The shipping industry is reliant on port authorities for the facilitation of safe entry and departure of ships at the ports. This role can not be fulfilled without the assistance of harbour tugs which are run by the marine operations section of the Transnet National Ports Authority. The tugs have to be safe and efficient in the process of pulling and pushing ships around the harbour. Harbour tugs are expensive to acquire and to maintain. The marine operations business has to make appropriate choices of tug propulsion design in order to realise the benefits of the tugs acquired by the ports authority. This can be achieved by analysing the current tugs that the operations are using, which will then serve as valuable information when the time for asset replacement is due. The researcher chose to use the two tug propulsion designs currently used by the Port Elizabeth harbour tugs as a basis for this analysis. The analysis links the three factors of maintenance management, equipment efficiency and equipment safety, to the minimisation of operational costs as perceived by the tug personnel, the pilots and the marine managers. This study seeks to verify the link between these factors and the perceived minimisation of operational costs. Available literature was reviewed and data was collected using a suitably designed questionnaire for this research. This research paper has led to recommendations that should inform the tug acquisition decisions and raise the awareness of the marine employees to relate the factors set out above to minimise operational costs.

On the one hand, airlines order new planes and the worldwide fleet increases, while, on the other hand, the market pressure, the rise of fuel prices and other factors contribute to regular changes in the technology. These drivers may impact maintenance activities and support to operators, and the number of issues occurring on in-service aircraft. In-service and production queries are a specific type of support activities followed-up by propulsion systems integration engineers from the aircraft manufacturer, such as Airbus. These technical questions can address any of the engine’s systems and must usually be answered to within a short timeframe as they might delay a flight or the delivery of an airplane. In the global scope of knowledge management inside the company, these engineers realized their loss of not capitalizing these activities and promoted this project. An adapted application has been developed to share the experience among programs and support the engineers for the treatment of such queries. As the focus of the project was put on assessing the actual need of the future users to provide an adapted tool, the database should prove its performance over the long term. This paper details the different steps of the project: analysis of the need, specifications, programming and testing, that led to meeting this specific need for capitalization. / <p>Presentation via videoconference for distance-based students</p>

The power requirements for future spacecraft power systems will be on the order of a few hundred kilowatts to a few megawatts. Because of these power levels, a high-voltage, high-power distribution subsystem may be utilized to transmit power from the source to the different loads. Using current state-of-the-art power conditioning electronics, complex series and parallel configurations will be required at the interface between the source and the distribution subsystem and between the distribution subsystem and the loads. The dynamic response of such a spacecraft power system may be obtained using a general purpose program such as SPICE2. However, for large and complex spacecraft power systems, the input file will be large and complex with correspondingly large computation times. As an alternative, the spacecraft power system can be considered as an interconnection of modular components. Each component is treated as a two-port network, and a state model is written with the port voltages as the inputs. The state model of each component is solved using the state transition matrix and assuming that the port voltages are . clamped for each time step. This calculation proceeds as if all two-port networks are decoupled. After the state variables have been updated, the inputs to all components are calculated using network analysis principles. The solution procedure alternates between solving the dynamic model of all components and the network equations for the component inputs. The modular state variable approach and SPICE2 are compared using two example systems. This comparison shows the advantages of the modular state variable approach. First, for the modular state variable approach the system is considered as an interconnection of modular components. In SPICE2, the system is treated as an interconnection of circuit elements. As a result, the system description for large and complex spacecraft power systems is much _ larger and more complex than a modular state variable description. Secondly, the modular state variable approach requires less CPU time than SPICE2. For one of the example systems presented here, the modular state variable approach uses one-twentieth of the CPU time used by SPICE2. / Ph. D.

