Transient stability of electric energy grids is defined as the ability of the power system to remain in synchronism during large disturbances. If the grid is not equipped with controllers capable of transiently stabilizing system dynamics, large disturbances could cause protection to trigger disconnecting the equipment and leading further to cascading system-wide blackouts. Today’s practice of tuning controllers generally does not guarantee a transiently stable response because it does not use a model for representing system-wide dynamic interactions. To overcome this problem, in this thesis we propose a new systems modeling and control design for provable transient stabilization of power systems against a given set of disturbances. Of particular interest are fast power-electronically-controlled Flexible Alternating Current Transmission System (FACTS) devices which have become a new major option for achieving transient stabilization. The first major contribution of this thesis is a framework for modeling of general interconnected power systems for very fast transient stabilization using FACTS devices. We recognize that a dynamic model for transient stabilization of power systems has to capture fast electromagnetic dynamics of the transmission grid and FACTS, in addition to the commonly-modeled generator dynamics. To meet this need, a nonlinear dynamic model of general interconnected electric power systems is derived using time-varying phasors associated with states of all dynamic components. The second major contribution of this thesis is a two-level approach to modeling and control which exploits the unique network structure and enables preserving only relevant dynamics in the nonlinear system model. This approach is fundamentally based on separating: a) internal dynamics model for ensuring stable local response of components; b) system-level model in terms of interaction variables for ensuring stability of the system when the components are interconnected. The two levels can be controlled separately which minimizes the need for communication between controllers. Both distributed and cooperative ectropy-based controllers are proposed to control the interaction-level of system dynamics. Proof of concept simulations are presented to illustrate and compare the promising performance of the derived controllers. Some of the most advanced FACTS industry installations are modeled and further generalized using our approach.

Human Herpes Simplex viruses and Simian Herpes Simplex viruses share a high degree of genome homology, but despite this, important differences arise when the viruses are compared at the level of gene expression and virulence in non-host primates. In Human Herpes viruses (HSV-1 and HSV-2); 5 genes (RL02, US01, RS01, UL54 and US12) are expressed with an immediate early kinetics, i.e. their transcriptional activation does not require de novo synthesis of host or viral factors. The five immediate early (IE) genes regulate the cascade of expression of the other early and late HSV genes. Literature indicates that in HSV-1 infections, ICP4, ICP27 and to a lesser extent, ICP0, are mandatory for the full expression of the early and late gene classes. In contrast, our data on the Simian simplexviruses SA8, HVP-2 and B virus indicate that ICP0 (RL2) is the only gene with true IE kinetics. It is possible that in Simian Herpes viruses, ICP0 is necessary for the expression of all other viral genes, and to test this hypothesis I have cloned and expressed in Vero cells the ICP0 protein for the simian simplexvirus SA8 and studied its effect on the SA8 genes that are homologous to the immediate early genes in HSV. Results demonstrate that ICP0 does not appear to be sufficient to activate the transcription of the other IE genes but it is likely that ICP0 functionality is a necessary component in the activation process.

Fluid flow network simulation codes are commonly used as a design and analysis tool for many engineering problems such as gas distribution networks, power plants and heat pumps. Two formulations of conservation of momentum have been widely applied in fluid flow network simulation models namely those based on static pressure and those based on total pressure. The total pressure formulations are convenient in that they eliminate the difficulties associated with the calculation of the convective terms and components such as pipe junctions are treated in a straightforward manner based on total pressure losses. However, the different formulations of total pressure for compressible and incompressible flow require different formulations of the momentum conservation equation, which is inconvenient for implementation in a generic network simulation code. In this thesis a united total pressure formulation is first derived which is valid for all fluids and therefore eliminates the inconvenience of switching between the compressible and incompressible formulations. A non-iterative method for the solution of the non-isothermal discretised equations based on the total pressure formulation is then introduced and consistency is illustrated. The method appears to be very stable for subsonic flows, while rapid steady state convergence is observed. A systematic comparison is also done with traditional static pressure based methods and the similarities and differences between the two formulations are illuminated. The different time scales involved in the simulation of transient flow in fluid networks are problematic when conventional fixed time step methods are used for time-wise integration. The time scales associated with acoustic and kinematic wave phenomena as well as storage effects can differ by orders in magnitude. This thesis also presents a simple adaptive time step algorithm which can be readily used in conjunction with all the commonly used first order methods for fluid flow networks. Two test problems are selected to demonstrate the efficiency and savings obtained with this procedure. The adaptive time step algorithm correctly selects appropriate time steps for all phenomena and significant computational savings are observed for accurate integration. In addition, a procedure is implemented which automatically selects the appropriate integration method. The resulting algorithm is a fully adaptive algorithm which switches between a fully implicit method and a semi-implicit method. Two test problems are once again used to demonstrate the efficiency and savings. The fully adaptive algorithm correctly selects appropriate methods for all phenomena and significant additional computational savings are observed. / Thesis (PhD (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2013

