汽车侧窗雨水管理的计算流体力学分析研究

为分析侧窗雨水管理中A柱漫流对侧窗视野区的影响,通过计算流体力学(CFD)仿真和环境风洞试验相结合的方法,对前风窗玻璃水流越过A柱后在侧窗表面流动的过程进行了分析和研究,证明了 CFD瞬态分析方法能够预测A柱漫流的位置和侧窗水流在风力作用下的运动轨迹.通过A柱优化方案的试验结果对比和流场分析,验证了A柱结构优化能够改善...     

Designing optimal autonomous vehicle sharing and reservation systems: A linear programming approach

Autonomous vehicle (AV) technology holds great promise for improving the efficiency of traditional vehicle sharing systems. In this paper, we investigate a new vehicle sharing system using AVs, referred to as autonomous vehicle sharing and reservation (AVSR). In such a system, travelers can request AV trips ahead of time and the AVSR system operator will optimally arrange AV pickup and delivery schedules and AV trip chains based on these requests. A linear programming model is proposed to efficiently solve for optimal solutions for AV trip chains and required fleet size through constructed AVSR networks. Case studies show that AVSR can significantly increase vehicle use rate (VUR) and consequentially reduce vehicle ownership significantly. In the meantime, it is found that the actual vehicle miles traveled (VMT) in AVSR systems is not significantly more than that of conventional taxis, despite inevitable empty hauls for vehicle relocation in AVSR systems. The results imply huge potential benefits from AVSR systems on improving mobility and sustainability of our current transportation systems.     

Impact of license plate restriction policy on emission reduction in Hangzhou using a bottom-up approach

Many emission models have been developed for estimating the impact of transport policies on vehicle emissions. Macroscopic models, such as MOBILE and COPERT, are used for area analysis, while microscopic models, such as CMEM, are applied for corridor analysis. It is well known that driving dynamics are critical for estimating vehicle emissions. MOVES can be used for both macroscopic and microscopic emission analysis, and its advantage lies in the consideration of driving dynamics. Using a bottom-up approach, we study the impact of license plate restriction policy on vehicle emission reduction by localizing the emission rates in MOVES according to the vehicle emission standards in China. We implement the approach to evaluate the impact on the total vehicle emissions in Hangzhou, China before and after the implementation of license plate restriction policy. In the restricted region, the reductions of total Vehicle Kilometer Traveled (VKT) and total emissions are 9.6% and 6.9%, respectively. The result shows that the license plate restriction policy is effective in achieving the targeted emission reduction.     

Promoting carsharing attractiveness and efficiency: An exploratory analysis

Carsharing has grown significantly over recent years. Understanding factors related to the usage and turnover rate of shared cars will help promote the growth of carsharing programs. This study sets station-based shared car booking requests and turnover rates as learning objectives, by which generalized additive mixed models are employed to examine various effects. The results are: (1) stations with more parking spaces, longer business hours and fewer nearby stations are likely to receive more booking requests and have a higher turnover rate; (2) an area with a higher population density, a higher percentage of adults, a higher percentage of males, a greater road density, or more mixed land use is associated with more car usage and a higher turnover rate; (3) stations nearby transit hubs, colleges, and shopping centers attract more shared car users; (4) shared cars are often oversupplied at transit hubs; (5) both transit proximity and housing price present high degrees of nonlinearity in relation to shared car usage and turnover rates. Findings provide evidence for optimizing the usage and efficiency of carsharing programs: carsharing companies should identify underserved areas to initiate new businesses; carsharing seems more competitive in a distance to a bus stop between 1.2 km and 2.4 km, and carsharing is more effectively served in areas with constraints in accessing metro services; carsharing should be optimally discouraged at transit hubs to avoid the oversupply of shared cars; local authorities should develop a location-based and geographically differentiated quota in managing carsharing programs.     

