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Mesoscopic properties of dense granular materials: An overview

Qicheng SUN, Feng JIN, Guohua ZHANG

《结构与土木工程前沿（英文）》 2013年 第7卷 第1期   页码 1-12 doi: 10.1007/s11709-013-0184-z

摘要： A granular material is a conglomeration of discrete solid particles. It is intrinsically athermal because its dynamics always occur far from equilibrium. In highly excited gaseous states, it can safely be assumed that only binary interactions occur and a number of kinetic theories have been successfully applied. However, for granular flows and solid-like states, the theory is still poorly understood because of the internally correlated structures, such as particle clusters and force networks. The current theory is that the mesoscale characteristics define the key differences between granular materials and homogeneous solid materials. Widespread interest in granular materials has arisen among physicists, and significant progress has been made, especially in understanding the jamming phase diagram and the characteristics of the jammed phase. In this paper, the underlying physics of the mesoscale structure is discussed in detail. A multiscale framework is then proposed for dense granular materials.

关键词： granular matter     macroscopic structure     jamming phase transition    

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Development of a constitutive model for rockfills and similar granular materials based on the disturbed

Mehdi VEISKARAMI, Ali GHORBANI, Mohammadreza ALAVIPOUR

《结构与土木工程前沿（英文）》 2012年 第6卷 第4期   页码 365-378 doi: 10.1007/s11709-012-0178-2

摘要： Behavior of rockfills was investigated experimentally and theoretically. A series of standard triaxial compression tests were carried out on a quarried rockfill material at different stress levels. It was found that both the stress level and the shear stress ratio, like most of granular materials, controls the behavior of rockfill materials. At lower shear stress ratios the behavior is much more similar to a nonlinear elastic solid. When the shear stress goes further, the stress-strain curve shows an elasto-plastic behavior which suggests using the disturbed state concept to develop a constitutive model to predict the stress-strain behavior. The presented constitutive model complies reasonably with the experimental data.

关键词： constitutive model     granular material     rockfill     plasticity     disturbed state concept     stress level    

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Two-scale modeling of granular materials: A FEM-FEM approach

Yun-Zhu CAI, Yu-Ching WU

《结构与土木工程前沿（英文）》 2013年 第7卷 第3期   页码 304-315 doi: 10.1007/s11709-013-0213-y

摘要： In the present paper, a homogenization-based two-scale FEM-FEM model is developed to simulate compactions of visco-plastic granular assemblies. The granular structure consisting of two-dimensional grains is modeled by the microscopic finite element method at the small-scale level, and the homogenized viscous assembly is analyzed by the macroscopic finite element method at large-scale level. The link between scales is made using a computational homogenization method. The two-scale FEM-FEM model is developed in which each particle is treated individually with the appropriate constitutive relations obtained from a representative volume element, kinematic conditions, contact constraints, and elimination of overlap satisfied for every particle. The method could be used in a variety of problems that can be represented using granular media.

关键词： homogenization     two-scale     representative volume element     compaction     granular assembly     finite element method    

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Multi-scale investigation of active failure for various modes of wall movement

《结构与土木工程前沿（英文）》 2021年 第15卷 第4期   页码 961-979 doi: 10.1007/s11709-021-0738-4

摘要： Retained backfill response to wall movement depends on factors that range from boundary conditions to the geometrical characteristic of individual particles. Hence, mechanical understanding of the problem warrants multi-scale analyses that investigate reciprocal relationships between macro and micro effects. Accordingly, this study attempts a multi-scale examination of failure evolution in cohesionless backfills. Therefore, the transition of retained backfills from at-rest condition to the active state is modeled using the discrete element method (DEM). DEM allows conducting virtual experiments, with which the variation of particle and boundary properties is straightforward. Hence, various modes of wall movement (translation and rotation) toward the active state are modeled using two different backfills with distinct particle shapes (spherical and nonspherical) under varying surcharge. For each model, cumulative rotations of single particles are tracked, and the results are used to analyze the evolution of shear bands and their geometric characteristics. Moreover, dependencies of lateral pressure coefficients and coordination numbers, as respective macro and micro behavior indicators, on particle shape, boundary conditions, and surcharge levels are investigated. Additionally, contact force networks are visually determined, and their influences on pressure distribution and deformation mechanisms are discussed with reference to the associated modes of wall movement and particle shapes.

