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Dissertations / Theses on the topic 'Transients modelling'
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1
Zitnik, Mihael. "Numerical modelling of transients in electrical systems /." Uppsala : Uppsala Univ. Library, 2001. http://www.gbv.de/dms/goettingen/342399799.pdf.
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Palav, Leena. "Modelling of custom power devices on an electromagnetic transients program." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0014/MQ35079.pdf.
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Rabiti, Cristian. "Modelling of fast neutron transients in an accelerator driven system." [S.l. : s.n.], 2007. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-30994.
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Dawson, Patricia Ann. "Gas release and the mathematical modelling of variable wavespeed pressure transients." Thesis, University of Leeds, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329048.
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Ametani, Akihiro. "Power system analyses, modelling and characteristics with special reference to transients." Thesis, University of Manchester, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.525975.
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Shokri-Kojori, Shokrollah. "Advanced source modelling with particular reference to fault transients in power systems." Thesis, University of Bath, 1987. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.760574.
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Fu, Wing Ming. "An investigation into real time modelling techniques for power system fault transients." Thesis, University of Bath, 1992. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306762.
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Rabiti, Cristian [Verfasser]. "Modelling of fast neutron transients in an accelerator driven system / vorgelegt von Cristian Rabiti." Stuttgart : IKE, 2007. http://d-nb.info/997049669/34.
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Macleod, Kenneth David. "Numerical modelling of air pressure transients resulting from detergent dosed annular flows within building drainage systems." Thesis, Heriot-Watt University, 2000. http://hdl.handle.net/10399/573.
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Morse, Brian. "Mathematical modelling of sediment transport and bed transients in multichannel river networks under conditions of unsteady flow." Thesis, University of Ottawa (Canada), 1991. http://hdl.handle.net/10393/7667.
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The fixed-bed, hydrodynamic and water quality model ONE-D has been successfully applied to virtually every major river system in Canada. In 1984 one of the supporting agencies, Environment Canada, expressed the desire to extend ONE-D for the simulation of sediment transport processes and river-bed dynamics. After performing a literature review it was found that currently available mobile-bed river models did not have the features that the basic ONE-D model had, particularly those required to model channel networks. Because of these numerical modelling limitations it was decided to proceed with this research effort. Sediment transport and bed dynamic routines were written in modular form and the resulting model (ONE-D-SED) became the mobile-bed version of ONE-D. ONE-D-SED was initially validated for hypothetical test cases. This initial application showed that the model reproduced analytical solutions for the 'linear' cases examined. In addition, these simulations provided documentation of the numerical properties of ONE-D-SED's finite difference schemes. Following these preliminary tests correction coefficients were generated for analytical solutions of bed transients of finite height. The subsequent application of ONE-D-SED to the Lower Fraser River was partly in response to the need expressed by Public Works Canada for accurate sediment budgets for certain reaches of this major river system. More importantly, part of this system is tidal, multi-channel network and hence is ideally suited for model validation purposes. Finally, superior sediment data were available for the study reach identified in this research. After analysis of Lower Fraser River sediment data, and calibration of the Ackers-White (A-W) sediment transport equation. ONE-D-SED was applied to the study reach at a "screening-level". Since the results of this application were encouraging, ONE-D-SED was then applied at a detailed level and simulated changes in bed elevation were compared to those observed. In addition to the work directly related to model development, application and validation work was also undertaken to address the issue of representing suspended sediment 'fractions' consisting of a range of grain sizes. This work was motivated by the findings of analyses of the suspended sediment load in the Lower Fraser River and by the necessity of characterizing the representative grain size for natural rivers where there is a large gradation in the bed material composition. This study revealed that the representative grain size of a fraction depends on certain local hydraulic conditions. In addition, correction factors for modelling suspended sediment concentrations were obtained when the geometric grain size of the fraction is used in lieu of the mathematically accurate representative size.
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Brauer, Patrik. "High-Frequency Voltage Distribution Modelling of a Slotless PMSM from a Machine Design Perspective." Thesis, KTH, Elkraftteknik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-224174.
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The introduction of inverters utilizing wide band-gap semiconductors allow for higher switching frequency and improved machine drive energy efficiency. However, inverter switching results in fast voltage surges which cause overvoltage at the stator terminals and uneven voltage distribution in the stator winding. Therefore, it is important to understand how next generation machine drives, with higher switching frequency, affect the voltage distribution. For this purpose, a lumped-parameter model capable of simulating winding interturn voltages for the wide frequency range of 0-10 MHz is developed for a slotless PMSM. The model includes both capacitive and inductive couplings, extracted from 2D finite element simulations, as well as analytically estimated resistive winding losses. The developed model of a single phase-winding is used to investigate how machine design aspects such as insulation materials and winding conductor distribution affects both voltage distribution and winding impedance spectrum. Validation measurements demonstrate that the model is accurate for the wide frequency range. The sensitivity analysis suggests that the winding conductor distribution affect both impedance spectrum and voltage distribution. For the slotless machine, capacitance between the winding and the stator is several times smaller than capacitance between turns. Therefore, the high-frequency effects are dominated by the capacitance between turns. Insulation materials that affect this coupling does therefore have an impact on the impedance spectrum but does not have any significant impact on the voltage distribution.<br>Nästa generations inverterare för styrning av elektriska maskiner, baserade på bredbandgaps komponenter, tillåter högre switchfrekvenser vilket skapar en energieffektivare drivlina. Nackdelen är att snabba spänningsflanker från den höga switchfrekvensen skapar överspänning på stators anslutningar och en ojämn spänningsfördelning i statorlindningen. Det är därför betydelsefullt att förstå hur dessa nya drivlinor påverkar lindningens spänningsfördelning. I denna rapport används en modell kapabel att simulera lindningens spänningsfördelning i det breda frekvensspektrumet 0-10 MHZ. Modellen är framtagen för en faslindning av en PMSM, utan statoröppning, som inkluderar både kapacitiva och induktiva kopplingar samt analytiskt beräknade lindningsförluster. Modellen används för att undersöka spänningsfördelningen i lindningen samt inverkan från designparametrar som isolationsmaterial och lindningsdistribution. Känslighetsanalysen visar att lindingsdistributionen har en signifikant påverkan på både impedansspektrumet och spänningsfördelningen. För den studerade maskintypen är det kapacitansen mellan varv som är dominerande för högfrekventa fenomen. Isolationsmaterial som påverkar denna koppling har en påverkan på impedansspektrumet men är liten för spänningsfördelningen.
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Mousavi, Seyedali. "Electromagnetic Modelling of Power Transformers for Study and Mitigation of Effects of GICs." Doctoral thesis, KTH, Elektroteknisk teori och konstruktion, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-159747.
