Aleksandar Karač

• PhD
• Professor (Full) at University of Zenica

A percolation model with nucleation and object growth is studied by Monte Carlo simulations on a triangular lattice with finite-size impurities. The growing objects are needle-like objects and self-avoiding random walk chains. Results are obtained for three different shapes of impurities covering three lattice sites—needle-like, angled and triangul...

Percolation properties of an adsorbed polydisperse mixture of extended objects on a triangular lattice are studied by Monte Carlo simulations. The depositing objects of various shapes are formed by self-avoiding walks on the lattice. We study polydisperse mixtures in which the size ℓ of the shape making the mixture increases gradually with the numb...

Percolation model with nucleation and object growth is studied by Monte Carlo simulations on a triangular lattice with point-like impurities. Growing objects are needle-like objects and self-avoiding random walk chains. In each run through the system the lattice is initially randomly occupied by point-like impurities at given concentration ρ i m p...

The electrohydrodynamics’ (EHD) perfect dielectric model was added into computational fluid dynamics (CFD) software OpenFOAM in order to improve its usability for the EHD field and specifically for the mentioned model. Based on the investigated literature, it can be said that this is the most complete implementatiton of the said model. Two sets of...

We consider the percolation model with nucleation and simultaneous growth of multiple finite clusters, taking the initial seed concentration ρ as a tunable parameter. Growing objects expand with constant speed, filling the nodes of the triangular lattice according to rules that control their shape. As growing objects of predefined shape, we conside...

A perfect dielectric model was incorporated into the OpenFOAM® software and used for investigation and, possibly, improvements of electrohydrodynamic calculations. Two different sets of numerical simulations were analyzed, in which two different fluids were present. The first set was one-dimensional, while in the second, a drop of one fluid was sur...

This paper explores the potential use of conductive alginate capsules encapsulating a bitumen rejuvenator as a new extrinsic self-healing asphalt method. The capsules combine two existing self-healing asphalt technologies: (1) rejuvenator encapsulation and (2) induction heating to create a self-healing system that will provide rapid and effective a...

Proteins diffuse to their sites of action within cells in a crowded, strongly interacting environment of nucleic acids and other macromolecules. An interesting question is how the highly crowded environment of biological cells affects the dynamic properties of passively diffusing particles. The Lorentz model is a generic model covering many of the...

We study a stochastic lattice model describing the dynamics of a group chasing and escaping between two species in an environment that contains obstacles. The Monte Carlo simulations are carried out on a two-dimensional square lattice. Obstacles are represented by non-overlapping lattice shapes that are randomly placed on the lattice. The model inc...

This paper describes a self-contained parallel fluid-structure interaction solver based on a finite volume discretisation, where a strongly coupled partitioned solution procedure is employed. The incompressible fluid flow is described by the Navier-Stokes equations in the arbitrary Lagrangian-Eulerian form, and the solid deformation is described by...

Over the past 30 years, the cell-centred finite volume method has developed to become a viable alternative to the finite element method in the field of computational solid mechanics. The current article presents an open-source toolbox for solid mechanics and fluid-solid interaction simulations based on the finite volume library OpenFOAM. The object...

This presentation discusses the development of the finite volume method for solid mechanics, with focus on the open-source software OpenFOAM. The similarities between fluids and solids, as well as finite difference, finite element and finite volume methods are briefly discussed. Finally, recent developments in the solids4Foam OpenFOAM toolbox are p...

In the preceding paper, Budinski-Petković et al (2016 J. Stat. Mech. 053101) studied jamming and percolation aspects of random sequential adsorption of extended shapes onto a triangular lattice initially covered with point-like impurities at various concentrations. Here we extend this analysis to needle-like impurities of various lengths . For a wi...

This work focuses on the development of a surrogate lung material (SLM) that reproduces the dynamic response of a human lung under various loading conditions and also allows for the analysis of the extent and distribution of damage. The SLM consists of polyurethane foam used to mimic the spongy lung tissue and fluid-filled gelatine microcapsules us...

Over the past 30 years, the cell-centred finite volume method has developed to become a viable alternative to the finite element method in the field of computational solid mechanics. The current presentation presents steps taken towards the development of an open- source toolbox for solid mechanics and fluid solid interaction simulations based on t...

