Papers by Keyword: Discrete Element Method

Abstract: This paper presents a study in the field of modelling the dynamics of spherical elements. The results obtained indicate the successful use of the discrete element method (DEM) as a numerical tool for analysing the behaviour of the system studied with the help of spheres. The results are based on the importance of correct consideration of the boundary conditions for the spheres, which determine the key aspects of modelling with the developed three-dimensional model. The developed model solves a number of important tasks, expanding the field of scientific research. Firstly, it allows studying the main parameters of the formation of a heterogeneous medium by analysing the compaction of spherical elements in different media. Next, the three-dimensional model is used to study the process of changing the structure of a heterogeneous medium from a static to an oscillatory state, which allows for a deeper understanding of this process. By modelling the mathematical behaviour of spherical elements under the influence of external and additional factors, a detailed understanding of their dynamics and contact interaction can be obtained. The application of the developed model to analyse the contact interaction of spherical elements in heterogeneous media allows predicting the main parameters of spheres and their heterogeneous environment with a reliable accuracy of up to ±1 %. It should be noted that the results obtained on the basis of the three-dimensional model are effective and indicate a number of practical applications in various fields.

Abstract: Concentrated solar power technology represents a novel approach to generating solar power, characterized by high solar radiation density and uninterrupted operation. To store thermal energy and extend system operating hours, concentrated solar power systems rely on thermal energy storage. Selecting the appropriate heat storage media is crucial for designing a cost-efficient and straightforward system capable of withstanding high processing conditions. Among many powder materials, bauxite powder stands out as alternatives to conventional molten salt for thermal storage media due to its widespread availability and suitability for operating conditions. Particle shape, particularly its sphericity, plays a vital role in efficiently packing particles which directly affects to heat transfer properties. To investigate this effect, three samples of particles with different shape were formed: spheres, ellipses, and cylinders using Discrete Element Method with equal volume and material properties, and only variation of their sphericity factors. The study focused on the analysis of the porosity of the packed bed of particles with different shapes and its influence on the packing structure properties. The analysis of local packing fraction revealed that elliptical and cylindrical particles samples exhibited reduced heap formation and a more uniform distribution along z direction during vertical packing. The coordination number and radial distribution function analyses for these non-spherical particles showed a greater number of contacts between particles and disordered distribution of particles due to mechanical interlocking of non-spherical particles. The results indicated that the deviation of sphericity has a positive impact on the denser packing of particles generated more contacts and higher local packing fraction.

Abstract: To gain better understanding of rheological transitions from suspension flow to granular deformation and shear cracking, this research conducted shear-deformation on globular semi-solid Al-Cu alloys to study the rheological behavior of semi-solid as a function of solid fraction (38% - 85%) and shear rate (10^-4 – 10^-1 s^-1) under real-time synchrotron radiography observation. By analyzing 17 X-ray imaging datasets, we define three rheological transitions: (i) the critical solid fraction from a suspension to a loosely percolating assembly; (ii) from the net contraction of a loose assembly to the net dilation of a densely packed assembly, and (iii) to shear cracking at high solid fraction and shear rate. Inspired by in-situ observations of semi-solid deformation showing a disordered assembly of percolating crystals in partially-cohesive contact with liquid flow, we reproduced a two-phase sample using the coupled lattice Boltzmann method-discrete element method (LBM-DEM) simulation approach for granular micromechanical modeling. In DEM, each globular Al grain is represented by a discrete element, and the flow of interstitial liquid is solved by LBM. The LBM-DEM simulations show quantitative agreement of semi-solid strain localization with the experiments and are used to explore the components involved in the shear rate dependence of the transitions, and the role of liquid pressure on the initiation of shear cracking.

Abstract: Metal additive manufacturing based on powder bed fusion processes is increasingly important. However, highly transient physical phenomena that occur in these processes at different length scales are difficult to observe. Challenging and costly experiments are usually needed to obtain data for process understanding and improvement. Computational modelling of powder-bed fusion processes is therefore important from several points of view. These include better process understanding, optimisation of process parameters and component designs, prediction of component properties, qualification of components and to assist process control. Several physical processes have to be treated to develop a complete model, namely the raking of the powder bed surface, the transfer of energy from the laser or electron beam to the metal, the melting and solidification of the powder, the flow of liquid metal in the melt pool, the heat transfer from the melt pool to the surrounding powder and solid metal, the evolution of the microstructure, and the residual stress and deformation of the component. These processes occur at very different scales, and have to be treated using several different computational techniques. In addition, the interdependency of some of the processes has to be accounted for. This paper discusses the rationale for developing a complete model, progress in developing sub-models of the different physical processes, and the framework that is envisaged to combine the sub-models into a predictive model of the additive manufacturing process.

Abstract: This paper presents a numerical simulation of powder sintering. The numerical model presented in this paper uses the discrete element method, which suggests that the material can be modeled by a large set of discrete elements (particles) of a spherical shape that interact with each other. A methodology has been developed to determine the DEM parameters of bulk materials based on machine vision and a neural network algorithm. The approach is suitable for obtaining the exact values of the DEM parameters of the investigated bulk material by comparing the visual images of the material’s behavior at the experimental stand in reality and in the model. Simulation of sintering requires an introduction of cohesive interaction between particles representing interparticle sintering forces. Numerical sintering studies were supplemented with experimental studies that provided data for calibration and model validation. The experimental results have shown a significant capability of the designed numerical model in modeling sintering processes. Evolution of microstructure and density during sintering have been studied under the laboratory conditions.

