变速器齿轮冲击试验的加载方式研究

通过对变速器疲劳寿命台架试验的故障分析，研究其齿轮在不同加载方式下的损坏情况。     

On vehicle/track impact at connection between a floating slab and ballasted track and floating slab track's effectiveness of force isolation

When a vehicle runs over the connection between a floating slab track (FST) and ballasted track, wheel/rail impact may occur because of the stiffness difference in the two kinds of track, and thus a transition sector is usually included at the connection to smoothen the stiffness change. This phenomenon is studied by numerical simulation using a time-domain model for an idealised case without such a transition to determine whether it is actually necessary. Calculation results show that the wheel/rail impact load is moderate for a light FST and increases with the vehicle speed or decreasing the natural frequency of the FST. From simulation the wheel/rail parametric excitation is observed, as a result of variation in the stiffness of the FST with the period of the single slab length. The wheel/rail load due to the parametric excitation also increases with the vehicle speed. In addition, good performance of vibration isolation can be seen for the FST in terms of the force transmitted to the infrastructure.     

The effect of railway local irregularities on ground vibration

The environmental effects of ground-borne vibrations generated due to localised railway defects is a growing concern in urban areas. Frequency domain modelling approaches are well suited for predicting vibration levels on standard railway lines due to track periodicity. However, when considering individual, non-periodic, localised defects (e.g. a rail joint), frequency domain modelling becomes challenging. Therefore in this study, a previously validated, time domain, three-dimensional ground vibration prediction model is modified to analyse such defects. A range of different local (discontinuous) rail and wheel irregularity are mathematically modelled, including: rail joints, switches, crossings and wheel flats. Each is investigated using a sensitivity analysis, where defect size and vehicle speed is varied. To quantify the effect on railroad ground-borne vibration levels, a variety of exposure–response relationships are analysed, including: peak particle velocity, maximum weighted time-averaged velocity and weighted decibel velocity. It is shown that local irregularities cause a significant increase in vibration in comparison to a smooth track, and that the vibrations can propagate to greater distances from the line. Furthermore, the results show that step-down joints generate the highest levels of vibration, whereas wheel flats generate much lower levels. It is also found that defect size influences vibration levels, and larger defects cause greater vibration. Lastly, it is shown that for different defect types, train speed effects are complex, and may cause either an increase or decrease in vibration levels.     

Measuring the car ownership impact of free-floating car-sharing – A case study in Basel,Switzerland

Free-floating car-sharing schemes operate without fixed car-sharing stations, ahead reservations or return-trip requirements. Providing fast and convenient motorization, they attract both public transport users and (former) car-owners. Thus, their impact on individual travel behavior depends on the user type. Estimating the travel behavior impact of these systems therefore requires quantitative data. Using a two-wave survey approach (shortly after launch of the scheme plus one year later) including travel diaries, this research indicates that (due to their membership) 6% of the free-floating car-sharing customers reduce their private vehicle ownership. Moreover, the results suggest that free-floating car-sharing both complements and competes with station-based car-sharing.     

A bi-objective bi-level signal control policy for transport of hazardous materials in urban road networks

A bi-objective bi-level signal control optimization for hazardous material (hazmat) transport is considered to assess trade-offs between travel cost and environment impacts such as public risk exposure. A least maxi-sum risk model with explicit signal delay is presented to determine generalized travel cost for hazmat carriers. Since the bi-level signal control problem is generally a non-convex program, a bundle method using generalized gradients is proposed. A bounding strategy is developed to stabilize solutions of the bi-level program and reduce relative gaps between iterations. Numerical comparisons are made with other risk-averse models. The results indicate that the proposed bi-objective bi-level model becomes even amiable to signal control policy makers since provides flexible solutions whilst is acceptable to carriers since takes account of travel delay at signal-controlled junctions. Moreover, the trade-offs between public risk and generalized travel costs are empirically investigated among different risk models with a variety of weights. As a result, the proposed model consistently exhibits highly considerable advantage on mitigation of public risk whilst incurred less cost loss as compared to other alternatives.     

