Thesis (PhD (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 1995. / Computer simulation programs were developed for the analysis of dry-cooling systems for power plant applications. Both forced draft direct condensing air"cooled condensers and hyperbolic natural draft indirect dry-cooling towers are considered. The results of a considerable amount of theoretical and experimental work are taken into account to model all the physical phenomena ofthese systems, to formu1ate the problems in formal mathematical terms and to design and apply suitable computational algorithms to solve these problems effectively and reliably. The dry-cooling systems are characterized by equation-based models. These equations are simultaneously solved by a specially designed constrained nonlinear least squares algorithm to determine the performance characteristics of the dry-cooling systems under fixed prescnoed operating conditions, or under varying operating conditions when coupled to a turbo-generator set. The solution procedure is very fast and effective. A capital and operating cost estimation procedure, based on information obtained from dry-cooling system component manufacturers and the literature, is proposed. Analytical functions express the annual cost in terms ofthe various geometrical and operating parameters ofthe dry-cooling systems. The simu1ation and the cost estimation procedures were coupled to a constrained nonlinear programming code which enable the design of minimum cost dry-cooling systems at fixed prescribed operating conditions, or dry-cooling systems which minimize the ratio of total annual cost to the annual net power output of the corresponding turbo-generator set. Since prevailing atmospheric conditions, especially the ambient temperature, influence the performance of dry-cooling systems, wide fluctuations in turbine back pressure occur. Therefore, in the latter case the optimal design is based on the annual mean hourly frequency ofambient temperatures, rather than a fixed value. The equation-based models and the optimization problems are simultaneously solved along an infeasible path (infeasible path integrated approach). The optimization model takes into consideration all the parameters that may affect the capital and operating cost of the dry-cooling systems and does not prescribe any limits, other than those absolutely essential due to practical limitations and to simulate the systems effectively. The influence that changes ofthe constraint limits and some problem parameters have on the optinmm solution, are evaluated (sensitivity analysis). The Sequential Quadratic Programming (SQP) method is used as the basis in implementing nonlinear optimization techniques to solve the cost minimirnti~n problems. A stable dual active set algorithm for convex quadratic programming (QP) problems is implemented that makes use of the special features ofthe QP subproblems associated with the SQP methods. TIrls QP algorithm is also used as part of the algorithm that solves the constrained nonlinear least squares problem This particular implementation of the SQP method proved to be very reliable and efficient when applied to the optimization problems based on the infeasible path integrated approach. However, as the nonlinear optimization problems become large, storage requirements for the Hessian matrix and computational expense of solving large quadratic programming (QP) subproblems become prohibitive. To overcome these difficulties, a reduced Hessian SQP decomposition strategy with coordinate bases was implemented. This method exploits the low dimensionality of the subspace of independent decision variables. The performance of this SQP decomposition is further improved by exploiting the mathematical structure of the engineering model, for example the block diagonal structure ofthe Jacobian matrix. Reductions ofbetween 50-90% in the total CPU time are obtained compared to conventional SQP optimization methods. However, more function and gradient evaluations are used by this decomposition strategy. The computer programs were extensively tested on various optimization problems and provide fast and effective means to determine practical trends in the manufacturing and construction of costoptimal dry-cooling systems, as well as their optimal performance and operating conditions in power plant applications. The dissertation shows that, through the proper application of powerful optimization strategies and careful tailoring of the well constructed optimization model, direct optimization of complex models does not need to be time consuming and difficult. Reconnnendations for further research are made. / Imported from http://etd.sun.ac.za April 2010.

Thesis (PhD (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2003. / The thermal performance prediction of wet-cooling towers is critically analyzed and refined. Natural draft counterflow towers and mechanical draft counterflow and crossflow towers are considered. The Merkel, Poppe and e-NTU heat and mass transfer methods of analysis are derived from first principles, as these methods form the cornerstone of wet-cooling tower performance evaluation. The critical differences between these methods, when applied to fill performance analyses and cooling tower performance evaluations, are highlighted. The reasons for these differences are discussed with the aid of psychrometric charts. A new extended empirical relation for the loss coefficient of fills is proposed where the viscous and form drag effects are accounted for as well as the buoyancy, momentum and fill height effects. The empirical equation for the transfer characteristic of fills is extended to include the effects of fill height and the inlet water temperature. Empirical equations to predict the temperature inversion profile, height of the temperature inversion and the height from which air is drawn into the cooling tower are developed. The influence of temperature and humidity inversions on the performance of wet-cooling towers is subsequently investigated. A comprehensive analytical computer program is developed to predict and optimize the performance of wet-cooling towers. Computer programs are also developed to generate cooling tower performance curves, analyze fill performance test data and plot psychrometric charts.

