Computational study on the effects of volume ratio of DOC/DPF and catalyst loading on the PM and NOx emission control for heavy-duty diesel engines

The use of a diesel particulate filter (DPF) in a diesel aftertreatment system has proven to be an effective and efficient method for removing particulate matter (PM) in order to meet more stringent emission regulations without hurting engine performance. One of the favorable PM regeneration technologies is the NO₂-assisted regeneration method due to the capability of continuous regeneration of PM under a much lower temperature than that of thermal regeneration. In the present study, the thermal behavior of the monolith during regeneration and the conversion efficiency of NO₂ from NO with an integrated exhaust system of a diesel oxidation catalyst (DOC) and DPF have been predicted by one-channel numerical simulation. The simulation results of the DOC, DPF, and integrated DOC-DPF models are compared with experimental data to verify the accuracy of the present model for the integrated DOC and DPF modeling. The effects of catalyst loading inside the DOC and the volume ratio between the DOC and DPF on the pressure drop, the conversion efficiency, and the oxidation rate of PM, have been numerically investigated. The results indicate that the case of the volume ratio of ‘DOC/DPF=1.5’ within the same diameter of both monoliths produced close to the maximum conversion efficiency and oxidation rate of PM. Under the engine operating condition of 175 kW at 2200 rpm, 100% load with a displacement of 8.1, approximately 55 g/ft³ of catalyst (Pt) loading inside the DOC with the active Pt surface of 5.3 m²/g_pt was enough to maximize the conversion efficiency and oxidation rate of PM.     

Can we reduce car use and, if so, how? A review of available evidence

Transport accounts for nearly a quarter of current energy-related carbon dioxide emissions with car travel constituting more than three quarters of all vehicle kilometres travelled. Interventions to change transport behaviour, and especially to reduce car use, could reduce CO₂ emissions from road transport more quickly than technological measures. It is unclear, however, which interventions are effective in reducing car use and what the likely impact of these interventions would be on CO₂ emissions. A two-stage systematic search was conducted focusing on reviews published since 2000 and primary intervention evaluations referenced therein. Sixty-nine reviews were considered and 47 primary evaluations found. These reported 77 intervention evaluations, including measures of car-use reduction. Evaluations of interventions varied widely in the methods they employed and the outcomes measures they reported. It was not possible to synthesise the findings using meta-analysis. Overall, the evidence base was found to be weak. Only 12 of the 77 evaluations were judged to be methodologically strong, and only half of these found that the intervention being evaluated reduced car use. A number of intervention approaches were identified as potentially effective but, given the small number of methodologically strong studies, it is difficult to draw robust conclusions from current evidence. More methodologically sound research is needed in this area.     

太平湖大桥二类稳定的风险分析

稳定是拱桥设计和施工过程中必须关注的关键性问题,而二类稳定能比较真实地反映拱桥的破坏历程,尤为重要。以主跨336 m的安徽太平湖大桥为背景,进行了其二类稳定的风险分析,详细介绍考虑和不考虑混凝土套箍效应的结构破坏历程,并讨论了计算模型精度对结构的影响,以及计算结构鲁棒性的问题,从而得到太平湖大桥二类稳定问题比较系统的结论。     

纳米SiO2和PVA纤维协同增强混凝土力学性能

为研究纳米SiO₂和PVA纤维对混凝土力学性能的影响,通过工作性试验和抗压试验,测得了混凝土拌和物的坍落度以及硬化混凝土的抗压强度和弹性模量。结果表明:在一定掺量范围内,纳米SiO₂和PVA纤维的掺入对混凝土的流动性和力学性能均有较大影响;随着纳米SiO₂掺量的增加,混凝土拌和物的坍落度逐渐降低,抗压强度和弹性模量均先增大后减小,在纳米SiO₂掺量为5%时达到最大值;随着PVA纤维体积掺量的增加,掺纳米SiO₂混凝土的坍落度逐渐降低,抗压强度和弹性模量也呈现先增大后减小的趋势,在PVA纤维体积掺量分别为1.5%和1.0%时达到最大值。纳米SiO₂提高了混凝土的抗压强度和弹性模量,PVA纤维提高了纳米混凝土的抗压强度,但降低了纳米混凝土的弹性模量。     

