Discrete Simulation Research Articles

A novel method for measurement of the angle of repose of granular seeds in discrete element methods

Discrete element numerical simulations can help researchers find potential problems in the design phase, shortening the development cycle and reducing costs. In the field of agricultural engineering, more and more researchers are using discrete element methods (DEM) to assist in designing and optimising equipment parameters. Model parameters calibration is a prerequisite for discrete element numerical calculations, and the angle of repose (AoR) is commonly used to calibrate the parameters. However, the measurement of AoR in DEM was not seriously considered in industrial or academic fields. In practice, AoR is measured manually, using 2D digital image processing or using a 3D scan. However, reliable and consistent measurements of AoR in DEM are rarely mentioned. This study suggests an accurate and consistent way to measure AoR in DEM using a novel method to read particle coordinate information directly from the data file; then, the AoR is calculated by linearly fitting the centre coordinates of the outermost particles. Influences of input variables on AoR acquisition are discussed through several examples using customised templates with known angles. Then a comparative study of the accuracy of the measurement of AoR in DEM and the reliability of the parameter calibration results by the manual measurement, 2D digital image processing, and algorithm proposed in this paper was conducted. In case studies with four seed materials, this method prevented the subjective selection of AoR, improved the identification accuracy, and increased the precision and accuracy of DEM calibration. In addition, the time consumption for obtaining AoR using the novel method for measurement is much less than that of 2D.

Linking dynamics between anchors and granular materials

The research quantitatively explores the linking properties between the circular plate anchor and the granular assembly during the failure process under the subject of a specified pullout force given to the anchor using three-dimensional discrete particle simulations. This circular anchor is created as a hard cluster of spherical grains and is initially buried at a depth in the granular assembly. The numerical method is constructed based on the frictional interaction force law. The linking dynamic is characterized by the variation of the drag force acting on such anchor due to interaction with grains at the bottom of the frustum which is formed during the uplifting movement of the anchor. The results show that the drag force acting on the anchor first reaches a nearly constant value corresponding to the loading phenomenon at small anchor movement, reflecting the plastic deformation of granular bed as a result of particle rearrangement, and then fluctuates in a wide range, this range increases with increasing the anchor movement as a result of the unloading/reloading events. These loading/unloading/reloading events provide evidence for the linking properties between the anchor movement and granular assembly, which are highlighted by the density and intensity of force network within the frustum.

Discrete Element Method Simulation and Field Evaluation of a Vibrating Root-Tuber Shovel in Cohesive and Frictional Soils

Soil-cutting forces are key indicators of root-tuber harvesters and other soil-engaging tools’ performance. To improve operational efficiency, minimise soil disturbance, and reduce fuel consumption, the draught and vertical forces involved in root and tuber crop harvesting must be minimised. Two field experiments assessed the harvester’s performance at a depth of 200 mm, varying frequencies, and travel speeds on clay and sandy loam soils. Discrete element models (DEM) were developed and subsequently used to replicate the field experiments and evaluate S-shaped and fork-shaped shovels. Linear regression and ANOVA (p < 0.05) were used to analyse the data. Draught force concurrently increased with speed in both soil textures but decreased with vibration frequency. The draught force decreased by approximately 41% in clay soil and 21% in sandy loam soil when the harvester was operated between 5 Hz and 14.5 Hz and between 10 Hz and 12.5 Hz, respectively. DEM simulations had relative errors of 4% (clay) and 4.7% (sandy loam) for draught force and drawbar power compared to experimental data. The S-shaped shovel was more efficient at crushing and translocating soil–crop mass to the rear of the harvester than the fork-shaped shovel. These DEM soil–crop models are reliable for evaluating other root-tuber harvesting tools.

