Supercavitating vehicles are characterized by substantially reduced hydrodynamic drag with respect to fully wetted underwater vehicles. Drag is localized at the nose of the vehicle, where a cavitator generates a cavity that completely envelops the body. This causes the center of pressure to be always ahead of the center of mass, thus violating a fundamental principle of hydrodynamic stability. This unique loading configuration, the complex and non-linear nature of the interaction forces between vehicle and cavity, and the unsteady behavior of the cavity itself make the control and maneuvering of supercavitating vehicles particularly challenging. This study represents an effort towards the evaluation of optimal trajectories for this class of underwater vehicles, which often need to operate in unsteady regimes and near the boundaries of the flight envelope. Flight trajectories and maneuvering strategies for supercavitating vehicles are here obtained through the solution of an optimal control problem. Given a cost function and general constraints and bounds on states and controls, the solution of the optimal control problem yields the control time histories that maneuver the vehicle according to a desired strategy, together with the associated flight path. The optimal control problem is solved using the direct transcription method, which does not require the derivation of the equations of optimal control and leads to the solution of a discrete parameter optimization problem. Examples of maneuvers and resulting trajectories are given to demonstrate the effectiveness of the proposed methodology and the generality of the formulation.

Direct methods are an alternative for power system transient stability analysis to avoid the enormous computational efforts of conventional time-domain method. The development of direct methods in last three decades makes it an effective potential approach to both on-line security assessment and off-line analysis tools. Among the direct methods, the Boundary of stability region based Controlling Unstable equilibrium point (BCU) method is the most successful, having a sound theoretical basis and practical application in power systems. It finds the controlling UEP of the original system via a reduced-state system. This thesis investigates the development of direct methods and the related theoretical foundation. Several widely used direct methods are presented and compared. The theoretical foundation and computational issues of BCU methods are discussed. Incorporation of more realistic power system models can be incorporated in BCU methods is introduced. Based on BCU method, some small system cases are tested for a given fault. / text

Philosophiae Doctor - PhD / Numerical simulations play a crucial role in testing current cosmological models of the formation and evolution of the cosmic structure observed in the modern Universe. Simulations of the collapse of both baryonic and non-baryonic matter under the influence of gravity have yielded important results in our understanding of the large scale structure of the Universe. In addition to the underlying large scale structure, simulations which include gas dynamics can give us valuable insight into, and allow us to make testable predictions on, the nature and distribution of baryonic matter on a wide range of scales. In this work we give an overview of cosmological simulations and the methods employed in the solution of many body problems. We then present three projects focusing on scales ranging from individual galaxies to the cosmic web connecting clusters of galaxies thereby demonstrating the potential and diversity of numerical simulations in the fields of cosmology and astrophysics. We firstly investigate the environmental dependance of neutral hydrogen in the intergalactic medium by utilising high resolution cosmological hydrodynamic simulations in Chapter 3. We find that the extent of the neutral hydrogen radial profile is dependant on both the environment of the galaxy and its classification within the group ie. whether it is a central or satellite galaxy. We investigate whether this effect could arise from ram pressure forces exerted on the galaxies and find good agreement between galaxies experiencing high ram pressure forces and those with a low neutral hydrogen content. In Chapter 4 we investigate the velocity–shape alignment of clusters in a dark matter only simulation and the effect of such an alignment on measurements of the kinetic Sunyaev–Zeldovich (kSZ) effect. We find an alignment not only exists but can lead to an enhancement in the kSZ signal of up to 60% when the cluster is orientated along the line-of-sight. Finally we attempt to identify shocked gas in clusters and filaments using intermediate resolution cosmological hydrodynamic simulations in Chapter 5 with a view to predicting the synchrotron emission from these areas, something that may be detectable with the Square Kilometer Array.

