Disertación/Tesis

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2021
Disertaciones
1
  • ISAMARA DE MENDONÇA SILVA
  • Investigating the teleconnection patterns associated with the rainy season and analyzing the homogeneity and the trend in extreme precipitation indices in the Northern of Northeast Brazil

  • Líder : DEUSDEDIT MONTEIRO MEDEIROS
  • MIEMBROS DE LA BANCA :
  • DAVID MENDES
  • DEUSDEDIT MONTEIRO MEDEIROS
  • MEIRY SAYURI SAKAMOTO
  • Data: 26-feb-2021


  • Resumen Espectáculo
  • A first study used the hidden Markov model in this dissertation to describe the daily rainfall occurrence and intensity at four meteorological stations in the Metropolitan Region of Fortaleza in the Northern Northeast Brazil (NNB) and the teleconnection patterns that influence precipitation regime during the rainy season (February, March, April, and May) from 1975 to 2013. A model with four hidden states was associated with climatic conditions: very rainy (1), rainy (2), less rainy (3), and dry (4), satisfactorily agreeing with the interannual variability of the rainy season in this region. State 2 was the only one that showed a statistical trend, indicating a probable decrease in the occurrence of precipitation in the rainy season. It was also shown that the meteorology associated with states 2 and 4 is strongly related to the El Niño-South Oscillation and the North Atlantic tripole and is intrinsically conditioned by the large-scale atmospheric patterns of the Northern Hemisphere. All of these mechanisms modulated the displacement of the Intertropical Convergence Zone (ITCZ) southward (state 2) or northward (state 4), affecting the occurrence of precipitation in the NNB. State 1 was distinguished by the influence of the Atlantic Meridional Mode and the ITCZ displacement further south, while state 3 was identified by the absence of teleconnection patterns. A second study investigated the homogeneity and trend of eleven extreme precipitation indices from a daily data set of 84 rain gauges in the state of Ceará, located in the NNB, from 1974 to 2018, on the annual and seasonal time scales. The data were initially submitted to the gap-filling and quality control processes. Most precipitation series were classified as "useful," and dry day precipitation indices were more susceptible to breaks than rainy day variables for homogeneity. The significant break years in the series agreed well with the El Niño and La Niña events, suggesting a further investigation of this possible connection. The precipitation indices for rainy and dry days presented mostly decreasing and increasing trends, respectively, indicating a decline in the rainfall regime in Ceará, mainly in the central-eastern, northwestern, and southern regions, in the annual and rainy seasons. The LOWESS curve showed changes in almost all series during the 1980s and 1990s, coinciding with the homogeneity breaks and the years of severe droughts in the region. The correlation coefficients were strong and significant between all precipitation indices and the other variables, seeming to induce changes in total rainfall.

2
  • ARTUR CRISTIANO PAULINO PEREIRA
  • Study of supersonic combustion in aerospace vehicle in atmospheric flight at Mach 5.8 and 20 km of altitude.
  • Líder : GEORGE SANTOS MARINHO
  • MIEMBROS DE LA BANCA :
  • DOUGLAS DO NASCIMENTO SILVA
  • GEORGE SANTOS MARINHO
  • JOÃO FELIPE DE ARAÚJO MARTOS
  • PAULO GILBERTO DE PAULA TORO
  • Data: 26-ago-2021


  • Resumen Espectáculo
  • In the present work, the thrust generation capacity of a scramjet integrated aerospace vehicle was evaluated from the combustion of hydrogen and atmospheric air at supersonic speed, for the flight of the scramjet vehicle at 20 km of altitude and speed of 1709.6 m/s, corresponding to Mach number of 5.79. A Theoretical-analytical method was used, considering the steady-state. The First Law of Thermodynamics, without and with reaction based on enthalpy of formation, was used to determine the properties. Correlations between the equivalence ratio with the mixture temperature, mixture speed, and exhausted gases temperature after combustion were obtained. The temperature and speed were also determined after the combustion gases expansion process. Mixing speed equal to 1152 m/s and exhaust gases temperature in the range of 2400 K to 2600 K was assumed, resulting in a fuel-air ratio in the range of 0.648 to 0.774 and mixing temperature of 875 K to 855 K. The temperature after the expansion varied from 865 K to 964 K, and the speed varied from 2425 m/s to 2532 m/s. A mean specific impulse equal to 4049.7 s was obtained, and positive non-installed thrust ranging from 760.8 N to 879.3 N.

