Thesis (Ph.D.)--University of Texas at Dallas, 2007. / Includes vita. Includes bibliographical references (leaves 217-223)

No description available.

A dissertation submitted in fulfillment of the requirements to the Faculty of Science, University of the Witwatersrand, Johannesburg, for the degree of Master of Science in the School of Electrical and Information Engineering, June 2019 / The objective of this study is to determine the quantity of charge transferred, in Coulombs, during the continuing current phase of natural cloud-to-ground (CG) lightning flashes over an area in Johannesburg, South Africa. Continuing current is responsible for most thermal related lightning damages such as destruction of property, electrical fires and physical human trauma. The mitigation of lightningrelated risks can be better managed through improved measurement methods of naturally occurring lightning. The application of a point-charge model used to infer charge transfer from changing electric field measurements is detailed. A flatplate antenna with an integrator is set up to record the changing electric fields from lightning flashes. These measurements, along with high-speed video footage to determine continuing current durations, are processed and charge transfer quantities are inferred. From 34 negative lightning strokes with long continuing current (i.e. > 40 ms), the quantity of charge transfer ranges from 0.3 C to 145.5 C and has a mean quantity of 18.3 C. For the 5 recorded positive strokes, the quantity of charge transfer ranges from 3.7 C to 66.6 C / NG (2020)

Digitized by Kansas State University Libraries

Digitized by Kansas State University Libraries

Digitized by Kansas State University Libraries

Call number: LD2668 .T4 1964 D265 / Master of Science

No description available.

No description available.

Computational simulations of air glow discharge plasma in the presence of supersonic flow are presented. The glow discharge model is based on a self-consistent, multi-species, continuum description of the plasma with finite-rate chemistry effects. The glow discharge model is coupled to a compressible Navier-Stokes solver to study the effect of the plasma on the flow and the counter-effect of the flow on the plasma. A finite-rate air chemistry model is presented and validated against experiments from the literature at a pressure of 600 mTorr. Computational results are compared with experimentally measured V-I characteristics, axial positive ion densities and electron temperature, and reasonably good qualitative and quantitative agreement is observed. The validated air plasma model is then used to study the effect of the surface plasma discharge on M=3 supersonic flow at freestream pressure 18 Torr and the corresponding effects of the flow on the discharge structure in two dimensions. The species concentrations and the gas temperature are examined in the absence and presence of bulk supersonic flow. The peak gas temperature from the computations is found to be 1180 K with the surface plasma alone in the absence of flow, and 830 K in the presence of supersonic flow. Results indicate that O- ions can have comparable densities to electrons in the pressure range 1-20 Torr, and that O2- ion densities are at least two orders of magnitude smaller over the pressure range considered. Different ion species are found to be dominant in the absence and presence of supersonic flow, highlighting the importance of including finite-rate chemistry effects in discharge models for understanding plasma actuator physical phenomena. Electrode polarity effects are investigated, and the cathode upstream actuation is found to be stronger than the actuation strength with the cathode downstream, which is consistent with experimental findings of several groups. A parallel computing implementation of the plasma and flow simulation tools has been developed and is used to study the three-dimensional plasma actuator configuration with circular pin electrodes. / text