System identification has importance in modeling and control of industrial systems. The main task of system identification is to build a suitable model that represents the relationship between input, output and disturbances of a real system. The thesis presents identification and discrete time linear modeling of a hydraulic actuator. This thesis demonstrates how to formulate hydraulic functions for both normal and faulty conditions with internal leakage using both offline and on-line measurements. Least square and recursive least square methods are used to estimate the model parameters based on the Auto Regressive technique with Exogenous input (ARX) model. For the offline case, square and sine wave signals are used as input control signals. For the online case, random input control signal is applied. Prediction error criterion is used for model validation based on experimental data. It is shown that the ARX model is capable of representing a valve-controlled hydraulic system dynamics.

Brytspänningen är den spänning som uppkommer när överkopplingsmotståndet i lindningskopplaren lämnar sitt föregående läge vid omkoppling. Storleken på brytspänningen i lindningskopplaren beror på hur stor läckinduktansen är. Är den inte känd så kan brytspänningen istället beräknas med hjälp av FEM-programmet ACE (internt ABB-program) i samband med Mathcad. I ACE beräknas först reaktanserna i p.u-enheter mellan lindningarna och hur stora de är beror på lindningslayouten. Det är tidskrävande att använda ACE och Mathcad och uppgiften är att utreda de parametrar som påverkar storleken på brytspänningen samt att ta fram en förenklad beräkning av densamma. Genom simulering i ACE av en mängd olika lindningslayouter visar det sig snart att det är alltför många parametrar som påverkar reaktanserna. De förenklingar som trots det har tagits fram är lite för grova för att det ska vara pålitligt. Mathcad är än mer komplext med tunga beräkningar som inte är lätta att förenkla. Arbetet har ändå gett mer kunskap om hur reaktanserna påverkas av geometrierna i lindningarna och kommer att vara till viss nytta, även om det inte gick att förenkla ACE- och Mathcadberäkningarna så som var tänkt. / The recovery voltage is the voltage that occur when the transition resistor in the tap-changer leaves its previous position during an operation cycle. The amplitude of the recovery voltage depends on the leakage inductance. If the leakage inductance is unknown, the recovery voltage can instead be calculated using a FEM-program called ACE (internal ABB-program) in conjunction with Mathcad. First, the reactances between the windings are calculated in per unit (p.u) using ACE and they depend on the winding layout. It is time consuming to use ACE and Mathcad and the task has been to investigate the parameters that affects the recovery voltage and to develop a simplified calculation of it. Through simulation using ACE of a number of different winding layouts one soon comes to the conclusion that there are simply too many parameters affecting the reactances. Although the simplified calculations that despite this has been developed, they soon prove to be too rough to be useful. Mathcad is even more complex with heavy calculations that are not easy to grasp. However, this thesis has given more knowledge about the way the reactances are affected by the geometry of the windings, even though it was not possible to in a reasonable way simplify the calculation of ACE and Mathcad.

Transverse-integrated nodal di usion methods currently represent the standard in full core neutronic simulation. The primary shortcoming of this approach is the utilization of the quadratic transverse leakage approximation. This approach, although proven to work well for typical LWR problems, is not consistent with the formulation of nodal methods and can cause accuracy and convergence problems. In this work, an improved, consistent quadratic leakage approximation is formulated, which derives from the class of higher-order nodal methods developed some years ago. In this thesis a number of iteration schemes are developed around this consistent quadratic leakage approximation which yields accurate node average results in much improved calculational times. The most promising of these iteration schemes results from utilizing the consistent leakage approximation as a correction method to the standard quadratic leakage approximation. Numerical results are demonstrated on a set of benchmark problems and further applied to realistic reactor problems for particularly the SAFARI-1 reactor operating at Necsa, South Africa. The nal optimal solution strategy is packaged into a standalone module which may be simply coupled to existing nodal di usion codes, illustrated via coupling of the module to the OSCAR-4 code system developed at Necsa and utilized for the calculational support of a number of operating research reactors around the world. / Thesis(PhD (Reactor Science))--North-West University, Potchefstroom Campus, 2013

Transverse-integrated nodal di usion methods currently represent the standard in full core neutronic simulation. The primary shortcoming of this approach is the utilization of the quadratic transverse leakage approximation. This approach, although proven to work well for typical LWR problems, is not consistent with the formulation of nodal methods and can cause accuracy and convergence problems. In this work, an improved, consistent quadratic leakage approximation is formulated, which derives from the class of higher-order nodal methods developed some years ago. In this thesis a number of iteration schemes are developed around this consistent quadratic leakage approximation which yields accurate node average results in much improved calculational times. The most promising of these iteration schemes results from utilizing the consistent leakage approximation as a correction method to the standard quadratic leakage approximation. Numerical results are demonstrated on a set of benchmark problems and further applied to realistic reactor problems for particularly the SAFARI-1 reactor operating at Necsa, South Africa. The nal optimal solution strategy is packaged into a standalone module which may be simply coupled to existing nodal di usion codes, illustrated via coupling of the module to the OSCAR-4 code system developed at Necsa and utilized for the calculational support of a number of operating research reactors around the world. / Thesis(PhD (Reactor Science))--North-West University, Potchefstroom Campus, 2013