基于二乘二取二架构的安全扩展平台研究

为节约时间和资金成本,在不改变既有CTCS-2/3级列控系统的前提下,进一步修改完善扩展其系统功能,提出采用二乘二取二架构安全扩展平台。平台内部双CPU之间采用时钟同步机制进行实时自检、互检,大大提高了安全扩展平台的安全性、可靠性和可用性。     

河道二维数值模拟糙率横向分布研究

糙率是河道对水流阻力大小的描述。文中系统地总结了推求糙率的各种常用方法,分析了糙率沿河道横断面分布的非统一性。采用横断面各个垂线能坡相同的假定原理,利用谢才—曼宁公式,推导出了断面糙率再分配函数。通过点绘多条河流不同河型的不同断面形态的实测水文资料,建立了可应用于平面二维水流数值模拟中阻力沿河宽分布的经验公式,将得到的断面糙率再分配函数应用到对应的河段的平面二维流场数值计算中,计算结果与实测结果吻合良好,解决了计算流速与天然实测流速断面分布不一致的问题,提高了水流二维数值模拟的精度。     

光催化材料在降解汽车尾气方面的应用研究

通过对配制的光催化降解汽车尾气的材料进行试验研究,观测到溶液的渗透深度和分散效果均满足实际应用需求,并通过实例阐述光催化材料在降解汽车尾气方面的具体应用,这为我国的汽车尾气的绿色降解研究提供了借鉴和依据。     

《中国舰船研究》2016年第2期目录

[1] 基于闭排队网络的弹射器数量配置方法…陈红召,杨大鹏(1)[2] 基于任务流程的舰船RMS建模与仿真…原宗(5)[3] 通风模式对住舱人员咳嗽液珠扩散过程的影响…郑立捷,许建,吴方良,徐文涛,龙正伟(12)[4] 破损舰船瘫船状态倾覆概率评估方法…吕振望,马坤,李新萌(21)[5] 水下爆炸条件下自由场压力载荷时频特征分析…谢耀国,崔洪斌,李新飞,姚熊亮(27)[6] 近场爆炸载荷作用下某大型舰船结构剩余强度分析…田正东,李烨,李朋波,靳易安(33)[7] V型无压载水船舱口角隅疲劳寿命计算新方法…王琳,夏孟龙,解德(39)[8] 厚钢板疲劳裂纹扩展前缘应力状态试验与数值仿真…党之凡,乐京霞,董岩(51)[9] 壳板厚度对船舶加筋板结构耐撞性能的影响…黄东,龚榆峰,刘敬喜(58)[10] 桩靴支护结构对桩端极限承载力的影响…张兆德,吕国兴,张心(66)[11] 水动力噪声计算方法综述…李环,刘聪尉,吴方良,陈灿(72)[12] 舷侧阀通海口结构形式对声学性能的影响…徐建龙,张盛,潘国雄,张生乐(90)[13] 复合材料螺旋桨模型的应变模态与振动特性…黄政,熊鹰,杨光(98)[14] 有限长半充液圆柱壳振动特性分析…李天匀,王露,郭文杰,杨国栋,朱翔(106)[15] 一种装舰约束条件下的武器通道作战能力计算方法…裴雪兵,胥文清,陈吉超(111)[16] 船用蒸汽发生器给水系统的容错控制…赵淑琴,张永生(117)[17] 舰船轴频电场的轴地有源补偿技术…张安明,张海鹏,程峥华(121)[18] 初步设计阶段桅杆外形的隐身性评估与改进…杜晓佳,崔玫(127)[19] MBR运行参数对处理船舶含油餐饮废水的影响…刘喜元,李树,谢承利,王良武(133)     

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.     

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.