Discrete Simulation Research Articles

Design of Sepic Converter Using PID Controller

Abstract: Single-Ended Primary Inductor Converter (SEPIC) is widely used in battery charging of renewable energy and electric/hybrid vehicles due to its output gains range flexibility,less complex switching design, providing an isolation by capacitor and producing non-inverted output. This project presents a modified PID controller to obtain excellent dynamic performance with zero steady-state error. The controller design is discussed and built in discrete model simulation on MatlabSimulink. The effectiveness of the proposed modified PID control strategy is tested for the transient cases in step-changed reference voltage, and varying input voltages. The results show the proposed controller can reach zero steady-state error and produce lower ripple in voltage.

Application of microscopic discrete event-based simulation in the modelling of the city logistics systems of concentrated sets of delivery locations

ABSTRACT Nowadays, city logistics issues are getting more and more attention. Within this, our City Logistics Research Group is currently focusing on the urban concentrated sets of delivery locations. MS Excel- and AnyLogic-based simulation models were developed in the last years to analyze them, but still, problems were encountered above a certain model size in both cases. For this reason, we started looking for a new tool that is flexible, fast, and available for everyone. The use of Python Programming Language was selected, with the primary goal of eliminating the previous technical problems and obtaining detailed information about the examined processes. In this paper, we are going to present the problems of the previous models, the development, operation, and main advantages of the new, Python-based DES model, the design and parameterization of the pilot models, the results of the tests, and the next steps of the research.

A graph database for feature characterization of dislocation networks

Three-dimensional dislocation networks control the mechanical properties such as strain hardening of crystals. Due to the complexity of dislocation networks and their temporal evolution, analysis tools are needed that fully resolve the dynamic processes of the intrinsic dislocation graph structure. We propose the use of a graph database for the analysis of three-dimensional dislocation networks obtained from discrete dislocation dynamics simulations. This makes it possible to extract (sub-)graphs and their features with relative ease. That allows for a more holistic view of the evolution of dislocation networks and for the extraction of homogenized graph features to be incorporated into continuum formulation. As an illustration, we describe the static and dynamic analysis of spatio-temporal dislocation graphs as well as graph feature analysis.

Calibration of Small-Grain Seed Parameters Based on a BP Neural Network: A Case Study with Red Clover Seeds

In order to enhance the accuracy of discrete element numerical simulations in the processing of small-seed particles, it is essential to calibrate the parameters of seeds within the discrete element software. This study employs a series of physical tests to obtain the physical and contact parameters of red clover seeds. A discrete element model of red clover seeds is established. Plackett–Burman Design, steepest ascent, and Central Composite Design experiments are sequentially conducted. The simulation deviation of the resting angle of red clover seeds is employed as the evaluation criterion for parameter optimization. The results indicate that the coefficients of static friction between red clover seeds, the coefficients of rolling friction between red clover seeds, and the coefficients of static friction between red clover seeds and the steel plates significantly influence the resting angle. Modeling was performed using a backpropagation neural network, a genetic algorithm–optimized BP network, particle swarm optimization, and simulated annealing. It was found that GA-BP ensured both accuracy and stability. Compared to the traditional response surface methodology, GA-BP showed better fitting performance. For the optimized red clover seed simulation, the error between the angle of repose and the physical experiment was 0.98%. This research provides new insights into the calibration of small-grain seed parameters, demonstrating the value of GA-BP for precision modeling.

Impact of Airflow Rectification on Spreading Uniformity for UAV-Based Multichannel Pneumatic Granular Fertilizer Spreader