Sažetak Pokusi delaminacije s grednim uzorcima se često koriste kod ispitivanja različitih suvremenih materijala sa slojevitom strukturom, i kod različitih vrsta ovih pokusa javljaju se i različiti načini loma (otvaranja pukotine). Kod pokusa s mješovitim načinom loma značajno je s aspekta dizajna napraviti podjelu energije loma na udjele od različ...

This paper explores the potential methods for evaluating a healing system for asphalt pavements. The healing system under investigation involves compartmented calcium-alginate fibres encapsulating an asphalt binder healing agent (rejuvenator). This system presents a novel method of incorporating rejuvenators into asphalt pavement mixtures. The comp...

The properties of the random sequential adsorption of objects of various shapes on a two-dimensional triangular lattice are studied numerically by means of Monte Carlo simulations. The depositing objects are formed by self-avoiding lattice steps, whereby the size of the objects is gradually increased by wrapping the walks in several different ways....

Mixed-mode fracture in delamination test utilizing double cantilever specimens loaded with bending moments is investigated in the paper. FEM simulations are performed using cohesive zone model where different configurations of test loadings and two critical fracture energy values, ie. two fracture process zone lengths, are considered. Fracture ener...

Original scientific paper Delamination (fracture) tests have been numerically investigated using various cohesive zone properties. The test utilises asymmetric and symmetric double cantilever beam specimens loaded with bending moment. Energy release rate contributions from mode I and mode II fracture are calculated using a global and local approach...

U radu je dat osvrt na mogućnosti primjene savremenih E-learning platformi u organizaciji nastave u visokom obrazovanju te njihovim prednostima i nedostacima u odnosu na tradicionalan pristup. Razmatrane su dvije platforme, Moodle i Blackboard, s posebnim akcentom na mogućnostima njihove primjene za provjere znanja. Data su dva primjera online orga...

Adsorption-desorption processes of polydisperse mixtures on a triangular lattice are studied by numerical simulations. Mixtures are composed of the shapes of different numbers of segments and rotational symmetries. Numerical simulations are performed to determine the influence of the number of mixture components and the length of the shapes making...

Mathematics has always been playing an important part in engineering education. However, there is an open discussion whether academic staff with engineering or with mathematical background should deliver mathematical courses at the engineering colleges and universities. The same dilemma exists in ICT education of mechanical engineers: what are the...

Fixed-ratio mode-mixity tests were numerically investigated using various cohesive zone properties. The deformation energy (mode I and mode II fracture) going into cohesive elements is monitored and fracture mode-mixities for different configurations are calculated and compared to existing analytical partitioning theories. Opposite to the theories,...

Forces generated in the muscles and tendons actuate the movement of the skeleton. Accurate estimation and application of these musculotendon forces in a continuum model is not a trivial matter. Frequently, musculotendon attachments are approximated as point forces; however, accurate estimation of local mechanics requires a more realistic applicatio...

For almost half a century, the Finite Element (FE) method has dominated the world of computational solid mechanics (CSM); however, the Finite Volume (FV) method is gradually gaining prominence within the field due to its attractively simple yet strongly conservative nature, as well as the increasing popularity of OpenFOAM. Nonlinearity in CSM analy...

Finite element simulations of a fixed-ratio mode-mixity test (single configuration) are performed using cohesive zone model. Different simulation parameters are varied: automatic stabilisation, cohesive element viscosity and mesh size. A global and local approach are presented and used for calculation of energy release rate contribution from mode I...

This paper describes the development and application of a frictionless contact stress solver based on the cell-centred finite volume method. The contact methodology, implemented in the open-source software OpenFOAM, is derived from the penalty method commonly used in finite element contact algorithms. The solver is verified on two benchmark tests u...

This paper describes a finite volume method for orthotropic bodies with general principal material directions undergoing large strains and large rotations. The governing and constitutive relations are presented and the employed updated Lagrangian mathematical model is outlined. In order to maintain equivalence with large strain total Lagrangian met...

The finite element (FE) and finite volume (FV) methods are commonly employed in computational solid mechanics (CSM) and computational fluid dynamics (CFD), where the FE method is traditionally associated with CSM and the FV method associated with CFD. However, the usage of FV analysis in CSM is becoming increasingly popular due to the attractively...

Rubber toughened epoxy adhesives are the most widely used structural adhesives in engineering applications. Recent work in UCD Centre for Adhesion and Adhesives demonstrated that addition of nano-sized core shell rubber (CSR) particles into an epoxy matrix could increase the fracture energy significantly. These studies found that failure initiated...