The present work proposes a methodology to define the electric propulsion system for PSVs. This methodology was applied to a case study: the conceptual design of a PSV for operation at the pre-salt fields at Santos basin. First, four different alternatives of electric propulsion systems for the PSV are presented and sized. The first one has induction motors as main propulsion motors, the second one has synchronous motors as main propulsion motors; the third and fourth alternatives are the same as the first and second, respectively, with a batteries bank connected to the main switchboard. Each of the four arrangements was contemplated with two options for Diesel generators: high speed and medium speed generator sets. The mass, volume, fuel consumption, exhaust gases emissions and reference capital costs for each arrangement are estimated and analyzed. Moreover, an economic analysis through the Net Present Value (NPV) is performed. The methodology ends with the Analytic Hierarchy Process (AHP) to support the decision making procedure. Some of the parameters obtained for each arrangement (mass, volume, fuel consumption, exhaust gases and NPV) are used as criteria and sub-criteria for selection. Two scenarios are evaluated, the first scenario gives more importance to the financial component of the design; the second scenario sets the exhaust gases emissions as the more significant parameter. The results were different, the arrangements 1 and 2 with medium speed Diesel generator sets appear as the most suitable option from the economical point of view; whereas the arrangements with batteries and high speed Diesel gensets are the best options to reduce the exhaust emissions. / O presente trabalho propôs uma metodologia para definir o sistema de propulsão elétrica para PSVs. A metodologia foi aplicada para um caso estudo: o projeto conceitual de um PSV para operar nos campos do pré-sal na Bacia de Santos. Primeiramente, as quatro diferentes alternativas de sistemas de propulsão elétrica para PSV são apresentadas e dimensionadas. A primeira alternativa tem motores de indução como motores de propulsão principal, a segunda alternativa tem motores síncronos como motores de propulsão principal; a terceira e quarta alternativas são as mesmas que a primeira e a segunda, respectivamente, com um banco de baterias conectado ao quadro principal. Cada um dos quatro arranjos foi considerado com duas opções para Diesel geradores: Diesel geradores de alta e média rotação. A massa, volumem, consumo de combustível, emissão de gases e os custos capitais de referência para cada arranjo são estimados e analisados. Adicionalmente, uma análise económica usando o Valor Presente Líquido (VPL) é feita. A metodologia finaliza com o Analytic Hierarchy Process (AHP) para apoiar o processo de escolha de alternativa. Alguns dos parâmetros obtidos para cada arranjo (massa, volumem, consumo de combustível, gases poluentes e o VPL) são utilizados como critérios de seleção. Dois cenários são avaliados, o primeiro cenário dá maior importância à parte financeira do projeto, o segundo cenário estabelece as emissões de gases poluentes como o parâmetro mais significativo. Os resultados foram diferentes, os arranjos 1 e 2 com Diesel geradores de média rotação se apresentam como a opção mais adequada desde o ponto de vista econômico; enquanto os arranjos com baterias e Diesel geradores de alta rotação são a melhor opção para reduzir as emissões de gases poluentes.

