Breve reseña de la investigación en Ingeniería en la Universidad Nacional de Córdoba

En este trabajo se traza una reseña breve de las investigaciones llevadas a cabo por profesores de la FCEFyN en áreas de Ingeniería, desde la creación de la Escuela de Ingeniería hasta aproximadamente 1975. La motivación del trabajo ha sido el 400 aniversario de la Universidad Nacional de Córdoba, lo que generó un tiempo de reflexión sobre la investigación en todos los ámbitos universitarios, en este caso concentrándonos en las Ingenierías. Para la reseña se han establecido (arbitrariamente) como periodos los que se inician a partir la creación de la Escuela de Ingeniería (1879), entre 1883 y 1918, la Reforma Universitaria de 1918, el periodo entre la Reforma y 1945, la década 1945-1955, y finalmente las dos décadas entre 1955 y 1975.Fil: Godoy, Luis Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentin

The general theory of elastic stability at the end of the XIX century

This paper reviews the research on the theory of elastic stability published at the end of the 19th century, with emphasis on the work by G. H. Bryan in Cambridge. The state of the studies on structural stability previous to Bryan is reviewed, and two lines of work are identified: one is a general stability of rigid bodies and the other is a collection of case studies of elastic stability. Bryan's theory is discussed next, presenting his arguments based on first energy principles, which led him to strong conclusions. The importance of the word "general" and the idea of having solved the problem in each case are explained. The impact of the contributions made by Bryan, together with the critiques that this generated, is also discussed.Fil: Godoy, Luis Augusto. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentin

On dynamic quasi-bifurcation of simple shell-like systems under impulsive loads

The nonlinear dynamic response and buckling of a simple, two degree of freedom system is investigated in this work under an impulsive load that simulates a nearby detonation-like explosion. The model considered in this work was originally studied by other researchers to explore static buckling. The system includes force and moment springs in much the same way as membrane and bending effects develop in shell structures. The static response is first obtained to evaluate bifurcation states and nonlinear equilibrium paths including geometric imperfections. The dynamic problem is modeled using Lagrange equation of motion involving the total potential and kinetic energies. The nonlinear dynamic response under impulsive load is next computed for the perfect configuration under increasing load levels. The presence of quasi-bifurcations is detected using stability coefficients based on second order derivatives of the total potential energy. For a given load level, it is found that one stability coefficient vanishes at the first maximum in the displacement versus time trajectory, at which the system passes through a state of zero velocity. This occurs for the same displacement configuration as in the static buckling mode. The results show that quasi-bifurcation loads thus obtained are independent of the amplitude of the geometric imperfection considered but display high sensitivity to changes in the membrane to bending stiffness ratio. Extensions of the present model to account for the behavior of oil storage tanks under loads due to nearby explosions are suggested.Fil: Ameijeiras, Mariano Pablo. Universidad Nacional de Córdoba; ArgentinaFil: Godoy, Luis Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Estudios Avanzados en Ingeniería y Tecnología; Argentin

Quasi-bifurcation and Imperfection-sensitivity of Cylindrical Shells under Pressures due to an Explosion

The static and dynamic behavior of a horizontal cylindrical shell (as used to store fuels in tanks) is investigated in this work by means of computational modeling. Under a distributed pressure commonly used to model effects due to explosions, the geometrically nonlinear behavior is explored to identify bifurcation and limit points along the static equilibrium path, and the associated displacements. Critical load reductions due to imperfections are found in the order of 25%. The dynamic analysis is next presented to identify the possibility of reaching a quasi-bifurcation. It is found that the first peak in the transient response at which the displacement reaches the same value as in the limit static case occurs for a load which is about 3.5 times the static bifurcation load. The velocity is zero at this state and is identified as a quasi-bifurcation, at which the shell is expected to display a static instability. Imperfection-sensitivity of the quasi-bifurcation load is found to be of the same order as the static one. This is the first quasi-bifurcation study of a shell to identify dynamic buckling due to a nearby explosion.Fil: Ameijeiras, Mariano Pablo. Universidad Nacional de Córdoba; ArgentinaFil: Godoy, Luis Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Estudios Avanzados en Ingeniería y Tecnología; Argentin

Inestabilidad de tanques de almacenamiento de petróleo con techo cónico durante un incendio

