Showing papers in "Computational particle mechanics in 2021"
TL;DR: A brief review of grand challenges of Smoothed Particle Hydrodynamics (SPH) method and a discussion on the areas for future development is presented.
Abstract: This paper presents a brief review of grand challenges of Smoothed Particle Hydrodynamics (SPH) method. As a meshless method, SPH can simulate a large range of applications from astrophysics to free-surface flows, to complex mixing problems in industry and has had notable successes. As a young computational method, the SPH method still requires development to address important elements which prevent more widespread use. This effort has been led by members of the SPH rEsearch and engineeRing International Community (SPHERIC) who have identified SPH Grand Challenges. The SPHERIC SPH Grand Challenges (GCs) have been grouped into 5 categories: (GC1) convergence, consistency and stability, (GC2) boundary conditions, (GC3) adaptivity, (GC4) coupling to other models, and (GC5) applicability to industry. The SPH Grand Challenges have been formulated to focus the attention and activities of researchers, developers, and users around the world. The status of each SPH Grand Challenge is presented in this paper with a discussion on the areas for future development.
103 citations
TL;DR: In this paper, the density of solid particles is obtained from ghost positions within the fluid domain by linear extrapolation, where the gap between fluid and boundary is reduced and pressures in still water converge to hydrostatic.
Abstract: Dynamic boundary conditions (DBC) for solid surfaces are standard in the weakly compressible smoothed particle hydrodynamics (SPH) code DualSPHysics. A stationary solid is simply represented by fixed particles with pressure from the equation of state. Boundaries are easy to set up and computations are relatively stable and efficient, providing robust numerical simulation for complex geometries. However, a small unphysical gap between the fluid and solid boundaries can form, decreasing the accuracy of pressures measured on the boundary. A method is presented where the density of solid particles is obtained from ghost positions within the fluid domain by linear extrapolation. With this approach, the gap between fluid and boundary is reduced and pressures in still water converge to hydrostatic, including the case of a bed with a sharp corner. The violent free-surface cases of a sloshing tank and dam break impact on an obstacle show pressures measured directly on solid surfaces in close agreement with experiments. The complex 3-D flow in a fish pass, with baffles to divert the flow, is simulated showing close agreement with measured water levels with weirs open and gates closed, but less close with gates open and weirs closed. This indicates the method is suitable for rapidly varying free-surface flows, but development for complex turbulent flows is necessary. The code with the modified dynamic boundary condition (mDBC) is available in DualSPHysics to run on CPUs or GPUs.
52 citations
TL;DR: In this paper, a numerical tool for modelling dense transient granular material flow is presented and validated against experiments, where granular materials are modelled as continuous materials using two different constitutive models.
Abstract: The prediction of transient granular material flow is of fundamental industrial importance. The potential of using numerical methods in system design for increasing the operating efficiency of industrial processes involving granular material flow is huge. In the present study, a numerical tool for modelling dense transient granular material flow is presented and validated against experiments. The granular materials are modelled as continuous materials using two different constitutive models. The choice of constitutive models is made with the aim to predict the mechanical behaviour of a granular material during the transition from stationary to flowing and back to stationary state. The particle finite element method (PFEM) is employed as a numerical tool to simulate the transient granular material flow. Use of the PFEM enables a robust treatment of large deformations and free surfaces. The fundamental problem of collapsing rectangular columns of granular material is studied experimentally employing a novel approach for in-plane velocity measurements by digital image correlation. The proposed numerical model is used to simulate the experimentally studied column collapses. The model prediction of the in-plane velocity field during the collapse agrees well with experiments.
20 citations
TL;DR: In this paper, a particle generation technique by integrating spherical harmonics and probability functions is presented. But the technique only requires morphological information from one particle to generate a large number of particles and eliminates the need for scanning many particles for particle generation.
Abstract: Three-dimensional imaging techniques, such as X-ray computed tomography, have been used to scan realistic particle geometries. However, these techniques are labor intensive, time-consuming, and costly to obtain a large number of particles. Therefore, it is desirable if computers can be taught to generate realistic particles based on given morphological properties. This paper develops a particle generation technique by integrating spherical harmonics and probability functions. This technique only requires morphological information from one particle to generate a large number of particles and eliminates the need for scanning many particles for particle generation. The spherical harmonics coefficients of this particle are analog of the morphological gene. The probability function is used to add variances to spherical harmonics coefficients to simulate gene mutation. A dimensionless factor is developed to control degrees of gene mutation. The effectiveness and accuracy of the proposed technique are verified by particle shape descriptors computed by the computational geometry techniques.