This research investigates the application of the AISC Direct Analysis Method for stability bracing design of columns, beams, beam-columns and frames. Emphasis is placed on out-of-plane flange bracing design in metal building frame systems. Potential improvements and extensions to the 2005 AISC Appendix 6 stability bracing provisions are studied and evaluated. The structural attributes considered include various general conditions encountered in practical metal building design: unequal brace spacing, unequal brace stiffness, nonprismatic member geometry, variable axial load or bending moment along the member length, cross-section double or single symmetry, combined bending and axial load, combined torsional and lateral bracing from girts/purlins with or without diagonal braces from these components to the inside flanges, load height, cross-section distortion, and non-rigid end boundary conditions. The research addresses both the simplification to basic bracing design rules as well as direct computation for more complex cases. The primary goal is improved assessment of the demands on flange bracing systems in metal building frames.

Along with the increasing scale of the power system and stressed operation in the transmission network, the stability margin is reduced considerably. As a traditional solution, the constructions of new transmission lines and generators sometimes are constrained by local environmental and regulatory constraints. Another characteristic of a modern network is the higher number of transmission inter-connections which appear in the large-scale power system. As an economic benefit, inter-connection can reduce the cost of electricity and enhance system reliability [1]. Those inter-connected tie lines are operated normally under heavy flow to maximize the usage benefit. This characteristic contributes to the complexity of operating and controlling the system. In recent years, along with the development of power electronic devices, the Flexible AC Transmission Systems (FACTS) has been used in the system as an alternative solution. It can maximize the usage benefit of the HV transmission line and make the large-scale power system more controllable. By using FACTS devices, the system can survive serious system contingencies with real-time control action, instead of providing a large steady state stability margin. Therefore, the system transfer capacity can be significantly increased. Electromechanical oscillations are observed in today's power system; such oscillations are recognized as a major concern in power system operation. Once begun, the oscillations may continue for a while before being halted by the damping torque from the system, or they may continue to grow (inadequate damping) and eventually cause system instability by losing synchronicity. The traditional and widely applied solution for oscillation damping is the Power System Stabilizer (PSS), which is efficient in damping local mode oscillation and inter-area oscillation in certain conditions. In recent years, research and development of the application of FACTS devices in suppressing system oscillations, especially for inter-area mode oscillation damping, has attracted increasing interest [1]. The primary objective of this thesis is to design robust FACTS controllers for enhancing power system dynamic stability by damping low frequency electromechanical oscillations. Recently, various nonlinear control techniques have been applied in power system control. The performance of nonlinear controllers is influenced by the parameter uncertainty and external disturbance. This thesis will present a novel approach of a robust Variable Structure Control (VSC)-based FACTS controller for damping multi-mode oscillations. Robust performances of the proposed controllers in different power systems are demonstrated by computer simulation.

As cold-formed steel decks are used in virtually every steel-framed structure for composite slab systems, efforts to develop more efficient composite floor systems continues. Efficient composite floor systems can be obtained by optimally utilizing the materials, which includes the possibility of developing long span composite slab systems. For this purpose, new deck profiles that can have a longer span and better interaction with the concrete slab are investigated. Two new mechanical based methods for predicting composite slab strength and behavior are introduced. They are referred to as the iterative and direct methods. These methods, which accurately account for the contribution of parameters affecting the composite action, are used to predict the strength and behavior of composite slabs. Application of the methods in the analytical and experimental study of strength and behavior of composite slabs in general reveals that more accurate predictions are obtained by these methods compared to those of a modified version of the Steel Deck Institute method (SDI-M). A nonlinear finite element model is also developed to provide additional reference. These methods, which are supported by elemental tests of shear bond and end anchorages, offer an alternative solution to performing a large number of full-scale tests as required for the traditional m-k method. Results from 27 composite slab tests are compared with the analytical methods. Four long span composite slab specimens of 20 ft span length, using two different types of deck profiles, were built and tested experimentally. Without significantly increasing the slab depth and weight compared to those of composite slabs with typical span, it was found that these long span slabs showed good performance under the load tests. Some problems with the vibration behavior were encountered, which are thought to be due to the relatively thin layer of concrete cover above the deck rib. Further study on the use of deeper concrete cover to improve the vibrational behavior is suggested. Finally, resistance factors based on the AISI-LRFD approach were established. The resistance factors for flexural design of composite slab systems were found to be f=0.90 for the SDI-M method and f=0.85 for the direct method. / Ph. D.

No description available.

