Evaluating performance of lignite pillars with 2D approximation techniques and 3D numerical analyses

This paper attempts to investigate the use of approximate 2D numerical simulation techniques for the evaluation of lignite pillar geomechanical response, formed via the room and pillar mining method.Performance and applicability of the developing methodology are assessed through benchmarking with a more direct and accurate 3D numerical model. This analysis utilizes an underground lignite mine which is being developed in soft rock environment. Through the decisions made for the optimum room and pillar layout, the design process highlights the strong points and the weaknesses of 2D finite element analysis, and provides useful recommendations for future reference. The interpretations of results demonstrate that 2D approximation techniques come near quite well to the actual 3D problem.However, external load approximation technique seems to fit even better with the respective outcomes from the 3D analyses.

Novel modeling on numerical computing the geo-deformation information in coalmine based on the GIS-Excel

Numerical simulation modeling is a hotspot in the geological engineering computing field. Tak- ing a fast Langrangian analysis of continua in 3 dimensions （FLAC3D） numerical modeling on com- puting the geo-deformation information caused by the mining subsidence in a coalmine for example, a new GIS-Excel modeling method is proposed to build geologic strata within the simulation range combined with the coal-seam dip angle of the underground mining working-planes. First of all, the coal-seam model of the numerical computing is built by using the geographic information system （GIS） according to the stripe-through principle and the calculating formula on the size of the model blocks in the paper defined, then the FLAC3D numerical computing model of all geologic strata with- in the simulation range is also built based on the calculating formula of thickness of each stratum and the Excel fast computing advantages. The GIS-Excel method is good at the higher modeling accuracy, seldom making mistakes and consuming less time. The reliability and validity of the method is veri- fied well by its practical applications in the coalmine area.

Dynamic response analysis of liquefiable ground due to sinusoidal waves of different frequencies of shield construction

Vibration induced by shield construction can lead to liquefaction of saturated sand.Based on FLAC3D software,a numerical model of tunnel excavation is established and sinusoidal velocity loads with different frequencies are applied to the excavation face.The pattern of the excess pore pressure ratio with frequency,as well as the dynamic response of soil mass under different frequency loads before excavation,is analyzed.When the velocity sinusoidal wave acts on the excavation surface of the shield tunnel with a single sand layer,soil liquefaction occurs.However,the ranges and locations of soil liquefaction are different at different frequencies,which proves that the vibration frequency influences the liquefaction location of the stratum.For sand-clay composite strata with liquefiable layers,the influence of frequency on the liquefaction range is different from that of a single stratum.In the frequency range of 5-30 Hz,the liquefaction area and surface subsidence decrease with an increase in vibration frequency.The research results in this study can be used as a reference in engineering practice for tunneling liquefiable strata with a shield tunneling machine.

3D Finite Element Simulation of Tunnel Boring Machine Construction Processes in Deep Water Conveyance Tunnel

Applying stiffness migration method,a 3D finite element mechanical model is established to simulate the excavation and advance processes.By using 3D nonlinear finite element method,the tunnel boring machine(TBM) excavation process is dynamically simulated to analyze the stress and strain field status of surrounding rock and segment.The maximum tensile stress of segment ring caused by tunnel construction mainly lies in arch bottom and presents zonal distribution.The stress increases slightly and limitedly in the course of excavation.The maximum and minimum displacements of segment,manifesting as zonal distribution,distribute in arch bottom and vault respectively.The displacements slightly increase with the advance of TBM and gradually tend to stability.

Application of FLAC3D in supporting engineering of deep foundation ditch

Based on the design principles of economic rationality and safety,multiple-pivot pile anchorage approach was used as the supporting engineering of a tall building with a deep foundation ditch.The designs,such as anchor arm,single pile and the whole,were set up in accordance with the calculations of the internal force from the equivalent beam and Yamagata Kunio methods.Moreover,the rationality of the design was estimated using the stability checks.FLAC3D was used for calculating the accuracy of the design.Using FLAC3D to simulating ditch cutting and supporting processes can obtain the equivalent results as the theory analysis in the displacement of ditch surrounding wall,the stress field and stress distribution.