18 citations
TL;DR: DualSPHysics as discussed by the authors is a weakly compressible smoothed particle hydrodynamics (SPH) Navier-Stokes solver initially conceived to deal with coastal engineering problems, especially those related to wave impact with coastal structures.
Abstract: DualSPHysics is a weakly compressible smoothed particle hydrodynamics (SPH) Navier–Stokes solver initially conceived to deal with coastal engineering problems, especially those related to wave impact with coastal structures. Since the first release back in 2011, DualSPHysics has shown to be robust and accurate for simulating extreme wave events along with a continuous improvement in efficiency thanks to the exploitation of hardware such as graphics processing units for scientific computing or the coupling with wave propagating models such as SWASH and OceanWave3D. Numerous additional functionalities have also been included in the DualSPHysics package over the last few years which allow the simulation of fluid-driven objects. The use of the discrete element method has allowed the solver to simulate the interaction among different bodies (sliding rocks, for example), which provides a unique tool to analyse debris flows. In addition, the recent coupling with other solvers like Project Chrono or MoorDyn has been a milestone in the development of the solver. Project Chrono allows the simulation of articulated structures with joints, hinges, sliders and springs and MoorDyn allows simulating moored structures. Both functionalities make DualSPHysics especially suited for the simulation of offshore energy harvesting devices. Lately, the present state of maturity of the solver goes beyond single-phase simulations, allowing multi-phase simulations with gas–liquid and a combination of Newtonian and non-Newtonian models expanding further the capabilities and range of applications for the DualSPHysics solver. These advances and functionalities make DualSPHysics an advanced meshless solver with emphasis on free-surface flow modelling.
18 citations
TL;DR: In this paper, modified contact detection and inter-processor communication schemes implemented in LAMMPS are presented for polydisperse granular media, which account for particles of different sizes separately, greatly improving efficiency.
Abstract: Discrete element modeling (DEM) of polydisperse granular materials is significantly more computationally expensive than modeling of monodisperse materials as a larger number of particles are required to obtain a representative elementary volume, and standard contact detection algorithms become progressively less efficient with polydispersity. This paper presents modified contact detection and inter-processor communication schemes implemented in LAMMPS which account for particles of different sizes separately, greatly improving efficiency. This new scheme is applied to the inertial number (I), which quantifies the ratio of inertial to confining forces. This has been used to identify the quasi-static limit for shearing of granular materials, which is often taken to be $$ I = 10^{ - 3} $$
. However, the expression for the inertial number contains a particle diameter term and therefore it is unclear how to apply this for polydisperse media. Results of DEM shearing tests on polydisperse granular media are presented in order to determine whether $$ I $$
provides a unique quasi-static limit regardless of polydispersity and which particle diameter term should be used to calculate $$ I $$
. The results show that the commonly used value of $$ I = 10^{ - 3} $$
can successfully locate the quasi-static limit for monodisperse media but not for polydisperse media, for which significant variations of macroscopic stress ratio and microscopic force and contact networks are apparent down to at least $$ I = 10^{ - 6} $$
. The quasi-static limit could not be conclusively determined for the polydisperse samples. Based on these results, the quasi-staticity of polydisperse samples should not be inferred from a low inertial number as currently formulated, irrespective of the particle diameter used in its calculation.
18 citations
TL;DR: In this article, the authors investigated the breakage behavior of individual biomass pellets under experimental compression tests and introduced a calibrated numerical model using discrete element method (DEM) in order to pave the way for further studies on pellet breakage.
Abstract: The presence and generation of fines and dust in the bulk of biomass pellets have inflicted several problems in the supply chain during transportation and storage, and the breakage behavior of pellets has been scarcely studied so far. Fines and dust are the consequences of impact and abrasive forces through the whole supply chain; however, the breakage happens at the particle level. Therefore, to study the fines generation, first, the breakage behavior of individual pellets should be understood, and then, the behavior of the bulk materials in operational conditions can be investigated. This paper aims to investigate the breakage behavior of individual pellets under experimental compression tests and to introduce a calibrated numerical model using discrete element method (DEM) in order to pave the way for further studies on pellet breakage. For that purpose, seven different types of biomass pellets were studied experimentally, and then, a calibrated model was introduced via the Timoshenko–Ehrenfest beam theory using DEM. Results show that the model could reasonably predict the breakage behavior of pellets under uniaxial and diametrical compressions. The findings could help to develop a new design of the equipment for transportation and handling of biomass pellets with the aim to reduce the amount of generating fines and dust.
