基于活动门试验的土拱数量对土拱效应演化的影响分析

土拱效应随相对位移的变化存在演化过程。本文改进了经典的Trapdoor试验,采用石英砂颗粒和工业白油配置而成的透明土,通过高速数字相机摄像并结合PIV技术处理分析得到试验过程中填土的位移场变化规律,结合土压力数据研究土拱数量对土拱效应演化的影响。试验结果表明单拱/群拱条件会影响土拱效应的形成与演化:单拱条件,更有利于土拱效应荷载传递作用的发挥,单拱条件下形成的土拱效应的高度较群拱条件下更低。     

干湿-冻融循环下水泥固化淤泥土的力学性能与裂隙发育特征

针对水泥固化淤泥土性能受干湿-冻融循环效应的影响,开展了不同干湿-冻融循环次数下的土体三轴剪切试验、CT扫描试验和SEM扫描试验,研究了干湿-冻融过程中水泥固化淤泥土的力学特征和微结构损伤规律.结果表明:水泥固化淤泥土的应力-应变曲线呈应变硬化特征,内摩擦角与黏聚力指标随干湿-冻融循环次数增加而逐渐减小,且分别表现为指...     

复合桩基桩土非线性相互作用的数值分析

为了对复合桩基桩土非线性相互作用的工作机理进行深入分析,利用ABAQUS对常规桩筏基础(3D桩距)和复合桩基(6D桩距)进行了三维弹塑性分析.利用无厚度接触面单元模拟筏板-桩-土的非线性接触特性,采用Mohr-Cou lomb弹塑性本构模型描述土的非线性特性,桩设为弹性,得到了沉降、桩土荷载分担比、土体绕桩流动等变化情况,并对二者进行了对比分析.分析结果基本反映了桩-土-筏的实际工作性状,并验证了复合桩基理论的正确性.     

a软黏土中静压桩挤土效应模型实验研究

通过模型实验,以丽水地区的软粘土为实验材料,以单桩为研究对象,研究了静压单桩入土过程中的挤土效应。比较并分析了单桩入土时的土体位移变化规律和土中的应力变化规律。实验结果表明,挤土效应的影响范围与径向距离成反比关系。静压单桩对土体的位移和应力的影响范围分别在0.7和0.45倍桩长左右。实验结果可以给丽水地区的静压桩的施工措施的制定提供参考。     

小型预制桩挤土效应模型实验研究

为了研究单桩和群桩产生的挤土效应的差异,设计了模型实验加以研究。实验土体采自丽水地区典型场地的粉土。通过锤击沉入3种不同桩径钢制单桩和20mm桩径的群桩,使用土压力计和位移计测量了土中的压力和土表位移。结果表明沉入单桩时,挤土效应随随桩径增加而增加且原始桩径越大,增大桩径后引起的挤土效应的增量越明显,沉入群桩时的挤土效应约为沉入单桩时的2～3倍。该实验结果可对丽水地区的预制桩工程施工提供参考。     

静力压桩的拉格朗日法模拟与桩周土体固结分析

静力压桩过程是一种稳态贯入过程,常规的有限元方法较难模拟。基于更新的拉格朗日列式法分析压桩时产生的大变形,引入桩-土界面间的接触作用,桩周土体采用MohrCoulomb模型,运用有限元方法进行数值分析,与传统有限元方法相比,更好地实现了静力压桩过程的数值模拟。在此基础上,进一步分析了压桩结束后桩周土体超静孔压消散的固结过程。     

改性黄土内摩擦角变化研究

通过改性黄土抗剪强度试验,研究出黄土在添加膨润土、石灰、水泥和水泥一粉煤灰混合材料后内摩擦角的变化趋势。黄土在添加膨润土过程中,随着膨润土的添量增大到一定程度时,土体的内摩擦角是减小的。这主要是因为黏粒舍量的增加,土体在抵抗剪切变形过程中,土体颗粒克服爬坡和咬合阻力所做的功减小,此时剪应力大部由黏聚力承担。石灰、水泥和水泥-粉煤灰混合材料加入土体中后,形成大的团聚体结构,加强了土体颗粒之间互相嵌合度和摩擦面积,土体的内摩擦角得到不同程度的增大。因此,根据工程需要,向黄土中添加不同的改性材料,使土体的性质满足工程需要是完全可行的。     