3-D Modelling of the Confederation Bridge Using Data of Full Scale Tests

Long-span bridges are special structures that require advanced analysis techniques to examine their performance. This paper presents a procedure developed to model the Confederation Bridge using 3-D beam elements. The model was validated using the data collected before the opening of the bridge to the public. The bridge was instrumented to conduct fullscale static and dynamic tests. The static tests were to measure the deflection of the bridge pier while the dynamic tests to measure the free vibrations of the pier due to a sudden release of the static load. Confederation Bridge is one of the longest reinforced concrete bridges in the world. It connects the province of Prince Edward Island and the province of New Brunswick in Canada. Due to its strategic location and vital role as a transportation link between these two provinces, it was designed using higher safety factors than those for typical highway bridges. After validating the present numerical model, a procedure was developed to evaluate the performance of similar bridges subjected to traffic and seismic loads. It is of interest to note that the foundation stiffness and the modulus of elasticity of the concrete have significant effects on the structural responses of the Confederation Bridge.

Numerical Analysis of Thermal Convections in a Three-dimensional Cavity: Influence of Difference in Approximation Models on Numerical Solutions

In order to develop the practical approximation models suitable to flow fields at low Mach number with large temperature difference, the influence of difference in approximation models on numerical solutions was investigated by solving the natural convection in the 3-D enclosures with vertical sidewalls differentially heated and the heated bottom wall using 3 approximation models, that is Boussinesq approximation, low Mach Number approximation and approximation model proposed by Mlaouah. As results of the simulation, the effects of the differences in the three approximation models on the numerical solutions become clear.

Three-dimensional mixed convection stagnation-point fow past a vertical surface with second-order slip velocity

This study is concerned with the three-dimensional(3D)stagnation-point for the mixed convection flow past a vertical surface considering the first-order and secondorder velocity slips.To the authors’knowledge,this is the first study presenting this very interesting analysis.Nonlinear partial differential equations for the flow problem are transformed into nonlinear ordinary differential equations(ODEs)by using appropriate similarity transformation.These ODEs with the corresponding boundary conditions are numerically solved by utilizing the bvp4c solver in MATLAB programming language.The effects of the governing parameters on the non-dimensional velocity profiles,temperature profiles,skin friction coefficients,and the local Nusselt number are presented in detail through a series of graphs and tables.Interestingly,it is reported that the reduced skin friction coefficient decreases for the assisting flow situation and increases for the opposing flow situation.The numerical computations of the present work are compared with those from other research available in specific situations,and an excellent consensus is observed.Another exciting feature for this work is the existence of dual solutions.An important remark is that the dual solutions exist for both assisting and opposing flows.A linear stability analysis is performed showing that one solution is stable and the other solution is not stable.We notice that the mixed convection and velocity slip parameters have strong effects on the flow characteristics.These effects are depicted in graphs and discussed in this paper.The obtained results show that the first-order and second-order slip parameters have a considerable effect on the flow,as well as on the heat transfer characteristics.

基于ABAQUS的平纹织物同面对向弯曲有限元模拟

为明晰织物结构对其弯曲性能的影响机制,对织物弯曲过程进行了有限元模拟和实验验证。以涤纶织物为例,通过VHX-5000型超景深数码显微镜观测织物,得到纱线几何参数;根据纱线实际尺寸,利用SolidWorks专业建模软件构建涤纶平纹织物的三维几何模型;基于有限元分析软件ABAQUS研究织物同面对向弯曲性能,分析纱线弹性模量、摩擦因数、泊松比等参数对弯曲实验的影响,并将有限元仿真结果与实验结果进行对比。结果表明:模拟所得抗弯力-位移曲线与实验曲线在0.01水平上呈显著相关,模拟结果与实验结果一致,证明用有限元模拟弯曲织物模型的有效性。