16 citations
TL;DR: In this article, the energy dissipation and loss factor of different configurations of particle dampers are analyzed via the complex power for a large excitation range, and a direct correlation of the loss factor to the motion modes of the rheology behavior is shown.
Abstract: Particle dampers show a huge potential to reduce undesired vibrations in technical applications even under harsh environmental conditions. However, their energy dissipation depends on many effects on the micro- and macroscopic scale, which are not fully understood yet. This paper aims toward the development of design rules for particle dampers by looking at both scales. This shall shorten the design process for future applications. The energy dissipation and loss factor of different configurations are analyzed via the complex power for a large excitation range. Comparisons to discrete element simulations show a good qualitative agreement. These simulations give an insight into the process in the damper. For monodisperse systems, a direct correlation of the loss factor to the motion modes of the rheology behavior is shown. For well-known excitation conditions, simple design rules are derived. First investigations into polydisperse settings are made, showing a potential for a more robust damping behavior.
16 citations
TL;DR: This paper presents the overall philosophy, the main design choices and some of the original algorithms implemented in Karamelo, an open source, fast, light and easy-to-modify framework for both conducting research on the material point method and research using the MPM.
Abstract: A simple and robust C++ code for the material point method (MPM) called Karamelo is presented here. It was designed to provide an open source, fast, light and easy-to-modify framework for both conducting research on the MPM and research using the MPM, instead of a finite element package. This paper presents the overall philosophy, the main design choices and some of the original algorithms implemented in Karamelo. Simulations of solids and fluids involving extreme deformation are provided to illustrate the capabilities of the code.
15 citations
TL;DR: Numerical results demonstrate the potential of these basis functions within MPM in terms of grid-crossing-error elimination and higher-order convergence and this paper presents an extension of BSMPM to unstructured triangulations.
Abstract: The Material Point Method (MPM) is a numerical technique that combines a fixed Eulerian background grid and Lagrangian point masses to simulate materials which undergo large deformations. Within the original MPM, discontinuous gradients of the piecewise-linear basis functions lead to the so-called grid-crossing errors when particles cross element boundaries. Previous research has shown that B-spline MPM (BSMPM) is a viable alternative not only to MPM, but also to more advanced versions of the method that are designed to reduce the grid-crossing errors. In contrast to many other MPM-related methods, BSMPM has been used exclusively on structured rectangular domains, considerably limiting its range of applicability. In this paper, we present an extension of BSMPM to unstructured triangulations. The proposed approach combines MPM with $$C^1$$
-continuous high-order Powell–Sabin spline basis functions. Numerical results demonstrate the potential of these basis functions within MPM in terms of grid-crossing-error elimination and higher-order convergence.
15 citations
TL;DR: In this article, the Particle Finite Element Method (PFEM) is used to solve the incompressible fluids and to track their evolving free surface, while the solid bodies are modeled with the standard FEM.
Abstract: This work presents a fully Lagrangian Finite Element Method (FEM) with nodal integration for the simulation of fluid–structure interaction (FSI) problems. The Particle Finite Element Method (PFEM) is used to solve the incompressible fluids and to track their evolving free surface, while the solid bodies are modeled with the standard FEM. The coupled problem is solved through a monolithic approach to ensure a strong FSI coupling. Accuracy and convergence of the proposed nodal integration method are proved against several benchmark tests, involving complex interactions between unsteady free-surface fluids and solids undergoing large displacements. A very good agreement with the numerical and experimental results of the literature is obtained. The numerical results of the nodal integration algorithm are also compared to those given by a standard Gaussian method, and their upper-bound convergent behavior is also discussed.
TL;DR: In this paper, the authors investigate the effects of particle size distribution (PSD), rotation speed, and rolling friction on overall wall-bed heat transfer using the validated codes and find that the variability in the PSD with same mean, μ, and standard deviation, σ, resulted in different heat transfer coefficients.
Abstract: Contact conduction heat transfer behavior in a rotary drum using the discrete element method (DEM)-based simulation codes MFIX-DEM (open-source) and EDEM (commercial) is investigated. Simulations are performed to compare the performance of open-source and commercial code models with experimental data. This study also aims to investigate the effects of particle size distribution (PSD), rotation speed, and rolling friction on overall wall–bed heat transfer using the validated codes. It is found that the variability in the PSD with same mean, μ, and standard deviation, σ, resulted in different heat transfer coefficients. Monodispersed particle beds exhibit better heat transfer when compared to polydispersed beds, because heat transfer is inhibited as the distribution broadens due to segregation. Rotation speed has minimal impact on conduction heat transfer. At lower values of rolling friction, particle circulation in the bed is enhanced and therefore better heat transfer is achieved.