Unmanned aerial vehicles (UAVs) are an important part of smart farms and have been widely used in granular fertilizer spreading. The multichannel pneumatic granular fertilizer spreader (MPGFS) has the advantages of light weight and precision spreading, and has been applied to UAV variable rate fertilization. Based on the problem that the airflow field disorder of the existing MPGFS reduces the uniformity of spreading, the aim of this study was to further improve the performance of the MPGFS through rectification. The computational fluid dynamics and discrete element method (CFD-DEM) and coupling simulation method were used to study the characteristics of the airflow field and fertilizer particle motion, and a honeycomb rectifier and grid rectifier were developed. The aperture of the honeycomb rectifier and the grid size of the grid rectifier were optimized. Then, the test bench was built to test the consistency of the discharge rate of each channel and the spreading uniformity of the MPGFS. The simulation results of the existing MPGFS showed that the airflow provided by the axial flow fan was rotational, and this caused the particles’ motion to be skewed in the shrinkage section, so the discharge rate of each channel was inconsistent. The airflow field analysis results of the shrinkage section showed that the airflow rotation was reduced after the rectification of the honeycomb rectifier and the grid rectifier. The bench test results showed that the coefficient of variation (CV) of each channel discharge rate of the existing MPGFS was 20.16%, the optimal honeycomb rectifier was 13.07%, and the optimal grid rectifier was 5.27%. The bench test results of spreading uniformity show that the CV of spreading uniformity of the existing MPGFS was 15.32%, the optimal honeycomb rectifier was 15.81%, and the optimal grid rectifier was 8.02%. The grid rectifier spread pattern was more reasonable and the CV of uniformity was better. This study demonstrated that the use of a grid rectifier to rectify the airflow field of MPGFS can effectively improve its spreading uniformity, which was of guiding significance for the design and research of MPGFS.

Numerical Study on the Damage Characteristics of Layered Shale Using 3D DEM

Layered shale is a kind of rock with obvious anisotropy, which is significantly influenced by the inclination angle of the rock. In this study, the influence of bedding dip on the strength characteristics, failure mode, and internal fracture evolution of layered shale was investigated through laboratory triaxial compression tests and three-dimensional discrete element numerical simulations. Results show that the numerical model of layered shale constructed using the bonded block model can simulate the layered shale in terms of U-shaped strength variation and failure modes very well. Based on the distribution of cracks and failure characteristics of layered rocks, the failure modes of layered rocks are classified as follows: Shear failure across the bedding plane, slip failure along bedding planes, combined tensile splitting and shear failure. The development of microcracks damage in the slip failure model is controlled by interlayer joints, while in other failure modes, it is jointly controlled by the rock matrix and interlayer joints. The relationship between microscopic joint parameters and the variations of Young's modulus and peak strength has been proposed.

A numerical study on the multi-cycle self-burrowing of a dual-anchor probe in shallow coarse-grained soils of varying density

Development of self-burrowing probes that can penetrate soils without the aid of external reaction force from drill rigs and trucks would facilitate site characterization activities and deployment of sensors underneath existing structures and in locations with limited access (e.g., toe of dams, extraterrestrial bodies). Successful deployment of self-burrowing probes in the field will require several cycles of expansion, penetration, and contraction motions due to the geometric constraints and the increase in soil strength with depth. This study explores the multi-cycle performance of a dual-anchor self-burrowing probe in granular assemblies of varying density using discrete element modeling simulations. The simulated probe consists of an expandable top shaft, expandable bottom shaft, and a conical tip. The expansion of the shafts are force-controlled, the shaft contraction and tip advancement are displacement-controlled, and the horizontal tip oscillation is employed to reduce the penetration resistance. The performance of the self-burrowing probe in terms of self-burrowing distance is greater in the medium dense specimen than in the dense and loose specimens due to the high magnitude of anchorage force in comparison with penetration resistance. For all three soil densities, most of the mechanical work is done by tip oscillation; however, this accounts for a greater percentage of the total work in the denser specimen. Additionally, while tip oscillation aids in enabling self-burrowing to greater depths, it also produces a greater work demand. The results presented here can help evaluate the effects of soil density on probe prototypes and estimate the work requited for self-burrowing.

