Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 400-410. / by Jose Ignacio Perez Arriaga. / Ph.D.

published_or_final_version / Applied Geosciences / Master / Master of Science

Bibliography: leaves 238-248 / xxix, 248 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This thesis is concerned with the design and coordination of linear, fixed parameter controllers for the purpose of enhancing the dynamic performance of a multimachine power system. The studies are based on linear control theory and involve state space analysis, modal analysis, eigenanalysis and conventional frequency response techniques. The emphasis is on the small-signal performance of the system / Thesis (Ph.D.)--University of Adelaide, Dept. of Electrical and Electronic Engineering, 1997?

Columns with three spans separated by elastic braces are analyzed. The influences of translational and rotational resistance at the braces, various end conditions, and the bracing locations for the perfect columns with equal and unequal spans subjected to uniform and nonuniform axial load are investigated. For imperfect columns with equal or unequal spans subjected to uniform compression, the effects of various end conditions at the top and various initial deflections are studied. "Ideal stiffness" and "full bracing" only exist for these columns with equal spans and translational restraints with identical spring stiffness at the braces. Rotational restraints at the braces or at the ends improve the load-carrying capacity of the column. For the imperfect column, three types of initial deflection on the columns with equal and unequal spans and various end conditions at the top are analyzed. Based on a linear elastic analysis, the bracing force induced by a cubic initial deflection for a three-span column often exceeds 20/0 of the axial load. The violation of this rule of thumb in practice is readily revealed. Design curves for the effect of the bracing stiffness on the deflection ratio and bracing force percentage are created for the determination of bracing requirements. / Master of Science

One of the major problems with surface-mounted or embedded induced strain actuator (ISA) patches are the considerably high stress gradients introduced at the edges of the actuator patches when an electric field is applied. These excessive stress gradients initiate debonding of the actuators from the substrate, thus affecting the mechanical reliability of the structure. This thesis is begun by investigating existing theoretical models of induced strain actuated structures, and will later use these to compare with the finite element analysis. The finite element analysis is used to explore the stress concentrations located at the edges of the actuators and begins by refining the mesh areas of the same structure focusing in on the ends of the ISA’s. This preliminary analysis is conducted on a structural configuration with a perfectly bonded actuator and proceeds to one with a finite bonding layer. After completion of the mesh refinement investigation several modifications in the design and implementation of the induced strain actuators are examined to reduce the stress concentrations at the edges of the actuators. In the finite element analysis two separate modeling considerations are examined: 1) The actuator is perfectly-bonded to the substrate. 2) A finite adhesive layer is incorporated between the actuator and the substrate. With each modeling consideration several design modifications are considered in this thesis including employing partial electrodes on the induced strain actuator surface regions instead of fully electroded surfaces, examining an actuator with a chamfered end, and using caps to reduce the stress concentrations and possibly increase the performance of the structure by allowing the induced strain actuators to utilize their piezoelectric strain coefficient in the thickness direction, d₃₃. The design modifications and different modeling techniques help to alleviate the critical stresses in the structure while gaining a better understanding of causes them. / Master of Science

Unreinforced masonry (URM) construction, which has been widely used in the United States, presents a large threat to life safety and regional economic development because of its poor seismic resistance. In this research, the nonlinear seismic properties of URM structures were investigated via a quasi-static test of a full-scale two-story URM building and associated analytical and numerical studies. The tests of the 24ft. by 24ft. in plan 22ft. high URM building revealed that the damage was characterized by (1) the formation of large discrete cracks in the masonry walls and (2) the rocking and sliding of URM piers. Both of these results were consistent with the predictions based on individual component properties obtained in previous research. However, the tests also revealed significant global behavior phenomena, including flange effects, overturning moment effects, and the formation of different effective piers in a perforated wall. This global behavior greatly affected the response of the URM building tested. In order to understand the nonlinear behavior of the test structure, a series of analytical studies were conducted. First, at the material level, a mechanical key model was proposed to describe the failure of URM assemblages under a biaxial state of stress. Second, at the component level, an effective pier model was developed to illustrate the mixed failure modes of a URM pier and its nonlinear force-deformation relationship. Third, at the structure level, a nonlinear pushover model was built using the mechanical models at the material and component levels to describe the nonlinear properties of a URM building. This nonlinear pushover model and a three-dimensional finite element model were employed to analyze the test structure. Both gave results in good agreement with the test data. Improvements to current provisions for the evaluation of existing masonry structures were proposed.

