DISSERTATION - Abstract in English Three Essays on Electricity Markets Author: PhDr. Petra Luňáčková Academic Year: 2017/2018 This thesis consists of three papers that share the main theme - energy. The articles introduce characteristics and behavior of electricity focusing on its unique properties. The dissertation aims at the Czech electricity market and analyzes also highly discussed solar power plants. The first article studies long term memory properties of electricity spot prices through the detrended fluctuation analysis, as electricity prices are dominated by cycles. We conclude that Czech electricity prices are strongly mean reverting yet non-stationary. The second part of the dissertation investigates possible asymmetry in the gas - oil prices adjustment. Oil prices determine the price of electricity during the times of peak demand, as the reaction of power plants fueled by oil is quick but marginal costs are high. We chose the gasoline - crude oil relationship known as "rockets and feathers" effect and offer two new tests to analyze such type of relationship as we believe that error correction model is not the most suitable tool. Analyzing international dataset we do not find statistically significant asymmetry. The third study assesses the impact of renewable energy sources, solar plants in...

In tracing the history of the TIROS meteorological satellite system, this dissertation details the convergence of two communities: the DOD space scientists who established US capability to launch and operate these remote sensing systems and the US Weather Bureau meteorologists who would be the managers and users of satellite data. Between 1946 and 1964, these persons participated in successive coalitions. These coalitions were necessary in part because satellite systems were too big—geographically, fiscally, and technically—to be developed and operated within a single institution. Thus, TIROS technologies and people trace their roots to several research centers—institutions that the USWB and later NASA attempted to coordinate for US R&D. The gradual transfer of persons and hardware from the armed services to the non-military NASA sheds light on the US’s evolution as a Cold War global power, shaped from the “top-down” (by the executive and legislative branches) as well as the “bottom-up” (by military and non-military scientific communities). Through these successive coalitions, actor terms centered on “basic science” or the circulation of atmospheric data were used to help define bureaucratic places (the Upper Atmospheric Rocket Research Panel, International Geophysical Year, NASA, and the World Weather Watch) in which basic research would be supported by sustained and collaboration could take place with international partners.

The recent interests in the necessity of high maneuverability and vertical launching triggered namely the unconventional control design techniques that are effective at high angle of attack flight regimes. For most of missile configurations, this interest required thrust vector control together with conventional aerodynamic control. In this study, nonlinear modeling and dynamical analysis of a surface to air missile with both aerodynamic and thrust vector control is investigated. Aerodynamic force and moment modeling of the presented missile includes the challenging high angle of attack aerodynamics behavior and the so called hybrid control, which utilizes both tail fins and jet vanes as control surfaces. Thrust vector and aerodynamic control effectiveness is examined during flight envelope. Different autopilot designs are accomplished with hybrid control. Midcourse and terminal guidance algorithms are implemented and performed on target sets including maneuverable targets. A different initial turnover strategy is suggested and compared with standard skid-to-turn maneuver. Comparisons of initial roll with aerodynamic and thrust vector control are examined. Afterwards, some critical maneuvers and hybrid control ratio is studied with a real coded genetic algorithm. Rapid turnover for low altitude targets, intercept maneuver analysis with hybrid control ratio and lastly, engagement initiation maneuver optimization is fulfilled.