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Geomagnetic disturbances that result from solar activities can affect technological systems such as power networks. They may cause DC currents in power networks and saturation of the core in power transformers that leads to destruction in the transformer performance. This phenomena result in unwanted influences on power transformers and the power system. Very asymmetric magnetization current, increasing losses and creation of hot spots in the core, in the windings, and the metallic structural parts are adverse effects that occur in transformers. Also, increasing demand of reactive power and malfunction of protective relays menaces the power network stability. Damages in large power transformers and blackouts in networks have occurred due to this phenomenon. Hence, studies regarding this subject have taken the attention of researchers during the last decades. However, a gap of a comprehensive analysis still remains. Thus, the main aim of this project is to reach to a deep understanding of the phenomena and to come up with a solution for a decrease of the undesired effects of GIC. Achieving this goal requires an improvement of the electromagnetic models of transformers which include a hysteresis model, numerical techniques, and transient analysis. In this project, a new algorithm for digital measurement of the magnetic materials is developed and implemented. It enhances the abilities of accurate measurements and an improved hysteresis model has been worked out. Also, a novel differential scalar hysteresis model is suggested that easily can be implemented in numerical methods. Two and three dimensional finite element models of various core types of power transformers are created to study the effect of DC magnetization on transformers. In order to enhance the numerical tools for analysis of low frequency transients related to power transformers and the network, a novel topological based time step transformer model has been outlined. The model can employ a detailed magnetic circuit and consider nonlinearity, hysteresis and eddy current effects of power transformers. Furthermore, the proposed model can be used in the design process of transformers and even extend other application such as analysis of electrical machines. The numerical and experimental studies in this project lead to understanding the mechanism that a geomantic disturbance affects power transformers and networks. The revealed results conclude with proposals for mitigation strategies against these phenomena.<br><p>QC 20150210</p>
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Noureldin, Kareem Verfasser], Robert [Akademischer Betreuer] Pitz-Paal, and Alexander [Akademischer Betreuer] [Mitsos. "Modelling and control of transients in parabolic trough power plants with single-phase heat transfer fluids / Kareem Noureldin ; Robert Pitz-Paal, Alexander Mitsos." Aachen : Universitätsbibliothek der RWTH Aachen, 2018. http://d-nb.info/1213678374/34.
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Dutton, Richard John. "Modelling transient storage processes." Thesis, University of Sheffield, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.419618.
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Chuthi, Noel Nelson Stima. "Current transformers transient response modelling using electromagnetic transient program (EMTP)." Master's thesis, University of Cape Town, 1997. http://hdl.handle.net/11427/19564.
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The subject of this thesis is Current Transformer Transient response study using an electromagnetic Transient program (EMTP). Current transformers are considered eyes for power system protection. Behaviours of protection systems depend largely on information fed to them by instrument transformers. Ferromagnetic current transformers have for many years provided practical method of current measurement, however there are limitations associated with current transformer operation:- notably, difficult in maintaining accuracy over the full range of operating conditions, and most particularly current transformers tendency to suffer saturation of iron core during severe faults, with accompanying severe ratio or loss of output. These limitations might lead to mal operation of protective relays due to distorted inputs from current transformers particularly in transient periods. This thesis involved studying the behaviour of current transformers in both steady state and transient periods. An emphasis being put on transient periods which are very crucial in behaviour of current transformers because transformation errors are greatest in these periods. Errors in current transformer transformation might affect operation of entire protection schemes. Maloperation of current transformers in transient periods have very bad effect on relay co-ordination and worst condition might be failure of protection scheme operation altogether. Over the past decades engineers have been trying to develop a current transformer model that would represent a current transformer well in transient periods. It has proved to be rather difficult to come up with a single detailed model that would satisfy all possible conditions. This is due to non-linearity of magnetising curve and saturation effects of current transformer iron cores. The author has considered different current transformer models with their merits and demerits being highlighted. It has been shown that different current transformer models have to be used when considering different operating conditions of a current transformer in a power system. ATP-EMTP an Electromagnetic Transient Program was developed in the sixties for the study of electromagnetic transients in power systems. It has proved to be a very useful tool in this regard. The program development is still going on today to accommodate a wide application in power systems. Several components have been developed to represent different components in a power system. It is only recently that there has been a growing interest to include modelling of protective equipment. This has been accelerated by the inclusion of MODELS in the EMTP program. This thesis explores the effect of transients taking into account different conditions like transient fault currents, effects of high frequency waves and surges. Effects of different types of burdens on current transformers were explored as well. Due to limitations of EMTP, simulation results are only applicable to current transformers with ARMCO M4 oriented steel with ungapped cores. The author arrived at several conclusions. The most important conclusion is that mal operation of protective relays due to current transformer saturation can be avoided easily if proper current transformer selection is given priority in power protection design. EMTP package proved to be very useful and handy when studying transients though one has to be careful with numerical oscillations which might be present during simulations. Problems of numerical oscillations have been discussed under current transformer simulation tools.
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Tikhomirova, Irina. "Electromagnetic Transient Modelling of Grounding Structures." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for elkraftteknikk, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-22535.
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Grounding is traditionally modelled as a pure resistance. This is a good approximation at low frequencies, but as the frequency gets higher, inductance starts to play an important role. To acquire accurate transient response of the system it is desirable to consider this fact. Special computer programs like CDEGS are required to analyze grounding structures, but this is not directly compatible with other programs for analysis of over-voltages and transients. The main objective of this project is to create a database containing frequency response for some common electrode types with different parameter combinations. This frequency response can be further used to create an equivalent time - domain grounding impedance that can be exported to EMTP programs. Three types of ground electrodes were analyzed in this project; earthing rod, counterpoise grounding with four radials, and horizontal ring electrode. A uniform soil model with variable values of resistivity and relative permittivity was used in all simulations. Geometrical dimensions of the electrodes were varied as well. All conductors were modelled as bare copper conductors. Parameters were determined based on the results of simulations in CDEGS and general recommendations for grounding of transmission towers given by Statnett. Unit current at different frequencies was injected into ground electrodes through a 0.1 meter long copper conductor. Ground potential rise of this conductor, which is equal to impedance to earth of the ground electrode, was extracted from HIFREQ in text format. Frequency resolution in the simulations is 10 points per decade between 0 and 0.1 MHz, 40 points between 0.1 and 1 MHz, and 80 points between 1 and 10 MHz. As a result of the project a database containing impedance and admittance as function of frequency for three types of electrodes has been created. Total number of responses stored in the database is 2268. Vector Fitting is used to convert frequency domain responses to time domain state - space models or RLC - networks. Vector fitting is a method to approximate measured or calculated frequency domain responses with a sum of rational functions. A Matlab routine interfit.m was developed to extract response of an electrode with given parameters. For parameters between the points in the database, linear interpolation is used. As a second step the function calls vector fitting that creates a time ? domain model from the frequency response of the defined ground electrode. Order of approximation in vector fitting should be adjusted for each case, starting with a low value and gradually increasing it till a sufficient approximation after passivity enforcement is achieved. Time ? domain simulations in CDEGS and ATPDraw gave similar results when order of approximation in vector fitting was chosen correctly. Negligible deviation was observed between the responses in time range between 0 and 5 µs in some cases. The results indicate that frequency - dependent models created by this method can be used in EMTP programs.
