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Multifrequency Eddy Current Signal Analysis, Avanindra Jan 1997

Multifrequency Eddy Current Signal Analysis, Avanindra

Retrospective Theses and Dissertations

This thesis presents a novel procedure for representing and processing multifrequency eddy current signals. Multifrequency eddy current NDE methods are used extensively for the inspection of steam generator tubes in nuclear power plants. Existing methods utilize computationally expensive time domain procedures to process the data. The procedure outlined in the thesis uses frequency domain methods to minimize the computational effort significantly. Two different approaches are evaluated. The first method uses the Fourier descriptor to represent the signal. The Fourier coefficients are utilized to obtain the rotation, scaling and translation parameters required for mixing. The second approach uses the cosine transform ...


Numerical Modeling Of Pulsed Eddy Current Techniques For Detection Of Corrosion And Cracks, Kiran Kumar Dasoju Jan 1997

Numerical Modeling Of Pulsed Eddy Current Techniques For Detection Of Corrosion And Cracks, Kiran Kumar Dasoju

Retrospective Theses and Dissertations

In this thesis we study pulsed eddy current based techniques for characterizing both corrosion and cracks in layered metallic structures. Our primary goal is to understand and model the characteristic features of time-domain current-voltage response functions for characterizing corrosion and cracks. Pulsed eddy current based approach is simpler and faster than frequency domain approaches, and the pulsed eddy current equipment developed for defect detection is less expensive than alternative approaches and easily portable. We take the layer approximation theory for corrosion and the boundary integral method for cracks as the basis for computing the change in impedance of the coil ...


Nde Data Fusion Using Morphological Approaches , Young-Won Song Jan 1997

Nde Data Fusion Using Morphological Approaches , Young-Won Song

Retrospective Theses and Dissertations

The objective of most data fusion algorithms is to combine information made available by various sensors synergistically in order to enhance the overall level of information. Since information obtained from data sources such as sensors is often incomplete or imprecise in nature, the application of data fusion techniques has evoked interest in a number of fields ranging from robotics to nondestructive evaluation (NDE). In NDE applications, such techniques can be used to integrate and fuse data obtained using multiple inspection modalities to produce a more comprehensive picture of the condition of the test specimen. As an example, ultrasonic and eddy ...


Adaptive Iir Filtering Using The Homotopy Continuation Method , Sangmin Bae Jan 1997

Adaptive Iir Filtering Using The Homotopy Continuation Method , Sangmin Bae

Retrospective Theses and Dissertations

The objective of this study is to develop an algorithmic approach for solving problems associated with the convergence to the local minima in adaptive IIR filtering. The approach is based on a numerical method called the homotopy continuation method;The homotopy continuation method is a "solution exhaustive method" for calculating all solutions of a set of nonlinear equations. The globally optimum filter coefficients correspond to the solutions with minimum mean square error. In order to apply the technique to the adaptive IIR filtering problem, the homotopy continuation method is modified to handle a set of nonlinear polynomials with time-varying coefficients ...


Strategic Bidding In An Energy Brokerage , Sundar Rajan Jan 1997

Strategic Bidding In An Energy Brokerage , Sundar Rajan

Retrospective Theses and Dissertations

The main contribution of this research is the definition, and the demonstration of use, of a framework for the development and evaluation of bidding strategies, for participants to use, in preparing and submitting bids to an energy brokerage market. The framework includes the rules under which the market operates, the different types of participants and their objectives, the factors that affect the bidding of the participants, strategies that consider these factors and achieve the objectives, and a simulator to simulate market conditions, including competition from other participants, with which to test these strategies;Strategies that attempt to include competitor behavior ...


Modelling Polarized Light For Computer Graphics , Sairam Sankaranarayanan Jan 1997

Modelling Polarized Light For Computer Graphics , Sairam Sankaranarayanan

Retrospective Theses and Dissertations

The quality of visual realism in computer generated images is largely determined by the accuracy of the reflection model. Advances in global illumination techniques have removed to a large extent, some of the limitations on the physical correctness achievable by reflection models. While models currently used by researchers are physically based, most approaches have ignored the polarization of light. The few previous efforts addressing the polarization of light were hampered by inherently unphysical light transport algorithms. This paper, besides taking polarization of light into account in the reflection computation, also provides a basis for modelling polarization as an inherent attribute ...


Advanced Eddy-Current Methods For Quantitative Nde , Cheng-Chi Tai Jan 1997

Advanced Eddy-Current Methods For Quantitative Nde , Cheng-Chi Tai

Retrospective Theses and Dissertations

The objectives of this dissertation were to devise and develop advanced eddy-current methods for quantitative NDE. The techniques used include time-domain methods (pulsed eddy current), frequency-domain methods (swept-frequency eddy current), and the photoinductive imaging method that combines eddy-current and laser-based thermal-wave techniques. We first developed theoretical models to predict the pulsed eddy current signal and showed this technique can be used to characterize metallic coatings on metal substrates. A feature-based rapid inversion method was developed to determine the conductivity and thickness of the coating simultaneously. In the second work, we studied the fundamentals of eddy current interactions with magnetic metals ...