Direct numerical simulation of fluid/solid particles flow inside a channel

The modeling of moving solid particles in fluid flow has been the focus of many studies and has succeeded to attract significant attention from researchers. However, commonly used modeling approaches such as discrete element modeling (DEM) and direct numerical simulations (DNS) lack simplicity and have been computationally intensive. The aim of this paper is to develop a new approach to simulate solid transport in an incompressible Newtonian fluid flow. This method is based on the Finite element method with penalization of the deformation tensor. The fluid behavior is governed by the Navier-Stokes equations within the investigation domain. To take into account collisions, we present an algorithm which allows us to handle contacts between rigid particles. In this paper, 2D fluid/particles flow simulations are performed; the results are validated by comparison with results from other methods. We attempt to simulate the conveying of solid particles behavior of circular particles in a fluid flow inside a pipe. The numerical tests show that the present method provides a very efficient approach to directly simulate the solid transport inside the channels.

Study on the dynamic influence of the distribution of cutting depth on the ground surface quality in a precision grinding process

Focusing on the excitation mechanisms of self-excited vibration and forced vibration, a time-delay differential model of the radial cutting depth of a single active abrasive grit is presented. Based on the principle of the layered superposition characteristics of each component of radial cutting depth, a full discrete simulation technology is used to analyze the dynamic mechanisms of different vibration excitations on the grinding characteristics. The reliability of the dynamic mechanisms is verified by the corresponding grinding experiments. The verification results demonstrate that static and dynamic components in the grinding dynamics, including radial cutting depth, grinding force, surface roughness and surface morphology of workpiece are greatly influenced by total material removal rate, followed by speed ratio and grinding directions. With the increase of cutting depth, the variation amplitude of grinding process influenced by forced-vibration mechanism are nearly twice larger than those influenced by self-excited vibration mechanism. When speed ratio reduces to a half, surface roughness of workpiece improves by nearly 33 %. The stability of machining process and finish surface of workpiece during up-grinding are better than those during down-grinding, where force reduction by up to 10 % and surface finish improvement by 37 %.

Anisotropic damage state modeling based on harmonic decomposition and discrete simulation of fracture

This study proposes an anisotropic damage state modeling of the effective (damaged) elasticity tensor E˜ as a function of damage based on (i) a discrete element model for quasi-brittle material and (ii) a decomposition of the elasticity tensor in covariants. A procedure is proposed to measure the evolution of effective elasticity tensors computed by a beam-particle model. Various multiaxial damaging loadings allow us to constitute a dataset of around 76 000 effective elasticity tensors (our virtual testing reference set). We then cross-identify the anisotropic/tensorial damage state for the whole dataset. A detailed analysis of the dataset, using the distance to orthotropy as a guideline, justifies representing the induced micro-cracking by a single second-order damage variable D, even in the final stages with strong micro-cracks interaction. To formulate the damage state coupling, we use a reconstruction formula of orthotropic elasticity tensors in terms of invariants and (tensor) covariants. Thanks to this formula, some parts of the effective elasticity tensors E˜ (such as the dilatation part) are modeled exactly from the single damage variable. Constitutive equations are proposed for the remaining parts of E˜ (such as its generalized shear modulus and fourth-order harmonic part) using physical assumptions from micro-mechanics and a sparse data driven approach. The proposed anisotropic damage state coupling E˜(D) accurately models the damaged elasticity tensors in multiaxial loading, proportional or non-proportional, up to high damages. The present study firstly highlights the need for an anisotropic damage model for quasi-brittle materials and, secondly, offers a methodology to formulate the damage state coupling by explicit formulas introducing at most two dedicated parameters: the (optional) nonlinear shear-damage coupling parameter m and the harmonic prefactor h.

An immersed moving boundary for fast discrete particle simulation with complex geometry

An immersed moving boundary (IMB) scheme in LBM-DEM is proposed for discrete particle simulation with arbitrarily complex geometry. Momentum exchange between fluid and unresolved particles can be exerted by a modified weighting function with drag force and a new solid operator in IMB, which can describe both particle–fluid interaction and complex geometry, and requires only local information in perspective of solution. Combined with stereolithography (STL) format for describing complex geometry, a GPU-based LBM-DEM-IMB is implemented, and its ability and accuracy for complex geometry from STL model is verified by simulating flow past a stationary sphere. Compared with CFD-DEM in discrete particle simulations of both fluidized bed with immersed tube and aerosol transporting in human nasal, proposed method has much higher efficiency and maintains comparable accuracy in dense and dilute particle–fluid systems with complex geometry, which demonstrates it to be a promising computational strategy for particle–fluid two-phase flows.

