Implementação computacional de um algoritmo que leva em conta o contato e atrito entre um corpo rígido e um corpo deformável

O contato entre corpos é um dos mecanismos básicos que se apresentam na mecânica do sólido. Através de tal efeito físico é que se aplicam cargas a uma estrutura e esta as transmite a seus apoios. Neste trabalho apresenta-se a teoria e implementação computacional de um algoritmo que permite considerar os efeitos de contato e atrito entre uma superfície rígida que prescreve deslocamentos sobre um corpo flexível de comportamento elástico linear. As restrições são impostas empregando o método das funções de penalidade. A lei geral do atrito associado à regra de Coulomb de deslocamento obtem-se por analogia com a teoria da plasticidade. Na implementação computacional apareceram problemas para contornar a sobrerestrição dos termos afetados pela função de penalidade, apresentando-se duas formas de tratar os mesmos. Finalmente são apresentados dois exemplos para testar o trabalho realizado.Contact is a basic mechanism in solid mechanics. Trhough this physical effects loads are applied to structures and transmited to their supports. The theoretical formulations and the computational implementation of an algorithm, that models contact and friction effects between a rigid surface prescrinbing and bidimensional linear elastic body are represented in this work. Restrictions are imposed using the panlaty function approach. A general law for friction associated with Coulomb displacement rule is obtained by analogy with plasticity theory. Computational difficulties to eliminate locking in terms influenced by penalty functions were detected, and two approachs were used to solve this problem. Finally, two numerical examples to test the computational code are presented

effectiveness of a lattice discrete element model to simulate mechanical wave shielding by using barriers into the ground

Abstract Several vibration sources can provoke propagation of mechanical waves into the ground. Such waves have to be taken into account both in designing of new buildings and in shielding of strategic structures. The vibration control systems may be either active systems or passive systems such as vertical barriers. One of the main problems encountered in the numerical simulation of wave shielding by using vertical barriers is the ground modeling. To such an aim, the method originally formulated by Riera is here employed to simulate both typical elastic-dynamic problems and a complex problem consisting in the numerical simulation of a vertical barrier wave shielding into a damaged ground where wave propagation occurs

DEVELOPMENT OF A TRIAXIAL FORCE PLATFORM FOR THE MEASUREMENT OF FORCE AT A BICYCLE PEDAL

The main purpose of this work is to present the methodology used to develop a triaxial force platform for the use at a pedal bicycle; this platform is based on the flexion of beams where strain gages are bonded for the measurements of force components FX, FY and FZ, as well as the force moments MX and MY. The theoretical analysis of this force platform was realized by the Finite Element method, with the simulation of 384 combinations of static loads (force and moments) at different directions. Deformation data numerically obtained is related to the position were sensors will be placed. Output signals obtained were numerically organized and graphically analyzed, in order to show the mathematical relation between force and strain, which is used to generate a "calibration matrix", free of mechanical coupling which usually appears in multiaxis systems. At last, a test was made, simulating an input load, and the output signal obtained was practically equal

Experimental analysis of physical magnitudes through films and its application in the classroom

En este trabajo mostramos cómo nuestros alumnos de secundaria y bachillerato han podido realizar, en los últimos 10 cursos, investigaciones sobre fenómenos o situaciones físicas de la vida cotidiana cercanas a sus intereses. El procedimiento consiste en realizar grabaciones de video digital y la posterior aplicación de un programa informático (Avimèca) que permite seguir la escena fotograma a fotograma asociando valores numéricos a cada punto elegido para poder analizar ciertas magnitudes físicas. En contra de lo que puede parecer, el procedimiento es sencillo y los elementos empleados son relativamente económicos. En cualquier caso, para facilitar la tarea a otros profesores, se agrega una guía del programa que, por otra parte, es de acceso gratuito. Además, se detalla el modo en que se hemos implementado esta actividad en el aula y enumeramos las dificultades encontradas, así como las soluciones propuestas.In this paper we show how our Secondary and High School students have been able to research phenomena or physical situation of their real lives closer to their interests in the last 10 years. The procedure is to make digital video recordings and then applying a computer program (Avimèca), which monitors the scene frame by frame and attaching numerical values to each selected point in order to analyze some physical magnitudes. Contrary to what may seem, the procedure is simple and relatively inexpensive elements are used. In any case, to make it easier for other teachers, a program guide is added which is free-access. In addition, the way in which we implemented this classroom activity is detailed, listing the difficulties encountered and the corresponding proposed solutions

