Documents published in Scipedia

• 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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• Computational Modeling of Cold Spray Process Using Particle-based Methods

  J. Qi, R. Raoelisin, J. Li, M. Rachik

  particles2023.

  
  

  Abstract

  Cold gas dynamic spraying (CGDS), as a high strain rate shearing and innovative solid-state technique enables to rapidly develop additive manufacturing and coating for metal deposition. This paper investigates the development and evolution of various interfacial bonding characteristics during high strain rate shearing process through Multiphysics numerical simulations of single particle impact. Two different particle-based modeling strategies such as smoothed particle hydrodynamics (SPH), molecular dynamics (MD) are investigated using commercial software ABAQUS/Explicit and LAMMPS, respectively. To separate the difficulties related to complex metallurgy of alloys, our first investigations focus on pure aluminum. The Johnson-Cook (J-C) constitutive model is used to describe the high strain rate self-consolidation process in SPH modeling. Embedded Atom Method (EAM) is used to describe the interactions between Aluminum atoms in MD modeling. The predictions from the different particle-based models are compared with each other and with experimental results. Through the investigations, SPH numerical approach has strong advantage in capturing the phenomena that occur during the cold spray process. It is able to describe the complex features of particle and substrate, especially in the interface vicinity. At the same time, MD numerical approach gives the fundamental understanding of the deposition behavior at the atomistic level. The key finding is the strong relationship between the un-uniform distribution of shear strain and jet formation during high-speed collision. Plastic strain along with an increase of temperature lead to thermal softening of pure Aluminum resulting in metallurgical bonding at the interface.

  Abstract
  Cold gas dynamic spraying (CGDS), as a high strain rate shearing and innovative solid-state technique enables to rapidly develop additive manufacturing and coating for metal [...]

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• Particle-based Flow Simulation of Molten Aluminum Alloy Through Casting Filters

  T. Deguchi, K. Taki, Y. Maeda

  particles2023.

  
  

  Abstract

  Casting defects can be predicted in advance of practice and countermeasures can be taken to improve casting quality and increase productivity. Applying the casting filters is a method of improvement methods for defects caused by unsuitable molten metal flow. Casting filters have the effect of removing inclusions in molten metal and rectifying the flow. However, specific conditions such as the type, pore size, and setting position of the casting filter are not clear. Casting filter conditions are determined by conventional empirical rules that are not theoretical. In the other view, the use of casting CAE is essential to realize front-loading for the process design process, in which casting defects are predicted in advance of practice and countermeasures are taken. In the previous study, K. Taki et al. performed direct observation of mold filling and flow simulations passing through the casting filter. The particle-based COMINA CAE software was used for the flow simulation of molten metal in complex interior geometries in the filter. The calculations used a model of the filter that was reproduced on an X-ray CT system. To inspect the filter performance it was necessary to make a small and simplified filter model, which is called the 1/4 model of filter. In the present study, the flow dynamics through the filter are investigated using various 1/4 models. The 1/4 model maintains permeability on the surface and porosity of volume while halving the dimensions. As a result, we succeed in reproducing the flow behaviour of molten metal when it passed through the filter by setting the particle size of molten metal to 1/16 of the filter’s pore diameter. Further, we try to evaluate the performance of the filter by extending the calculation target from only the area around the filter to the entire mold. If mold filling behavior for the mold with filter could be simulated, it wouldbe used effectively in casting geometry design and defect countermeasure.

  Abstract
  Casting defects can be predicted in advance of practice and countermeasures can be taken to improve casting quality and increase productivity. Applying the casting filters [...]

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• Examination of Variable Tilting Speed on Flow Behaviour during Ladle Pouring in Die Casting using SPH Simulation

  F. Itakura, T. Yamada, Y. Maeda, A. Hasuno, Y. Mochida

  particles2023.

  
  

  Abstract

  Disturbance of the molten metal flow during ladle pouring before the plunger advancing in the aluminium alloy die casting process can cause entrapment defects of air and oxide film. Slow pouring to control the turbulence of the flow front reduces productivity due to increased cycle time. Further, the risk of cold flake formation increases caused by large temperature drops in accordance with the long cycle time. On the other hand, rapid pouring is desired to improve productivity, but the risk of air entrapment increases. Therefore, quick and quiet pouring is desired in the ladle pouring process. In the present study, we focus on variable tilting speed as a method to achieve good ladle pouring. The effects of variable ladle tilting speed and switching time on the wave behavior of molten metal are investigated in visualization experiments and simulations. The flow behaviours in ladle pouring are simulated using ”COLMINA CAE”, which is the casting analysis software by particle-based SPH method. Furthermore, the plunger advancing process is also examined. From the simulation results, the variable tilting speed from fast to low can suppress the rise of the maximum wave height of molten aluminium alloy. However, the pouring completion time is longer. Further, the falling position of molten metal poured from the ladle varied with changing tilting speed. And then, the wave height is influenced not only by ladle pouring but also by the plunger advancing process. These trends of wave behaviour obtained in the simulation are similar to that of the actual phenomenon. Therefore, the present simulation method can accurately estimate the ladle pouring process and plunger advancing process. So, casting CAE is an effective tool for exploring die casting conditions.

  Abstract
  Disturbance of the molten metal flow during ladle pouring before the plunger advancing in the aluminium alloy die casting process can cause entrapment defects of air and oxide [...]

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• Comparison of Incompressible and Weakly-Compressible SPH for the Simulation of Laser Beam Welding

  D. Sollich, P. Eberhard

  particles2023.

  
  

  Abstract

  The process of laser beam welding is simulated using the Weakly-Compressible Smoothed Particle Hydrodynamics (WCSPH) and the Incompressible SPH (ISPH) methods. The presented models consider significant physical effects such as heat conduction, temperature-dependent surface tension with wetting, the phase transitions melting and solidification, and an evaporation-induced recoil pressure. Here, particular emphasis is placed on the modeling differences between the WCSPH and ISPH methods. Then, both methods are evaluated in terms of their accuracy and performance in the simulation of deep penetration laser beam welding with oscillating laser power.

  Abstract
  The process of laser beam welding is simulated using the Weakly-Compressible Smoothed Particle Hydrodynamics (WCSPH) and the Incompressible SPH (ISPH) methods. The presented [...]

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• Calibration of AM powders for Optimization of Recoating Applications using DEM

  N. Sani, J. Quist, K. Jarateg, A. Bilock, L. Cordova, F. Edelvik

  particles2023.

  
  

  Abstract

  Additive Manufacturing (AM) has been a subject of significant attention from both industrial manufacturers and research communities. However, several challenges hinder the widespread implementation of this technology in the industry. Powder recoating is a crucial step in powder-bed AM process that involves achieving a uniformly packed bed of powder particles that are later melted by an energy source, such as a laser or electron beam. One of the main challenges is calibrating the contact model parameters accurately to match the flowability and spreadability of specific powder alloys. This paper proposes a Discrete Element Method (DEM) model calibration framework based on surrogate model optimisation. The study utilises a Revolution Powder Analyser (RPA) as the experimental reference system. The proposed method is demonstrated with two AM powder samples, Ti64 and Inconel 718. The results indicate that particle-particle friction, rolling resistance, and van der Waals (vdW) surface energy significantly affect the system responses. Furthermore, the validation results show good correspondence between the simulation with calibrated parameters and experimental data. Overall, proposed calibration framework has the potential to optimise powder recoating and to improve the accuracy and effectiveness of the additive manufacturing.

  Abstract
  Additive Manufacturing (AM) has been a subject of significant attention from both industrial manufacturers and research communities. However, several challenges hinder the [...]

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