This paper presents an analysis of the stress distribution on the outer surface of the riding ring of rotary cement kiln during working cycle using both the theory and finite element simulation. In the theoretical analysis, the total stress is obtained as a combination of bending, thermal and contact stresses. To obtain bending stress the kiln is c...

This paper establishes a procedure for numerical analysis of hip joint using the Finite Volume method. Patient-specific hip joint geometry is segmented directly from computed tomography and magnetic resonance imaging datasets and the resulting bone surfaces are processed into a form suitable for volume meshing. A high resolution continuum tetrahedr...

Correct calculation of stresses at the interface of bonded or otherwise joined materials plays a significant role in many applications. It is therefore important that traction at the material interface is calculated as accurately as possible. This paper describes procedures that can be employed to achieve this goal by using centre-based finite-volu...

The current work is a combined experimental-numerical study of the fracture behaviour of a nano-toughened, structural epoxy adhesive. The mode I fracture toughness of the adhesive is measured using tapered double-cantilever beam (TDCB) tests with various bond gap thicknesses ranging from 0.25 mm to 2.5 mm. Circumferentially deep-notched tensile spe...

This work is focused on the development of a surrogate lung material that not only reproduces the dynamic response of a human lung under various loading conditions but also allows the analysis of the extent and distribution of damage, thus potentially eliminating the practice of live animal testing. The surrogate material consists of polyurethane f...

The current work examines the growth of a single void in an elastic–plastic material as a function of stress triaxiality. Using finite volume (FV) stress analysis, growth of a spherical void is simulated and compared to the classic Rice and Tracey model for the different material models considered.

This work is conducted as a part of a wider international activity on mixed mode fractures in beam-like geometries under the coordination of European Structural Integrity Society, Technical Committee 4. In its initial phase, it considers asymmetric double cantilever beam geometry made of a linear elastic material with varying lower arm thickness an...

Finite element analysis has dominated the world of computational structural mechanics for the past half century, however, since seminal work by Demirdˇzi ́c et al. [1] finite volume stress (FV) analysis has become a viable alternative. The apparently simple problem of a body undergoing large rotation is far from trivial when considered numerically....

This work is conducted as a part of a wider international activity on mixed mode fractures in beam-like geometries under the coordination of European Structural Integrity Society, Technical Committee 4. In its initial phase, it considers asymmetric double cantilever beam geometry made of a linear elastic material with varying lower arm thickness an...

Total Hip Arthroplasty is a surgical procedure that reforms the hip joint, replacing the patho- logical joint with an artificial prosthesis. Due to post-operative joint instability, complications such as dislocation are still a significant problem. This research aims to develop a realistic numerical model of a healthy hip joint and examine its stab...

Forces generated in the muscles and tendons actuate the movement of the skeleton. During total hip arthroplasty the position of these musculo-tendon units may be altered to produce a more stable joint, which has less propensity to dislocate. A realistic numerical model of the hip joint including soft tissues would allow confident predictions to be...

In this study the adhesive joint fracture behaviour of a nano-toughened epoxy adhesive was investigated. Two experimental test methods were used; (i) the standard tapered double cantilever beam (TDCB) test to measure the mode I adhesive joint fracture energy, GIC, as a function of bond gap thickness and (ii) a circumferentially deep notched tensile...

In the present study, the mixed-mode fracture toughness of an adhesively bonded composite joint system was examined using a variety of linear elastic fracture mechanics (LEFM) based tests. These tests include the mode I double cantilever beam (DCB), mixed-mode asymmetrical DCB (ADCB) and mode II end load split (ELS) test. The joint system was also...

Tapered-double cantilever-beam joints were manufactured from aluminium-alloy substrates bonded together using a single-part, rubber-toughened, epoxy adhesive. The mode I fracture behaviour of the joints was investigated as a function of loading rate by conducting a series of tests at crosshead speeds ranging from 3.33 × 10−6 m/s to 13.5 m/s. Unstab...

Tapered-double cantilever-beam joints were manufactured from aluminium-alloy substrates bonded together using a single-part, rubber-toughened, epoxy adhesive. The mode I fracture behaviour of the joints was investigated as a function of loading rate by conducting a series of tests at crosshead speeds ranging from 3.33 x10-6 m/s to 13.5 m/s. Unstabl...