关键词： discrete-element modelling     granular materials     retaining walls     particle shape     arching    

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Application of granular solid hydrodynamics to a well-graded unbound granular material undergoing triaxial

Shixiong SONG, Qicheng SUN, Feng JIN, Chuhan ZHANG

《结构与土木工程前沿（英文）》 2013年 第7卷 第1期   页码 83-88 doi: 10.1007/s11709-012-0148-8

摘要： Unbound granular materials (UGMs) are widely used as a base or a subbase in pavement construction. They are generally well graded and exhibit a higher peak strength than that of conventional cohesionless granular materials. By using a simplified version of granular solid hydrodynamics (GSH), a set of GSH material constants is determined for a UGM material. The deviatoric stress and volumetric strain caused by triaxial compression are calculated and then compared with experimental data. The results indicate that the GSH theory is able to describe such a special type of granular materials.

关键词： granular solid hydrodynamics     unbound granular material (UGM)     triaxial tests    

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Hypoplastic constitutive modeling of wetting deformation of weathered rockfill materials

Erich BAUER, Zhongzhi FU, Sihong LIU,

《结构与土木工程前沿（英文）》 2010年 第4卷 第1期   页码 78-91 doi: 10.1007/s11709-010-0011-8

摘要： The wetting deformation of weathered rockfill materials has been attracting growing attention from both engineers and scientists. The importance of realistic predictions of wetting deformations for high earth and rockfill dams is a strong motivation to establish a suitable constitutive model. Recently, the hypoplastic constitutive model by Gudehus and Bauer was extended by introducing solid hardness depending on the state of weathering. The extended model takes into account the influence of the current density, the effective stress state, the rate of deformation, and the time dependent process of degradation of the solid hardness. In the present paper, the performance of this model is evaluated by comparing numerical simulations with experiments obtained from a water sensitive rockfill material. In particular, triaxial compression paths and creep deformation under deviatoric stress states are considered. Finally, the constitutive model proposed is used to study the influence of a degradation of the solid hardness on the long term behavior of a hypothetical fill dam.

关键词： rockfill dams     weathered granular materials     hypoplasticity     solid hardness     creep     stress relaxation    

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Effects of shear force on formation and properties of anoxic granular sludge in SBR

Xinyan ZHANG, Binbin WANG, Qingqing HAN, Hongmei ZHAO, Dangcong PENG

《环境科学与工程前沿（英文）》 2013年 第7卷 第6期   页码 896-905 doi: 10.1007/s11783-013-0539-7

摘要： This paper reports the effects of shear force on anoxic granular sludge in sequencing batch reactors (SBR). The study was carried out in two SBRs (SBR1 and SBR2) in which sodium acetate (200 mg COD·L ) was used as the sole substrate and sodium nitrate (40 mgNO -N·L ) was employed as the electron acceptor. The preliminary objective of this study was to cultivate anoxic granules in the SBR in order to investigate the effects of shear force on the formation of anoxic granular sludge and to compare the properties of anoxic sludge in the SBR. This study reports new results for the values of average velocity gradient, a measure of the applied shear force, which was varied in the two SBRs (3.79 s and 9.76 s for SBR1 and SBR2 respectively). The important findings of this research highlight the dual effects of shear force on anoxic granules. A low shear force can produce large anoxic granules with high activity and poor settling ability, whereas higher shear forces produce smaller granules with better settling ability and lower activity. The results of this study show that the anoxic granulation is closely related to the strength of the shear force. For high shear force, this research demonstrated that: 1) granules with smaller diameters, high density and good settling ability were formed in the reactor, and 2) granular sludge formed faster than it did in the low shear force reactor (41days versus 76 days). Once a steady-state has been achieved, the nitrate and COD removal rates were found to be 98% and 80%, respectively. For low shear force, such as was applied in SBR1, this research demonstrated that: 1) the activity of anoxic granular sludge in low shear force was higher than that in high shear force, 2) higher amount of soluble microbial products (SMPs) were produced, and 3) large pores were observed inside the larger granules, which are beneficial for nitrogen gas diffusion. Electron microscopic examination of the anoxic granules in both reactors showed that the morphology of the granules was ellipsoidal with a clear outline. Coccus and rod-shaped bacteria were wrapped by filamentous bacteria on the surface of granule.