Abstract: The paper presents the results of a computational study of the influence of the geometry of the working chamber on the energy-force interaction of grinding bodies in the process of the mixture processing in a planetary mill. The method of computer simulation, using the software system, based on the ideology of discrete elements, shows the high efficiency of processing in a planetary mill, using a working chamber with a square-shaped cavity. The values of the factors that have a dominant influence on the mechanical processing of the charge are determined. A comparison with the process of processing in the working chamber of the traditional cylindrical shape is made. The research results will be used in the appointment of large-size charge processing regimes that provide a high-energy grinding process.

Abstract: In this article, the effect of particle shape is examined from the comparison of results of numerically simulated constant volume compression tests carried out on planes assemblies of disks and ellipses with equal porosity and similar gradation and test conditions. The results show that particle shape is a decisive fabric component that contributes directly and indirectly to the strength of assemblies of particles to resist shearing deformation. The results confirm previously established facts that elongated particle shapes favour particle interlocking and create, more easily than ideal spheres, stable clusters of particles through which external loads can be transferred hence resisting higher shearing stresses.

Abstract: The Conservation of Historical Architectural Heritage Cannot Be Limited only to a Series of Isolated Interventions on Materials and Structures, but must Include Also the Maintenance or Insertion of Compatible Uses, which can Guarantee a Continuous Upkeep. the Exploitation of Heritage, nevertheless, is a Wedge Issue, as it Involves New Loads, more Wear, Different Environmental Conditions, which can Induce Changes in their Behaviour which are Hard to Foresee.This Contribution Aims to Analyse in Particular the Structural Issues Involved in the Use Changes or in the Adaptation of a Pre-Existing Use to New Functional or Normative Requirements. Indeed, for a Correct Management of the Built Heritage, the Choice of the Structurally Compatible Uses Cannot Disregard a Specific Analysis Aimed at the Identification of the Structure Bearing Capacity and Focusing on the Indications to Combine Functional and Structural Needs.The Proposed Case Study, on which the Approach is Applied, Regards the Pilotta National Museum, in Parma, that is Undergoing a Reorganization of the Visit Paths and a Reconsideration on the Uses Allocated to some Spaces. more Specifically, a Vaulted Room over a Long Barrel Vault is Asked to Host New Functions and Carry New Loads, Whose Compatibility with the Preservation of the Monumental Structure must Be Assessed.For the Assessment of the Structural Compatibility Levels, Different Modelling Approaches Have been Tested, in Order to Compare their Results and to Analyze their Pros and Cons in this Type of Evaluation. on One Side, Traditional Methods were Chosen: the Graphic Méry Method and the Heyman Limit Analysis Have been Applied to a System of 2D Arches Composing the Vault. on the other Side, the Edge Cutting Chronoengine Distinct Element Model Have been Also Tested, under the same Conditions. in all Cases, Calculations Have been Made Changing both Values and Positions of the Loads, Depending on the Requests for the New Use of the Vault.The Results are Compared both in Terms of Stresses inside the Masonry and in Terms of Deformation of the Structural Elements, Evaluating the Types of Information and Detail that the Different Approaches can Supply. the Results of the Numerical Method Allow to Assess the Validity of the Traditional Approaches. on the other Side, the Possible Contribution of the Traditional Methods to the Calibration of the Parameters for the Numerical Models is Also Discussed.The Results, at Last, will Be Adopted to Propose Limitations to the Possible Uses and to Give Specific Indications about the Setting up of the Museum Exhibitions.

Abstract: The dynamic behaviour and the seismic vulnerability of different masonry “Apennine Churches”, dramatically damaged by the last shocks sequence of 2016 that occurred in Central Italy, have been studied in this paper by means of advanced 3D numerical analyses with the Discrete Element Method (DEM). Thus, a discontinuous approach has been used to assess the dynamic properties and the vulnerability of the masonry structure, through large deformations regulated by the Signorini’s law, concerning the impenetrability between the rigid bodies, and by the Coulomb’s law, regarding the dry-friction model. The major purpose of this study is to highlight that relevant data on the real structural behaviour of historical masonry can be provided through advanced numerical analyses. The comparison between the results of the numerical simulation and the survey of the existing crack pattern of the churches permitted to validate the used approach. Finally, from the results and conclusions of these cases study, it is possible to affirm that the used methodology can be applied to a wide variety of historical masonry structure in Europe.

Abstract: The adhesively bonded joints behaviour under cyclic loading is not yet well understood due to its inherent complexity. Numerical approaches appear, therefore, as the easiest way to simulate such mechanical behaviour. In this work, double strap bonded joints with Carbon Fibres Reinforced Polymers (CFRP) and aluminium are numerically simulated and subjected to a cyclic loading history. In the numerical simulation, the Distinct Element Method (DEM) is used and it is assumed cohesive bi-linear bond-slip models with local damage of the interface. The evaluation of the bonded joints under cyclic loading is made by comparing the results with those simulated with a monotonic loading.