铝合金6063焊接接头性能分析

本文通过对铝合金6063焊接前后材料机械性能、耐腐蚀性能等的测试,分析了该合 金焊后接头性能发生变化的原因。结果表明:6063铝合金具有良好的工艺可焊性和耐 大气腐蚀性能,但焊后热影响区发生了软化,强度下降较大,自然时效能力较差.焊后 固溶处理和人工时效处理在一定程度上是提高接头机械性能必要而有效的手段.      

高寒地区平屋顶保温层厚度反演

建筑节能的发展和新型保温材料的使用中,合理的设计墙体及屋顶保温层的厚度,日益成为目前建筑节能的重要问题.将高寒地区平屋顶保温层厚度设计问题抽象为热传导方程几何边界反问题,通过不断地数值模拟,分析比较结果,得出保温层(文中为加气混凝土层)厚度为250 mm～300 mm时,屋顶内表面的温度变化值落在16℃～24℃之间,此时的保温层厚度为所求得最佳保温层厚度.     

高速铁路桥上无缝线路断轨力计算模型

在吸收前人研究成果的基础上,采用实体单元模拟桥梁及桥梁墩台,采用空间梁单元模拟钢轨及轨枕,采用弹簧单元模拟钢轨、轨枕、桥梁与墩台之间的连接,建立了断轨三维有限元空间力学模型。以秦沈客运专线10跨32 m简支双线整孔箱形梁桥为例,对其进行断缝值影响因素分析。研究结果表明:对于多跨简支梁桥,断缝与梁温度变化幅度、断缝位置、支座摩擦阻力关系不大;断缝值与扣件纵向阻力、钢轨温度变化幅度、桥墩纵向刚度、钢轨类型关系比较密切;断缝值及采用的力学计算模型也有一定的关系,相比传统计算模型,空间力学模型计算结果偏小。     

国外反卫星武器技术及其对抗措施分析

随着卫星在现代战争中的作用日益明显,卫星对抗技术已成为各国军事家十分关心的一个领域。在总结当前国外反卫星技术发展现状的基础上,比较了各种反卫星武器的性能,并探讨了对抗反卫星武器的一些措施。     

中小型船厂的建造计划管理及优化方法研究

针对中小型船厂,以加强建造计划管理为目的,分析船舶建造计划管理中涉及的相关问题,详述设计计划与生产计划建立的过程及彼此的关系,利用累计负荷和PERT网络方法给出对计划进行动态控制与合理优化相应的结果。研究表明,建造计划管理从整体上可控制船舶的建造节奏,使复杂过程以系统和有序的方式进行。     

基于随机骨料模型的混凝土劈拉强度数值模拟

采用随机骨料模型模拟混凝土的细观结构,利用有限元方法数值模拟混凝土劈拉的细观损伤断裂,并对其劈拉破坏过程进行了研究。结果表明：该种随机骨料的数值模拟方法基本可行．混凝土骨料与砂浆的界面是其劈拉破坏的薄弱环节。     

204国道东台段改扩建工程Superpave20沥青混合料配合比设计

Superpave沥青混合料设计方法是一种新型的混合料设计方法,Superpave是Superior Performing Asphalt Pavement的缩写,中文意思是"高性能沥青路面",是美国战略公路研究计划(SHRP)的研究成果之一。从目前国内的应用来看,它较传统的马歇尔设计方法沥青混合料性能有较大的改善,有效地防止了沥青路面早期损害的发生。该文以204国道盐城南段(东台段)改扩建工程沥青面层试验为基础,依据Superpave沥青混合料设计实例对其进行探讨,以求指导路面设计与施工。     

Effect of direct in-cylinder CO2 injection on HCCI combustion and emission characteristics

Fuel injection during negative valve overlap period was used to realize diesel homogeneous charge compression ignition (HCCI) combustion. In order to control the combustion, CO₂ in-cylinder injection was used to simulate external EGR. Effects of CO₂ injection parameters (injection timing, quantity, pressure) on HCCI combustion and emission characteristics were investigated. Experimental results revealed that CO₂ in-cylinder injection can control the start of combustion and effectively reduce NO_x emission. Either advancing CO₂ injection timing or increasing CO₂ injection quantity can reduce peak cylinder pressure and mean gas temperature, delay the starts of low temperature reaction (LTR) and high temperature reaction (HTR), and lower pressure rise rate; NO_x emission was reduced, while smoke, HC, and CO emissions increased. Since the combustion phase was improved, the indicated thermal efficiency was also improved. Injection pressure determines the amount of disturbance introduced into the cylinder. Generally, with the same injection quantity, higher injection pressure results in higher momentum flux and total momentum. Larger momentum flux and momentum has a stronger disturbance to air-fuel mixture, resulting in a more homogeneous mixture; therefore, larger injection pressure leads to lower NO_x and smoke emissions.     

Pedestrian crosswalk overflow violation in China: Characteristics and countermeasure

The phenomenon that pedestrians do not walk in the crosswalk during pedestrian green is defined as overflow violation, which is illegal but common. Broadly varying crossing positions at far-side cross-section may result in widely distributed conflict points with left-turning and right-turning vehicles, which may cause the occurrence of severe conflicts. This paper proposes a model to estimate the overflow pedestrians’ crossing positions at the far-side cross-section of signalized crosswalk, which enables us to better understand pedestrian overflow violation behavior and finally facilitate their safety. After analysis, the intersection geometry and destination are determined as the critical factors causing pedestrians to overflow. And then, Weibull distribution is employed to describe the stochastic characteristics of overflow pedestrians’ crossing position distribution at the far-side cross-section. A crossing position distribution model which takes the crosswalk length, width and distance between crosswalk and destination into account is developed. The established model is validated by comparing the observed pedestrian crossing positions with the estimated crossing positions. The validation results suggest that the established model is capable of being adopted to estimate the overflow pedestrians’ crossing positions at far-side cross-section. Based on the model, countermeasure for overflow violation can be put forward to prevent pedestrians from walking outside the crosswalk.     

基于多任务学习和层次分析法的公路隧道支护方案优化设计

为提升公路隧道施工过程中支护的实时性和合理性, 以浙江省龙丽温高速的围岩地质特征和支护方案为研究背景。 分析围岩特征与支护参数的相关性, 确定了以围岩风化程度、 坚硬程度、 岩体完整程度、 地下水状态、 围岩稳定情况为输入围岩特征, 锚杆间排距、 锚杆长度、 喷砼厚度、 钢拱架型号为输出支护参数的多任务学习模型结构。 针对多任务学习模型获得的预测支护参数, 通过层次分析法评价预测支护参数中部分强于实际支护参数, 部分弱于实际的支护设计, 结果表明预测支护参数综合得分高于实际支护参数。 研究成果为实现公路隧道快速支护方案选型和评估提供了指导。