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Article

A. Munjiza, D.R.J. Owen and N. Bicanic

This paper discusses the issues involved in the development of combined finite/discrete element methods; both from a fundamental theoretical viewpoint and some related…

Abstract

This paper discusses the issues involved in the development of combined finite/discrete element methods; both from a fundamental theoretical viewpoint and some related algorithmic considerations essential for the efficient numerical solution of large scale industrial problems. The finite element representation of the solid region is combined with progressive fracturing, which leads to the formation of discrete elements, which may be composed of one or more deformable finite elements. The applicability of the approach is demonstrated by the solution of a range of examples relevant to various industrial sections.

Details

Engineering Computations, vol. 12 no. 2
Type: Research Article
ISSN: 0264-4401

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Article

Jani Paavilainen, Jukka Tuhkuri and Arttu Polojärvi

The purpose of this paper is to present a 2D combined finite‐discrete element method (FEM‐DEM) to model the multi‐fracture of beam structures and an application of the…

Abstract

Purpose

The purpose of this paper is to present a 2D combined finite‐discrete element method (FEM‐DEM) to model the multi‐fracture of beam structures and an application of the method to an ice‐structure interaction problem.

Design/methodology/approach

In the method, elastic beams and their fracture are modelled according to FEM by using nonlinear Timoshenko beam elements and cohesive crack model. Additionally, the beam elements are used to tie the discrete elements together. The contact forces between the colliding beams are calculated by using the DEM.

Findings

Three numerical examples are given to verify the method. Further, the method is applied to model the failure process of a floating ice beam against an inclined structure. Based on the comparison of the experiments and the simulation, a good agreement between the results is observed.

Originality/value

In the context of combined FEM‐DEM, the two novel features presented in this paper are: the use of Timoshenko finite element beams with damping to calculate internal forces and to combine the discrete elements; and the bending failure by the cohesive crack approach while simultaneously keeping track of the position of the neutral axis of the beam.

Details

Engineering Computations, vol. 26 no. 6
Type: Research Article
ISSN: 0264-4401

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Article

D.R.J. Owen and Y.T. Feng

This paper outlines a dynamic domain decomposition‐based parallel strategy for combined finite/discrete element analysis of multi‐fracturing solids and discrete systems…

Abstract

This paper outlines a dynamic domain decomposition‐based parallel strategy for combined finite/discrete element analysis of multi‐fracturing solids and discrete systems. Attention is focused on the parallelised interaction detection between discrete objects. Two graph representation models for discrete objects in contact are proposed which lay the foundation of the current development. In addition, a load imbalance detection and re‐balancing scheme is also suggested to enhance the parallel performance. Finally, numerical examples are provided to illustrate the parallel performance achieved with the current implementation.

Details

Engineering Computations, vol. 18 no. 3/4
Type: Research Article
ISSN: 0264-4401

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Article

Luis Kosteski, Ignacio Iturrioz, Ruben Galiano Batista and Adrián P. Cisilino

The purpose of this paper is to further develop the truss‐like discrete element method (DEM) in order to make it suitable to deal with damage and fracture problems.

Abstract

Purpose

The purpose of this paper is to further develop the truss‐like discrete element method (DEM) in order to make it suitable to deal with damage and fracture problems.

Design/methodology/approach

Finite and boundary elements are the best developed methods in the field of numerical fracture and damage mechanics. However, these methods are based on a continuum approach, and thus, the modelling of crack nucleation and propagation could be sometimes a cumbersome task. Besides, discrete methods possess the natural ability to introduce discontinuities in a very direct and intuitive way by simply breaking the link between their discrete components. Within this context, the present work extends the capabilities of a truss‐like DEM via the introduction of three novel features: a tri‐linear elasto‐plastic constitutive law; a methodology for crack discretization and the computation of stress intensity factors; and a methodology for the computation of the stress field components from the unixial discreteelement results.

Findings

Obtained results show the suitability and the performance of the proposed methodologies to solve static and dynamic crack problems (including crack propagation) in brittle and elasto‐plastic materials. Computed results are in good agreement with experimental and numerical results reported in the bibliography.