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Shannon, Julie. "Modelling transient flows in ephemeral channels." Thesis, King's College London (University of London), 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.404965.
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Bukvišová, Zuzana. "Modelování rychlých přechodných dějů." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2017. http://www.nusl.cz/ntk/nusl-316921.
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This thesis deals with the high speed transient modelling in the electrical networks. The introduction of this work discusses mathematical models of the individual devices used in the system and focuses on the line representation. It also contains a more detailed description of Bergeron and frequency dependent line model. The objective of this thesis is to design a network model using ATP-EMTP simulation program. In this model, the switching overvoltage caused by shunt reactor switching and lightning overvoltage are simulated. The thesis thoroughly describes the settings of the components used in the model of analysed network and in conclusion evaluates obtained simulation results in a relation to the insulation coordination.
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Pérez, Roca Sergio. "Model-based robust transient control of reusable liquid-propellant rocket engines." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASS017.
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La tendance actuelle vers un accès plus abordable à l'espace se traduit par des lanceurs et moteurs réutilisables. Du point de vue du contrôle, ces moteurs fusée à propergol liquide (MFPL) réutilisables impliquent des spécifications de robustesse plus exigeantes que ceux à usage unique, principalement en raison de leurs capacités de redémarrage multiple et de modulation de poussée. Classiquement, le système de contrôle gère les opérations des MFPL autour d'un ensemble fini de points prédéfinis. Cette approche réduit leur domaine de modulation à un intervalle restreint dans lequel ils sont conçus pour être sûrs. De plus, les phases transitoires, qui ont un impact important sur la vie du moteur, ne sont pas exécutées de manière robuste. L’objectif de ce travail est donc de développer une boucle de régulation adaptée à l’ensemble des phases d'opération (transitoire et régime permanent) et robuste aux variations paramétriques internes. Plusieurs blocs ont été développés pour constituer la boucle de régulation : simulation de moteur, génération de référence et contrôleurs. Des simulateurs représentatifs des moteurs à cycle générateur de gaz ont tout d'abord été construits. La modélisation purement thermodynamique du cycle a ensuite été adaptée au contrôle, afin d'obtenir des modèles non-linéaires sous forme d'état. Dans ces modèles, l'influence des entrées de commande continues (ouvertures des vannes) et des entrées discrètes (activation des allumeurs et démarreur) est considérée dans un cadre hybride simplifié. La sous-phase continue du transitoire de démarrage est contrôlée en boucle fermée pour suivre des trajectoires de référence pré-calculées. Outre le démarrage, les scénarios de modulation présentent également un algorithme pour le suivi des états finaux. Une méthode de contrôle à base de modèles, la commande prédictive, a été appliquée de manière linéarisée avec des considérations de robustesse à tous ces scénarios, dans lesquels des contraintes dures doivent être respectées. Le suivi des points de fonctionnement en pression (poussée) et du rapport de mélange dans l'enveloppe de conception est atteint en simulation tout en respectant les contraintes. La robustesse aux variations des paramètres, qui sont identifiés comme prédominants par des analyses, est également démontrée. Ce travail ouvre la voie à la validation expérimentale par des simulations hardware-in-the-loop ou des tests sur banc d'essai<br>The current trend towards a more affordable access to space is materialising in reusable launchers and engines. From the control perspective, these reusable liquid-propellant rocket engines (LPRE) imply more demanding robustness requirements than expendable ones, mainly due to their multi-restart and thrust-modulation capabilities. Classically, the control system handles LPRE operation at a finite set of predefined points. That approach reduces their throttability domain to a narrow interval in which they are designed to be safe. Moreover, transient phases, which have a great impact on engine life, are not robustly operated. Hence, the goal of this work is to develop a control loop which is adapted to the whole set of operating phases, transient and steady-state, and which is robust to internal parametric variations. Several blocks have been developed to constitute the control loop: engine simulation, reference generation and controllers. First, simulators representative of the gas-generator-cycle engines were built. The purely thermo-fluid-dynamic modelling of the cycle was subsequently adapted to control, obtaining nonlinear state-space models. In these models, the influence of continuous control inputs (valve openings) and of discrete ones (igniters and starter activations) is considered within a simplified hybrid approach. The continuous sub-phase of the start-up transient is feedback controlled to track pre-computed reference trajectories. Beyond the start-up, throttling scenarios also present an end-state-tracking algorithm. A model-based control method, Model Predictive Control, has been applied in a linearised manner with robustness considerations to all these scenarios, in which a set of hard constraints must be respected. Tracking of pressure (thrust) and mixture-ratio operating points within the design envelope is achieved in simulation while respecting constraints. Robustness to variations in the parameters, which are checked to be predominant according to analyses, is also demonstrated. This framework paves the way to experimental validation via hardware-in-the-loop simulations or in test benches
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Van, Aken G. J. "Transient modelling of finned tube heat exchangers /." Title page, contents, abstract and summary only, 1993. http://web4.library.adelaide.edu.au/theses/09ENS/09ensv217.pdf.
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Brace, Chris. "Transient modelling of DI TCi diesel engine." Thesis, University of Bath, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362260.
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Naylor, Philip. "Gas turbine transient performance : heat soakage modelling." Thesis, Cranfield University, 2004. http://dspace.lib.cranfield.ac.uk/handle/1826/10698.
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The
ability to accurately extract steady state performance information from transient
engine test data has the potential to significantly reduce test bed time and cost,
depending upon the accuracy with which engine phenomena such as heat soakage and
transient
tip clearance changes can be modelled within the context of a whole
engine
performance code.
This thesis describes
improvements to the GTTrans generic Whole engine
performance code thermo mechanical heat
soakage and tip clearance methods. This
thesis describes the streams method in which a collection of definite volumes are used
to
represent engine component hardware and perform transient heat transfer
calculations
accounting for both conduction and convection to and from non-trivial
engine component geometries. Transient metal and gas temperature profiles are then
used to estimate transient blade
tip clearances. The streams method has been
incorporated into a Rolls-Royce Trent 500 engine performance code. Accounting for
heat
soakage, tip clearances, and bleed temperature Variations within the engine code
affected the
predicted steady state operation as well as making spool accelerations
more
sluggish and raising compressor working lines during transient manoeuvres.
Although all three effects were significant, heat soakage appeared to have the largest
effect on transient
performance, particularly during the hot reslam manoeuvre.
Rolls-Royce PLC sponsored this EngD project laying down 5 project requirements
that enhanced heat
soakage and tip clearance methods should meet, i.e. handle both
heat
soakage and tip clearances, be physics based, run at or near to real time, meet
given accuracy targets, and be capable of being calibrated. The streams method met
the first three of these
requirements, although with further development it might be
possible to meet all five.
This thesis also contains analysis and recommendations regarding the process of
technology transfer from the Cranfield University Technology Centre in Gas Turbine
Performance to within
Rolls-Royce.