This project presents an attempt to construct a setup and implement a reliable technique for measuring the magnetocaloric effect (MCE) on various materials via a direct method for the acquisition of the data. The main objective of the latter is to produce a ∆Tadiabatic vs T graph over a reasonable temperature span (-100◦C up to 220◦C) by thermal monitoring of a magnetic material exposed to an oscillating magnetic field with a maximum strength of 1.2T. The setup consists of a vacuum-insulated glass tube containing the sample placed between two electromagnets of a vibrating-sample magnetometer (VSM) and increasingly heated by a resistance wire, while the temperature is recorded directly by a thermocouple. The first experiments are performed on Gadolinium (Gd) samples as a reference material in order to verify the overall reliability of the system. The obtained results on Gadolinium show that meaningful data can be acquired with this direct method, although the initially-extracted ∆Tadiabatic near room temperature stands at the accuracy limit (25%) generally accepted with this method. Unexpected interference signals from the thermocouple are encountered for high temperatures and are shown to be due to magnetic dependence from one of its constituents. Data from high temperatures can however be reliably corrected with respect to a baseline signal from a neutral nonmagnetic material. As such magnetocaloric properties of two Manganese-rich high entropy alloys are investigated with one exhibiting at most ∆Tadiabatic = 0.2◦C at its Curie temperature TC = 60◦C. Suggestions regarding the possibility of operating the setup at sub-zero temperatures are put forward and promising results from a new spot- welded thermocouple show a significantenhancement of the initial setup accuracy. / Detta projekt presenterar ett försök att konstruera en installation och implementera en pålitlig teknik för att mäta den magnetokolorisk effekten (MCE) på olika material via en direkt metod för insamling av data. Det sistnämnda syftet är att producera en ∆Tadiabatisk vs T över ett rimligt temperaturintervall (-100◦C up to 220◦C). Detta genom en termisk övervakning av ett magnetiskt material utsatt för ett oscillerande magnetfält med en maximal magnitud på 1.2 T. Utrustningen utgörs av ett vakuumisolerade glasrör som innehåller provet, vilket är placerat mellan två elektromagneter från en vibrating-sample magnetometer (VSM) och som stegvis värms upp av en resistanstråd, medan temperaturen registreras direkt av ett termoelement. De inledande experimenten utförs på prover av Gadolinium (Gd) som referensmaterial för att verifiera systemets totala tillförlitlighet. De erhållna resultaten från Gadolinium proverna visar att meningsfulla data kan produceras med denna direkta metod. Även om de extraherade ∆Tadiabatisk vid rumstemperatur befinner sig inom precisions gränsen (25%), vilken är allmänt accepterad med avseende på den direkta metoden. Oväntade missvisande signaler från termoelementet uppträder vid höga temperaturer och visar sig bero på magnetiskt beroende från instumentet. Data från höga temperaturer kan emellertid pålitligt korrigeras med en baslinjesignal från ett neutralt icke-magnetiskt material. Därmed undersöks de magnetokoloriska egenskaper hos två Mangan-rika hög entropi legeringar, där en uppvisar som högst ∆Tadiabatisk = 0.2◦C vid dess Curie-temperatur TC = 60◦C. Förslag beträffande möjligheten att använda installationen vid temperaturer under noll läggs fram. Lovande resultat från ett nytt punktsvetsat termoelement visar en betydande förbättringav den inledande installationens noggrannhet.