Towards a better understanding of granular flows

Understanding the transport of particles immersed in a carrier fluid (bedload transport) is still an exciting challenge. Among the different types of gas–solid flows, when the dynamics of solid particles is essentially dominated by collisions between them, kinetic theory can be considered as a reliable tool to derive continuum approaches from a fundamental point of view. In a recent paper, Chassagne et al. (J. Fluid Mech., vol. 964, 2023, A27) proposed a two-fluid model based on modifications to a classical kinetic theory model (Garzó & Dufty, Phys. Rev. E, vol. 59, 1999, pp. 5895–5911). First, in contrast to the classical model, the model proposed by Chassagne et al. takes into account the interparticle friction not only in the radial distribution function but also through an effective restitution coefficient in the rate of dissipation term of granular temperature. As a second modification, at the top of the bed where the volume fraction is quite small, the model accounts for the saltation regime in the continuum framework. The theoretical results derived from the model agree with discrete simulations for moderate and high densities and they are also consistent with experiments. Thus, the model proposed by Chassagne et al. (J. Fluid Mech., vol. 964, 2023, A27) helps provide a better understanding of the combined impact of friction and inelasticity on the macroscopic properties of granular flows.

Simultaneous optimization of design and maintenance for systems using multi-objective evolutionary algorithms and discrete simulation

When projecting and building new industrial facilities, getting integrated design alternatives and maintenance strategies are of critical importance to achieve the physical assets optimal performance, which is needed to be competitive in the actual global markets. Coupling Evolutionary Algorithms with Discrete Event Simulation has been explored both in relation to systems design and their maintenance strategy. However, it was not simultaneously considered when both the corrective and the preventive maintenance—consisting of achieving the optimum period of time to carry out a preventive maintenance activity—are taken into account before being considered by the authors of the present paper. This work couples Multi-objective Evolutionary Algorithms with Discrete Event Simulation in order to enhance the knowledge and efficiency of the methodology presented, which consists of exploring and optimizing simultaneously systems design alternatives and their preventive maintenance strategies. The aim consists of finding the best set of non-dominated solutions by using the system availability (first maximized objective function) with taking into consideration associated operational cost (second minimized objective function), while automatically selecting the system devices. Each solution proposed by the Multi-Objective Evolutionary Algorithm is analyzed by using Discrete Event Simulation in a procedure that looks at the effect of including periodic preventive maintenance activities all along the mission time. An industrial application case study is solved, and a comparison of the performance of five state-of-the-art and three more recently developed Multi-objective Evolutionary Algorithms is handled; moreover, the gap in the literature reviewed about the analysis regarding the effect of the discrete event simulation sampling size is faced with useful insights about the synergies of Multi-objective Evolutionary Algorithms and Discrete Event Simulation. Finally, the methodology is expanded to more complex systems which are successfully solved.

Discrete Element-Based Simulation Analysis and Research of Potato Soil Agglomerate Fragmentation and Separation

To study the influence law of the overburden rotating plate mechanism on the fragmentation and separation of potato soil agglomerates, a single-factor test and a response surface test simulation analysis of the soil fragmentation process were conducted in EDEM 2022 software. The results of the single-factor test show that the triangular rack blade of the overburdened rotating plate mechanism has the best effect on soil fragmentation and separation. With the increase in the lower blade speed, the upper lift chain bar line speed, and the tilt angle of the mechanism, the effect on the fragmentation and separation of potato soil agglomerates decreases. The response surface test results show that the debris removal rate decreases with the increase in blade speed and tilt angle, the percentage of bond breakage between potato soil particles declines with the rise of blade speed and lift chain bar line speed, and the percentage of bond breakage between soil particles increases with the increase in blade speed and lift chain bar line speed. The optimal solution was obtained by using the optimization function in Design-Expert 13 software, which was adjusted as follows: the blade rack type was triangular, the lift chain bar line speed was 0.307 m/s, the blade speed was 0.4 m/s, and the tilt angle was 40°. The research methods and results provide a reference for the simulation of potato soil crushing and separation motion in a sandy loam soil cultivation area.

DEM study on the effect of particle shape on the shear behaviour of granular materials

This study investigates the effects of particle convexity, sphericity and aspect ratio (AR) on the behaviour of sheared granular materials using two-dimensional discrete element method simulations. Isotropic, dense and loose assemblies with different particle shapes were prepared and subjected to drained shearing via biaxial compression until the critical state was reached. Macroscopic characteristics such as strength and dilatancy are presented. The factors underlying the macroscopic behaviour are then investigated by considering the coordination number, fabric anisotropy, particle moment, friction mobilisation at contacts and particle rotation. For the range of shapes considered here, the data indicate that the shear strength decreases as particle convexity and sphericity increases while the shear strength increases with increasing AR. The shear strength and convexity are weakly correlated, however a stronger correlation is observed between AR and strength. The volumetric strain at large strains tends to increase with increasing AR. There is a stronger correlation between the critical state strength and both the critical state coordination number and the critical state mechanical void ratio than there is between the critical state void ratio and the critical state strength. The contact fabric anisotropy, the magnitude of the moment transmitted by particles and the friction mobilised at the contacts are important factors underlying strength. The critical state strength increases as both the mean particle moment and the mean mobilised friction increased. Analysis of particle rotation provides insights into the response of the granular materials to shearing.