TL;DR: In this article, an alternative numerical approach that can efficiently and accurately predict the influence of different discrete element method (DEM) parameters on various sought macroscopic responses, where, accordingly, model validation based on experimental data is applied.
Abstract: One of the key challenges in the implementation of discrete element method (DEM) to model powder’s flow is the appropriate selection of material parameters, where empirical approaches are mostly applied. The aim of this study is to develop an alternative systematic numerical approach that can efficiently and accurately predict the influence of different DEM parameters on various sought macroscopic responses, where, accordingly, model validation based on experimental data is applied. Therefore, design of experiment and multivariate regression analysis, using an optimized quadratic D-optimal design model and new analysis tools, i.e., adjusted response and Pareto graphs, are applied. A special focus is laid on the impact of six DEM microscopic input parameters (i.e., coefficients of static and rolling friction, coefficient of restitution, particle size, Young’s modulus and cohesion energy density) on five macroscopic output responses (i.e., angle of repose, porosity, mass flow rate, translational kinetic energy and computation time) using angle of repose tests applied to free-flowing and cohesive powders. The underlying analyses and tests show, for instance, the substantial impact of the rolling friction coefficient and the minor role of the static friction coefficient or the particle size on the angle of repose in cohesive powders. In addition, in both powders, the porosity parameter is highly influenced by the static and rolling friction coefficients.
TL;DR: An explicit incompressible smoothed particle hydrodynamics formulation with stabilized pressure distribution and its implementation in a multiple graphics processing unit environment and a simulation of the famous Fukushima Dai-ichi Power Plant inundation by the tsunami from The Great East Japan Earthquake in 2011 are presented.
Abstract: We present an explicit incompressible smoothed particle hydrodynamics formulation with stabilized pressure distribution and its implementation in a multiple graphics processing unit environment. The pressure Poisson equation is stabilized via both pressure invariance and divergence-free conditions, and its explicit formulation is derived using the first step of the Jacobi iterative solver. Also, we show how to adapt the fixed wall ghost particle for the boundary condition into our explicit approach. Verification and validation of the method include hydrostatic and dam break numerical tests. The computational performance in the multi-GPU environment was notably high with reasonable speedup values compared to our single-GPU implementation. In particular, our code allows simulations with very large number of particles reaching up to 200 million per GPU card. Finally, to illustrate the potential of our formulation in simulating natural disasters, we present a simulation of the famous Fukushima Dai-ichi Power Plant inundation by the tsunami from The Great East Japan Earthquake in 2011, in Japan.
TL;DR: In this article, a multiscale simulation of continuous crushing of granular sand under one-dimensional compression in consideration of particle-scale anisotropy through modeling planes of weakness inside individual particles, with reference to granular materials rich in minerals and containing cleavages.
Abstract: Natural granular materials such as sands often possess complex microstructural features including cleavage and minerals interfaces. Those features bring apparent mechanical anisotropy to particles and are known to have pronounced influence on particle crushing characteristics. This paper presents a multiscale simulation of continuous crushing of granular sand under one-dimensional compression in consideration of particle-scale anisotropy through modeling planes of weakness inside individual particles, with reference to granular materials rich in minerals and containing cleavages. The multiscale modeling is based on a coupled peridynamics and non-smooth contact dynamics method where peridynamics is used to model crushing of individual particles and non-smooth contact dynamics is employed to simulate discrete granular system. Weak microstructural planes are simulated by breaking a fraction of peridynamic bonds as an initial condition. Simulation results show that anisotropic particles containing weak planes result in larger number of fragments and exhibit relatively higher fractal dimension with respect to particle size. Particle shape is found to approach a steady state profile with continuous crushing. Anisotropic particles generally bear smaller sphericity, aspect ratio, elongation and flatness than those isotropic particles. The anisotropy in particles seems to mitigate shape effect on particle strength and crushing energy. Macromechanical yield stress of the sample is related to single particle strength monotonically, but the relationship appears to be nonlinear when different microstructural features are involved.
