Tornadic debris plays an important role in the study of tornadoes due to the dramatic threat it poses to human life, and the devastation it causes to commercial and residential property. Radar cross section (RCS) modeling on plate-like and cylindrical objects is developed in this tornadic debris study. The sheets, plates, and cylinders used in this study are designed to represent leaves, wood board, flat building forms, metal rods, tree trunks, and branches, respectively. Different techniques are evaluated in terms of the geometry of the object, accuracy, and math complexity and computation efficiency. Geometrical Optics (GO), Geometrical Theory of Diffraction (GTD), Finite Element Method (FEM), Finite Difference Time Domain method (FDTD), Moment of Method (MoM) and Physical Optics (PO) are introduced. Finally, the decision to use PO for deriving the formulation for plate-like objects throughout the dissertation was made. Non-metal objects such as cylinder broadside, endcap, general circular sheets and plates, surface impedance circular plates, rectangular sheets and plates, as well as metal circular plates are derived by hand. Metal objects such as cylinder broadside and rectangular plates, as well as resistive rectangular thin sheet approximations, are verified and cited from published research books and papers. Full wave simulation Ansys HFSS validates the analytical results in most cases. FEKO commercial software is used to compare the analytical results for two layer plates with different media and leaf sample applications. After testing, metal vs. non-metal plates and thin vs. thick plates are distinguished by 5 dB, 10 dB, and 20 dB from the simulation results, respectively; this fact confirms the accuracy and limitations of theory. By adding endcaps, one is able to compensate the deficiency from normal to the cap surface of the finite cylinder by at least several wavelengths in length and at least half of a wavelength in radius. The theoretical analysis of the extension of PO indicates that more accurate results appear as the incident angle gets closer to normal. The errors and limitations of PO are described and demonstrated by comparison plots of analytical results vs. HFSS throughout. The leaf library and wood board (dry and wet) studies are performed as sample applications for “real” debris types under the radar coordinate transformation system for all polarizations at oblique TEM incident wave. Research questions are answered in the conclusions. Advisors/Committee Members: Cruz, J.R (advisor), Palmer, Robert (committee member), Yang, Zhibo (committee member), Fulton, Caleb (committee member), Yeary, Mark (committee member).

[pt] Esta dissertação apresenta resultados de simulação física e numérica do comportamento mecânico de cavidades circulares em meios contínuos. Na simulação numérica foi possível reproduzir o comportamento tensão-deformação registrado nos ensaios. O comportamento mecânico do contínuo foi abordado de duas formas: i) Teoria clássica e ii) Modelo generalizado de Cosserat. A segunda abordagem, por dispor de um grau de liberdade extra, permite a reprodução numérica de algumas feições observadas ao redor das cavidades circulares em testes de laboratório de maneira mais realística. A teoria clássica de contínuo foi associada somente ao modelo constitutivo de Mohr-Coulomb. Já para Cosserat, foram utilizados dois modelos constitutivos: Mohr-Coulomb e Bogdanova-Lippmann Modificado. A motivação para apresentar contínuo generalizado neste trabalho é que o mesmo inclui a parcela referente ao comportamento das partículas. Em todos os testes foram utilizadas amostras do arenito Botucatu, obtidas em São Paulo e Paraná. Para caracterização mecânica deste material foram realizados ensaios uniaxiais, triaxiais e brasileiros. Já a simulação física do comportamento de cavidades circulares foi analisada segundo duas geometrias: cúbica (com aplicação de estado de tensão biaxial) e cilíndrica (TWC – Thick Walled Cylinder). O acompanhamento da ruptura das cavidades cilíndricas foi feito de forma visual (amostras cúbicas) e com monitoramento tomográfico em tempo real (amostras cilíndricas). Com base na observação experimental da ruptura das cavidades cilíndricas e nas simulações numéricas considerando o contínuo clássico e de Cosserat, foi possível verificar que, ambas as abordagens possibilitaram a reprodução das feições observadas.

[en] This work seeks to realize physical and numerical simulation of the mechanical behavior of the wellbore stability for continuum environment.The Continunm s mechanical behavior is approach by two ways: i) Classic Continuum Theory and ii) Cosserat Continuum. On the second approach, the theory allows an extra degree of freedom, which plays an important rule on instabilities and bifurcation problems; this allows a more realistic numerical simulation of the failure mechanism observed on circular cavity. The Classic Continuum Theory is associated to a Mohr-Coulomb constitutive model. On the other hand for Cosserat Theory s applied tow constitutive models: Mohr-Coulomb and Modified Bogdanova-Lippmann.The generalized continuum takes in account the microstructure of the material.It s used on all tests Botucatu s specimens, which were acquired at São Paulo and Paraná. For characterize the rock s behavior it s realized triaxial, uniaxial and brazilian tests. Then the physical simulation of the circular cavity s behavior was analyzed for two geometries: cubic samples (biaxial stress) and cylindric samples (TWC – Thick Walled Cylinder). The failure mechanism of circular cavity was followed visually (cubic samples) and with CT X-Ray in real time (cylindric samples).From the experimental observations of the failure…

Advisors/Committee Members: EURIPEDES DO AMARAL VARGAS JUNIOR.