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Numerical Investigation of the Gas-Solid Flow Characteristics in a Three-Dimensional Spouted Bed with a Draft Tube

CHEMICAL ENGINEERING & TECHNOLOGY 2013年第12期36卷 2035-2043页

作者： Yang, Shi-Liang Luo, Kun Fang, Ming-Ming Zhang, Ke Fan, Jian-Ren Zhejiang Univ State Key Lab Clean Energy Utilizat Hangzhou 310027 Zhejiang Peoples R China

Gas-solid motions in a three-dimensional conical spouted bed with a draft tube are investigated based on a simulation carried out by the coupling approach of computational fluid dynamics combined with the discrete-element method. The distribution properties of the velocity, the concentration, and the flux of the solid phase are discussed. The vertical solid velocity in the central region initially increases, diminishes gradually, and finally decreases sharply in the region above the draft tube. Vigorous lateral solid motion occurs in the periphery of the fountain and the spout-annulus interface. In addition, the vertical solid flux shows a large value in the spout. A larger vertical velocity but a more dilute solid concentration can be detected along the axial direction when enlarging the gas flow rate.

关键词： discrete-element method Draft tube Mathematical modeling Multiphase flow Spouted bed

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Coupled DEM and FDM Algorithm for Geotechnical Analysis

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INTERNATIONAL JOURNAL OF GEOMECHANICS 2018年第6期18卷 4018040.1-4018040.1页

作者： Zhao, Xueliang Xu, Jian Zhang, Youhu Xiao, Zhong Southeast Univ Sch Civil Engn Nanjing 210096 Jiangsu Peoples R China Shanghai Municipal Engn Design Inst Grp Co Ltd Shanghai 200092 Peoples R China Norwegian Geotech Inst Offshore Geotech Sognsveien 72 N-0855 Oslo Norway Tianjin Univ State Key Lab Hydraul Engn Simulat & Safety Tianjin 300072 Peoples R China

The purpose of this paper is to present a new algorithm for coupling discrete-element and finite-difference methods for three-dimensional problems. The finite-difference method (FDM) and the discrete-element method (DEM) are commonly used in geotechnical engineering. However, the continuous characteristics and the computational cost are the main obstacles to accurate and efficient simulation of practical problems for these individual methods. Coupling is thought to be an effective and promising way to combine the advantages and overcome the inability of these two methods. In this paper, an algorithm for coupling of DEM and FDM is presented. A two-stage searching methodnamely, global domain searching and local domain searchingis proposed for detecting contact on the interface. A calculation method for force transmitting is presented. Conventional soil element tests were simulated to verify the validity of the proposed coupled algorithm by checking the constitutive behaviors, deformation compatibility, and transmission of normal and shear contact force.

关键词： Finite-difference method discrete-element method Coupling algorithm Global searching Local searching Contact force transmitting

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CFD-DEM Modeling of Shaft Furnaces Using the Volume Fraction Smoother Approach

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CHEMICAL ENGINEERING & TECHNOLOGY 2023年第7期46卷 1333-1339页

作者： Spijker, Christoph Pollhammer, Werner Raupenstrauch, Harald Montan Univ Leoben Chair Thermal Proc Technol Franz Josef Str?18 A-8700 Leoben Austria Montan Univ Leoben Franz Josef Str ?18 A-8700 Leoben Austria

Shaft furnaces are widely used in high-temperature processes for granular materials due to their high energy efficiency. The modeling of these furnaces is challenging because of large domains and long process times. Small geometric details like the natural gas burner nozzles demand a fine grid on the computational fluid dynamics (CFD) side, resulting in a grid size smaller than the particle size. Resolving a discrete element particle over several cells is computationally expensive. Interpolation methods on non-structured grids are complex. In order to provide a fast and simple solution, the volume fraction smoother was developed, and to shorten the calculation time, the time scale splitting method, which separates the time steps for CFD and the discrete-element method (DEM), was introduced.

关键词： Computational fluid dynamics discrete-element method Shaft furnace Time scale splitting method Volume fraction smoother

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Studies of the performance of particle dampers attached to a two-degrees-of-freedom system under random excitation

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JOURNAL OF VIBRATION AND CONTROL 2011年第10期17卷 1454-1471页

作者： Lu, Zheng Masri, Sami F. Lu, Xilin Univ So Calif Viterbi Sch Engn Los Angeles CA 90089 USA Tongji Univ State Key Lab Disaster Reduct Civil Engn Shanghai 200092 Peoples R China

This paper presents an investigation of the performance of particle dampers attached to a two-degrees-of-freedom system, using the discrete-element method. Correlation functions, the amount of dissipated energy due to impact and friction, and the concept of ''effective momentum exchange'' are shown to be suitable ways of interpreting the physics involved in the behavior of particle dampers. Using three different types of excitation, the optimum operating regions are determined, within which particles move in a plug flow pattern and correlation functions decay fast, while the dissipated energy and the effective momentum exchange are large compared with inefficient operating conditions. The paper also evaluates the effects of many system parameters (such as the mass ratio, coefficient of restitution, excitation levels, damping ratio of the primary system, container dimensions and shape, number of particles, and the coefficient of friction), using high-fidelity simulations. It is shown that: increasing the mass ratio can improve the damper's effectiveness, but only up to a certain level;applying particles with a high value of the coefficient of restitution can result in a broader range of acceptable response levels;friction has a complex influence on particle dampers in a generally detrimental form;a lightly-damped primary system can achieve a considerable reduction in its response with a small weight penalty;and that a cylindrical-shaped container provides a higher level of effectiveness than a rectangular-shaped one. Finally, the behavior of the particle damper is compared to a multi-unit impact damper to enhance the understanding of the two passive control devices, and it is shown that a particle damper is more robust when considering arbitrary levels of excitation in different directions.