Research limitations/implications

This paper demonstrates the versatility of the truss‐like DEM to deal with damage mechanics problems. The approach used in this work can be extended to the implementation of time‐dependent damage mechanisms. Besides, the capabilities of the discrete approach could be exploited by coupling the truss‐like DEM to finite and boundary element methods. Coupling strategies would allow using the DEM to model the regions of the problem where crack nucleation and propagation occurs, while finite or boundary elements are used to model the undamaged regions.

Originality/value

The scope of the truss‐like DEM has been extended. New procedures have been introduced to deal with elastoplastic‐crack problems and to improve the post processing of the stress results.

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Article

M.G. Cottrell, J. Yu, Z.J. Wei and D.R.J. Owen

In recent years, developments in the field of lightweight armour have been of primary importance to the defence industry. This necessity has led to many organisations…

Abstract

In recent years, developments in the field of lightweight armour have been of primary importance to the defence industry. This necessity has led to many organisations adopting composite armours comprising both the traditional heavy armours and new lighter weight ceramic armours. The numerical modelling of metal based armour systems has been well documented over the years using purely continuum based methods; and also the modelling of brittle systems using discrete element methods, therefore it is the objective of this paper to demonstrate how a coupled finite and discrete element approach, can be used in the further understanding of the quantitative response of ceramic systems when subjected to dynamic loadings using a combination of adaptive continuum techniques and discrete element methods. For the class of problems encountered within the defence industry, numerical modelling has suffered from one principal weakness; for many applications the associated deformed finite element mesh can no longer provide an accurate description of the deformed material, whether this is due to large ductile deformation, or for the case of brittle materials, degradation into multiple bodies. Subsequently, two very different approaches have been developed to combat such deficiencies, namely the use of adaptive remeshing for the ductile type materials and a discrete fracture insertion scheme for the modelling of material degradation. Therefore, one of the primary objectives of this paper is to present examples demonstrating the potential benefits of explicitly coupling adaptive remeshing methods to the technique of discrete fracture insertion in order to provide an adaptive discontinuous solution strategy, which is computationally robust and efficient.

Details

Engineering Computations, vol. 20 no. 1
Type: Research Article
ISSN: 0264-4401

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Article

GRANT HOCKING

This paper is concerned with the determination of the transient stress and deformational state of plate‐like discontinua subject to flexural cracking. Such a phenomenon…

Abstract

This paper is concerned with the determination of the transient stress and deformational state of plate‐like discontinua subject to flexural cracking. Such a phenomenon can be easily visualized as the type of fragmentation to floating sea ice impacted by an ice‐breaker or offshore platform. The discrete element method is used to solve the dynamic equilibrium equations for each distinct deformable body and the interaction between bodies. Each body may deform elastically and fracture into further pieces if a brittle failure criterion for flexure is exceeded. The discrete plate element is a hybrid thin‐plate (Kirchhoff) mode lumped at element boundaries with transverse shear deformation computed at element centroids. Errors in computed stresses near point loads and cracks by the current element warrant the use of an improved mixed mode plate element. A three‐dimensional application of the discrete element method is presented for the case of fragmentation of floating sea ice impacting an arctic offshore platform. A semi‐implicit solution scheme is introduced to overcome the stringent explicit time step stability conditions due to stiff members in the discrete element formulation.

Details

Engineering Computations, vol. 9 no. 2
Type: Research Article
ISSN: 0264-4401

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Article

John R. Williams

There has been interest recently in analysing soil, ceramic powders and other materials on the microscopic level so that macroscopic phenomena, such as failure, can be…

Abstract

There has been interest recently in analysing soil, ceramic powders and other materials on the microscopic level so that macroscopic phenomena, such as failure, can be related to microscopic properties. The discrete element method provides a numerical tool for conducting such analyses. Here the basic theory behind the method is reviewed and various formulations derived from a finite element basis. The automatic detection of contact surfaces between bodies is a major problem in analysing the interaction of numerous bodies, common to both finite elements and discrete elements. Various approaches to geometric contact detection and the need for efficient algorithms and data structures utilizing recent developments in the field of computer graphics and solid modelling are discussed. Examples are given of the collapse of a soil embankment, penetration of a projectile into a soil and the large deformation of a space structure.

