An augmented Lagrangian origin‐based algorithm for link‐capacitated traffic assignment problem

The origin‐based algorithm is embedded into the augmented Lagrangian method for the link‐capacitated traffic assignment problem. In order to solve the “nonexistence” problem due to the second partial derivatives of the augmented Lagrangian function at some specific points, the approximate expressions of the second partial derivatives are amended in the origin‐based algorithm. The graph of last common nodes is developed on the basis of the restricted single‐origin network. A method is proposed for finding n–1 last common nodes of the restricted single‐origin network, resulting in computational complexity of O(n²) in finding last common nodes. Numerical analysis on the Sioux Falls network and Chicago Sketch network demonstrated the effectiveness and characteristics of the proposed algorithm. Copyright © 2014 John Wiley & Sons, Ltd.     

斜拱结构的强度及经济性探讨

探讨了竖直拱两种衍生形式——斜拱和出平面有约束斜梁的强度及经济性问题。通过斜拱平面内和平面外内力的比较,可以得出当跨度较大时,不宜采用斜拱面结构;通过竖直拱和斜拱在不同跨度下的应力比较,可以充分肯定竖直拱的经济性;通过斜拱在不同倾斜角下应力的比较,可以得出当角从45°增大到55°就可以大大减小斜拱出平面的内力。竖直拱的另一种衍生结构——出平面有约束斜梁,通过增加斜拱出平面方向的位移约束可以大大改善斜拱的内力,同时可以满足经济性的要求。最后还讨论了斜拱的曲线形状对结构内力的影响。     

城市轨道交通网络规划的站点布局标准探讨

为了提高轨道交通网络中站点分布规划的合理性，分析巴黎、东京等城市的轨道交通网络层次和站点分布特征，总结不同区域站点分布密度及不同线路站间距指标特性，从区域协调性、交通功能需求等角度，分析轨道交通网络站点合理分布的理论化，确定具体的规划指标和标准。表明轨道交通站点分布应系统考虑区域协调性，通过网络层面的覆盖率指标考量对出行需求的满足，以及轨道交通服务水平。     

A bi-level model of dynamic traffic signal control with continuum approximation

This paper proposes a bi-level model for traffic network signal control, which is formulated as a dynamic Stackelberg game and solved as a mathematical program with equilibrium constraints (MPEC). The lower-level problem is a dynamic user equilibrium (DUE) with embedded dynamic network loading (DNL) sub-problem based on the LWR model (Lighthill and Whitham, 1955; Richards, 1956). The upper-level decision variables are (time-varying) signal green splits with the objective of minimizing network-wide travel cost. Unlike most existing literature which mainly use an on-and-off (binary) representation of the signal controls, we employ a continuum signal model recently proposed and analyzed in Han et al. (2014), which aims at describing and predicting the aggregate behavior that exists at signalized intersections without relying on distinct signal phases. Advantages of this continuum signal model include fewer integer variables, less restrictive constraints on the time steps, and higher decision resolution. It simplifies the modeling representation of large-scale urban traffic networks with the benefit of improved computational efficiency in simulation or optimization. We present, for the LWR-based DNL model that explicitly captures vehicle spillback, an in-depth study on the implementation of the continuum signal model, as its approximation accuracy depends on a number of factors and may deteriorate greatly under certain conditions. The proposed MPEC is solved on two test networks with three metaheuristic methods. Parallel computing is employed to significantly accelerate the solution procedure.     

柔性基层永久变形试验研究

控制永久变形是柔性基层应用的关键。本文应用MTS试验机,对改良的级配碎石材料试件进行重复加载永久变形试验,通过对不同级配的试件在各应力水平下采集的永久变形量进行综合分析,得到级配碎石材料的永久变形规律。研究表明,级配碎石材料的永久变形随加载次数的增加而增加,主要永久变形在1000次重复加载后完成,级配是永久变形量的重要影响因素。     

基于学理性认知的高职院校校企文化融合探析

应用型人才培养模式呼唤校企合作,要破解校企合作模式植入中的瓶颈问题,必须实现校企文化的融合．文章从学理上构建了校企文化融合的基本理念,从文化学的角度分析了文化从文化接触、文化冲突到文化融合的过程．以期为校企文化实践提供有益借鉴,     

基于归约的几何约束求解策略

针对几何约束系统归约分解中高阶顶点的求解问题,提出高阶低代的低维数值迭代求解算法.通过去除部分约束,使得高阶顶点分解为含有欠约束顶点的低阶求解序列,对求解序列中的欠约束顶点添加虚拟参数变量,以虚拟参数变量的部分迭代求解,替代系统的整体数值求解,提高求解效率和稳定性,算法具有很强的通用性,并在实际应用中得到验证.     

粉细砂土填筑压实技术试验研究

通过室内及现场试验,对粉细砂土物理力学性质和压实工艺进行研究,结果表明:粉细砂土颗粒均匀集中,通过增加单位击实功的方法不能有效提高粉细砂土的最大干密度;粉细砂土对较高含水率具有很强的敏感性,且最优含水率右侧强于左侧;粉细砂土压缩至稳定所用时间很短,碾压过程较为省时;依靠增大碾压压力来提高粉细砂土压实度的方法不可行;粉细砂土的抗剪强度峰值随法向压力增大而提高;总结了粉细砂土有约束碾压的技术参数。     

General stochastic user equilibrium traffic assignment problem with link capacity constraints

This paper addresses a general stochastic user equilibrium (SUE) traffic assignment problem with link capacity constraints. It first proposes a novel linearly constrained minimization model in terms of path flows and then shows that any of its local minimums satisfies the generalized SUE conditions. As the objective function of the proposed model involves path‐specific delay functions without explicit mathematical expressions, its Lagrangian dual formulation is analyzed. On the basis of the Lagrangian dual model, a convergent Lagrangian dual method with a predetermined step size sequence is developed. This solution method merely invokes a subroutine at each iteration to perform a conventional SUE traffic assignment excluding link capacity constraints. Finally, two numerical examples are used to illustrate the proposed model and solution method.     

An optimization model for bus fleet replacement with budgetary and environmental constraints

ABSTRACT

As maintenance and operation costs increase with usage over time, equipment is replaced when the value of new equipment is more attractive. Some methods have been developed to solve this problem. In the public transport sector, such problems are frequently analyzed by fleet managers and determined by bus age restriction regulations. We propose an Integer Programming model that integrates both budgetary and environmental constraints (CO₂ emissions) which, as far as we know, have not previously been studied in conjunction. The study aims to determine the optimal replacement plan for a fleet of diesel buses of different size, age, maintenance costs and emissions rates, with new (less polluting) diesel buses over a time horizon of 50 years. The results indicate that it is possible to reduce emissions with a low annual budget using an optimal replacement policy.