[pt] Apresenta-se uma análise não-linear da estabilidade de torres suportadas por cabos. A estrutura é dividida em dois subconjuntos, coluna e cabos, inicialmente estudados separadamente. Na obtenção da matriz de rigidez de estrutura utiliza-se a formulação de viga-colunas e a forma catenária dos cabos, com uma relação força-deslocamento não-linear. A solução é obtida supondo a linearidade do sistema entre dois estados consecutivos no processo iterativo. Coeficientes da flambagem são calculados para três casos individuais: variação de carga vertical de peso próprio e compressão devido aos cabos, variação da carga horizontal de vento, e para o momento de inércia crítico da coluna. / [en] A nonlinear stability analysis of towers supported by cables is presented. The structure is divided in two groups, column and cables, and first analysed separately. Beam-column formulation and catenary cables are used in obtaining the stiffness matrix of the structure, with a nonlinear force-displacement relationship. Solution is achieved through stepwise linearization. Buckling coefficients are calculated in three individual casas: variation of vertical loads from deade weight and tension in cables, wind load variation, and critical mmoment of inertia of the column.

Ingeniero Civil / El trabajo de esta memoria tiene por finalidad analizar el impacto del daño y la geometría de un cable en la resistencia residual que éste presente. Los cables son elementos estructurales ampliamente usados y es importante caracterizarlos apropiadamente y validar ecuaciones analíticas que se han planteado hasta ahora. Para poder realizar este trabajo se realizan ocho modelos 3D en el programa ANSYS de elementos finitos (EF) que representarán una misma configuración geométrica de cable para dos diámetros con tres niveles de daño distintos cada uno, además del caso no dañado. El nivel de daño se cuantifica en función del índice de asimetría (IA) de la sección y la pérdida porcentual de área neta. La configuración geométrica de los cables analizados es 1x19 (1+6+12: una fibra en el núcleo, seis en la segunda capa, doce en la tercera) y los diámetros son 3,5 y 22,22 mm. Los cables se someten a un desplazamiento axial monotónico incremental en uno de sus extremos, los que están restringidos al giro. Para elaborar los modelos en EF se utilizaron elementos cúbicos de ocho nodos con interpolaciones lineales entre ellos como mallado de los componentes. Se utilizó coeficiente de fricción de 0,115 entre fibras. Para simular el daño se eliminaron los alambres de la sección que presentarían rotura en la realidad. Se validó el análisis seccional, es decir, alejado una cierta distancia de las condiciones de apoyo, la distribución de tensiones y deformaciones se comporta invariante a lo largo del resto del eje del cable. Las interacciones de contacto juegan un rol fundamental a la hora de cuantificar la carga y capacidad de deformación última de los cables, además de disminuir su rigidez, comparado con modelos simplificados que no incorporan estos efectos. Se observó que la asimetría del daño impacta directamente en la capacidad última de deformación del cable, disminuyendo ésta al aumentar el IA. Es posible aproximar la rigidez de un cable a través de modelos simplificados o del modelo EF sin daño de manera satisfactoria. Existen efectos de flexión local en las fibras externas producto del contacto entre capas. Además, se presenta una deformación por flexión global de forma radial en los casos que presentan asimetría de daño. El cálculo de capacidad a través de las ecuaciones analíticas de área neta sobreestima la carga última de los cables. En líneas similares, la resistencia residual de los cables disminuye en mayor tasa que la pérdida de área neta. Los resultados muestran mayores presiones inter-fibra y mayores gradientes de tensiones y deformaciones cuando el cable posee un mayor diámetro de sus componentes.

Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2017. / In South Africa, squid fishing vessels need to find and then anchor above benthic squid egg beds to effect viable catches. However, waves acting on the vessel produce a dynamic response on the anchor line. These oscillatory motions produce impact forces of the chain striking the seabed. It is hypothesised that this causes damage to the squid egg bed beneath the vessels. Different mooring systems may cause more or less damage and this is what is investigated in this research. The effect of vessel mooring lines impact on the seabed during squid fishing is investigated using a specialised hydrodynamic tool commercial package ANSYS AQWA models. This study analysed the single-point versus the two-point mooring system’s impact on the seabed. The ANSYS AQWA models were developed for both mooring systems under the influence of the wave and current loads using the 14 and 22 m vessels anchored with various chain sizes. The effect of various wave conditions was investigated as well as the analysis of three mooring line configurations. The mooring chain contact pressure on the seabed is investigated beyond what is output from ANSYS AQWA using ABAQUS finite element analysis. The real-world velocity of the mooring chain underwater was obtained using video analysis. The ABAQUS model was built by varying chain sizes at different impact velocities. The impact pressure and force due to this velocity was related to mooring line impact velocity on the seabed in ANSYS AQWA. Results show the maximum impact pressure of 191 MPa when the 20 mm diameter chain impacts the seabed at the velocity of 8 m/s from video analysis. It was found that the mooring chain impact pressure on the seabed increased with an increase in the velocity of impact and chain size. The ANSYS AQWA impact pressure on the seabed was found to be 170.86 MPa at the impact velocity of 6.4 m/s. The two-point mooring system was found to double the seabed mooring chain contact length compared to the single-point mooring system. Both mooring systems showed that the 14 m vessel mooring line causes the least seabed footprint compared to the 22 m vessel.

Um dos acidentes comuns em estruturas de armazenamento é o colapso da estrutura de cobertura do silo. Na prática, observa-se que as ruínas estruturais nesse sistema são na maior parte devidas ao desconhecimento das ações nestas estruturas. Devido à escassa informação disponível sobre os esforços de cabos de termometria fixados em estruturas de cobertura de silos cilíndricos verticais, a ênfase desta pesquisa é a análise teórica e experimental da avaliação destes esforços com o objetivo de fornecer subsídios para os projetistas e informações para uma futura normalização no dimensionamento de estruturas de cobertura para silos metálicos cilíndricos. Inicialmente realizou-se uma ampla revisão bibliográfica sobre as ações, esforços e sistemas estruturais e construtivos de cobertura para silos cilíndricos. Com base na análise teórica e experimental realizada dos esforços em cabos de termometria conclui-se que as equações propostas pela norma Argentina IRAM 8 015: 1977 são as mais adequadas para avaliação desses esforços / One of the common accidents in storage structures is the silos roof failure. In practice, it is observed that the structural problems in this system are mostly due to the lack of knowledge about the actions in these structures. Due to limited available information on temperature cables loads fixed to roof structure of vertical silos, this work has the aim in the theoretical and experimental analysis of these efforts in two different silos: the pilot-silo in LaMEM - SET - EESC-USP and silo Kepler Weber Industry, in order to provide support for designers and informations for the development of a future Brazililan Standard for the design of roof structures of cylindrical steel silos. Initially was carried out an extensive literature review on the loads, efforts and structural systems for silos roofs. The conclusions obtained from the experimental and theoretical analyzes are that the equations proposed by Argentina Standard IRAM 8015: 1977 is the most suitable for the evaluation of these loads

M.B.A. / One of the most basic motivations for acquisitions is growth. Acquisitions provide means whereby a firm can grow quickly. Firms acquire other firms with the hope of experiencing economic gains. These economic gains may come as a result of economies of scale or scope. Economies of scale are the reductions in per — unit costs that come as the size of the firm's operations, in terms of revenues or units of production, increases. Economies of scope occur when a firm can offer a broad range of services to its customer base. The growth of Voltex involved horizontal acquisition of ELCENTRE, and other Electrical wholesalers throughout South Africa. The pursuit of "Market Power" was the main motive in the formation of Voltex in 1990. The buyout of ELGRO, the parent company of ELCENTRE was the vertical integration in pursuit of financial synergy. The financial synergy lowered the volatility of cash flows, by gaining the confidence of the suppliers of capital, and investors viewed Voltex less risky. The takeover of ELGRO was caused by the failure of Bennet & Fountain (B&F), a UK subsidiary of Voltex. Successful acquisitions can be a source of value creation and growth. Unsuccessful acquisitions can destroy value rapidly, as could seen in this dissertation, B & F did destroy value, which led to operating problems. Top executives could also lose their jobs when acquisitions fail.