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Naylor, Philip H. "Gas turbine transient performance : heat soakage modelling." Thesis, Cranfield University, 2004. http://dspace.lib.cranfield.ac.uk/handle/1826/10698.
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The ability to accurately extract steady state performance information from transient engine test data has the potential to significantly reduce test bed time and cost, depending upon the accuracy with which engine phenomena such as heat soakage and transient tip clearance changes can be modelled within the context of a whole engine performance code. This thesis describes improvements to the GTTrans generic Whole engine performance code thermo mechanical heat soakage and tip clearance methods. This thesis describes the streams method in which a collection of definite volumes are used to represent engine component hardware and perform transient heat transfer calculations accounting for both conduction and convection to and from non-trivial engine component geometries. Transient metal and gas temperature profiles are then used to estimate transient blade tip clearances. The streams method has been incorporated into a Rolls-Royce Trent 500 engine performance code. Accounting for heat soakage, tip clearances, and bleed temperature Variations within the engine code affected the predicted steady state operation as well as making spool accelerations more sluggish and raising compressor working lines during transient manoeuvres. Although all three effects were significant, heat soakage appeared to have the largest effect on transient performance, particularly during the hot reslam manoeuvre. Rolls-Royce PLC sponsored this EngD project laying down 5 project requirements that enhanced heat soakage and tip clearance methods should meet, i.e. handle both heat soakage and tip clearances, be physics based, run at or near to real time, meet given accuracy targets, and be capable of being calibrated. The streams method met the first three of these requirements, although with further development it might be possible to meet all five. This thesis also contains analysis and recommendations regarding the process of technology transfer from the Cranfield University Technology Centre in Gas Turbine Performance to within Rolls-Royce.
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Yaacob, Zulkefli. "Modelling and simulation of transient gas flow." Thesis, University of Salford, 1996. http://usir.salford.ac.uk/26975/.
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One of the objectives of this research was to develop mathematical models for transient flow in a gas transmission system. Models were developed from the continuity and the momentum equations. Different approximations in the equations result in the formulation of two different sets of partial differential equations, and these are the hyperbolic and the parabolic models. The Partial Differential Equations were numerically solved by an implicit finite difference technique. A Four Point Scheme was use to approximate the pressures, flows and their partial derivatives. With this scheme a second order accuracy for both spatial and time variables was achieved for both hyperbolic and parabolic models. The nonlinear equation sets from the finite differences discretization process are solved by using a Newton-Raphson iterative procedure. This procedure resulted in the formation of a sparse Jacobian Matrix. This large matrix was then compacted algebraically to reduce the time of the numerical solution. Although an implicit finite difference approximation was used in simulating the models, the important of the correct choice of the magnitude of the temporal and spatial steps should not be overlooked, particularly for high frequency disturbances 'Aliasing' problems will occur if temporal or spatial steps which are too large relative to the frequency of disturbance are used. Comparisons between the response of the hyperbolic and the parabolic models with different input boundary conditions were performed. As a result, recommendations are made on how the different models should be used in simulating real pipeline systems.
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Hoshmeh, Abdullah. "Entwicklung eines frequenzabhängigen Kabelmodells unter Verwendung einer komplexen π-Ersatzanordnung". Universitätsverlag der Technischen Universität Chemnitz, 2018. https://monarch.qucosa.de/id/qucosa%3A31193.
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Kabel sind ein wichtiger Bestandteil des Elektroenergiesystems. Für die Kenntnis des Verhaltens von Kabeln sind Modelle erforderlich, die ihr Verhalten im stationären Zustand und bei transienten Vorgängen hinreichend genau abbilden können. Eine Methode zur Modellierung von Kabeln basiert auf konzentrierten Parametern. Hierbei wird das Kabel durch eine Ersatzanordnung, in der Regel durch eine Kaskade von π-Gliedern, modelliert. Das Prinzip dieser Modelle ist relativ einfach. Allerdings vernachlässigt das bisher verwendete π-Glieder-Kabelmodell die Frequenzabhängigkeit der Kabelparameter. Deshalb wird dieses Modell nur im stationären Zustand verwendet. In dieser Arbeit erfolgt die Entwicklung eines auf π-Gliedern basierenden Kabelmodells, mit dem der stationäre Zustand und die transienten Vorgänge beschrieben werden können. Dabei wird der Einfluss unterschiedlicher Faktoren auf die Resultate des neu entwickelten Kabelmodells sowohl im Frequenz- als auch im Zeitbereich ausführlich untersucht.<br>Cables are an important part of the electrical energy system. Describing the cable behavior by stationary or transients phenomena requires cable models with proper accuracy. The simulation of transients is more complicated than the calculation of currents and voltages in the nominal frequency range. The model has to represent the frequency dependency and the wave propagation behavior of cable lines. The introduced model is based on a cascaded π-section. A modal transformation technique has been used for the calculation in the time domain. The frequency-dependent elements of the related modal transformation matrices have been fitted with rational functions. The frequency dependence of cable parameters has been reproduced using a vector fitting algorithm and has been implemented into a RLC-network for each π-section. The proposed full model has been validated with measured data.
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Darabi, Ahmad. "Dynamic transient modelling of a diesel generating set." Thesis, Queen's University Belfast, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269101.
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Cheung, Joseph. "Computer modelling of transient heat flow in mines." Thesis, University of Newcastle upon Tyne, 1989. http://hdl.handle.net/10443/3594.
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The traditional method to predict air temperatures in mine roadways is based on the assumption that the ventilation air temperature remains constant over the ventilated age of the roadway. Hence, a steady-state solution prevails. As the capital investment of providing an acceptable working environment in hot and deep mines is increasing, more accurate and reliable temperature predictions in mine roadways will be needed in future mine ventilation planning. For this reason, a transient model to predict weekly air temperatures in mine roadways is developed. The transient model is presented in the form of a computer program. It is constructed from the mathematical techniques developed for calculating the transient heat flow from strata (Cheung, 1988), conveyed coal (Cheung and Rabia, 1989) and structural steel (Maneylaws, 1988), and the empirical equations developed by Browning et al (1981) for estimating the heat from machinery. Duhamel's Theorem is used in the mathematical technique for calculating the transient heat flow from strata and conveyed coal. Details of these techniques are derived. In addition, the algorithm of the computer program is presented in terms of flow charts. Climatic investigations were undertaken at British Coal Collieries; three sites at Wearmouth Colliery, Sunderland, and one site at Whitemoor Colliery, Selby. During the investigations, temperature surveys were conducted at all the sites. Using the data collected from these sites, the transient model is validated against field measurements and agreeable correlation achieved. Moreover, recommendations are made to improve the model.
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Brito, Parada Pablo Rafael. "Modelling the transient drainage of liquid in foams." Thesis, Imperial College London, 2010. http://hdl.handle.net/10044/1/6335.