Foram medidos, através do chamado Método Direto, as seções de choque de interação (sigmaBARRA) e os raios reduzidos de interação (r IND.o) de isótopos deficientes em nêutrons do ANTIND 31 Ga, ANTIND 32 Ge, ANTIND 33 As, ANTIND 34 Se e ANTIND 35 Br; com massa A DA ORDEM DE 60 - 80. O feixe radioativo, incidente em um detetor alvo de Si, foi produzido plea fragmentação de um feixe de ANTPOT 78 Kr, com energia de 73 MeV/núcleon, num alvo de ANTPOT nat Ni, no Laboratório GANIL, França. Verificou-se um suave decréscimo dos valores de r IND.o com o aumento do número de nêutrons N para praticamente todas as cadeias isotópicas, exceto para a do ANTIND 35 Br. Estes resultados não mostraram correlação com deformações, observadas em alguns núcleos desta região. Cálculos teóricos para os raios destes núcleos utilizando-se o modelo de Glauber, baseado em densidades de matéria nuclear obtidas a partir da teoria de Campo Médio Relativístico, apresentaram uma boa concordância com os valores medidos, sem contudo conseguirem reproduzir a tendência decrescente com N experimentalmente observada. São apresentados, também, os resultados de tentativas feitas para viabilizar o estudo de núcleos exóticos no Laboratório Pelletron do IFUSP. Desenvolveu-se o Método Direto para funcionar nas energias disponíveis neste laboratório, e também determinaram-se as providências necessárias para a produção e separação de núcleos radioativos nas condições ali reinantes. / The interaction cross section sigmaBARRAIND.R and the reduced interaction radii r IND.0 of neutron-deficient, radioactive ANTIND.31 Ga, ANTIND.32 Ge, ANTIND.33 As, ANTIND.34 Se and ANTIND.35 Br isotopes with A DA ORDEM DE 60 80 were measured. The secondary radioactive beam, hitting a Si target/detector system, was produced by the fragmentation of ANTPOT.78 Kr, with 73 MeV/nucleon energy on a ANTPOT.nat Ni target, at the GANIL Laboratory in France. Most elements show reduced radii which decrease slowly with N, with the exception of ANTIND.35 Br. No clear correlations is found between deformation and r IND.0, as observed for charge radii of Kr and Sr. theoretical values of r IND.0 were calculated from Glauber reaction cross-section, based on proton and neutron densities calculated in the Relativistic Mean Field framework. The agreement between theoretical r IND.0 and the data is reasonable, however the decreasing tendency with N is not reproduced. We also present our efforts to produce radioactive beams at Pelletron Laboratory of IFUSP. The Direct Method was implemented at the energies available at Pelletron Laboratory and the problem of the conditions to produce and separate radioactive beams was also addressed.

A Identificação de Sistemas é uma tarefa significativa em termos de tempo e custo no trabalho de implementação de sistemas de controle que usam Controle Preditivo baseado em Modelos (MPC). Após a implementação, o controlador tende a permanecer com o mesmo modelo por muito tempo, ignorando mudanças que tenham ocorrido com o processo, perdendo qualidade e podendo até ser abandonado. Este trabalho propõe uma metodologia simples e eficaz para se proceder à reidentificação de uma planta industrial que use MPC mantendo o processo em malha fechada. Os principais aspectos deste problema são discutidos, e as escolhas que foram feitas para a realização dos experimentos e obtenção dos modelos são explicadas. Apresenta-se um caso em Matlab sobre um sistema 2x2 cobrindo diferentes situações, e é feita uma comparação de identificação realizada através de sinais PRBS e de testes com degraus, sempre em malha fechada. Aplica-se a metodologia a um controlador industrial, e os modelos identificados são introduzidos no controlador. O princípio básico desta metodologia consiste em efetuar perturbações multivariáveis nos set-points ou restrições ativas das controladas e determinar o modelo através da estrutura ARX. Entre as vantagens da metodologia proposta, estão a facilidade de automatizar a identificação do processo e a garantia de manter o processo sob controle durante os testes. / System identification is a major task in the process of implementing Model-based Predictive Control (MPC) algorithms in industrial applications. Once the controller is working, there is a tendency to leave it with the original model for a long time, neglecting changes to the process during this time, leading to performance degradation. This work proposes a simple and effective methodology to re-identify plants under MPC in closed loop. The main issues concerning this problem are discussed, and choices for experiments are made. A Matlab case involving a 2x2 problem is presented, covering a range of different situations, and a comparison between identification using PRBS reference signals and standard step tests is shown. An industrial case is studied, applying the proposed method to a real situation, re-identifying an existing MPC model and reconfiguring it afterwards. This methodology is based on the application of multivariable perturbations on the controlled variables set-points or active restrictions, obtaining an ARX model structure. It uses an automatic process identification proceeding, keeping the process under control along the tests.