Documents published in Scipedia

• 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 [...]

  • 1
  •  read

• 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, [...]

  • 2
  •  read

• 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 [...]

  • 26
  •  read

• SPH modeling of advanced materials in hypervelocity impact simulations

  A. Cherniaev, A. Gudisey

  particles2023.

  
  

  Abstract

  Spacecraft must be analyzed for their ability to survive hypervelocity impacts (HVI) by orbital debris, as collision of a space vehicle with even a millimeter-sized object traveling at a typical orbital speed (7 km/s and higher) can be detrimental for both the spacecraft and the orbital environment. Due to the high cost of the physical HVI experiments, numerical modeling plays a significant role in conducting such analyses. In particular, the smoothed particles hydrodynamics technique (SPH) was previously found applicable for simulating scenarios involving extreme deformations and fragmentation, including hypervelocity impact. With the extensive use of advanced lightweight materials in space structures, it is important to find a rational way of representing them using the SPH framework. This study reports the results of SPH modeling of two distinct types of lightweight materials often employed in space structures: open-cell foams and fiber-reinforced composites. For foams, explicit representation of their complex mesoscopic architecture was achieved by filling the STL exteriors (generated using X-ray computed tomography) with SPH particles. For laminated composites, ply-wise representation was obtained using finite elements that could locally and adaptively transform to SPH particles when the elements become highly distorted and inefficient. Results of HVI simulations involving foams and composites were compared with available experimental data. The advantages and limitations of the modeling techniques are discussed. Spacecraft must be analyzed for their ability to survive hypervelocity impacts (HVI) by orbital debris, as collision of a space vehicle with even a millimeter-sized object traveling at a typical orbital speed (7 km/s and higher) can be detrimental for both the spacecraft and the orbital environment. Due to the high cost of the physical HVI experiments, numerical modeling plays a significant role in conducting such analyses. In particular, the smoothed particles hydrodynamics technique (SPH) was previously found applicable for simulating scenarios involving extreme deformations and fragmentation, including hypervelocity impact. With the extensive use of advanced lightweight materials in space structures, it is important to find a rational way of representing them using the SPH framework. This study reports the results of SPH modeling of two distinct types of lightweight materials often employed in space structures: open-cell foams and fiber-reinforced composites. For foams, explicit representation of their complex mesoscopic architecture was achieved by filling the STL exteriors (generated using X-ray computed tomography) with SPH particles. For laminated composites, ply-wise representation was obtained using finite elements that could locally and adaptively transform to SPH particles when the elements become highly distorted and inefficient. Results of HVI simulations involving foams and composites were compared with available experimental data. The advantages and limitations of the modeling techniques are discussed. Spacecraft must be analyzed for their ability to survive hypervelocity impacts (HVI) by orbital debris, as collision of a space vehicle with even a millimeter-sized object traveling at a typical orbital speed (7 km/s and higher) can be detrimental for both the spacecraft and the orbital environment. Due to the high cost of the physical HVI experiments, numerical modeling plays a significant role in conducting such analyses. In particular, the smoothed particles hydrodynamics technique (SPH) was previously found applicable for simulating scenarios involving extreme deformations and fragmentation, including hypervelocity impact. With the extensive use of advanced lightweight materials in space structures, it is important to find a rational way of representing them using the SPH framework. This study reports the results of SPH modeling of two distinct types of lightweight materials often employed in space structures: open-cell foams and fiber-reinforced composites. For foams, explicit representation of their complex mesoscopic architecture was achieved by filling the STL exteriors (generated using X-ray computed tomography) with SPH particles. For laminated composites, ply-wise representation was obtained using finite elements that could locally and adaptively transform to SPH particles when the elements become highly distorted and inefficient. Results of HVI simulations involving foams and composites were compared with available experimental data. The advantages and limitations of the modeling techniques are discussed.

  Abstract
  Spacecraft must be analyzed for their ability to survive hypervelocity impacts (HVI) by orbital debris, as collision of a space vehicle with even a millimeter-sized object [...]