关键词： Particle damper multi-unit impact damper discrete-element method vibration control

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The relationship between contact-based and void-based fabrics of granular media

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COMPUTERS AND GEOTECHNICS 2020年 125卷 103677-103677页

作者： Wei, Jiangtao Zhang, Yinbing Southwest Jiaotong Univ Sch Civil Engn Dept Geotech Engn Chengdu Peoples R China

Fabrics of granular media play an important role in understanding sophisticated soil behaviors and developing constitutive models. In this study, the evolution of fabric anisotropy in terms of both contact normals and local void distributions under drained and undrained loading conditions is explored using DEM simulations. It is observed that the anisotropy degree of both contact-based and void-based fabric increases when granular packing is subjected to monotonic loading. However, the mobilization of the contact-based fabric is much faster than that of the void-based fabric. The contact-based fabric is significantly influenced by static liquefaction, while the influence of static liquefaction on the void-based fabric is almost negligible. Furthermore, one of the descriptors by which to quantify the void-based fabric, E-d, has a strong correlation with the void ratio and mean effective stress. Various manifestations of dilative (or contractive) behaviors of granular soils can be further unified by the evolution of E-d.

关键词： discrete-element method Fabric anisotropy Void distribution

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Effect of particle adhesion and interactions on motion by traveling waves on an electric curtain

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JOURNAL OF ELECTROSTATICS 2010年第2期68卷 179-189页

作者： Liu, G. Q. Marshall, J. S. Univ Vermont Sch Engn Burlington VT 05405 USA Tsinghua Univ Dept Thermal Engn Minist Educ Key Lab Thermal Sci & Power Engn Beijing 100084 Peoples R China

A discrete-element/boundary-element method is developed for simulation of adhesive particle transport by traveling waves on an electric curtain. The study shows that both wall adhesion and particle-particle collisions have an important influence on particle transport on electric curtains at different wave frequencies. The most significant effect of particle collisions occurs for cases with medium frequencies in which particles with large negative-charge collect in high-concentration bands and move in a synchronous surfing mode, pushing forward particles with lower charge. Cases with higher and lower frequencies exhibited hopping motion, for which adhesion determines the range of non-transported particles. (C) 2009 Elsevier B.V. All rights reserved.

关键词： discrete-element method Electric curtain Dust mitigation Traveling waves

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Modeling and experimental study of a honeycomb beam filled with damping particles

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JOURNAL OF SOUND AND VIBRATION 2017年 391卷 20-34页

作者： Ahmad, Nazeer Ranganath, R. Ghosal, Ashitava Indian Space Res Org ISRO Satellite Ctr Vimanapura Post Bangalore 560017 Karnataka India Indian Inst Sci Dept Mech Engn Bangalore 560012 Karnataka India

Honeycomb sandwich laminates which are the basic structural element of spacecraft have inherently low damping. In this paper, we propose to improve the damping characteristics of such structures by adding damping particles in the cells of the honeycomb. This paper presents modeling of a cantilever beam constructed with honeycomb structure with the hexagonal honeycomb cells, filled with particles. The beam is subjected to external dynamic loads and the interactions of damping particles with the walls of the cells and its overall effect on the frequency response function (FRF) and the damping of the beam are obtained. The discrete-element-method (DEM) is used to model the dynamics of the particles in conjunction with the governing equations of motion of the beam and the cell walls. The particle-particle and particle-wall impact is modeled using Hertz's non-linear dissipative contact model for normal component and Coulomb's laws of friction for tangential component. Contiguous block of cells near the tip of the cantilever beam were filled with the damping particles and the beam was excited with a random signal near the fixed end. The damping and transfer functions obtained experimentally are compared to those obtained from the mathematical model and they are found to match very well. Further the model was used to study the effect of fill fraction, mass ratio, and the level of excitation signal on transfer function. Depending on the mass ratio and fill fraction, significant reductions in vibration levels are observed. (C) 2016 Elsevier Ltd. All rights reserved.