DYNAMIC MODELING, GUIDANCE, AND CONTROL OF HOMING MISSILES &Ouml / ZKAN, B&uuml / lent Ph. D., Department of Mechanical Engineering Supervisor: Prof. Dr. M. Kemal &Ouml / ZG&Ouml / REN Co-Supervisor: Dr. G&ouml / kmen MAHMUTYAZICIOgLU September 2005, 236 pages In this study, the dynamic modeling, guidance, and control of a missile with two relatively rotating parts are dealt with. The two parts of the missile are connected to each other by means of a roller bearing. In the first part of the study, the governing differential equations of motion of the mentioned missile are derived. Then, regarding the relative rotation between the bodies, the aerodynamic model of the missile is constructed by means of the Missile Datcom software available in T&Uuml / BiTAK-SAGE. After obtaining the required aerodynamic stability derivatives using the generated aerodynamic data, the necessary transfer functions are determined based on the equations of motion of the missile. Next, the guidance laws that are considered in this study are formulated. Here, the Linear Homing Guidance and the Parabolic Homing Guidance laws are introduced as alternatives to the Proportional Navigation Guidance law. On this occasion, the spatial derivation of the Proportional Navigation Guidance law is also done. Afterwards, the roll, pitch and yaw autopilots are designed using the determined transfer functions. As the roll autopilot is constructed to regulate the roll angle of the front body of the missile which is the controlled part, the pitch and yaw autopilots are designed to realize the command signals generated by the guidance laws. The guidance commands are in the form of either the lateral acceleration components or the flight path angles of the missile. Then, the target kinematics is modeled for a typical surface target. As a complementary part of the work, the design of a target state estimator is made as a first order fading memory filter. Finally, the entire guidance and control system is built by integrating all the models mentioned above. Using the entire system model, the computer simulations are carried out using the Matlab-Simulink software and the proposed guidance laws are compared with the Proportional Navigation Guidance law. The comparison is repeated for a selected single-body missile as well. Consequently, the simulation results are discussed and the study is evaluated.

The work presented here pertains to investigations on gas-on-liquid type of impinging injectors with a generic approach with prospective applications in several areas, and at places with particular emphasis on cryogenic or semi-cryogenic liquid propellant rockets. In such rockets, one of the components arrives at the injector in a gaseous phase after passing through the regenerative coolant passages or a preceding combustion stage. Most often, the injectors in such systems are of shear coaxial type. The shear coaxial injectors suffer from several disadvantages like complexity in design, manufacture and quality control. Adoption of impinging jet configuration can alleviate these problems in addition to providing further benefits in terms of cost, robustness in high temperature environment and manifolding. However, there is very little literature on gas-on-liquid injectors either in this context or in any other Even for the simplest form of impinging injectors such as like-on-like doublets, literature provides no conclusive direction at describing a spray from the theoretical models of physical mechanisms. Empirical approach is still the prime mode of obtaining a proper understanding of the phenomena. Steady state spray characterization includes mainly of describing the spatial distribution of liquid mass and drop size distribution as a function of geometric and injection parameters. The parameters that are likely to have an impact on spray characteristics are orifice diameter, ratio of orifice length to diameter, pre-impingement length of individual jets, inter orifice distance, impingement angle, jet velocity and condition of the jet just before impingement. The gas-on- liquid configuration is likely to experience some qualitative changes because of the expansion of the gas jet. The degree to which each one of the above variables influences the drop size and mass distribution having implication to combustion performance forms the core theme of the thesis. A dedicated experimental facility has been built, calibrated and deployed exhaustively. While spray drop size measurement is done largely by a laser diffraction instrument, some of the cases warranted an image processing technique. Two different image processing algorithms are developed in-house for this purpose. The granulometric image processing method developed earlier in the group for cryogenic sprays is modified and its applicability to gas-on-liquid impinging sprays are verified. Another technique based on the Hough transform which is feature extraction technique for extracting quantitative information has also been