Documents published in Scipedia

• Particle Morphological Effects on the Behaviour of Dry Granular Flow Against Rigid Obstacles

  P. DHANAI, D. Bhattacharya

  particles2023.

  
  

  Abstract

  Geohazards such as rockfall, catastrophic landslides, and debris flow pose a significant risk due to the rapid movement of the vast amount of granular material carrying tremendous destructive potential and energy. Experimental and numerical studies on channelized flumes have been prevalent in analyzing the kinematics and dynamics of the flow and their interaction with various mitigation measures along the projected flow path. Continuum, discontinuum, and hybrid numerical methods have been successfully employed in the past to comprehend the complex material behaviour of granular mass flows. Although the numerical schemes within a continuum setting offer some insights into critical factors like flow velocity, flow depth, runout distance, etc., the granular interaction within the particle ensemble and the impact force on the barrier system for a better estimate of the force-transmission paths cannot be accounted for. The present study employs the Discrete Element Method to investigate the underlying physics of the micromechanical interaction of the granular assembly with the rigid barrier. Although past studies have explored granular flow-like events within a discrete setting, such studies did not incorporate particle morphology. This paper explores the effect of particle shape on kinematics and impact dynamics against a rigid obstacle. First, the numerical results have been benchmarked against the experimental studies for conventional spherical particles, and then we explore the effect of particle morphology. The present findings indicate that the particle shape significantly influences the flow kinematics and leads to a reduction in impact force on the barrier due to the higher angularity of particles with different morphological features than spherical particles, generally considered in the existing literature. A more significant implication of this study is to better understand and design mitigation measures against geohazards.

  Abstract
  Geohazards such as rockfall, catastrophic landslides, and debris flow pose a significant risk due to the rapid movement of the vast amount of granular material carrying tremendous [...]

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• Examination of the Influence of Particle Parameters on Contact Heat Transfer on a Single Hearth Furnace Floor Using DEM

  N. Hilse, S. Scherer

  particles2023.

  
  

  Abstract

  In the present paper, contact heat transfer on a batch-operated single circular floor of a multiple hearth furnace is numerically examined using the Discrete Element Method (DEM). The particles are agitated on the floor by a single rabble arm equipped with mixing blades. Two different rabble arm configurations are studied, a rabble arm with three blades covering just the area from the centre of the floor to the wall enclosing the circular floor, and a rabble arm with six blades, which covers the whole diameter of the floor. The floor temperature is set to 100°C, and the initial particle temperature is 20°C. Spherical particles made of aluminium and polyoxymethylene (POM) with two particle diameters (10 and 20 mm) are examined. Blade angle inclination is varied, namely, 0°, 45° and 90°. The major results are that for POM spheres the major mechanism dominating contact heat transfer is the gas layer in the vicinity of the contact point particle-floor, whereas for aluminium the heat transfer through the direct contact point of floor and particle is of equal importance as the heat transfer through the gas layer. For the first configuration with three blades, a larger blade angle leads to lower heat up rates, while the second configuration with six blades, increases the heating rate for larger blade angles.

  Abstract
  In the present paper, contact heat transfer on a batch-operated single circular floor of a multiple hearth furnace is numerically examined using the Discrete Element Method [...]

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• Non-Fourier heat conduction with phase change using Hyperbolic Lattice Boltzmann Method by modifying the Equilibrium distribution function

  S. Srivastava, M. Mariappan

  particles2023.

  
  

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• Skin Layer Formation in Plate Model for Coupled Analysis of Injection Molding Process of Bonded Magnets

  Y. Uematsu, K. Hirata, F. Miyasaka, T. Kitamura, T. Kikugawa

  particles2023.

  
  

  Abstract

  The bonded magnet, which is formed by mixing magnet materials such as neodymium-based and ferrite-based materials with resin, has the characteristic of being able to be formed into small and complex shapes due to the resin being the binding material. It is used in small motors embedded in hard disk drives and motors for home appliances. The major methods for forming bonded magnets are compression molding and injection molding. In this study, injection molding is selected, which can easily apply to complex shape compared to compression molding. However, injection molding has the disadvantage of variability in density and magnetic properties of the molded products. This is due to the difficulty in observing the material flow, as the molding process progresses inside the mold and multiple processes occur simultaneously such as injection, compression, magnetization, and curing. Therefore, determining the optimal molding parameters for injection molding of bonded magnets requires numerous experimental trials. Based on the above, it is believed that predicting the behavior of resin inside the mold during the molding process using numerical simulation can provide guidelines for determining the optimal molding parameters. The authors have previously proposed a coupled analysis method of "fluid analysis and temperature analysis using MPS (Moving Particle Simulation) method, and magnetic field analysis using magnetic moment method." The objective of this study is to assess the solidification process of resin on the mold surface, utilizing a rectangular-shaped mold model.

