Physics of failure analysis of power section assembly for positive displacement motor

Power section assembly is the core part of positive displacement motor (PDM), and its mechanical behavior and service life determine the drilling efficiency and cycle. In this paper, fault tree of power section assembly was established, failure reasons were analyzed and improvement measures were put forward. Finite element models of conventional lining and uniform wall thickness lining of 5/6 PDM were established, and the mechanical behaviors were investigated. Working parameters such as drilling fluid pressure, rubber hardness, downhole temperature and pressure difference were discussed. The results show that wear and rust are the main failure modes of the rotor. Failure modes of rubber lining are wear, tear, rupture, peeling off, thermal failure and fatigue failure. Under the action of drilling fluid pressure, the maximum effective stress of rubber lining appears in the bottom of arc, and the minimum stress appears at the top of arc. But deformation distribution is opposite to the effective stress. Deformation of uniform wall thickness lining is more uniform. Effective stress of the lining increases with the increasing of drilling fluid pressure and rubber hardness, but it decreases with the downhole temperature increases. Deformation of the lining increases with the drilling fluid pressure increases, but it decreases with the increasing of rubber hardness and downhole temperature. Effective stress and deformation distribution of rubber lining are more uneven with the pressure difference increases. High stress area lies between the two smallest chambers.     

“一带一路”沿线国家PM2.5污染与人口暴露风险的时空分布特征

使用1999—2016年0.01°×0.01°高空间分辨率的卫星反演PM_2.5浓度数据集，结合精度为1 km×1 km的人口栅格数据，分析了"一带一路"沿线65个国家PM_2.5污染与暴露风险的时空变化特征.结果表明：①PM_2.5浓度存在着明显的区域分布差异，PM_2.5浓度高值区（>35 μg·m^-3）主要分布在地形平坦、人口密集的恒河平原、华北平原和中南半岛等区域，中值区（10~35 μg·m^-3）主要集中在俄罗斯西部、中东欧、沙特东部和缅甸等区域，而低值区（<10 μg·m^-3）主要分布在高海拔、高纬度与荒漠化地区，如青藏高原、西伯利亚、西亚卢特沙漠等区域；②65国年均PM_2.5浓度从1999年的12.0 μg·m^-3上升到2016年的14.1 μg·m^-3，年均增长超过0.1 μg·m^-3，累计有22.5%的区域有显著的增加趋势，仅有5.2%的区域呈显著下降趋势；③2000—2016年，PM_2.5浓度在35 μg·m^-3以上的区域面积比重从2.2%上升到7.2%，暴露人口占比从18.9%增加至41.9%；④人口暴露风险平均值从2000年的665.2增加至2016年的1140.4，Hurst总体均值为0.59，其中大于0.5的持续性区域占82.3%，持续性特征以弱持续性为主.     

Evaluating the short-term effect of ambient temperature on non-fatal outdoor falls and road traffic injuries among children and adolescents in China: a time-stratified case-crossover study

● A study assessing the temperature-injury relationship was conducted among students. ● The maximum risks of injury appeared at moderate temperatures. ● The temperature effect on outdoor falls was greater in older students. Although studies have suggested that non-optimal temperatures may increase the risk of injury, epidemiological studies focusing on the association between temperature and non-fatal injury among children and adolescents are limited. Therefore, we investigated the short-term effect of ambient temperature on non-fatal falls and road traffic injuries (RTIs) among students across Jiangsu Province, China. Meteorological data and records of non-fatal outdoor injuries due to falls and RTIs among students aged 6–17 were collected during 2018–2020. We performed a time-stratified case-crossover analysis with a distributed lag nonlinear model to examine the effect of ambient temperature on the risk of injury. Individual meteorological exposure was estimated based on the address of the selected school. We also performed stratified analyses by sex, age, and area. A total of 57322 and 5455 cases of falls and RTIs were collected, respectively. We observed inverted U-shaped curves for temperature-injury associations, with maximum risk temperatures at 18 °C (48th of daily mean temperature distribution) for falls and 22 °C (67th of daily mean temperature distribution) for RTIs. The corresponding odds ratios (95% confidence intervals) were 2.193 (2.011, 2.391) and 3.038 (1.988, 4.644) for falls and RTIs, respectively. Notably, there was a significant age-dependent trend in which the temperature effect on falls was greater in older students (P-trend < 0.05). This study suggests a significant association between ambient temperature and students’ outdoor falls and RTIs. Our findings may help advance tailored strategies to reduce the incidence of outdoor falls and RTIs in children and adolescents.     

Required hours of practice for learner drivers: A comparison between two Australian jurisdictions

Problem

This study considers whether requiring learner drivers to complete a set number of hours while on a learner license affects the amount of hours of supervised practice that they undertake. It compares the amount of practice that learners in Queensland and New South Wales report undertaking. At the time the study was conducted, learner drivers in New South Wales were required to complete 50 hours of supervised practice while those from Queensland were not.

