汽车涡轮增压器压气机噪声的定常流动研究

研究涡轮增压器噪声的产生和传播机理是一项具有挑战性的工作,极具科研和工程应用价值.在增压器设计阶段,稳定和快速的定常流动仿真,辅以声学类比法可以作为快速评估增压器噪声问题的重要手段,同时这也为后续进行非定常流动仿真打好基础.在大型项目初期,首先对某款增压器压气机几何模型进行定常流动雷诺平均法/雷诺平均数值模拟(RANS...     

基于轻型商用车柴电混合动力总成的模块化平台

商用车动力总成的电气化应用已变得日益广泛.欧盟排放法规要求使得一些技术相比以往更具开发潜力,而这些技术对于成本敏感型市场而言过于昂贵.AVL公司提供了1种可用于柴电混合动力总成的模块化平台.该平台基于排放、效率和成本进行了重点开发.     

加筋含细粒土砂的大型三轴试验分析

为研究在不同加筋情况下土工格栅加筋土的力学特征及加筋效果进行大型三轴实验。首先进行土工实验确定土壤参数及最佳含水率,然后进行大型三轴实验以确定在不同加筋及围压条件下加筋土的性质变化。根据实验结果分析得知,土的性质随加筋情况和围压的变化表现出一定的规律特征,可利用Duncan-Chang模型参数对加筋效果进行定量分析。试验结果表明:加筋后土体的强度明显增强;对加筋效果系数和强度参数分析发现,随着围压的增加加筋效果系数会降低;土工格栅加筋主要提高了土体的黏聚力。     

Why are cities removing their freeways? A systematic review of the literature

ABSTRACT

A scientific consensus has recently emerged suggesting that the dominant twentieth century paradigm of solving transportation congestion problems by building more freeways failed. The legacy of the freeway construction era is clearly visible in polluted and congested cities worldwide. To battle these ills, planning academics have been promoting more sustainable built form aligned with dedicated public/active transport provision. Partly as a result of the push coming from academia, a number of cities have sought to remove their freeways and replace the freed up space with alternate transport infrastructure, such as streets and boulevards. To discern if the transportation planning profession is currently undergoing a paradigm shift or whether freeway removal is merely a temporary fad, we have conducted a systematic review of the literature. In this article, we unpack the underlying reasons which have led some cities to removing their freeways. Results reveal that a paradigm shift has arguably not yet taken place in transportation planning. While many cities are creating human-scale and active transport spaces, currently these spaces tend to coexist alongside freeways. American cities, which were once the pioneers of freeway construction, appear to be lagging behind cities in Europe and Asia in this respect. If the current pace of freeway removal continues, it may take a few decades before the transportation planners, politicians, policy makers, and communities adopt radically different norms, methods, and goals. However, a radical approach may need to be taken sooner given alarming global warming predictions.     

Static Load Test of Low Vibration Track under Heavy Haul TrainEI北大核心

Research purposes: Low vibration track is a suitable track structure in the heavy haul railway long tunnel. Taking the low vibration track in the middle-south channel tunnel as the research object, through the full-scale model static load test, this paper studies the mechanical properties of a single bearing block under the vertical load at the end of the track bed slab (working condition 1), the horizontal and vertical load at the end of the track bed slab (working condition 2), the vertical load at the middle of the track bed slab (working condition 3) and track's crack development trend. Research conclusions:(1) Taking the static load of 30 t axle load train as a reference, the track slab and bearing block concrete of working condition 1 reach the axial tensile strength at 3.3 and 3.1 times static wheel load, the track slab and bearing block concrete of working condition 2 reach the axial tensile strength at 3.0 and 3.1 times static wheel load, the track slab and bearing block concrete of working condition 3 reach the axial tensile strength at 4.9 and 2.9 times static wheel load. (2) Track slab's crack of working condition 1 appears at the corner of the bearing block and the midline of the long side of the bearing block and extends to the short side of the track slab. The crack extension at the corner point is in the shape of \"eight\". There is no obvious crack of working condition 3 in the track slab. (3) The horizontal load of the train leads to the increase of the force of the concrete in the corner of the bearing block. (4)The research results have guiding significance for the design, construction and maintenance of low vibration track. © 2018, Editorial Department of Journal of Railway Engineering Society. All right reserved.     

Congestion relief toll tunnels

Changing urban land-use patterns have reduced the importance of traditional downtowns as the origin and destination of numerous vehicular trips. Much traffic on downtown-area freeways seeks merely to get past downtown, thereby worsening the level of congestion for those seeking access to downtown.A number of European cities have begun to develop a new type of transportation facility: congestion-relief toll tunnels in downtown areas. These projects appear to be economically feasible largely or entirely from premium-price tolls paid by users. Hence, they are being developed by private consortia, operating under long-term franchises from government. Other keys to the feasibility of such projects are peak/off-peak pricing structures (congestion pricing), nonstop electronic toll collection, and restriction of use to auto-size vehicles only (to reduce tunnel dimensions and therefore capital investment).Preliminary analysis indicates that congestion-telief bypass runnels for downtown Los Angeles and San Francisco would be economically feasible as private business ventures, if developed along European lines. Similar approaches might be applied to other controversial freeway projects in both cities, and to restructuring Boston's huge and controversial Central Artery/Tunnel project.Congress has already authorized public-private partnerships of this type, permitting private capital and private owner/operation to be used, both for new projects and to rebuild existing highway, bridge, and tunnel facilities. Six states and Puerto Rico have enacted private-tollway legislation under which such projects could be developed and operated.This type of project should be politically feasible, since it offers a way to make significant transportation improvements in impacted downtowns with little or no public funding. While transit proponents may oppose the construction of toll tunnels, highway users are likely to support such projects, and some environmental groups may support this method of implementing congestion pricing in urban areas, because of its potential for reducing air emissions.