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Froth flotation is the largest tonnage separation process worldwide and is used for paper deinking, water purification and, particularly, mineral separation. One of the key aspects of the performance of flotation cells is the behaviour of the liquid within the froth, as it is crucial to the purity of the product and a major influence on the overall recovery. Nonlinearities in models for liquid motion in the froth make them complex to solve and existing numerical solutions have been in two dimensions at most. In order to predict the performance of industrial flotation cell designs, a three-dimensional solution for these equations is desirable. Moreover, the understanding of the process would be enhanced if a transient model were used to predict the dynamics of foam drainage. In this work, the equations for the liquid drainage have been rearranged in order to make them analogous to a compressible version of the Navier-Stokes equations, coupled to an equation of state. A model for predicting the movement of the flowing foam has also been developed, which is able to solve for the foam velocity in two and three dimensions. This has allowed the transient behaviour of liquid in flotation foams to be modelled using Fluidity, a general purpose finite element method code that allows simulations to be carried out on unstructured adaptive meshes. This is an important feature for improving the computational cost of modelling these systems, as there are boundary layers present in the process, whose size is independent of the scale of the flotation system being modelled. These models have allowed, for the first time, to carry out numerical investigations of drainage for arbitrary flotation tank geometries in up to three dimensions, and have been verified against analytical solutions and compared to laboratory scale experiments with satisfactory agreement.
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Chen, Jenq-Renn. "Modelling of transient flow in pipeline blowdown problems." Thesis, Imperial College London, 1993. http://hdl.handle.net/10044/1/8732.
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King, Matthew James Stuart. "Experimental and modelling studies of transient slug flow." Thesis, Imperial College London, 1998. http://hdl.handle.net/10044/1/8270.
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Bonizzi, Marco. "Transient one-dimensional modelling of multiphase slug flows." Thesis, Imperial College London, 2003. http://hdl.handle.net/10044/1/8746.
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Acevedo, Salvador. "Modelling of HVDC converters for real-time transient simulators." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0034/NQ27101.pdf.
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Seddon, Caroline Michelle. "Modelling transient dynamic fluid-structure interaction in aerospace applications." Thesis, University of Salford, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492434.
Full textAbstract:
Although significant progress has been made in the study of dynamic loading of aircraft structures, several areas have been identified that require further research. In particular, attention is drawn to problems involving transient, dynamic fluid-structure interaction, where fluids play an important role, heavily influencing the response of the structure to the applied dynamic load. In this work the use of existing numerical modelling techniques for the evaluation of such problems is investigated.
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Emmerson, Stephen. "Modelling of transient dynamics of gas flow in pipes." Thesis, University of Reading, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305045.
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AVELLAR, VINICIUS PIMENTA DE. "TRANSIENT MODELLING OF INDUSTRIAL GAS TURBINE FOR POWER GENERATION." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2010. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=16332@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO<br>As turbinas a gás são equipamentos de vital importância para o setor
industrial, fornecendo trabalho e calor para diversos setores, do transporte aos
sistemas de cogeração. A crescente necessidade de geração de energia elétrica
confiável tem incentivado o projeto de turbinas a gás industriais, inclusive no
Brasil, que operam com vários combustíveis como o diesel, gás natural, álcool e
de combustíveis de baixo poder calorífico. Para melhor monitorar e controlar estes
motores, uma análise completa da previsão de funcionamento em regime
transitório é necessária. Durante o regime transitório das turbinas a gás industriais
(heavy-duty), o sistema de controle deve manter os limites de certos parâmetros,
tais como a temperatura na entrada da turbina e a velocidade de rotação do eixo,
no seu valor nominal. Além disso, o tempo de resposta necessário para o sistema
de controle atuar deve ser o mais breve possível para garantir uma operação de
qualidade, segura e confiável. A temperatura de entrada da turbina, que é um
parâmetro muito importante no desempenho de uma turbina a gás, é limitada pela
resistência mecânica do material das pás da turbina. A velocidade de rotação do
eixo deve permanecer constante, devido à ligação ao sistema elétrico, que não
pode suportar altas flutuações de freqüência. Este trabalho tem como motivação o
incremento da capacidade de simulação de um modelo computacional existente,
incorporando, para este fim, rotinas de sistemas de controle. Como resultado, o
novo modelo é capaz de simular qualquer condição de funcionamento de turbinas
a gás industriais, em regime permanente e transitório controlado. Os resultados
obtidos pelo programa computacional se mostraram fiéis ao comportamento real
da máquina. Além disso, mostraram a flexibilidade do modelo ao lidar com
diferentes condições de operação.Um programa computacional capaz de simular o
desempenho transitório controlado de turbinas a gás é de extrema relevância para
o desenvolvimento de softwares que auxiliam os operadores destes equipamentos.
Dentre estes, estão os sistemas de monitoramento e diagnóstico dos equipamentos
em questão.<br>Gas turbine engines are a vital part of today’s industry, providing both work
and heat for several industry sectors, from transportation to cogeneration systems.
The growing need for reliable electricity has encouraged the design of stationary
gas turbines, including in Brazil, which operates on multiple fuels such as diesel,
natural gas and low calorific fuels. To better monitor and control these engines, a
complete analysis for prediction of transient operation is required. During
transient operation of heavy duty gas turbines, the control system must keep the
limits of certain parameters, such as turbine inlet temperature (TIT) and the
rotational shaft speed within their design range. Moreover, the time required for
the control system to react should be as short as possible to guarantee a safe and
reliable operation. The turbine inlet temperature, which is a very important
parameter in the performance of a gas turbine, is limited by the turbine blades
material mechanical resistance. Furthermore, the rotational speed should remain
constant due to the electric grid connection, which cannot withstand high
frequency fluctuations. This work is motivated by the need to increase the ability
of a computer model to simulate the performance of industrial gas turbines,
incorporating, for this purpose, control system routines. As a result, the new
model will be able to simulate any operating condition of industrial gas turbines,
in both steady state and transient. The results obtained by the computer program
proved to be faithful to the actual behavior of the engine. Furthermore, they
showed the flexibility of the model to deal with different operating conditions. A
computer program capable of simulating the transient performance of gas turbines
is very important for the development softwares to help operators of such
equipment. In addition, it could be used in on-line intelligent diagnostic program.
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MORAES, ADELIO JOSE DE. "CONTRIBUITIONS TO THE LOAD MODELLING FOR TRANSIENT STABILITY STUDIES." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1992. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=8361@1.
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UNIVERSIDADE FEDERAL DE UBERLÂNDIA<br>Este trabalho, relacionado com a área de modelagem de
cargas para estudos de estabilidade transitória de
sistemas elétricos, tem por objetivo discutir a adequação
dos modelos clássicos normalmente utilizados, bem como o
aprimoramento e desenvolvimento de representações para
cargas com características específicas.
Inicialmente, são enfocados os aspectos das representações
clássicas de cargas e, através de desenvolvimentos
teóricos e estudos computacionais, ressaltadas as
adequações destas estratégias ao contexto atual.
