砂井地基堆载沉降的PFC2D模拟

砂井是利用土的排水固结原理来处理软弱地基的代表性施工技术。针对现有的软基沉降计算和预测方法存在的不足,利用离散单元法中二维颗粒元法PFC2D建立了砂井二维模型,对砂井地基堆载沉降过程进行二维离散元仿真模拟。采用由2～7个不同组合方式的簇单元来体现软基的孔隙率,改进了PFC2D中的水位降深模型,分析了软基沉降过程中水位的变化规律。模拟与现场实测结果的对比表明:模拟沉降值与实测值基本吻合。     

连云港港赣榆港区起步工程泥沙问题研究

泥沙问题是连云港港北翼的赣榆港区和航道建设的关键问题之一。文中在进行自然条件分析的基础上,利用MOHID二、三维潮流泥沙数学模型对该港区实施后的潮流场及港池、航道泥沙回淤进行了计算模拟,对不同工况潮流流态、航道横流及对周围海区影响范围进行了分析,不仅给出不同工况下港池和航道的年回淤值,还对9711号台风作用下港池和航道的骤淤情况进行了计算预报。综合以上研究成果,提出推荐方案。     

数字化部队指控系统效能评估指标体系的构建

数字化部队是军队信息化建设的必然趋势。指控系统作为数字化部队信息系统的核心,对其效能进行评估,验证其能否满足基于信息系统的体系作战需求具有重要的理论和应用价值。分析了数字化部队的特点,建立了针对数字化部队的指控系统效能评估指标体系,并给出了指标的内涵和详细算法。     

正交频分复用技术在IEEE802．16标准中的应用及仿真分析

文章介绍了正交频分复用技术在802．16中的应用及802．16的帧结构,并在NS2中对IEEE802．16进行了仿真,接着分析了实验结果,最后提出了下一步研究方向。     

船舶氮氧气体制备工艺

介绍了现阶段采用空气分离方法制备氮气和氧气的工艺。在船舶上安装空分装置,以舱室空气为原料,现场制备是解决船舶用氮气和氧气的有效方法。空分法主要有4种工艺:燃烧法、变压吸附法、膜分离法与深冷法。分析比较了4种工艺的原理、实施流程、特点及船舶适应性,提出了当前须解决的技术难点。在船舶设计过程中,根据不同类型、不同吨位的船舶对气体的需求及船舶的具体任务,而选择相应的气体制备工艺和装置。     

客车车身骨架焊接质量控制

通过对CO2气体保护焊焊接焊接形式的分析,找出了影响焊接质量的原因及解决方法,并探讨了提高焊接质量的改进措施。     

宁波江南污水处理厂设计介绍

详细介绍了宁波江南污水处理厂工程的工程规模、工艺设计方案、工艺流程、进出水水质指标、主要构筑物的设计参数及工艺特点。     

Modeling the information flow propagation wave under vehicle-to-vehicle communications

Vehicle-to-vehicle (V2V) communications under the connected vehicle context have the potential to provide new paradigms to enhance the safety, mobility and environmental sustainability of surface transportation. Understanding the information propagation characteristics in space and time is a key enabler for V2V-based traffic systems. Most existing analytical models assume instantaneous propagation of information flow through multi-hop communications. Such an assumption ignores the spatiotemporal relationships between the traffic flow dynamics and V2V communication constraints. This study proposes a macroscopic two-layer model to characterize the information flow propagation wave (IFPW). The traffic flow propagation is formulated in the lower layer as a system of partial differential equations based on the Lighthill-Whitham-Richards model. Due to their conceptual similarities, the upper layer adapts and modifies a spatial Susceptible-Infected epidemic model to describe information dissemination between V2V-equipped vehicles using integro-differential equations. A closed-form solution is derived for the IFPW speed under homogeneous conditions. The IFPW speed is numerically determined for heterogeneous conditions. Numerical experiments illustrate the impact of traffic density and market penetration of V2V-equipped vehicles on the IFPW speed. The proposed model can capture the spatiotemporal relationships between the traffic and V2V communication layers, and aid in the design of novel information propagation strategies to manage traffic conditions under V2V-based traffic systems.     

Scalable stability analysis on large connected vehicle systems subject to stochastic communication delays

In this paper large connected vehicle systems are analyzed where vehicles utilize vehicle-to-vehicle (V2V) communication to control their longitudinal motion. It is shown that packet drops in communication channels introduce stochastic delay variations in the feedback loops. Scalable methods are developed to evaluate stability and disturbance attenuation while utilizing the mean, second moment, and covariance dynamics in open chain and closed ring configurations. The stability results are summarized using stability diagrams in the plane of the control parameters while varying the packet delivery ratio and the number of vehicles. Also, the relationship between the stability of different configurations is characterized. The results emphasize the feasibility of V2V communication-based control in improving traffic flow.     

Dry milling of the ultra-high-strength steel 30CrMnSiNi2A with coated carbide inserts

The ultra-high-strength steel (UHSS) plays an important role in the mechanical industry because of their special performances. The machinability of 30CrMnSiNi2A steel was studied in dry milling with two different coated tools in the present work. This paper introduced that 30CrMnSiNi2A steel was a kind of difficult-to-machine materials. The results showed that the cutting force components of feed direction and cutting width direction, i.e. F x and F y , increased slightly with increasing the cutting speed and feed rate. The values of axial force component F z were much larger than F x and F y , and increased obviously with increasing the milling speed. The workpiece surface had the minimum roughness at the cutting speed of 150 m/min. The physical vapor deposition (PVD) coated ((Ti, Al)N-TiN) insert was more suitable for machining 30CrMnSiNi2A steel than the chemical vapor deposition (CVD) coated (Ti(C, N)-Al 2 O 3 ) insert. Moreover, the main failure modes of PVD-coated insert were micro-chipping and coating spalling. The wear modes of CVD-coated insert were ploughing, coating spalling, and cratering. The serious adhesive wear and the abrasion with some adhesion were the main wear mechanism of PVD- and CVD-coated inserts, respectively.