOC) signals. The algorithm compensates for unbalanced code sequences to ensure a code tracking bias does not result from the use of asymmetric correlation kernels. The algorithm does not require explicit knowledge of the propagation channel model. Design recommendations for selecting the algorithm parameters to mitigate precorrelation filter distortion are also provided.
ContributorsMiller, Steven (Author) / Spanias, Andreas (Thesis advisor) / Tepedelenlioğlu, Cihan (Committee member) / Tsakalis, Konstantinos (Committee member) / Zhang, Junshan (Committee member) / Arizona State University (Publisher)
Created2013
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Description
Loading a cavity-backed slot (CBS) antenna with ferrite material and applying a biasing static magnetic field can be used to control its resonant frequency. Such a mechanism results in a frequency reconfigurable antenna. However, placing a lossy ferrite material inside the cavity can reduce the gain or negatively impact the

Loading a cavity-backed slot (CBS) antenna with ferrite material and applying a biasing static magnetic field can be used to control its resonant frequency. Such a mechanism results in a frequency reconfigurable antenna. However, placing a lossy ferrite material inside the cavity can reduce the gain or negatively impact the impedance bandwidth. This thesis develops guidelines, based on a non-uniform applied magnetic field and non-uniform magnetic field internal to the ferrite specimen, for the design of ferrite-loaded CBS antennas which enhance their gain and tunable bandwidth by shaping the ferrite specimen and judiciously locating it within the cavity. To achieve these objectives, it is necessary to examine the influence of the shape and relative location of the ferrite material, and also the proximity of the ferrite specimen from the probe on the DC magnetic field and RF electric field distributions inside the cavity. The geometry of the probe and its impacts on figures-of-merit of the antenna is of interest as well. Two common cavity backed-slot antennas (rectangular and circular cross-section) were designed, and corresponding simulations and measurements were performed and compared. The cavities were mounted on 30 cm $\times$ 30 cm perfect electric conductor (PEC) ground planes and partially loaded with ferrite material. The ferrites were biased with an external magnetic field produced by either an electromagnet or permanent magnets. Simulations were performed using FEM-based commercial software, Ansys' Maxwell 3D and HFSS. Maxwell 3D is utilized to model the non-uniform DC applied magnetic field and non-uniform magnetic field internal to the ferrite specimen; HFSS however, is used to simulate and obtain the RF characteristics of the antenna. To validate the simulations they were compared with measurements performed in ASU's EM Anechoic Chamber. After many examinations using simulations and measurements, some optimal designs guidelines with respect to the gain, return loss and tunable impedance bandwidth, were obtained and recommended for ferrite-loaded CBS antennas.
ContributorsAskarian Amiri, Mikal (Author) / Balanis, Constantine A. (Thesis advisor) / Aberle, James T. (Committee member) / Pan, Geroge (Committee member) / Arizona State University (Publisher)
Created2013
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Description
Derived from the necessity to increase testing capabilities of hybrid rocket motor (HRM) propulsion systems for Daedalus Astronautics at Arizona State University, a small-scale motor and test stand were designed and developed to characterize all components of the system. The motor is designed for simple integration and setup, such that

Derived from the necessity to increase testing capabilities of hybrid rocket motor (HRM) propulsion systems for Daedalus Astronautics at Arizona State University, a small-scale motor and test stand were designed and developed to characterize all components of the system. The motor is designed for simple integration and setup, such that both the forward-end enclosure and end cap can be easily removed for rapid integration of components during testing. Each of the components of the motor is removable allowing for a broad range of testing capabilities. While examining injectors and their potential it is thought ideal to obtain the highest regression rates and overall motor performance possible. The oxidizer and fuel are N2O and hydroxyl-terminated polybutadiene (HTPB), respectively, due to previous experience and simplicity. The injector designs, selected for the same reasons, are designed such that they vary only in the swirl angle. This system provides the platform for characterizing the effects of varying said swirl angle on HRM performance.
ContributorsSummers, Matt H (Author) / Lee, Taewoo (Thesis advisor) / Chen, Kangping (Committee member) / Wells, Valana (Committee member) / Arizona State University (Publisher)
Created2013
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Description
Doppler radar can be used to measure respiration and heart rate without contact and through obstacles. In this work, a Doppler radar architecture at 2.4 GHz and a new signal processing algorithm to estimate the respiration and heart rate are presented. The received signal is dominated by the transceiver noise,