关键词： denitrification     anoxic granular sludge     sequencing batch reactors (SBR)     shear force    

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Force fluctuations in sheared granular disks

Mingbo YUAN, Qicheng SUN, Feng JIN

《结构与土木工程前沿（英文）》 2013年 第7卷 第1期   页码 46-49 doi: 10.1007/s11709-013-0189-7

摘要： The internal structure established within granular materials, often observed as force chains, is dominant in controlling bulk mechanical properties. We designed a two-dimensional Hele-Shaw cell to contain photoelastic disks, and two servos were used on the top and right boundaries individually. We experimentally monitored the fluctuations in force on the top plate while slowing the shearing of the well-confined disks and keeping the right boundary at a contact-confined force of 0.2 kN. The particle rearrangements were found to correspond to bulk force drops and were observed in a localized zone with a length of approximately 5 particle diameters. These results help reveal the structure and mechanics of granular materials, and further investigations are ongoing.

关键词： granular matter     force chain     stick and slip    

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Visualization of force networks in 2D dense granular materials

Jianguo LIU, Qicheng SUN, Feng JIN,

《结构与土木工程前沿（英文）》 2010年 第4卷 第1期   页码 109-115 doi: 10.1007/s11709-010-0003-8

摘要： Dense granular matter is a conglomeration of discrete solid and closely packed particles. As subjected to external loadings, the stress is largely transmitted by heavily stressed chains of particles forming a sparse network of larger contact forces. To understand the structure and evolution of force chains, a photoelastic technique was improved for determining stresses and strains in the assemblies of photoelastic granular disks in this paper. A two-dimensional vertical slab was designed. It contains 7200 polydispersed photoelastic disks and is subjected to a localized probe penetrating at the top of the slab to mimic the cone penetration test. The interparticle contact force distribution was found a peak around the mean value, a roughly exponential tail for greater force and a dip toward zero for smaller force. The force chain network around the probe tip was depicted, and the contact angle distribution of particles in force chains was found to be well aligned in the directions of major principal stress.

关键词： granular matter     force chain     multiscale modeling    

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Buffer capacity of granular matter to impact of spherical projectile based on discrete element method

Ying YAN, Pengfei LI, Shunying JI

《结构与土木工程前沿（英文）》 2013年 第7卷 第1期   页码 50-54 doi: 10.1007/s11709-013-0186-x

摘要： Granular matter possesses impact-absorbing property due to its energy dissipation character. To investigate the impact-absorbing capacity of granular matter, the discrete element method (DEM) is adopted to simulate the impact of a spherical projectile on to a granular bed. The dynamic responses of the projectile are obtained for both thin and thick granular bed. The penetration depth of the projectile and the first impact peak are investigated with different bed thicknesses and impact velocities. Determining a suitable bed thickness is crucial to the buffering effect of granular matter. The first impact peak is independent of bed thickness when the thickness is larger than the critical thickness.

关键词： granular matter     impact peak     buffer capacity     discrete element method     critical thickness    

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Concept and application of anaerobic suspended granular sludge bed (SGSB) reactor for wastewater treatment

Mingxia ZHENG,Zhong YAN,Jiane ZUO,Kaijun WANG

《环境科学与工程前沿（英文）》 2014年 第8卷 第5期   页码 797-804 doi: 10.1007/s11783-013-0597-x

摘要： Bed expansion serves an important function in the design and operation of an upflow anaerobic reactor. An analysis of the flow pattern of expanded granular sludge bed (EGSB) reactors shows that most EGSB reactors do not behave as expanded bed reactors, as is widely perceived. Rather, these reactors behave as fluidized bed reactors based on the classic chemical reactor theory. In this paper, four bed expansion modes, divided as static bed, expanded bed, suspended bed, and fluidized bed, for bioreactors are proposed. A high-rate anaerobic suspended granular sludge bed (SGSB) reactor was then developed. The SGSB reactor is an upflow anaerobic reactor, and its expansion degree can be easily controlled within a range to maintain the suspended status of the sludge bed by controlling upflow velocity. The results of the full-scale reactor confirmed that the use of SGSB reactors is advantageous. The full-scale SGSB reactor runs stably and achieves high COD removal efficiency (about 90%) at high loading rates (average 40 kg-COD·m ·d , maximum to 52 kg-COD·m ·d ) based on the SGSB theory, and its expansion degree is between 22% and 37%.

