舰艇特殊进水过程的流量差值迭代算法研究

目前,在进行静水情况下的破损舰艇进水过程中的姿态计算时,通常使用流量差值迭代算法。然而,该算法的使用有一定的局限性。对于存在进满水舱室的特殊进水过程,破口流线的伯努利方程将发生改变,这导致了不能使用目前的迭代公式进行计算。因此,本文以该特殊的进水过程为对象,在对流线伯努利方程修正的基础上,利用隐函数求导模型和克莱姆法则,对此时的流量差值迭代算法进行了建模,并对该算法进行了船模实验验证。最后,针对某船的进水过程进行了仿真计算,横倾角时域变化曲线上的不连续点直观地表明了流量差值迭代算法的改变对进水过程仿真计算的影响。     

公共自行车动态调度系统需求预测模型研究

基于交通出行理论,将公共自行车需求分为直接需求和间接需求,并研究需求等待、转移和消退的变化规律.根据各租赁点的历史出行OD和以往时段的借、还车信息,预测出调度车辆从当前位置到达任意租赁点时该位置的车辆数,从而确定调度车数并制定调度计划,建立租赁点短期多时段的需求预测模型.将需求预测模型与调度计划模型组合成具有迭代反馈特性的双层模型,并通过计算机仿真方法求解,得到最优动态调度方案下的需求预测结果.通过算例对模型进行了验证,结果表明:公共自行车动态调度系统需求预测模型与调度计划模型结合后能有效改善公共自行车实际运营中借车时无车可借、还车时车位已满的情况.     

蝶形拱桥主梁的非线性行为及影响因素分析

蝶形拱桥造型独特其主梁部分的非线性行为规律相对其他拱桥较为难掌握,传统未充分考虑非线性影响的设计方法已不再适用.在自编程序的基础上,全面分析了各种非线性因素下蝶形拱桥主梁部分的非线性行为并研究了外倾角、矢跨比、含钢率等设计参数的影响及规律.结果表明:拱肋单元的梁柱效应对主梁弯矩的影响是不利的,而主梁单元的梁柱效应能够有效地抵消这种不利影响;主梁弯矩的非线性行为规律相对挠度更加复杂;未加载侧边梁的影响系数受偏载距离的影响较大;各梁跨中挠度和弯矩的影响系数均随主拱肋外倾角的增大而增大;主拱肋含钢率和索拱平面间夹角对主梁非线性行为的影响可以忽略.     

Viability of new road infrastructure with heterogeneous users

This paper explores the importance of heterogeneity in value of time and route choice when assessing the viability of new road infrastructure to alleviate congestion problems. The model incorporates strategic interaction between road operators in a cost-benefit framework and several competitive regimes are considered. It is then employed to establish the financial and socio-economic viability of a congestion pricing demonstration entering Madrid city centre, where road users have to choose between a free but highly congested road and a priced free-flowing road (semi-private regime). A logit estimation is undertaken with information from a questionnaire among road users in the Eastern Madrid area to obtain users’ value of time and of congestion.The tolls obtained generate a traffic reallocation towards the new roadway such that revenues suffice to render the infrastructure socio-economically viable. The private and the low toll regimes generate similar welfare gains that are close to the first best. Yet the former supposes large losses to users. The low toll and the semi-private regimes do not raise such distributional concerns. However, the low toll regime requires a sufficiently high traffic growth rate to make it financially viable; this does not happen for the other competitive regimes.     

五自由度船舶靠泊装置机构设计及运动分析

为提高船舶靠泊安全系数,减少大型船舶靠泊事故的发生,设计一种以两转动一平移3-RPU并联机构为主体结构的5自由度船舶靠泊装置。基于螺旋理论和修正G-K公式,计算出并联机构的自由度;利用齐次位姿变换建立各连杆矢量方程,推导出并联机构位置正反解数学表达式,基于位置反解表达式求出并联机构的雅克比矩阵,根据雅克比矩阵对3-RPU机构的三类运动学奇异性进行分析;建立机构驱动关节速度与动平台速度之间的关系,对正反解的研究结果进行数值验证,并运用MATLAB对位置和速度反解进行仿真;采用蒙特卡洛法求解并联机构的可达工作空间,并运用MATLAB编程绘制出工作空间三维图和截面图,验证了3-RPU并联机构的可行性,为3-RPU并联机构的应用提供理论依据。     

侧方扰动下圆柱体异步并联入水实验研究

为研究圆柱体低速并联入水的空泡演化特性,基于高速摄像方法,开展圆柱体单独入水和异步并联入水的实验研究,通过对比得到侧方扰动下并联双空泡的演化规律,并分析了入水时差对不同闭合方式空泡演化的影响。实验结果表明：侧方扰动的主要表现为次发圆柱体空泡对首发圆柱体空泡的排挤,其对首发圆柱体的影响远大于次发圆柱体,且在入水时差较小时次发圆柱体会使首发圆柱体空泡的喷溅薄膜提前回卷;对于深闭合空泡,随着入水时差的增大,首发圆柱体的空泡闭合时间增加,次发圆柱体空泡的不对称性增强,回射流的角度和高度均减小。对于表面闭合空泡,随着入水时差的增大,双空泡的闭合时间与首发圆柱体空泡的气团脱落时间都会推迟,侧方扰动对空泡闭合时间的影响减弱,在空泡闭合后,空泡的特征长度逐渐增大。     

采用平导超前和无轨运输方式的长大瓦斯隧道施工六阶段通风技术

合理的通风设计是降低隧道长距离穿越煤系地层时所面临的严峻瓦斯灾害风险的重要措施。文章针对成贵高铁老房子隧道长距离穿越高瓦斯地层时的通风难题,设计出一套随施工进度变化可进行调整的先压入后巷道式的六阶段通风方案,并采用Fluent软件模拟分析,最后以实际监测结果进行验证。结果表明,第四阶段通风效果最差,为通风最不利工况,该阶段隧道内瓦斯浓度均未超过0.5%的限值,其它阶段隧道内风流中最大瓦斯浓度为0.08%,所有指标均满足规范的要求。由此可知,六阶段通风方案通风效果良好,可为类似工程设计和施工提供良好的借鉴作用。     

Sustainability assessment of inland transportation in China: A triple bottom line-based network DEA approach

The transport sector accounts for nearly one third of the world’s total energy use, while inland transport alone is responsible for half of the global petroleum consumption. The expansion of motorization in newly industrialized economies necessitates setting realistic targets. To support decision-makers in better assessment of transport sustainability performance, we introduce a systematic triple bottom line-based approach to evaluate inland transport, considering social, economic, and environmental dimensions of sustainability. The proposed network data envelopment analysis (DEA) measure organizes the three components of the system into a parallel structure, allocates shared input across subsystems, and incorporates undesirable output. The empirical application determines the efficiency of regional inland transportation systems in China from 2006 to 2015. The results indicate a rise in overall transport efficiency between China’s 11th and 12th five-year development plan periods and link the economic growth with a decrease in environmental transport efficiency in the Central and Western zones and with a decline in social efficiency in the Eastern zone. Since 2012, the social sustainability remains the weakest component of inland transport, which requires special attention by policy-makers to support vulnerable groups of transport users. This study provides further insight into the investigated measures and proposes recommendations for the improvement of inland transport in China.