Artur Portela - Academia.edu (original) (raw)

Papers by Artur Portela

Research paper thumbnail of High Performance of Local Meshfree Method with Reduced Integration

Boundary Elements and other Mesh Reduction Methods XLI, Sep 11, 2018

Research paper thumbnail of A local meshless analysis of dynamics problems / Uma análise local desordenada dos problemas dinâmicos

Brazilian Journal of Development, 2021

This paper is concerned with new formulations of local meshfree numerical method, for the solutio... more This paper is concerned with new formulations of local meshfree numerical method, for the solution of dynamic problems in linear elasticity, Integrated Local Mesh Free (ILMF) method. The key attribute of local numerical methods is the use of a modeling paradigm based on a node-by-node calculation, to generate the rows of the global system of equations of the body discretization. In the local domain, assigned to each node of a discretization, the work theorem is kinematically formulated, leading thus to an equation of mechanical equilibrium of the local node, that is used by local meshfree method as the starting point of the formulation. The main feature of this paper is the use of a linearly integrated local form of the work theorem. The linear reduced integration plays a key role in the behavior of local numerical methods, since it implies a reduction of the nodal stiffness which, in turn, leads to an increase of the solution accuracy. As a consequence, the derived meshfree and fin...

Research paper thumbnail of Approximation Methods

Finite Elements Using Maple, 2002

Research paper thumbnail of Introduction to Maple

Finite Elements Using Maple, 2002

Maple is a symbolic computational system. This means that it does not require numerical values fo... more Maple is a symbolic computational system. This means that it does not require numerical values for all variables, as numerical systems do, but manipulates information in a symbolic or algebraic manner, maintaining and evaluating the underlying symbols, like words and sentence-like objects, as well as evaluates numerical expressions. As a complement to symbolic operations, Maple provides the user with a large set of graphic routines, numerical algorithms and a comprehensive programming language.

Research paper thumbnail of Shape optimal design of structures with dual boundary elements

This paper is concerned with the numerical implementation of the dual boundary element method for... more This paper is concerned with the numerical implementation of the dual boundary element method for shape optimal design of two-dimensional linear elastic structures. The design objective is to minimize the structural compliance, subject to an area constraint. Sensitivities of objective and constraint functions, derived by means of Lagrangean approach and the material derivative concept with an adjoint variable technique, are computed through analytical expressions that arise from optimality conditions. The dual boundary element method, used for the discretization of the state problem, applies the stress equation for collocation on the design boundary and the displacement equation for collocation on other boundaries. The use of the stress boundary integral equation, discretized with discontinuous quadratic elements, allows an efficient and accurate computation of stresses on the design boundary. The perturbation field is described with linear continuous elements, in which the position of each node is defined by a design variable. Continuity along the design boundary is assured by forcing the end points of each discontinuous boundary element to be coincident with a design node. The optimization problem is solved by the modified method of feasible directions available in the program ADS. Examples of a plate with a hole are analyzed with the present method, for different loading conditions. The accuracy and efficiency of the implementation described herein make this formulation ideal for the study of shape optimal design of structures.

Research paper thumbnail of Local Mesh Free Methods in Linear Elasticity and Fracture Mechanics

Fundamental Concepts and Models for the Direct Problem

Research paper thumbnail of Optimized Mesh-free Analysis for the Singularity Subtraction Technique of Linear Elastic Fracture Mechanics

Global journal of research in engineering, Jan 11, 2022

Research paper thumbnail of Método Sem Malha Local Com Integração Reduzida Para Configuração Nodal Com Grande Irregularidade

Tópicos em ciências exatas e da Terra, 2021

Research paper thumbnail of Generalized-strain mesh-free method (GSMF) for two-dimensional elasticity problems

Research paper thumbnail of Comparative Study of the Weak-Form Collocation Meshless Formulation and Other Meshless Methods

Abstract. This paper is concerned with the numerical comparison of the weak-form collocation, a n... more Abstract. This paper is concerned with the numerical comparison of the weak-form collocation, a new local meshless method, and other meshless methods, for the solution of two-dimensional problems in linear elasticity. Four methods are compared, namely, the Generalized-Strain Mesh-free (GSMF) formulation, the Rigid-body Displacement Mesh-free (RBDMF) formulation, the Element-free Galerkin (EFG) and the Meshless Local Petrov-Galerkin Finite Volume Method (MLPG FVM). While the RBDMF, EFG and MLPG FVM rely on integration and quadrature process to obtain the stiffness matrix, the GSMF is completely integration free, working as a weighted-residual weak-form collocation. This weak-form collocation readily overcomes the well-known difficulties of the strong-form collocation, such as low accuracy and instability of the solution. A numerical example was analyzed with these methods, in order to assess the accuracy and the computational effort. The results obtained are in agreement with those of...