行動電話基地台設施近年來已逐漸成為一另類「鄰避設施」，然而其對於周遭不動產價值減損程度如何，國內尚缺乏相關研究。本文首先採用問卷調查法以瞭解居民對於行動電話基地台的相關看法及居民認知行動電話基地台對於住宅價格的影響程度；其次運用特徵價格法對於實際不動產成交價格資料，以迴歸分析方式驗證行動電話基地台對周遭住宅價格是否有影響及其影響程度。 研究結果發現無論問卷調查或特徵價格實證分析皆顯示行動電話基地台對周遭住宅價格影響是負面的，問卷調查的受訪者普遍對基地台設施存有負面觀感，且有高達54.4﹪的受訪者認為該設施對周遭住宅價格的負面影響程度在10﹪以上；而在特徵價格實證分析方面，研究地區內房屋所在樓層較高者（七樓以上）相較於較低者（七樓以下），其住宅價格更容易受到行動電話基地台設施的負面影響，而住宅價格因距離行動電話基地台遠近因素所受到折損程度平均約為2.35﹪，惟行動電話基地台設施之可視性因素對住宅價格的影響並不顯著。 / The cellular phone towers has become another NIMBY, although the absence of domestic research for how detract from real estate's value. The article first use the Questionnaire Investigation method’s way to realize that people’s opinion of cellular phone towers and cognition of the effective level of cellular phone towers on house’s price ; secondly use Hedonic Price Method on real estate's value, by using Regression Analysis’s way to prove the impact of cellular phone towers on house’s price . In which we found no matter Questionnaire Investigation or Regression Analysis both announces that the effective level of cellular phone towers on house’s price is negative, there are up to 54.4% of subjects involved in the survey though that the negative influence is above 10% ; on Hedonic Price Method’s way, the house whereabouts higher stairs on the area of researchs, its price is more easy effected by cellular phone towers than the lower one. And the house's price is effected by the distance of cellular phone towers that the average of detractive level is about 2.35%.Only the effect on cellular phone towers of the cause of visual by house price was not broad.

On s'intéresse dans cette thèse à la détermination du rang de tenseur de la multiplication dans $mathbb{F}_{q^n}$, l'extension de degré $n$ du corps fini $mathbb{F}_q$ ; ce rang de tenseur correspond en particulier à la complexité bilinéaire de la multiplication dans $mathbb{F}_{q^n}$ sur $mathbb{F}_q$. Dans cette optique, on présente les différentes évolutions de l'algorithme de type évaluation-interpolation introduit en 1987 par D.V. et G.V. Chudnovsky et qui a permis d'établir que le rang de tenseur de la multiplication dans $mathbb{F}_{q^n}$ était linéaire en~$n$. Cet algorithme en fournit désormais les meilleures bornes connues dans le cas d'extensions de degré grand relativement au cardinal du corps de base — le cas des petites extensions étant bien connu. Afin d'obtenir des bornes uniformes en le degré de l'extension, il est nécessaire, pour chaque $n$, de déterminer un corps de fonctions algébriques qui convienne pour appliquer l'algorithme pour $mathbb{F}_{q^n}$, c'est-à-dire qui ait suffisamment de places de petit degré relativement à son genre $g$ et pour lequel on puisse établir l'existence de diviseurs ayant certaines propriétés, notamment des diviseurs non-spéciaux de degré ${g-1}$ ou de dimension nulle et de degré aussi près de ${g-1}$ que possible ; c'est pourquoi les tours de corps de fonctions sont d'un intérêt considérable. En particulier, on s'intéresse ici à l'étude des tours de Garcia-Stichtenoth d'extensions d'Artin-Schreier et de Kummer qui atteignent la borne de Drinfeld-Vlu{a}duc{t}. / In this thesis, we focus on the determination of the tensor rank of multiplication in $mathbb{F}_{q^n}$, the degree $n$ extension of the finite field $mathbb{F}_q$, which corresponds to the bilinear complexity of multiplication in $mathbb{F}_{q^n}$ over $mathbb{F}_q$. To this end, we describe the various successive improvements to the evaluation-interpolation algorithm introduced in 1987 by D.V. and G.V. Chudnovsky which shows the linearity of the tensor rank of multiplication in $mathbb{F}_{q^n}$ with respect to $n$. This algorithm gives the best known bounds for large degree extensions relative to the cardinality of the base field (the case when the degree of the extension is small is well known). In order to obtain uniform bounds, we need to determine, for each $n$, a suitable algebraic function field for the algorithm on $mathbb{F}_{q^n}$, namely a function field with sufficiently many places of small degree relative to its genus $g$ and for which we can prove the existence of divisors with some good properties such as non-special divisors of degree ${g-1}$ or zero-dimensional divisors with degree as close to ${g-1}$ as possiblestring; these conditions lead us to consider towers of algebraic function fields. In particular, we are interested in the study of Garcia-Stichtenoth towers of Artin-Schreier and Kummer extensions which attain the Drinfeld-Vlu{a}duc{t} bound.

