Modelling the energy exchange between the snowpack and the atmosphere is critical for many hydrological applications. Of the terms present in the snow energy balance, the turbulent fluxes of sensible and latent heat are the most challenging to estimate, particularly within mountain environments where the hydrological importance is great. Many of the flux estimation techniques, such as the bulk transfer method, are poorly adapted for use in complex terrain. In order to characterize the turbulence and to assess the suitability of flux estimation techniques, eddy covariance flux measurements and supporting meteorological data were collected from two mountain valley forest openings in Kananaskis Country, AB. These sites were generally calm, however wind gusts were frequently observed which markedly affected the turbulence characteristics and increased the rates of momentum and heat transfer. In order to successfully apply the bulk transfer technique at these sites, it was necessary to use environment-specific transfer coefficients to account for the effect of the surrounding complex terrain. These observations were compared with data collected on a treeless alpine ridge near Whitehorse, YT, where it was found that many of the turbulence characteristics were similar to flat sites. However, the boundary layer formed over the alpine ridge was very thin and the site was poorly suited for estimating surface fluxes. The mountain results were further contrasted with data collected over a homogeneous and flat prairie site located near Saskatoon, SK. This site included measurement of all of the snow energy terms, permitting an estimate of the energy balance closure obtainable over snow surfaces. The observed energy balance residual was very large, indicating that the eddy covariance technique was unable to capture all of the turbulent energy. It was concluded that an unmeasured transfer of sensible heat was occurring which was strongly correlated with the long-wave radiation balance. Mechanisms for this relationship were hypothesized. Two snow energy balance models were used to investigate the energy imbalance, where it was observed that the flux terms could be suitably simulated if effective parameters were used to augment the sensible heat transfer rate. The results from this thesis contribute to the understanding of heat transfer processes over snow surfaces during mid-winter conditions and improve the ability to model turbulent heat and mass fluxes from snow surfaces in complex environments.

The in-mold electromagnetic stirrer is a kind of device which is utilized to stir the molten steel in the steel factory. This thesis provides a detailed three-dimensional electromagnetic analysis of an in-mold electromagnetic stirrer driven by the moving magnetic field produced from stator winding currents. A commercial finite element analysis software will be utilized to calculate the flux density, eddy current, and electromagnetic force from static and dynamic analyses, and the above three physical phenomena are also discussed to obtain the 3-D electromagnetic characteristics. In order to improve the operational properties of the in-mold electromagnetic stirrer, the various position of the stator is modified to observe the distribution of the electromagnetic force. Besides, the magnitude and frequency of the input currents are also adjusted to predict the probable performances during on-site operation.

For the evaluation of non-ferrous heat exchanger tube, there are many non-destructive testing methods; however, the eddy current testing (ECT) method is the most popular one. By using of ECT, you may find out the defects existing inside or outside the tube wall, diagnose the heat exchanger system and find out the latent problems. The problem is that an improper signal analysis will result in error in the range of 15〜25% of the tube wall thickness, or even over 40% error. This is a great discouragement to the ECT inspectors, and will reduce the confidence of the proprietors of power plants or petro-chemical industries to the use of ECT. Therefore, in this thesis, the study is mainly focus on the problems of the aluminum brass tubes in condenser using ECT method. This thesis will analyze the causes of error of aluminum brass tubes when using ECT, prepare calibration and reference tubes, and test them using eddy current instruments. The relationship among the raw data with volts, phase angle and depth has been found. Two data evaluation methods are developed, one is the defect depth modification equation and the other is the auxiliary evaluation curve. The new methods are proved to be more accurate and practical in the evaluation of heat exchanger tube after more than one year of verification by field testing in the power plant. The results obtained in this thesis are very helpful to reduce the probability of tube failure.

