Norm approximation method for handling traffic count inconsistencies in path flow estimator

Path flow estimator (PFE) is a one-stage network observer proposed to estimate path flows and hence origin–destination (O–D) flows from traffic counts in a transportation network. Although PFE does not require traffic counts to be collected on all network links when inferring unmeasured traffic conditions, it does require all available counts to be reasonably consistent. This requirement is difficult to fulfill in practice due to errors inherited in data collection and processing. The original PFE model handles this issue by relaxing the requirement of perfect replication of traffic counts through the specification of error bounds. This method enhances the flexibility of PFE by allowing the incorporation of local knowledge, regarding the traffic conditions and the nature of traffic data, into the estimation process. However, specifying appropriate error bounds for all observed links in real networks turns out to be a difficult and time-consuming task. In addition, improper specification of the error bounds could lead to a biased estimation of total travel demand in the network. This paper therefore proposes the norm approximation method capable of internally handling inconsistent traffic counts in PFE. Specifically, three norm approximation criteria are adopted to formulate three L_p-PFE models for estimating consistent path flows and O–D flows that simultaneously minimize the deviation between the estimated and observed link volumes. A partial linearization algorithm embedded with an iterative balancing scheme and a column generation procedure is developed to solve the three L_p-PFE models. In addition, the proposed L_p-PFE models are illustrated with numerical examples and the characteristics of solutions obtained by these models are discussed.     

基于NURBS的船体曲面自适应三角网格剖分

针对面向曲面的三维船体性能计算和真实感图形显示问题,应用NURBS曲线、曲面理论,提出一种新颖的船体NURBS曲面三角形网格自动生成算法,运用四角编码方法和改进的曲面片平坦性检验方法,保证在递归分割船体NURBS曲面时,能够快速有效地分割出四边形网格,在曲面片的高度方向和边界处同时满足给定的精度要求,在此基础上,应用割角剖分算法将一个四边形网格剖分成两个或多个三角形网格。应用结果表明,应用该算法生成的三角形平面片能够较好地逼近船体曲面,避免出现网格间的裂缝,与二叉树、四叉树方法相比,四角编码方法明显节省了时间和空间,提高了算法效率。     

Dynamic pricing for managed lanes with multiple entrances and exits

Priced managed lanes are increasingly being used to better utilize the existing capacity of the roadway to relieve congestion and offer reliable travel time to road users. In this paper, we investigate the optimization problem for pricing managed lanes with multiple entrances and exits which seeks to maximize the revenue and minimize the total system travel time (TSTT) over a finite horizon. We propose a lane choice model where travelers make online decisions at each diverge point considering all routes on a managed lane network. We formulate the problem as a deterministic Markov decision process and solve it using the value function approximation (VFA) method for different initializations. We compare the performance of the toll policies predicted by the VFA method against the myopic revenue policy which maximizes the revenue only at the current timestep and two heuristic policies based on the measured densities on the managed and general purpose lanes (GPLs). We test the results on four different test networks. The primary findings from our research suggest the usefulness of the VFA method for determining dynamic tolls. The best-found objective value from the method at its termination is better than other heuristics for all test networks with average improvements in the objective ranging between 10% and 90% for revenue maximization and 0–27% for TSTT minimization. Certain VFA initializations obtain best-found toll profiles within first 5–50 iterations which warrants computational time savings. Our findings also indicate that the revenue-maximizing optimal policies follow the “jam-and-harvest” behavior where the GPLs are pushed towards congestion in the earlier time steps to generate higher revenue in the later time steps, a characteristic not observed for the policies minimizing TSTT.     

NUCLEAR OPERATORS ON C（Ω，X）

ＮＵＣＬＥＡＲＯＰＥＲＡＴＯＲＳＯＮＣ（Ω，Ｘ）ＨｅＣｈｅｎ（ＤｅｐａｒｔｍｅｎｔｏｆＡｐｐｌｉｅｄＭａｔｈｅｍａｔｉｃｓ）ＡｂｓｔｒａｃｔＴｈｉｓｐａｐｅｒｉｓｔｏｄｅｃｉｄｅｔｈｅｎｕｃｌｅａｒｏｐｅｒａｔｏｒｏｎｔｈｅｓｐａｃｅｏｆｖｅｃｔｏｒ...     