碎石土斜坡场地土体水平抗力分布模式研究

碎石土斜坡场地因坡度不同,水平抗力的大小差异明显,斜坡坡度对土体水平抗力的影响能否保证工程结构安全稳定,其如何弱化土体水平抗力的仍需探明。本文以碎石土斜坡土体为研究对象,通过开展桩基室内水平静载荷试验,深入分析不同坡度(斜坡坡度0～45°)对桩侧土体水平抗力分布规律的影响。研究表明：因不同深度土体抗力发挥程度的时效性,土体抗力随深度、位移的分布形式可按土体进入极限抗力状态的不同分为三个阶段;在抗力极值深度以上斜坡场地与水平场地下两者土体抗力极值比值近似1/1+tanθ关系,以下近似为1,这也充分说明斜坡坡度对桩侧土体抵抗桩身变形能力具有弱化效应;进一步参考坡度对桩侧土体抗力的变化的影响,给出了各土体极限抗力p_u和土体抗力系数k_x等参数的取值方法。本研究对斜坡场地结构水平抗力计算的取值有一定的借鉴作用,具一定的实际价值。     

大直径盾构下穿房屋建筑群超前注浆数值模拟研究

盾构掘进过程中会对周围土体具有扰动效应。当盾构下穿房屋建筑群时,若与桩基距离较近,使得桩基沉降较大,将导致房屋发生不均匀沉降。因此,研究盾构下穿桩基群对土体的扰动效应具有重要意义。本文通过模拟大直径盾构穿越房屋建筑群,研究地表沉降及桩基的性能;并验证采用超前注浆法进行加固的有效性。结果表明,桩土之间存在差异加剧了地表沉降,这种影响与桩距密切相关。通过超前注浆后,能有效改善地表沉降、桩土沉降差以及桩基的倾斜。     

载体桩设计浅谈

载体桩是选择下部层位稳定、土性较好的土体为被加固土层,以桩端土体为研究对象,利用柱锥冲击成孔,对周围土体进行挤密加固,当沉管到设计标高后,对桩端进行连续填料夯实操作,并以三击贯入度做为控制指标再填以干硬性混凝土,使桩端以下深度为3～5m,直径为2～3m区域的土体得到有效的加固挤密,形成由内到外——依次由干硬性混凝土、填充料、挤密土体组成的载体,使桩端土体得到最优的密实,将上部荷载有效传递给下面的持力土层,达到提高承载力的目的。     

Design,fabrication and mechanical properties of multidimensional graded ceramic tool materials

A type of multidimensional graded ceramic tool materials (MGTMs) was designed and fabricated by vacuum hot-pressing sintering technology. The microstructure and compositional distribution of tool simultaneously changed in two different directions. The tool-chip and tool-workpiece contact regions were designed to have high hardness, and metal phases Mo and Ni were added to produce a gradual increase in toughness from the outer layer to core layer. The effect of orientation angle, thickness ratio and sintering parameters on the mechanical properties and microstructure were investigated. The experimental results showed that the composites, sintered at 1700 °C for 15 min, with the orientation angle of 30° and a thickness ratio of 0.4, had the optimal comprehensive mechanical properties. In addition, the crack propagation paths were observed to analyze the toughening mechanisms for the multidimensional graded ceramic tool materials. It was found that there is a crack resistance behavior when the crack extended from the outer layer to transition layer. The effect of the angle between the crack and graded interface on crack propagation paths was also investigated and the results indicated that the small angle was favorable for the crack deflection when the cracks passed through the graded interface. The residual thermal stress contributed to the occurrence of the crack bridging and transgranular fracture inside the Al₂O₃ grains, while the intergranular fracture and crack deflection were observed around the TiC grains.     