This paper deals with the determination of stress concentration factors using numerical methods. The cases of the bar with circular cross section and U-shaped groove subjected to tension and bending are considered. Determination of model parameters is achieved by combining the design-of-experiment, implemented in MATLAB, and Finite Element analysis...

This paper investigates the applicability of a cohesive zone model for simulating the performance of bituminous material subjected to quasi-static loading. The Dugdale traction law was implemented within a finite volume code in order to simulate the binder course mortar material response when subjected to indirect tensile loading. A uniaxial tensil...

This paper investigates the applicability of a cohesive zone model for simulating the performance of bituminous material subjected to quasi-static loading. The Dugdale traction law was implemented within a finite volume code in order to simulate the binder course mortar material response when subjected to indirect tensile loading. A uniaxial tensil...

Research is being undertaken in University College Dublin to investigate the effect of blast trauma to human lungs. Specifically the research is aimed at developing a material to act as surrogate lung tissue [1], thus allowing for simulation of damage to be examined without conducting tests on live animals. This surrogate lung material consists of...

In this work, the behaviour of fluid-filled plastic containers under base drop impact is investigated using a combined experimental/numerical approach. In addition, theoretical predictions from two approaches, waterhammer theory and a mass-spring model, are also given. Experimental tests are conducted using a specially designed rig for testing plas...

The current work examines the fracture behaviour of adhesively bonded joints by conducting a series of low rate tapered double cantilever beam (TDCB) tests and simulating them numerically. Single part, nano-rubber toughened, structural epoxy adhesive was used throughout the current research. Particular emphasis is given to the effect of the bond th...

The interaction between the flowing blood and the deforming arterial wall is critical in blood flow dynamics and understanding the role of hemodynamic forces such as wall shear stress in atherosclerosis. Numerical studies have become an invaluable tool in providing this understanding. Unfortunately most of these studies have been based on rigid art...

Atherosclerosis is a chronic medical condition in which thickening and loss in the elasticity of the artery wall leads to impaired blood circulation[1]. Cholesterols and other proliferating cells accumulate at localized regions within the artery wall. This has the effect of stiffening and thickening the wall at that point. The presence of an emergi...

This paper presents the work on a Finite Volume model representing wave propagation through the lung. One and two dimensional cases are used for the analysis and the results are validated against measured known values of stress wave propagation velocities. The results of the one dimensional model show that the known low wave propagation velocity ha...

Drop impact resistance of fluid-filled plastic containers is of considerable concern to containers manufacturers as well as distribution industries using the containers for transportation of various liquids. This is due to potential failure of the containers following the drop impact and subsequent spillage of the transported liquid, and consequent...

Blood flow through arteries represents a very complex, fluid-structure interaction (FSI) problem. Strong coupling between the blood and artery is due to the relatively low stiffness of the artery compared to that of blood. Hence, the pressure exerted by the flowing blood on the artery wall can result in considerable deformations of the artery, and...

Drop impact of fluid-filled flexible containers made of blow moulded high density polyethylene (HDPE) is of a considerable concern to containers' manufacturers and distribution industries for safety and economical reasons. This is due to potential failure of the containers following the drop impact and subsequent spillage of the transported liquid....

Drop impact resistance of fluid-filled plastic containers is of considerable concern to plastics and containers manufacturers as well as distribution industries utilising containers for transportation of various liquids. This is due to potential failure of the containers following the drop impact and subsequent spillage of the transported liquid. I...

This presentation deals with methods for ∞uid-structure (FSI) and ∞uid-structure-fracture interaction (FSFI) and their application to a variety of ∞exible problems. Here, the term '∞exible' is associated with problems having comparable stifnesses for both ∞uid (bulk modulus) and structure (modulus of elasticity) parts in a simulation. For such prob...

This work presents a 3D coupled solid-fluid model for predicting fast fractures in pressurised plastic pipes. It is developed within a unified computational procedure where both solid pipe and pressurising media are discretised using the Finite Volume method. The coupling is achieved across the pipe-fluid interface (pipe bore) via newly developed i...

Drop impact of fluid-filled flexible containers made of blow moulded high density polyethylene is of a considerable concern to containers' manufacturers and distribution industries for safety and economical reasons. This is due to potential failure of the containers following the drop impact, and subsequent spillage of the transported liquid. Accur...