Void nucleation at dislocation boundaries aided by the synergy of multiple dislocation pile-ups

Void nucleation is of great significance in understanding ductile fracture. Recent experiments have shown that voids are nucleated via vacancy condensation and dislocation boundaries are the main nucleation sites. However, it is unclear what role is played exactly by dislocation boundaries in promoting void nucleation. Here we propose a new mechanism for dislocation boundary-induced void nucleation and develop a corresponding model based on the classical nucleation theory and vacancy diffusion theory. The model suggests that void nucleation is mainly influenced by hydrostatic stress, temperature, and relative vacancy concentration, whose contributions are systematically studied. It is also suggested that the vacancy formation energy and the interaction energy of hydrostatic stress and vacancy, which are absent in the previous models and introduced in ours, exhibit a clear tendency to lower the activation free energy barrier. Analysis of the nucleation kinetic suggests that the growth rate of void depends on the vacancy diffusion coefficient and vacancy concentration; the higher the values of these parameters, the faster the growth rate of the void. The kinetic feasibility of the newly proposed mechanism is examined using three-dimensional discrete dislocation dynamics simulations. The results predict that the size of incipient voids nucleated at the dislocation boundary is ∼35 nm, which is consistent with the experimental characterization value of ∼50 nm. Finally, when the relaxation of the dislocation boundary is considered, the synergistic effect is weakened.

Erosion Life Prediction of Metal Mesh Screen Pipes in Oil Wells Based on Numerical Simulation of Discrete Particle Flow.

High-speed fluid-carried sand particles pose a significant challenge to oil well screen pipes, leading to sand control failure and adversely affecting the well's production and recovery rates. This research targets the commonly used metal mesh screen pipe in oil well sand production and establishes a full-sized three-dimensional structure model. A fluid-solid coupling of discrete particle flow numerical simulation algorithm is incorporated to formulate a novel method for predicting the screen pipe's erosion life. This method provides a solution to the complex task of predicting the pipe's lifespan under oil sand fluid erosion. The analysis elucidates the impact of sand particles on the velocity distribution and erosion rate of the metal mesh at varying velocities, facilitating the prediction of the mesh screen pipe's erosion life. Key findings reveal that the velocity and erosion rate vary across the different layers. The first layer screen experiences velocity and erosion rates that are 3.6-3.76 times and 2.45-2.50 times, respectively, higher than those at the inlet. The second layer screen undergoes velocity and erosion rates 2.32-2.43 times and 1.04-1.06 times, respectively, higher than those at the inlet. Erosion failure primarily occurs in the first layer screen due to velocity expansion instigated by the screen tube's structure. The discrete flow numerical simulation method proves valuable in predicting the mesh screen's erosion life at different flow rates, with a maximum error of 6.38% when compared with field monitoring life values. This method introduces a new technical approach to predicting the life span of metal mesh screens in oil wells. The study concludes by suggesting measures to extend the screen pipe's lifespan, thereby enhancing oil recovery.

A data-based derivation of the internal stress in the discrete-continuum transition regime of dislocation based plasticity

Effectively homogenizing microstructure heterogeneity within the coarse-graining volume is a long-lasting challenge in crystal plasticity theories. In this paper, we propose a data-based homogenization method that utilizes discrete dislocation dynamic simulations to derive the nearfield correction stress (back stress) for continuum models. This stress accounts for the effective stress field induced by microstructure heterogeneity under the length scale of a coarse-graining volume, providing a physically based homogenization approach. To bridge the gap between discrete and continuous regimes, we introduce two versions of the nearfield correction stress, as well as a criterion based on microstructure and numerical parameters to determine the discrete and continuous transition. Moreover, by analyzing the mathematical connections with the work-conjugated gradient plasticity theory, we further provide a physical explanation for the observed material length scale in the thermodynamically consistent back stress term. This work presents a novel methodology for effectively addressing microstructure heterogeneity and advancing the understanding and modeling of material behavior bridging different length scales.