TL;DR: In this article, a novel approach to numerical modeling of selective laser melting (SLM) processes characterized by melting and solidification of the deposited particulate material is presented, based entirely on two homogeneous methods, such as cellular automata and Lattice Boltzmann.
Abstract: This paper presents a novel approach to numerical modelling of selective laser melting (SLM) processes characterized by melting and solidification of the deposited particulate material. The approach is based entirely on two homogeneous methods, such as cellular automata and Lattice Boltzmann. The model components operate in the common domain allowing for linking them into a more complex holistic numerical model with the possibility to complete full-scale calculations eliminating complicated interfaces. Several physical events, occurring in sequence or simultaneously, are currently considered including powder bed deposition, laser energy absorption and heating of the powder bed by the moving laser beam leading to powder melting, fluid flow in the melted pool, flow through partly or not melted materials and solidification. The possibilities and benefits of the proposed solution are demonstrated through a series of benchmark cases, as well as model verifications. The presented case studies deal mainly with melting and solidification of the powder bed including the free surface flow, wettability, and surface tension. An example of process simulation shows that the approach is generic and can be applied to different multi-material SLM processes, where energy transfer including solid–liquid phase transformation is essential, by integrating the developed models within the proposed framework.
TL;DR: In this paper, a moving particle full-implicit (MPFI) method was developed, where the discretized interaction forces are related to an analytical mechanical framework for the systems with dissipation.
Abstract: In general, mechanical energy monotonically decreases in a physically consistent system, constructed with conservative force and dissipative force. This feature is important in designing a particle method, which is a discrete system approximating continuum fluid with particles. When the discretized system can be fit into a framework of analytical mechanics, it will be a physically consistent system which prevents instability like particle scattering along with unphysical mechanical energy increase. This is the case also in incompressible particle methods. However, most incompressible particle methods do not satisfy the physical consistency, and they need empirical relaxations to suppress the system instability due to the unphysical energy behavior. In this study, a new incompressible particle method with the physical consistency, moving particle full-implicit (MPFI) method, is developed, where the discretized interaction forces are related to an analytical mechanical framework for the systems with dissipation. Moreover, a new pressure evaluation technique based on the virial theorem is proposed for the system. Using the MPFI method, static pressure, droplet extension, standing wave and dam break calculations were conducted. The capability to predict pressure and motion of incompressible free surface flow was presented, and energy dissipation property depending on the particle size and time step width was studied through the calculations.
TL;DR: In this article, a combined finite-discrete element method (FDEM) is employed to simulate the collapse behavior of dry-joint masonry arches induced by spreading supports.
Abstract: Masonry arches are usually composed of individual blocks or voussoirs, which are highly discontinuous and nonlinear, and it is extremely difficult or even impossible to simulate their collapse behavior using finite element methods. Therefore, a combined finite–discrete element method (FDEM) is employed to simulate the collapse behavior of dry-joint masonry arches induced by spreading supports. With finite elements incorporated into discrete elements, both the deformation of arch voussoirs and the interaction between them such as contact can be predicted accurately. Moreover, a cohesive fracture model is implemented to simulate the potential rupture of masonry voussoirs. Based on them, several examples are validated with experiments, and the results indicate that the FDEM is able to simulate the collapse of masonry arches well. Furthermore, a parametric study is conducted on selected geometric and physical parameters to investigate the collapse of masonry arches due to support movements. The influences of friction and voussoir fracture where limited attention was paid to are also examined.
TL;DR: In this paper, the change in flow characteristics was analyzed in terms of the velocity and angular velocity, to clarify the special effect of the flow pattern transition and time variation during discharge, and the study on the distribution and dynamic evolution of flow characteristics in silos provides theoretical basis for structural optimization design of self-weight discharge silos.
Abstract: The silos have a complex flow behavior: The lower part presents a “funnel flow” and the upper part presents a “mass flow”. It is necessary to study the flow characteristics of the silos in mixed flow on mesoscale. In this paper, the change in flow characteristics was analyzed in terms of the velocity and angular velocity, to clarify the special effect of the flow pattern transition and time variation during discharge. The results show that the flow characteristics change significantly during the flow pattern transition, the flow characteristics would not variety uniformly with height, and the flow pattern and shear zone have a great influence on them: the flow characteristics change more dramatically in funnel flow; the particles in the shear zone move slowly and rotate sharply with friction couples. The flow transformation can be characterized by more flow characteristics, not only the vertical velocity. Moreover, the profiles of velocity and angular velocity almost would not evolve with time, but only with the particles’ position. The study on the distribution and dynamic evolution of flow characteristics in silos provides theoretical basis for structural optimization design of self-weight discharge silos.