Experimental and numerical investigation of design optimization of a partial admitted supersonic turbine

To obtain a high specific work output,the large pressure ratios across the turbine are required.This can be achieved using a supersonic turbine.When the fluid mass flow is low,the impulse kind of one or two stages supersonic turbine is employed.To prevent losses due to low blade aspect ratio and issues related to manufacturing and industrial problems,the turbine is used in partial admission conditions.Studies show that the turbine efficiency is highly dependent on the amount of partial admission coefficient.The turbine efficiency in full admission is high,but the use of partial admission lowers the additional losses.Therefore,there will be a degree of partial admission in which the turbine will have the highest efficiency.The aim of this work is to achieve the optimum partial admission for a special impulse turbine as a case study.Therefore,in the beginning,an appropriate model of losses is presented.Then,using a nonlinear design optimization code,the partial admission of an impulse supersonic turbine is optimized.This code is written using a genetic algorithm.Then,using three-dimensional numerical analysis,the optimal model will be selected.In the optimization problem,the turbine efficiency is the objective function.The amount of design parameters and constraints used in this process are ten and eight,respectively.After the optimization process,prototypes of designed and modified turbines are made and tested.Test results were compared and analyzed.The results showed that the turbine efficiency is improved between 2.5%and 3%depending on various operation conditions.

Three-dimensional numerical modeling of single geocellreinforced sand

This paper summarizes the development of a three-dimensional numerical model for analyzing single geocell-reinforced soil.In this model,the infill soil was modeled using the Duncan-Chang model,which can simulate non-linearity and stress-dependency of soil.Geocell was modeled using linearly elastic plate elements,which can carry both bending and membrane stresses.A linear interface stress-strain relationship with a MohrCoulomb yield criterion was adopted to model the interface friction between the geocell wall and the soil.By modeling the geocell and the soil separately,the interaction between the soil and the geocell can be accurately simulated.To verify this model,a plate load test was conducted in the laboratory,in which a 12-cmthick sand layer reinforced by a single geocell was subjected to a vertical load from a circular steel plate.The load-displacement curves and the horizontal tensile strain of the geocell were recorded during the test.A numerical model was created according to the setup of the load test.The numerical results compared reasonably well with the test data.

基坑工程下地铁隧道隆起位移数值模拟分析

结合南京龙蟠路隧道(南侧)西段上跨既建成的地铁1号线双线盾构隧道的基坑工程,针对未经加固以及运用高压旋喷法加固基坑坑内地基两种工况,采用ANSYS对已建地铁盾构隧道隆起位移进行三维弹塑性有限元数值模拟。模拟计算结果表明,坑内未经加固基坑开挖后下部隧道隆起位移过大;坑内加固后基坑开挖不会造成下部隧道过大的隆起位移是安全可行的,该结论与工程实际监测结果相符。

煤岩瓦斯电磁辐射耦合理论研究

实验研究表明煤体内存在瓦斯气体时，随着瓦斯压力的升高、煤体强度降低，同时测得的电磁辐射信号脉冲数也比较低。在此实验基础上，本文结合煤岩力电耦合方程，提出了煤岩瓦斯电磁辐射耦合理论及耦合方程，并提出了使用FLAC^(3D)计算煤岩瓦斯电磁辐射耦合方程的计算方法，为使用电磁辐射法预测煤与瓦斯延迟突出提供了理论基础。

