Optimization of mid-block pedestrian crossing network with discrete demands

In many cases, pedestrian crossing demands are distributed discretely along an arterial segment. Demand origins, destinations and crosswalks comprise a pedestrian crossing network. An integrated model for optimizing the quantity, locations and signal settings of mid-block crosswalks simultaneously is proposed to best trade-off the operational performances between pedestrians and vehicles. Pedestrian behavior of choosing crosswalks is captured under a discrete demand distribution. Detour distance and delay at signalized crosswalks are formulated as a measure of pedestrian crossing cost. Maximum bandwidths are modeled in analytical expressions as a measure of vehicular cost. To solve the proposed model, the Non-dominated Sorting Genetic Algorithm II (NSGA II) based algorithm is designed and employed to obtain the Pareto frontier efficiently. From the numerical study, it is found that there exists an optimal number of mid-block crosswalks. Excess available crosswalks may make no contributions to improvement in pedestrian cost when the constraint of the minimum interval between crosswalks and vehicular cost are taken into account. Two-stage crosswalks are more favorable than one-stage ones for the benefits of both pedestrian and vehicles. The study results show promising properties of the proposed method to assist transportation engineers in properly designing mid-block crosswalks along a road segment.     

Investigating the nature and impact of reporting bias in road crash data

This paper investigates the nature, and impact of the reporting bias associated with the police-reported crash data on inferences made using this data. In doing so, we merge a detailed emergency room data and police-reported crash data for a specific region in Denmark. To disentangle potentially common observable and unobservable factors that affect drivers’ injury severity risk and their crash reporting behavior, we formulate a bivariate ordered-response probit model of injury severity risk and crash reporting propensity. To empirically identify the reporting bias in this joint model, we exploit an exogenous police reform that particularly affects some specific municipalities of the region under consideration. The empirical analysis reveals substantial reporting bias in the commonly used police-reported road crash data. This non-random sample selection associated with the police-reported crash data leads to biased estimates on the effect of some of the explanatory variables in injury severity analysis. For instance, estimates based on the police-reported crash data substantially underestimate the effectiveness of seat belt use in reducing drivers’ injury severity risk.     

中高职衔接道路桥梁工程技术专业教学标准探索与实践

通过3年的中高职衔接试点的工作,制定出了中高职衔接、一体化道路桥梁工程技术专业三二分段教学标准与课程标准,总结出一条行之有效的中高职衔接的人才培养途径,供相同或相近的专业在建设时借鉴或参考。     

Optimizing train operational plan in an urban rail corridor based on the maximum headway function

The train operational plan (TOP) plays a crucial role in the efficient and effective operation of an urban rail system. We optimize the train operational plan in a special network layout, an urban rail corridor with one terminal yard, by decomposing it into two sub-problems, i.e., the train departure profile optimization and the rolling stock circulation optimization. The first sub-problem synthetically optimizes frequency setting, timetabling and the rolling stock circulation at the terminal without a yard. The maximum headway function is generated to ensure the service of the train operational plan without considering travel demand, then we present a model to minimize the number of train trips, and design a heuristic algorithm to maximize the train headway. On the basis of a given timetable, the rolling stock circulation optimization only involves the terminal with a yard. We propose a model to minimize the number of trains and yard–station runs, and an algorithm to find the optimal assignment of train-trip pair connections is designed. The computational complexities of the two algorithms are both linear. Finally, a real case study shows that the train operational plan developed by our approach enables a better match of train headway and travel demand, and reduces the operational cost while satisfying the requirement of the level of service.     

基于Vega Prime的ROV柔性脐带缆动态模拟

模拟柔性脐带缆在深海作业环境中的动态形态变化是构建遥控潜器（ROV）作业视景仿真系统的重点和难点之一。由于柔性脐带缆在海流作用下受力情况复杂、运动形态多变,利用现有成熟的视景仿真软件难以做到逼真模拟。采用凝聚参数法建立柔性脐带缆的模型、运动方程及变长度算法并进行仿真求解,结合所得数值解,利用OpenGL语言和纹理映射技术动态绘制柔性脐带缆三维模型,并将柔性脐带缆动态模型与在Vega Prime平台建立的ROV主体进行衔接,获得了逼真的柔性脐带缆跟随ROV运动的动态模拟效果。     

贝壳砂颗粒破碎及抗剪强度研究

对贝壳砂的的破碎机抗剪强度进行了系统的研究。在原有颗分曲线的形式上,对其进行创新,提出了相对颗分曲线,能够直观地反映出颗粒破碎过程中某一粒径内颗粒含量的变化,也能较为简单地表达出颗粒破碎程度。此外,对贝壳砂的固结排水和不排水强度进行了系统的分析,指出在颗粒破碎过程中,粘聚力对颗粒破碎的影响较内摩擦大,而在应力应变过程中,内摩擦角对峰值应力的影响占据了主动地位。当相对密度及围压相同时,固结排水达到峰值应力差要比固结不排水大很多。     