A phase field-based framework for electro-chemo-mechanical fracture: Crack-contained electrolytes, chemical reactions and stabilisation

We present a new theoretical and computational framework for modelling electro-chemo-mechanical fracture. The model combines a phase field description of fracture with a fully coupled characterisation of electrolyte behaviour, surface chemical reactions and stress-assisted diffusion. Importantly, a new physics-based formulation is presented to describe electrolyte-containing phase field cracks, appropriately capturing the sensitivity of electrochemical transport and reaction kinetics to the crack opening height. Unlike other existing methods, this approach is shown to accurately capture the results obtained with discrete fracture simulations. The potential of the electro-chemo-mechanical model presented is demonstrated by particularising it to the analysis of hydrogen embrittlement in metallic samples exposed to aqueous electrolytes. The finite element implementation takes as nodal degrees-of-freedom the electrolyte potential, the concentrations of relevant ionic species, the surface coverage, the concentration of diluted species, the displacement field and the phase field order parameter. Particular attention is devoted to improve stability and efficiency, resulting in the development of strategies for avoiding ill-constrained degrees of freedom and lumped integration schemes that eliminate numerical oscillations. The numerical experiments conducted showcase the ability of the model to deliver assumptions-free predictions for systems involving both free-flowing and crack-contained electrolytes. The results obtained highlight the role of electrolyte behaviour in driving the cracking process, evidencing the limitations of existing models.

The Energy Saving Renovation of Regional Buildings Based on Bayesian Estimation

With China's new urbanization vision and existing urban renewal and building energy efficiency improvement project, large-scale energy conservation renovation of regional buildings has become an important content of ecological environmental protection and low-carbon and an important means to improve the regional energy efficiency level. Of energy-saving reform foundation database is presented in this paper, including construction, power consumption, equipment, operation, technology and willingness to word stock, statistics obtained the regional energy complex parameter (envelope thermal performance, elevator equipment, power and efficiency of cooling and heat sources, etc.) statistical rule and can use the benchmark, build the regional buildings energy consumption prediction model based on bayesian estimation, The probability matrix of large-scale reconstruction of regional buildings is obtained. At the same time, the global sensitive parameter analysis method and the single parameter regression model of energy saving transformation factor are established, and it is found that the internal load factor has the most significant effect on energy consumption. By adjusting energy parameters, the probability distribution curve of energy saving and the distribution of normalized value under the constraint conditions of different reconstruction scenarios were simulated, and the discrete MC simulation method was used to predict the regional overall energy saving reconstruction based on renovation intention, which could realize the trade-off judgment and gradual optimization of the strategy package of energy saving measures combination.

Effects of MWCNT nanoparticles injection points on incompressible laminar hydrogen flow through discrete phase modeling by CFD approach

Discrete phase model used in the aerospace industry to stimulate the behavior of particles inside the aircraft engines. The application of the discrete phase modeling (DPM) is extensive in solving the real-time engineering problems in optimization of numerous systems. In the current study, the DPM model has been simulated to examine the effect of injection point on the hydrogen flow field. A domain has been proposed and the injection point has been positioned in the four different places at the regular intervals. The location of the injection points was 0.2 m, 0.3 m, 0.4 m and 0.6 m. Dense discrete Eulerian lagrangian numerical simulation has been employed to analyze the effect of the multi-walled carbon nanotubes (MWCNT) nanoparticles. The hydrogen has been supplied at the injection velocity of 2 m/s. ANSYS implicit simulation setup has been tested across various injection points. The research found that the location of injection points plays a significant role in DPM concentration, with the highest concentration at 0.2 m and the lowest at 0.6 m, but has no significant impact on dynamic pressure. MWCNT nanoparticles had a negligible effect on skin friction coefficient, but shifting the injection point could reduce skin friction rates. The inclusion of MWCNT nanoparticles increased hydrogen flow velocity through downstream effects, vortices, and the nano-enhancement effect. The study suggests that MWCNT can significantly enhance hydrogen flow velocity in various applications, and DPM concentration data can provide valuable insights for optimizing injection locations to prevent unwanted nanoparticle effects.

