Discrete Simulation Research Articles

Soil arching in ground with tunnel: Effect of distance between tunnel and trapdoor

The effects of existing tunnels on the evolution of soil arching require further investigation. In this study, trapdoor models with different distances between the trapdoor and tunnel are examined via discrete element method simulations after a numerical model is established based on experiments. The results show that as the distance between the tunnel and trapdoor (L) increases, the minimum soil arching ratio, ultimate soil arching ratio, and load recovery decrease, thus indicating that the shadowing effect of the tunnel becomes less distinctive. The essential distance affected by the tunnel is between 150 and 200 mm. The stress ratio in region L1 first decreases significantly and then gradually as the trapdoor displacement increases, reaching an ultimate value at L = 50 and 100 mm. The reverse trend is observed when L exceeds 150 mm, which is similarly observed in regions L2 and L3. The height of the equal-displacement region decreases steadily as L increases. Two distinct types of soil-arching structures are identified for interaction and independent arches. The displacement of the trapdoor increases the anisotropy of contact forces within the soil mass. The reorientation and destruction of the contact force fabric provide further insights into the formation of soil arching.

Evaluating the shear behavior of rooted soil by discrete element method simulations in two dimensions

Evaluating the shear behavior of rooted soil by discrete element method simulations in two dimensions

MAES: a ROS 2-compatible simulation tool for exploration and coverage algorithms

With the aim of allowing the efficient and realistic simulation of swarm algorithms for exploration and coverage, we present the tool Multi-Agent Exploration Simulator (MAES), which is an open-source physics-based discrete step multi-robot simulator. MAES features movement in a continuous 2D space, realistic physics based on the Unity framework, advanced visualization techniques such as heatmaps, custom wireless signal degradation, both randomly generated and custom user-provided maps, and a ROS (Robot Operating System) interface. This latter characteristic could allow to port the simulated algorithms to real-world robots. We present performance tests, conducted with rather modest hardware, showing that MAES is able to simulate up to 5 robots in ROSMode (using the ROS integration) and up to 120 robots in UnityMode (development performed directly into the C# Unity Editor). A usability test was conducted which hinted that the target audience of robotics researchers and developers is able to quickly install, setup, and use MAES for implementing simple robot logic.

DES and IIoT fusion approach towards real-time synchronization of physical and digital components in manufacturing processes

Today's manufacturing systems offer more products to meet specific needs. Complex production systems in rapidly changing environments result from product variation, shorter product life cycles, and supply chain expansion. A cyber-physical production system (CPPS) can use manufacturing and logistics data to plan, monitor, and control production. Discrete event simulation (DES) and digital twin (DT) technology can model and evaluate manufacturing and logistics processes using high-level decision support and process monitoring. The cost of collecting input data from different enterprise data sources and mapping it into models and the lack of qualified experts prevent the widespread use of these methods in industry, especially in small and medium-sized enterprises and larger multinational companies. This research aims to create a modular digital twin framework for manufacturing process optimization and real-time monitoring in an industrial environment with few components. The system can identify and track the product through the manufacturing cycle while updating the DT in real-time and can be used independently to collect input parameters for discrete event-driven simulations and even for automatic simulation building in the future. The framework's operation will be shown through an example. With the proposed IIoT (industrial internet of things) system integration, it can detect faults and warn of deviations from normal operation, and DT can drastically reduce data collection and model building and support model reusability, increasing sustainability.

Size-dependent yield criterion for single crystals containing spherical voids

A micromechanics-based yield criterion is derived for a porous single crystal containing a random distribution of spherical voids, using homogenization and limit analysis of a hollow spherical representative volume element obeying a strain gradient crystal plasticity model. The criterion captures the effect of plastic anisotropy due to crystallographic slip on a set of discrete slip systems, as well as the void size dependence of yielding. The yield criterion is formally similar to the well known Gurson model for isotropic porous materials, and reduces to existing results in the literature in the limiting case of large void sizes relative to the length scale in the gradient plasticity model. The yield criterion is validated by comparison with rigorous upper bound yield loci obtained using a numerical limit analysis procedure. Predictions for the size dependence of void growth are obtained by integrating the porous plasticity model, and shown to be consistent with the observations from lower scale discrete dislocation dynamics simulations. The loading path dependence of void growth in the size-independent limit are compared with finite element simulations of void growth in a single crystal using the unit cell model.