  Abstract
  The bonded magnet, which is formed by mixing magnet materials such as neodymium-based and ferrite-based materials with resin, has the characteristic of being able to be formed [...]

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• Numerical Investigation of Pressuremeter Test with Material Point Method

  H. Kurugodu, D. Bhattacharya, P. Vangla, D. Frost

  particles2023.

  
  

  Abstract

  In situ tests for geotechnical investigations can provide a reliable prediction of the soil behaviour because they accurately represent the stress state while preserving the soil structure and the inherent material fabric. These tests complement the information obtained from laboratory element tests on undisturbed or reconstituted specimens. The pressuremeter test is one such example of an in-situ tool that is used to obtain soil properties based on measured pressure-volume data. The pressuremeter test is considered a large deformation problem within a numerical framework. Furthermore, it is commonly idealized as a cylindrical cavity expansion within the realms of conventional finite element schemes. In order to address the issue related to excessive mesh distortion aspects, the Eulerian-Lagrangian approach developed within a continuum framework, namely the Material Point Method (MPM), has been adopted in the present study to investigate the pressuremeter expansion process. First, the results obtained are benchmarked against those from classical cavity expansion problems for a pressure-dependent frictional material. The computed results are in good agreement with both the closed-form solutions and displacement-controlled experiments reported in the literature. A parametric study was performed to further investigate the influence of the loading rate, material properties, and heterogeneities on the pressuremeter test simulations.

  Abstract
  In situ tests for geotechnical investigations can provide a reliable prediction of the soil behaviour because they accurately represent the stress state while preserving the [...]

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• Importance of Periodic Boundaries or Frictionless Walls in Simulating Elementary Response of Angular Particles

  U. Ali, M. Kikumoto, M. Ciantia, M. Prevatali, Y. Cui

  particles2023.

  
  

  Abstract

  In the discrete element method (DEM), the granular response is affected by the selection of boundary conditions, thereby emphasizing the importance of their careful consideration [1]. Replicating the boundary conditions employed in experiments is crucial to have a quantitative agreement between the response observed in the simulation and laboratory test [2]. In this study, a calibrated and validated DEM model was utilized to perform a series of simulations featuring regular polygons with varying numbers of corners subjected to different boundary conditions. The aim was to examine the combined effect of particle shape and boundary conditions on the mechanical response of granular assemblies. Simulations were performed under three boundary conditions: rigid frictional walls (in which the friction between the particle-wall interface is equal to that between the particle-particle interface), rigid frictionless walls, and periodic boundary conditions (PBC). Interestingly, it was observed that qualitatively, the effect of particle shape on granular response was invariant, irrespective of boundary conditions employed. However, quantitatively, the shear strength of all shapes was significantly affected by boundary settings, with the maximum and minimum strengths exhibited under rigid frictional walls and periodic boundaries, respectively. The magnitude of the decrease in shear strength due to boundary conditions was contingent upon the particle shape, with angular assemblies demonstrating a significant change in strength relative to round assemblies. Angular particles in contact with rigid wall frictional boundaries exhibited lesser rotations, thereby inducing relatively significant shear forces on the walls, particularly those parallel to the shearing direction. On the other hand, round particles in contact with walls rotated to a greater extent, resulting in little or negligible shear forces with the walls. Furthermore, boundary conditions also affected deformation patterns, including the development of shear bands.

  Abstract
  In the discrete element method (DEM), the granular response is affected by the selection of boundary conditions, thereby emphasizing the importance of their careful consideration [...]

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• Failure of Cohesive Granular Columns: Friction and Contact Adhesion

  L. Staron, L. Duchemein, P. Lagree

  particles2023.