[pt] Nesse trabalho, estuda-se o desempenho de um absorsor pendular no controle de vibrações de torres altas e esbeltas, ocasionadas por carregamentos dinâmicos, tais como, por exemplo, cargas ambientais. Em virtude da possibilidade de oscilações de grande amplitude, considera- se na modelagem do problema a não-linearidade do pêndulo. O principal objetivo é estudar o comportamento do sistema torre-pêndulo, submetido a um carregamento harmônico, no regime não-linear, abordando-se aspectos gerais ligados à estabilidade dinâmica. Apresenta-se, inicialmente, a formulação necessária para obter o funcional de energia do sistema coluna-pêndulo, tanto para o caso linear quanto para o caso não-linear, do qual derivam-se as equações diferenciais parciais de movimento. A partir das equações lineares, obtêm-se as freqüências naturais e modos de vibração para alguns casos relevantes de coluna. A seguir, com base na análise modal do sistema coluna-pêndulo, deriva-se um modelo de dois graus de liberdade capaz de descrever com precisão o comportamento do sistema na vizinhança da freqüência fundamental da coluna, do qual obtêm-se as equações de movimento e as equações de estado não- lineares. Uma análise paramétrica detalhada das oscilações não-lineares do sistema coluna-pêndulo demonstra que o absorsor pendular passivo pode reduzir ou amplificar a resposta da coluna. No estudo da influência da não-linearidade geométrica do pêndulo, verifica-se a importância dessa na resposta do sistema, evidenciando que a nãolinearidade não pode ser desprezada nessa classe de problema. Por fim, com base nos resultados, propõe-se um absorsor pendular híbrido. Os estudos revelam que este controle é mais eficiente que o passivo e que não requer grande gasto de energia. / [en] In the present work the performance of a pendulum absorber in the vibration control of tall and slender towers, caused by dynamic loads, such as, environmental loads, is studied in detail. Due to the possibility of large amplitude oscillations, the non-linearity of the pendulum is considered in the modeling of the problem. The main objective of this research is to study the behavior of the tower-pendulum system, submitted to a harmonic load, in the nonlinear regimen, with emphasis on general aspects related to its dynamic stability. It is presented, initially, the formulation necessary for the derivation of the system´s energy functional, both for the linear and the nonlinear cases, from which the partial differential equations of motion are derived and the vibration frequencies and related vibration modes are obtained. Then, based on the modal analysis of the column-pendulum system, a two degrees of freedom model, capable of describing with precision the behavior of the system in the neighborhood of the fundamental frequency of the column is derived, from which the equations of motion and the nonlinear state-space equations are obtained. A detailed parametric analysis of the nonlinear oscillations of the system is carried out. It shows that the pendulum may reduce or amplify the response of the column. The results show a marked influence of the geometric not-linearity of the pendulum on the response of the system, showing that its not-linearity cannot be neglected in this class of problems. Finally, based on the results, a hybrid control approach is proposed. These studies show that this control strategy is more efficient than the passive control alone and that it does not require a large amount of energy.