Details

Engineering Computations, vol. 5 no. 3
Type: Research Article
ISSN: 0264-4401

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Article

Nikolina Zivaljic, Hrvoje Smoljanovic and Zeljana Nikolic

The purpose of this paper is to present a new numerical model based on a combined finite-discrete element method, capable of predicting the behaviour of reinforced…

Abstract

Purpose

The purpose of this paper is to present a new numerical model based on a combined finite-discrete element method, capable of predicting the behaviour of reinforced concrete structures under dynamic load up to failure.

Design/methodology/approach

An embedded model of reinforcing bars is implemented in combined finite-discrete element code. Cracking of the structure was enabled by a combined single and smeared crack model. The model for reinforcing bars was based on an approximation of the experimental curves for the bar strain in the crack. The developed numerical model includes interaction effects between reinforcement and concrete and cyclic behaviour of concrete and steel during dynamic loading.

Findings

The findings provide a realistic description of cracking in the concrete structure, where all non-linear effects are realized in joint elements of the concrete and reinforcing bars. This leads to a robust and precise model for non-linear analysis of reinforced concrete structures under dynamic load.

Originality/value

This paper presents new robust finite-discrete element numerical model for analysis and prediction of the collapse of reinforced concrete structures. The model is capable of including the effects of dynamic loading on the structures, both in the linear-elastic range, as well as in the non-linear range including crack initiation and propagation, energy dissipation due to non-linear effects, inertial effects due to motion, contact impact, and the state of rest, which is a consequence of energy dissipation in the system.

Details

Engineering Computations, vol. 30 no. 7
Type: Research Article
ISSN: 0264-4401

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Article

Nanlei Chen and Naiming Xie

The purpose of this paper is to propose an uncertainty representation and information measurement method for characterizing grey numbers, estimating their internal laws…

Abstract

Purpose

The purpose of this paper is to propose an uncertainty representation and information measurement method for characterizing grey numbers, estimating their internal laws and solving how to generate them based on available information data in the real world.

Design/methodology/approach

This paper attempts to present a new mathematical methodology in the field of grey numbers. The generalized grey number is defined at first with the concept of information elements and information samples. Then, the probability function of a grey number is proposed to describe the internal law of the grey number. By finding the feasible information elements from information samples, the probability calculation method for the true value of a grey number is presented. Finally, some numerical examples and comparisons are carried out to assess the efficiency and performance.

Findings

The results show that the uncertainty representation and information measurement method is effective in characterizing and quantifying grey numbers based on available information data.

Practical implications

Uncertain information is widespread in practical applications. In this manuscript, the grey number is represented and its information is measured through some existing data in discrete or interval forms, which provides a grey information concept that utilizes information elements to represent uncertainty in the real world.

Originality/value

The proposal presents a novel data-driven method to generate a grey number representation from available data rather than the classical whitening weight function constructed from experience, and the dynamic evolution process of a grey number is measured by the increase of information samples.

Details

Grey Systems: Theory and Application, vol. 10 no. 4
Type: Research Article
ISSN: 2043-9377

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Article

M. Talbot and G. Dhatt

The comparative efficiency of three flat triangular shell elements is being assessed for analysing non‐linear behaviour of general shell structures. The bending…

Abstract

The comparative efficiency of three flat triangular shell elements is being assessed for analysing non‐linear behaviour of general shell structures. The bending formulation of the three elements is based on a discrete Kirchhoff model (namely the well‐known 3‐node DKT element and a new 6‐node DKTP element). The in‐plane behaviour is defined by constant (CST), linear (LST)and quadratic (QST) strain approximations. The super‐position of bending and membrane elements leads to the 3‐node DCT element (DKT plus CST), the 3‐node DQT element (DKT plus QST) and the 6‐node DLT element (DKTP plus LST). The geometrically non‐linear formulation is based on an approximate updated Lagrangian formulation (AULF) and the solution is obtained by using the Newton‐Raphson method with an automatic arc‐length control method. Illustrative examples include pre‐ and post‐buckling of different shell structures showing, in particular, some bifurcation points, large rotations and displacements and very important membrane‐bending coupling.

Details

Engineering Computations, vol. 4 no. 1
Type: Research Article
ISSN: 0264-4401

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