Orientadores: Luiz Felipe Mendes de Moura, João Batista Campos Silva / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-17T00:52:39Z (GMT). No. of bitstreams: 1 Pereira_VanessaDavanco_D.pdf: 25543252 bytes, checksum: e4c1c00ac828271186af3bc2fc3654d5 (MD5) Previous issue date: 2010 / Resumo: Neste trabalho foram desenvolvidos e aplicados códigos computacionais baseados em métodos de elementos finitos estabilizados, principalmente, a versão de mínimos quadrados (LSFEM - Least Squares Finite Element Method) que leva a sistemas algébricos sempre simétricos e positivos definidos, independentemente dos sistemas de equações diferenciais parciais dos casos considerados. Um método conhecido como CBS (Characteristic Based Split) também tem sido aplicado o qual possibilita a aplicação do método de Galerkin (GFEM - Galerkin Finite Element Method) para solução de problemas de escoamento de fluidos, sem oscilações na solução. Resultados têm sido obtidos para problemas de convecção-difusão bi e tridimensional discretizando os domínios por malhas estruturadas de elementos quadráticos, e para solução de escoamentos incompressíveis bidimensionais usando malhas não estruturadas de elementos finitos triangulares lineares / Abstract: In this study we developed and implemented computer codes based on stabilized finite element methods, especially the version of least squares (LSFEM - Least Squares Finite Element Method) that leads to algebraic systems always symmetric and positive defined, independently of the systems of partial differential equations of the cases considered. A method known as CBS (Characteristic Based Split) has also been implemented which allows the application of the Galerkin method (GFEM - Galerkin Finite Element Method) to solve problems of fluid flow without oscilations in the solution. Results have been obtained for two-and three-dimensional problems of convection-diffusion type discretizing the domains by structured meshes of quadratic elements and for solution of two-dimensional incompressible flows using unstructured meshes of linear triangles / Doutorado / Termica e Fluidos / Doutor em Engenharia Mecânica

Orientador: Hyun Mo Yang / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Matematica, Estatistica e Computação Cientifica / Made available in DSpace on 2018-08-05T18:54:32Z (GMT). No. of bitstreams: 1 Rosales_JuanCarlos_M.pdf: 1360240 bytes, checksum: 84fee5e0958180b35a0f098cc5b87f4d (MD5) Previous issue date: 2005 / Resumo: Neste trabalho fizemos a modelagem da leishmaniose começando com o ciclo doméstico ou urbano com 2-hospedeiros para estender os resultados ao ciclo peridoméstico com n-hospedeiros. No caso urbano, consideramos a população do vetor constante e, após, com capacidade de suporte. Simplificamos o modelo para analisar um dos fatores de risco da leishmaniose, o desmatamento. Derivamos as expressões correspondentes ao número de reprodutibilidade basal em todos os casos por meio de análise de estabilidade. Realizamos simulações com dados de zonas endêmicas. Ao final aplicamos a análise de sensitividade para o número de reprodutibilidade basal para o caso de 2-hospedeiros / Abstract: We are dealing with a modelling of leishmaniasis considering initially the urban cycle with 2-hosts aiming to extend the results to a peridomestic cycle for n-hosts. In the urban case we consider the vector population constant, also, variable. We simplify the model the assess the factor regarded to risk of leishmaniasis analysis, which is the deforestation. We derive the expression for the basic reproduction number from the stability analysis. The model was simulated whit respect to endemics zone. Finally we performed the sensibility analysis of the basic reproduction number to the case of 2-hosts / Mestrado / Epidemiologia Matematica. Biomatematica / Mestre em Matemática Aplicada

Shear links are used as fuse elements in lateral load resisting systems to provide ductility and dissipate seismic energy. These links have traditionally been employed in eccentrically braced frames, but have more recently been suggested for use in the innovative linked column frame system (LCF). Current design specifications for shear links require intermediate web stiffeners to provide out-of-plane web stability so ductility requirements can be achieved. This research focused on moving from discrete transverse web stiffening to continuously stiffened webs in built up shear links. Built up links were designed to yield in shear when subjected to severe cyclic loading, however the webs of the links were designed using two metal sheets joined by an elastic core. These composite "sandwich" webs allowed for an increase in web thickness (and inherent flexural rigidity) without increasing the shear strength of the links. Numerical and experimental investigations were conducted to assess the performance of composite sandwich links subjected to severe loading. Numerical results showed improved web behavior in sandwich links in which the core material was assigned an elastic modulus greater than 5000psi. Due to fabrication limitations, experimental specimens were fabricated with a core material elastic modulus of 1000psi. These specimens did not perform as well as unstiffened base case links in terms global hysteretic behavior or ductility.

Comparisons were made on the behavior of two full-sized reticulated domes subjected to uniform static loads only and uniform static loads with earthquake excitations. Space truss elements were used in the dome models. The stiffness matrix of the space truss element allows for the nonlinear strain-displacement behavior and the stress-strain behavior of the material is modeled with a bilinear approximation. The nonlinear solution technique is the Newton-Raphson method while the direct integration technique is the Newmark- Beta method. The joint displacements for the static and the dynamic analyses were compared for both domes along with the axial stresses in all members. The percentage increases in the axial stresses of the dynamic analyses as compared to those of the static analyses were determined. The reticulated domes used in the study were found to bet capable of withstanding the earthquake excitations when subjected to various uniform loads without failure. / Master of Science