En este trabajo se presenta un análisis del comportamiento estructural de tanques de almacenamiento de petróleo con techo bajo temperaturas procedentes de fuego adya-cente a la estructura. En la simulación numérica se modela la cáscara con elementos finitos de doble curvatura utilizando el código de propósitos generales ABAQUS. Se determinan las configuraciones deformadas y las temperaturas que identifican el es-tado crítico de pandeo y también el comportamiento poscrítico, mediante análisis de bifurcación lineal (conocido como LBA), análisis no lineal geométrico (GNA) y análisis no lineal geométrico con imperfecciones (GNIA). Para el análisis se modelan dos geo-metrías de tanques de almacenamiento de petróleo con techo fijo en su parte superior (representativas de diferentes volúmenes de almacenamiento) expuestos a una dis-tribución de temperatura externa y una carga hidrostática interna, a fin de evaluar la influencia de las diferentes relaciones de esbeltez altura-diámetro del tanque en la respuesta y la posible estabilización producida por el fluido almacenado en el interior. Los resultados muestran que la inestabilidad se produce a temperaturas muy bajas, del orden de 70ºC a 150ºC, con modos de pandeo que afectan la cara directamente ex-puesta al fuego. La inestabilidad se produce en régimen elástico del material.Fil: Calabro, Horacio Daniel. Universidad Nacional del Comahue; ArgentinaFil: Godoy, Luis Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; ArgentinaFil: Jaca, Rossana Claudia. Universidad Nacional del Comahue; Argentin

Reduced stiffness buckling analysis of aboveground storage tanks with thickness changes

The Reduced Stiffness Analysis (RSA) to compute lower bounds to buckling loads of shells has been employed by a number of researchers as a simple way to evaluate the buckling capacity of shells that display unstable behavior and imperfection-sensitivity. It allows the use of simple eigenvalue analysis, without having to perform incremental nonlinear analysis, and is based on the physical behavior of the shell which recognizes that a significant contribution to the stability of a shell under lateral pressure is provided by its membrane stiffness. Unstable post-critical behavior is associated with the loss of this stabilizing membrane contribution. Past use of the approach has been mainly restricted to cases of uniform shell thickness and uniform pressures in the circumferential direction, in which case analytical solutions are possible. Recent applications by the authors and other researchers have shown ways to compute the lower bounds using finite element analysis, for which a modified eigenvalue analysis is constructed by neglecting the membrane contributions to the matrix containing the initial stresses. This paper illustrates the application of the methodology to cases of pressure loaded shells with thickness changes in the meridional direction. A semi-analytical finite element code has been employed for the buckling analysis when uniform pressures act on aboveground steel tanks. The tanks are representative of those constructed for the oil industry, with diameter to thickness ratios of the order of 3000, and height to diameter ratios lower than one.Fil: Jaca, Rossana Claudia. Universidad Nacional del Comahue; ArgentinaFil: Godoy, Luis Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Estudios Avanzados en Ingeniería y Tecnología; ArgentinaFil: Croll, James G. A.. University College London; Reino Unid

Failure of steel tanks during their construction: experiments and computational modeling