The main purpose of this thesis is to utilize transformer oil dissolved gas for abnormal conditions diagnose. The thesis also develops an analysis method which based on three different existing theories to obtain fast and accurate new diagnosis procedures. The procedure by using transformer oil dissolved gas can define the types and locations of transformer abnormal parts. The sample oil from an on-line transformer can give variable and useful data which can be analyzed the total amount of flammable gas in the laboratory. The type of faults of transformer can be diagnosed easily from the data. Also the over-heat uncovered metal parts of the transformer can be identified. Furthermore, the displacement of silicon sheet core caused by vibration can be obtained after disassembling the transformer. This displacement will cause over-heating phenomenon due to eddy current circulation. After improvement of silicon steel structure, the over-heating phenomenon is disappear and the amount of sample oil dissolved gas keep almost constant. The method which is proposed in the thesis improves the fault identification significantly. A practical transformer rated at 336 MVA combined by three single 23.75kV/345kV transformers have been selected to support the diagnosis program. Periodic collecting sample oil and analysis the total quantity of dissolved gas can diagnose abnormal conditions primarily. The diagnosis program can identify the types and locations of the faults with the diagnosis information. The transformer then can be stripped down for repair and maintenance. The diagnosis analysis program from the dissolved gas can identify the transformer faults efficiently. The data also can make right decision whether the transformer operating normally or not. To obtain the best maintenance conditions, periodic collecting oil sample and carrying on the analysis in the laboratory is most efficiently method. The method which proposed in the thesis can offer the best maintenance data to secure the transformer operating reliability and safety.

<p>A theoretical approach to calculating impedance of metallicmagnetic/conductor layered structures is developed. Thefrequency range considered extends to the ferromagneticresonance region of soft magnetic films (of the order of 1GHz). The analysis includes the effects of screening of thehigh frequency fields by eddy currents as well as the dynamicsand relaxation of the magnetization of the ferromagneticsub-system. Analytical expressions for the impedance as afunction of frequency and material parameters and geometry ofmagnetic sandwich stripes are obtained. Two maincross-sectional layouts are considered: amagnetic/conductor/magnetic sandwich stripe with and withoutflux closure at the edges along the stripe length - with andwithout the magnetic film enclosing the conductor strip. Theimportance of good magnetic flux closure for achieving largespecific inductance gains and high efficiency at GHzfrequencies is emphasized.</p><p>The theoretical results obtained were used to design andanalyze magneticfilm inductors produced using iron nitridealloy films. Patterned sandwiches, consisting of two Fe-N filmsenclosing a conductor film made of Cu, were fabricated onoxidized Si substrates using lift-off lithography. Theinductors exhibited a 2-fold specific inductance enhancement at1 GHz. The magnetic contribution to the total flux in thenarrow devices was less then predicted theoretically, which wasattributed to hardening of the magnetic material at the edgesof the strip leading to incomplete flux closure. Material anddesign issues important for further improving the performanceof the devices are discussed.</p>

Thesis (Ph. D.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains xviii, 130 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 98-104).

Eddy current sensing has been successfully used in various applications from testing heat exchange tubes for nuclear power plants to assessing dielectric thickness on printed circuit boards. However, in civil infrastructures cosmetic or cementitious surface material often keeps the probe or reader coil from accessing conductive medium inside the structure, resulting in reduced coupling as the distance increases between the DUT (device under test) and probe. Thus, the direct application of existing eddy current sensing technique is not very useful to detect flaws in civil infrastructures. To address this weak coupling problem, a simple scheme is proposed in which a resonant passive repeater tag is placed between the reader coil and the conducting test target. The feasibility of detecting defects like cracks or fractures in conductive medium using a passive resonant tag and measuring the impedance as a method of interrogation is shown. The electromagnetic waves are transmitted into and detected from a resonant tag and the conductive medium underneath the tag without direct physical contact using a reader coil above the resonant repeater tag. Experimental data taken from simple setups to demonstrate the advantage of the proposed scheme are presented. In addition, the theoretical background, such as the self and mutual inductance, and image theory, are discussed extensively. It is also shown that the theories can be applicable to build the equivalent circuit with the proper calibration process. The analyses have been carried out to characterize the responses resulting from the various experiments. Furthermore, new measurands, the effective normalized inductance and resistance, were devised and employed to reanalyze the same experimental data. An effort to construct equivalent circuit model of the system has been made to correctly predict the response without the actual experiment. To improve the process of building the equivalent circuit, the total 4 types of tags and 6 types of DUT are built and tested. The analysis is also given for the constructed equivalent circuit model.

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Conditional sampling techniques were used to analyze airbourne carbon dioxide and water vapour flux traces recorded during the FIFE experiment. Two analysis methods based on quadrant analysis were used to isolate and examine extreme contributions to estimates of the mean flux. The first method was a graphical analysis based on 'hyperbolic holes'. This method was used to attain the result that 80% of the flux-fraction is carried by 20% of the time-fraction. The second method, based on quadrant analysis, permitted the distinction of physical structures which are thought to represent the signatures of turbulent flux structures such as eddies or thermals. Overall results indicate that mean flux estimates over the FIFE site are dominated by a very few intermittent extreme events.