Evolution Characteristics of Plastic Zone in Jointed Rock Mass of High-Temperature Hydraulic Tunnel

The evolution characteristics and the extent of the plastic zone in rock mass can reflect the failure characteristics and destruction degree of a hydraulic tunnel. In this research, we derived the equation of a plastic zone range based on a gateway-like structure high-temperature tunnel through a theoretical analysis. On-site monitoring and discrete element model simulation were combined to analyze the temperature field law and plastic zone evolution characteristics of the jointed rock mass at high temperatures. The results show that the joints affect the temperature field variation in rock mass, and the vertical and horizontal joint groups pose significantly greater influence than the inclined joint group on temperature field. The sensitivity of the joint internal friction angle and thermal expansion coefficient to the range of the plastic zone is relatively small. Under various joint spacings, the influence of horizontal and inclined joint groups on the plastic zone morphology decreases, while the vertical joint group exhibits an incremental influence on the plastic zone morphology. Similar to the influence of the temperature field, the vertical and horizontal joint groups have a significantly greater influence on the plastic zone range than the inclined joint group. Under various rock mass temperatures, the plastic zone in rock mass results in the occurrence of uneven expansions along the direction of the joint dip angle, which changes the potential failure direction of rock mass and increases the potential destruction degree of rock mass, whereas it exhibits a smaller uniform expansion perpendicular to the joint dip angle, and the boundary of the plastic zone coincides with the joint surface, relatively hindering the potential destruction degree of rock mass. The research results of this study have certain reference values for the stability control of jointed rock mass in high-temperature hydraulic tunnels.

Research on the Development Mechanism of Three Kinds of Cracks in Rock Cutting

In order to study the mechanism of crack propagation in rock cutting, experiments and discrete element numerical simulation of rock cutting at different depths were adopted in this paper. The rock fragmentation can be divided into mini-size fragmentation and normal-size fragmentation from a size viewpoint. The discrete element method (DEM) is used to further investigate the mechanism of normal size fragmentation at different depths and record the process of crack initiation and propagation. Additionally, the paper characterizes the process of crack initiation and examines the representative rock fragmentation. According to the mechanism of crack development, rock fragmentation can be divided into three categories: conventional failure, fracture failure, and damage failure. The fragmentation of three kinds of failure has one common point. To form semi-dislodged rock fragmentation, the macroscopic shear cracks are first formed. Subsequently, the tensile failure at weak places causes fragmentation ejection. Therefore, the mechanism of fragmentation generation in rock cutting is investigated in terms of crack initiation and extension. In this study, the fracture phenomenon of previous rock cutting experiments is reproduced by an experiment, and the failure process is analyzed in detail by the discrete element method, which reveals the essence of producing fragment phenomena and summarizes the fracture phenomenon and damage crack propagation mechanism in rock cutting.

Unveiling Medin Folding and Dimerization Dynamics and Conformations via Atomistic Discrete Molecular Dynamics Simulations.

Medin is a principal component of localized amyloid found in the vasculature of individuals over 50 years old. Its amyloid aggregation has been linked to endothelial dysfunction and vascular inflammation, contributing to the pathogenesis of various vascular diseases. Despite its significance, the structures of the medin monomer, oligomer, and fibril remain elusive, and the dynamic processes of medin aggregation are not fully understood. In this study, we comprehensively investigated the medin folding and dimerization dynamics and conformations using atomistic discrete molecular dynamics simulations. Our simulation results suggested that the folding initiation of the medin involved the formation of β-sheets around medin30-41 and medin42-50, with subsequent capping of other segments to their β-sheet edges. Medin monomers typically consisted of three or four β-strands, along with a dynamic N-terminal helix. Two isolated medin peptides readily aggregated into a β-sheet-rich dimer, displaying a strong aggregation propensity. Dimerization of medin not only enhanced the β-sheet conformations but also led to the formation of β-barrel oligomers. The aggregation tendencies of medin1-18 and medin19-29 were relatively weak. However, the segments of medin30-41 and medin42-50 played a crucial role as they primarily formed a β-sheet core and facilitated medin1-18 and medin19-29 to form intra- and interpeptide β-sheets. The findings highlight the critical role of the medin30-41 and medin42-50 regions in stabilizing the monomer structure and driving the medin amyloid aggregation. These regions could potentially serve as promising targets for designing antiamyloid inhibitors against amyloid aggregation of medin. Additionally, our study provides a full picture of the monomer conformations and dimerization dynamics for medin, which will help better understand the pathology of medin aggregation.

