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Effective simulation of flexible lateral boundaries in two-and three-dimensional DEM simulations

Particuology 2008年第6期6卷 483-500页

作者： Geraldine Cheung Catherine O'Sullivan department of civil and Environmental engineering Imperial College London

Discrete element method （DEM） models to simulate laboratory element tests play an important role in advancing our understanding of the mechanics of granular material response, including bonded or cemented, particulate materials. Comparisons of the macro-scale response observed in a real physical test and a ＂virtual＂ DEM-simulated test can calibrate or validate DEM models. The detailed, particle scale information provided in the DEM simulation can then be used to develop our understanding of the material behaviour. It is important to accurately model the physical test boundary conditions in these DEM simulations. This paper specifically considers triaxial tests as these tests are commonly used in soil mechanics. In a triaxial test, the test specimen of granular material is enclosed within a flexible latex membrane that allows the material to deform freely during testing, while maintaining a specified stress condition. Triaxial tests can only be realistically simulated in 3D DEM codes, however analogue, 2D, biaxial DEM simulations are also often considered as it is easier to visualize particle interactions in two dimensions. This paper describes algorithms to simulate the lateral boundary conditions imposed by the latex membrane used in physical triaxial tests in both 2D and 3D DEM simulations. The importance of carefully considering the lateral boundary conditions in DEM simulations is illustrated by considering a 2D biaxial test on a specimen of frictional unbonded disks and a 3D triaxial test on a bonded （cemented） specimen of spheres. The comparisons indicate that the lateral boundary conditions have a more significant influence on the local, particle-scale response in comparison with the overall macro-scale observations.

关键词： Triaxial testing Discrete element simulations Boundary conditions

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Effect of embedment length of untreated natural fibres on the bond behaviour in cement mortar

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Frontiers of Structural and civil engineering 2018年第4期12卷 454-460页

作者： Gudimella RAMAKRISHNA Sriraman PRIYADHARSHINI department of civil engineering Pondicherry Engineering CollegePuducherry 605014lndia

The present investigation is focused on studying the effects of various matrices with 1:3, 1:4 and 1:5 mortars and fibre types of sisal and coir on the bond behavior at various ages of curing, i.e., 24 h, 3 d, 7 d and 28 d. The other parameters included in the investigation are water/cement (w/c) ratio, sand gradation and embedment length of fibres. In addition, the type of failure of sisal and coir fibres for different mixes of mortars at various curing ages is also reported. From the results, it is seen that the bond strength is improving with respect to age of curing in case of sisal fibres, but decreases in case of coir fibres. The failure of fibres due to fibre fracture is observed in sisal fibres and fibre pullout is observed in coir fibres. The other varying parameters such as mortar mixes, sand gradation, w/c ratio and embedded length also showed significant effect on bond behaviour of sisal and coir fibre with the cement mortar mixes.

关键词： bond strength cement mortar natural fibre pullout test type of failure

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Experimental and Numerical Investigation of Local Scour Around Submarine Piggyback Pipeline Under Steady Current

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Journal of Ocean University of China 2018年第2期17卷 244-256页

作者： ZHAO Enjin SHI Bing QU Ke DONG Wenbin ZHANG Jing college of engineering Ocean University of China college of Marine Science and Technology China University of GeosciencesWuhan School of Hydraulic engineering Changsha University of Science & Technology department of civil engineering City College The City University of New York college of Water Resources and civil engineering Shandong Agricultural University

As a new type of submarine pipeline, the piggyback pipeline has been gradually adopted in engineering practice to enhance the performance and safety of submarine pipelines. However, limited simulation work and few experimental studies have been published on the scour around the piggyback pipeline under steady current. This study numerically and experimentally investigates the local scour of the piggyback pipe under steady current. The influence of prominent factors such as pipe diameter, inflow Reynolds number, and gap between the main and small pipes, on the maximum scour depth have been examined and discussed in detail. Furthermore, one formula to predict the maximum scour depth under the piggyback pipeline has been derived based on the theoretical analysis of scour equilibrium. The feasibility of the proposed formula has been effectively calibrated by both experimental data and numerical results. The findings drawn from this study are instructive in the future design and application of the piggyback pipeline.

关键词： piggyback pipeline local scour scour depth current volume of fluid experiment numerical simulation

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Comparison of eigensensitivity and ANN based methods in model updating of an eight-story building

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Earthquake engineering and engineering Vibration 2015年第3期14卷 453-464页

作者： Prabakaran K Ashok Kumar Shashi Kant Thakkar department of civil engineering PSG College of Technology department of Earthquake engineering IIT Roorkee

Analytical models prepared from field drawings do not generally provide results that match with experimental *** error may be due to uncertainties in the property of materials,size of members and errors in the modelling *** is important to improve analytical models using experimentally obtained *** the past several years,data obtained from ambient vibration testing have been successfully used in many cases to update and match dynamic behaviors of analytical models with real *** paper presents a comparison between artificial neural network(ANN) and eigensensitivity based model updating of an existing multi-story building.A simple spring-mass analytical model,developed from the structural drawings of the building,is considered and the corresponding spring stiffness and lumped mass of all floors are chosen as updating *** advantages and disadvantages of these updating methods are *** advantage is that both methods ensure a physically meaningful model which canbe further employed in determining structural response and health monitoring.