中国盛夏褐飞虱北迁过程的动态数值模拟

以控制和影响褐飞虱Nilaparvatalugens(St l)迁飞过程的生理生态参数为依据 ,应用时空分辨率较高的中尺度数值预报模式—MM4和三维轨迹计算方法对我国盛夏褐飞虱的北迁过程进行了动态模拟。模拟结果及其与实测虫情资料的对比研究表明 :(1)我国盛夏褐飞虱北迁的虫源地主要在 2 2 5°N～ 2 7°N ,110°E～ 116°E之间。 (2 )空中迁飞路径有三条 :主径取 32°方位角 ,副径分别取 10°和 75°方位角。 (3)降落虫汇区有三个 :主降区为长江中下游稻区 ,副降区分别为鄂西北、川东北稻区和浙东南、闽北稻区。 (4)理论模拟与实际虫情普查分析比较吻合 。

地震地基液化大变形对桥梁桩基危害性三维数值分析

为研究地震地基液化大变形对桥梁桩基的危害性,建立了含液化层的二层与三层土体系计算模型,考虑桩土共同作用的非线性关系,利用FLAC-3D有限差分软件对液化侧扩地基中的单桩、群桩进行了动力有限差分分析,探讨了地基液化大变形条件下桩基位移与内力变化分布规律。分析结果表明:二层与三层土体中,液化土层和非液化土层交界面处产生的桩身弯矩极值是控制桩身破坏的关键因素,液化土层本身对桩身弯矩的影响很小;桩帽对桩顶的侧移有一定制约作用,但对桩身弯矩极值的影响不显著;群桩中上坡桩与下坡桩的侧向位移与桩身弯矩分布模式相似,但上坡桩发生的侧向位移和桩身弯矩要略大于下坡桩情况。

九华山隧道穿越段明城墙沉降的三维数值分析

为减小穿越引起的明城墙不均匀沉降甚至城墙开裂,采取了城墙基础加固和超前支护等控制措施。采用三维数值方法,选取典型城墙基础断面,计算了未采取控制措施与采取控制措施后明城墙的沉降,并与部分实测数据对比。分析结果表明:采取控制措施后沉降量可以减少38%;隧道在通过城墙下部时,沉降量增加较快,应加强变形监测;计算值与实测值吻合较好。工程成功穿越明城墙证明,采取有效的超前支护和加固措施对地表建筑物变形控制具有重要的作用。

水平荷载作用下群桩相互作用的弹塑性数值分析

本文利用三维弹塑性有限元法对水平荷载作用下群桩基础特性进行了分析,讨论了群桩基础水平荷载作用下的承载性状和破坏机理,并探讨了桩距、桩数、桩长、桩径和土质各种因素对群桩效应的影响,指出桩距和桩数是影响群桩效应的主要因素。

结构层模量对路面力学响应影响的三维数值分析

目前关于路面结构层模量对路面结构力学响应影响的研究一般是利用弹性层状理论进行分析。从三维数值分析的角度 ,分别从路表弯沉、面层和基层内的压应力及拉应力等方面说明了结构层模量及基层条件对路面结构力学响应的影响。分析认为路面各结构层模量的提高能减小路面表面弯沉 ,较高的基层模量会增大面层内的压应力 ,较高的底基层模量能减小基层底面的拉应力。

东坪金矿采空区开挖过程的三维有限元数值模拟

结合东坪金矿南山采区1号空区的工程实际,采用Plaxis 3D Tunnel对其建立三维数值模型,并对其不同开挖顺序的开挖过程进行数值模拟。通过对开采过程中的地压活动规律和围岩稳定性进行分析,论证了地下采空区开挖方案的可行性,揭示了采空区不同开挖阶段应力的集中部位和围岩的潜在破坏部位。计算表明该空区由上向下开挖顺序较为有利,其开挖过程总体可以保持稳定,但也存在不安全隐患。计算结果对该矿山的安全生产具有指导意义。

一个考虑土体流变的修正剑桥粘弹塑性模型

在修正剑桥模型的基础上 ,考虑土的流变性 ,提出一种可较全面地反映土体变形的各种粘弹塑性特征的修正剑桥粘弹塑性模型 .进而运用该模型对室内三轴固结排水剪流变试验进行三维有限元模拟 ,并通过与其他模型的对比分析 。