Fluid flow network simulation codes are commonly used as a design and analysis tool for many engineering problems such as gas distribution networks, power plants and heat pumps. Two formulations of conservation of momentum have been widely applied in fluid flow network simulation models namely those based on static pressure and those based on total pressure. The total pressure formulations are convenient in that they eliminate the difficulties associated with the calculation of the convective terms and components such as pipe junctions are treated in a straightforward manner based on total pressure losses. However, the different formulations of total pressure for compressible and incompressible flow require different formulations of the momentum conservation equation, which is inconvenient for implementation in a generic network simulation code. In this thesis a united total pressure formulation is first derived which is valid for all fluids and therefore eliminates the inconvenience of switching between the compressible and incompressible formulations. A non-iterative method for the solution of the non-isothermal discretised equations based on the total pressure formulation is then introduced and consistency is illustrated. The method appears to be very stable for subsonic flows, while rapid steady state convergence is observed. A systematic comparison is also done with traditional static pressure based methods and the similarities and differences between the two formulations are illuminated. The different time scales involved in the simulation of transient flow in fluid networks are problematic when conventional fixed time step methods are used for time-wise integration. The time scales associated with acoustic and kinematic wave phenomena as well as storage effects can differ by orders in magnitude. This thesis also presents a simple adaptive time step algorithm which can be readily used in conjunction with all the commonly used first order methods for fluid flow networks. Two test problems are selected to demonstrate the efficiency and savings obtained with this procedure. The adaptive time step algorithm correctly selects appropriate time steps for all phenomena and significant computational savings are observed for accurate integration. In addition, a procedure is implemented which automatically selects the appropriate integration method. The resulting algorithm is a fully adaptive algorithm which switches between a fully implicit method and a semi-implicit method. Two test problems are once again used to demonstrate the efficiency and savings. The fully adaptive algorithm correctly selects appropriate methods for all phenomena and significant additional computational savings are observed. / Thesis (PhD (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2013

Soot is formed whenever the combustion of hydrocarbon fuels is incomplete. Since soot particles are very small, they can be inhaled and cause severe health problems, such as pulmonary diseases. They can also cause environmental pollution, and have a significant effect on global warming and melting of polar ice sheets. The environmental and health impact of soot depends strongly on soot particle size and morphology, so there is a pressing need for measuring techniques that characterize aerosolized soot. Laser-Induced incandescence (LII) has proved to be a reliable technique for making spatial and temporal measurements of soot primary particle sizes and soot volume fractions. Nevertheless, there are some unresolved issues in LII, which may cause large errors in soot primary particle size inferred from LII data. One of these issues is anomalous cooling, which is the unexpectedly high initial rate of soot particle cooling observed in experiments, which can not be predicted by LII models. Among the speculations about the possible causes of this phenomenon is the transient gas dynamics effects which have been ignored in LII models. Another phenomena that has been speculated to affect LII predictions in high fluence LII, is how the gas dynamics of sublimed carbon clusters impact the local gas dynamics surrounding the particle during the cooling phase. The focus of this thesis is to investigate transient effects on heat conduction in low fluence LII, and the gas dynamics of sublimed species in high fluence LII using Direct Simulation Monte Carlo (DSMC) method. DSMC is a statistical/numerical method which works based on the physics of Boltzmann equation. In this method a large number of real molecules are represented by the so called simulated molecules and the state of these molecules is tracked during the simulation as they undergo collisions with each other and with the boundaries. The results show that transient effects contribute to anomalous cooling but are not the only cause of this phenomenon. The time scale over which transient effects are significant is also found to be very close to that of anomalous cooling which implies the real cause of anomalous cooling has some similarities to transient effects. Also regarding gas dynamics of sublimation, two effects in particular have been investigated using DSMC, namely, back flux of sublimed species and formation of shock waves. DSMC results confirm the back flux of sublimed species but no shock wave was observed for the boundary conditions considered in this study.

