Otimização do controle do diagrama de radiação de radares de varredura para rastreio de foguetes usando o método GAMMC para o Caso Planar (GAMMC-P)

Launching centers are designed for scientific and commercial activities with aerospace vehicles. Rockets Tracking Systems (RTS) are part of the infrastructure of these centers and they are responsible for collecting and processing the data trajectory of vehicles. Generally, Parabolic Reflector Radars (PRRs) are used in RTS. However, it is possible to use radars with antenna arrays, or Phased Arrays (PAs), so called Phased Arrays Radars (PARs). Thus, the excitation signal of each radiating element of the array can be adjusted to perform electronic control of the radiation pattern in order to improve functionality and maintenance of the system. Therefore, in the implementation and reuse projects of PARs, modeling is subject to various combinations of excitation signals, producing a complex optimization problem due to the large number of available solutions. In this case, it is possible to use offline optimization methods, such as Genetic Algorithms (GAs), to calculate the problem solutions, which are stored for online applications. Hence, the Genetic Algorithm with Maximum-Minimum Crossover (GAMMC) optimization method was used to develop the GAMMC-P algorithm that optimizes the modeling step of radiation pattern control from planar PAs. Compared with a conventional crossover GA, the GAMMC has a different approach from the conventional one, because it performs the crossover of the fittest individuals with the least fit individuals in order to enhance the genetic diversity. Thus, the GAMMC prevents premature convergence, increases population fitness and reduces the processing time. Therefore, the GAMMC-P uses a reconfigurable algorithm with multiple objectives, different coding and genetic operator MMC. The test results show that GAMMC-P reached the proposed requirements for different operating conditions of a planar RAV.

A influência do amortecimento viscoelástico na estabilidade aeroelástica de painéis aeronáuticos

Since the creation of supersonic vehicles, during the Second World War, the engineers have given special attention to the interaction between the aerodynamic efforts and the structures of the aircrafts due to a highly destructive phenomenon called flutter in aeronautical panel. Flutter in aeronautical panels is a self-excited aeroelastic phenomenon, which can occurs during supersonic flights due to dynamic instability of inertia, elastic and aerodynamic forces of the system. In the flutter condition, when the critical aerodynamic pressure is reached, the vibration amplitudes of the panel become dynamically unstable and increase exponentially with time, affecting significantly the fatigue life of the existing aeronautical components. Thus, in this paper, the interest is to investigate the possibility of reducing the effects of the supersonic aeroelastic instability of rectangular plates by applying passive constrained viscoelastic layers. The rationale for such study is the fact that as the addition of viscoelastic materials provides decreased vibration amplitudes it becomes important to quantify the suppression of plate flutter coalescence modes that can be obtained. Moreover, despite the fact that much research on the suppression of panel flutter has been carried out by using passive, semi-active and active control techniques, very few of them are adapted to deal with the problem of estimating the flutter speeds of viscoelastic systems, since they must conveniently account for the frequency- and temperature-dependent behavior of the viscoelastic material. In this context, two different model of viscoelastic material are developed and applied to the model of sandwich plate by using finite elements. After the presentation of the theoretical foundations of the methodology, the description of a numerical study on the flutter analysis of a three-layer sandwich plate is addressed.

Estudo do efeito da radiação ionizante por feixe de elétrons sobre o polietileno de ultra alto peso molecular virgem e reciclado industrial

Dissertacao (Mestrado)

Radiação-x no diagnóstico em Medicina Dentária

A radiação-x foi descoberta há mais de uma centena de anos e com o avanço tecnológico diversas formas de aplicação têm vindo a ser descobertas. A utilização constante, devido à ajuda preciosa que estes dispositivos fornecem aos clínicos de Medicina Dentária, faz com que o paciente venha, de forma crescente, a ser exposto a este tipo de radiação. Este trabalho de revisão descritiva tem como principal propósito analisar os riscos, as formas de avaliação e de proteção da radiação-x, no âmbito do seu uso em Medicina Dentária. Para o efeito, realizou-se uma revisão da literatura, tendo-se recorrido ao motor de busca EBSCO host©, utilizando as frases boleanas: (X-ray risk OR Radiography risk OR Dental x-ray risk) AND (Dental Medicine OR Oral), foi substituída a palavra risk por “evaluation” e por “protection”. Desta pesquisa resultaram 82 documentos como referências bibliográficas. Esta revisão de literatura permitiu compreender a diferença entre radiação ionizante e não ionizante, quais os dispositivos utlizados na Medicina Dentária e o seu funcionamento geral, quais as unidades de medida da radiação, quais os riscos iminentes à exposição cumulativa e quais as suas consequências biológicas, perceber de que forma a legislação Portuguesa tem evoluído em matéria de radiação ionizante, quais as diversas formas de redução da dose absorvida pelo paciente e quais as medidas de proteção para os profissionais de saúde expostos à radiação ionizante.

Efeito da radiação micro-ondas na sinterização em fases sólida e líquida de pós de aço inoxidável 3I6L

Tese submetida à Universidade de Coimbra, Faculdade de Ciências e Tecnologia e aprovada em provas públicas para a obtenção do Grau de Doutor em Engenharia Mecânica (especialidade de Ciência dos Materiais)

Comparação do controle do inversor trifásico conectado à rede com filtro LCL considerando o amortecimento passivo e ativo

Distributed generation systems must fulfill standards specifications of current harmonics injected to the grid. In order to satisfy these grid requirements, passive filters are connected between inverter and grid. This work compares the characteristic response of the traditional inductive (L) filter with the inductive-capacitive-inductive (LCL) filter. It is shown that increasing the inductance L leads to a good ripple current suppression around the inverter switching frequency. The LCL filter provides better harmonic attenuation and reduces the filter size. The main drawback is the LCL filter impedance, which is characterized by a typical resonance peak, which must be damped to avoid instability. Passive or active techniques can be used to damp the LCL resonance. To address this issue, this dissertation presents a comparison of current control for PV grid-tied inverters with L filter and LCL filter and also discuss the use of active and passive damping for different regions of resonance frequency. From the mathematical models, a design methodology of the controllers was developed and the dynamic behavior of the system operating in closed loop was investigated. To validate the studies developed during this work, experimental results are presented using a three-phase 5kW experimental platform. The main components and their functions are discussed in this work. Experimental results are given to support the theoretical analysis and to illustrate the performance of grid-connected PV inverter system. It is shown that the resonant frequency of the system, and sampling frequency can be associated in order to calculate a critical frequency, below which is essential to perform the damping of the LCL filter. Also, the experimental results show that the active buffer per virtual resistor, although with a simple development, is effective to damp the resonance of the LCL filter and allow the system to operate stable within predetermined parameters.

Avaliação da dose de radiação: angiotomografia coronariana - métodos retrospectivo e prospectivo

The aim of this study was to evaluate the effective dose received by patients undergoing CCTA in both acquisition methods in the period June 1st to October 30th, 2013. Data collection was performed at the Clínica Sabedotti in Ponta Grossa/PR, with General Electric Equipment VCT XT, 64 detections lines. The effective dose was measured from the thirty cases randomly selected of Picture Archival and Communication System – PACS, reported by Dose Lenght Product (DLP) equipment for each examination and the conversion factor (EDLP) set by the European Commission for cardiac region (EDLP = 0.014). The results showed significant differences in radiation dose delivered to the patient according to the employee acquisition method, Retrospective or Prospective of ECG.