燃煤烟气低温NH3-SCR脱硝工艺中试

国内对于低温脱硝催化剂的研究主要集中在实验室的小试规模，对无钒低温NH₃-SCR蜂窝催化剂在燃煤烟气条件下的脱硝活性和中毒机理研究较少，无法完全反映出催化剂在真实烟气条件下的运行状况。本文采用自行设计的低温NH₃-SCR装置在石河子市某热电厂进行了中试研究，得到了该催化剂在实际烟气条件下的最佳工艺条件，并深入分析了实际烟气中复杂成分对低温脱硝催化剂的影响机理。研究结果表明：SO₂浓度低于35mg/m³、空速约为4200h^-1、烟气温度约为100℃、氨氮比约为1.2时催化剂的脱硝效率最佳；高浓度的SO₂会促进硫酸盐类的形成和催化剂活性组分的硫酸化，是催化剂活性降低的主要原因。环境友好型低温脱硝催化剂表现出优异的低温脱硝性能和抗硫性能；脱硝工艺改造方便；具有广阔的工业应用前景。     

Oxidation of hydrosulphide ions on gold Part II: Characterization of gold/aqueous hydrosulphide solution interface

The results of studies to characterize the gold/aqueous hydrosulphide solution interface are presented in this paper. The interface was characterized with impedance spectroscopy, contact angle and cathodic charge transfer measurements. The studies complement the cyclic voltammetry investigations presented in Part I. A detailed mechanism of the oxidation and reduction of sulphur species at gold electrodes has been suggested on the basis of this investigation. The results show that the surface becomes hydrophobic under the conditions when polysulphide ions or elemental sulphur are present at the interface.     

基于VOF-DPM的气体辅助式污泥雾化破碎的数值模拟

为实现污泥雾化破碎的数值模拟,探究污泥雾化特征和操作参数对污泥雾化效果的影响,在污泥雾化试验平台试验的基础上基于Fluent软件对污泥在气体辅助式雾化器的雾化破碎进行模拟研究,模拟结果确定了污泥的雾化特征和最优操作参数。通过耦合流体体积法(VOF)与离散相模型(DPM),对较大的液体团采用VOF方法直接求解,对小液滴采用双向耦合的离散相模型进行追踪,能最大程度地提高计算的准确性。结果表明,污泥的密度和黏度随着含水率升高逐渐降低,气体速度、气液比和雾化角度是影响污泥雾化破碎的最重要的三个操作参数。在雾化过程中,中心区域的雾滴密度大于边缘区域且有少量大颗粒的聚集。对于含水率为87%、密度为1.065×103 kg/m3的污泥,在风速为180 m/s,气液比为126.3,雾化角度为55°时雾化效果最佳,雾滴颗粒的平均粒径约为0.193 mm,试验结果与模拟结果的颗粒粒径吻合度较好,最大相对误差为5.80%。     

An elucidation for the central stress minimum in granular piles using the smoothed particle hydrodynamics

Stress distributions on bases of granular piles were predicted based on the constitutive relations obtained by the discrete element method (DEM) using the smoothed particle hydrodynamics to elucidate the mechanism of the central stress minimum beneath piles. The calculated stress distributions are in good agreement with the experimental data of many researchers. A stress peak and a central stress minimum are mainly formed by the granular flows in a pile construction. The location of the stress peak was the same location of the minimum granular velocity before the granular pile became stationary. This suggests that the location of the stress peak corresponds to the base of the granular arching. The stresses distributions on the bases by a homogeneous falling showed the central stress maximum. The low shear stress gradient by the homogeneous falling produces a central stress peak with a gentle slope. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1417–1429, 2016     

Novel phenomenon of quasi-volcanic corrosion on the alumina refractory-slag-air interface

A novel phenomenon of quasi-volcanic corrosion at refractory – slag – air interface under simulated normal smelting conditions was discovered when alumina refractory came in contact with CaO-Al₂O₃-SiO₂ slags and soaked at 1600°C. Based on thermodynamic and microstructure analysis, the mechanism of quasi-volcanic corrosion was revealed and the effect of CaO/SiO₂ mass ratio (C/S ratio) on corrosion was discussed. The results indicate that a two-stage intensified convection led to the severe upwelling corrosion of the refractory at the triple-phase interface. Furthermore, the critical intensity of the corrosive convection at the first stage on the formation of “slag volcano” was determined. This can serve as guidance for prolonging the service life of alumina refractory.     

