Bruna Caroline Campos, Felicio Bruzzi Barros and Samuel Silva Penna
The aim of this paper is to present a novel data transfer technique to simulate, by G/XFEM, a cohesive crack propagation coupled with a smeared damage model. The efficiency of…
Abstract
Purpose
The aim of this paper is to present a novel data transfer technique to simulate, by G/XFEM, a cohesive crack propagation coupled with a smeared damage model. The efficiency of this technique is evaluated in terms of processing time, number of Newton–Raphson iterations and accuracy of structural response.
Design/methodology/approach
The cohesive crack is represented by the G/XFEM enrichment strategy. The elements crossed by the crack are divided into triangular cells. The smeared crack model is used to describe the material behavior. In the nonlinear solution of the problem, state variables associated with the original numerical integration points need to be transferred to new points created with the triangular subdivision. A nonlocal strategy is tailored to transfer the scalar and tensor variables of the constitutive model. The performance of this technique is numerically evaluated.
Findings
When compared with standard Gauss quadrature integration scheme, the proposed strategy may deliver a slightly superior computational efficiency in terms of processing time. The weighting function parameter used in the nonlocal transfer strategy plays an important role. The equilibrium state in the interactive-incremental solution process is not severely penalized and is readily recovered. The advantages of such proposed technique tend to be even more pronounced in more complex and finer meshes.
Originality/value
This work presents a novel data transfer technique based on the ideas of the nonlocal formulation of the state variables and specially tailored to the simulation of cohesive crack propagation in materials governed by the smeared crack constitutive model.
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R. de Borst, G.N. Wells and L.J. Sluys
The formulation of finite elements with incompatible discontinuous modes is examined rigorously. Both weak and strong discontinuities are considered. Starting from a careful…
Abstract
The formulation of finite elements with incompatible discontinuous modes is examined rigorously. Both weak and strong discontinuities are considered. Starting from a careful elaboration of the kinematics for both types of discontinuities a comprehensive finite element formulation is derived based on a three‐field variational statement. Similarities and differences are highlighted between the various formulations which ensue.
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William Wells, Bradley Campbell, Yudu Li and Stryker Swindle
Social scientific research is having a substantial impact on eyewitness identification procedural reforms. Police agencies in the USA have changed their eyewitness practices based…
Abstract
Purpose
Social scientific research is having a substantial impact on eyewitness identification procedural reforms. Police agencies in the USA have changed their eyewitness practices based on the results of social scientific research. The purpose of this paper is to contribute new knowledge by using a unique set of data to describe detailed aspects of eyewitness identification procedures conducted as part of robbery investigations in Houston, TX.
Design/methodology/approach
Robbery investigators completed surveys following identification procedures conducted during a six-month period of time. The sample includes 975 identification procedures. The analysis describes important features of identification procedures and places results in the context of existing research.
Findings
Results show that photo spreads were the most frequently used lineup procedure and selection outcomes were similar to recent field studies conducted in the USA. Results also show that the type of procedure, presence of a weapon, cross-race identifications, and viewing opportunity were significantly correlated with selection outcomes.
Originality/value
Police are reforming their eyewitness identification procedures based on findings from social science research. The study measures and describe the characteristics of a large sample eyewitness procedures conducted by investigators in the field.
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Myae Han, Nancy Edwards and Carol Vukelich
The purpose of this chapter is to suggest ways for early childhood teachers to teach science content knowledge, vocabulary, respect, and an appreciation for nature while children…
Abstract
The purpose of this chapter is to suggest ways for early childhood teachers to teach science content knowledge, vocabulary, respect, and an appreciation for nature while children engage in meaningful outdoor nature activities. Science concepts such as nature, life cycle, observation, and experimentation can be woven into outdoor activities as children pretend to be nature scientists. Intentional planning provides teachers with the opportunity to integrate science content knowledge and vocabulary learning during the nature study. The careful selection of content vocabulary related to the scientific process and science content knowledge helps children learn new words in meaningful and developmentally appropriate ways. This chapter provides several examples of outdoor nature activities with science content knowledge and vocabulary embedded into each activity.
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Agustina Felipe, Ruben Sevilla and Oubay Hassan
This study aims to assess the accuracy of degree adaptive strategies in the context of incompressible Navier–Stokes flows using the high-order hybridisable discontinuous Galerkin…
Abstract
Purpose
This study aims to assess the accuracy of degree adaptive strategies in the context of incompressible Navier–Stokes flows using the high-order hybridisable discontinuous Galerkin (HDG) method.
Design/methodology/approach
The work presents a series of numerical examples to show the inability of standard degree adaptive processes to accurately capture aerodynamic quantities of interest, in particular the drag. A new conservative projection is proposed and the results between a standard degree adaptive procedure and the adaptive process enhanced with this correction are compared. The examples involve two transient problems where flow vortices or a gust needs to be accurately propagated over long distances.
Findings
The lack of robustness and accuracy of standard degree adaptive processes is linked to the violation of the free-divergence condition when projecting a solution from a space of polynomials of a given degree to a space of polynomials with a lower degree. Due to the coupling of velocity-pressure in incompressible flows, the violation of the incompressibility constraint leads to inaccurate pressure fields in the wake that have a sizeable effect on the drag. The new conservative projection proposed is found to remove all the numerical artefacts shown by the standard adaptive process.