TL;DR: In this article, the discharge characteristics of binary particles in a rectangular hopper with an inclined bottom were investigated using the discrete element method (DEM) to simulate the discharge process and the accuracy of DEM was validated by comparing calculated and experimental values.
Abstract: The stable discharge of particles through the hopper plays a key role in many industrial applications. In order to investigate the discharge characteristics of binary particles in a rectangular hopper with an inclined bottom, the discrete element method (DEM) was used to simulate the discharge process. The accuracy of DEM was validated by comparing calculated and experimental values. The influences of geometric parameters (hopper width, orifice width, and hopper angle) and particle parameters (friction coefficient between particles, friction coefficient between particles and wall, fine particle mass fraction, and particle size ratio) on the discharge were studied. Some interesting results have been found that the effect of hopper width on discharge is minimal. The mass discharge rate is linearly related to the 3/2 power of orifice width, and it can be predicted by the modified Beverloo correlation which developed for a rectangular hopper with flat bottom. The mass discharge rate increases exponentially with the decrease in hopper angle, which is different from that of monosized particles. The mass discharge rate is more sensitive to low friction coefficient, and the friction coefficient between particles plays a leading role. Fine particles can promote the discharge process, and this effect is enhanced as particle size ratio increases.
TL;DR: This work describes the atomic manner of this virus in contact with various metallic matrix such as Fe, Al, and steel with equilibrium molecular dynamic method and shows that coronavirus removes and destroyed with steel surface, and this metallic structure can be a promising material for use in medical applications.
Abstract: Coronavirus causes some illnesses to include cold, COVID-19, MERS, and SARS. This virus can be transmitted through contact with different atomic matrix between humans. So, this atomic is essential in medical cases. In this work, we describe the atomic manner of this virus in contact with various metallic matrix such as Fe, Al, and steel with equilibrium molecular dynamic method. For this purpose, we reported physical properties such as temperature, total energy, distance and angle of structures, mutual energy, and volume variation of coronavirus. In this approach, coronavirus is precisely simulated by O, C, S, and N atoms and they are implemented dreiding force field. Our simulation shows that virus interaction with steel matrix causes the maximum removing of the virus from the surfaces. After 1 ns, the atomic distance between these two structures increases from 45 to 75 A. Furthermore, the volume of coronavirus 14.62% increases after interaction with steel matrix. This atomic manner shows that coronavirus removes and destroyed with steel surface, and this metallic structure can be a promising material for use in medical applications.
TL;DR: A version of the Discrete Element Method considering the particles as rigid polyhedra as basis for a multibody dynamics model, and proposes a combined interface law composed of a penalty and a barrier approach to fulfill the contact constraints.
Abstract: We present a version of the Discrete Element Method considering the particles as rigid polyhedra. The Principle of Virtual Work is employed as basis for a multibody dynamics model. Each particle surface is split into sub-regions, which are tracked for contact with other sub-regions of neighboring particles. Contact interactions are modeled pointwise, considering vertex-face, edge-edge, vertex-edge and vertex-vertex interactions. General polyhedra with triangular faces are considered as particles, permitting multiple pointwise interactions which are automatically detected along the model evolution. We propose a combined interface law composed of a penalty and a barrier approach, to fulfill the contact constraints. Numerical examples demonstrate that the model can handle normal and frictional contact effects in a robust manner. These include simulations of convex and non-convex particles, showing the potential of applicability to materials with complex shaped particles such as sand and railway ballast.
TL;DR: In this paper, the authors study the erosion dynamics of wet particle agglomerates inside a simple shear flow of noncohesive granular materials by relying on the three-dimensional discrete-element simulations.
Abstract: We study the erosion dynamics of wet particle agglomerates inside a simple shear flow of noncohesive granular materials by relying on the three-dimensional discrete-element simulations. The simulation model is discretized by assembling of wet and dry spherical particles. By systematically varying different parameters related to the shear flow of dry particles (the shear rate), the wet agglomerates (the amount of the binding liquid in the “pendular” state, the liquid viscosity, and the liquid–vapor surface tension), and the relative dry–wet density as well as the initial position of wet agglomerates, we measure the erosion of these agglomerates on their surface by quantifying the cumulative number of eroded particles. We show that the erosion rate increases proportionally to the inertial number and the height of the agglomerates decreases linearly with the liquid content and the liquid viscosity and decreases nonlinearly with the cohesion index (or liquid–vapor surface tension) for each value of the inertial number, whereas this rate is nearly independent to the relative dry–wet density with a low shear rate. It is worth noting that the normalized erosion rate by the shear rate collapses well on a master curve as a cutoff function of the erosion scaling parameter (combining the inertial number, the cohesion index, and the Stokes number), thus providing clear evidence for the unified description of the material and flow parameters on the erosion of wet agglomerates.