关键词： ambient vibration measurement model updating artif

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Mechanism of cement-stabilized soil polluted by magnesium sulfate

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Journal of Central South University 2015年第5期22卷 1869-1877页

作者：韩鹏举王帅陈幼佳白晓红 college of Architecture and civil engineering Taiyuan University of Technology department of civil engineering The Penn State University

In order to simulate and study the mechanism of cement stabilized soils polluted by different contents of magnesium sulfate(MS), a series of tests were conducted on the cemented soil samples, including unconfined compression strength(UCS) tests of blocks, X-ray diffraction(XRD) phase analysis of powder samples, microstructure by scanning electronic microscopy(SEM),element composition by energy dispersive spectrometry(EDS), and pore distribution analysis by Image Processed Plus 6.0(IPP 6.0)software. The UCS test results show that UCS of cemented soils reaches the peak value when the MS content is 4.5 g/kg. While, the UCS for Sample MS4 having the MS content of 18.0 g/kg is the lowest among all tested samples. Based on the EDS analysis results,Sample MS4 has the greater contents for the three elements, oxygen(O), magnesium(Mg) and sulfur(S), than Sample MS1. From the XRD phase analysis, C-A-S-H(3Ca O·Al2O3·3Ca SO4·32H2O and 3Ca O·Al2O3·Ca SO4·18H2O), M-A-H(Mg O·Al2O3·H2O), M-S-H(Mg O·Si O2·H2O), Mg(OH)2 and Ca SO4 phase diffraction peaks are obviously intense due to the chemical action associated with the MS. The pore distribution analysis shows that the hydrated products change the distribution of cemented soil pores and the pores with average diameter(AD) of 2-50 μm play a key role in terms of the whole structure of cemented soil. The microscopic structure of the cemented soil with MS exhibits the intertwined and embedded characteristics between the cement and granular soils from the SEM images of cemented soils. The microstructure analysis shows that the magnesium sulfate acts as the additive, which is beneficial to the soil strength when the MS content is low(i.e., Sample MS2). However, higher MS amount involving a chemical action makes samples crystallize and expand, which is adverse to the UCS of cemented soils(i.e., Sample MS4).

关键词： unconfined compression strength(UCS) magnesium sulphate(MS) X-ray diffraction(XRD) microstructure energy dispersive spectrometer(EDS)

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Experimental and numerical investigation on pure aluminum by ECAP

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中国有色金属学会会刊：英文版 2009年第5期19卷 1303-1311页

作者：张静张克实 WU Hwai-Chung 于梅花 college of civil and Architectural engineering Guangxi University department of civil and Environmental engineering Wayne State University

The equal channel angular pressing(ECAP)experiments were carried out with industrial pure aluminum and an in-house *** comparison of material grain size before and after ECAP was performed by applying the technique of electron back scattered diffraction(EBSD).The results show that the grains in the material after ECAP are refined and the yield stress and ultimate strength are *** order to investigate the deformation mechanism during ECAP and the reason for driving grain size refinement,three-dimensional numerical simulations of the ECAP process were carried *** on the Lode parameter analysis, the deformation of the material sample is found very complicated,not just pure shear during extrusion through the angular channel. The simulation confirms that a strong strain gradient in the sample material is imposed by the ECAP.

关键词：工业纯铝等径角挤压数值研究等通道转角挤压塑性变形实验晶粒尺寸挤压过程

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Three-dimensional seismic isolation bearing and its application in long span hangars

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Earthquake engineering and engineering Vibration 2013年第1期12卷 55-65页

作者： Li Xiongyan Xue Suduo Cai Yancheng The college of Architecture and civil engineering Beijing University of Technology department of civil engineering The University of Hong Kong

Based on the seismic response characteristics of space frame structures,a new type of seismic isolation bearing defined as a three-dimensional seismic isolation bearing（3DSIB） is developed in this *** bearing offers excellent properties such as multi-dimensional seismic isolation,reasonable rotation capability,good ability to resist lifting load,uncoupled stiffness in horizontal and vertical directions,*** the 3DSIB,the horizontal dimension is designed by combining the Teflon sliding device and helical spring,while the vertical dimension is developed by introducing disk springs or helical *** mathematical model of the 3DSIB was established and its performance with the critical parameters was tested on a shaking ***,the 3DSIB was applied in a 120 m span hangar structure and simulated using SAP2000 software to evaluate its performance in practical *** performance of the structures with and without 3DSIB was *** is shown that the hangar structure with 3D bearings achieves a better *** axial force and acceleration response of the structures with 3DSIB are effectively reduced,while the displacement response of the bearing is within the predetermined range.