developed and used for gas-on-liquid impinging injectors. A comparative study of conventional liquid-on-liquid doublet with gas-on-liquid impinging injectors are first made to establish the importance of studying gas-on-liquid impinging injectors. The study identifies the similarities and differences between the two types and highlights the features that make such injectors attractive as replacements to coaxial configuration. Spray structure, drop-size mass distributions are quantified for the purpose of comparison. This is followed by a parametric study of the gas-on-liquid impinging injectors carried out using identified control variables. Though momentum ratio appeared to be a suitable parameter to describe the spray at any given impingement angle, the variations due to impingement angle had to be factored in. It was found that normal gas momentum to liquid mass is an apt parameter to generalize the spray characteristics. It was also found that using identical nozzles for desired mass ratio could lead to rather large deflection of the spray which may not be acceptable in combustion chamber design. One way of overcoming this is to work with unequal orifice sizes for gas and liquid. It was found that using smaller gas orifice for a given liquid orifice resulted in lower SMD (Sauter Mean Diameter of the spray) for constant gas and liquid mass flow rates. This is attributable to the high dynamic pressure of gas in the case of smaller gas orifices for the same mass flow rate. The impinging liquid jets with unequal momentum in the doublet configuration would result in non-uniform mass and mixture ratio distribution within the combustion chamber which may have to operate under varying conditions of mass flow rates and/or mixture ratio. The symmetrical arrangement of triplet configuration can eliminate this problem at the same time generating finely atomized spray and a homogeneous mixture ratio. In view of the scanty literature available in this field, the atomization characteristics of the spray generated by liquid centered triplet jets are examined in detail. It was found that as in the case of gas-on-liquid impinging doublets, normal gas momentum to liquid mass is an ideal parameter in describing the spray. Variants of this configuration are studied recently for many other applications too. As done in the case of doublets, efforts have also been made to compare gas centered triplet to liquid-liquid triplet. It was found that the trend of SMD of gas centered triplet is different from that of liquid-liquid triplets, thus pointing to a different mechanism in play. The SMD in the case of liquid-liquid triplets decreases monotonically with increasing specific normal momentum. It is to be noted that specific normal momentum is an ideal parameter for describing the spray characteristics of liquid-liquid triplets and doublets. In the case of gas centered triplet the SMD first increases and then decreases with specific normal momentum, the inversion point depends on the gas mass flow rate for a constant specific normal momentum. The thesis concludes with a summary of the major observations of spray structures for all the above injector configurations and quantifies the parametric dependencies that would be of use to engineering design

Made available in DSpace on 2016-04-28T20:38:43Z (GMT). No. of bitstreams: 1 Fabiane Morais Borges.pdf: 3503545 bytes, checksum: 7297b721aeaa0cb975f5cbd2df5be8ad (MD5) Previous issue date: 2013-06-14 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This thesis has arisen from the complex Internet networks intending to build up new Space paradigms based on practices of free software and hardware and open source systems, as they appeared, roughly, since the turn of the century. In order to examine these new paradigms, I consider prior processes connected to the Space Culture. The text goes back to the history of the Space Race; the first rockets, the first satellites, some tenets of the international politics that guided the cold war in the years after the Second World War. I bring up interesting elements of the Space programs both of the US and the USSR, as well as the main technicians and scientists behind the engineering of the rockets. The research dives in the rockets of Nazi Germany who first invested in the production of rockets, goes to communist Russia as well as to liberal post-war America. The thesis brings up ideas concerning Space utopias, science fiction in literature and cinema and engages with the difference between Space exploration taken up by humans and by robots. It examines the first rocket flights and the first artificial satellites placed in outer Space, paying attention to the particulars of each of those first endeavors, to their purpose and to how much they accomplished their mission. The thesis is therefore ready to question the importance of the Space Race to human imagination and to analyse the realm of Space dreams from the late 19th century up to now. The last part