Objetivo deste trabalho foi o de caracterizar e estudar o processo de transferência de massa da absorção de CO2 em soluções aquosas de aminas em coluna recheada operando em pressão atmosférica. Com este objetivo, construíram-se dois equipamentos, sendo um constituído de coluna em escala laboratório com recheio estruturado e outro de uma coluna em escala piloto com recheio randômico. Empregou-se a absorção de CO2, diluído em ar, em solução de NaOH, para a determinação da área interfacial efetiva. Os coeficientes globais de transferência de massa foram determinados para a absorção de CO2, diluído em ar, em diferentes soluções aquosas absorvedoras a base de aminas, a saber: 25% em massa de MEA, MEA-MDEA nas concentrações mássicas 5% MDEA 25% MEA, 10% MDEA 20% MEA e 15% MDEA 15% MEA. Constatou-se uma forte correlação entre a proporção da solução MDEA-MEA e o coeficiente global de transferência de massa. O planejamento dos ensaios em coluna piloto foi realizado com o emprego de simulador de processos, para a verificação hidrodinâmica da coluna e especificação das vazões de gás e de solução absorvente. Compararam-se, também, os resultados obtidos experimentalmente com os previstos pela simulação, no caso da absorção em MEA. / The aim of the present work was to characterize and study the mass transfer process of the CO2 absorption into single and blended alkanolamines in a packed column under atmospheric pressure. For this purpose, two systems were built, one of the columns is a laboratory structure packed column and the other is a pilot random packed column. The absorption of CO2 into NaOH was performed to determine the effective mass-transfer area and the overall mass-transfer coefficient. The absorption performance was evaluated in terms of the overall mass-transfer coefficient for the absorption of CO2 in air into single and blended alkanolamines: MEA 25% wt, and MEA-MDEA mixtures, MEA-MDEA (25% /5% wt), MEA-MDEA (20% /10% wt) and MEA-MDEA (15% /15% wt). The CO2 absorption performance of MEA-MDEA mixture has a high correlation with the proportion MEA-MDEA. Experimental series were designed employing a process simulator for the hydrodynamic checking and determination of gas and liq flow rates. Comparison of the experimental data and simulation results was made for the absorption into MEA.

Desde 1814, quando então se deram seus primeiros estudos, a mecânica de sistemas de massa variável tem se constituído como um ramo particular dentro da mecânica clássica. Suas aplicações encontram-se espalhadas por diversas áreas do conhecimento e vão desde a engenharia até a medicina, por exemplo. No entanto, apesar dessas aplicações de sucesso, ainda hoje são encontradas na literatura discussões acerca dos fundamentos da mecânica de sistemas de massa variável. Nesse cenário, figuram os chamados aparentes paradoxos que envolvem diferentes equações de movimento para um mesmo sistema de massa variável. É o que pode ser encontrado, por exemplo, com relação ao problema de Wagner, no âmbito do estudo do impacto de corpos sólidos contra superfícies de líquidos, e ao problema da corrente em queda. Nessa tese, questões como essas serão abordadas. Mas o cerne do escopo do presente trabalho é a apresentação de uma discussão de caráter mais geral e interpretativa sobre a teoria e aplicação da mecânica de sistemas de massa variável, mantendo-se como foco principal a contribuição para um melhor entendimento desse importante ramo da mecânica. Para tal, resultados teóricos originais serão apresentados, e discussões e aplicações sobre os mesmos serão feitas. Inicialmente, uma discussão sobre os primeiros trabalhos que fundamentam a dinâmica de uma partícula de massa variável é feita. Nesse contexto, interpretações originais do autor dessa tese são apontadas. Em seguida, a aplicação da equação de Lagrange a sistemas de massa variável é abordada. Nesse cenário, esse autor apresenta a chamada equação de Lagrange para um volume de controle onde a massa varia com as coordenadas e velocidades generalizadas. Esse também é um dos resultados originais dessa tese. Por fim, é apresentada a extensão do princípio variacional para um líquido para um volume de controle, que também é um resultado original desse trabalho. Dois problemas clássicos dentro da teoria de sistemas de massa variável são então tratados, i.e. o problema da corrente em queda e o problema de Wagner. Trata-se de dois problemas aparentemente paradoxais. A resolução desses aparentes paradoxos é abordada, o que também se constitui em um dos resultados originais dessa tese. Uma breve discussão sobre o problema do colapso das torres gêmeas do World Trade Center à luz da mecânica de sistemas de massa variável é também feita. / Since 1814, when the first researches on the topic were carried out, variable mass system mechanics has become a particular branch within classical mechanics. Applied problems involving variable mass systems are sparsely distributed over a wide range of different areas of knowledge, and go from engineering to medicine, for example. However, despite these successful applications, even today one