The dispersion curve applied in guided wave propagation in prismatic rods

The early detection of failures in structures is a subject of great interest in engineering; several of these techniques are linked with the elastic wave propagation, using guided waves is one of these alternatives. Several structures of interest in engineering are laminar arrangements; the wave propagation in this type of structures depends not only on the material properties, but also on the geometric parameters, such as the plate thickness. Tubular structures, pressure vessels, tanks and also parts of ships hulls could be considered laminar. The elastic wave propagation in laminar structures could be considered as a sum of modal shapes that have its wave length and frequencies defined. These mode families are characteristics of each structure and could be represented through the dispersion curves. The definition of these dispersion curves is of crucial importance to understand the propagation of guided waves in the structure studied. In the present work the dispersion curves were generated using three different methodologies, specific for metallic rectangular stems that compound the strengthening armor in flexible riser duct. Each approach presented in the analysis were carried out using standard finite element commercial packages and an experimental verification, as well. The premise is to present the topics in the simplest way, not only to understand how the dispersion curves are built but also how these curves must be interpreted

A numerical study on the aerodynamic performance of building cross-sections using corner modifications

A numerical investigation is performed in this work in order to evaluate the aerodynamic performance of building cross-section configurations by using corner modifications. The CAARC tall building model is utilized here as reference geometry, which is reshaped considering chamfered and recessed corners. The numerical scheme adopted in this work is presented and simulations are carried-out to obtain the wind loads on the building structures by means of aerodynamic coefficients as well as the flow field conditions near the model’s location. The explicit two-step Taylor-Galerkin scheme is employed in the context of the finite element method, where eight-node hexahedral finite elements with one-point quadrature are used for spatial discretization. Turbulence is described using the LES methodology, with a dynamic sub-grid scale model. Predictions obtained here are compared with experimental and numerical investigations performed previously. Results show that the use of corner modifications can reduce significantly the aerodynamic forces on the building structures, improve flow conditions near the building locations and increase the Strouhal number, which may have an important influence on aeroelastic effects

Análise dinâmica de uma torre estaiada submetida à tormenta EPS

No presente trabalho faz-se uma análise dinâmica de uma torre treliçada estaiada submetida à tormenta EPS através de um registro de vento obtido a partir de sua componente média registrada experimentalmente in loco e da simulação numérica do espectro de sua componente flutuante. A torre estudada está localizada na Universidade de Passo Fundo, na cidade de Passo Fundo, RS, Brasil. Esta torre se encontra instrumentada, registrando velocidades de vento de forma contínua, sendo possível determinar, nos registros existentes, ventos característicos de tormentas TS e EPS. Conta-se também com a caracterização dinâmica desta torre para a qual foram determinadas suas freqüências naturais de vibração. Para determinar um histórico de vento foi usado um registro anemométrico proveniente de uma tormenta do tipo EPS. A taxa de aquisição utilizada foi baixa, razão pela qual as flutuações do registro experimental foram perdidas. Utilizando expressões teóricas foi possível regenerar a componente flutuante a qual foi somada ao registro anemométrico. A metodologia empregada para realizar esta implementação é um aspecto original do presente trabalho

La expansión urbana de la ciudad de Tandil 1991-2020 mediante el uso del Landscape Expansion Index (LEI)

Los índices del paisaje se han usado comúnmente para cuantificar las formas, magnitudes y patrones de distribución espacial. Existen diversos índices, dentro de los cuales la dinámica del crecimiento urbano es una de ellas. Cuantificar los patrones paisajísticos y analizar sus cambios es esencial para el monitoreo y la evaluación de las consecuencias ecológicas de la urbanización derivadas de los procesos de fragmentación urbana.En este trabajo, se aplica un nuevo índice de expansión urbana (LEI, Landscape Expansion Index), que permite capturar la información acontecida de los procesos espacio-temporales de formación de un patrón de expansión e identifica tres tipos de crecimiento urbano: “de relleno”, “expansión de borde” y “periférico”.Se extrajeron las superficies edificadas y se aplicó LEI sobre ellas en la ciudad de Tandil para los períodos 1991-2001, 2001-2010 y 2010-2020, constatando que el tipo de crecimiento “periférico” es el predominante en los últimos años