Method

Participants were approached outside driver licensing centers after they had just completed their practical driving test to obtain their provisional (intermediate) license. Those agreeing to participate were interviewed over the phone later and asked a range of questions to obtain information including socio-demographic details and amount of supervised practice completed.

Results

There was a significant difference in the amount of practice that learners reported undertaking. Participants from New South Wales reported completing a significantly greater amount of practice (M = 73.3 hours, sd = 29.12 hours) on their learner license than those from Queensland (M = 64.1 hours, sd = 51.05 hours). However, the distribution of hours of practice among the Queensland participants was bimodal in nature. Participants from Queensland reported either completing much less or much more practice than the New South Wales average.

Summary

While it appears that the requirement that learner drivers complete a set number of hours may increase the average amount of hours of practice obtained, it may also serve to discourage drivers from obtaining additional practice, over and above the required hours.

Impact on Industry

The results of this study suggest that the implications of requiring learner drivers to complete a set number of hours of supervised practice are complex. In some cases, policy makers may inadvertently limit the amount of hours learners obtain to the mandated amount rather than encouraging them to obtain as much practice as possible.     

单层带支撑异形柱框架的高温性能研究

针对单层异形柱框架,通过高温数值分析,考察了支撑设置和受火位置对结构高温变形及内力的影响。研究结果表明:对于单层多跨异形柱框架,当只有一端有支撑跨时,会在一定程度上增大另一端的边节点水平位移和边柱侧向变形,对结构整体抗火不利;当左、右两端均有支撑跨时,非支撑跨在火灾作用下的梁轴力比很大,升温后期可能因梁跨中竖向位移急剧增大而发生破坏。基于上述研究结果,给出了4类单层带支撑异形柱框架火灾行为的初步判定方法。     

春季禁渔对常熟江段渔业群落结构及物种多样性影响的初步研究

以2000~2004年4~6月渔业资源动态监测资料为依据,分析研究了3年春季禁渔(2002~2004)对常熟江段渔业资源群落结构及物种多样性的影响。研究结果表明：4~6月间常熟江段出现的鱼、虾、蟹类渔获物共有11目、18科、46种;春禁后,该江段总CPUE（单位捕捞努力渔获量）显著增加;优势种更替不明显,历年以刀鲚、鲻鱼、长春鳊等经济鱼类为主;刀鲚CPUE有所回升,资源衰退受到遏制;小型鱼类、幼鱼在渔获物中的比例明显上升; Margalef物种丰富度指数、Wilhm改进指数呈明显上升趋势,均匀度指数J′、优势度数Dw在窄幅范围波动。春禁对常熟江段渔业资源保护的生态效果较明显,春禁后渔业资源群落种间结构得到一定程度的改善,生物多样性上升。     

长江九江段水环境容量研究

针对长江九江段污染物的稀释扩散,通过现场实测和数值模拟的方法,建立了近岸区域二维水质数学模型及水质限制使用区临界点水质与污染负荷的响应关系。本文从实际应用出发,提出了近岸区可分配水环境容量的计算方法,并利用优化模型计算了长江九江段不同水文条件和不同水质限制使用区范围的允许排放负荷。      

神经网络分布式多通道协同控制声屏障原理研究

声屏障的高度,材料,结构,重量和风载荷等要素受到景观要求和承载结构等条件的制约,进一步劣化了常屏障在低频宽带噪声衍射和透射控制方面的缺陷,本文为此提出了神经网络分布式多通道智能化协同控制声屏障方法,神经网络自组织形成空二维非线性控制矢量,以形成优化的分布式消声器阵列,采用多目标优化,神经网络通过自学习,首先优化各传感器和次声源的空间配置,以形成适当的消声空间分布并降低硬件开销,其次简化控制器结构,     

山西煤炭基地矿井水的环境影响及利用研究

本文研究了山西矿井水水质特征及其环境影响.结果表明,矿井水中50％为高硬度、高矿化度水,42％为中性淡水,8％为酸性水,其污染特征为SS占第一位,依次为COD、硫化物、BOD_5、As等.文章还对山西矿井水的涌水量、利用现状与利用潜力进行了调查研究,指出山西矿井水应主要回用煤矿本身,实行清污分流和分质供水.     

清除废气中VOCs的流向变换催化燃烧技术进展

一、引　　言环境恶化严重地威胁人类的生存和社会的可持续发展 ,是当前全世界共同面临的一个重大问题。作为空气污染的主要来源之一 ,易挥发有机物 (ＶＯＣｓ)不仅是一次污染源而且还可能造成光化学烟雾等二次污染[1 ] 。因此 ,控制大气中挥发性有机物非常重要。美国 1 990年开始实施的清洁空气法修正案要求在其后的九年内使大气中有毒化学品的排放量减少 90 % ,其中 70 %为易挥发有机物 (ＶＯＣｓ) ,其他发达国家也都围绕改善生态环境和有效利用资源的战略性要求采取了相应的措施。尤其是投入了大量的人力、物力 ,致力于控制空气中挥发性…