can find in the specialized literature discussions on the fundamentals of the variable mass system mechanics. In this scenario, apparent paradoxes, which are based on different equations of motion for a same variable mass system, figure out. In this sense, the Wagners problem, in the context of the study of the impact of solid bodies into liquid surfaces, and the falling chain problem can be cited as didactic examples. In this thesis, topics like this one will be treated. However, the main scope of this work is to present a more general and interpretative discussion on both the theory and application of the mechanics of variable mass systems, but keeping the focus on contributions that enable a better understanding of such an important branch of mechanics. For that, original theoretical results will be presented, as also discussions and applications of them. In the beginning, a discussion on the first fundamental works about the dynamics of a variable mass particle is done. In such a context, original interpretations of this author are pointed out. Then, the application of Lagrange equations on variable mass systems is discussed. In this scenario, this author shows the so-called Lagrange equation for a control volume where mass varies with generalized coordinates and velocities. This is also an original result of this thesis. By the end, an extension of a variational principle to a control volume is shown, also an original result of this work. Two classical problems within the theory of variable mass systems are then treated, i.e. the falling chain problem and the Wagners problems. Both are apparently paradoxical problems. The resolution of such apparent paradoxes is addressed, what is also an original result. Within the present context of the mechanics of variable mass systems, a brief discussion on the problem of the collapse of the World Trade Center twin towers is also done.

Lightning is a natural phenomenon involving transient high current discharge in the atmosphere. Cloud-to-ground lightning, wherein the discharge occurs between the cloud and the ground is quite hazardous to systems on the ground. Apart from threat to life, the devastating effects of lightning can be mainly of thermal, mechanical and electromagnetic origin. Many a times, thermal and electromagnetic effects are of main concern. A direct hit, wherein the system under consideration becomes a part of the lightning path, could be quite catastrophic to many vulnerable systems like oil rigs, chemical factories, missile/satellite launch pads. From the safety and operational point of view, lightning is of serious concern for electrical systems including transmission lines and substations, nuclear power stations, telecommunication station and data banks. Lightning cannot be avoided, however, by employing a suitable Lightning Protection System (LPS), adequate protection against a direct hit can be provided to ground based systems. A typical lightning protection system involves: 1) Air termination network, which is responsible for stroke interception, 2) Down conductor system, which provides to the stroke current a minimal impedance path to the ground and 3) Earth termination network, for safe dissipation of current into the ground. Similarly, for the indirect effects, which are basically of electromagnetic origin, suitable protection can be designed. The key factors in a protective action involve interception of the dangerous strokes, minimization of the consequential potential rise on down conductors, as well as, at earth termination and keeping the field in the protective volume within an acceptable level. The last aspect can be generally categorized into secondary level protection. For critical systems, the lightning protection system is generally isolated from it. In such designs, potential rise on LPS governs the physical isolation required between the protected and protection system. For a given level of bypass strokes, cost of the LPS increases with the amount of physical separation employed. All most all of the earlier works have concentrated on lightning surge response of power transmission line towers. Apart from their relatively moderate heights, the intention was to arrive at a model, which can be incorporated in circuit simulation software like EMTP. Consequently, they envisage or approximate the mode of propagation to be TEM. In reality, for down conductors of height greater than say 30 m, only TM mode prevails during the initial critical time period. Hence the earlier models cannot be extended to general lightning protection schemes and for down conductor of larger lengths. Only limited literature seems to be available on the characteristics of general down conductor configurations. The problem in hand is very important and some serious research efforts are very much essential. In view of the above, the present work aims to evaluate the rise in potential as well as current injected into the soil at the base for: (i) practical range of down conductor configurations involving single down conductor (with height exceeding 30 m) and (ii) pertinent values of