Influence of interface energy of primary particles on the deformation and breakage behaviour of agglomerates sheared in a powder bed

In this paper, the parameters that affect the deformation and breakage of agglomerates embedded in a bed of particles subjected to rapid shearing are identified and analysed. The influences of interface energy between the primary particles and the size ratio (between agglomerates and particles of the bed) on the deformation characteristics of the agglomerate are addressed. The study is based on computer simulations using the distinct element method (DEM). It has recently been shown that for agglomerates having a size ratio greater than about 7, the nature of stresses experienced by the agglomerates when sheared inside a particulate bed is predominantly hydrostatic, hence it is difficult to break them (Hassanpour et al., 2007). However, the role of the interface energy between primary particles coupled with the effect of size ratio on the breakage and deformation characteristics of agglomerates during shearing has not been analysed. This feature is of great interest in the agglomeration process and is hence addressed in the present study. It is found that despite the predominantly hydrostatic nature of stresses responsible for retarding the breakage, agglomerates with size ratio greater than about 7 could undergo macroscopic deformation when the surface energy between the primary particles is decreased below a critical value. Furthermore, a failure map of agglomerates is presented in terms of their size ratio and the value of interface energy of the primary particles.     

T型复合材料长桁承载能力设计研究

应用商业有限元软件ABAQUS中的内聚单元,对复合材料T型长桁的缘条／蒙皮界面失效进行了分析,计算结果与试验数据吻合良好。基于有限元结果,提取了缘条／蒙皮界面内力,研究结构的失效机理。以缘条和蒙皮厚度为参数进行参数化建模,研究缘条／蒙皮刚度比对界面失效乃至承载能力的影响。最后对缘条／蒙皮刚度比提出了设计建议。     

孔隙特性参数对排驱过程影响的实验研究

两相宏观排驱特性是由微观孔隙尺度排驱特性决定的,而微观孔隙尺度多孔介质又处处不均匀、各向不均匀。为了研究孔隙尺度孔隙结构特征对驱替特性的影响,采用了独特设计的微多孔实验段,固定骨架圆柱间距离而变动驱替流体可流通方向,在此基础上研究了孔隙结构特征对驱替特性的影响。对于孔隙特性的表征采取了孔隙方向、关键比率（最大孔隙尺度与最小孔喉尺度比值）、迂曲度和孔隙率四个参数。结果表明：同流量时,微多孔结构的孔隙角越大、迂曲度越小,则对应的非浸润相（十二烷和十六烷）的饱和度（驱替效率）越高;对于不同流量,所有的微多孔结构都按照流量越大,则非浸润相（十二烷和十六烷）饱和度越高的规律变化;关键比率和孔隙率影响必须结合孔隙结构来判断;孔隙角、流量相同时,两相黏度接近的驱替效率更高。     

旋风分离器入口结构影响的研究现状与进展

综述了近年来关于入口结构包括入口结构类型、入口截面形状以及入口下倾角度等对旋风分离器性能影响的研究。认为不同的入口结构参数设计对旋风分离器的性能及能耗有较大影响;随着入口数量增多,分离器压降降低,分离效率先升高后减少,双进口分离器的性能较优。入口截面形状采用倒三角形有利于提高分离效率,但压力损失增加;对于矩形入口旋风分离器,增大高宽比有利于提高分离效率,但也会增大压力损失。随着入口截面角的增加,压力损失降低,分离效率先升高后减小,存在有最优的入口截面角;螺旋下倾角能够改善旋风分离器的分离性能,降低压力损失并有效减少上灰环现象的发生。