Investigation on the effectiveness of the repair method 8.3 “Corrosion protection by increasing the electrical resistivity” in chloride-containing concrete Part 2: Chloride redistribution in concrete after application of a system sealing surface protective coating

This DFG-funded research project aimed to gain a better understanding of the mechanisms of the W-Cl repair principle within the framework of fundamental investigations, to contribute to the creation of the necessary basis for a broader application of the repair principle in practice. The focus was on the development of a model to describe the chloride redistribution after the application of a system sealing surface protective coating. On the basis of Fick's second law of diffusion, a mathematical model with a self-contained analytical solution was developed, with the help of which the chloride redistribution after application of a system sealing surface protective coating can be calculated under the idealized assumption of complete water saturation of the concrete. Furthermore, the influence of the dehydration of the concrete, expected as a result of the application of the repair principle W-Cl, on the chloride redistribution was investigated. On the basis of laboratory tests and numerical simulations, material-specific reduction functions were developed to quantify the relationship between the chloride diffusion coefficient and the ambient humidity.     

Machining accuracy improvement for a dual-spindle ultra-precision drum roll lathe based on geometric error analysis and calibration

This paper performs a comprehensive analysis and calibration on the geometric error of the ultra-precision drum roll lathe with dual-spindle symmetrical structure and cross slider layout. Firstly, the volumetric error model which contains all geometric errors of the dual-spindle ultra-precision drum roll lathe (DSUPDRL) is developed based on the combination of the homogenous transfer matrix (HTM) and multi-body system (MBS) theory. Secondly, sensitivity analysis for the volumetric error model is conducted to identify the sensitive geometric error components of the DSUPDRL using an improved Sobol method based on the quasi-Monte Carlo algorithm. The result of sensitivity analysis laid the foundation for the subsequent geometric error calibration. Then, some sensitive error components along the X and Z directions are calibrated using a laser interferometer and a pair of inductance displacement probes. Besides the volumetric error model, the concentricity error caused by dual-spindle symmetrical structure is proposed and calibrated by the on-machine measurement using a classic reversal method. Finally, a large-scale roller mold with a diameter of 250 mm and a length of 600 mm is machined using the DSUPDRL after calibration. The experimental result shows that 1.4 μm/600 mm generatrix accuracy is obtained, which validate the effectiveness of the geometric error analysis and calibration.     

Numerical study of hydrodynamic flow of a Casson nanomaterial past an inclined sheet under porous medium

The main aim of the current paper is to investigate the mass and heat transportation of a Casson nanomaterial generated by the inclination of the surface. The magnetic field effect along with suction or injection are considered. The working nanomaterial is taken into consideration based on the concept of the Buongiorno nanofluid theory, which explores the thermal efficiencies of liquid flows under movement of Brownian and thermophoretic phenomena. The emergent system of differential expressions is converted to dimensionless form with the help of the appropriate transformations. This system is numerically executed by the implementation of Keller–Box and Newton's schemes. A good agreement of results can be found with the previous data in a limiting approach. The behavior of the physical quantities under concern, including energy exchange, Sherwood number, and wall shear stress are portrayed through graphs and in tabular form. The Nusselt number and Sherwood number are found to diminish against the altered magnitudes of Brownian motion and the inclination parameter. Moreover, the velocity profile decreases with the growth of the inclination effect. In the same vein, the buoyancy force and solutal buoyancy effects show a direct relation with the velocity field. The outcomes have promising technological uses in liquid‐based systems related to stretchable constituents.     

Influence of particle contact models on soil response of poorly graded sand during cavity expansion in discrete element simulation