关键词： expansion characteristic     high-rate bioreactor     anaerobic suspended granular sludge bed     expanded granular sludge bed reactor    

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Methanogenic community structure in simultaneous methanogenesis and denitrification granular sludge

Yujiao Sun, Juanjuan Zhao, Lili Chen, Yueqiao Liu, Jiane Zuo

《环境科学与工程前沿（英文）》 2018年 第12卷 第4期 doi: 10.1007/s11783-018-1067-2

摘要：

• UASB with SMD granules was operated with high removal efficiency of COD and NO3--N.

• Methanosaetaceae was absolute predominant methanogen in SMD granules.

• The methanogen quantity and activity decreased as C/N decreased from 20:1 to 5:1.

• Bacterial community succession happened with C/N decreasing.

关键词： Simultaneous methanogenesis and denitrification (SMD)     Methanogens     Community structure     Diversity index     Granular sludge    

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A miniature triaxial apparatus for investigating the micromechanics of granular soils with

Zhuang CHENG, Jianfeng WANG, Matthew Richard COOP, Guanlin YE

《结构与土木工程前沿（英文）》 2020年 第14卷 第2期   页码 357-373 doi: 10.1007/s11709-019-0599-2

摘要： The development of a miniature triaxial apparatus is presented. In conjunction with an X-ray micro-tomography (termed as X-ray μCT hereafter) facility and advanced image processing techniques, this apparatus can be used for investigation of the micro-scale mechanical behavior of granular soils under shear. The apparatus allows for triaxial testing of a miniature dry sample with a size of (diameter height). triaxial testing of a 0.4–0.8 mm Leighton Buzzard sand (LBS) under a constant confining pressure of 500 kPa is presented. The evolutions of local porosities (i.e., the porosities of regions associated with individual particles), particle kinematics (i.e., particle translation and particle rotation) of the sample during the shear are quantitatively studied using image processing and analysis techniques. Meanwhile, a novel method is presented to quantify the volumetric strain distribution of the sample based on the results of local porosities and particle tracking. It is found that the sample, with nearly homogenous initial local porosities, starts to exhibit obvious inhomogeneity of local porosities and localization of particle kinematics and volumetric strain around the peak of deviatoric stress. In the post-peak shear stage, large local porosities and volumetric dilation mainly occur in a localized band. The developed triaxial apparatus, in its combined use of X-ray μCT imaging techniques, is a powerful tool to investigate the micro-scale mechanical behavior of granular soils.

关键词： triaxial apparatus     X-ray μCT     in situ test     micro-scale mechanical behavior     granular soils    

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Fluorescence spectroscopic studies of the effect of granular activated carbon adsorption on structural