Establishment of a Dredged Material Disposal Site in the Exclusive Economic Zone: New Zealand

Disposal options for muddy dredged material, especially if lightly contaminated, is an issue facing many countries, particularly if environmental protection and adherence to the Protocols of the London Dumping Convention is a regulatory requirement. For the case of the oceanic islands of New Zealand, disposal of muddy dredged material has become an issue for the prime city of Auckland. Accordingly, it has been necessary to investigate a suitable marine disposal site outside of the territorial seas in the exclusive economic zone (EEZ). Ideal properties for such a disposal site include a near flat surface on the continental shelf, with sediments of similar textural characteristics to the material being disposed, a site of non-critical benthic ecology, water depths sufficient to enable the disposal site to be monitored (as required under the London Dumping Convention), a site experiencing low shelf currents, not affected by significant wave agitation, and a site not of cultural significance. The approach for site establishment and gaining consent for disposal activities is reviewed. Preliminary investigations supporting a proposed site on the continental shelf in the EEZ are presented.     

The Economics of Using Ocean Observing Systems to Improve Beach Closure Policy

Beach closure policies in the United States suffers from two shortcomings. Type I errors, in which clean beaches are closed, results when managers resort to extensive beach closures because they are unsure of the spatial extent of water contamination. Type II errors, in which contaminated beaches remain open, occur because the time from sampling to public notification can be between two and nine days. Coastal Ocean Observing Systems (COOS) could reduce the impact of both Type I and II errors. The COOS could reduce the spatial extent of beach closures by better predicting the fate of contaminants in coastal waters. An improved COOS also could reduce the time from sampling to public notification of contamination events. I estimate the lost recreational value associated with Type I errors (unnecessary closures) and the public health costs associated with Type II errors (unnecessary exposure to waterborne illnesses) for beaches in Southern California.     

Road pricing: some further comments

This paper extends the discussion of certain problems associated with road pricing raised in an earlier contribution to this journal. Firstly it is shown that where the value of time varies between different groups of traffic using the same congested road, optimal road pricing requires price discrimination between the groups such that those with the lowest value of time pay the highest charge and suffer the greatest losses. However, a uniform price based on an “equity” value of time would reduce the relative distributional effects. Secondly the paper takes up the suggestion that queueing (and by extension congestion) may be positively helpful in the allocation of resources and shows that this is not in general correct although there are situations in which the use of queueing alongside conventional pricing may have a role to play. Finally it is argued that governments’ apparent lack of enthusiasm for road pricing stems as much from political considerations as the more technical problems of applying it.     

负离子发生器车内微颗粒净化效率研究

由于汽车的普及,车内的空气质量引发消费者越来越多的关注。糟糕的车内空气质量会增大人们罹患某种特定疾病的概率,因此控制与减少车内空气污染成为汽车生产设计商所追求的目标。微颗粒污染物,即PM2.5是车内空气污染物的重要来源之一。负离子因能有效沉降空气中的微颗粒,成为车内快速去除微颗粒污染的重要手段。在文章中,我们通过在车内进行微颗粒沉降实验,记录微颗粒物浓度在负离子仪以及车内空调内/外循环净化模式下的变化,并通过SPSS与MATLAB对污染物浓度进行数学建模分析。结果表明:单独使用负离子仪器并无法有效降低车内空气的颗粒浓度,而必须配合车内空气循环系统。在负离子作用下,结合车内空气循环系统,微颗粒浓度迅速下降,下降速度与空气交换速度和微颗粒在空气中的迁移速度相关。     

Exposure of Fauna to Off-Road Vehicle (ORV) Traffic on Sandy Beaches

Driving of off-road vehicles (ORVs) on sandy beaches is common and widespread, but is not universally embraced due to putative environmental impacts on beach biota. For ORVs to impact the beach fauna, traffic areas must overlap with faunal habitat: a fundamental pre-requisite for impact assessments but as yet un-quantified for sandy beaches. Thus, this study quantified the spatial and temporal patterns of ORV traffic on five Australian beaches, and measured the degree to which the distribution of intertidal macro-invertebrates overlaps with traffic zones. Traffic volumes on beaches can be considerable (up to 500 vehicles per day). The position of beach traffic across the beach-face is principally governed by tides and driver behavior. Despite driver education campaigns to the contrary, a considerable fraction of vehicles (16–67%) traverses the soft, upper shore near the foredunes. The majority (65%) of burrowing invertebrate species of the intertidal zone is directly exposed to traffic, save for species inhabiting the swash zone. Because beach traffic presents a formidable management challenge, a fundamental first step in identifying whether ecological impacts are indeed likely, is to assess the potential for spatial and temporal conflict between human pressures (e.g., ORVs) and biological resources (e.g., beach fauna). Although this potential is certainly substantial for sandy shores used by ORVs, the actual ecological impacts on the intertidal fauna can only be predicted in situations where the responses (e.g., direct mortality, behavioral changes) of individual species to beach traffic are known.