The discrete element method (DEM) has been extensively adopted to investigate many complex geotechnical related problems due to its capability to incorporate the discontinuous nature of granular materials. In particular, when simulating large deformations or distortion of soil (e.g. cavity expansion), DEM can be very effective as other numerical solutions may experience convergence problems. Cavity expansion theory has widespread applications in geotechnical engineering, particularly to the problems concerning in situ testing, pile installation and so forth. In addition, the behaviour of geomaterials in a macro-level is utterly determined by microscopic properties, highlighting the importance of contact models. Despite the fact that there are numerous contact models proposed to mimic the realistic behaviour of granular materials, there are lack of studies on the effects of these contact models on the soil response. Hence, in this study, a series of three-dimensional numerical simulations with different contact constitutive models was conducted to simulate the response of sandy soils during cylindrical cavity expansion. In this numerical investigation, three contact models, i.e. linear contact model, rolling resistance contact model, and Hertz contact model, are considered. It should be noted that the former two models are linear based models, providing linearly elastic and frictional plasticity behaviours, whereas the latter one consists of nonlinear formulation based on an approximation of the theory of Mindlin and Deresiewicz. To examine the effects of these contact models, several cylindrical cavities were created and expanded gradually from an initial radius of 0.055 m to a final radius of 0.1 m. The numerical predictions confirm that the calibrated contact models produced similar results regarding the variations of cavity pressure, radial stress, deviatoric stress, volumetric strain, as well as the soil radial displacement. However, the linear contact model may result in inaccurate predictions when highly angular soil particles are involved. In addition, considering the excessive soil displacement induced by the pile installation (i.e. cavity expansion), a minimum distance of 11a (a is the cavity radius) is recommend for practicing engineers to avoid the potential damages to the existing piles and adjacent structures.     

1000MW等级超超临界锅炉张力板结构的强度计算及优化

张力板是锅炉螺旋管圈水冷壁的重要部件,其主要作用是通过槽型钢、张力板、手指板等一系列结构将螺旋管圈荷载传递至垂直管圈。本文利用有限元计算方法,对1000MW等级超超临界n型布置锅炉张力板及手指板结构强度进行计算分析。并根据计算结果,对该结构提出了优化方案。     

张庄铁矿高阶段矿房切割天井施工工艺试验

张庄铁矿设计采矿方法为大直径深孔阶段空场嗣后充填法。为了最大化发挥采矿设备性能，降低采切工程量，提高回采效率，通过实施一系列技术攻关，实现了将采矿阶段高度由原来的60 m提高到90 m。而作为最初爆破回采的自由面及爆破补偿空间，切割天井施工工艺为影响高阶段矿房爆破回采效果的关键因素，施工质量的优劣，直接影响矿房爆破回采生产作业能否顺利进行，而二次处理在增加施工成本的同时将带来安全隐患。张庄铁矿在面临可参考的成熟经验较少的情况下，结合现场可用的作业条件采取了对比试验的方法，在安全、技术及经济多方面综合分析比较下，确定了最终方案，为张庄铁矿安全稳定生产奠定了基础，同时研究成果可为大型地下矿山生产实践提供一定的参考。     

近距离煤层群采空区漏风规律及防控措施研究

贵州地区煤层赋存条件复杂,煤层间距小,相邻采空区存在漏风通道的问题。采用SF6示踪法及重点区域指标气体数据分析法,对发耳煤矿采空区漏风规律及其治理措施进行研究。分析结果表明,由于相邻密闭效果欠佳,导致31004开切眼联络巷及31004工作面回风巷密闭漏风严重。31004采空区漏风通道主要是31004开切眼联络巷密闭及10^#煤层开采过程中对上部7^#煤层采空区造成二次扰动形成的纵向漏风通道;漏风量为83 m^3/min,采空区风速约为0.17 m/s。对存在的煤自燃隐患采取了注水降温措施,CO体积分数显著下降至(5~9)×10^-6。为即将开采的50105、50107工作面的煤自燃防控提供了科学依据和管控措施方案。     

浅谈城市废水水质检测方法与应用

国家与地区的经济发展水平一定离不开工业的发展,我国作为工业大国,工业发展对于国家整体经济有着不可取代的作用。然而随着工业的发展,全球性的环境污染和生态破坏越来越严重。特别是我国经济正处于快速发展阶段,城市化进程不断推进,城市污染情况日益严重,城市污水治理工作逐渐被大众所关注,逐渐开始进入公众可能给事业。我国二十世纪七十年代开始逐渐开始现代城市污水的治理工作。因此,对城市污水的水质监测工作成为了极为重要的一个环节。从城市污水检测方式这一角度进行研究,分析当前城市污水水质检验方法提升实际效果的应用模式,希望能够更好的处理我国城市日益严峻废水处理问题。     

基于MSA的土石坝群体地震易损性研究

针对地震发生后亟需对土石坝群体震害进行快速评估的问题,基于统计数据和MSA方法,提出了土石坝群体震害易损性分析方法。通过分析土石坝群体震害数据,对震损大坝进行等级划分,结合地震破坏损失比和破坏比建立土石坝地震易损性矩阵。并引入MSA方法,建立土石坝群体震害易损性评估模型,计算出四种烈度下易损性参数及易损性曲线和概率,为土石坝群体震害快速评估提供了依据。