Brittle and ductile failure of rocks: Embedded discontinuity approach for representing mode I and mode II failure mechanisms

In this work, we present a discrete beam lattice model with embedded discontinuities capable of simulating rock failure as a result of propagating cracks through rock mass. The developed model is a two‐dimensional (plane strain) microscale representation of rocks as a two‐phase heterogeneous material. Phase I is chosen for intact rock part, while phase II stands for pre‐existing microcracks and other defects. The proposed model relies on Timoshenko beam elements enhanced with additional kinematics to describe localized failure mechanisms. The model can properly take into account the fracture process zone with pre‐existing microcracks coalescence, along with localized failure modes, mode I of tensile opening and mode II of shear sliding. Furthermore, we give the very detailed presentation for two different approaches to capturing the evolution of modes I and II, and their interaction and combination. The first approach is to deal with modes I and II separately, where mode II can be activated but compression force may still be transferred through rock mass which is not yet completely damaged. The second approach is to represent both modes I and II being activated simultaneously at a point where complete failure is reached. A novel numerical procedure for dealing with two modes failure within framework of method of incompatible modes is presented in detail and validated by a set of numerical examples. Copyright © 2015 John Wiley & Sons, Ltd.     

Displacement Discontinuity or Complex Shape of Sample: Assessment of Accuracy and Adaptation of Local DIC Approach

In this paper, we study the impact of a complex shape of sample and the appearance of a displacement discontinuity on performances of measurement by local Digital Image Correlation (DIC). Both cases are modelled from synthetic images into two parts: one with a speckle field and another part without speckle or two parts with similar speckle fields but with different kinematics. The accuracy of displacement measurements assessed for DIC subsets crossing the boundary between the two parts is lower than the one obtained without discontinuity and justifies adapting DIC method. A new local DIC process is presented in detail. It is an alternative way able to take into account any shape of sample and several curved lines of discontinuity in the same subset. Two experimental examples are presented: displacement and strain fields obtained by DIC and adapted DIC are compared. We can conclude that it is possible to lead a mechanical analysis until the limits of the sample and even during the appearance and the propagation of a crack.     

宽带相控阵雷达信号的二分推理提取算法

宽带相控阵雷达是电子对抗侦察的重点关注对象,在接收机截获的交错脉冲数据中将这一类雷达信号优先提取出来具有重要军事价值。针对接收机截获的全脉冲数据,文中提出了一种宽带相控阵雷达信号优先提取方法。该方法利用宽带相控阵雷达采用电子扫描方式的特点,分析其在同一工作模式下脉冲幅度的不变特性,引入一种生物信息学中的二分推理算法,并结合宽带信号的脉宽特性。首先,对经过脉宽阈值过滤的全脉冲数据按照脉幅大小重新排序;然后,利用二分推理算法进行脉幅突变点检测,将脉冲序列分为若干个脉幅相同的片段;最后,对每一片段进行脉冲个数阈值过滤,实现对宽带相控阵雷达脉冲的提取。仿真实验验证了方法的有效性。     

User perceptions of ICT impacts in Swedish construction companies: ‘it’s fine,just as it is’

The use of information and communication technologies (ICT) in construction companies has been growing steadily during the last decade. However, few studies inquire into either perceptions of the impact of actual ICT use or perceptions among different occupational groups in construction companies. The aim of the paper is to explore users’ general perceptions of ICT impacts in the post-adoption stage and analyse the implications for construction management practice. A mixed methods approach was used. Quantitative data were collected using a web-based survey both in a major construction company and among medium-sized companies in Sweden. Data from 294 returned completed questionnaires were analysed with t-tests and multiple regression analysis. In addition, participant observations and semi-structured interviews were conducted within the major construction company in order to strengthen the analysis. It can be concluded that respondents are generally fairly satisfied with the ICT. Differences in perceptions among occupational groups can be explained by the nature of work tasks and the original intentions for using ICT as a means of control and calculation. Even if respondents perceive that a further development of ICT could improve competitiveness, they do not want to increase their use of it in their workplaces. They basically think that ‘it is fine, just as it is’. This indicates that a challenge in construction management is to investigate how prevailing and new ICT applications can be used to develop the industry.     