Cmos Circuits For High Speed Serial Data Communication, Xiaoyu Xi Jan 1997

Cmos Circuits For High Speed Serial Data Communication, Xiaoyu Xi

Retrospective Theses and Dissertations

The serial data link has been dominant in network connections, such as Ethernet, FDDI or ATM, and will find even wider application in the future. This work focuses on the implementation of some basic building blocks for very high speed serial data communication using CMOS technology. At the transmitter end, a novel parallel-to-serial converter is presented, whose core is a 5 by 4 register matrix which combines the selection and shift schemes for conversion. Using this architecture, a pipelined data loading is applied to multiple data paths running at a sub-multiple of the data rate. This significantly reduces the dynamic ...


Nonlinear Control Design For Stressed Power Systems Using Normal Forms Of Vector Fields , Gilsoo Jang Jan 1997

Nonlinear Control Design For Stressed Power Systems Using Normal Forms Of Vector Fields , Gilsoo Jang

Retrospective Theses and Dissertations

Large stressed interconnected power systems exhibit complicated dynamic behavior when subjected to disturbances. This nonlinear complex behavior is not well analyzed with present tools, and a complete theoretical analysis of this is not feasible in large systems. In stressed power systems, due to the presence of increased nonlinearity and the existence of nonlinear modal interactions, there exist some limitation to the use of conventional linear control design techniques. Therefore there is a need to understand the nature of nonlinear modal interactions and their influences on control performance for optimal controller setting;This work deals with control design in power systems ...


Development Of A Pulsed Eddy Current Instrument And Its Application To Detect Deeply Buried Corrosion, William Westfall Ward Iii Jan 1997

Development Of A Pulsed Eddy Current Instrument And Its Application To Detect Deeply Buried Corrosion, William Westfall Ward Iii

Retrospective Theses and Dissertations

Eddy current techniques have historically been valuable to nondestructive evaluation and testing. They allow detection of cracks, corrosion, and other inhomogeneities in conducting materials. However, due to the fact that traditionally eddy currents only use one frequency to excite the coil, limited information about the detected flaw is available. Swept frequency eddy current methods, which sweep the frequency of excitation over a specified range, allow much more information about the flaw to be extracted from the data. This method is much slower due to the amount of time required to sweep the frequency. The pulsed eddy current method was developed ...


Theoretical Study: Depth Of Small Cracks (Circa 100 Microns) From Photoinductive Data , Ananth Sethuraman Jan 1997

Theoretical Study: Depth Of Small Cracks (Circa 100 Microns) From Photoinductive Data , Ananth Sethuraman

Retrospective Theses and Dissertations

The reconstruction of small, tight surface-breaking cracks is one of the key problems of nondestructive evaluation. Many of the established methods of nondestructive evaluation have been defeated by the smallness and the tightness of such cracks. The photoinductive method, which combines a laser with the eddy current method, is known to have a particularly fine spatial resolution. Consequently we have investigated whether it would be well-suited for determining the size and the shape of small, tight surface-breaking cracks. A fundamental feature of the photoinductive method is that it uses a coil to induce an eddy current in the test specimen ...


Diffraction-Corrected Synthetic Aperture Focusing For Spherical Ultrasonic Radiators , Wassef Munther Masri Jan 1997

Diffraction-Corrected Synthetic Aperture Focusing For Spherical Ultrasonic Radiators , Wassef Munther Masri

Retrospective Theses and Dissertations

Synthetic Aperture Focusing Techniques (SAFT) represent a special class of beam-steering algorithms. They are employed to improve the signal-to-noise ratio (SNR) and resolution of ultrasonic images. Such techniques have traditionally been implemented assuming a geometrical model that neglects the effects of diffraction. This dissertation accounts for diffraction effects by using an analytical model based on the Rayleigh-Sommerfeld formula. The model has been extended to characterize the acoustic fields in an immersed solid; a case frequently encountered in scanning acoustic microscopy applications. The results are then verified by comparing them with results obtained using a finite element model;The analytical model ...


Auction Implementations Using Lagrangian Relaxation, Interior-Point Linear Programming, And Upper-Bound Linear Programming, Somgiat Dekrajangpetch Jan 1997

Auction Implementations Using Lagrangian Relaxation, Interior-Point Linear Programming, And Upper-Bound Linear Programming, Somgiat Dekrajangpetch

Retrospective Theses and Dissertations

No abstract provided.


Efficient Processor Management Strategies For Multicomputer Systems , Chung-Yen Chang Jan 1997

Efficient Processor Management Strategies For Multicomputer Systems , Chung-Yen Chang

Retrospective Theses and Dissertations

Multicomputers are cost-effective alternatives to the conventional supercomputers. Contemporary processor management schemes tend to underutilize the processors and leave many of the processors in the system idle while jobs are waiting for execution;Instead of designing faster processors or interconnection networks, a substantial performance improvement can be obtained by implementing better processor management strategies. This dissertation studies the performance issues related to the processor management schemes and proposes several ways to enhance the multicomputer systems by means of processor management. The proposed schemes incorporate the concepts of size-reduction, non-contiguous allocation, as well as job migration. Job scheduling using a bypass-queue ...


