Documents published in Scipedia

• 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 [...]

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• 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, [...]

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• 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 [...]

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• 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 [...]

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• 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 [...]

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• 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 [...]

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• Fast Point-To-Mesh Distance Computation Technique Based On Cell Linked List For Polygon-Wall Boundary In Moving Particle Semi-Implicit Method

  M. Teixeira, L. Pereira, R. Amaro, L. Cheng

  particles2023.

  
  

  Abstract

  The simulation of fluid-structure interaction (FSI) problems usually involves many degrees of freedom, and a considerable number of particles is generally required to model both fluid and solid domains. In relation to the modeling of solid walls by particles, the use of triangular meshes provides more efficient and smoother representation of complex-shaped solid surfaces as well as the straight coupling between particle and mesh-based methods, which is suitable for FSI applications. However, in the particle-based simulations with solid boundaries modeled by mesh, the computation of the particle-mesh distances is a critical time-consuming task, and a fast technique is of major importance. Taking advantage of the cell linked list structure widely adopted for fixed-radius neighborhood search algorithms in particle methods, we proposed a Fast Point-to-mesh Distance computation technique based on Cell linked list (FPDC). Alongside this new technique, a particle-polygon wall contact model was introduced to enable simulations of the collision between the surface of the moving bodies and fixed wall represented, respectively, by particles and mesh. The results show that the proposed technique provides a significant processing time speedup and can be used for practical large-scale problems.

  Abstract
  The simulation of fluid-structure interaction (FSI) problems usually involves many degrees of freedom, and a considerable number of particles is generally required to model [...]

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• A coupled DEM-CFD model to study the physical behavior of loose armor revetments in maritime waterways

  J. Sorgatz, M. Herbst, H. Konietzky, M. Pohl

  particles2023.

  
  

  Abstract

  Revetments serve to protect a canal or river bank against erosion caused by natural and ship-induced waves and currents. A profound understanding of loads and resistances acting on revetments is indispensable for an economic and sustainable, but also safe revetment design. This paper presents a coupled CFD-DEM model (Computational Fluid Dynamics and Discrete Element Method) to study the physical behavior of loose armor stone revetments in maritime waterways. The waves and currents are modelled with a CFD add-on for the particle-based DEM software PFC3D. The DEM approach allows to simulate the shape, size and mass distribution and displacement of the individual armor stones realistically. DEM and CFD are coupled to capture the response of the armor stones to the hydraulic loads. In this paper, the model calibration and validation are presented using data derived from a full-scale flume experiment. The numerical model is compared to the flume tests where a slope is subjected to flow at different velocities. It can be shown that the implementation of revetment and hydraulic loads provides results that are consistent with the experimental data. Both flow velocities and armor stone displacements agree well between the physical and the numerical model. The herein presented study thus provides the basis for the application of the numerical model to more advanced stability analyses of revetments that are, e. g., subjected to wave and current attack.

  Abstract
  Revetments serve to protect a canal or river bank against erosion caused by natural and ship-induced waves and currents. A profound understanding of loads and resistances [...]

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• Elastic Behaviour of Linear Structures Using Modal Superposition and Lagrangian Differencing Dynamics

  M. Paneer, J. Basic, I. Lozina, D. Sedlar, C. Peng

  particles2023.

  
  

  Abstract

  Elastic deformation and dynamics response of the linear structures due to fluid loads are studied to understand the Fluid Structure Interaction (FSI). A modal coupling solver is developed by solving dynamic equation of motion with external loads, using the mode superposition method with the help of relevant mode shapes and natural frequencies associated with the structure. Natural frequencies and mode shapes have been pre-calculated and provided as input for the simulation. Modal coupling is integrated into the Lagrangian Differencing Dynamics (LDD) method, utilizes finite differences within the framework of Lagrangian context, and strong and implicit formulation of Navier Stokes equations to model the incompressible free-surface fluid. Elastic deformation of the structure due to fluid force obtained from the flow solver is calculated in the modal coupling algorithm using direct numerical integration. Then the elastic deformation is imposed in the flow solver to account for change of the geometry and obtain new flow pressure and velocity fields. The two-way coupling of fluid and structure is successfully validated by simulating dam-break through an elastic gate. Since the LDD method works directly on surface meshes, the simulation is quickly setup and direct coupling of structural deformation eliminated the usual step of mapping of fluid results on the structural mesh and vice-versa

  Abstract
  Elastic deformation and dynamics response of the linear structures due to fluid loads are studied to understand the Fluid Structure Interaction (FSI). A modal coupling solver [...]

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• A DEM-FEM Coupling Framework Applied to Railroad Infrastructure Simulations

  A. Ullrich, J. Quist, C. Cromvik, K. Jarateg, A. Bilock

  particles2023.

  
  

  Abstract

  Swedish and other European governments invest significant resources in railroad infrastructure, including maintenance and construction. The degradation of track ballast layers is one of the most critical maintenance issues. Hence, it is of significant interest for infrastructure owners to find novel solutions to mitigate the problem by improving design and maintenance operations. However, established tools for the simulation of railroad systems typically consider the ballast as a solid continuum structure, while in practice, the discrete nature of the particle assembly has to be accurately represented in the model. The sleepers and rails must be modelled as solid structures, which results in the complex coupled problem of combining particulate and structural analysis models. In this paper, the simulation of railroad infrastructure with the example of a transition zone is performed with an explicit surface coupling algorithm of the Discrete Element Method (DEM) and the Finite Element Method (FEM). The ballast layer is represented by individual particles in DEM, where the computations are performed on the GPU. This study focuses on the comparison between a convex and a non-convex particle shape. The rail system with sleepers and the subground with varying stiffness is modelled with solid structures in FEM. Properties of the ballast bed, such as the particle shape, are found to have a significant impact on the stiffness within the bed and the deflection of the sleepers and rails. Furthermore, the sudden transition from low to high stiffness causes a peak in tensile stress in the subground. The results show that accurate particle shape representation and high computational performance are critical aspects of achieving predictions on a relevant scale. Studying the ballast layer as a particulate system provides a new perspective on dynamics in tracked ballast structures.

  Abstract
  Swedish and other European governments invest significant resources in railroad infrastructure, including maintenance and construction. The degradation of track ballast layers [...]

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