Abstracts
| José Luiz Antunes de Oliveira e Sousa
Luiz Fernando Campos Ramos Martha Paul A. Wawrzynek Anthony R Ingraffea |
| Simulation of non-planar crack propagation in structures of concrete and rock |
| The purpose of this paper is to describe features for simulation of crack propagation being implemented in FRANSYS, a fracture simulation system currently under development at the Program of Computer Graphics at Cornell University. Routines for the computation of stress intensity factors for three-dimensional cracks in arbitrary bodies are described. An example application is presented and compared with an analytical solution. Features to update the model to accommodate additional surfaces required by crack propagation are also described. Preliminary results for three-dimensional crack propagation are presented in an example application. |
| Anthony R Ingraffea
Túlio N. Bittencourt José Luiz Antunes de Oliveira e Sousa |
| Automatic fracture propagation for 2D finite element models |
| A strategy for automatic propagation of arbitrary fracture in 2D liner elastic finite element models is presented. This strategy has been implemented in FRANC (Fracture Analysis Code), a CAE system for 2D simulation of solids containing fractures, developed by the Fracture Group at the Program of Computer Graphics at Cornell University. The underlying winged-edge data structure organization enables local modifications of the mesh along the propagation path without losing any unaffected structural information. The propagation process is driven by the linear elastic fracture mechanics concepts. The system includes capabilities to incorporate discontinuities and regenerate the finite element mesh. Some examples, using different approaches to stress intensity factor calculation and mode interaction are presented. |
| José Luiz Antunes de Oliveira e Sousa
Anthony R Ingraffea |
| A numerical energy-based approach for three-dimensional fracture propagation |
| The problem of arbitrary fracture propagation in three-dimensional structures is addressed here. An approach based on the maximization of the potential energy released as the crack propagates is discussed. The approach has been implemented in FRANSYS, Fracture Analysis System, a system for simulation of arbitrary three-dimensional fracture propagation. The propagation process is performed in steps corresponding to specified area increments of propagated crack surface. The new shape which creates this area, and which simultaneously maximizes the total energy released is then found. Semi-automatic rezoning is then performing and the process repeated. Two examples of application are presented for propagation of buried elliptical cracks in Mode I. The extension of the approach for more general cases is discussed. |
| José Luiz Antunes de Oliveira e Sousa
Earlin D. Lutz Anthony R Ingraffea |
| Three-dimensional simulation of hydraulically driven fracture propagation in a rock mass |
| This paper describes numerical simulation of near-wellbore phenomena related to hydraulic fracturing from a perforated wellbore. The objective is to compare numerical results with records of an experiment performed |
| José Luiz Antunes de Oliveira e Sousa
Bruce J. Carter Anthony R. Ingraffea |
| Numerical simulation of three-dimensional hydraulic fracturing using Newtonian and power-law fluids |
| Three-dimensional numerical simulations of hydraulic fracturing processes associated with arbitrarily oriented, cased and perforated wellbores are presented. The objective is to enable the simulation of multiple non-planar fractures in the near-wellbore region of cased and perforated wellbores. A system that couples the structural response of a fractured rock with the flow of a Newtonian or power-law fluid between the fracture walls is described. Example applications are presented and compared to published solutions to validate the system. Capabilities to handle complex geometries are illustrated by examples of propagation of fractures oriented arbitrarily with respect to the in situ stress field. |
| José Luiz Antunes de Oliveira e Sousa
Túlio N. Bittencourt Luiz Fernando C. R. Martha Martha Anthony R Ingraffea |
| Aspectos de modelagem geométrica em simulação tri-dimensional de fraturas em materiais frágeis |
| Este trabalho discute alguns aspectos no desenvolvimento de ferramentas de modelagem para simulação tridimensional de propagaçào de fraturas em materiais frágeis. O trabalho está baseado na experiência do Grupo de Mecânica da Fratura da Universidade Cornell, EUA (CFG-Cornell Fracture Group), neste tipo de desenvolvimento. São abordados problemas de representação de dados para modelagem geométrica e numérica, algoritmos e estratégias computacionais para análises numéricas, comportamento coesivo de fraturamento em materiais cerâmicos e acoplamento fluido-rocha em processos de fraturamento hidráulico para estimulação de reservatórios de petróleo. |
| José Luiz Antunes de Oliveira e Sousa
Anthony Richard Ingraffea |