一类双线性规划的线性逼近算法

讨论了一类双线性规划的优化问题，利用对偶原理，将双线性规划问题转化为极大极小问题，研究了该极大极小问题的线性逼近算法，并证明了该算法在有限步内收敛，采用Karmarkar算法优化初始迭代点，使线性逼近算法更为有效。     

巴尔姆流的模拟与应用

巴尔姆流是交通运输生产与控制过程中普遍存在的一种事件流 ;通过对巴尔姆流的模拟 ,提出了一种将排队服务系统马尔可夫化的方法 ;运用该方法能科学定量地分析排队服务系统的各项运营指标 ;所提出的理论在交通运输生产过程与控制的研究中有广泛的应用价值     

基于阻力和伴流不均匀度的多用途船型线优化

为探究多用途船首尾型线变化对船舶水动力性能的影响,采用RBF(Radial Basis Functions)曲面变形方法分别对多用途船首尾型线进行变换,使用优化拉丁超立方法设计计算样本,引入Kriging近似模型解决传统CFD计算耗时的问题。在此基础上,以船舶的阻力性能以及桨盘面伴流不均匀度作为优化目标,利用带精英策略的非支配排序遗传算法(NSGA-Ⅱ)完成整个型线优化流程。计算结果表明,对于该多用途船,船首形状朝V型发展有利于减小兴波阻力,船尾的V型横剖面在接近推进器处逐渐向U型转变,可以在获得更均匀伴流场的同时对阻力性能影响较小。     

Capacity investment model for airport facilities under demand uncertainty

This paper addresses strategic airport facility planning under demand uncertainty. Existing studies are improved by (1) allowing capacity contraction and (2) adopting more flexible delay functions. A mixed‐integer nonlinear program, which incorporates scale economies in construction, time value of money, nonlinear congestion effect, and other factors, is proposed for optimizing the capacity expansion/contraction decisions over time for multiple airport components. The stochastic problem is converted into its deterministic equivalent because the number of demand scenarios considered is finite. A discrete approximation technique is used to remove the nonlinearities. Numerical studies are presented to demonstrate the capability of the proposed model and the computational efficiency of the solution method. The “Flaw of Averages” due to faulty decisions based on the average future condition is illustrated, and trade‐offs among various costs are discussed in the numerical analyses. Copyright © 2016 John Wiley & Sons, Ltd.     

船舶回转性能分析

在对船舶作回转性能分析时，采用战术直径表征其他回转特征量，计算出不同舵角、航速、纵倾及排水体积下的回转圈战术直径。衡量各因素对战术直径的影响程度，总结战术直径随各因素变化的规律，得到不同排水量之间战术直径的简化算法，为试航回转试验的特征量从设计吃水转化为满载吃水提供了一种较简捷的近似换算方法。     

Adaptive sliding control of active suspension systems with uncertain hydraulic actuator dynamics

An adaptive sliding controller is proposed in this article to control the active suspension systems of a quarter-car model with hydraulic actuator. The highly nonlinear actuator dynamics is assumed to have some time-varying uncertainties with unknown bounds. Owing to its time-variant nature, traditional adaptive designs are not feasible. As the variation bounds are not given, the conventional robust controllers cannot be applied either. In this article, we use the function approximation technique to represent the uncertainties with finite combinations of some basis functions, and the Lyapunov method is employed to find update laws for the coefficients of the approximating series. The actuator force can track the desired force generated from the skyhook dynamics with ultimately bounded performance. If a sufficient number of basis functions are used and the approximation error can be ignored, asymptotic convergence performance can be proved. If the bound of the approximation error is available, asymptotic convergence of the output error still can be obtained with some modifications of the proposed control law. Simulation results show that the controller proposed can give significant improvement of ride comfort when compared with the performance of its passive counterpart.