A tomographic view of the Gulf Stream southern recirculation gyre at 38°N, 55°W

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 1993Reciprocal acoustic transmissions made in a region just south of the Gulf Stream are analyzed to determine the structure and variability of temperature, current velocity, and vorticity fields at the northern extent of the southern recirculation gyre. For ten months (November, 1988 through August, 1989), a pentagonal array of tomographic transceivers was situated in a region centered at 38°N, 55°W as part of the eastern array of the SYNOP (SYNoptic Ocean Prediction) Experiment. The region of focus is one rich in mesoscale energy, with the influence of local Gulf Stream meandering and cold-core ring activity strikingly evident. Daily-averaged acoustic transmissions yielded travel times which were inverted to obtain estimates of range-averaged temperature and current velocity fields, and area-averaged relative vorticity fields. The acoustically determined estimates are consistent with nearby current meter measurements and satellite infrared imagery. The signature of cold-core rings is clearly evident in the sections. Spectral estimates of the fields are dominated by motions with periodicities ranging from 32-128 days. Second-order statistics, such as eddy kinetic energies, and heat and momentum fluxes, are also estimated. The integrating nature of the tomographic measurement has been exploited to shed some light on the radiation of eddy energy from the Gulf Stream. The Eliassen-Palm flux diagnostic has been applied to an investigation of wave radiation from the Gulf Stream. Results of the diagnosis suggest that the Gulf Stream itself is the source of wave energy radiating into the far field and found in the interior of the North Atlantic subtropical gyre.This research was carried out under Office of Naval Research (ONR) University Research Initiative contract N00014-86-K-0751 and ONR contract N00014- 90-J-1481. Construction of the tomographic instruments was supported by grants and contracts with MIT: National Science Foundation grant OCE 85-12430 and by ONR. The field work was supported by ONR under contract N00014-85-G-0241 (Secretary of the Navy Professorship (C. Wunsch))

Spatiotemporal analysis of the runaway distribution function from synchrotron images in an ASDEX Upgrade disruption

Synchrotron radiation images from runaway electrons (REs) in an ASDEX Upgrade discharge disrupted by argon injection are analysed using the synchrotron diagnostic tool Soft and coupled fluid-kinetic simulations. We show that the evolution of the runaway distribution is well described by an initial hot-tail seed population, which is accelerated to energies between 25-50 MeV during the current quench, together with an avalanche runaway tail which has an exponentially decreasing energy spectrum. We find that, although the avalanche component carries the vast majority of the current, it is the high-energy seed remnant that dominates synchrotron emission. With insights from the fluid-kinetic simulations, an analytic model for the evolution of the runaway seed component is developed and used to reconstruct the radial density profile of the RE beam. The analysis shows that the observed change of the synchrotron pattern from circular to crescent shape is caused by a rapid redistribution of the radial profile of the runaway density

On Control and Estimation of Large and Uncertain Systems

This thesis contains an introduction and six papers about the control and estimation of large and uncertain systems. The first paper poses and solves a deterministic version of the multiple-model estimation problem for finite sets of linear systems. The estimate is an interpolation of Kalman filter estimates. It achieves a provided energy gain bound from disturbances to the point-wise estimation error, given that the gain bound is feasible. The second paper shows how to compute upper and lower bounds for the smallest feasible gain bound. The bounds are computed via Riccati recursions. The third paper proves that it is sufficient to consider observer-based feedback in output-feedback control of linear systems with uncertain parameters, where the uncertain parameters belong to a finite set. The paper also contains an example of a discrete-time integrator with unknown gain. The fourth paper argues that the current methods for analyzing the robustness of large systems with structured uncertainty do not distinguish between sparse and dense perturbations and proposes a new robustness measure that captures sparsity. The paper also thoroughly analyzes this new measure. In particular, it proposes an upper bound that is amenable to distributed computation and valuable for control design. The fifth paper solves the problem of localized state-feedback L2 control with communication delay for large discrete-time systems. The synthesis procedure can be performed for each node in parallel. The paper combines the localized state-feedback controller with a localized Kalman filter to synthesize a localized output feedback controller that stabilizes the closed-loop subject to communication constraints. The sixth paper concerns optimal linear-quadratic team-decision problems where the team does not have access to the model. Instead, the players must learn optimal policies by interacting with the environment. The paper contains algorithms and regret bounds for the first- and zeroth-order information feedback