TL;DR: The results demonstrate that the proposed phenomenological modeling strategy successfully captures the concrete–steel interaction and provides an accurate estimation of the macro behavior, and valuable inferences are made regarding discontinuum analysis of reinforced concrete members, including concrete– steel interaction and their macro behavior.
Abstract: This study presents a numerical investigation on the fracture mechanism of tension stiffening phenomenon in reinforced concrete members A novel approach using the discrete element method (DEM) is proposed, where three-dimensional randomly generated distinct polyhedral blocks are used, representing concrete and one-dimensional truss elements are utilized, representing steel reinforcements Thus, an explicit representation of reinforced concrete members is achieved, and the mechanical behavior of the system is solved by integrating the equations of motion for each block using the central difference algorithm The inter-block interactions are taken into consideration at each contact point with springs and cohesive frictional elements Once the applied modeling strategy is validated, based on previously published experimental findings, a sensitivity analysis is performed for bond stiffness, cohesion strength, and the number of truss elements Hence, valuable inferences are made regarding discontinuum analysis of reinforced concrete members, including concrete–steel interaction and their macro behavior The results demonstrate that the proposed phenomenological modeling strategy successfully captures the concrete–steel interaction and provides an accurate estimation of the macro behavior
TL;DR: In this article, the impact dynamics of a single wet agglomerate composed of primary spherical particles impacting a flat plane was investigated by using three-dimensional discrete element method simulations, where the primary particle was assumed to be rigid and interacted with its near-neighboring particles by introducing approximate analytical expressions of capillary cohesion forces and lubrication forces induced from the liquid in addition to their elastic and frictional interactions.
Abstract: We investigate the impact dynamics of a single wet agglomerate composed of primary spherical particles impacting a flat plane by using three-dimensional discrete element method simulations. The primary particle is assumed to be rigid and interacted with its near-neighboring particles by introducing approximate analytical expressions of capillary cohesion forces and lubrication forces induced from the liquid in addition to their elastic and frictional interactions. The paper analyzes the mechanical strength, the deformation, and the connectivity of wet particle agglomerate during the impact as well as in its early-stage impact and the final-stage deposition. We show that the mechanical strength, deformation, and connectivity of granule strongly depend on the key parameters (the liquid–vapor surface tension, the liquid viscosity, and the impact speed of agglomerate). In particular, the early-stage strength and the height of wet agglomerate at its final-stage deposition nicely behave as a function of the Capillary–Stokes inertial number that combines the Capillary number and Stokes number, and the macroscopic strength of the agglomerate at its early-stage impact has the microscopic origin from the normal compressive forces between primary particles. These observations are consistent that represent the relationship between the rheological properties and the liquid properties and the impact conditions of wet granular materials.
TL;DR: A new hybrid discrete–continuum numerical approach that explores the key advantages of both discrete and continuum approaches is proposed to model unsaturated seepage flows through porous media and is capable of describing the nature of flow in unsaturated porous media at the microscale level.
Abstract: A new hybrid discrete–continuum numerical approach that explores the key advantages of both discrete and continuum approaches is proposed to model unsaturated seepage flows through porous media. In contrast to existing approaches where a porous medium is often represented by a continuum medium or required a background mesh, the proposed approach explicitly exploits the discrete contact network formed by an assembly of discrete solid particles. Each solid particle is assumed to occupy an equivalent-continuum space, over which the governing equations for unsaturated seepage flow are derived. These governing equations are then discretised and solved on the discrete contact network through a new numerical procedure that links micro-diffusivity to the macro-one. Thanks to this concept, the proposed approach is capable of describing the nature of flow in unsaturated porous media at the microscale level. This unique feature also enables the proposed approach to naturally simulate the water flow through the heterogeneous porous media without any ad hoc treatments. In this paper, the mathematical concept of the proposed approach together with its implementation features and performances for a rigid porous media is presented and discussed. The focus is placed on its application to the discrete element method (DEM), although the proposed concept, in general, can be applied to any other methods possessing similar features.