三点弯曲-剪切试样的应力强度因子

利用一种边界元法研究具有偏移边裂纹的三点弯曲-剪切试样.该边界元方法由Crouch与Starfield提出的常位移不连续单元和笔者最近提出的裂尖位移不连续单元构成.在该边界元方法实施过程中,左、右裂尖位移不连续单元分别置于裂纹的左、右裂尖处,而常位移不连续单元则分布于除了裂尖位移不连续单元占据的位置之外的整个裂纹面及其他边界.算例说明这种边界元法不论对无限大还是对有限大平面弹性复杂裂纹问题的应力强度因子的计算都是非常有效的.对具有偏移边裂纹的三点弯曲-剪切试样的应力强度因子进行了详细的研究,给出了数值结果.     

一种外LET柔顺半铰的动力学建模与分析

对一种外LET柔顺半铰进行建模与动力学特性分析。采用斜率不连续的绝对节点坐标法（ANCF）建立了该柔顺半铰系统动力学方程;对外力作用下半铰中心线和外轮廓的运动变形进行仿真,与实验结果对比,证明了绝对节点坐标法对柔顺半铰动力学建模的有效性;进一步分析了半铰外形尺寸变化对其变形规律的影响。     

基于网格平均的跟踪法应用于Euler方程组

设计了一种求解Euler方程组的基于网格平均框架的守恒型激波跟踪法,算例表明利用该方法求解守恒方程组的数值解很有效,并且编制程序相对容易,尤其是能给出很精确的间断位置。     

露天煤矿生物多样性调查技术导则研究（增刊）

露天煤矿采-剥-运-排-覆等开采环节会对矿区范围内的生物多样性造成巨大破坏,而生物多样性调查是进行矿区土地复垦、恢复矿区生物多样性的基础。相关生物多样性调查技术导则研究可为科学有效进行露天煤矿生物多样性调查提供技术支撑,然而国内尚无针对露天煤矿开采-损毁-复垦特点的生物多样性调查技术导则研究。本文在整合现有生物多样性调查方法的基础上,重点对技术导则中应明确的生物多样性调查层次、调查阶段、调查范围、调查频率、调查单元等基本调查原则,以及不同层次露天煤矿生物多样性调查对象和调查方法进行了研究,以期为编制露天煤矿生物多样性调查技术导则、推动露天煤矿生物多样性保护工作,进而建设绿色矿山提供参考和依据。     

岩体结构面网络模拟的改进与应用

随着计算机技术的发展,以统计学为基础的结构面网络模拟技术日益完善,被广泛的应用到工程实践中。但在传统的结构面网络模拟中,随机生成的结构面一直未能很好表现出结构面间距的概率分布模型。针对这一点,对随机结构面中心点的生成方式进行了改进,使随机结构面在模拟区内反应出结构面间距的概率分布模型。改进方法使结构面网络模型具有更强的不均匀性,更符合自然状态中结构面的分布形态。改进方法还可以通过控制随机结构面中心点的分布形式来控制模拟区结构面的分布形态,再结合工程实际可以让结构面网络模型更接近其实际形态。     

Real-time data mining of massive data streams from synoptic sky surveys

The nature of scientific and technological data collection is evolving rapidly: data volumes and rates grow exponentially, with increasing complexity and information content, and there has been a transition from static data sets to data streams that must be analyzed in real time. Interesting or anomalous phenomena must be quickly characterized and followed up with additional measurements via optimal deployment of limited assets. Modern astronomy presents a variety of such phenomena in the form of transient events in digital synoptic sky surveys, including cosmic explosions (supernovae, gamma ray bursts), relativistic phenomena (black hole formation, jets), potentially hazardous asteroids, etc. We have been developing a set of machine learning tools to detect, classify and plan a response to transient events for astronomy applications, using the Catalina Real-time Transient Survey (CRTS) as a scientific and methodological testbed. The ability to respond rapidly to the potentially most interesting events is a key bottleneck that limits the scientific returns from the current and anticipated synoptic sky surveys. Similar challenge arises in other contexts, from environmental monitoring using sensor networks to autonomous spacecraft systems. Given the exponential growth of data rates, and the time-critical response, we need a fully automated and robust approach. We describe the results obtained to date, and the possible future developments.