Electromagnetic effects of lightning currents during a direct hit to tall communication towers, other instrumented towers and chimneys can be hazardous to associated cables, as well as, electrical and electronics systems. The standard practice in telecommunication and other related fields is to bond the cable sheath to the tower and ground connection is made before it enters the base station. However, in some specific cases when power, signal and data logging cables are to be supported on the same tower, isolation of power cables is demanded. In a totally different situation, attempts are also made to have a dedicated isolated down conductor. A critical review of the situation demanded a more quantitative answer to the following questions: (i) whether it is possible to electrically isolate a dedicated down conductor, (ii) is it possible to electrically isolate the cables and their terminal equipment both mounted on towers serving as down conductor and if so, what will be the nature of current induced in the cables and (iii) as per the standard practice, if the cable sheaths are connected to the tower/structure, what will be the nature of the current shared by them. Addressing these important issues formed the scope of the present work. For the tall structures considered in this work, for the critical time periods, wave nature of the current dominates. This called for electromagnetic modeling covering Transverse Magnetic (TM) mode of the wave propagation. Owing to the complex geometrical features involved with the problem, both experiments on electromagnetically scaled laboratory models, as well as, theoretical simulation is attempted. An electromagnetically scaled laboratory model is employed for the time domain experimental investigation. This approach, which has been validated earlier, is further scrutinized to ensure its adequacy. In order to achieve generality and noting the fact that the associated parameters are rather difficult to be varied in the experimentation, theoretical investigation is also employed. For this, both NEC-2, as well as, an in-house thin wire time domain code developed for this work is employed. NEC-2 could handle multi-wire multi-radius junctions, while in-house time domain code could handle proximity and non-cylindrical shapes encountered with tower lattice elements. The investigation of induction to isolated cables on simple down conductors and towers is considered first. The induced current is shown to be bipolar oscillatory with the period of oscillation governed by the length of the cable. It is shown that the level of induction for good earth termination is below 5 – 10 % while that with moderate inductance in the earth termination can enhance the induction to higher levels. The level of induction is shown to be not critically dependent on the length of the cable, gap between cable and down conductor/tower. When multiple cables are mounted, they seem to influence each other and individually carry currents of lower amplitude. Also, the effect of shape and proximity of the tower lattice elements on induction is investigated. If the cable is housed inside a metallic tray, the amplitude of induced current is shown to be quite small. Subsequently, the evaluation of electrical stress between the isolated down conductor on tower and simplified representation of the structure is considered. A suitable definition of the electric stress for the wave regime is evolved and then it is shown that, at present, the voltage difference defined by the path integral of electric field across shortest path between the two entities is the best indicator for the stress. The electrical stress in the case of isolated down conductor on tower, as well as, down conductor with isolated cable is shown to reach very dangerous levels. On the other hand, the stress on the isolated cables on towers also serving as down conductors is shown to be relatively moderate. Interestingly, it is shown that the electrical stress and the voltage difference is dependent on the gap and for the critical time period, can be much lower than that calculated as a product of equivalent tower surge impedance and the stroke current, even before the arrival of ground end reflections. Finally, the current shared by cables connected to the down conductor is investigated. For the case of simple cylindrical down conductor with cable connected to it at the top, it is shown that the amount of current shared by the cable is not dependent on its length and the relative radii (cross section) have only a weak influence. For the case with down conductor formed by L and + angles, it is shown that the placement of cable at their interior corner can reduce the initial current shared by the cable. In order to model best possible situation with towers, experiments are conducted with cable inside an aluminum pipe. Even in this case, cable current builds up with successive reflections to become comparable with the current through the pipe itself. Subsequent investigation with 1:40 and 1:20 tower models lead to several interesting observations. Cables running along leg/face of the tower whether placed inside or outside the tower, always shares good amount of current. Further, frequent bonding of the sheath to the tower increases the current shared by the cable. Cable when housed in a metallic tray shares less than 50% of the current shared without the tray. Even though a complete quantification is not to be achieved in this work, it has made a good beginning with some significant contribution towards lightning protection issues pertaining to tall towers and structures.