Characterizing infection risk in a restaurant environment due to airborne diseases using discrete droplet dispersion simulations

The use of masks as a measure to control the spread of respiratory viruses has been widely acknowledged. However, there are instances where wearing a mask is not possible, making these environments potential vectors for virus transmission. Such environments can contain multiple sources of infection and are challenging to characterize in terms of infection risk. To address this issue, we have developed a methodology to investigate the role of ventilation in reducing the infection risk in such environments. We use a restaurant setting as a representative scenario to demonstrate the methodology. Using implicit large eddy simulations along with discrete droplet dispersion modeling we investigate the impact of ventilation and physical distance on the spread of respiratory viruses and the risk of infection. Our findings show that operating ventilation systems, such as mechanical mixing and increasing physical distance between subjects, can significantly reduce the average room infection risk and number of newly infected subjects. However, this observation is subject to the transmissibility of the airborne viruses. In the case of a highly transmissible virus, the use of mechanical mixing may be inconsequential when compared to only fresh air ventilation. These findings provide valuable insights into the mitigation of infection risk in situations where the use of masks is not possible.

Bi-Objective Modeling and Optimization for Stochastic Two-Stage Open Shop Scheduling Problems in the Sharing Economy

Nowadays, many manufacturing and service industries prefer to share resources such as facilities and workers to cooperatively perform tasks, which can efficiently improve resource utilization and customer satisfaction. Generally, the decision-makers need to pay more for resource usage, leading to an urgent demand to decrease operational costs. This article proposes a stochastic bi-objective two-stage open shop scheduling problem that models a vehicle maintenance process where tasks are appointed to be completed by multiple third-party companies with professional equipment. We formulate this optimization problem by minimizing the total tardiness and processing cost subject to various resource constraints. A hybrid multiobjective migrating birds optimization combined with a genetic operation and a discrete event system is designed by considering problem characteristics to solve the problem. In this method, the migrating birds optimization with some particular strategies aims at searching candidate solutions from the entire solution domain. Simultaneously, the discrete event system, by using stochastic simulation and discrete event-based simulation approaches, focuses on evaluating the performance of searched solutions. Simulation experiments are performed, and state-of-the-art algorithms are used as competitive approaches. The results confirm that this approach has an excellent performance in handling our considered problem.

Performance Evaluation of QUIC Protocol in Message Replication Overhead in PBFT Consensus using NS-3

The development of protocols in the ICT world to increase reliability and speed in data traffic gave an inspiration to a new protocol called the QUIC protocol. The QUIC protocol is expected to improve the performance of Transport Control Protocol (TCP). In addition, developments also occur in blockchain technology where the protocol used in this technology still uses the existing TCP protocol. In this paper, we aimed to research whether the QUIC protocol implementation in blockchain infrastructure could improve the performance of the blockchain infrastructure itself, in terms of the time required for transactions. We focus on conducting research to measure the overhead time reduction of Practical Byzantine Fault Tolerance (PBFT) consensus by implementing the QUIC protocol, the consensus propagation process is a crucial phase in Blockchain. For simulation we used NS-3 discrete simulation environment to conduct scenario and our simulation result showed that the QUIC Protocol have potential significant performance compared to TCP Protocol in large datasets, on the other hand QUIC protocols have more room for improvement by implementing appropriate congestion algorithms.