La construcción de tanques de acero destinados al almacenamiento de petróleo plantea un estado de solicitaciones frente a la acción de viento que no está contemplado en las normativas. En la Patagonia Argentina, como en otros lugares reportados en la bibliografía, se han registrado casos de colapso de este tipo de estructuras durante la etapa constructiva a moderadas velocidades de viento. Estudios numéricos anteriores condujeron a determinar como factor desencadenante del mecanismo de colapso, la falta de integridad estructural por las irregularidades en la continuidad del apoyo en el sentido circunferencial. Un mayor conocimiento del comportamiento fluido-dinámico del viento permite ajustar las acciones actuantes usadas en el abordaje del estudio numérico. Este trabajo completa el análisis de tanques no anclados que colapsaron por acción del viento durante su etapa constructiva evaluando el patrón del flujo interior en los tanques mediante ensayos en túnel de viento, incluyendo estos resultados en el estudio numérico. La estructura se modela por elementos finitos mediante un código de propósitos generales, evaluando la inestabilidad del equilibrio mediante un análisis de bifurcación lineal (LBA) y análisis no lineal geométrico con imperfecciones (GNIA). Los ensayos permitieron determinar la formación de un vórtice interior que produce una depresión mayor que el de la estela a sotavento del tanque.During the construction of steel storage oil tanks, a state of stresses under wind loads is induced which is not covered by the regulations. Cases of collapse of such structures during their construction occurred in Patagonia Argentina and elsewhere under moderate wind speeds, as reported in the literature. Previous numerical studies concentrated on the identification of the collapse mechanism, which was related to the loss of structural integrity due to discontinuity of the support in the circumferential direction. An increased knowledge of the fluid dynamic behavior under wind allows obtaining an improved input used in the subsequent numerical study. This paper provides new insight into the wind behavior of unanchored tanks that collapsed during their construction by wind tunnel tests to evaluate the flow pattern inside the tanks, which is an input for the subsequent numerical study. The structure is modeled using a general purpose finite element code, in which instability is evaluated by Linear Bifurcation Analysis (LBA) and by Geometrically Nonlinear Analysis with Imperfections (GNIA). Tests allowed identifying that an inner vortex is induced which produces a greater depression than the downwind wake in the leeward region of the tank.Fil: Jaca, Rossana Claudia. Universidad Nacional del Comahue; ArgentinaFil: Cicerone, Esteban. Universidad Nacional del Comahue; ArgentinaFil: Hernandez, Facundo C.. Universidad Nacional del Comahue; ArgentinaFil: Lassig, Jorge Luis. Universidad Nacional del Comahue; ArgentinaFil: Godoy, Luis Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados En Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Cs.exactas Físicas y Naturales. Instituto de Estudios Avanzados En Ingeniería y Tecnología; Argentin

Design of the austempering heat treatment of a ductile iron differential case aided by computer simulation

Austempered ductile iron is frequently employed in the fabrication of automobile parts due to its good mechanical properties, and its simplicity and low cost of the manufacturing process. The heat treatment design is an important stage, in which parameters such as temperatures and durations are chosen according to the required microstructure, part dimension, and initial characteristics of ductile iron. A coupled thermo-mechanicalmetallurgical model is employed in this work to facilitate the heat treatment design of a ductile iron differential case. The thermal-mechanical model is solved by using a general-purpose software, and the metallurgical model is implemented into it by means of user-defined subroutines. To perform the austempering heat treatment simulation of the part, experimental results were required to complete some basic parameters of the model. In order to select appropriated values of thermal cycle parameters, the numerical model was employed to analyze the influence of austenitizing temperature, and austempering time and temperature in the microstructure, dimensional change of the part, cooling rate, and minimum required time of the heat treatment to obtain a full ausferritic matrix. A good performance of the computational tool was found by comparison of numerical and experimental results.Fil: Boccardo, Adrian Dante. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Departamento de Ingeniería Mecanica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Estudios Avanzados en Ingeniería y Tecnología; ArgentinaFil: Dardati, Patricia Mónica(EXT). Universidad Tecnológica Nacional; ArgentinaFil: Godoy, Luis Augusto. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Estudios Avanzados en Ingeniería y Tecnología; ArgentinaFil: Lopensino, Juan. Universidad Tecnológica Nacional; Argentin

EFEITO DA VARIÁVEL SEMÂNTICA DE CONCRETUDE NO ACESSO LEXICAL

Objetivo: Verificar a influência da concretude no ato de julgamento sobre a imageabilidade da palavra. Método: Foi aplicado numa população de 10 adolescentes universitárias do sexo feminino o teste de imageabilidade, que se trata de um método on line de investigação. Neste teste, foram pesquisadas duas variáveis: o julgamento do participante sobre a imageabilidade da palavra (numa escala de 1 a 7) e o tempo de reação (resposta ao estímulo visual – palavra escrita –). Resultado: o tempo de resposta é sensivelmente maior quando as palavras representavam conceitos abstratos do que quando representavam conceitos concretos. Conclusão: verificou-se que, mesmo em tarefas como fazer o julgamento de imageabilidade de uma palavra, o fator semântico de concretude estará influenciando

Dual-energy X-ray absorptiometry study of body composition in patients with lipodystrophy

Inst Estadual Diabet & Endocrinol, Metab Unit, Rio de Janeiro, BrazilUniversidade Federal de São Paulo, Dept Endocrinol & Metab, São Paulo, BrazilDENSSO, Rio de Janeiro, BrazilUniversidade Federal de São Paulo, Dept Endocrinol & Metab, São Paulo, BrazilWeb of Scienc