3
  • PEDRO PAULO BATISTA DE ARAÚJO
  • Supersonic combustion technology applied to the second stage of the nanoSats launch vehicle

  • Líder : PAULO GILBERTO DE PAULA TORO
  • MIEMBROS DE LA BANCA :
  • ROBERTO DA CUNHA FOLLADOR
  • DOUGLAS DO NASCIMENTO SILVA
  • PAULO CELSO GRECO JÚNIOR
  • PAULO GILBERTO DE PAULA TORO
  • SANDI ITAMAR SCHAFER DE SOUZA
  • Data: 15-oct-2021


  • Resumen Espectáculo
  • Current rocket engines have a low specific thrust compared to the airbreathing propulsion technologies. Airbreathing supersonic combustion engines/vehicles are an alternative to improve the efficiency of access to space in a flight through the dense Earth’s atmosphere, below 60 km of geometric altitude. In this work, aerodynamic analysis of the conceptual model of supersonic combustion engine/vehicle (scramjet) was carried out to operate as a second-stage propulsion engine of a nanoSats launch vehicle. Two engineering approaches, analytical and computational numerical methodology, were used to perform the preliminary analysis of the proposed scramjet model, coupled to the third propulsion stage, at an altitude of 20 km with flight speed equivalent to Mach 5.8. Atmospheric air was considered a calorically perfect gas, and the viscous effects were neglect in a preliminary analysis. Supersonic combustion was modeled as heat adding to the supersonic flow without fuel injection. Then, numerical simulations were carried out considering the effects of the boundary layer development to verify the aerodynamic feasibility of the model. Optimization of the compression angles at the scramjet compression section was used to minimize the entropy generation and increase the vehicle’s compression efficiency, aiming to reach the temperature and Mach number at the combustion chamber entrance. The temperature required at the combustion chamber entrance is estimated to self-ignite the air-fuel mixture. Korkegi limit was evaluated through oblique shock waves in the compression section and in the heat addition process. Using the Korkegi limit, in the preliminary analytical design, as an indication of unstart due to the separation of the boundary layer caused by the adverse pressure gradient, we investigated to identify in numerical simulations considering the viscous effects whether the unstart phenomenon would occur. Numerical simulations were performed using commercial software, ANSYS Fluent, using the turbulence model known as transition SST. We also performed mesh convergence tests, numerical experiment validation on top of numerical data validated by HyShot flight data. Both meshes used in the validation and the analysis of the present work have equivalent levels of refinement in the direction of the wall, satisfying the condition of the turbulence model (𝑦+ < 1). The analytical calculations showed good quantitative and qualitative consistency with the numerical simulation results considering the same simplifications adopted in the analytical. An adaptation of the analytical method is proposed to take into account the effects of the interaction of the expansion fan with the oblique shock wave incident on the compression section of the scramjet. The results of the viscous simulations indicated that should be made improvements in the geometry due to the low temperature at the combustion chamber entrance, as well as reduced mass flow captured by the combustor, as a consequence of solution used to prevent unstart.

4
  • IAGO VINICIUS MACEDO SANTOS
  • EVALUATION OF THE IMPACT OF DENSITY ON ROCKET FLIGHT
  • Líder : DOUGLAS DO NASCIMENTO SILVA
  • MIEMBROS DE LA BANCA :
  • CAMILA PACELLY BRANDÃO DE ARAÚJO
  • DOUGLAS DO NASCIMENTO SILVA
  • HEIDI KORZENOWSKI
  • Data: 19-nov-2021


  • Resumen Espectáculo
  • In this present work, the implementation of the ordinary differential equations developed in the literature and which govern the movement of a rocket is presented, with the chosen vehicle being the VS-30 rocket. The code, which is developed in Matlab, is designed so that it is possible to compare the Earth's atmosphere as one composed of ideal gas, that is, an atmosphere in which the gases obey the Ideal Gas Law, and in another scenario , like being a type of Van der Waals. The final aim is to verify whether or not there is a large impact on the flight phenomenon as a whole, applying the Euler method to the solution of the equations already mentioned above.

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