Abstract

This paper deals with the construction of analytic-numerical solutions of random linear differential equations by means of a power series method. Sufficient conditions for the mean square convergence of the series solution are established. The mean and variance functions of the approximate solution stochastic process are also computed. Lastly, several illustrative examples where the proposed methods is compared with respect to Monte Carlo approximations are included.

Abstract

Packing- particle methods to simulate compact and spongy bone-tissue are presented. The methods ara based on moddified front-advance algorithms, able to reduce the density of large sets of circles or spheres. As well, elliptical shape holes to represent trabeculae in spongy bone are allowed. Some preliminary results of bone modeling using the methods proposed are presented and discussed.

Abstract

This work deals with the computational modeling of Friction Stir Welding (FSW) processes including the discretization of the tools. The mechanical problem has been solved using a Stokes viscoplastic flow model with a suitable constitutive law for the range of deformation rates induced in the process. The thermal problem has been solved using an advection-diffusion model using an ALE formulation. Finite element formulations have been implemented for both problems. Two-dimensional and three-dimensional FSW problems have been solved under a number of particular process conditions and a particular tool geometry. Results obtained for the material flow around the tool have been compared with published experimental results, obtained under the same process conditions. A good correlation has been obtained between the numerical and the experimental results. The patterns of the material flow reported in the references, which were obtained using experimental techniques with tracers, have been identified performing the post-process of the results obtained for the material flow using computational visualization techniques with tracers. The role played by those visualization techniques in the analysis of the material flow around the tool, leading to a better understanding of the phenomena involved in the FSW process, is pointed out.

Abstract

This article describes an implementation of the Local Discontinuous Galerkin (LDG) method applied to a general elliptic boundary value problem in 2D. The implementation takes advantage of some intrinsic properties of the method, in particular, the use of non conforming meshes with an arbitrary but fixed number of hanging nodes and polynomial approximations with variable degree. A detailed description of efficient data structures yielding a fast assembly of the linear system in its mixed formulation is presented. This implementation can be used as a model for hp adaptive codes.

Abstract

Neste trabalho de pesquisa desenvolve-se um estudo paramétrico para análise da resposta dinámica de pontes rodoviárias de concreto armado, devido à travessia de comboios de veículos sobre o pavimento irregular dessas obras-de-arte. O estudo é feito com base em uma metodologia de análise, no dominio do tempo, de acordo com um modelo estatástico. O modelo matemático empregado para simular o comportamento do sistema "veículo-ponte" considera a participação da massa e da rigidez das viaturas na definição das freqüências do sistema e, conseqüentement, a força de interação entre os veículos e a ponte é afetada pela flexibilidade desta. A ponte é modelada a partir do emprego de elementos finitos de barra unidimensionais e discretizado com massas concentradas e flexibilidade distribuída. O modelo de veículo empregado baseia-se no veículo TB-12 preconizado pela norma brasileira NBR 7188. Este veículo é simulado por sistemas de massas, molas e amortecedores sendo descrito por graus de liberdade à translaçãó e rotação no plano. As irregularidades da pista são definidas por um modelo não-determinístico com base na densidade espectral do pavimento. O carregamento sobre a ponte é constituído por sucessões de vículos deslocando-se com velocidade constante sobre a obra. Devido à própria natureza das irregularidades da pista e do comboio de veículos, atenção especial é concetrada na fase permanente da resposta do sistema. São estudadas as respostas de dois modelos estruturais existentes, com base em tabuleiros isitáticos, em concreto armado, com e sem balanços, em seção do tip "T" e duplo "T", respectivamente, em termos de deslocamentos e esforços nas seçõesonde ocorrem os efeitos máximos. As conclusões do trabalho versam sobre a influência da velocidade, espaçamento e do número de veículos, referentes a situações distintas de carregamento, no que tange a resposta dinâmica das pontes rodoviárias de concreto armado. A magnitude dos efeitos dinâmicos associados à interação dos veículos com o pavimento irregular também é investigada.

Abstract

Neste trabalho a dependencia da capacidade de rotaçao plástica com relaçao às características físicas, geométricas e construtivas das vigas de concreto armado, ou dependencia estrutural da capacidade de rotaçao plástica em vigas de concreto armado, conforme definiçao por Bigaj [1] é avaliada através do Método dos Elementos Finitos. O termo dependencia estru- tural refere-se a relaçao necessária ou interaçao entre o comportamento da estrutura e seus materiais constituintes, tais como concreto e aço ou mesmo fatores geométricos como efeito de escala. O objetivo é conseguir uma melhor compreensao sobre o comportamento nao-linear de elementos de concreto armado e executar estudos paramétricos extensivos por meio do modelo analítico desenvolvido por Bigaj [1] afim de analisar o fenómeno da capacidade de rotaçao plástica em elementos de concreto armado. Supoe-se que somente a ruptura por flexao é relevante devido à capacidade resistente suficiente do elemento ao cisalhamento e torçao. O trabalho inicia-se com uma revisao de literatura a respeito do desenvolvimento da rotaçao plástica em vigas de concreto armado, atentando tanto para aspectos experimentais quanto a aspectos de modelagem analítica. Dá-se enfase especial na introduçao da dependencia estrutural da capacidade de rotaçao plástica em vigas de concreto armado. A dependencia do tamanho do elemento e a propriedade dos materiais de construçaao sao enfatizados. Os componentes essenciais do modelo de Bigaj para o cálculo da capacidade de rotaçao plástica sao discutidos. O comportamento da rotaçao plástica é analisado levando-se em consideraçao a deformaçao localizada em zonas de dano da regiao plastificada. O Modelo de Fissura Fictícia e o Modelo de Zona de Dano na Compressao sao adaptados à Mecanica da Fratura a fim de modelar o comportamento do concreto a traçao e compressao respectivamente. Nas simulaçoes numéricas utilizou-se o programa FEMOOP, um "solver" desenvolvido segundo o Método Elementos Finitos e aplicado para avaliar a ductilidade em vigas segundo uma análise 2D. Exemplos de aplicaçaão são apresentados para avaliar o potencial das implementações cujos modelos forma gerados com o programa GiD desenvolido pelo CIMNE.