TL;DR: In this article, a solid-velocity-liquid-vein-based hydro-mechanical governing formulation is adopted to construct a two-phase single-point explicit generalized interpolation material point (GIMP) method, and the XPIC(m) method is extended to erase null space noise and damp highfrequency waves in both solid and liquid phases.
Abstract: The material point method (MPM) has been increasingly used to simulate coupled hydro-mechanical problems involving large deformations. However, when addressing saturated porous media with an almost incompressible liquid phase, the classic explicit MPM with low-order interpolation functions is not stable if no further stabilization approach is used. In this study, a solid-velocity–liquid-velocity-based hydro-mechanical governing formulation is adopted to construct a two-phase single-point explicit generalized interpolation material point (GIMP) method. To stabilize this set of formulation, the XPIC(m) (extended PIC of order m) method is extended to erase null space noise and damp high-frequency waves in both solid and liquid phases; additionally, a cell-based averaging approach is adopted to solve locking issues and smooth stress field variables. Several numerical examples have been presented to demonstrate the capabilities of the stabilized coupled GIMP method in simulating coupled hydro-mechanical problems involving dynamic effects and large deformations.
TL;DR: In this paper, a range of quasi-spherical particles are designed, represented by a number of small satellites connected rigidly to a larger center sphere, and the packing density is controlled by the interplay between particle shape, size and interparticle cohesion and friction.
Abstract: Fine and cohesive powders typically exhibit low packing density, with solid volume fraction around 0.3. Discrete element modelling (DEM) of particulate materials and processes typically employs spherical particles which have much larger solid fractions (e.g. 0.64 for dense random packing of frictionless spheres). In this work a range of quasi-spherical particles are designed, represented by a number of small satellites connected rigidly to a larger centre sphere. Using DEM, packing density is found to be controlled by the interplay between particle shape, size and inter-particle cohesion and friction. Low packing density is obtained for an appropriate combination of (1) particle shape that allows the creation of geometrically loose structures via separation of the central particles by the satellites, (2) particle size that should be sufficiently small so that adhesive forces between particles become dominant over gravity, (3) adhesive forces, determined from surface energy, should be sufficiently large, and (4) friction (static friction was found to have a dominant role compared to rolling friction, but negligible compared to adhesive forces for small particle size). By using the proposed quasi-spherical particle designs it becomes possible to calibrate more realistic DEM models for particulate processes that reproduces not only packing, but also other behaviours of bulk powders.
TL;DR: A unique software library where users can easily add particles with arbitrary geometries and new contact laws that model either rigid-body interaction or peridynamic constitutive relationships is designed.
Abstract: ParticLS (Particle Level Sets) is a software library that implements the discrete element method (DEM) and meshfree methods. ParticLS tracks the interaction between individual particles whose geometries are defined by level sets capable of capturing complex shapes. These particles either represent rigid bodies or material points within a continuum. Particle-particle interactions using various contact laws numerically approximate solutions to energy and mass conservation equations, simulating rigid body dynamics or deformation/fracture. By leveraging multiple contact laws, ParticLS can simulate interacting bodies that deform, fracture, and are composed of many particles. In the continuum setting, we numerically solve the peridynamic equations—integro-differential equations capable of modeling objects with discontinuous displacement fields and complex fracture dynamics. We show that the discretized peridynamic equations can be solved using the same software infrastructure that implements the DEM. Therefore, we design a unique software library where users can easily add particles with arbitrary geometries and new contact laws that model either rigid-body interaction or peridynamic constitutive relationships. We demonstrate ParticLS’ versatility on test problems meant to showcase features applicable to a broad selection of fields such as tectonics, granular media, multiscale simulations, glacier calving, and sea ice.
TL;DR: In this article, the macroscopic behavior of concrete taking into account the presence of free water in pores, thanks to a new interaction law between spherical discrete elements (DE), is addressed.
Abstract: The discrete element model proposed in this paper addresses the macroscopic behavior of concrete taking into account the presence of free water in pores, thanks to a new interaction law between spherical discrete elements (DE). When concrete structures are subjected to a severe loading, e.g., an impact, material exhibits high triaxial compressive stresses which are highly influenced by the saturation ratio. In this new constitutive model, cracking and compaction are modeled at the interaction level between DEs and free water effects are taken into account by introducing a dependency between the water saturation ratio and the inelastic deformation due to the pore closure. The present numerical model has been implemented in the Yet Another Dynamic Engine code in order to deal with extreme loading situations leading to stress states characterized by a high mean stress level.