Stress-induced collapse in horizontally layered rock and a yielding support strategy: A case study

Squeezing problems pose a serious challenge for tunnel engineers because they can slow down a project, increase the project budget, and potentially lead to catastrophic collapse. The choice of an adequate support is also often difficult owing to complex geological environments. Lack of sufficient understanding of geological conditions such as high geostress and horizontal layered rock mass could cause tunnel collapse and further lead to economic loss and endanger human life. In an attempt to deal with in-situ squeezing problem, this paper focus on the investigation of the mechanical behavior of tunneling in horizontal layered rock mass with high geostress and the proposal of proper engineering measures. A tunnel collapse incident occurred in northeastern China is analyzed using comprehensive methods including photographing, laboratory tests, discrete element numerical simulations, and site monitoring. The discrete element method was applied to investigate the tunneling mechanical behavior under high-geostress conditions in a horizontally layered rock mass. Numerical simulations show that the dominant horizontal stress and joints cause the maximum deformation at the corner of the arch region. The effect of horizontal joints and horizontal dominant stress were analyzed and found to be the main causes of the collapse. Based on the simulation results, an innovative, simple and efficient tangential yielding element is developed and implemented to test its applicability in a tunnel engineering scenario. Load-displacement curves of the tangential yielding element were obtained through laboratory tests and introduced to the numerical model using the 3D discrete element method. The performance of the developed tangential yielding element was validated in the simulation. Site monitoring was also conducted to determine the in-situ performance of the yielding support using the tangential yielding element. The monitored settlement at the crown region is in agreement with the simulation. The in-situ tests show that the yielding element was considerably deformed while the tunnel remained stable, which confirms the applicability of this technique. The effectiveness of the yielding element is also confirmed in terms of a comparative cost analysis of the yielding and resistant support schemes.

Optimal explicit stabilized postprocessed τ-leap method for the simulation of chemical kinetics

The simulation of chemical kinetics involving multiple scales constitutes a modeling challenge (from ordinary differential equations to Markov chains) and a computational challenge (multiple scales, large dynamical systems, time step restrictions). In this paper, we propose a new discrete stochastic simulation algorithm: the postprocessed second kind stabilized orthogonal τ-leap Runge–Kutta method (PSK-τ-ROCK). In the context of chemical kinetics, this method can be seen as a stabilization of Gillespie's explicit τ-leap algorithm combined with a postprocessor. The stabilized procedure allows to simulate problems with multiple scales (stiff), while the postprocessing procedure allows to approximate the invariant measure (e.g. mean and variance) of ergodic stochastic dynamical systems. We prove stability and accuracy of the PSK-τ-ROCK for a reference system. Numerical experiments illustrate the high reliability and efficiency of the scheme when compared to other τ-leap methods.

Study on the Basic Mechanical Properties and Discrete Element Method Simulation of Permeable Concrete

Permeable concrete pavement material has many voids and a good water permeability, which can reduce surface runoff and alleviate the problem of urban water logging. It also has the functions of acting as a supplementary source of groundwater, purifying water, bodies reducing the urban heat island effect, reducing road noise, and so on. It is an effective solution for urban infrastructures. However, at the same time, because it has a large number of pores, this also affects the strength of permeable concrete. The main factors affecting permeable concrete are particle size and the shape of the aggregate, the content of the cement paste and aggregate, the compaction degree of the mixture, and so on. In this study, the single-factor test method was used to study the effects of aggregate size, slurry-to-bone ratio and loose paving coefficient on the basic mechanical properties and permeability of permeable concrete. Here, the numerical model for permeable concrete is established by using the particle flow discrete element (Particle Flow Code (PFC)modeling method, and a numerical simulation test is carried out. It can be seen from the test results that the permeability coefficient of 50% 5–10 mm + 50% 10–15 mm mixed aggregate permeable concrete is slightly lower than that of 5–10 mm and 10–15 mm single-size aggregate, but has a higher compressive and splitting tensile strength. With the increase in paste-to-bone ratio, the permeability coefficient of permeable concrete decreases, and the compressive strength increases. The loose paving coefficient has a significant effect on the mechanics and permeability of permeable concrete with the increase in the loose paving coefficient, the water permeability decreases and the compressive strength increases. The numerical simulation results show that under the condition that the loose paving coefficient is 1.10 and the slurry-to-bone ratio is 0.5, compared with the experimental results, the error of the numerical simulation results of the compression test is less than 3%. The reliability of the simulation is verified. The discrete element modeling method in this study can be used to simulate the shape of the aggregate in permeable concrete, and the numerical model can effectively simulate the crack development and failure form of permeable concrete in compression tests.