Abstract

The effects of the thermal properties of three flooring materials on the spread rate of polymer melt over the surface were studied using a model based on the Particle Finite Element Method (PFEM). The high thermal conductivity of steel keeps the steel floor at a nearly uniform temperature throughout, whereas the ceramic and oak floors are able to sustain a higher temperature beneath the point at which the hot melt is dripping onto the surface. In general, the spread rate is controlled by the viscosity at the outer edges of the melt pool. The spread rate over steel is therefore fastest, especially for a thin floor that rapidly increases in temperature. The low thermal inertia of oak results in rapid changes in surface temperature, which traps the heat close to the interface between the floor and the melt and maintains a high temperature and low viscosity in the center of the melt pool. The ceramic floor transports heat more readily and may develop a hot spot underneath. The material properties of ceramic lie between those of oak and steel, but although the spread rate over a steel floor is always faster than over ceramic, the spread rate over oak may not always be slower.

Abstract

The design and evaluation of parachute-payload systems is an important field of applications in which numerical analysis tools can make very important contributions. This work describes new numerical developments carried out at CIMNE in this field, which involve a coupled fluid-structural solver intended for the unsteady simulation of ram-air type parachutes and a set of complementary tools aimed at studying trajectory and control systems effects. For an efficient solution of the aerodynamic problem, an unsteady panel method has been chosen exploiting the fact that large areas of separated flow are not expected under nominal flight conditions of ram-air parachutes. Besides, a dynamic explicit solver based on a finite element technique is chosen for the structure. This approach yields a robust solution even when highly non-linear effects due to large displacements and material asymmetric behaviours are present. The numerical results show considerable accuracy and robustness. An added benefit of the proposed aerodynamic and structural techniques is that they can be easily vectored and thus suitable for use in parallel architectures. The main features of the developed computational tools are described in this work and several numerical examples are provided to illustrate the good performance and potential of the proposed techniques. Further improvements of the methodology being carried out and future lines of investigation are also presented.

Abstract

We present some developments in the formulation of the Particle Finite Element Method (PFEM) for analysis of complex coupled problems in fluid and solid mechanics accounting for fluid-structure interaction and coupled thermal effects. The PFEM uses an updated Lagrangian description to model the motion of nodes (particles) in both the fluid and the structure domains. Nodes are viewed as material points which can freely move and even separate from the main analysis domain representing, for instance, the effect of water drops. A mesh connects the nodes defining the discretized domain where the governing equations are solved as in the standard FEM. The necessary stabilization for dealing with the incompressibility of the fluid is introduced via the finite calculus (FIC) method. An incremental iterative scheme for the solution of the non linear transient coupled fluid-structure problem is described. Extensions of the PFEM to allow for frictional contact conditions at fluid-solid and solid-solid interfaces via mesh generation are described. A simple algorithm to treat erosion in the fluid bed is presented. Examples of application of the PFEM to solve a number of coupled problems such as the effect of large wave on structures, the large motions of floating and submerged bodies, bed erosion situations and melting and dripping of polymers under the effect of fire are given.

Abstract

The numerical modeling of historic buildings is an essential tool for understanding the structural behavior, even more whit the aim is to assume an analysis for conservation and / or rehabilitation. At present time, most building’s numerical simulation software is divided into three parts: the preprocessor, which prepares all the necessary information (geometry, boundary conditions, loads, etc.), the Analysis, where all calculations take place (FEM) and the postprocessing where decisions are taking based on the analysis of the results obtained in the previous steps (Muñoz, Maristany 1999). At that last point is, where the user of the computer programs usually find limitations in the graphical interpretation of the results. Some numerical results with endless list of numbers are not the best way to address the problem and its graphical output is not yet fully developed. That is, graphic interface is still very basic, let alone a real-time dynamic visualization in 3D. It`s important to have both powerful hardware and software tools to visualize the obtained results. Currently, there are emerging many structural analysis programs that have highly advanced postprocessing, but they still display limitations in space, they operate only on 2 or 3 dimensions with space constraints. For this reason, this paper seeks to integrate different current computer programs with 3D graphical representation. Thus, the visualization of numerical results (tension, stress and strain values) can be much more interesting. This is to enable users to virtually navigate in real time, through any 3D structure and better understand their behavior. In short, this research aims to develop an interface between the computer programs of structural calculations and representation software with virtual 3D graphics (vrml- virtual reality modeling language), with practical application to historic buildings. As a closure for the paper we develop a practical example based on Mexico City’s Cathedral tabernacle.