| An object-oriented system for three-dimensional simulation of hydraulic fracturing processes in rock |
| This paper describes an object oriented system for three-dimensional simulation of hydraulic fracturing processes in rock. The system is inserted in a computational environment for three-dimensional structural modeling of solids containing arbitrary fractures. The linear elastic structural behavior of the rock is coupled to the flow of a Newtonian or a power-law fluid between the fracture walls. Linear Elastic Fracture Mechanics governs fracture stability and geometry evolution. The system has been validated against published solutions, and used in the simulation of non-planar hydraulic fracture propagation in the near-wellbore region of perforated, arbitrarily oriented wellbores. |
| José Luiz Antunes de Oliveira e Sousa
Túlio Nogueira Bittencourt Luiz Fernando Campos Ramos Martha |
| Modelagem Geométrica de propagação tridimensional de fissuras |
| Este trabalho descreve o desenvolvimento e utilização de ferramentas de modelagem de sólidos para simulação tridimensional de propagação de fissuras. São abordados problemas de representação de dados para modelagem geométrica e numérica, e ainda algoritmos e estratégias computacionais para simulações tridimensionais de processos de fraturamento. São apresentados exemplos que ilustram sua aplicação. |
| Philippe Remy Bernard Devloo
José Luiz Antunes de Oliveira e Sousa Cezar Augusto Moteiro Siqueira |
| Sobre a implementação da condição inicial em problemas de poroelasticidade acoplada |
| O estudo de fenômenos poroelásticos em rochas tem se mostrado importante na análise de estabilidade de poços e de processos de fraturamento hidráulico para estimulação de reservatórios petrolíferos. Esse estudo é baseado na teoria da poroelasticidade acoplada, apresentada pela primeira vez em sua forma geral em 1941, por Maurice A. Biot. Em todas as publicações consultadas, referentes à solução numérica do problema de Biot, foram encontradas poucas referências ao tratamento numérico da condição inicial, principalmente quando esta corresponde a um estado compressível. Este trabalho apresenta uma formulação consistente com a realidade física para a aproximação da condição inicial da teoria da poroelasticidade acoplada. A formulação é validada através de exemplos. |
| José Luiz Antunes de Oliveira e Sousa
Philippe Remy Bernard Devloo Cezar Augusto Moteiro Siqueira |
| Um sistema orientado por objetos para a simulação acoplada de efeitos poroelásticos em rochas de reservatório petrolíferos |
| Diversos problemas de Engenharia de Petróleo requerem modelagem precisa de efeitos poroelásticos de rochas. Dentre estes, destacam-se problemas de fraturamento hidráulico e de estabilidade de poços, em que, freqüentemente efeitos poroelásticos são simplesmente ignorados. Fenômenos não satisfatoriamente explicados sob hipóteses simplificadoras apontam para a necessidade de se desenvolver meios para que efeitos poroelásticos possam ser facilmente simulados. Neste trabalho é descrita a implementação de funcionalidades para a simulação de poroelasticidade acoplada,em estado plano de deformações em um ambiente computacional orientado por objetos, empregando a técnica dos elementos finitos. |
| Túlio Nogueira Bittencourt
José Luiz Antunes de Oliveira e Sousa |
| A numerical implementation of J-Integral for elasto-plastic fracture mechanics |
| In this paper, a review of the basic concepts related to the J-Integral is presented. The implementation of the equivalent domain approach for computing J-values is described. In addition, an extension of J-Integral for elasto-plastic problems is discussed and illustrated in example applications. Results for generalized yielding problems are provided. |
| José Luiz Antunes de Oliveira e Sousa
Túlio Nogueira Bittencourt Luiz Fernando Campos Ramos Martha |
| Simulação tridimensional de propagação de fissuras não planas em sólidos de geometria arbitrária |
| O objetivo deste trabalho é a implementação de funcionalidades básicas para propagação de fissuras em um ambiente computacional para análise tridimensional de sólidos. São apresentadas rotinas para o cálculo de fatores de intensidade de tensões em fissuras não planas em sólidos arbitrários. Funcionalidades para determinar a descrição geométrica de superfícies adicionais criadas pela propagação de fissuras são também descritas. São apresentados exemplos de aplicação, validados por soluções analíticas. |
| Túlio Nogueira Bittencourt
Paul A. Wawrzynek Anthony R. Ingraffea José Luiz Antunes de Oliveira e Sousa |
| Quasi-automatic simulation of crack propagation for 2D LEFM problems |