Originality/value
This work proposes a new conservative projection for the degree adaptive process. The projection does not introduce a significant overhead because it requires to solve an element-by-element problem and only for those elements where the adaptive process lowers the degree of approximation. Numerical results show that, with the proposed projection, non-physical oscillations in the drag disappear and the results are in good agreement with reference solutions.
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Xiaodong Zhang and Tinh Quoc Bui
– The purpose of this paper is to achieve numerical simulation of cohesive crack growth in concrete structures.
Abstract
Purpose
The purpose of this paper is to achieve numerical simulation of cohesive crack growth in concrete structures.
Design/methodology/approach
The extended finite element method (XFEM) using four-node quadrilateral element associated with the fictitious cohesive crack model is used. A mixed-mode traction-separation law is assumed for the cohesive crack in the fracture process zone (FPZ). Enrichments are considered for both partly and fully cracked elements, and it thus makes the evolution of crack to any location inside the element possible. In all. two new solution procedures based on Newton-Raphson method, which differ from the approach suggested by Zi and Belytschko (2003), are presented to solve the nonlinear system of equations. The present formulation results in a symmetric tangent matrix, conveniently in finite element implementation and programming.
Findings
The inconvenience in solving the inversion of an unsymmetrical Jacobian matrix encountered in the existing approach is avoided. Numerical results evidently confirm the accuracy of the proposed approach. It is concluded that the developed XFEM approach is especially suitable in simulating cohesive crack growth in concrete structures.
Research limitations/implications
Multiple cracks and crack growth in reinforced concretes should be considered in further studies.
Practical implications
The research paper presents a very useful and accurate numerical method for engineering application problems that has ability to numerically simulate the cohesive crack growth of concrete structures.
Originality/value
The research paper provides a new numerical approach using two new solution procedures in solving nonlinear system of equations for cohesive crack growth in concrete structures that is very convenient in programming and implementation.
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‐ One of the consequences of the present long period of economic depression, which has been felt with particular severity by most Third World countries, has been a necessary…
Abstract
‐ One of the consequences of the present long period of economic depression, which has been felt with particular severity by most Third World countries, has been a necessary critical reassessement of many development strategies. Especially in Africa, the balance sheet between efforts and results has not been very encouraging. The massive industrialization programmes and the large projects of the last three decades have neither helped to achieve a more competitive production nor have introduced widespread prosperity, as hoped. Gradually the accent is now shifting toward new “soft options”, one of which is tourism. We remember that only 15–20 years ago many African governments or international development agencies were still considering tourism as a marginal economic activity, to be left to poor nations without much prospects for industrialization. Since then much has changed and ‐ especially in the present post‐industrial economies ‐ tourism and the whole gamut of other leisure industries have become one of the most dynamic fields of expansion, even in the developing world.
Ramon Codina, Javier Principe and Matías Ávila
The purpose of this paper is to describe a variational multiscale finite element approximation for the incompressible Navier‐Stokes equations using the Boussinesq approximation to…
Abstract
Purpose
The purpose of this paper is to describe a variational multiscale finite element approximation for the incompressible Navier‐Stokes equations using the Boussinesq approximation to model thermal coupling.
Design/methodology/approach
The main feature of the formulation, in contrast to other stabilized methods, is that the subscales are considered as transient and orthogonal to the finite element space. These subscales are solution of a differential equation in time that needs to be integrated. Likewise, the effect of the subscales is kept, both in the nonlinear convective terms of the momentum and temperature equations and, if required, in the thermal coupling term of the momentum equation.
Findings
This strategy allows the approaching of the problem of dealing with thermal turbulence from a strictly numerical point of view and discussion important issues, such as the relationship between the turbulent mechanical dissipation and the turbulent thermal dissipation.
Originality/value
The treatment of thermal turbulence from a strictly numerical point of view is the main originality of the work.
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Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Council, Reports and Technical Notes of the United States National…
Abstract
Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Council, Reports and Technical Notes of the United States National Advisory Committee for Aeronautics and publications of other similar Research Bodies as issued
Rodrigo Rossi, Marcelo Krajnc Alves and Hazim Ali Al‐Qureshi
The purpose of this paper is to investigate the application of the element‐free Galerkin (EFG) method to the simulation of metal forming processes and to propose a strategy to…
Abstract
Purpose
The purpose of this paper is to investigate the application of the element‐free Galerkin (EFG) method to the simulation of metal forming processes and to propose a strategy to deal with volumetric locking problem in this context.
Design/methodology/approach
The J2 elastoplastic material model, employed in the work, assumes a multiplicative decomposition of the deformation gradient into an elastic and a plastic part and incorporates a non‐linear isotropic hardening response. The constitutive model is written in terms of the rotated Kirchhoff stress and the logarithmic strain measure. A Total Lagrangian formulation of the problem is considered in order to improve the computational performance of the proposed algorithm. The imposition of the essential boundary conditions and also of the unilateral contact with friction condition are made by the application of the Augmented Lagrangian method. Here, aspects related to the volumetric locking are investigated and an F‐bar approach is applied.
Findings
The results show that the proposed approach presents no volumetric locking phenomenon when using the mean dilation approach. Moreover, differently from finite element approximations, no hour‐glass instabilities in the deformation pattern are observed, avoiding in this way the need to devise additional stabilization procedures in the proposed procedure.
Originality/value
This paper demonstrates the implementation and validation of the mean dilation approach, in the scope of the EFG, which was successful in coping with the volumetric locking phenomena and presented no hour‐glass instabilities in the problem cases considered in this work.