stroke current parameters. The protection schemes considered are isolated vertical down conductor, isolated tower (both square and triangular cross-section) and, tower with insulated lightning mast carrying ground wires. The parameters under consideration are: (i) height and cross section for the down conductor, (ii) clearance between the down conductor and the protected system, (iii) channel geometry, wherein only inclination is to be considered, (iv) velocity of current along the channel and (v) wave shape and rise time for the stroke current. For the evaluation of lightning surge response of transmission line towers, many theoretical and experimental approaches are found in the literature. However, works considering the TM mode of current propagation is relatively limited. In that both experimental and theoretical approaches have been adopted. Theoretical approach invariably adopted numerical field computation in frequency domain using Numerical Electromagnetic code (NEC-2). Fourier Transform techniques are employed to extract the time domain quantities. This approach is very economical, free from experimental errors and least time consuming. Hence it is selected for the present work. However, there are certain limitations in this approach. In NEC simulation, there is a restriction on the size and the arrangement of individual elements. Therefore, although fairly complex tower structures can be simulated, some simplification in the geometry is unavoidable. Such an approximation has been reported to cause insignificant error. NEC is not accurate for calculations in low frequency regime. But in the present work, the initial time regime is of concern wherein the high frequency components dominate. Therefore the above said limitation is not of any serious concern. In order to validate the approach, potential rise is computed for 120 m tall cylindrical down conductor and tower. Results are compared favorably with earlier works, which are based on potential lead wire method. A careful re-look into the ’potential rise’ on the down conductors reveal several things. The electric field in the region between the protection system and protected system is the root cause for the breakdown/flashover. For a given geometry, the integral of the electric field along the shortest path between the two systems must be representing the overall stress on the air gap. Further, for the later time periods, this integral coincides with the well-known quasi-static potential. All the available data and models for breakdown of long air gaps are basically in terms of this quasi-static potential. In view of this, the above path integral is defined as ’equivalent potential rise’ (which will be hereafter termed as ’potential rise’), and taken as the index for surge response. Further, observation of the computed spatio-temporal radial electric field around the down conductor reveals some additional features, which are not common in the quasi-static regime. Electric field reverses its polarity in space, which is due to the opposite current flowing in the lightning channel. Therefore, ’potential rise’, which is taken as the representative for the dielectric stress on the air, should not be evaluated for larger distances. Considering this and noting that the protected system generally lies well within a distance of 50% of the H, height of the down conductor, potential rise is evaluated by integrating electric field within this distance (12.5%H, 25%H, 50%H). Three heights (100%H, 75%H, 50%H) are considered for the evaluation of the potential. The influences of various down conductor and lightning channel parameters are analyzed. Finally vertical channel with full velocity for current propagation is arrived for the investigations. Also, the influence of neighboring conducting objects is briefly studied. It is argued that it needs to be ignored for the general study. Analysis is carried out for a range of down conductor configurations of heights ranging from 45 m to 120 m. Cylindrical down conductor is selected for the detailed study on the overall characteristics and its dependency on pertinent parameters. The characteristics of potential rise are found to be significantly different from that given by the commonly employed uniform transmission line model. In the regime of very fast front currents, down conductor of comparable heights have comparable potential rise. For the larger time to crest, behavior tends more to wards that for quasi-static regime. The dependency of the potential rise on radius of the down conductor seems to be logarithmic in nature. Surge response of isolated towers of both square and triangular cross sections is studied for heights ranging from 45 m to 120 m. The overall characteristics are found to be similar to cylindrical down conductor. Dispersive propagation is found to exist on towers. As a result, the base currents are slightly lower and potential rise exhibits less oscillations. Data curves on potential rise at three different heights and for three different spatial extents are generated for the range of down conductor heights with rise time