| A strategy for quasi-automatic simulation of propagation of arbitrary cracks in two-dimensional, linear elastic finite element models is presented. This strategy has been implemented in FRANC2D (FRacture ANalysis Code 2D). An underlying winged-edge data structure enables automatic local modifications of the mesh along the propagation of any unaffected structural information. The finite element mesh is locally regenerated after each step of propagation by means of a robust remeshing algorithm. The propagation process is driven by linear elastic fracture mechanics concepts which are used to calculate mixed-mode stress intensity factors, predict incremental changes in trajectory, and assess local crack stability. Crack trajectories, obtained for different theories, are presented and favorably compared to experimentally obtained paths |
| Túlio Nogueira Bittencourt
José Luiz Antunes de Oliveira e Sousa |
| Cohesive crack propagation in a ceramic composite beam |
| The application of the fictitious cohesive crack model for two-dimensional problems is explored. The use of interface elements and the finite element method is considered. A defined crack path approach is employed to simulate the propagation process. The fracture zone propagation is closely associated to the interface constitutive model. An example problem for a fiber-reinforced ceramic is presented to illustrate the simulation procedure. The cohesive crack zone is represented by Evans’ model, where fiber bridging and pull-out effects are considered. |
| Romero Gomes Silva Araújo
José Luiz Antunes de Oliveira e Sousa Mauro Bloch |
| Experimental investigation on the influence of temperature on the mechanical properties of reservoir rocks |
| This paper reports an investigation on mechanical properties of reservoir rocks obtained in laboratory at room temperature, and their pertinence to characterize the actual rock behavior under normal downhole or steam injection conditions. The investigation was based on triaxial tests performed by a servo-controlled system on samples of friable sandstones cored from a reservoir in the Potiguar Basin, Northeastern Brazil. The samples were tested at 24° C, 80° C and 150° C, with confining pressure varying from 2.5MPa to 20MPa. A finite element elastic-plastic analysis of wellbore stability was performed using mechanical properties obtained at these temperatures, showing quite different yielding zones. Although the results obtained so far are not sufficient to characterize completely these effects, they indicate that a more appropriate range of temperature must be used in laboratory to better represent real downhole and steam injection conditions. |
| José Eduardo de Lima Garcia
José Luiz Antunes de Oliveira e Sousa |
| A quasi-analytical model for three-dimensional analysis of hydraulic fracture propagation in reservoir rocks |
| The development of a quasi-analytical pseudo-three-dimensional model (Q3DFRAC) is presented. The fracture is assumed planar and elliptical. The structural response of the rock (strains, stresses, stress intensity factors, etc.), are computed assuming that the net pressure in the fracture is described by a third degree polynomial in two variables, according to analytical expressions developed by Shah and Kobayashi. These assumptions were previously used by Palmer, Luiskutty, Boutéca and Rueda, varying the number of polynomial terms. The model proposed here is based on Rueda’s work, using all the terms respecting symmetry about the wellbore axis. An alternative approach is presented to model leakoff and the average apparent viscosity for non-Newtonian fluids. Simulations with two different fracture propagation criteria, based on stress intensity factors, are presented and compared. |
| José Luiz Antunes de Oliveira e Sousa
Philippe Remy Bernard Devloo Marcelo Utiyama |
| A Formulation for Hydraulic Fracture Propagation in a PoroelasticMedium |
| This paper draws on the simulation of hydraulic fracturing processes combining a model for fluid flow in the fracture with Biot’s model of coupled poroelasticity for the rock behavior. The theoretical background for the computational implementation is discussed. |
| Túlio Nogueira Bittencourt
José Luiz Antunes de Oliveira e Sousa |
| Modeling of crack propagation in fiber reinforced composites through a cohesive crack approach based on micro-mechanical effects |
| In this paper the application of the fictitious cohesive crack model for fiber-reinforced ceramic composites is explored. The cohesive crack zone is represented by Evans’ model, where fiber bridging and pull-out effects are considered. Bi-dimensional problems are studied. The use of interface elements and the finite element method is considered. A pre-defined crack path approach is employed to simulate the propagation process. The propagation of the fracture zone is closely related to the interface constitutive model associated with micro-mechanical effects. An example problem for a fiber-reinforced ceramic beam is presented to illustrate the modelling procedure |
| José Luiz Antunes de Oliveira e Sousa
Aluizio Fontana Margarido |
| Análise estrutural de pontes estaiadas em teoria de segunda ordem |