Shuang XUE, Qingliang ZHAO, Liangliang WEI, Xiujuan HUI, Xiping MA, Yingzi LIN

《环境科学与工程前沿（英文）》 2012年 第6卷 第6期   页码 784-796 doi: 10.1007/s11783-012-0436-5

摘要： This work investigated the effect of granular activated carbon adsorption (GACA) on fluorescence characteristics of dissolved organic matter (DOM) in secondary effluent, by means of excitation–emission matrix (EEM) spectra, the fluorescence regional integration (FRI) method, synchronous spectra, the fluorescence index defined as the ratio of fluorescence emission intensity at wavelength 450 nm to that at 500 nm at excitation ( )=370 nm, and the wavelength that corresponds to the position of the normalized emission band at its half intensity ( ). DOM in the secondary effluent from the North Wastewater Treatment Plant (Shenyang, China) was fractionated using XAD resins into 5 fractions: hydrophobic acid (HPO–A), hydrophobic neutral (HPO–N), transphilic acid (TPI–A), transphilic neutral (TPI–N) and hydrophilic fraction (HPI). Results showed that fluorescent materials in HPO–N and TPI–N were less readily removed than those in the other fractions by GACA. The relative content of fluorescent materials in HPO–A, TPI–A and HPI decreased whereas that in HPO–N and TPI–N increased as a consequence of GACA. Polycyclic aromatics in all DOM fractions were preferentially absorbed by GACA, in comparison with bulk DOM expressed as DOC. On the other hand, the adsorption of aromatic amino acids and humic acid-like fluorophores exhibiting fluorescence peaks in synchronous spectra by GACA seemed to be dependent on the acid/neutral properties of DOM fractions. All five fractions had decreased fluorescence indices as a result of GACA. GACA led to a decreased value for HPO–A, increased values for HPO–N, TPI–A and HPI, and a consistent value for TPI–N.

关键词： granular activated carbon adsorption     dissolved organic matter     fractionation     fluorescence    

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Iterative finite element model of nonlinear viscoplastic analyses for blended granular porous media

WU Yuching, ZHU Cimian

《结构与土木工程前沿（英文）》 2007年 第1卷 第4期   页码 464-473 doi: 10.1007/s11709-007-0063-6

摘要： The iterative finite element model, in which an element is used to represent a single particle, is generated to analyze the global behavior of multiple-material aggregates of materially nonlinear viscoplastic particles. The genera

关键词： nonlinear viscoplastic     iterative     behavior     multiple-material    

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标题 作者 时间 类型 操作

Mesoscopic properties of dense granular materials: An overview

Qicheng SUN, Feng JIN, Guohua ZHANG

期刊论文

Development of a constitutive model for rockfills and similar granular materials based on the disturbed

Mehdi VEISKARAMI, Ali GHORBANI, Mohammadreza ALAVIPOUR

期刊论文

Two-scale modeling of granular materials: A FEM-FEM approach

Yun-Zhu CAI, Yu-Ching WU

期刊论文

Multi-scale investigation of active failure for various modes of wall movement

期刊论文

Application of granular solid hydrodynamics to a well-graded unbound granular material undergoing triaxial

Shixiong SONG, Qicheng SUN, Feng JIN, Chuhan ZHANG

期刊论文

Hypoplastic constitutive modeling of wetting deformation of weathered rockfill materials

Erich BAUER, Zhongzhi FU, Sihong LIU,

期刊论文

Effects of shear force on formation and properties of anoxic granular sludge in SBR

Xinyan ZHANG, Binbin WANG, Qingqing HAN, Hongmei ZHAO, Dangcong PENG

期刊论文

Force fluctuations in sheared granular disks

Mingbo YUAN, Qicheng SUN, Feng JIN

期刊论文

Visualization of force networks in 2D dense granular materials

Jianguo LIU, Qicheng SUN, Feng JIN,

期刊论文

Buffer capacity of granular matter to impact of spherical projectile based on discrete element method

Ying YAN, Pengfei LI, Shunying JI

期刊论文

Concept and application of anaerobic suspended granular sludge bed (SGSB) reactor for wastewater treatment

Mingxia ZHENG,Zhong YAN,Jiane ZUO,Kaijun WANG

期刊论文

Methanogenic community structure in simultaneous methanogenesis and denitrification granular sludge

Yujiao Sun, Juanjuan Zhao, Lili Chen, Yueqiao Liu, Jiane Zuo

期刊论文

A miniature triaxial apparatus for investigating the micromechanics of granular soils with

Zhuang CHENG, Jianfeng WANG, Matthew Richard COOP, Guanlin YE

期刊论文

Fluorescence spectroscopic studies of the effect of granular activated carbon adsorption on structural

Shuang XUE, Qingliang ZHAO, Liangliang WEI, Xiujuan HUI, Xiping MA, Yingzi LIN

期刊论文

Iterative finite element model of nonlinear viscoplastic analyses for blended granular porous media

WU Yuching, ZHU Cimian

期刊论文