This thesis reports theoretical and experimental investigations carried out to better understand the effect of process parameters on the microstructure of transient liquid phase (TLP) joint. The theoretical investigations were carried out using analytical and numerical models to simulate base metal dissolution and isothermal solidification stages of the TLP bonding process. The experimental investigation was carried out by using standard metallographic technique to study the microstructure of bonded materials using optical and Scanning Electron Microscopes. Deviation from parabolic relationship between solid/liquid interface migration and holding time during TLP bonding is suggested as a new alternate phenomenon responsible for the anomalous increase in processing time required to produce eutectic microconstituent free joint with increase in bonding temperature. The results of TLP joining of commercial pure nickel using a Ni-P filler alloy showed that an increase in bonding temperature would be beneficial provided that sufficient holding time is allowed for complete isothermal solidification of liquated insert. Otherwise, an increase in bonding temperature may result in formation of thicker deleterious eutectic along the TLP joint. Furthermore, it was observed that the joint centerline eutectic product and interface second phase particles that form during TLP bonding of Inconel 738 using Ni-P filler can be significantly reduced by post bond heat treatment. The effectiveness of this approach, however, requires proper selection of heat treatment temperature above Ni-P binary eutectic temperature.

This thesis presents a linearized technique to determine a risk-based index for dynamic security. The method is an extension to an existing technique in which the risk of steady state security is calculated using the mean and variance of load uncertainty. The proposed method is applied to calculate the risk indices for the New England 39 bus test system. The results obtained from the proposed method are validated against those estimated by Monte Carlo simulation. Both approaches produce virtually the same results for small load deviations.

Human Herpes Simplex viruses and Simian Herpes Simplex viruses share a high degree of genome homology, but despite this, important differences arise when the viruses are compared at the level of gene expression and virulence in non-host primates. In Human Herpes viruses (HSV-1 and HSV-2); 5 genes (RL02, US01, RS01, UL54 and US12) are expressed with an immediate early kinetics, i.e. their transcriptional activation does not require de novo synthesis of host or viral factors. The five immediate early (IE) genes regulate the cascade of expression of the other early and late HSV genes. Literature indicates that in HSV-1 infections, ICP4, ICP27 and to a lesser extent, ICP0, are mandatory for the full expression of the early and late gene classes. In contrast, our data on the Simian simplexviruses SA8, HVP-2 and B virus indicate that ICP0 (RL2) is the only gene with true IE kinetics. It is possible that in Simian Herpes viruses, ICP0 is necessary for the expression of all other viral genes, and to test this hypothesis I have cloned and expressed in Vero cells the ICP0 protein for the simian simplexvirus SA8 and studied its effect on the SA8 genes that are homologous to the immediate early genes in HSV. Results demonstrate that ICP0 does not appear to be sufficient to activate the transcription of the other IE genes but it is likely that ICP0 functionality is a necessary component in the activation process.

With the increased complexity of modern power systems, it may be required more than one platform to do an intended study efficiently and accurately. This research was carried out to investigate the use of co-simulation in an application of power system. A back-to-back Voltage Source Converter (VSC) transmission system was modeled in PSCAD/EMTDC which is an Electro-Magnetic Type (EMT) software. Results were analyzed for some operating points of the system. Then the control system of the above system was modelled in MATLAB/SIMULINK while the rest of the system was modeled in PSCAD/EMTDC. Both of these systems were interfaced to obtain the complete system and results were analyzed under same operating points as the original PSCAD case.

This thesis presents a new way of combining non-linear optimization algorithms and electromagnetic transient (EMT) simulation. In this new combination, a non-linear optimization algorithm utilizes a real-time EMT simulation environment as objective function evaluator. However, as more applications of the off-line EMT simulation software implementation were made, the combination between non-linear optimization algorithms and off-line EMT simulation software revealed new need, which this research work attempts to address. The first need arose from the speed of simulation of the off-line EMT simulation software. With a certain breed of non-linear optimization algorithms, heuristics bases algorithms in particular, a large number of objective function evaluations are required before the termination or convergence criterion in the selected algorithms is satisfied. Sometimes, the number of evaluations as well as the complexity of the simulation case where the objective function is based upon translates into a very long simulation time, which goes beyond the boundary of given resources. This research work attempts to address this simulation timing issue by capitalizing on the real timeness of the simulation environment as well as utilizing the multiple instances of the simulation environment in parallel. The second need arose from the modeling requirement of the off-line EMT simulation software. In order to properly design the necessary objective function evaluator, which is largely a simulation case, a large amount of information needs to be embedded into the case. Under certain circumstances, the necessary information would not be available. Therefore, the simulation case needs to include approximations which may cause compromise in the end result. This limitation becomes more obvious when a real world device such as a commercial controller becomes involved. On the contrary, this limitation can be addressed by the real-time simulation environment because this environment can be directly interfaced with the real world device. In this way, the need for detailed information regarding the device is eliminated. This elimination would enlarge the application of the combination, between the non-linear optimization algorithm and EMT type simulation environment. The effectiveness of the proposed approach is demonstrated by various examples throughout this thesis.