Research paper thumbnail of Computational Mechanics

Finite Elements Using Maple, 2002

Research paper thumbnail of Local Meshfree Method Optimization with Genetic Algorithms

Coleção desafios das engenharias: Engenharia de computação 3

Research paper thumbnail of Trefftz boundary element method applied to fracture mechanics

The linear elastic problem is solved by means of Trefftz functions which automatically satisfy th... more The linear elastic problem is solved by means of Trefftz functions which automatically satisfy the elasticity equations in a 2D domain. Using Kolosov–Muskhelishvili's complex variable representation, complex potentials are expanded in power series. Trial elementary elastic ...

Research paper thumbnail of Efficient boundary element analysis of sharp notched plates

Research paper thumbnail of Dual boundary element incremental analysis of crack propagation

Research paper thumbnail of Boundary solutions for the linear theory of structures and the generalization of the work theorem

Research paper thumbnail of Dual boundary element analysis of cracked plates: singularity subtraction technique

Research paper thumbnail of Formulation of local numerical methods in linear elasticity

Multidiscipline Modeling in Materials and Structures

PurposeThis paper is concerned with new formulations of local meshfree and finite element numeric... more PurposeThis paper is concerned with new formulations of local meshfree and finite element numerical methods, for the solution of two-dimensional problems in linear elasticity.Design/methodology/approachIn the local domain, assigned to each node of a discretization, the work theorem establishes an energy relationship between a statically admissible stress field and an independent kinematically admissible strain field. This relationship, derived as a weighted residual weak form, is expressed as an integral local form. Based on the independence of the stress and strain fields, this local form of the work theorem is kinematically formulated with a simple rigid-body displacement to be applied by local meshfree and finite element numerical methods. The main feature of this paper is the use of a linearly integrated local form that implements a quite simple algorithm with no further integration required.FindingsThe reduced integration, performed by this linearly integrated formulation, play...

Research paper thumbnail of Performance of the Weak-form Collocation Meshless Formulation

Proceedings of the 6th International Symposium on Solid Mechanics

Research paper thumbnail of Cracked plate analysis with the dual boundary element method and Williams׳ eigenexpansion

Engineering Analysis with Boundary Elements

ABSTRACT This paper provides a numerical verification that the singular term of Williams׳ series ... more ABSTRACT This paper provides a numerical verification that the singular term of Williams׳ series eigenexpansion can be used as a singular solution, valid in the neighborhood of each crack tip, in a single-region dual boundary element analysis of two-dimensional piece-wise flat multi-cracked plates, either with edge or internal cracks, in mixed-mode deformation, as an intermediate and necessary research step towards the implementation of the singularity subtraction technique.

Research paper thumbnail of High Performance of Local Meshfree Method with Reduced Integration

Boundary Elements and other Mesh Reduction Methods XLI, Sep 11, 2018

Research paper thumbnail of A local meshless analysis of dynamics problems / Uma análise local desordenada dos problemas dinâmicos

Brazilian Journal of Development, 2021

This paper is concerned with new formulations of local meshfree numerical method, for the solutio... more This paper is concerned with new formulations of local meshfree numerical method, for the solution of dynamic problems in linear elasticity, Integrated Local Mesh Free (ILMF) method. The key attribute of local numerical methods is the use of a modeling paradigm based on a node-by-node calculation, to generate the rows of the global system of equations of the body discretization. In the local domain, assigned to each node of a discretization, the work theorem is kinematically formulated, leading thus to an equation of mechanical equilibrium of the local node, that is used by local meshfree method as the starting point of the formulation. The main feature of this paper is the use of a linearly integrated local form of the work theorem. The linear reduced integration plays a key role in the behavior of local numerical methods, since it implies a reduction of the nodal stiffness which, in turn, leads to an increase of the solution accuracy. As a consequence, the derived meshfree and fin...

Research paper thumbnail of Approximation Methods

Finite Elements Using Maple, 2002

Research paper thumbnail of Introduction to Maple

Finite Elements Using Maple, 2002

Maple is a symbolic computational system. This means that it does not require numerical values fo... more Maple is a symbolic computational system. This means that it does not require numerical values for all variables, as numerical systems do, but manipulates information in a symbolic or algebraic manner, maintaining and evaluating the underlying symbols, like words and sentence-like objects, as well as evaluates numerical expressions. As a complement to symbolic operations, Maple provides the user with a large set of graphic routines, numerical algorithms and a comprehensive programming language.

Research paper thumbnail of Shape optimal design of structures with dual boundary elements

This paper is concerned with the numerical implementation of the dual boundary element method for... more This paper is concerned with the numerical implementation of the dual boundary element method for shape optimal design of two-dimensional linear elastic structures. The design objective is to minimize the structural compliance, subject to an area constraint. Sensitivities of objective and constraint functions, derived by means of Lagrangean approach and the material derivative concept with an adjoint variable technique, are computed through analytical expressions that arise from optimality conditions. The dual boundary element method, used for the discretization of the state problem, applies the stress equation for collocation on the design boundary and the displacement equation for collocation on other boundaries. The use of the stress boundary integral equation, discretized with discontinuous quadratic elements, allows an efficient and accurate computation of stresses on the design boundary. The perturbation field is described with linear continuous elements, in which the position of each node is defined by a design variable. Continuity along the design boundary is assured by forcing the end points of each discontinuous boundary element to be coincident with a design node. The optimization problem is solved by the modified method of feasible directions available in the program ADS. Examples of a plate with a hole are analyzed with the present method, for different loading conditions. The accuracy and efficiency of the implementation described herein make this formulation ideal for the study of shape optimal design of structures.