Erosion and Transport of Dry Soil Bed by Collisional Granular Flow: Insights From a Combined Experimental–Numerical Investigation

AbstractCollision‐induced stresses on soil beds under granular geophysical flows have been demonstrated to be highly erosive. However, it remains mostly elusive as to how a collisional granular flow erodes and transports soil bed material. This paper presents a combined experimental and numerical investigation into the mechanisms underlying collision‐induced erosion and transport of dry soil beds. A series of flume experiments are conducted where collisional granular flows erode dry sand beds under varied conditions. The experiments are then back‐analyzed using a hybrid continuum–discrete simulator to gain physical insight into the erosion and transport processes. Results show that the key mechanism of collision‐induced erosion and transport is the retexturing of the soil bed surface. This implies that bed morphology, which has often been overlooked in mobility and hazard assessments, has profound effects on erosion and transport potential. Further, contrary to most existing models that assume all the eroded bed volume is carried away by granular flow, it is found that only up to 80% of the eroded material is transported. Also found is that the collisional stresses of the monodisperse grains in this study follow the Pareto distribution in which 80% of differences in the outcomes are due to 20% of causes. This finding suggests that there is measurable certainness in a seemingly random process of coarse grain collisions with an erodible soil bed.

VARIASI POLA SIMETRI ROTASI 90 DERAJAT DARI SIMULASI SISTEM DINAMIK DENGAN TIGA TES KONVERGENSI

This article reviews the symmetry pattern which has rotational symmetry and translational symmetry along the -axis and -axis. The symmetry pattern is generated through the implementation of Matlab application using discrete dynamical system simulation, after analysing the requirements and determining the appropriate dynamical function. In this context, each point on the plane serves as the starting point in the iteration of the dynamical system. The colour assigned to each point is determined by the number of iterations performed. The generation of the symmetry pattern involves three convergence tests, namely the Euclidean Test, the Fractional Distance Test, and the Maximum Distance with Weighted test. Through a variety of dynamic function parameter combinations, a more visually appealing and diverse range of symmetry patterns is obtained.

Modeling Charge Transport in Flowable Suspension Electrolytes

Flowable suspension electrolytes (FSEs) consist of electrically conductive, redox-active, and/or energy-storing particles suspended in aqueous or non-aqueous electrolyte solutions (supporting salt + solvent). These particles, which can range in size from nanometers to micrometers, are subjected to Brownian forces, hydrodynamic forces, hydrophobic interactions, and van der Walls interactions among others. FSEs may enable electrochemical processes where solid reactants can be integrate with flow cells potentially unlocking new approaches to materials processing (e.g., synthesis, extraction/recovery). For example, FSEs has been demonstrated in redox flow batteries, facilitating higher energy densities without sacrificing independent power and energy scaling However, understanding and controlling charge transport through the deformable particle microstructures, especially under shear, is key to enable desirable current distributions and thus effective electrode utilization.In this presentation, we investigate the impact of interparticle interactions, particle volume fractions, and applied shear rate on charge transport through FSEs. At sufficiently large volume fractions above the percolation threshold and stationary conditions, particle interactions in an FSE can drive the formation of networks that span the cell dimensions and provide electronic transport similar to stationary freestanding porous electrodes. However, under flowing conditions, shear forces can break these networks, hampering charge transport. Conversely, increasing attractive particle interactions or particle concentration can strengthen the particle networks and fortifying charge transport, albeit at the expense of fluid viscosity. To better understand these processes, we model the charge transport through these dynamic particle networks, using a combination of local charge transport models and discrete particle simulations, considering the Peclet number (ratio of shearing to Brownian forces) and Mason number (ratio of shearing to attractive forces). Our results contribute to the development of continuum models for charge transport in FSEs, which, in turn, can facilitate efficient and accurate system-level analysis. Acknowledgments This work was funded by the Skoltech – MIT Next Generation Program.

