Adolescents and their aspirations for private car-based transport

Transportation - The need to transition away from the current car-dominated transport system is well documented in sustainability, health and transportation literatures. Despite growing interest in...     

What are the determinants of the willingness to share rides in pooled on-demand services?

Transportation - Simulation studies suggest that pooled on-demand services (also referred to as Demand Responsive Transport, ridesharing, shared ride-hailing or shared ridesourcing services) have...     

通气空泡流中洞壁效应对空化数和压力场影响的研究

文章在均质平衡多相流模型的基础上耦合输运方程型空化模型,通过求解混合介质的RANS方程、RNG k-ε湍流输运方程以及各相的质量输运方程,采用通用CFD软件—FLUENT数值模拟了水洞中带圆盘空化器航行体模型的定常通气空泡流动,研究了圆形截面闭式空泡水洞中洞壁效应对通气空化数和压力场的影响。得到的阻塞空化数线性正比于圆盘水洞直径比,且与三维圆盘自然空泡流的势流近似解基本一致,分析了洞壁效应作用下空化流场内的压力分布特点,并根据计算结果拟合了一定适用条件下通气空泡长度、最大直径和模型阻力系数的近似公式。     

基于焊缝疲劳寿命预测的后桥设计改进

运用焊缝疲劳寿命预测技术对某扭杆梁后桥进行疲劳失效重现,并提出了改进方案。通过物理台架和整车道路试验,建立了仿真分析-台架-道路3者之间的相关性,缩减了产品开发周期,降低了开发成本,提高了产品质量。     

Valuing Freight Transport Time using Transport Demand Modelling: A Bibliographical Review

The value of time for freight transport is of major importance in infrastructure-related cost–benefit analysis and yet its study has been largely neglected when compared with its passenger counterpart. In fact, one of the attributes that could decide the profitability of a project is how much can be saved if freight vehicles use new infrastructure. Despite being the primary benefit of most investments in transport infrastructure, researchers have not yet reached agreement over either the size or the nature of the values of time that should be used when evaluating projects. This article provides a review of the estimation of freight value of time through transport demand modelling and extant empirical evidence on this topic. Similarly, the bibliographic review of studies undertaken has allowed us to pinpoint the most critical issues when modelling freight transport demand and the position of various research teams regarding these aspects. Such issues include identifying the decision-maker, heterogeneity in the transport flows and transport attributes considered by decision-makers.     

浅水中高速排水型船舶尾浪的理论和试验研究

文章将势流理论方法与波谱分析方法相结合,对浅吃水中高速排水型船舶的尾浪进行了数值计算,采用势流理论方法对船舶近域的波浪进行计算,将获取的部分波高数据(或试验数据)作为已知数据,采用波谱函数法进行分析求解,获取波幅谱函数,从而求解远域船舶的尾浪.文中采用试验数据对理论计算结果进行了验证,两者吻合较好.同时结合船模试验结果,探讨了水深、浮态等对单、双体船船舶尾浪的影响,该研究结果可为低尾浪船型的设计和优化提供参考.     

Representing mental maps and cognitive learning in micro-simulation models of activity-travel choice dynamics

This paper develops a model, based on Bayesian beliefs networks, for representing mental maps and cognitive learning into micro-simulation models of activity-travel behavior. Mental maps can be used to address the problem that choice sets in models of travel demand are often ad hoc specified. The theory underlying the model is discussed, a specification is derived and numerical simulation is used to illustrate the properties of the model.     

同步碎石封层技术在公路预防性养护中的应用研究

同步碎石封层技术是一种新型高性价比的公路预防性养护技术。文章介绍了该技术相对其他传统公路养护技术的特点,分析了其材料技术要求与施工工艺,探讨了同步碎石封层的路面选择标准,并给出同步碎石封层质量评定和验收标准。     

轨枕间距对钢轨波磨的影响

主要研究轨枕间距对钢轨波磨发展的影响。研究小半径曲线内轨的小矢跨比波磨。这些出现问题的曲线段属于西班牙毕尔巴鄂区域的地铁轨道,铺设着混凝土道床和两层STEDEF型支承垫层。当初始轨枕间距为1000mm时,仅有92万组轮对通过后所测得的波磨深度峰-峰值已经达到0.42mm。随后更换产生波磨的钢轨,比较列车通过时轨枕上方和轨间中部的内轨垂向、横向加速度。当轨枕间距为1000mm时,轨间中部出现频率为204和244Hz的强烈响应,在轨枕上方却未出现。在相邻轨枕中间铺设一个轨枕,使轨枕间距变为500mm,钢轨波磨停止发展。该结论是根据2年的观测结果得到的。     

Effects of bulbous bow on cross-flow vortex structures around a streamlined submersible body at intermediate pitch maneuver: A numerical investigation

A flow field around a streamlined body at an intermediate angle of incidence is dominated by cross-flow separation and vortical flow fields. The separated flow leads to a pair of vortices on the leeside of the body; therefore, it is essential to accurately determine this pair and estimate its size and location. This study utilizes the element-based finite volume method based on RANS equations to compute a 3D axisymmetric flow around a SUBOFF bare submarined hull. Cross-flow vortex structures are then numerically simulated and compared for a submarine with SUBOFF and DRDC STR bows. Computed results of pressure and shear stress distribution on the hull surface and the strength and locations of the vortex structures are presented at an intermediate incidence angle of 20°. A wind tunnel experiment is also conducted to experimentally visualize the vortex structures and measure their core locations. These experimental results are compared with the numerical data, and a good agreement is found.