Stability And Electronic Properties Of Amorphous Silicon P-I-N Devices Fabricated Using Ecr Plasma Enhanced Chemical Deposition , Sanjeev Kumar Kaushal Jan 1997

Stability And Electronic Properties Of Amorphous Silicon P-I-N Devices Fabricated Using Ecr Plasma Enhanced Chemical Deposition , Sanjeev Kumar Kaushal

Retrospective Theses and Dissertations

The prime objective of the research was to investigate the fabrication, stability and electronic properties of a-Si:H devices deposited using electron cyclotron resonance (ECR) plasma deposition technique. Both reactive (hydrogen) and non-reactive (helium) gases were used as the primary plasma gas. The reactants generated by the ECR plasma from these gases were allowed to flow towards the substrate, where they reacted with silane to give rise to growth of a-Si:H. In general, we used a high dilution ratio of plasma gas (H2 or He) to silane, about 15:1 to 20:1; for growing a-Si:H. Very high ...


500mv Low-Voltage Operational Amplifier Design, Jian Zhou Jan 1997

500mv Low-Voltage Operational Amplifier Design, Jian Zhou

Retrospective Theses and Dissertations

With the dramatic increase in the number of transistors on a chip and the increasing needs for battery-powered applications, low-voltage circuit design techniques have been widely studied in recent year. However, these low supply voltage research efforts have been focused mainly on digital circuits, especially on high density memory circuits. Reported success in achieved high performance low voltage operation in analog circuits lags far behind. Recent results have been presented on CMOS low-voltage operational amplifiers, where the supply voltage has been reduced to less than 2.5V in which the complementary input stages were used to keep the gm constant ...


Signal Processing And Image Restoration Techniques For Two-Dimensional Eddy Current Nondestructive Evaluation , Bing Wang Jan 1997

Signal Processing And Image Restoration Techniques For Two-Dimensional Eddy Current Nondestructive Evaluation , Bing Wang

Retrospective Theses and Dissertations

This dissertation presents a comprehensive study on the forward modeling methods, signal processing techniques, and image restoration techniques for two-dimensional eddy current nondestructive evaluation. The basic physical forward method adopted in this study is the volume integral method. We have applied this model to the eddy current modeling problem for half space geometry and thin plate geometry. To reduce the computational complexity of the volume integral method, we have developed a wavelet expansion method which utilizes the multiresolution compression capability of the wavelet basis to greatly reduce the amount of computation with small loss in accuracy. To further improve the ...


Fuel, Environmental, And Transmission Pricing Considerations In A Deregulated Environment , Emmanouil Vlassios Obessis Jan 1997

Fuel, Environmental, And Transmission Pricing Considerations In A Deregulated Environment , Emmanouil Vlassios Obessis

Retrospective Theses and Dissertations

The 1992 National Energy Policy Act drastically changed the traditional structure of the vertically integrated utility. To facilitate increased competition in the power utility sector, all markets related to power generation have been opened to free competition and trading. To survive in the new competitive environment, power producers need to reduce costs and increase efficiency. Fuel marketing strategies are thus, getting more aggressive and fuel markets are becoming more competitive, offering more options regarding fuel supplies and contracts. At the same time, the 1990 Clean Air Act Amendments are taking effect. Although tightening the emission standards, this legislation offers utilities ...


Eddy Current Automatic Flaw Detection System For Heat Exchanger Tubes In Steam Generators , Sheng-Fa Chuang Jan 1997

Eddy Current Automatic Flaw Detection System For Heat Exchanger Tubes In Steam Generators , Sheng-Fa Chuang

Retrospective Theses and Dissertations

In this dissertation we present an automatic flaw detection system for heat exchanger tubes in steam generators. The system utilizes two well-known techniques, wavelets and fuzzy logic, to automatically detect the flaws in tubing data. The analysis of eddy current inspection data is a difficult task which requires intensive labor by experienced human analysts. To aid the analysts, an accurate and consistent automatic data analysis package was developed. The software development is divided into three parts: data preprocessing, wavelet analysis, and a fuzzy inference system. The data preprocessing procedure is used to set up a signal analysis standard for different ...


Stable Inversion Based Output Tracking Control Of Robotic Systems , Hongchao Zhao Jan 1997

Stable Inversion Based Output Tracking Control Of Robotic Systems , Hongchao Zhao

Retrospective Theses and Dissertations

This thesis addresses stable inversion based output tracking control and its applications to robotic systems. It considers the non-causal invertibility (stable inversion) problem of control systems in its various aspects including properties of stable inverses and algorithms for constructing stable inverses. Then, the stable inversion approach is applied to solve a control problem of long-standing interest: output tracking control for non-minimum phase nonlinear systems;A minimum energy property of stable inverses is firstly established. The property claims that given any desired output trajectory, out of infinitely many possible inverse solutions, the one provided by the stable inversion process is the ...