The present work proposes a methodology to define the electric propulsion system for PSVs. This methodology was applied to a case study: the conceptual design of a PSV for operation at the pre-salt fields at Santos basin. First, four different alternatives of electric propulsion systems for the PSV are presented and sized. The first one has induction motors as main propulsion motors, the second one has synchronous motors as main propulsion motors; the third and fourth alternatives are the same as the first and second, respectively, with a batteries bank connected to the main switchboard. Each of the four arrangements was contemplated with two options for Diesel generators: high speed and medium speed generator sets. The mass, volume, fuel consumption, exhaust gases emissions and reference capital costs for each arrangement are estimated and analyzed. Moreover, an economic analysis through the Net Present Value (NPV) is performed. The methodology ends with the Analytic Hierarchy Process (AHP) to support the decision making procedure. Some of the parameters obtained for each arrangement (mass, volume, fuel consumption, exhaust gases and NPV) are used as criteria and sub-criteria for selection. Two scenarios are evaluated, the first scenario gives more importance to the financial component of the design; the second scenario sets the exhaust gases emissions as the more significant parameter. The results were different, the arrangements 1 and 2 with medium speed Diesel generator sets appear as the most suitable option from the economical point of view; whereas the arrangements with batteries and high speed Diesel gensets are the best options to reduce the exhaust emissions. / O presente trabalho propôs uma metodologia para definir o sistema de propulsão elétrica para PSVs. A metodologia foi aplicada para um caso estudo: o projeto conceitual de um PSV para operar nos campos do pré-sal na Bacia de Santos. Primeiramente, as quatro diferentes alternativas de sistemas de propulsão elétrica para PSV são apresentadas e dimensionadas. A primeira alternativa tem motores de indução como motores de propulsão principal, a segunda alternativa tem motores síncronos como motores de propulsão principal; a terceira e quarta alternativas são as mesmas que a primeira e a segunda, respectivamente, com um banco de baterias conectado ao quadro principal. Cada um dos quatro arranjos foi considerado com duas opções para Diesel geradores: Diesel geradores de alta e média rotação. A massa, volumem, consumo de combustível, emissão de gases e os custos capitais de referência para cada arranjo são estimados e analisados. Adicionalmente, uma análise económica usando o Valor Presente Líquido (VPL) é feita. A metodologia finaliza com o Analytic Hierarchy Process (AHP) para apoiar o processo de escolha de alternativa. Alguns dos parâmetros obtidos para cada arranjo (massa, volumem, consumo de combustível, gases poluentes e o VPL) são utilizados como critérios de seleção. Dois cenários são avaliados, o primeiro cenário dá maior importância à parte financeira do projeto, o segundo cenário estabelece as emissões de gases poluentes como o parâmetro mais significativo. Os resultados foram diferentes, os arranjos 1 e 2 com Diesel geradores de média rotação se apresentam como a opção mais adequada desde o ponto de vista econômico; enquanto os arranjos com baterias e Diesel geradores de alta rotação são a melhor opção para reduzir as emissões de gases poluentes.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2009. / This thesis describes the development of a vacuum arc thruster (VAT) to be used as a potential low mass (< 500 g), low power (< 5–10W) propulsion system for nanosatellites. The thruster uses a high voltage capacitive circuit to initiate and power the arc process with a 400 ns high current (150–800A) pulse. A one-dimensional steady state analyticalmodel describing the cathode region of the vacuum arc was developed. The model made use of mass and energy balances at the sheath region and cathode surface respectively to predict key quantities such as thrust, ion velocity, ion-to-arc current ratio and erosion rate. Predicted results were shown to be within the limits of reported literature (∼63 μN/A, 26.12 km/s, 0.077 and 110 μg/C respectively). A sensitivity analysis of the analytical model found that a high electric field in the cathode region impedes and decelerates ion flow, which is used for thrust. This was confirmed experimentally for thrust values at arc voltages greater than 2000 V. Both direct and indirect means of measuring thrust were achieved by using a deflecting cantilever beam and an ion collector system, respectively. The transient response of the cantilever beam to impulsive thrust was analytically modeled, whilst the ion current was found by measuring the current induced on a plate subject to ion bombardment. Knowledge of the ion current density distribution was successfully used to approximate the effective normal thrust vector. Direct and indirect thrust levels were roughly 140 and 82 μN/A of average arc current, respectively. Measured thrust was found to be higher than predicted thrust due to thrust contributions fromthe ablation of Teflon insulation. The discrepancy is also due to the uncertainty in quantifying free parameters in the analytical model such as the fraction of generated ions flowing away from the cathode region. The thrust-topower ratio, specific impulse and efficiency of the vacuum arc thruster at an average arc current of 200 A was measured to be 0.6 μN/W, 160 s and 0.05 %, respectively. A thruster performance analysis and specification showed that the VAT is capable of achieving specific orbital and slew manoeuvres within a constant 5–10 W average power. It was concluded that thruster performance could be improved by using a two-stage arc circuit consisting of a high voltage, low current, short pulse trigger and a low voltage, high current, long pulse driver.

Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Grain regression analysis forms an essential part of solid rocket motor simulation. In this thesis a numerical grain regression analysis module is developed as an alternative to cumbersome and time consuming analytical methods. The surface regression is performed by the level-set method, a numerical interface advancement scheme. A novel approach to the integration of the surface area and volume of a numerical interface, as defined implicitly in a level-set framework, by means of Monte-Carlo integration is proposed. The grain regression module is directly coupled to a quasi -1D internal ballistics solver in an on-line fashion, in order to take into account the effects of spatially varying burn rate distributions. A multi-timescale approach is proposed for the direct coupling of the two solvers. / AFRIKAANSE OPSOMMING: Gryn regressie analise vorm ’n integrale deel van soliede vuurpylmotor simulasie. In hierdie tesis word ’n numeriese gryn regressie analise model, as ’n alternatief tot dikwels omslagtige en tydrowende analitiese metodes, ontwikkel. Die oppervlak regressie word deur die vlak-set metode, ’n numeriese koppelvlak beweging skema uitgevoer. ’n Nuwe benadering tot die integrasie van die buite-oppervlakte en volume van ’n implisiete numeriese koppelvlak in ’n vlakset raamwerk, deur middel van Monte Carlo-integrasie word voorgestel. Die gryn regressie model word direk en aanlyn aan ’n kwasi-1D interne ballistiek model gekoppel, ten einde die uitwerking van ruimtelik-wisselende brand-koers in ag te neem. ’n Multi-tydskaal benadering word voorgestel vir die direkte koppeling van die twee modelle.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / This project investigates two problems related to satellites that contain cold gas thrusters and reaction wheels. The first problem concerns the estimation of the thruster force response to a pulse command. An optimal data integration method is developed and implemented to estimate the thruster force output from a number of noisy sensors. The second problem occurs when the output force vector of a thruster mounted on a satellite is misaligned with the centre of mass with the satellite. As a result a disturbance torque is generated on the satellite during thruster operation.