关键词： Particle damping discrete-element method Honeycomb sandwiched beam Passive vibration control Spacecraft structures

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Morphological characterization and mechanical analysis for coarse aggregate skeleton of asphalt mixture based on discrete-element modeling

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CONSTRUCTION AND BUILDING MATERIALS 2017年 154卷 1048-1061页

作者： Ding, Xunhao Ma, Tao Gao, Wang Southeast Univ Sch Transportat 2 Sipailou Nanjing 210096 Jiangsu Peoples R China Changsha Univ Sci & Technol State Engn Lab Highway Maintenance Technol Changsha 410114 Hunan Peoples R China

Focused on the aggregate microstructures to characterize the aggregate mechanical properties, this paper proposed a modeling method of coarse aggregate based on the particle morphological characteristics. By using the Aggregate Image Measurement System (AIMS), the realistic shape of granular aggregates was captured and the statistical analysis was made to quantify the morphological differences firstly. Then by using discrete-element method (DEM) software named as Particle Flow Code in two dimensions (PFC2D) and with the help of the image processing techniques, an algorithm was developed to model the two-dimensional shape of aggregates. Through linking the shape to the morphological index for each aggregate, the coarse aggregate skeleton was built which is consistent with the actual composition and structure of the laboratory specimens. After that, based on laboratory penetration test for granular aggregates, virtual penetration test was built by PFC2D to verify the validity of the developed modeling algorithm. An optimized method was proposed further then to improve the simulation efficiency. This is because of the time-consuming process when modeling the actual specimen which was composed of numerous coarse aggregates with various shapes. Some representative particles were selected and reconstructed based on the angularity index to form the virtual specimens with aggregates of gradations AC-13 and SMA-13. At last the virtual penetration test of AC-13, SMA-13 was conducted to predict the mechanical behavior and the coarse aggregate skeleton structure characteristics were analyzed from the point of micro-contact state. It is proved that the proposed modeling algorithm could well capture the realistic shape of aggregates and virtual test based on the aggregates model could characterize the granular aggregates mechanical properties accurately. (C) 2017 Elsevier Ltd. All rights reserved.

关键词： discrete-element method AIMS Aggregate Angularity Penetration test

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Interaction of Soil Arching under Trapdoor Condition: Insights from 2D discrete-element Analysis

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INTERNATIONAL JOURNAL OF GEOMECHANICS 2022年第6期22卷 04022066-04022066页

作者： Bao, Ning Wei, Jing Chen, Jian-feng Sun, Rui Tongji Univ Coll Civil Engn Dept Geotech Engn Shanghai 200092 Peoples R China Beijing Jiaotong Univ Sch Civil Engn Beijing 100044 Peoples R China

The trapdoor/trapdoor-like model test has been widely utilized to investigate the evolution of soil arching. However, the primary focus of previous studies has been on the mechanical and deformation behaviors of the arching field under the single-trapdoor condition, while the interaction of soil arching between adjacent trapdoors has not been well understood. In this paper, a series of discrete numerical models based on the plane-strain laboratory trapdoor test were established to investigate the interaction effect, with respect to stress redistributions, particle movement, anisotropy of contact forces, and energy regime. The effects of motion mode, namely the simultaneous and nonsimultaneous movement, and the spacing (B) between adjacent trapdoors on the arching performance were examined. The numerical results revealed that the simultaneous movement of twin trapdoor slightly influences earth pressures resting on the surface of both trapdoors. The deformation pattern is deeply influenced by a narrow spacing of 0.25B and characterized by two arching fields interacting with each other, resulting in a noticeable subsidence at the crest. The subsequent lowering of the second-lowered trapdoor under the nonsimultaneous movement condition increases pressures resting on the first-lowered trapdoor, yields additional settlement within the former arching field, and distorts adjacent arched force chains. An increase in spacing from 0.25B to 1B is beneficial for reducing the pressure increment, decreasing the arching deformations, minimizing the rotation of the major principal direction, and decreasing the friction energy distribution density above the stationary supports.

关键词： Interaction of soil arching Trapdoor discrete-element method Earth pressure Force chain Energy regime

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Simulation of particulate fouling at a microchannel entrance region

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MICROFLUIDICS AND NANOFLUIDICS 2015年第2期18卷 253-265页

作者： Marshall, Jeffrey S. Renjitham, Simtha Univ Vermont Sch Engn Burlington VT 05405 USA

A computational study is reported on the dynamics of particles near the entrance of a microchannel, as used in microfluidic flow systems. The collision of particles with fins separating the microchannels in these entrance regions makes them particularly susceptible to particle fouling. The study employs a soft-sphere discrete-element method with van der Waals and electric double-layer forces between the particles and the wall. A multi-block-structured grid fit to the flow domain boundaries is used to compute the fluid velocity field using a finite-volume method. The fluid flow is interpolated onto a Cartesian grid for efficient flow field interpolation at the particle locations, and a level-set method is used to represent the flow field boundaries in the particle computation. Particles adhering to the upstream face of the fin separating two microchannels are found to form clusters, which are pulled laterally by the stagnation-point flow near the fin. Even under conditions where the adhesion is sufficiently strong that there is little or no particle rolling on the fin face, the particles are still removed from the fin due to collisions with other particles. Individual particles are removed quickly from the fin face due to collision with upstream particles, whereas particle clusters have sufficient adhesion force with the fin surface that they can withstand collision with other particles for longer periods of time before they are removed in a cascade-like process.

关键词： Microchannel fouling discrete-element method Particle adhesion Entrance region

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