关键词： three-dimensional seismic isolation bearing (3DSIB) seismic isolation hangar axial force acceleration response

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Integrated numerical model for vegetated surface and saturated subsurface flow interaction

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Applied Mathematics and Mechanics(English Edition) 2012年第7期33卷 881-898页

作者： K. S. ERDURAN department of civil engineering Faculty of Engineering University of Nigde department of civil engineering College of Engineering American University of Sharjah

The construction of an integrated numerical model is presented in this paper to deal with the interactions between vegetated surface and saturated subsurface flows. A numerical model is built by integrating the previously developed quasi-three-dimensional （Q3D） vegetated surface flow model with a two-dimensional （2D） saturated groundwater flow model. The vegetated surface flow model is constructed by coupling the explicit finite volume solution of 2D shallow water equations （SWEs） with the implicit finite difference solution of Navier-Stokes equations （NSEs） for vertical velocity distribution. The subsurface model is based on the explicit finite volume solution of 2D saturated groundwater flow equations （SGFEs）. The ground and vegetated surface water interaction is achieved by introducing source-sink terms into the continuity equations. Two solutions are tightly coupled in a single code. The integrated model is applied to four test cases, and the results are satisfactory.

关键词： vegetated surface flow saturated groundwater flow flow interaction tightcoupling finite volume method finite difference method flow resistance

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The use of the node-based smoothed finite element method to estimate static and seismic bearing capacities of shallow strip footings

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Journal of Rock Mechanics and Geotechnical engineering 2022年第1期14卷 180-196页

作者： H.C.Nguyen T.Vo-Minh department of civil and environmental engineering imperial college londonuk department of civil engineering and industrial design university of liverpoolliverpooluk Faculty of civil engineering ho chi minh city university of technology(hutech)ho chi minh cityviet nam

The node-based smoothed finite element method(NS-FEM)is shortly presented for calculations of the static and seismic bearing capacities of shallow strip footings.A series of computations has been performed to assess variations in seismic bearing capacity factors with both horizontal and vertical seismic *** results obtained agree very well with those using the slip-line method,revealing that the magnitude of the seismic bearing capacity is highly dependent upon the combinations of various directions of both components of the seismic *** upward vertical seismic acceleration reduces the seismic bearing capacity compared to the downward vertical seismic acceleration in *** addition,particular emphasis is placed on a separate estimation of the effects of soil and superstructure inertia on each seismic bearing capacity *** the effect of inertia forces arising in the soil on the seismic bearing capacity is non-trivial,and the superstructure inertia is the major contributor to reductions in the seismic bearing *** tables and charts are given for practical application to the seismic design of the foundations.

关键词： Limit analysis Node-based smoothed finite element method(NS-FEM) Second-order cone programming(SOCP) Seismic bearing capacity Strip footing

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Petrography and geochemistry of Jumara Dome sediments, Kachchh Basin: Implications for provenance, tectonic setting and weathering intensity

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Chinese Journal Of Geochemistry 2014年第1期33卷 9-23页

作者： Ahmad A.H.M Noufal K.N Masroor Alam M Tavheed Khan department of Geology department of civil engineering ZH College of Engineering and Technology

In the Kachchh Mainland, the Jumara Dome mixed carbonate-siliciclastic succession is represented by the Jhurio and Patcham formations and siliciclastic-dominating Chari Formation(Bathonian to Oxfordian). The Jumara Dome sediments were deposited during sea-level fluctuating, and were interrupted by storms in the shallow marine environment. The sandstones are generally medium-grained, moderately sorted, subangular to subrounded and of low sphericity. The sandstones are mineralogically mature and mainly composed of quartzarenite and subarkose. The plots of petrofacies in the Qt-F-L, Qm-F-Lt, Qp-Lv-Ls and Qm-P-K ternary diagrams suggest mainly the basement uplift source(craton interior) in rifted continental margin basin setting. The sandstones were cemented by carbonate, iron oxide and silica overgrowth. The Chemical Index of Alteration values(73% sandstone and 81% shale) indicate high weathering conditions in the source area. Overall study suggests that such strong chemical weathering conditions are of unconformity with worldwide humid and warm climates during the Jurassic period. Positive correlations between Al2O3 and Fe2O3, TiO2, Na2O, MgO, K2O are evident. A high correlation coefficient between Al2O3 and K2O in shale samples suggests that clay minerals control the major oxides. The analogous contents of Si, Al, Ti, LREE and TTE in the shale to PAAS with slightly depleted values of other elements ascribe a PAAS like source(granitic gneiss and minor mafics) to the present study. The petrographic and geochemical data strongly suggest that the studied sandstones/shales were deposited on a passive margin of the stable intracratonic basin.

关键词：大陆边缘盆地地球化学数据沉积物岩相学风化强度构造背景源区圆顶

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