Effects of countdown timers on queue discharge characteristics of through movement at a signalized intersection

This study investigates how countdown timers installed at a signalized intersection affect the queue discharge characteristics of through movement during the green phase. Since the countdown timers display the time remaining (in seconds) until the onset of the green phase, drivers waiting in the queue at the intersection are aware of the upcoming phase change, and are likely to respond quicker. Thus, the countdown timers could reduce the start-up lost time, decrease the saturation headway, and increase the saturation flow rate. This study observed vehicle flow at an intersection in Bangkok for 24 h when the countdown timers were operating, and for another 24 h when the countdown timers were switched off. The signal plans and timings remained unchanged in both cases. Standard statistical t-tests were used to compare the difference in traffic characteristics between the “with timer” and “without timer” cases. It was found that the countdown timers had a significant impact on the start-up lost time, reducing it by 1.00–1.92 s per cycle, or a 17–32% time saving. However, the effects on saturation headway were found to be trivial, which implies that the countdown timers do not have much impact on the saturation flow rate of signalized intersections, especially during the off-peak day period and the late night period. The savings in the start-up lost time from the countdown timers was estimated to be equivalent to an 8–24 vehicles/h increase for each through movement lane at the intersection being studied.     

Multi‐objective highway alignment optimization using a genetic algorithm

The available highway alignment optimization algorithms use the total cost as the objective function. This is a single objective optimization process. In this process, travel‐time, vehicle operation accident earthwork land acquisition and pavement construction costs are the basic components of the total cost. This single objective highway alignment optimization process has limited capability in handling the cost components separately. Moreover, this process cannot yield a set of alternative solutions from a single run. This paper presents a multi‐objective approach to overcome these shortcomings. Some of the cost components of highway alignments are conflicting in nature. Minimizing some of them will yield a straighter alignment; whereas, minimizing others would make the alignment circuitous. Therefore, the goal of the multiobjective optimization approach is to handle the trade‐off amongst the highway alignment design objectives and present a set of near optimal solutions. The highway alignment objectives, i.e., cost functions, are not continuous in nature. Hence, a special genetic algorithm based multi‐objective optimization algorithm is suggested The proposed methodology is demonstrated via a case study at the end.     

高速公路合理收费标准确定方法研究

随着投入运营的时间增加,高速公路运营管理中的矛盾日益突出,如何确定科学合理的道路收费率,成为道路经营者普遍关注的问题。在收费标准基本模型的基础上提出了收费标准方案评估模型,利用判断矩阵选择最佳方案,并制定了相应的收费标准的动态调整方法。     

船舶动力定位系统

船舶动力定位技术在航运业具有举足轻重的地位.介绍动力定位技术的发展历史,系统的结构组成、工作原理和工作模式,提出了动力定位技术的研究热点.     

创新设计、资源节约、环境友好和低碳发展的长江口深水航道治理工程

介绍了长江口深水航道治理工程创新的治理理念、设计方案、施工技术和科学的动态管理方法,同时还介绍了该工程在资源节约、环境友好及促进低碳发展方面采取的措施和取得的效果。     

高频雷达信号的双线性时频分布性能研究

针对海杂波背景下高频地波雷达的目标探测问题,采用时频分析方法研究对海杂波中的非平稳多分量目标探测。讨论了海杂波背景下的目标检测问题,以及信号的双线性时频分布,通过仿真研究了时频分布性能,尤其是核函数抑制多分量目标的交叉项作用。仿真结果显示,伪Wigner-Ville分布较Wigner-Ville分布对于交叉项的抑制作用较大,而平滑伪Wigner-Ville分布降低交叉项的效果更好。     

舰用齿轮箱抗冲击能力时域计算

为找出舰船设备的潜在问题或薄弱环节，从而保证舰船的战斗力；以及为避免由于对设备的抗冲击性能不了解即进行冲击试验可能对设备造成的损坏，抗冲击数值模拟分析对于舰用设备是必要的。对舰用齿轮箱抗冲击能力进行时域数值模拟，使用MDT软件建立齿轮箱三维几何模型，利用HyperMesh软件进行前处理以及有限元网格划分，并将有限元模型导入ABAQUS软件，对齿轮箱抗冲击能力进行时域计算。分析数值模拟结果得到了齿轮箱典型部位处冲击响应，总结了齿轮箱抗冲击的一些规律，并找出了齿轮箱结构抗冲击的薄弱环节，为齿轮箱结构优化设计提供了参考。     

一种螺旋桨参数化建模方法

对螺旋桨进行优化时,需要建立起优化计算的样本空间,即要实现初始桨的参数化建模。本文基于贝塞尔曲线拟合原理编程实现了螺旋桨的参数化建模,对螺旋桨的径向参数分布分别用一条贝塞尔曲线进行拟合,曲线的控制点通过遗传算法寻优求得。文中以4382桨为例,对其进行参数化建模,讨论了三、四、五、六阶贝塞尔曲线的拟合效果,发现三阶贝塞尔曲线拟合光顺性最好、拟合平均误差可以控制在0.3%以内,而且控制点个数较少,最适合拟合螺旋桨径向参数分布。最后通过调整三次贝塞尔曲线控制点的位置调整了原桨叶的几何形状,得到光顺性较好的新桨叶模型,表明该参数化建模方法合理。     

船舶六自由度转台电液伺服系统参数整定方法

针对船舶六自由度转台电液伺服系统的参数整定问题,提出一种基于多目标遗传算法和多属性决策的PID参数设计方法,综合考虑了系统超调量、稳定时间和ITAE指标,采用多目标遗传算法求出Pareto最优解。使用客观赋权的信息熵法对最优解的属性进行权值计算,然后采用逼近理想解的排序方法（TOP—SIS）进行多属性决策（MADM）研究。计算了转台电液伺服控制的数值算例,结果表明本文提出的联合方法通用性好,所设计的PID性能优异,适合工程实际应用。     

行星齿轮传动齿根动应力计算

针对功率分流行星齿轮传动齿轮重合度大,齿根应力计算工作量大的问题,对齿根动应力的计算问题进行了详细的研究。并以功率分流差动级太阳轮为例,对模型的建立方法、网格的划分方法、载荷的施加方法进行了详细的分析。利用Ansys中的APDL语言形成载荷文件,来控制在1个啮合周期内若干对接触线位置上载荷的施加。本文的计算方法可以精确、快速地得到1个齿在啮合过程中齿根的动应力。