Interaction between 1/2[formula omitted]110[formula omitted]{001} dislocations and {110} prismatic loops in uranium dioxide: Implications for strain-hardening under irradiation

Plasticity of irradiated UO2 is of major interest to improve the risk assessment of the nuclear fuel cladding failure in the case of design basis accidents. In this study, we investigate the main irradiation-hardening processes induced by {110} irradiation loops interacting with glissile dislocations of the primary slip system, 1/2<110>{001}, of UO2. The interactions are simulated at two scales using molecular dynamics and discrete dislocation dynamics, to characterise local interactions and identify strengthening configurations as a function of the dislocation-irradiation loop geometry. In particular, we show that 1/2<110>{001} screw dislocations can be strongly pinned by helical turn configurations. Statistical large-scale discrete dislocation simulations are performed to investigate the collective behaviour of a large density of irradiation defects and quantify irradiation hardening. Several microstructural processes including loop drag and shovelling are observed and their involvement in clear band formation and hardening of UO2 fuel at high temperature is discussed.

Damage features and dynamic formation mechanism of the Tangjiashan landslide triggered by the Wenchuan earthquake with a composite hypocenter

The Wenchuan earthquake triggered many landslides, which caused many casualties and led to considerable property losses. Due to the compositionality of the hypocenter mechanism of the Wenchuan earthquake, research on the effects of a composite hypocenter on the dynamic responses of landslides is urgently necessary. Using geological field investigations, a block discrete element method simulation, and related theoretical analysis, the dynamic formation mechanism and main controlling mechanical factors of the Tangjiashan landslide were revealed. The results demonstrated the following. Firstly, the dynamic responses of the slope involved progressive deformation, critical failure, disintegration, fragmentation, collision, climb, return, and accumulation. Secondly, when the earthquake lasted for approximately 23 s, the critical failure occurred, and the sliding mass near the shoulder reached a vertical acceleration of approximately 2.8 g at this time. Thirdly, the second and third subhypocenters contributed to the progressive deformation and critical failure, and vertical seismic forces were dominant contributions to these responses. Fourthly, the disintegration, fragmentation, collision, climb, return, and accumulation were mainly controlled by the self-gravity and local topography and were slightly influenced by subhypocenters. Based on these conclusions, the study of the dynamic formation mechanism of this type of landslide has increased the level of understanding.

A Simulation-Based Model for Evacuation Demand Estimation under Unconventional Metro Emergencies

When metro networks are shut down due to an unconventional emergency, numerous passengers will get stranded and wait to be evacuated. A clear understanding of the stranded passengers in the network is the basis for designing an efficient evacuation strategy. Previous studies focused more on disruption management and assumed a known evacuation demand. Few studies considered the distribution of stranded passengers, especially when the metro network is shut down due to unconventional emergencies. This motivates us to develop a discrete event-based simulation model to estimate the number and distribution of stranded passengers. The proposed model takes the numbers of stranded passengers at stations and trains as the state variables and develops the state evolution rule of the metro system. The numbers and destinations of stranded passengers at trains and on stations at each time step, including the transfer and non-transfer stations, are calculated to describe the state evolution of the metro system. Chongqing Rail Transit (CRT) network is taken as an example. The result shows that the stations with the most stranded passengers are located downtown. Origin-Destinations (ODs) with more stranded passengers have a relatively shorter travel distance, while ODs with fewer stranded passengers have a relatively long travel distance. The average directional disequilibrium factor of stranded passengers of ODs in the whole network is high, especially for those ODs with many stranded passengers. These findings reveal the distribution characteristics of stranded passengers and can provide significant assistance to an emergency manager who is designing an efficient emergency evacuation plan.

