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Dissertation (Ph.D.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographic references (p.75-81).

Thesis (M.S.)--Auburn University, 2008. / Abstract. Includes bibliographical references (p. 67-68).

Inaug.-diss.--Greifswald. / Lebenslauf.

A finite difference algorithm for solving the forward modelling problem of geo-electromagnetic induction in three-dimensional structures has been developed in this thesis. Novel features of the method include the incorporation of a thin sheet of anomalous conductance at the surface of an otherwise quite general three-dimensional structure in which the anomalous region is allowed to approach two-dimensional configurations at infinity; the use of magnetic rather than the electric field components for obtaining the solution; the use of integral boundary conditions at the top and bottom of the model; and the application of new cell-integral finite difference equations to the main body of the model. The algorithm has been tested for synthetic models against results delivered by existing two and three dimensional modelling programs which are already well established. The results are found to be very satisfactory. Applications of the algorithm have been shown for two cases. First, the dependence of the induction vectors on the period ranging from 10 to 10000 s has been studied for a model with two perpendicular lateral conductivity contrasts; the directions of induction vectors vary from site to site reflecting the combined effect of the two perpendicular contrasts. In the second case, the distortion effect due to small surface inhomogeneities over a buried 2D anomaly was studied using induction vectors and difference vectors. There is evidence of mutual coupling in a certain region which invalidates a simple subtraction of the vectors to reveal the form of the buried anomaly, but elsewhere the procedure appears to be quite valid. Since surface anomalies can be simulated by an anomalous thin sheet over the general 3D structure, it is suggested that this algorithm could be very useful for testing the validity of existing schemes for impedance tensor decompositions used in MT studies when surface anomalies are thought to be distorting the real data. / Graduate

Understanding the trajectories of particulate solids inside a flow-through reactor, such as the riser of a recirculating fluidized bed, is a basic requisite to accurately modelling the reactor. However, these trajectories, which are complicated by gross internal recirculation, are not readily measurable. Conventional means of measuring the residence time distribution can be applied to closed boundaries, such as the exit of the riser. Doing so, however, does not directly provide the details of the trajectories within the riser. In order to determine these trajectories, meaningful measurements must be made at the open boundaries between the adjacent axial regions which, in total, make up the riser. Transient tracer concentration measurements at open boundaries are ambiguous because, as tracer material recirculates past the sensor, its concentration is repeatedly recorded, with no distinction as to which region (above or below the boundary) it has just resided in. A method designed to eliminate this ambiguity at open boundaries is reported in this thesis. By repeatedly introducing single tracer particles into the riser, and measuring the time of passage through each axial region, the residence time distributions for each region can be obtained from the frequency density of these times. The crux of this approach is being able to sense individual tracer particles. The major thrust of this investigation has been to find a practical means to this end. The final sensor considered in this investigation is based on electromagnetic induction: a magnetic primary field induces an eddy current in a conductive tracer particle, and the resulting secondary field is sensed, indicating the presence of the tracer particle in the sensing volume. Noise, resulting from direct coupling between transmitter and receiver coils, electrostatics, and vibrations, determines the sensitivity of the device. The final prototype sensor is limited in sensitivity to relatively large tracer particles, and it is incapable of measuring tracer velocity. Nevertheless, the trajectory of large particles is of practical significance for circulating fluidized beds. Limited tests were conducted in a 0.15 m ID x 9.14 m tall acrylic riser where the tracer particles were injected opposite the solids re-entry point, and were sensed by a single sensor located at an open boundary 7.5 m downstream. At each of the two superficial gas velocities considered, and above a threshold solids flux, the time-of-flight frequency density between the injector and the sensor for these large tracer particles does not change with increasing flux of the fine solids. This result is incongruous with obvious changes in the macro-flow structure occurring in the riser. Recommended changes in the sensor would allow measurement of the direction and speed of the tracer, as it passes by the sensor, as well as potentially reducing noise. With these improvements, it would be useful to install multiple sensors along the full length of the riser. The information obtainable from such a configuration would greatly enhance understanding of the detailed trajectories within the riser. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

The analyses presented in this thesis are based on a consideration of induction effects below transmission lines and the hazards as presented to the public. The rapid increase of transmission voltages has caused a great deal of concern among utilities about these hazards. The induction effects are a function of line height and at present there is conflict concerning-these dimensions. Primarily, this thesis is concerned with the establishment of the minimum line-to-ground clearances of EHV ac and dc transmission lines. These clearances are established in terms of the electric field under the line based on the "electric field recognition level". Equations are derived for the electric field, and potential at any point below the line in Chapter 2. These equations are then used in Chapter 3 to show the effect of conductor spacing, height and size on the field. Also, the effect of sky wires and bundle conductors is noted. Chapter 4 derives an allowable value of electric field which is used in Chapter 5 to derive the required heights. Chapter 6 considers a reduction of these clearances or induction effects using ground wires below the line conductors for shielding purposes. Experimental readings are obtained in Chapter 7 to verify the equations derived in Chapter 2 and the effects of sky wires and bundle conductors on the electric field below the line. Chapter 8 establishes right-of-way widths based on induction effects. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

A detailed study of electromagnetic induction in a sequence of conductive layers has been completed for the case when the inducing fields are generated by an alternating current in a horizontal loop. The study was undertaken with a view to the development of a computer program to perform automatic inversion of horizontal loop electromagnetic (HLEM) frequency soundings taken over horizontally stratified ground. The program constitutes a new implementation of the general approach of Backus and Gilbert (1967, 1968, 1970). By means of a linearised iterative scheme, it constructs layered conductivities which satisfy a given set of observations to an accuracy consistent with the observational uncertainties. Subsequently, the non-uniqueness admitted by the limited amount of data can be appraised by computing averages of the original constructed model and comparing them with averages corresponding to other dissimilar models which also satisfy the data. In examples the Backus-Gilbert averages faithfully reflect the character of the "true" conductivity in regions of high conductivity, but they are of limited value in delineating resistive zones. The program has been applied successfully to the inversion of real data from Grass Valley, Nevada. A uniqueness theorem is presented for inversion of HLEM frequency soundings. It has been proved that an unlimited quantity of perfectly accurate HLEM frequency soundings (at a fixed receiver location) suffices to completely determine the conductivity as a function of depth. This result, which is believed to be new, enhances the credibility of conclusions based on inversion of HLEM soundings. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Ocean bottom magnetometer data from a site on the Pacific plate above 3 my old lithosphere are inverted for electrical conductivity as a function of depth. Magnetotelluric impedances are calculated by the vertical gradient method using the fields at the OBM in conjuction with those measured at the Victoria Geomagnetic Observatory. The approximations involved are examined. Winnowing criteria are proposed which isolate those impedances compatible with all the model and source field assumptions. These then define the best possible data set. A number of inversion algorithms are applied to the data and a wide range of acceptable conductivity profiles are constructed. All profiles exhibit a uniform, relatively high conductivity of about 0.2 S/m from the surface down to a depth of 100 km. Exact and approximate bounds on the conductance are calculated in an effort to quantify the non-uniqueness of the diverse conductivity models. Profiles with a minimum of structure are used to calculate the partial melting and temperature variations beneath the 3 my old site. All results are compared with three other magnetotelluric analyses above 1, 30 and 72 my old lithosphere. The 3 my old datum is discordant and does not fit the trends interpreted from the other three studies. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

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