  • 0
  •  read

• Comparative Study of Methods to Generate C^2 Continuous Mesh-free Basis using the Moving Least Squares Method

  G. Bridhani, . U.Saravanan

  particles2023.

  
  

  Abstract

  This study investigates the ability of three different approaches for constructing smooth and continuous mesh-free basis functions, namely: (i) assuming one degree of freedom per node with the moving least squares method, (ii) assuming six degrees of freedom per node with moving least squares method, and (iii) assuming six degrees of freedom per node with Hermite-type moving least squares method. Further, it provides evidence that all three approaches can generate continuous mesh-free basis functions;however, the first and third approach results in a C^2 continuous mesh-free basis, where the function and its first and second-order derivatives are related. Finally, a comparative study is performed among the three approaches using fourth-order polynomial basis and fifth-order spline weight function.

  Abstract
  This study investigates the ability of three different approaches for constructing smooth and continuous mesh-free basis functions, namely: (i) assuming one degree of freedom [...]

  • 13
  •  read

• Advanced Structure Modelling Using the Bonded-Particle Method: Enabling Complex Capabilities for Structures in DEM Simulations

  E. Fimbinger

  particles2023.

  
  

  Abstract

  Bonded-particle modelling is a powerful approach for simulating particle made structures with enhanced abilities, i.e., structures that are able to deform, brake/fracture, and thus interact with other particles of a DEM simulation in an enhanced complex manner. This modelling approach is based on connecting particles with beam elements (commonly termed bondings, with each bonding connecting two particles) to create a bonded-particle model (BPM), typically consisting of a large number of particles and bondings. The behaviour of such a BPM can be adjusted in two categories: via properties related to the particles, e.g. their mass, shape, or frictional characteristics, and via properties related to the bondings, e.g. their Young’s moduli or breakage criteria. This contribution presents developments in complex bonded-particle modelling for achieving flexible/deformable and breakable/fracturable structures and highlights the enhanced capabilities made possible by using this approach. For this purpose, various applications for bonded-particle modelling in DEM simulations are presented, with selected case studies each demonstrating the effectiveness of bonded-particle modelling in solving practical engineering problems, including: - 1D BPMs, e.g., deformable beams or ropes and chains, - 2D BPMs, e.g., membranes, textiles, nets, bags, shell-like parts (e.g. silos), or conveyor belts (with particular reference to dynamic belt simulation), and - 3D BPMs, e.g., complex-breakable structures (e.g. with considering crack formation or dynamic impact handling; e.g. illustrated on filter cake material). Furthermore, possible interaction scenarios, including interactions of BPMs to particles, rigid parts, other BPMs, or even in terms of SPH (Smoothed-Particle Hydrodynamic) or MBD (Multibody Dynamics), are addressed. Finally, current developments and potential future directions in this field are outlined, and potentials for extending this modelling approach to further application areas are discussed.

  Abstract
  Bonded-particle modelling is a powerful approach for simulating particle made structures with enhanced abilities, i.e., structures that are able to deform, brake/fracture, [...]

  • 3
  •  read

• Contact Detection Algorithm for Convex NURBS Particles

  M. Craveiro, A. Gay-Nieto, P. Wriggers

  particles2023.

  
  

  Abstract

  The present work proposes a contact detection algorithm for convex particles whose boundaries are mathematically defined by non-uniform B-splines (NURBS). This algorithm involves a hierarchy of contact searches, including both global and local steps. The focus is on the formulation of the local contact problem (LCP) using a master-to-master approach. It is based on computer graphics and optimization techniques. Besides the algorithm, the paper also discusses strategies for modeling particle geometry and their implications in contact detection. The use of multiple parameterizations (patches) assembled in space, for instance, provides more flexibility in the construction of particles and avoids numerical singularities. However, it leads to local geometric imperfections at the connection between patches. The LCP formulation proposed herein can deal with such imperfections through a contact degeneration technique. An example shows the robustness of the method.

  Abstract
  The present work proposes a contact detection algorithm for convex particles whose boundaries are mathematically defined by non-uniform B-splines (NURBS). This algorithm involves [...]