of the thesis is concerned with the groups that are building Space travels in an independent way, moved either by ideological or by commercial reasons. The investigation uncovers the ideas of each of those groups concerning Space exploration. It then goes on to think the relation between the makers of such exploration and a possible industrial revolution. Finally, the thesis raises some criticisms to the creative processes of individuals, groups, networks and social movements that are concerned with the outer Space / Essa tese surge a partir das complexas redes de internet voltadas à construção de novos paradigmas espaciais, baseadas em práticas de software e hardware livre e sistemas open source que surgiram, a grosso modo, a partir dos anos 2000. Mas para chegar nesse ponto foi preciso investigar processos anteriores em relação à Cultura Espacial. O texto retoma a história da Corrida Espacial, os primeiros foguetes, os primeiros satélites, a política que estava em voga durante os anos da Guerra Fria pós II Guerra Mundial. Ela tenta levantar os pontos de tensão dos programas espaciais da União Soviética e dos Estados Unidos, assim como dos principais técnicos que estavam por traz de toda a engenharia de foguetes. Vai mergulhar na Alemanha Nazista que foi a primeira a investir irrestritamente na produção de foguetes, passeia pela Russia comunista e o liberalismo americano. A tese traz à tona ideias sobre utopias espaciais, ficção científica na literatura e no cinema, e analisa a diferença entre exploração espacial humana e robótica. Traz tabelas dos primeiros vôos espaciais e os primeiros satélites levados ao Espaço, atentando para as particularidades de cada um deles, para que serviam e que fim levaram. Levanta questionamentos sobre a importância da Corrida Espacial para a imaginação humana e analisa o arco dos sonhos espaciais desde o final do século XIX até os dias atuais. O final da tese é dedicada aos grupos que estão retomando a questão das viagens espaciais de forma independente, sejam grupos ideológicos ou mais empresariais e as ideias de cada um a respeito da exploração espacial. Pensa a relação dos makers com uma possível revolução industrial e levanta algumas críticas aos processos criativos de indivíduos, grupos, redes e movimentos sociais que se dedicam ao espaço

The present research is an experimental and numerical study of aeroacoustic phenomena occurring in large solid rocket motors (SRM) as the Ariane 5 boosters. The emphasis is given to aeroacoustic instabilities that may lead to pressure and thrust oscillations which reduce the rocket motor performance and could damage the payload. The study is carried out within the framework of a CNES (Centre National d'Etudes Spatiales) research program. <p><p>Large SRM are composed of a submerged nozzle and segmented propellant grains separated by inhibitors. During propellant combustion, a cavity appears around the nozzle. Vortical flow structures may be formed from the inhibitor (Obstacle Vortex Shedding OVS) or from natural instability of the radial flow resulting from the propellant combustion (Surface Vortex Shedding SVS). Such hydrodynamic manifestations drive pressure oscillations in the confined flow established in the motor. When the vortex shedding frequency synchronizes acoustic modes of the motor chamber, resonance may occur and sound pressure can be amplified by vortex nozzle interaction.<p><p>Original analytical models, in particular based on vortex sound theory, point out the parameters controlling the flow-acoustic coupling and the effect of the nozzle design on sound production. They allow the appropriate definition of experimental tests.<p><p>The experiments are conducted on axisymmetric cold flow models respecting the Mach number similarity with the Ariane 5 SRM. The test section includes only one inhibitor and a submerged nozzle. The flow is either created by an axial air injection at the forward end or by a radial injection uniformly distributed along chamber porous walls. The internal Mach number can be varied continuously by means of a movable needle placed in the nozzle throat. Acoustic pressure measurements are taken by means of PCB piezoelectric transducers. A particle image velocimetry technique (PIV) is used to analyse the effect of the acoustic resonance on the mean flow field and vortex properties. An active control loop is exploited to obtain resonant and non resonant conditions for the same operating point.<p><p>Finally, numerical simulations are performed using a time dependent Navier Stokes solver. The analysis of the unsteady simulations provides pressure spectra, sequence of vorticity fields and average flow field. Comparison to experimental data is conducted.<p><p>The OVS and SVS instabilities are identified. The inhibitor parameters, the chamber Mach number and length, and the nozzle geometry are varied to analyse their effect on the flow acoustic coupling.<p><p>The conclusions state that flow acoustic coupling is mainly observed for nozzles including cavity. The nozzle geometry has an effect on the pressure oscillations through a coupling between the acoustic fluctuations induced by the cavity volume and the vortices travelling in front of the cavity entrance. When resonance occurs, the sound pressure level increases linearly with the chamber Mach number, the frequency and the cavity volume. In absence of cavity, the pressure fluctuations are damped.<p><p> / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished

The present research project is carried out at the von Karman Institute for Fluid Dynamics (Rhode-Saint-Genèse, Belgium) with the financial support of the European Space Agency.<p><p>The first stage of spacecrafts (e.g. Ariane 5, Vega, Shuttle) generally consists of large solid propellant rocket motors (SRM), which often consist of segmented structure and incorporate a submerged nozzle. During the combustion, the regression of the solid propellant surrounding the nozzle integration part leads to the formation of a cavity around the nozzle lip. The propellant combustion generates liquefied alumina droplets coming from chemical reaction of the aluminum composing the propellant grain. The alumina droplets being carried away by the hot burnt gases are flowing towards the nozzle. Meanwhile the droplets may interact with the internal flow. As a consequence, some of the droplets are entrapped in the cavity forming an alumina puddle (slag) instead of being exhausted through the throat. This slag reduces the performances.<p><p>The aim of the present study is to characterize the slag accumulation process in a simplified model of the MPS P230 motor using primarily optical experimental techniques. Therefore, a 2D-like cold-gas model is designed, which represents the main geometrical features of the real motor (presence of an inhibitor, nozzle and cavity) and allows to approximate non-dimensional parameters of the internal two-phase flow (e.g. Stokes number, volume fraction). The model is attached to a wind-tunnel that provides quasi-axial flow (air) injection. A water spray device in the stagnation chamber realizes the models of the alumina droplets, which are accumulating in the aft-end cavity of the motor.<p><p>To be able to carry out experimental investigation, at first the the VKI Level Detection and Recording(LeDaR) and Particle Image Velocimetry (PIV) measurement techniques had to be adapted to the two-phase flow condition of the facility.<p><p>A parametric liquid accumulation assessment is performed experimentally using the LeDaR technique to identify the influence of various parameters on the liquid deposition rate. The obstacle tip to nozzle tip distance (OT2NT) is identified to be the most relevant, which indicates how much a droplet passing just at the inhibitor tip should deviate transversally to leave through the nozzle and not to be entrapped in the cavity.<p><p>As LeDaR gives no indication of the driving mechanisms, the flow field is analysed experimentally, which is supported by numerical simulations to understand the main driving forces of the accumulation process. A single-phase PIV measurement campaign provides detailed information about the statistical and instantaneous flow structures. The flow quantities are successfully compared to an equivalent 3D unsteady LES numerical model.<p><p>Two-phase flow CFD simulations suggest the importance of the droplet diameter on the accumulation rate. This observation is confirmed by two-phase flow PIV experiments as well. Accordingly, the droplet entrapment process is described by two mechanisms. The smaller droplets (representing a short characteristic time) appear to follow closely the air-phase. Thus, they may mix with the air-phase of the recirculation region downstream the inhibitor and can be carried into the cavity. On the other hand, the large droplets (representing a long characteristic time) are not able to follow the air-phase motion. Consequently, a large mean velocity difference is found between the droplets and the air-phase using the two-phase flow measurement data. Therefore, due to the inertia of the large droplets, they may fall into the cavity in function of the OT2NT and their velocity vector at the level of the inhibitor tip.<p><p>Finally, a third mechanism, dripping is identified as a contributor to the accumulation process. In the current quasi axial 2D-like set-up large drops are dripping from the inhibitor. In this configuration they are the main source of the accumulation process. Therefore, additional numerical simulations are performed to estimate the importance of dripping in more realistic configurations. The preliminary results suggest that dripping is not the main mechanism in the real slag accumulation process. However, it may still lead to a considerable contribution to the final amount of slag.<p> / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Includes Van Allen thesis (M.S.)--University of Iowa, 1936, and thesis (Ph.D.)--University of Iowa, 1939.