of the stroke current as the variable. Several interesting observations have been made. Next the investigation is taken up for the insulated mast scheme. The parameters of the study are taken as the number of ground wires, grounding location of ground wires and length of the insulation cylinder. Potential across the insulation, tower base currents, and ground wire end currents are deduced. The basic characteristics of the potential rise are shown to be quite similar to that for the transmission line. For fast front currents the temporal variation is bipolar with a smooth decay. In other words, oscillations are sustained for considerably longer duration. Voltage stress across the insulation surface for one ground wire design is found to be higher by 1.4 - 2.4 times than that for isolated tower. The highest amplification of the ground end current, which occurs for fast front currents, is about 1.8 times. Potential difference across the insulation for two-ground wire design is higher by a factor of 1.3 - 1.85 than that for isolated tower. For the design with four ground wires, potential across the insulation is comparable with that for the tower. However, the mechanical strength of the insulating support should also be considered in the selection of number of ground wires. There exists, especially for fast front strokes, significant induction to the supporting tower. The height of the insulation seems to possess no appreciable influence on the potential rise and base currents. Several issues need to be considered before selecting this design. The contribution made by the present work can be summarized as follows. It basically deals with lightning surge response of isolated down conductors of height in the range 45 - 120 m. The configurations considered are, cylindrical down conductor, tower with both square and triangular cross section and insulated mast scheme. It makes a careful study on the ’potential rise’ on down conductors and a suitable definition for the same is proposed. Basic characteristics of potential rise and ground end currents are studied for the above-mentioned designs. Their salient features are enumerated. For the towers, design data curves are provided for relevant range of stroke current rise time. The issues that need to be considered in the insulated mast scheme are discussed along with the data on potential rise and base currents. The findings of this work are believed to be very useful for the design of lightning protection scheme involving isolated down conductor. Further the results are useful in analyzing the consequential lightning generated threat of being close to tall towers.

In the last years multilevel preconditioners like BPX became more and more popular for solving second-order elliptic finite element discretizations by iterative methods. P. Oswald has adapted these methods for discretizations of the fourth order biharmonic problem by rectangular conforming Bogner-Fox-Schmidt elements and nonconforming Adini elements and has derived optimal estimates for the condition numbers of the preconditioned linear systems. In this paper we generalize the results from Oswald to the construction of BPX and Multilevel Diagonal Scaling (MDS-BPX) preconditioners for the elasticity problem of thin smooth shells of arbitrary forms where we use Koiter's equations of equilibrium for an homogeneous and isotropic thin shell, clamped on a part of its boundary and loaded by a resultant on its middle surface. We use the two discretizations mentioned above and the preconditioned conjugate gradient method as iterative method. The parallelization concept is based on a non-overlapping domain decomposition data structure. We describe the implementations of the multilevel preconditioners. Finally, we show numerical results for some classes of shells like plates, cylinders, and hyperboloids.

This study has analyzed the relationship between trauma and otherness in two autobiographical graphic narratives. The study suggests that autobiographical graphic narratives are better equipped to represent the effects, mainly that of otherness, on the self as a result of trauma. In the ten volume manga series Barefoot Gen, Keiji Nakazawa details his childhood survival of the atomic bombing of Hiroshima during World War II. As he rebuilds his life, fellow survivals that look like his deceased family members recall his trauma of the bombing. Like we see in Nakazawa’s Barefoot Gen, Art Spiegelman also uses repetitious imagery and a fragmentary form of comic narration to represent the experience of trauma throughout In the Shadow of No Towers. However, while Nakazawa repeats specific imagery of the atomic bombing throughout Barefoot Gen based on his eyewitness testimony, Spiegelman manipulates imagery of the September 11, 2001, terrorist attacks to reject the notion that only one specific set of images can represent a traumatic event. Thus, by the end of the second section of In the Shadow of No Towers, Spiegelman creates a multiplicity of images to reenact the trauma of 9/11. / Access to thesis permanently restricted to Ball State community only.