A bounding surface plasticity model for methane hydrate-bearing sediments in deep seabed

This study proposes a new constitutive model to simulate the mechanical behavior of methane hydrate-bearing sediments, by modifying the SANISAND-C model originally designed for sands with low cement content. To capture the distinctive cementation effect of methane hydrate (MH), modifications are made to the state parameter and bonding degradation law of the SANISAND-C model. In addition, the initial bonding strength of MH is not only determined by MH saturation but also by a condition parameter that depends on temperature, pore pressure, and salinity. The densification effect caused by MH pore-filling and grain-coating is captured by replacing the original void ratio in the elastic and plastic moduli of the SANISAND-C model with a reduced void ratio. The model is verified through a comparison of its predictions not only with experimental data but also through discrete element method simulations that cover a wide range of loading paths including drained and undrained true triaxial tests. The model successfully captures the stiffness, strength and dilatancy enhancements induced by MH, as well as the temperature, pore pressure, and salinity-dependent behavior of sediment. Additionally, the model developed can account for different hydrate occurrence habits by adjusting a single parameter related to bonding strength.

Benchmarking discrete dislocation dynamics simulations with dark-field X-ray microscopy movies

Benchmarking discrete dislocation dynamics simulations with dark-field X-ray microscopy movies

Statistical analysis of discrete dislocation dynamics simulations: initial structures, cross-slip and microstructure evolution

Over the past decades, discrete dislocation dynamics simulations have been shown to reliably predict the evolution of dislocation microstructures for micrometer-sized metallic samples. Such simulations provide insight into the governing deformation mechanisms and the interplay between different physical phenomena such as dislocation reactions or cross-slip. This work is focused on a detailed analysis of the influence of the cross-slip on the evolution of dislocation systems. A tailored data mining strategy using the ‘discrete-to-continuous (D2C) framework’ allows to quantify differences and to quantitatively compare dislocation structures. We analyze the quantitative effects of the cross-slip on the microstructure in the course of a tensile test and a subsequent relaxation to present the role of cross-slip in the microstructure evolution. The precision of the extracted quantitative information using D2C strongly depends on the resolution of the domain averaging. We also analyze how the resolution of the averaging influences the distribution of total dislocation density and curvature fields of the specimen. Our analyzes are important approaches for interpreting the resulting structures calculated by dislocation dynamics simulations.

Model for Land Use Optimisation for Flood Management in Lasolo Watershed, Indonesia

Changes in land use from vegetation to non-vegetation in the Lasoso watershed contribute to an increase in the run-off coefficient caused by inundation during the wet season. Therefore, engineering is required to reduce discharge from surfaces. This study seeks to optimize land use in order to manage flooding. This study employs the paimin (modified) method with three different scenarios: Business as usual (BAU), simultaneous, and discrete. Results indicated that the BAU scenario has throughfall and retention capacity values of 15.55 percent and 19.39 percent of the total watershed area, respectively. scenario-2 (simultaneous) decreased throughfall and increased storage capacity (15.35 and 24.65%, respectively); scenario-3 (discrete) also improved. Comparing throughfall values reveals that the discrete simulation (-0.0020) is greater than the simultaneous scenario (-0.008), whereas the retention capacity has the same value (0.0020). The discrete simulation is superior to the simultaneous simulation in terms of optimizing its use for flood management in the Lasolo catchment.

Macro-micro Performances of Granular Materials Considering the Influences of Density and Stress Path under True Triaxial Conditions: A DEM Investigation

The mechanical behaviors of granular materials are dominated by internal structure, which are related to fabric evolution during loading. This study investigated the fabric evolution of granular materials with different densities and stress paths under true triaxial conditions. A series of discrete element numerical simulations with different intermediate principal stress coefficient b were carried out along the constant mean stress p and the constant minor principal stress σ3 stress paths for both loose and dense specimens. The results indicated that the constant-p stress path produced a faster increase in stress ratio than the constant-σ3 stress path at the same b. The effects of specimen density on the peak friction angle are greater than that of stress path. The microscopic analyses revealed that the constant-p stress path facilitates a much more preferential distribution of normal contact force network along the major principal direction. The discrepancies in the peak stress ratio under two stress paths were thus interpreted. The dense specimen will rapidly form a higher anisotropic distribution of the normal contact force network upon shearing, and its anisotropic intensity was almost twice that of the loose specimen at the peak stress state. In addition, a unique relationship between the strong deviatoric fabric ratio and stress ratio was presented. The ratio of the two was approximately 1.0 regardless of stress path, density and b value. Finally, an underlying relationship between the stress components and the whole fabric components at the critical state was confirmed by introducing a new stress tensor. The three principal components (F1, F2 and F3) of the whole fabric tensor can be quantitatively represented with the imposed three principal stress components (σ1, σ2 and σ3) by employing a relationship of F1:F2:F3 = σ10.27:σ20.27:σ30.27. It provides a more comprehensive perspective to analyze the macro-micro performances of granular materials at the critical state.