System identification has importance in modeling and control of industrial systems. The main task of system identification is to build a suitable model that represents the relationship between input, output and disturbances of a real system. The thesis presents identification and discrete time linear modeling of a hydraulic actuator. This thesis demonstrates how to formulate hydraulic functions for both normal and faulty conditions with internal leakage using both offline and on-line measurements. Least square and recursive least square methods are used to estimate the model parameters based on the Auto Regressive technique with Exogenous input (ARX) model. For the offline case, square and sine wave signals are used as input control signals. For the online case, random input control signal is applied. Prediction error criterion is used for model validation based on experimental data. It is shown that the ARX model is capable of representing a valve-controlled hydraulic system dynamics.

Composite insulators are widely being used in power industry to alternate traditional porcelain-based insulators for their advantages, including better pollution performance, low maintenance cost, light weight, compact line design. However, due to the short application history and experience, the degradation of composite insulators in natural environment is a big concern for the power utilities. The knowledge on the degradation of composite insulators is being studied world wide. The methods to assess the working conditions of composite insulators are being studied and created. In Queensland University of Technology (QUT), the approach based on chemical analysis methods was first developed. The work in this thesis based on the previous research work is focused on correlating electrical characteristics with chemical analysis results of the composite insulators and physical observations results. First,the electrical characteristics of composite insulators were presented and analysed, including leakage current, cumulative current, peaks of leakage current, the statistic results of the leakage current. Among them, the characteristics of leakage current were mainly studied. The shape of waveforms was found to relate to the degree of discharge activities of the composite insulators. The waveforms analysed by FFT revealed that the odd harmonic components became obvious during the discharge activities. The correlations between the electrical characteristics of composite insulators and chemical analysis results showed that the composition of composite insulators plays significant roles in terms of electrical performance. The oxidation index (O.I.) and the ester/ketone ratio (E/K) differentiated the different degradation reasons of the composite insulators in the test conditions. Finally, the thesis presents one approach, which aims to assess the surface conditions of composite insulators in an easy manner and in short time.

Title page, table of contents and abstract only. The complete thesis in print form is available from the University of Adelaide Library. / The occurrence of palaeo-oil columns in Late Jurassic and Cretaceous reservoirs in the Vulcan sub-basin indicates that hydrocarbon accumulations have leaked. It is unclear whether accumulations have leaked through breach of top seal or fault seal. This study evaluates the top seal potential for hydrocarbon accumulations in the Vulcan Sub-basin. For this purpose a top seal potential assessment methodology was developed. Seal potential (SP) combines seal capacity (the hydrocarbon column height that can physically be held back by seal), seal geometry (the areal extent and thickness of the seal) and seal integrity (rock mechanical properties of the seal). Seal capacities are measured using mercury injection capillary pressure calculations. Areal extent is evaluated using sedimentological and sequence stratigraphic principles. Thickness is determined empirically from well logs and seismic data. Seal integrity is derived from a brittleness index. In addition, a component relating to data quality and quantity is included in seal potential evaluation. The main sample set for this study is composed of drill cuttings. For this reason a comparison of seal capacity results measured from cuttings and cores has verified that cuttings samples provide accurate seal capacity measurements. Lower Vulcan Formation SP ranges from low to high due to variations in seal capacity and thickness risks as well as data quality and quantity. High SP occurs in the main depocentres and low SP occurs on the palaeo-highs and basin margins. Upper Vulcan Formations SP ranges from low to moderate due to variations in seal capacity. Moderate SP occurs in the depocentres and low SP on the basin margins. In the Echuca Shoals Formations seal capacity. Formation seal extent and integrity as well as data quality and quantity are good. However seal thickness is inconsistent, resulting in SP variations from good to poor as a function of thickness. Jamieson Formation has high seal capacities, is thick and areally extensive, however the seal potential is locally moderate (for example on the Ashmore Platform) due to seal integrity risk. SP for the Jamieson is controlled by the thickness and the amount of calcite present in the rock, which affects the brittleness of the formation and hence the seal integrity. The Woolaston, Gibson and Fenelon (WGF) Formations are grouped together as a regional seal and in this group SP varies from low to high. The WGF rocks generally have high seal capacities, are areally extensive and thick with good data quality and quantity sample set wise. Where the WGF is predominantly marl and calcilutite some of the highest brittleness index values were recorded and hence the WGF has a low SP in these areas. Based on the overall seal potential analysis, almost all seals in the area are capable of holding back hydrocarbon columns greater then present or palaeocolums recorded. This suggests that hydrocarbon leakage in the Vulcan Sub-Basin did not occur as a result of top seal capillary failure. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1313021 / Thesis (Ph.D.) -- University of Adelaide, Australian School of Petroleum, 2008

Thesis (M.S.)--University of Michigan, 1988.

Thesis (M.S.)--University of Michigan, 1973.

Thesis (M.S.)--University of Michigan, 1971.