  • 1
  •  read

• Improving asphalt discrete numerical modelling with realistic particle shapes

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

  particles2023.

  
  

  Abstract

  Micromechanical modelling based on the Discrete Element Method (DEM) has been widely used to investigate asphalt behaviour due to its ability to represent an irregular microstructure with variable-sized aggregates, bitumen and voids. The 3D rigid particle models with randomly distributed spherical particles and adopting elastic and/or simple viscoelastic models at the contacts are the standard approach, however, in recent years, a significant research effort is noted to incorporate real particle morphologies in the numerical models. In this study, a previously developed 3D DEM model of asphalt employing a generalised Kelvin contact model formulation for the viscoelastic contacts is further improved with realistic particle shapes representing the coarse aggregates. A digital library of aggregate shapes was created from the X-ray computed tomography (CT) scan of an asphalt specimen, using an adaptive image-processing method to separate the aggregates in the CT images and the Delaunay triangulation method to define the aggregate 3D surface model. Several virtual aggregates with different sizes were selected from the library to represent the coarse aggregate gradation of the modelled 3D DEM asphalt specimen. Each virtual aggregate is discretized with smaller spherical particles and its deformability is taken into account through the inner particle contacts. The numerical asphalt specimens with realistic particle shapes were submitted to uniaxial tension-compression cyclic tests to determine the stiffness properties, and the results were compared with those of the numerical specimens with all constituents represented by single spherical rigid particles. As shown, the proposed methodology greatly enhances the 3D DEM model's ability to simulate the asphalt behaviour.

  Abstract
  Micromechanical modelling based on the Discrete Element Method (DEM) has been widely used to investigate asphalt behaviour due to its ability to represent an irregular microstructure [...]

  • 1
  •  read

• Investigation of Dynamic Characteristics of Rolling-Ball Dampers

  K. Nagashima, M. Saeki

  particles2023.

  
  

  Abstract

  Tuned mass dampers, consisting of a mass, spring, and damper, are widely used for vibration suppression in structures. Despite being small and lightweight, these dampers exhibit excellent damping effectiveness. However, there are issues such as performance degradation due to the aging of the spring and damper, as well as the need for frequent maintenance. Therefore, as an alternative vibration control device that does not rely on these components, a rolling-ball damper is proposed. This damper consists of a container with a lid and multiple enclosed particles on its curved surface. By utilizing the contact between particles and the friction between particles and the container, the rolling-ball damper can absorb and suppress the vibration energy imposed on the structure to which the container is attached. In this study, we investigated the characteristics of the rolling-ball damper in a horizontal vibration system. We experimentally verified the effects of the size and number of enclosed particles on damping performance. Furthermore, numerical simulations were conducted by the discrete element method using EDEM® software and the multibody dynamics simulation method using MotionSolve® software. A comparison between experimental and numerical simulation results demonstrated the effectiveness of numerical calculations in predicting the amplitude response

  Abstract
  Tuned mass dampers, consisting of a mass, spring, and damper, are widely used for vibration suppression in structures. Despite being small and lightweight, these dampers exhibit [...]

  • 1
  •  read

• Experimental and Numerical Studies on the Efficiency of Damping upon Horizontal Stirring of Granular Materials

  K. Ishizeki, M. Saeki

  particles2023.

  
  

  Abstract

  In this study, the damping torque exerted on a horizontally rotating blade in granular materials under gravity was investigated. To capture the stirring behaviour of the granular materials in detail, a mechanical stirring apparatus was fabricated. The rotating blade was driven sinusoidally by a shaker through a ball screw mechanism. It was found that energy dissipation depends on various parameters such as particle material and particle size. Energy dissipation was also calculated using the EDEM® software based on the discrete element method. To verify the validity of the numerical simulation model, numerical simulation results were compared with experimental results.

  Abstract
  In this study, the damping torque exerted on a horizontally rotating blade in granular materials under gravity was investigated. To capture the stirring behaviour of the granular [...]

  • 1
  •  read