A pesar de que un cable es un elemento estructural diseñado esencialmente para transmitir cargas de tracción, su geometría helicoidal es tal que los componentes que lo forman no sólo desarrollan esfuerzos de tracción sino que también esfuerzos de flexión, corte, torsión, fricción y fuerzas de contacto. Ante la acción de cargas axisimétricas, la magnitud y distribución de las tensiones resultantes en los componentes de un cable determinan el comportamiento de éste, el cual puede ser expresado en términos de su elongación y rotación axial. Este trabajo de título tiene dos objetivos principales: (1) validar y analizar las limitaciones de modelos matemáticos discretos 2D desarrollados para predecir el comportamiento de cables sometidos a cargas axisimétricas; y (2) estudiar el efecto del daño simétrico y asimétrico en la magnitud y distribución de los esfuerzos internos y en la respuesta global (rigidez, capacidad máxima y deformación de falla) del cable cuando es solicitado por cargas axisimétricas. En este estudio se entiende por daño en un cable a que elemento(s) de éste presenta(n) discontinuidad en su longitud en una o varias secciones del cable. Para alcanzar los objetivos planteados se utiliza una modelación del cable 3D en base al método de Elementos Finitos (MEF) utilizando el programa ANSYS, datos experimentales reportados en la literatura y modelaciones 2D lineales y no lineales. El análisis se restringe a cables homogéneos formados por elementos de materiales con comportamiento lineal y no lineal cuyos diámetros varían entre 6 y 40 milímetros y que poseen distintos tipos de configuraciones geométricas de la sección transversal. Mediante la comparación de la respuesta global de cables obtenida utilizando modelos numéricos 3D (MEF), 2D y datos experimentales y el estudio de la distribución de tensiones y deformaciones obtenida con la modelación 3D (MEF), se concluye que los modelos 2D predicen de forma adecuada la curva de capacidad de un cable sometido a cargas axisimétricas, considerando secciones transversales sin daño y con daño distribuido simétricamente. De esta forma se validan las hipótesis sobre las cuales los modelos 2D están sustentados. El estudio del impacto del daño y su distribución (simétrica y asimétrica) en la respuesta global y distribución de tensiones y deformaciones de un cable se realiza mediante la comparación de datos experimentales con los resultados obtenidos con la modelación 3D (MEF) de cables dañados y sin daño. Se concluye que el efecto del daño en un cable depende de la cantidad de elementos dañados y de si la distribución del daño es simétrica o asimétrica. Una distribución asimétrica de daño tiene un mayor impacto que una simétrica en la reducción de la capacidad axial y de la deformación axial máxima del cable y en la distribución de tensiones y deformaciones internas en la sección transversal. Se observó que para una misma cantidad de elementos dañados en una sección, para una distribución de daño simétrica, la capacidad axial se reduce en la misma proporción de área dañada, mientras que para una distribución asimétrica esta reducción puede alcanzar un 5%. La deformación axial máxima para una distribución de daño simétrica sufre una reducción menor al 1% con respecto al caso sin daño y para una distribución asimétrica esta reducción puede superar el 30% dependiendo de la configuración geométrica del cable. Las tensiones y deformaciones internas en una sección transversal con distribución de daño simétrica experimentan una variación de 5% entre valores extremos con respecto al valor promedio de la sección, mientras que para una distribución de daño asimétrica, esta variación puede superar el 50%.

The purpose of this thesis is to analyse alternative discharging methods of HVDC cables for a DC test in a real situation. It is necessary to research relevant data and consult contacts in order to solve the task. The project is based on the implementation of a developed system on the testing object and preceded by tests in the High Voltage Laboratory in Karlskrona. Simultaneously the main requirement is to completely exclude any human contribution in the discharging process of the DC cable and to maintain the highest safety standards in line with ABB policy. Currently the discharge process after DC testing is completed manually. Testing is carried out by increasing the voltage until the test voltage is reached and kept constant throughout the test period. Followed by switching off the voltage and allowing the cable to initially self-discharge, before it forces the discharge through the discharging water resistor. When the voltage is zero, cable termination ground by providing a secure grounding. Initially the cable charges out through self-discharge and this must continue down to the Uo. To avoid damaging the test object by maintaining the voltage for too long, discharge can begin after 45 minutes if the voltage drops below under 1,2 Uo. The forced discharge occurs by an earth rod connecting the discharge resistance to the ground. Past tests have shown the occasional use of a linked up Water Conditioning Unit system consisting of the pump and filters to ground out by hoses filled with deionized water. This method has been reviewed and modernized which made it more accessible and reliable.