Methodologies for characterization, evaluation, and improvement of logistics in the food supply chain

The food supply chain (FSC) is made up of producers, traders and processors who bring the product from supply to demand through logistical processes. Food supply chains require specific methodologies for their current diagnosis, evaluation and improvement. Logistics in food supply chain requires to be managed according to its nature. This article identifies the different methodologies through a systematic literature review of publications from 2005 to 2022, using Web of Science, Scopus and Google Scholar search engines, in order to establish the state of the art. As a result of this review, a new taxonomy is proposed and includes the following methodological groups: management, qualitative, quantitative, multi-criteria decision-making (MCDM), statistics, machine learning, mathematical modelling, discrete simulation, system dynamics and others. The methodologies of characterization, evaluation and improvement are classified into two main groups of logistical means and modes. The performance measures most commonly used in the methodologies by the researchers were also identified. From the article, discussions, challenges and trends are generated to identify possible future research and different gaps.

Failure mechanism and deformation prediction of soft rock tunnels based on a combined finite–discrete element numerical method

The large deformation mechanisms and predictions of soft rock tunnels have always been important but difficult to solve problems in the field of geotechnical engineering. A combined finite–discrete element numerical simulation method (FDEM) was used to study large deformation mechanism, classification and prediction. The deformations or failure mechanisms of tunnel surrounding rock were revealed, and the failure modes and displacement value prediction of surrounding rock with different strength-stress ratios were also investigated. The following conclusions were obtained: (1) Critical hysteresis damping can be adopted to simulate the progressive large deformation process of soft rock tunnels, which can obtain the final deformation of unsupported tunnels and avoid a dynamic response. (2) Under concentrated tangential stress, the surrounding rock undergoes X-shaped conjugate shear fracture, and this type of fracture network continues to propagate toward the depth of the surrounding rock until the model reaches a stable state; the reduction in tunnel cross-section is mainly caused by the macroscopic movement and volume expansion of rock fragments, and the latter is due to the generation of a large number of macroscopic voids. (3) As the strength-stress ratio decreases, the deformation or failure modes of the surrounding rock can be divided into four categories: elastic–plastic deformation, closed fracturing, shear dilation and broken expansion. (4) Finally, a prediction equation for isotropic and homogeneous soft rock unsupported tunnel deformation with general size driven by hydrostatic in situ stress is obtained, which indicates that with an increasing strength-stress ratio, the surrounding rock displacement decreases as an exponential function, with a correlation coefficient of R2 = 0.997. In addition, the robustness and reliability of the prediction equation is verified.

Investigation on Bearing Characteristics of Gravity Wharf Rubble-Mound Foundation in Different Influencing Factors

The use of the heavy hammer compaction method can enhance the bearing characteristics of underwater rubble-mound foundations. This is crucial to ensure the safety and stability of port and coastal engineering projects. In the present work, a combination of image-recognition technology, 3D laser scanning technology, a discrete element numerical simulation, and a field test was first utilized to establish riprap particles and reconstruct a discrete element numerical model of a rubble-mound foundation, and then the effects of various influencing factors on the bearing characteristics of the rubble-mound foundation were studied. The main conclusions are as follows. (1) The load–settlement curve of the rubble-mound foundation can be divided into three stages: rapid growth stage, slow growth stage, and failure stage. (2) The ultimate bearing capacity of the rubble-mound foundation is positively correlated with the vibration time and vibration amplitude. The riprap particle size and the foundation thickness have negligible effects on the ultimate bearing capacity of the rubble-mound foundation. (3) When adjusting the vibration time, vibration amplitude, and foundation thickness, the settlement value of the rubble-mound foundation tends to increase as the compactness increases. On the other hand, the effects of factors such as the riprap particle size, riprap particle gradation, and vibration frequency on the compactness and settlement value of the rubble-mound foundation are less significant.

A computational study of the influence of evaporation and molecular transport on temporally-evolving droplet-laden plane jets

Numerical simulations of temporally-evolving droplet-laden plane jets are performed in conditions relevant to rocket main engines fed with liquid oxygen (LOx) and gaseous methane (CH4). The computations are performed using a direct numerical simulation (DNS) solver with the liquid phase represented within the discrete particle simulation (DPS) framework. Considering the multiplicity of the physical phenomena that are involved in such conditions – e.g., atomization, dispersion, evaporation – a progressive and phenomenological methodology is retained to proceed with a complexity-increasing set of computations. Thus, the development of a purely gaseous jet is first studied with the corresponding set of data providing a reference or baseline condition. Then, other conditions are considered to analyze the influence of (i) liquid droplet evaporation and (ii) molecular mixing processes as described by two distinct multicomponent transport models. The analysis of the obtained results shows that both evaporation and molecular transport representation play a crucial role in the plane jet development and may drastically alter its characteristics before ignition and subsequent combustion stabilization may take place. Finally, the obtained results also unambiguously put into evidence the influence of the Lewis number onto the vaporization rate.

