On the fundamental diagram and supply curves for congested urban networks

Macroscopic fundamental diagrams (MFD) of traffic for some networks have been shown to have similar shape to those for single links. They have erroneously been used to help estimate the level of travel in congested networks. We argue that supply curves, which track vehicles in their passage through congested networks, are needed for this purpose, and that they differ from the performance curves generated from MFD. We use a microsimulation model, DRACULA and two networks, one synthesizing the network for Cambridge, England, and one of the city of York, England, to explore the nature of performance curves and supply curves under differing patterns of demand.We show that supply curves differ from performance curves once the onset of congestion is reached, and that the incorrect use of performance curves to estimate demand can thus seriously underestimate traffic levels, the costs of congestion, and the value of congestion relief measures. We also show that network aggregated supply curves are sensitive to the temporal distribution of demand and, potentially, to the spatial distribution of demand. The shape of the supply curve also differs between origin–destination movements within a given network.We argue that supply curves for higher levels of demand cannot be observed in normal traffic conditions, and specify ways in which they can be determined from microsimulation and, potentially, by extrapolating observed data. We discuss the implications of these findings for conventional modelling of network management policies, and for these policies themselves.     

水下隧道合理覆盖层厚度的有限元模拟研究

水下隧道覆盖层厚度目前基本上是凭经验确定的,采用不同的经验公式得到的计算结果差异很大。文章针对目前情况提出了采用有限元的求解方法,并结合公路隧道施工规范,模拟了拟建的重庆朝天门两江隧道在不同隧道覆盖层厚度时的拱顶位移和拉应力的分布及大小。通过与标准隧道的比较,得出了该隧道的合理覆盖层厚度,对同类工程有一定的参考价值。     

基于数码摄影技术的隧道围岩变形非接触量测方法研究

基于数码摄影技术的隧道围岩变形非接触量测法是一种与传统测量完全不同的新方法,具有设备简单、不干扰施工、自动化程度高等特点,能更好地满足现在长大隧道各种技术要求。文章对数码摄影测量技术原理及其实现过程进行了比较全面的研究,并对现场试验获取的测量数据加以分析,得到了较好的结论。该方法为地下工程量测技术开辟了一条新的途径。     

Storage space allocation in container terminals

Container terminals are essential intermodal interfaces in the global transportation network. Efficient container handling at terminals is important in reducing transportation costs and keeping shipping schedules. In this paper, we study the storage space allocation problem in the storage yards of terminals. This problem is related to all the resources in terminal operations, including quay cranes, yard cranes, storage space, and internal trucks. We solve the problem using a rolling-horizon approach. For each planning horizon, the problem is decomposed into two levels and each level is formulated as a mathematical programming model. At the first level, the total number of containers to be placed in each storage block in each time period of the planning horizon is set to balance two types of workloads among blocks. The second level determines the number of containers associated with each vessel that constitutes the total number of containers in each block in each period, in order to minimize the total distance to transport the containers between their storage blocks and the vessel berthing locations. Numerical runs show that with short computation time the method significantly reduces the workload imbalance in the yard, avoiding possible bottlenecks in terminal operations.     

桃树坪隧道、胡麻岭隧道第三系富水粉细砂层围岩含水率与稳定性关系浅析

文章通过对桃树坪隧道、胡麻岭隧道第三系富水粉细砂岩地层开挖后不降水、先开挖后降水、先降水后开挖三种情况下围岩含水率、围岩稳定性现场监测结果,分析得出围岩含水量变化规律和围岩稳定性与含水量之间的关系及其规律,为制定降水及开挖方案提供了重要依据。     

海底盾构隧道孤石爆破预处理关键技术

文章针对基于孤石形状、分布位置的随机性及其高强度,盾构机无法直接掘进通过这一工程难题,在前期物探及钻孔验证的基础上,对钻孔参数和爆破方案设计进行了分析;通过采用对临近隧洞爆破震动跟踪监测和爆破后炮孔取芯验证的方法,总结出了一套针对海底盾构区间孤石爆破预处理的施工方法.     

A link-node complementarity model and solution algorithm for dynamic user equilibria with exact flow propagations

In this paper, we propose a link-node complementarity model for the basic deterministic dynamic user equilibrium (DUE) problem with single-user-class and fixed demands. The model complements link-path formulations that have been widely studied for dynamic user equilibria. Under various dynamic network constraints, especially the exact flow propagation constraints, we show that the continuous-time dynamic user equilibrium problem can be formulated as an infinite dimensional mixed complementarity model. The continuous-time model can be further discretized as a finite dimensional non-linear complementarity problem (NCP). The proposed discrete-time model captures the exact flow propagation constraints that were usually approximated in previous studies. By associating link inflow at the beginning of a time interval to travel times at the end of the interval, the resulting discrete-time model is predictive rather than reactive. The solution existence and compactness condition for the proposed model is established under mild assumptions. The model is solved by an iterative algorithm with a relaxed NCP solved at each iteration. Numerical examples are provided to illustrate the proposed model and solution approach. We particularly show why predictive DUE is preferable to reactive DUE from an algorithmic perspective.     

改进振动法在地下工程动力时程计算中的应用

地下工程受到周围土体的约束作用,其动力反映与地面工程有所区别,如将源于地面工程的振动法用于地下工程的动力时程计算分析,需要进行相应的改进.文章通过计算分析发现,振动法用于地下工程动力时程计算时,在计算模型边界条件和波动传播时间效应方面不能反映波动对地下工程作用的实质;通过对比分析,在这两个方面对常规振动法进行了改进;提出了适用于地下工程动力时程计算的改进振动法.该方法的计算模型采用左右两侧粘弹性底部固定的人工边界条件,波动输入采用能够反映波动传播时间效应的分层加速度动态输入法,其计算分析结果与理论解吻合较好,适用于地下工程的动力时程计算分析.     

隧道岩溶病害危险性分区在超前地质预报中的应用

针对厦蓉高速公路沙井街隧道岩溶的发育特点,提出了“隧道岩溶病害危险性分区”概念,并应用于超前地质预报工作中;根据中导洞开挖揭露的地质条件,对隧道岩溶病害危险性分区进行了修正,以指导主洞的超前预报工作,从而提高了预报工作的针对性并突出了重点;同时,基于高密度电法对不同介质电阻率的敏感性,在预报方法上将地表高密度电法与洞内地质雷达法相结合,提高了对重大岩溶病害预报的准确性.实际开挖结果显示:超前地质预报结果与实际情况高度吻合.     

软土隧道岩体参数正交反演分析

岩体参数是影响隧道安全性分析的关键因素,参数的确定往往依借助于现场监测数据和数值模拟手段。文章依托隧道多点位移计现场监测数据和有限元数值计算,以误差平方和为目标函数,提出了参数正交反演分析方法,与其它方法相比,该方法具有较高的精度和效率。计算结果表明,以围岩位移为基准的参数正交反演分析方法是可行的,研究结果可供同类地下工程施工和设计参考。