Metal encapsulation with compressed sulphur hexafluoride gas insulation has reduced the size of power substations and improved their reliability. Due to the superior insulating properties of this gas, its application in Gas Insulated Transmission lines (GITL) and Gas Insulated Substations (GIS) is increasing. Such systems invariably require solid support spacers for supporting high voltage conductors and for compartmentalizing sections of the systems. It has been found that, although the dielectric strength of sulphur hexafluoride is high compared to other gases, in the presence of a solid spacer, the dielectric integrity of the system is impaired. For DC GIS and GITL, free of any particulate contamination, anomalous flashover during a polarity reversal of the applied voltage has been attributed to charge accumulation on the spacer surface. The present work examines the effect of switching impulse voltages on the charge accumulation on support spacers in sulphur hexafluoride gas and the effect of AC precharging on impulse flashover. The charge accumulation on the spacer has been measured using a capacitive probe. A three-dimensional surface charge simulation technique has been developed to convert the probe potential measurements to an equivalent charge distribution. Electric field variation on the spacer surface due to this computed charge can be then obtained with this program. The results indicate that spacers acquire charges even under impulse voltage application in non-uniform field gaps. These charges affect the prebreakdown phenomenon and the breakdown behavior of spacer gaps. Under AC voltages, spacers in uniform fields do not acquire charges as has been reported by previous investigators. Under non-uniform field conditions however, AC precharging of spacers does affect the impulse flashover. The variation however, seems to fall within the statistical scatter of pure impulse flashover. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

Ingeniera Civil / El comportamiento de los cables ha sido estudiado por décadas dado su amplio uso en diferentes estructuras y como parte de sistemas de alzamiento. A partir de los estudios realizados sobre el daño de éstos como consecuencia del desgaste natural que sufren por el uso se ha querido ahondar en este tema. El objetivo de la memoria es analizar los efectos de daños ocasionados superficialmente en cables de acero y aluminio de modo de determinar cómo afecta en la distribución de deformaciones y la relación del daño del cable con el diámetro de éste. La metodología empleada se basa en la confección e instrumentación con strain gauges, extensómetros y LVDT de cables de acero y aluminio de diferentes diámetros y la posterior evaluación de la deformación y capacidad de éstos, sometidos a ensayos de tracción. Los resultados obtenidos de esta investigación tienen que ver con el comportamiento de los cables ante los daños realizados, es así como se logró determinar el desempeño de los cables estudiados, como consecuencia su módulo de elasticidad. Además se determinó cualitativa y cuantitativamente un gradiente de deformaciones en donde los alambres más próximos a los daños poseen mayores deformaciones que los que se encuentran opuestos a éste; y una disminución de las deformaciones del cable de manera global en función del aumento de los daños realizados. Conjuntamente, se encontró una relación de no linealidad entre el porcentaje de pérdida de área y de la capacidad en función de los daños realizados a los cables, siendo ésta última menor a la esperada según el modelo biela. Con respecto a la instrumentación utilizada, el uso de strain gauges es acertado como instrumento para medir las deformaciones locales de los cables en cada hebra analizada ya que es bastante sensible, de tamaño suficientemente pequeño para ser colocado en alambres finos y de alta confiabilidad, pero que al mismo tiempo no logra medir las deformaciones hasta el momento de la rotura debido a que antes se despega por falta de adherencia o se corta. El extensómetro no se recomienda como instrumento para el caso de los cables en los cuales fue utilizado, por el mal agarre que éste posee dada la disposición helicoidal de los cables y por consecuencia del gradiente de deformaciones que presentaba. Con respecto al uso de LVDT, este es confiable al momento de determinar los valores de las cargas máximas y niveles de deformación globales, además de ser el único instrumento capaz de resistir las deformaciones propias del acomodamiento de los cables debido a los daños a lo largo de todo el ensayo. La evaluación de los daños en cables al momento de realizar criterios de descarte es relevante para analizar la posibilidad de reforzar o reemplazar una pieza, en este punto la investigación realizada establece una averiguación necesaria del comportamiento de los cables con respecto a la variación de las deformaciones y en la capacidad que sufren por causa del uso.