Controlo de qualidade de dados de sísmica de muito alta resolução em tempo real

Mestrado em Engenharia GeológicaA aquisicção de grandes volumes de dados durante uma campanha sísmica exige, necessariamente, mais tempo para o controlo de qualidade (QC). No entanto, o tempo de QC não pode ser extendido devido a limitações do tempo de operação, tendo de ser feito mais rápido, o que pode comprometer a qualidade. A alternativa, alocar mais pessoas e recursos para QC e melhorar a eficiência, leva a aumentos de custo e à necessidade de maiores embarcações. Além disso, o QC tradicional requer tempo de análise após a aquisição, atrasando a desmobilização da embarcação, aumentando assim os custos da aquisição. A solução proposta passou pelo desenvolvimento de um QC automático em tempo real eficiente, testando a Comparação Espetral e o Atributo Razão Sinal-Ruído - ferramentas desenvolvidas no software SPW, usado para processamento de dados sísmicos. Usando este software foi testada a deteção e identificação de dados de fraca qualidade através das ferramentas de QC automáticas e os seus parâmetros ajustados para incluir pelo menos todos os maus registos encontrados manualmente. Foi também feita a deteção e identificação de vários problemas encontrados durante uma campanha de aquisição, tais como fortes ondulações e respetiva direção, o ruído de esteira provocado pelas hélices da embarcação e consequente Trouser’s Effect e mau funcionamento das fontes ou dos recetores. A deteção antecipada destes problemas pode permitir a sua resolução atempada, não comprometendo a aquisição dos dados. Foram feitos vários relatórios para descrever problemas encontrados durante os testes de versões beta do software SPW e os mesmos reportados à equipa da Parallel Geoscience, que atualizou o software de forma a preencher os requisitos necessários ao bom funcionamento do QC em tempo real. Estas atualizações permitiram o correto mapeamento dos headers dos ficheiros, otimização da velocidade de análise das ferramentas automáticas e correção de erros em processamento dos dados em multi-thread, para evitar atrasos entre o QC em tempo real e a aquisição dos dados, adaptação das ferramentas à leitura de um número variável de assinaturas das fontes, otimização dos limites de memória gráfica e correção de valores anómalos de semelhança espetral. Algumas atualizações foram feitas através da simulação da aquisição de dados na empresa, de forma a efetuar alguns ajustes e posteriormente serem feitos testes numa campanha futura. A parametrização destas ferramentas foi alcançada, assegurando-se assim a correta deteção automática dos vários problemas encontrados durante a campanha de aquisição usada para os testes, o que levará à redução do tempo gasto na fase de QC a bordo e ao aumento da sua eficácia.The acquisition of larger volumes of seismic data during a survey requires, necessarily, more time for quality control (QC). Despite this, QC cannot be extended due operational time constraints and must be done faster, compromising its efficiency and consequently the data quality. The alternative, to allocate more people and resources for QC to improve efficiency, leads to prohibitive higher costs and larger vessel requirements. Therefore, traditional QC methods for large data require extended standby times after data acquisition, before the vessel can be demobilized, increasing the cost of survey. The solution tested here consisted on the development of an efficient Real- Time QC by testing Spectral Comparison and Signal to Noise Ratio Attribute (tools developed for the SPW seismic processing software). The detection and identification of bad data by the automatic QC tools was made and the parameters adapted to include at least all manual QC flags. Also, the detection and identification of common problems during acquisition, such strong wave motion and its direction, strong propeller’s wash, trouser’s effect and malfunction in sources or receivers were carried out. The premature detection of these problems will allow to solve them soon enough to not compromise the data acquisition. Several problem reports from beta tests of SPW were transmitted to the Parallel Geoscience team, to be used as a reference to update the software and fulfil Real-Time QC requirements. These updates brought the correct mapping of data headers in files, optimization of data analysis speed along with multi-thread processing debug, to assure it will be running fast enough to avoid delays between acquisition and Real-Time QC, software design to read a variable number of source signatures, optimization of graphic memory limits and debugging of anomalous spectral semblance values. Some updates resulted from a data acquisition simulation that was set up in the office, to make some adjustments to be later tested on an upcoming survey. The parameterization of these tools was finally achieved, assuring the correct detection of all major issues found during the survey, what will eventually lead to the reduction of time needed for QC stage on board, as also to the improvement of its efficiency

FUN3D Manual: 13.2

This manual describes the installation and execution of FUN3D version 13.2, including optional dependent packages. FUN3D is a suite of computational fluid dynamics simulation and design tools that uses mixed-element unstructured grids in a large number of formats, including structured multiblock and overset grid systems. A discretely-exact adjoint solver enables efficient gradient-based design and grid adaptation to reduce estimated discretization error. FUN3D is available with and without a reacting, real-gas capability. This generic gas option is available only for those persons that qualify for its beta release status