Research paper thumbnail of Local Mesh Free Methods in Linear Elasticity and Fracture Mechanics

Fundamental Concepts and Models for the Direct Problem

Research paper thumbnail of Optimized Mesh-free Analysis for the Singularity Subtraction Technique of Linear Elastic Fracture Mechanics

Global journal of research in engineering, Jan 11, 2022

Research paper thumbnail of Método Sem Malha Local Com Integração Reduzida Para Configuração Nodal Com Grande Irregularidade

Tópicos em ciências exatas e da Terra, 2021

Research paper thumbnail of Generalized-strain mesh-free method (GSMF) for two-dimensional elasticity problems

Research paper thumbnail of Comparative Study of the Weak-Form Collocation Meshless Formulation and Other Meshless Methods

Abstract. This paper is concerned with the numerical comparison of the weak-form collocation, a n... more Abstract. This paper is concerned with the numerical comparison of the weak-form collocation, a new local meshless method, and other meshless methods, for the solution of two-dimensional problems in linear elasticity. Four methods are compared, namely, the Generalized-Strain Mesh-free (GSMF) formulation, the Rigid-body Displacement Mesh-free (RBDMF) formulation, the Element-free Galerkin (EFG) and the Meshless Local Petrov-Galerkin Finite Volume Method (MLPG FVM). While the RBDMF, EFG and MLPG FVM rely on integration and quadrature process to obtain the stiffness matrix, the GSMF is completely integration free, working as a weighted-residual weak-form collocation. This weak-form collocation readily overcomes the well-known difficulties of the strong-form collocation, such as low accuracy and instability of the solution. A numerical example was analyzed with these methods, in order to assess the accuracy and the computational effort. The results obtained are in agreement with those of...

Research paper thumbnail of Computational Mechanics

Finite Elements Using Maple, 2002

Research paper thumbnail of Local Meshfree Method Optimization with Genetic Algorithms

Coleção desafios das engenharias: Engenharia de computação 3

Research paper thumbnail of Trefftz boundary element method applied to fracture mechanics

The linear elastic problem is solved by means of Trefftz functions which automatically satisfy th... more The linear elastic problem is solved by means of Trefftz functions which automatically satisfy the elasticity equations in a 2D domain. Using Kolosov–Muskhelishvili's complex variable representation, complex potentials are expanded in power series. Trial elementary elastic ...

Research paper thumbnail of Efficient boundary element analysis of sharp notched plates

Research paper thumbnail of Dual boundary element incremental analysis of crack propagation

Research paper thumbnail of Boundary solutions for the linear theory of structures and the generalization of the work theorem

Research paper thumbnail of Dual boundary element analysis of cracked plates: singularity subtraction technique

Research paper thumbnail of Formulation of local numerical methods in linear elasticity

Multidiscipline Modeling in Materials and Structures

PurposeThis paper is concerned with new formulations of local meshfree and finite element numeric... more PurposeThis paper is concerned with new formulations of local meshfree and finite element numerical methods, for the solution of two-dimensional problems in linear elasticity.Design/methodology/approachIn the local domain, assigned to each node of a discretization, the work theorem establishes an energy relationship between a statically admissible stress field and an independent kinematically admissible strain field. This relationship, derived as a weighted residual weak form, is expressed as an integral local form. Based on the independence of the stress and strain fields, this local form of the work theorem is kinematically formulated with a simple rigid-body displacement to be applied by local meshfree and finite element numerical methods. The main feature of this paper is the use of a linearly integrated local form that implements a quite simple algorithm with no further integration required.FindingsThe reduced integration, performed by this linearly integrated formulation, play...

Research paper thumbnail of Performance of the Weak-form Collocation Meshless Formulation

Proceedings of the 6th International Symposium on Solid Mechanics

Research paper thumbnail of Cracked plate analysis with the dual boundary element method and Williams׳ eigenexpansion

Engineering Analysis with Boundary Elements

ABSTRACT This paper provides a numerical verification that the singular term of Williams׳ series ... more ABSTRACT This paper provides a numerical verification that the singular term of Williams׳ series eigenexpansion can be used as a singular solution, valid in the neighborhood of each crack tip, in a single-region dual boundary element analysis of two-dimensional piece-wise flat multi-cracked plates, either with edge or internal cracks, in mixed-mode deformation, as an intermediate and necessary research step towards the implementation of the singularity subtraction technique.