Reconhecendo algumas limitações quanto às técnicas para a
obtenção dos parâmetros de motores de indução, apresenta-
se procedimentos sistematizados para o tratamento destes
componentes de carga.
Tendo em vista a busca da melhoria de modelos e respostas
aos questionamentos a respeito da relevância da inclusão
dos efeitos da variação da freqüência sobre as cargas e
parâmetros da rede, o trabalho prossegue com investigações
nesta direção.
Objetivando a análise do desempenho dos modelos
simplificados de cargas através de funções algébricas, são
discutidas as propostas atuais e verificadas suas
adequações aos estudos de estabilidade.
Finalmente, considerando a importância atual das cargas
conversoras estáticas, são desenvolvidos modelos
apropriados e realizados os estudos necessários à
incorporação de unidades retificadoras em programas de
estabilidade.<br>This work, involved with the load modeling for electrical
system transiente stability analysis, aim to discuss the
classical load models normally used, and to develop and
improve representations of specific types of loads.
Initially, aspects concerned with classical load
representations are dealt with aiming to evaluate, through
theoretical and computational analyses, the current
employment of such models. Knowing that the techiques to
obtain induction motor parameters are still deficient,
this work presents some systematic procedures for the
treatment of such loads.
Additionally, it continues seeking improvements in
electrical system component models and answers to the
questions about the need for inclusion of the frequency
variation effects on loads and network parameters.
Moreover, it takes into account the tendencies of using
simplified load models represented by algebraic
expressions. Some recent proposals in this area are
discussed and tested with a view to acess the perfomance
of the models in stability studies.
Finally, considering the present importance of static load
converters, it is developed the related models and
presented the necessary studies to include rectifier units
in stability programs.
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Price, Daniel James. "Forward modelling of transient events in the solar atmosphere." Thesis, Aberystwyth University, 2017. http://hdl.handle.net/2160/50cf4525-e93c-4c15-9c63-c5ed7daba471.
Full textAbstract:
The solar atmosphere is a highly magnetised plasma covering a wide range of temperatures from the thousands of Kelvin to the millions. How exactly it reaches such extreme temperatures remains unknown. There are however numerous events that take place, concerned with the movement of energy and plasma throughout the solar atmosphere. This thesis makes use of four instruments that have studied the Sun in the past, and in three cases continue to do so today. Observations from these instruments are combined with synthetic observations obtained from a detailed non-equilibrium ionisation hydrodynamic radiation code to understand the nature of what was observed and deduce physical information. One study presents the replication of light curves of a loop obtained by the Atmospheric Imaging Assembly (AIA). It finds that it was a cold loop heated by a pulse of energy at its footpoint consistent with the energy of a nano are. Another study replicates line proles of a structure observed by the Extreme-Ultraviolet Imaging Spectrometer (EIS) within an outflow region. We find that it is best modelled by a long loop consisting of at least 100 strands undergoing a cyclical process of heating and cooling on timescales of approximately 80 minutes. A final study replicates line profiles from the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) instrument, and uses images from the Transition Region and Coronal Explorer (TRACE) to add context to the interpretation.
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Liu, Wei. "Parallel computational strategies for modelling transient Stokes fluid flow." Thesis, Swansea University, 2006. https://cronfa.swan.ac.uk/Record/cronfa42737.
Full textAbstract:
The present work is centred on two main research areas; the development of finite element techniques for the modelling of transient Stokes flow and implementation of an effective parallel system on distributed memory platforms for solving realistic large-scale Lagrangian flow problems. The first part of the dissertation presents the space-time Galerkin / least-square finite element implicit formulation for solving incompressible or slightly compressible transient Stokes flow with moving boundaries. The formulation involves a time discontinuous Galerkin method and includes least-square terms in the variational formulation. Since the additional terms involve the residual of the Euler- Lagrangian equations evaluated over element interiors, it prevents numerical oscillation on the pressure field when equal lower order interpolation functions for velocity and pressure fields are used, without violating the Babuska-Brezzi stability condition. The space-time Galerkin / least-square formulation has been successfully extended into the finite element explicit analysis, in which the penalty based discrete element contact algorithm is adopted to simulate fiuid-structure or fluid-fluid particle contact. The second part of the dissertation focuses on the development of an effective parallel processing technique, using the natural algorithm concurrency of finite element formulations. A hybrid iterative direct parallel solver is implemented into the ELFEN/implicit commercial code. The solver is based on a non-overlapping domain decomposition and sub-structure approach. The modified Cholesky factorisation is used to eliminate the unknown variables of the internal nodes at each subdomain and the resulting interfacial equations are solved by a Krylov subspace iterative method. The parallelization of explicit fluid dynamics is based on overlapping domain decomposition and a Schwarz alternating procedure. Due to the dual nature of the overlapping domain decomposition a buffer zone between any two adjacent subdomains is introduced for handling the inter-processor communication. Both solvers are tested on a PC based interconnected network system and its performances are judged by the parallel speed-up and efficiency.
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Roberts, Ian Frank. "Modelling and experimental studies of transient stratified multiphase flows." Thesis, Imperial College London, 1996. http://hdl.handle.net/10044/1/7433.
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Bassi, Welson. "Estudo de surtos em redes secundárias de distribuição devido a descargas atmosféricas diretas na rede primária." Universidade de São Paulo, 1999. http://www.teses.usp.br/teses/disponiveis/3/3143/tde-10102017-100131/.
Full textAbstract:
Este trabalho apresenta uma análise dos surtos em redes aéreas secundárias de distribuição causados por descargas atmosféricas diretas no circuito primário. Alguns trabalhos publicados sobre o fenômeno são comentados, sendo também analisados vários outros estudos relativos à modelagem de componentes. No trabalho, os principais componentes da rede foram modelados e incluídos na representação de uma topologia típica (com as linhas primária e secundária). Assim, foram considerados: transformador de distribuição, isoladores, pára-raios, cargas (consumidores) e resistências de aterramento. Os modelos foram validados, quando possível, através de ensaios em laboratório. Algumas alternativas de proteção da rede secundária foram consideradas. Foi verificada a influência de alguns parâmetros relevantes tais como amplitude e tempo de frente da corrente da descarga, resistências de aterramento, modelos de cargas e posição da descarga. Os resultados foram obtidos por simulações computacionais realizadas através do programa ATP (Alternative Transients Program). São apresentadas formas de onda de sobretensões nos consumidores. Também são apresentados e discutidos valores de corrente e energia nos dispositivos de proteção, fornecendo informações sobre as alternativas de proteção.<br>This work presents an evaluation of surges in low-voltage overhead distribution lines caused by direct lightning strikes in medium voltage lines. Some publications concerning the phenomenon are commented and several other studies used during the process of modeling of the components are also analysed. The main components of the distribution system were modeled and included. So, a typical distribution network topology (with the primary and secondary lines) was represented including its components: distribution transformer, insulators, surge arresters, loads and ground resistances. The performance of the developed models, whenever possible, was verified by laboratory tests. Some possibilities of the secondary protection were included. Parameters having major effect on the results, such as the lightning current amplitude and front time, the values of grounding resistances, the models of the loads and the lightning strike position were taken into consideration in the study. The results were obtained by simulations performed using the ATP (Alternative Transients Program). Waveforms are presented in order to provide information on the characteristics of the overvoltages in the consumers along the line. Currents, as well as energy absorbed by the low-voltage surge arresters are aldo presented and discussed, providing useful information about the performance of some protection alternatives.