Doppler radar can be used to measure respiration and heart rate without contact and through obstacles. In this work, a Doppler radar architecture at 2.4 GHz and a new signal processing algorithm to estimate the respiration and heart rate are presented. The received signal is dominated by the transceiver noise, LO phase noise and clutter which reduces the signal-to-noise ratio of the desired signal. The proposed architecture and algorithm are used to mitigate these issues and obtain an accurate estimate of the heart and respiration rate. Quadrature low-IF transceiver architecture is adopted to resolve null point problem as well as avoid 1/f noise and DC offset due to mixer-LO coupling. Adaptive clutter cancellation algorithm is used to enhance receiver sensitivity coupled with a novel Pattern Search in Noise Subspace (PSNS) algorithm is used to estimate respiration and heart rate. PSNS is a modified MUSIC algorithm which uses the phase noise to enhance Doppler shift detection. A prototype system was implemented using off-the-shelf TI and RFMD transceiver and tests were conduct with eight individuals. The measured results shows accurate estimate of the cardio pulmonary signals in low-SNR conditions and have been tested up to a distance of 6 meters.
ContributorsKhunti, Hitesh Devshi (Author) / Kiaei, Sayfe (Thesis advisor) / Bakkaloglu, Bertan (Committee member) / Bliss, Daniel (Committee member) / Kitchen, Jennifer (Committee member) / Arizona State University (Publisher)
Created2013
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Description
This thesis work mainly examined the stability and reliability issues of amorphous Indium Gallium Zinc Oxide (a-IGZO) thin film transistors under bias-illumination stress. Amorphous hydrogenated silicon has been the dominating material used in thin film transistors as a channel layer. However with the advent of modern high performance display technologies,

This thesis work mainly examined the stability and reliability issues of amorphous Indium Gallium Zinc Oxide (a-IGZO) thin film transistors under bias-illumination stress. Amorphous hydrogenated silicon has been the dominating material used in thin film transistors as a channel layer. However with the advent of modern high performance display technologies, it is required to have devices with better current carrying capability and better reproducibility. This brings the idea of new material for channel layer of these devices. Researchers have tried poly silicon materials, organic materials and amorphous mixed oxide materials as a replacement to conventional amorphous silicon layer. Due to its low price and easy manufacturing process, amorphous mixed oxide thin film transistors have become a viable option to replace the conventional ones in order to achieve high performance display circuits. But with new materials emerging, comes the challenge of reliability and stability issues associated with it. Performance measurement under bias stress and bias-illumination stress have been reported previously. This work proposes novel post processing low temperature long time annealing in optimum ambient in order to annihilate or reduce the defects and vacancies associated with amorphous material which lead to the instability or even the failure of the devices. Thin film transistors of a-IGZO has been tested for standalone illumination stress and bias-illumination stress before and after annealing. HP 4155B semiconductor parameter analyzer has been used to stress the devices and measure the output characteristics and transfer characteristics of the devices. Extra attention has been given about the effect of forming gas annealing on a-IGZO thin film. a-IGZO thin film deposited on silicon substrate has been tested for resistivity, mobility and carrier concentration before and after annealing in various ambient. Elastic Recoil Detection has been performed on the films to measure the amount of hydrogen atoms present in the film. Moreover, the circuit parameters of the thin film transistors has been extracted to verify the physical phenomenon responsible for the instability and failure of the devices. Parameters like channel resistance, carrier mobility, power factor has been extracted and variation of these parameters has been observed before and after the stress.
ContributorsRuhul Hasin, Muhammad (Author) / Alford, Terry L. (Thesis advisor) / Krause, Stephen (Committee member) / Kitchen, Jennifer (Committee member) / Arizona State University (Publisher)
Created2013