| A não linearidade geométrica conduz a variações inferiores a 15% em relação à análise linear em pontes estaiadas, com o que resultados suficientemente precisos podem ser obtidos mesmo com hipóteses simplificadoras. Neste trabalho a ponte estaiada é analisada como um pórtico plano onde as equações de equilíbrio e de compatibilidade são estabelecidas com base na configuração deformada. As relações entre esforços e deslocamentos nas extremidades de uma barra são estabelecidas com base nas ordenadas de sua linha elástica. O estai é simulado por uma barra reta, em cuja rigidez axial é considerada a influência da curvatura devida ao peso próprio, admitido uniformemente distribuído ao longo da barra |
Master of Science Dissertations:
| Luiz Eduardo Teixeira Ferreira, MSc. Dissertation
José Luiz Antunes de Oliveira e Sousa (advisor) |
| Analysis of parameters for fracture toughness of concrete obtained from beam tests (in Portuguese) |
| Concrete is a composite that behaves inelasticaly, with failure characterized by softening. Crack in this kind of material is said to be cohesive. The development of an inelastic process zone ahead of the crack front as well as the formation of the cohesive interface, at laboratory level, are directly influenced by the specimen size. The effect of the specimen scale on the Fracture Energy, GC, for concrete and other cementitious materials has been addressed by several investigators in the last two decades. Important advances were accomplished towards the validation of models that conduct to the determination of the Fracture Energy, independently of the so called Size Effect. In this work the Size Effect on Fracture Energy and Fracture Toughness, KIC, is investigated for plain concrete, using three-point bend tests on specimens with initial through notches. The investigation is conducted using similar beams, with height varying from 3 cm to 12 cm. The Fracture Toughness is determined using the Two-Parameter Crack Model and the Effective Crack Model suggested by RILEM (International Union of Testing and Research Laboratories for Materials and Structures), and the linearization procedure proposed by ISRM (International Society of Rock Mechanics). The Fracture Energy is determined using the Size Effect Model, also proposed by RILEM. The Fracture Toughness values obtained from the laboratory tests appear to be strongly influenced by the Size Effect, within the range of sizes investigated. In this dissertation the phenomenon of relaxation, observed at peak load under a constant CMOD condition, was investigated and associated to a possible break down of the cohesive interface. Under these circumstances, the length of the cohesive interface at peak load was modeled. The results of Fracture Toughness originated from these lengths appear to be almost constant, independently of specimen size. |
| Armando Diório Filho
José Luiz Antunes de Oliveira e Sousa (advisor) |
| An object oriented computational environement for the analysis of three-dimensional frames (in Portuguese) |
| This dissertation describes the development of an object oriented system for the numerical analysis of three-dimensional framed structures. The system consists of a library of object classes, written in C++ language, which are designed to be used in different applications, thus allowing that new theories and ideas be implemented with most of the work concentrated in the new features under development. The result is an optimization of the time and work necessary for the implementation of new funcionalities to the system. An example of this characteristic of the object oriented philosophy observed in the development of this work is the use of classes for the solution of linear systems, developed, tested and optimized by other member of the research group. The developed system was tested and validated by comparison with a largely used commercial code. Due to the characteristics inherent to the object oriented philosophy, and the design bases for the developed system, extensions to handle problems involving geometric and physical nonlinearities, dynamic analysis, structural optimization and other problems related to framed structures can be readily implemented. |
| Antonio Carlos dos Santos
José Luiz Antunes de Oliveira e Sousa (advisor) |
| Determination of concrete fracture toughness using short rod specimens (in Portuguese) |
| A metodology was developed for the detemination fracture toughness (KIc) of concrete, by deformation-controlled tests on short-rod specimens, according to ISRM recommended procedures. Four groups of 18 short rod specimens were tested, varying strength and coarse aggregate size. Each group was tested at three different ages. Simultaneously, tests on 150 x 300 mm cylindical specimens were conducted to obtain compressive and tensile strengths. The metodology for determination shows adequate for determination fracture toughness (KIc) for concrete. The results indicate dependency of fracture toughness on size of course agregates, compressive strength and concrete age. |
| Paulo Dore Fernandes
José Luiz Antunes de Oliveira e Sousa (advisor) |
| A semi-analytical pseudo three-dimensional model for analysis of induced fractures in rock, |