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Lima, P. C. R. "Modelling of transient gas-liquid flow and pigging in pipes." Thesis, Cranfield University, 1999. http://hdl.handle.net/1826/4176.
Full textAbstract:
More
and more transient gas-liquid operations in pipes are being successfully applied in the oil
and gas industry. Pigging in two-phase pipelines, to remove liquid accumulation or for cleaning
purposes, is an important transient operation. Another important operation is the injection of (-)-as
to transport the accumulated liquid in the pipeline to process facilities. Analysis of such transient
two-phase flow in a pipeline is necessary not only for designing the liquid and (Yas handling
facilities, but also for safe operating procedure. In pipeline-fiser system such operations cause
even more severe changes in flow conditions.
A two-fluid model has been developed to determine the transient behaviour of fluids during these
operations.T he derived one-dimensionasl et of equationsf or each flow pattern describet he flow
of fluids in all regions. Semi-implicit finite difference schemes were used to solve the initial and
boundary value problem for each phase of the process- gas/pig injection, gas shut-in, slug
production and gas flow out of the system.
An extensive experimental program has been carried out to acquire two-phase transient flow and
pigging data on a 67 m long, 0.0525 m diameter, 9.9 m high pipeline-riser system. A computer
based data acquisition system has been utilised to obtain rapidly changing and detailed information
of the flow behaviour during the transient tests. The model results compare well with the
experimental data for characteristics such as inlet pressure, hold-up and pig velocity.
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Manfletti, Chiara [Verfasser]. "Transient Behaviour Modelling of Liquid Rocket Engine Components / Chiara Manfletti." Aachen : Shaker, 2010. http://d-nb.info/1124364943/34.
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Oliver, Jacobus Coenraad. "Network modelling of transient heat exchanger performance / Jacobus C. Olivier." Thesis, North-West University, 2005. http://hdl.handle.net/10394/490.
Full textAbstract:
This study investigates the applicability of the thermal-fluid network approach to the modelling of transient
heat exchanger performance.
Two different solution algorithms, namely the Implicit Pressure Correction Method (IPCM) and the Runge
Kutta method with Trapezoidal Damping (RKTD) for the solution of the one-dimensional governing equations
in thermal-fluid network problems are presented. The advantages and disadvantages of two types of
numerical discretisation schemes used in thermal-fluid network problems are discussed and the discretised
one-dimensional governing equations for the staggered grid discretisation scheme used in the IPCM and
RKTD method is presented. The RKTD method is used as a time integration scheme for the generalised
thermal-fluid network solver Xnet. Several test cases are introduced and the basic primitive elements
available in Xnet are compared to the commercial thermal-fluid network code, Flownex (which uses the
IPCM), for both steady-state and transient conditions.
Two different network topologies are introduced for the discretisation of heat exchangers when a network
approach is followed and the thermal-fluid network solver Xnet is applied to a basic parallel and counter flow
configured pipe-in-pipe type heat exchanger to investigate the effect on the type of discretisation scheme
used. The results obtained are compared to primitive element models in Flownex as well as the composite
RX element in Flownex.
The extent to which thermal-fluid network solvers are able to predict transient heat exchanger performance
are further investigated by modelling a complex shell-and-tube heat exchanger using Xnet and comparing
the steady-state and transient results to both a primitive element model in Flownex as well as the composite
STX element in Flownex. This contributes to the validation of Flownex’s heat exchanger models by using a
different approach than Flownex.
The results showed that the explicit method used in Xnet is capable of solving large arbitrary structured
thermal-fluid networks with a high level of accuracy. The result of Flownex compares very well with that of
Xnet, which proves (verifies) that the solution algorithm is correctly implemented in both codes. Even though
the explicit thermal-fluid network code, Xnet, can accurately predict fast transients, a drawback of this
method is the large computational time required to simulate transient heat exchangers with large thermal
masses.<br>Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2005.
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Cheng, Li. "Transient modelling of a diesel engine and air-path control." Thesis, University of Sussex, 2015. http://sro.sussex.ac.uk/id/eprint/55340/.
Full textAbstract:
Due to the inherent nonlinearity of the diesel engine, real-time control of the variable geometry turbocharger (VGT) and exhaust gas recirculation (EGR) valve still remains a challenging task. A controller has to be capable of coping with the transient operating condition of the engine, the interactions between the VGT and EGR, and also the trade-off effect in this control problem. In this work, novel real-time fuzzy logic controllers (RFLC) were developed and tested. Firstly, the proposed controllers were calibrated and validated in a transient diesel engine model which was developed and validated against the Caterpillar 3126B engine test bed located at the University of Sussex. The controllers were then further tested on the engine test bed. Compared to conventional controllers, the proposed controllers can effectively reduce engine emissions as well as fuel consumption. Experimental results show that compared to the baseline engine running on the Nonroad Transient Cycle (NRTC), mean values of the exhaust gas opacity and the nitrogen oxides (NOx) emission production were reduced by 36.8% and 33%, respectively. Instant specific fuel consumption of the RFLC engine was also reduced by up to 50% compared to the baseline engine during the test. Moreover, the proposed fuzzy logic controllers can also reduce development time and cost by avoiding extensive engine mapping of inlet air pressure and flow. When on-line emission measurements were not available, on-board emission predictors were developed and tested to supply the proposed fuzzy logic controller with predictions of soot and NOx production. Alternatively, adaptive neuro fuzzy inference system (ANFIS) controllers, which can learn from fuzzy logic controllers, were developed and tested. In the end, the proposed fuzzy logic controllers were compared with PI controllers using the transient engine model.
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Ogbonna, Nneoma. "Decoupled overlapping grids for modelling transient behaviour of oil wells." Thesis, Heriot-Watt University, 2010. http://hdl.handle.net/10399/2401.
Full textAbstract:
This research presents a new method, the decoupled overlapping grids method, for the numerical modelling of transient pressure and rate properties of oil wells. The method is implemented in two stages: a global stage solved in the entire domain with a point or line source well approximation, and a local (post-process) stage solved in the near-well region with the well modelled explicitly and boundary data interpolated from the global stage results. We have carried out simulation studies in two- and three- dimensions to investigate the accuracy of the method. For homogeneous case studies in 2D, we have demonstrated the convergence rate of the maximum error in the quantities of interest of the global and local stage computations by numerical and theoretical means. We also proposed a guideline for the selection of the relative mesh sizes of the local and global simulations based on error trends. Comparison to other methods in the literature showed better performance of the decoupled overlapping grids method in all cases. We carried out further investigations for heterogeneous case studies in 2D and partially-penetrating wells in 3D which show that the error trends observed for the 2D homogeneous case deteriorate only slightly, and that a high level of accuracy is achieved. Overall the results in this thesis demonstrate the potential of the method of decoupled overlapping grids to accurately model transient wellbore properties for arbitrary well con gurations and reservoir heterogeneity, and the gain in computational e ciency achieved from the method.