Parametric numerical study of dislocation density distribution in Czochralski-grown germanium crystals

Dislocations strongly affect the quality of Czochralski-grown germanium crystals used for various applications, however, the influence of different growth parameters on the dislocation distribution has not been extensively studied in the literature. In the present work, a simplified parametric crystal growth model is introduced which is suitable for large-scale numerical studies. The time-dependent temperature and dislocation density distributions in the crystal are calculated and analyzed. The Alexander–Haasen model is applied for dislocation modeling. Model parameters are taken from previously published discrete dislocation dynamics simulations, establishing a novel coupling between mesoscopic and macroscopic simulations. A W-shaped radial distribution of the dislocation density is obtained in the simulations. It is shown that the effective ambient temperature and crystallization front deflection have the strongest influence on the dislocation distribution. The results are compared to the experiment, showing a qualitative agreement, but also several deviations. Limitations of the considered dislocation modeling approach and the simplified thermal model are discussed.

Surface instabilities generated by a slider pulled across a granular bed.

We report an instability of a slider slowly dragged at the surface of a granular bed in a quasistatic regime. The boat-shaped slider sits on the granular medium under its own weight and is free to translate vertically and to rotate around the pitch axis while a constant horizontal speed is imposed. For a wide range of parameters (mass, length, shape, velocity) a regular pattern of peaks and troughs spontaneously emerges as the slider travels forward. This instability is studied through experiments using a conveyor belt and by means of two-dimensional discrete elements method simulations. We show that the wavelength and amplitude of the pattern scale as the length of the slider. We also observe that the ripples disappear for low and high masses, indicating an optimal confining pressure. The effect of the shape, more specifically the inclination of the front spatula, is studied and found to drastically influence both the wavelength and the amplitude. Finally, we show that the mechanical details (friction, cohesion) of the contact point between the slider and the pulling device is critical and remains to be fully understood.

Efficient reciprocating burrowing with anisotropic origami feet.

Origami folding is an ancient art which holds promise for creating compliant and adaptable mechanisms, but has yet to be extensively studied for granular environments. At the same time, biological systems exploit anisotropic body forces for locomotion, such as the frictional anisotropy of a snake's skin. In this work, we explore how foldable origami feet can be used to passively induce anisotropic force response in granular media, through varying their resistive plane. We present a reciprocating burrower which transfers pure symmetric linear motion into directed burrowing motion using a pair of deployable origami feet on either end. We also present an application of the reduced order model granular Resistive Force Theory to inform the design of deformable structures, and compare results with those from experiments and Discrete Element Method simulations. Through a single actuator, and without the use of advanced controllers or sensors, these origami feet enable burrowing locomotion. In this paper, we achieve burrowing translation ratios-net forward motion to overall linear actuation-over 46% by changing foot design without altering overall foot size. Specifically, anisotropic folding foot parameters should be tuned for optimal performance given a linear actuator's stroke length.

Application of mean-force potential lattice element method to modeling complex structures

Natural hazards such as windstorms, earthquakes, and floods cause damage and failure to both structural and non-structural elements, significantly impacting the functional integrity and overall performance of the building systems. The economic loss due to such events and the often tortuous path to recovery call for revisiting engineering approaches to resilience assessment through developing simulation methods that provide a balance between fidelity and efficiency, particularly if the post-event assessment is to be performed at a large scale, e.g., the scale of a community. In this paper, we develop a discrete simulation framework for modeling the response of structures as a middle-ground solution between overly simplistic multi-degree-of-freedom models on the one hand and intricate FE models on the other. The framework draws upon the Potential-of-Mean-Force (PMF) approach to Lattice Element Method (LEM) where the main idea is to discretize the system into a set of particles that interact with each other through prescribed interaction potentials. These potentials are calibrated beforehand at member scale, for different structural and non-structural components. Here we focus on providing the main elements and the steps necessary for adaptation to modeling structural components in linear regime and leave the extension to nonlinear regime and the modeling of damage for future developments. This includes calibration of the potentials for structural members of different types (1D vs. 2D) under different actions (axial, bending, in-plane and out-of-plane actions) through an energetic handshake between the lattice model and continuum theories, e.g., the Timoshenko beam theory and Kirchhoff–Love plate theory. We explore the utility of the proposed method through its application to simulation of a set of building systems with different levels of complexity and under various loading conditions.