Effects of small-scale turbulence on the growth of two diatoms of different size in a phosphorus-limited medium

The effect of turbulence on the nutrient flux towards osmotrophic cells is predicted to be size dependent. This should translate into growth. We experimentally followed and modelled the growth of two marine diatoms of different size (Thalassiosira pseudonana, 6 μm in diameter and Coscinodiscus sp., ca. 109 μm in diameter) under still water and turbulent conditions, using a shaker table. Experiments were done with phosphorus-limited cultures and lasted for ca. 5 days. Turbulence enhanced the growth of Coscinodiscus sp. in agreement with theory but not the growth of T. pseudonana, which was actually slightly lower under turbulence. At the end of the experiments there were about 1.7 times as many Coscinodiscus sp. cells in the turbulent treatment than in the still treatment, while for T. pseudonana almost the same cell concentration was found in both conditions. In addition, the Coscinodiscus sp. cells growing under still conditions presented a higher specific alkaline phosphatase activity than those growing in turbulence which indicates a higher need for phosphorus in the still cultures. A simple dynamic model, based on Michaelis–Menten nutrient uptake kinetics, needed nearly no optimisation other than using observed initial conditions of phosphate and cell concentrations. The model showed how an increased nutrient flux towards the cells translates non-linearly into cell growth, most likely by affecting the half-saturation constant (K_M). However, since Coscinodiscus sp. experienced significant mortality and cells partially settled to the bottom of the containers, unequivocal support for the size-dependent effect of turbulence on nutrient uptake will require further experiments and more sophisticated modelling. The mechanisms to connect an increased nutrient flux towards cells with population growth and whether this process is size dependent are important in parameterizing the effects of turbulence on marine plankton in coupled physical–biological models.     

加筋土桥台筋带最大拉力试验研究

通过室内大比例模型试验,研究自重作用下加筋土桥台的最大筋带拉力的变化规律。加筋土桥台最大筋带拉力作用线的上部是离面板约为墙高0.2倍左右距离的垂直顶面的直线,下部渐渐向面板靠拢,近似为一条以面板顶点为极点的对数螺旋线。最大筋带拉力上部(垂线段)较大,下部渐小。基于试验结果与现场实测结果,提出最大筋带拉力与对应最大筋带拉力作用线距面板的水平距离成正比的计算模型。与其他理论及实验结果的比较表明,该计算模型对最大筋带拉力的预测能有效地反映刚性面板影响,能更准确地预测实际的最大筋带拉力,其预测值与实测结果的误差只有14%,而其他理论预测值与实测结果的误差均大于50%。     

VBA编程在土工击实试验中的应用

土工试验技术人员面对大量击实试验数据,采用手工描点、曲线尺绘图的办法,不仅工作量大繁琐,并且极易受个人因素影响,得出的试验结果可信度较差。本文直接在工程实际使用的击实试验电子表格中添加计算控件,应用数值分析的最小二乘法编写VBA程序,对土工击实试验数据进行高次方的曲线拟合处理,求解出曲线的趋势方程及相关系数,进一步求解出最优含水率和最大干密度。本方法使对土工试验数据整理与计算变得直观、方便、准确,而且可方便地移植到其他电脑中,能帮助土工试验人员准确高效地处理击实试验数据,减少计算误差。     

高炉渣改良填料大型直剪试验分析

将原状高炉渣掺拌粉煤灰分层碾压并重锤夯实作为换填地基的填料,进行分层取样后,以处于干、湿状态下各层土样的混和土作为试样开展大型直剪试验。为了探究高炉渣改良填料的直剪力学特性,以及现有大型直剪仪的不足,对不同法向应力作用下试样的抗剪强度、法向加载板的竖向位移进行了量测,并对试验过程中剪力与剪切位移曲线特性、剪切盒张开状态、完成直剪试验后试样的破碎状态进行了分析。结果表明:因细颗粒不足以填充粗颗粒之间的孔隙,含水量对改良填料力学指标影响很小,改良填料表现为良好的水稳定性;高炉渣改良填料在法向应力小于150kPa时几乎没有黏聚力,而在法向应力大于150kPa时表现出咬合黏聚力;高炉渣混合料直剪试验过程中法向应力越大,初期剪缩量越大,后期剪胀量越小,发生剪胀时对应的剪切位移也越大;在法向应力大于150kPa后,直剪试验的剪胀量有了较大程度的减小,此时剪切面的形成主要以剪切区粗颗粒的剪碎与断裂为主。最后,考虑到现有大型直剪仪随着剪切位移的增加,理论剪切面上的剪切应力与法向应力分布越来越不均匀,且有效剪切面积逐渐减小,为此对大型直剪仪提出了改进建议,使有效剪切面面积保持恒定不变,测试结果与实际情况更加接近,可提高粗颗粒土剪切强度的测试精度。