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Westlund, Anders. "Measuring and Predicting Transient Diesel Engine Emissions." Licentiate thesis, KTH, Machine Design (Div.), 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-10202.
Full textAbstract:
<p> </p><p>Due to its impact on human health and the nature surrounding us, diesel engine emissions have been significantly reduced over the last two decades. This reduction has been enforced by the legislating organs around the world that gradually have made the manufacturers transform their engines to today’s complex high-tech products. One of the most challenging areas to meet the legislations is transient operation where the inertia in gas-exchange system makes transition from one load to another problematic.</p><p> </p><p>Modern engines have great potential to minimize the problems associated with transient operation. However, their complexity also imposes a great challenge regarding optimization and systematical testing of transient control strategies in an engine test bed could be both expensive and time consuming.</p><p> </p><p>The objective of this project is to facilitate optimization of transient control strategies. This should be done by identifying appropriate measurement methods for evaluation of transients and by providing models that can be used to optimize strategies off-line.</p><p> </p><p>Measurement methods for evaluation of transients have been tested in several experiments, mainly focusing on emission but also regarding e.g. EGR flow. Applicable instruments for transient emission measurements have been identified and used. However, no method to measure soot emissions cycle resolved has yet been found. Other measurements such as EGR flow and temperatures are believed to have significantly decreased accuracy during transients.</p><p> </p><p>A model for prediction of NOx emissions have been used and complemented with a new approach for soot emission predictions that has been developed in this project. The emission models have been shown to be applicable over a wide range of operating conditions with exception for highly premixed combustion. It has also been shown that models developed for steady state conditions can be used for transients operation.</p>
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Johansson, Linnéa. "Modelling and interpretation of VTEM data from Soppero, Sweden." Thesis, Luleå tekniska universitet, Geovetenskap och miljöteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-64879.
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The geological and geophysical knowledge about the northernmost part of Sweden has recently increased due to the Barents project, which includes acquisition of modern geophysical and geological information on behalf of the Swedish Geological Survey (SGU). During August 2013, a helicopter-borne versatile time domain electromagnetic (VTEM) survey was performed by Geotech Ltd, in the Soppero area northeast of Kiruna. From the VTEM measurements, a number of TEM anomalous zones have been identified and two of them are located south and southeast of the Lannavaara village. The main conductive features in the Lannavaara area can be explained by the presence of graphitic schist, which is spatially associated with a number of sulphide and iron oxide mineralisation occurrences. In this project, Maxwell thin sheet modelling and EM Flow conductivity-depth-imaging (CDI) software have been applied to selected anomalies in the Lannavaara area, for the purpose of extracting geometrical parameters of conductive features. This information has been used in order to confirm the structural framework of the area and evaluate the utility of VTEM measurements in this geological environment. In general, Maxwell thin sheet models of anomalies with small amplitudes show a better correlation with existing drill holes than models of anomalies with large amplitudes. The use of small amplitudes managed to confirm the structural model in the central part of the investigated area, which is an anticline. However, the use of different models and their distribution across the area is limited. Compared with Maxwell, CDIs from EM Flow provided a better way of confirming the general structural model in the area, although they include artefacts due to strong lateral gradients in conductivity. The Lannavaara area has also been investigated by VLF, Slingram and magnetic measurements and based on these data, multivariate analysis in SiroSOM reveals a strong correlation between VTEM and Slingram data, while VLF data appears to have much less or more complicated correlation with the other data sets. In summary, the results from the various software raise a question about the geological complexity in parts of the Lannavaara area, which may include multiple layers of graphitic schist, possibly expressed as smooth transitions in conductivity when represented by data from electromagnetic methods.
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Bassi, Welson. "Caracterização de equipamentos e instalações residenciais de baixa tensão aplicada ao estudo de transitórios de origem atmosférica." Universidade de São Paulo, 2005. http://www.teses.usp.br/teses/disponiveis/3/3143/tde-10102017-111817/.
Full textAbstract:
Este trabalho apresenta um estudo de caracterização das impedâncias de entrada, em função da frequência, de instalações residenciais de baixa tensão e diversos equipamentos eletro-eletrônicos comumente encontrados. As respostas em frequência medidas são ajustadas e modeladas por redes RLC simples, mas efetivas, que podem ser utilizadas em qualquer programa computacional para simulações de transitórios. A faixa de frequências, até 5 MHz, permite o uso desses modelos em estudos associados a transitórios atmosféricos ou causados por chaveamentos. É importante ressaltar a existência de muito poucos trabalhos nesse assunto, pois, usualmente, as instalações de baixa tensão, ou os equipamentos conectados, são representadas por simples elementos concentrados, resistores, indutores ou capacitores. Por outro lado, sabe-se que os níveis de sobretensões em um sistema, ou instalação, são fortemente dependentes das cargas conectadas e, quanto mais precisos os modelos, melhores e mais confiáveis simulações são obtidas. Este trabalho inclui simulações com o programa computacional ATP utilizando os modelos desenvolvidos para avaliação de surtos em uma rede de distribuição típica submetida a descargas atmosféricas diretas no circuito primário. Além disso, utilizando o programa Pspice, são realizadas simulações da resposta interna de uma instalação residencial, com diversos equipamentos conectados, e submetida a surtos atmosféricos em sua entrada. O trabalho concentra informações práticas e úteis sobre estudos de surtos em sistemas e instalações de baixa tensão<br>This work presents a study of impedance characteristics, over a wide range of frequencies, of residential low-voltage installations and electric-electronic appliances, commonly found in residential installations. The measured frequency responses are fitted and modeled by simple, but effective, RLC networks, that can be used in any software for transient simulations. The range of frequencies, up to 5 MHz, allows the use of these models considering lightning or switching studies. It is of importance to point the lack of publications focusing this topic, because usually the low-voltage installations, or connected equipment, are represented by simple lumped components inductances, resistances or capacitances. Otherwise, it is well known that the overvoltage level of a system, or installation, is strongly dependent on the connected loads and for more precise models, better and more reliable simulation results are obtained. This work includes ATP software simulations using the developed models for evaluation of surges in a typical distribution network subjected to direct lightning strikes at the primary circuit. Furthermore, simulations of internal response of a low-voltage installation with connected equipment and subjected to lightning surges in its entrance is performed using the Pspice software. The work summarizes practical and useful information about the low-voltage surge studies on low-voltage systems.
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Doan, Luong T. "Analytical and numerical modelling of transient convective transfers on SAGD performance." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ60286.pdf.
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Liu, Yaqing. "Transient Response of Grounding Systems Caused by Lightning: Modelling and Experiments." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4556.
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