Individual trip rate transferability analysis based on a decision tree approach

Transferring trip rates to areas without local survey data is a common practice which is typically performed in an ad hoc fashion using household-based cross-classification tables. This paper applies a rule-based decision tree method to develop individual-level trip generation models for eight different trip purposes as defined in the US National Household Travel Survey in addition to daily vehicle miles traveled. For each trip purpose, the models are obtained by finding the best fitted statistical distribution to each of the final decision tree clusters while considering the correlation between the trip rates for other trip purposes. The rule-based models are sensitive to changes in demographics. The performance of the models is then tested and validated in a transferability application to the Phoenix Metropolitan Region. These models can be employed in a disaggregate microsimulation framework to generate trips with different purposes at the individual or household level.     

Is in-cabin exposure to carbon monoxide and fine particulate matter amplified by the vehicle’s self-pollution potential? Quantifying the rate of exhaust intrusion

In-cabin exposure has increased in recent years due to longer commute and/or prolonged times in cars. The intrusion of the vehicle’s own exhaust into the passenger’s compartment has been recognized as a process that amplifies in-cabin passenger exposure. Quantifying its contribution is hampered by uncertainties associated with its measurement method such as trace tests and the lack of data regarding certain critical physical parameters, particularly those pertaining to air exchange rate (AER) and particulate matter deposition rate (DR). In this study, we present a hybrid methodology combining field measurements with a single-zone mass balance to estimate these parameters as well as the source term that represents vehicle self-pollution. In- and out-vehicle carbon monoxide (CO) and fine particulate matter (PM_2.5) were monitored concurrently in test vehicles under idle and moving conditions using several common ventilation modes. In addition to defining a hybrid methodology to characterize the underlying physical parameters, this study found that vehicle self-pollution can account for approximately 15 and 30% of CO and PM_2.5 exposure experienced by vehicle occupants respectively. Vehicle self-exhaust intrusion may constitute a significant PM exposure route for vehicle-based occupations or commuters with prolonged time in vehicles.     

不规则波在斜坡地形破碎区波高分布的数值试验研究

在近岸浅水波浪分布的研究中,格鲁霍夫斯基给出适用于深水波至破碎波的整个浅水域(相对水深η>2)的波高经验分布公式,但该式在波浪发生破碎后的适用性研究欠缺。基于FLOW-3D软件对深水不规则波传播到斜坡地形上波浪发生破碎进行模拟,验证波高沿程分布与试验值的一致性,并模拟在130斜坡地形条件下波浪从有限水深传播到近岸破碎区的沿程波高分布变化。结果表明,在该坡度相对水深η<2.75情况下,格鲁霍夫斯基经验分布公式出现较大误差,不再适用;破碎区各累积率波高与平均波高的比值随相对水深变小呈递减趋势,经验公式值与之相比,总体上呈现出大波偏大、小波偏小的情况。     

基于节流方法的被动式吊机升沉补偿系统设计

设计一种基于蓄能器和液压缸的被动式船舶吊机升沉补偿系统,为了提高系统补偿率,对其进行动力学分析和性能指标分析,提出一种基于节流阀的改进方案,即在液压管路中加入节流阀,通过改变节流阀通径和个数,调整系统阻尼比至合适值,从而提高系统补偿率。改进前后的系统仿真对比结果表明:基于节流阀改进方案的被动式升沉补偿系统具有更好的补偿效果。     

必要费率在经济船型论证和方案比选中的应用

必要费率是港口工程多方案项目经济比选方法之一。本文通过经济船型论证,介绍了必要运费率的计算过程,进而计算出综合必要费率并进行方案经济比选,从经济角度方面推荐合理的建设方案。     

燃烧室形状对大功率机车柴油机工作性能的影响

针对大功率铁路机车柴油机的工作过程进行仿真计算,仿真计算得到的数据与实际试验数据相符合,将整个缸内工作过程按放热率规律分为三个阶段并分别进行研究分析.设计两种不同的燃烧室方案与原机型进行比较,讨论燃烧室喉口直径和燃烧室深度对于柴油机放热量、污染物排放量和缸内微观流场的影响.对比结果显示,当喉口直径为198 mm、燃烧室深度18.16 mm时,碳烟排放量和氮氧化物排量比喉口直径为188 mm、深度20 mm时分别下降了84.2％和43.4％;当喉口直径增加到208 mm时,缸内温度整体有所升高,氮氧化物排放量有所下降但是碳烟排放量增大.