The effect of central gap and wind screens on the aeroelastic stability of long-span bridge decks: Comparison of numerical analyses and experimental results

As long-span bridges are usually built at exposed locations and high winds can cause disruptions to traffic, relatively tall wind screens are often used to protect vehicles which are prone to suffer from wind induced accidents. This paper presents the results of a series of two-dimensional discrete vortex method simulations of laminar incompressible flow past standard aerofoil mono-boxes and twin-boxes, conducted to investigate the aerodynamic impact of wind screens on bridge decks in relation to steady-state and divergent instability (classical flutter) behaviour. A comparison against the outcome of a series of parametric wind tunnel tests is also presented. The quality of the agreement between the numerical simulations and the observed experimental behaviour is such that designers, under certain conditions, could rely on computational bridge aerodynamics at feasibility or early design stages to identify potential instabilities and introduce mitigation measures aimed at optimizing the aerodynamic performance of the deck.

Combining DEVS simulation and ontological modeling for hierarchical analysis of the SARS-CoV-2 replication

This article presents an hybrid and hierarchical model in which two modeling and simulation approaches, discrete event system specification simulation (DEVS) and semantic technologies, were used together in order to help in the analysis of a major healthcare problem, the severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2). Indeed, the complexity of the SARS-CoV-2 replication process, and the range of hierarchical scales over which it interacts with cellular components (extending from genomic and transcriptomic to proteomic and metabolomic scales), and the intricate way in which they are interwoven, make its understanding very challenging. It is therefore crucial to model the different scales of the replication process, by taking into account all interactions with the infected cell. By combining the advantages of both DEVS simulation and ontological modeling, we propose a hierarchical ontology-based DEVS simulation model of the SARS-CoV-2 viral replication at both the micro-molecular (proteomic and metabolomic) and macro-molecular (genomic and transcriptomic) scales. First, we demonstrate the usefulness of combining DEVS simulation and semantic technologies in a common modeling framework to face the complexity of the SARS-CoV-2 viral replication at different scales. Second, the modeling and simulation of the SARS-CoV-2 replication process on different levels provide valuable information on the different stages of the virus’s life cycle and lays the foundation for a system to anticipate future mutations selected by the virus.

Estimation of rough fracture network permeability using fractal and topology theories

Accurate characterization of the rough fracture network in real rocks is an essential prerequisite for precise estimation of fracture network permeability. The characterization of a fracture network in previous theoretical models is usually based on statistical theory, ignoring the topological characteristics of the real fracture network. In this paper, based on fractal and topological theories, the rough characteristics of real rock fractures are considered, and fracture network branch lengths and connectivity are introduced. A new theoretical prediction equation of fractal permeability for rough fracture networks is derived. Subsequently, the reliability of the proposed theoretical model is verified based on discrete fracture network (DFN) modeling and numerical simulation, and the main influencing factors of the rough fracture network permeability are analyzed. The results show that the rough fracture network permeability theoretical model proposed in this paper can effectively evaluate fractured rock permeability. Connectivity is linearly related to permeability. The better the connectivity of the rough fracture network, the denser the streamlines within the fractured rock and the higher the flow rate. The rough fracture network permeability increases with the increase of connectivity, minimum branch length, maximum branch length, tortuosity, and aperture proportionality coefficient, and decreases with the increase of tortuosity fractal dimension and fracture dip angle. When the branch length ratio lbmin/lbmax is less than 0.2, the larger the fractal dimension of the rough fracture network, the lower the permeability. When the ratio is greater than 0.2, the opposite is true. The sensitivity of the rough fracture network permeability to the fracture dip angle θ and the aperture proportionality coefficient β is higher, while the sensitivity to the fractal dimension Df of the rough fracture network is lower.