As conventional chemical rockets reach the outer limits of their abilities, significant research is going into alternative thruster technologies, some of which decouple the maximum thrust and efficiency from the propellant's internal chemical energy by supplying energy to the propellant as needed. Of particular interest and potential is the electrically powered thruster, which promises very high specific thrust using relatively inexpensive and stable propellant gasses. Some such thrusters, specifically ion thrusters, have achieved significant popularity for various applications. However, there exist other classes of electrical thrusters which promise even higher levels of efficiency and performance. This thesis will focus on one such thruster type - the magnetoplasmadynamic thruster - which uses an ionized propellant flow and large currents to accelerate the propellant gas by electrical and magnetic force interactions. The necessary background will be presented in order to understand and characterize the operation of such devices, and a theoretical model will be developed in order to estimate the levels of performance which can be expected. Simulations will be performed and analyzed in order to better understand the principles on which these devices are designed. Finally, a thruster package will be designed and built in order to test the performance of the device and accuracy of the model. This will include a high-current power supply, ignition circuit, gas delivery system, and nozzle. Finally, the measured performance of this thruster package will be measured and compared to the theoretical predictions in order to validate the models constructed for this type of thruster.

The rectangular pulsed plasma thruster (PPT) is an electromagnetic thruster that ablates Teflon propellant to produce thrust in a discharge that lasts 5-20 microseconds. In order to integrate PPTs onto spacecraft, it is necessary to investigate possible thruster plume-spacecraft interactions. The PPT plume consists of neutral and charged particles from the ablation of the Teflon fuel bar as well as electrode materials. In this thesis a novel application of quadruple Langmuir probes is implemented in the PPT plume to obtain electron temperature, electron density, and ion speed ratio measurements (ion speed divided by most probable thermal speed). The pulsed plasma thruster used is a NASA Glenn laboratory model based on the LES 8/9 series of PPTs, and is similar in design to the Earth Observing-1 satellite PPT. At the 20 J discharge energy level, the thruster ablates 26.6 mg of Teflon, creating an impulse bit of 256 mN-s with a specific impulse of 986 s. The quadruple probes were operated in the so-called current mode, eliminating the need to make voltage measurements. The current collection to the parallel to the flow electrodes is based on Laframboise's theory for probe to Debye length ratios between 5 and 100, and on the thin-sheath theory for ratios above 100. The ion current to the perpendicular probe is based on a model by Kanal and is a function of the ion speed ratio, the applied non-dimensional potential and the collection area. A formal error analysis is performed using the complete set of nonlinear current collection equations. The quadruple Langmuir probes were mounted on a computer controlled motion system that allowed movement in the radial direction, and the thruster was mounted on a motion system that allowed angular variation. Measurements were taken at 10, 15 and 20 cm form the Teflon fuel bar face, at angles up to 40 degrees off of the centerline axis at discharge energy levels of 5, 20, and 40 J. All data points are based on an average of four PPT pulses. Data analysis shows the temporal and spatial variation in the plume. Electron temperatures show two peaks during the length of the pulse, a trend most evident during the 20 J and 40 J discharge energies at 10 cm from the surface of the Teflon fuel bar. The electron temperatures after the initial high temperature peak are below 2 eV. Electron densities are highest near the thruster exit plane. At 10 cm from the Teflon surface, maximum electron densities are 1.04e20 ± 2.8e19 m-3, 9.8e20 ± 2.3e20 m-3, and 1.38e21 ± 4.05e20 m-3 for the 5 J, 20 J and 40 J discharge energy, respectively. The electrons densities decrease to 2.8x1019 ± 8.9e18 m-3, 1.2e20 ± 4.2e19 m-3, and 4.5e20 ± 1.2e20 m-3 at 20 cm for the 5 J, 20 J, and 40 J cases, respectively. Electron temperature and density decrease with increasing angle away from the centerline, and with increasing downstream distance. The plume is more symmetric in the parallel plane than in the perpendicular plane. Ion speed ratios are lowest near the thruster exit, increase with increasing downstream distance, but do not show any consistent angular variation. Peak speed ratios at a radial distance of 10 cm are 5.9±3.6, 5.3±0.39, and 4.8±0.41 for the 5 J, 20 J and 40 J discharge energies, respectively. The ratios increase to 6.05±5.9, 7.5±1.6, and 6.09±0.72 at a radial distance of 20 cm. Estimates of ion velocities show peak values between 36 km/s to 40 km/s, 26 km/s to 30 km/s, and 26 km/s to 36 km/s for the % J, 20 J, and 40 J discharge energies, respectively.