  
  

  Abstract

  This contribution focuses on the influence of the existence of a debonding length onto the behaviour of a cohesive granular sample. We apply a contact dynamics algorithm to study the effect of both contact adhesion strength and debonding length on the failure of a cohesive step, analysing a set of independent simulations. Contact adhesion strength coincides with stronger pile stability and larger apparent friction in the absence of any debonding length. We show that the existence of a larger debonding length amplifies this phenomenology. At large adhesion strength, we observe the existence of a sharp modification of the behaviour of the system even in the case of a very small debounding length, compared to the case of the absence of the latter. We compare the performance of the algorithm in the different cases, and show how increasing the debonding length leads to a better precision of the hard-core.

  Abstract
  This contribution focuses on the influence of the existence of a debonding length onto the behaviour of a cohesive granular sample. We apply a contact dynamics algorithm to [...]

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• One Discrete Element vs. Two Finite Elements and the Arbelos of Archimedes

  D. Reischl

  particles2023.

  
  

  Abstract

  In this article, a visual proof is given that for a certain simple, yet analytically challenging mechanical system a unique solution exists, which can be found by simple fixed-point iteration as easily to be performed by the reader. As turns out, this system is mostly intractable by means of the finite element method, yet being easily manageable by means of the distinct/discrete element method. Thus, this article gives evidence to the assumption that systems exist which may yield almost arbitrarily wrong results when treated with the finite element method, while giving arbitrarily accurate results when handled by means of the discrete element or similar method.

  Abstract
  In this article, a visual proof is given that for a certain simple, yet analytically challenging mechanical system a unique solution exists, which can be found by simple fixed-point [...]

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• Comparative Analysis of Softening Contact laws in Particle Models: Application to Rock and Concrete

  M. Braga-Farinha, N. Monteiro-Azevedo, S. Oliveira

  particles2023.

  
  

  Abstract

  In this work three constitutive contact models that include softening are adopted for particle model fracture studies in both rock and concrete. For a single local contact, the constitutive contact model performance is initially compared in tensile, pure shear and shear tests under constant axial. Additionally, compression, direct tensile, and confined triaxial tests of quasi-britlle material discretized with spherical particles are presented and the predicted macroscopic response is compared. For a single local contact, the three contact models predict a similar behaviour. As shown, it is possible to calibrate each contact model to reproduce complex macroscopic behaviour observed in rock and concrete, but each contact model requires different contact properties or particle generation procedures

  Abstract
  In this work three constitutive contact models that include softening are adopted for particle model fracture studies in both rock and concrete. For a single local contact, [...]

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• Discrete numerical modelling of capsule-asphalt mixture system for self-healing purposes

  G. Câmara, N. Monteiro-Azevedo, R. Micaelo

  particles2023.

  
  

  Abstract

  Asphalt mixture faces damage due to vehicle speed, repeated loads, and ultraviolet radiation over time, regardless of being a self-healing material. Induced healing mechanisms are necessary to promote autonomous pavement recovery due to adverse in-service conditions, and the capsule-asphalt mixture system incorporating low-viscosity oils (rejuvenators) has shown to be a possible solution in laboratory tests. This study aims to numerically investigate the effect of rejuvenator-modified mastic (activated capsules) on the stiffness properties of asphalt mixtures within the discrete element method. A three-dimensional model previously validated for rejuvenator-modified mastics with different rejuvenator-to-bitumen ratios (0, 2.5, and 10 wt%) is adopted. A generalised Kelvin contact model represents the time-dependent contacts, and its contact parameters define the rejuvenator amount in the mastic phase. The analysis assesses the impact of the modified mastic amount and the rejuvenator-to-bitumen ratio. Results show that the increasing modified mastic content progressively reduces the mixture dynamic modulus. When the total mastic phase has rejuvenator-modified properties, the mixture stiffness modulus significantly reduces, and the phase angle performs differently from the expected (decrease with frequency) at a 10% rejuvenator-to-bitumen ratio due to the excessively softened state, possibly compromising the pavement mechanical performance. For a 0.30 wt% modified mastic ratio case adopting a local effect, the embedded elements do not significantly influence the mixture rheological properties, especially the stiffness modulus, which may be insufficient for self-healing purposes. Nevertheless, the negligible impact on the phase angle highlights the potential of the rejuvenator-modified asphalt mixture across different traffic and temperature condition

  Abstract
  Asphalt mixture faces damage due to vehicle speed, repeated loads, and ultraviolet radiation over time, regardless of being a self-healing material. Induced healing mechanisms [...]

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