Roll-induced bifurcation in ship maneuvering under model uncertainty

In this paper, a mathematical model is developed for the maneuvering motion of a naval ship and bifurcations of its equilibrium are identified in roll-coupled motion. The subject ship is a high-speed surface combatant with twin-propeller twin-rudder system. Captive model tests are conducted for the ship using planar motion mechanism. Maneuvering coefficients are calculated by polynomial curve fitting of the test data. Uncertainty distribution in the coefficients is assumed same as that of the curve fitting errors. Uncertainty in the model coefficients is propagated to full-scale simulation results by the stochastic response surface method (SRSM). This method is computationally efficient as compared to standard Monte Carlo simulation technique. The SRSM uses polynomial chaos expansion of orthogonal to fit any probability distribution. Bifurcation analysis of the mathematical model is performed by varying the vertical center of gravity as the bifurcation parameter. Hopf bifurcation is identified. It is found that the bifurcations occur due to the coupling of roll motion with sway, yaw motion and rudder angle. In the presence of wind, roll angle response in bifurcation diagram is discussed.     

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货运车辆行车途中能否有安全便利的休息站,关系到联邦关于司机工作时间规定的执行及高效的车队运营.由于货运车辆的激增,中途停车站能力短缺问题日益凸显.本研究开发了一个基于互联网的地理信息系统,用于从用户大范围收集停车位短缺的地理信息.为了分析这些停车紧张点的地理分布,采用了点聚合和排名的方法来发现停车问题最严重的地区.另外,提出一种沿公路方向的单测度的聚合方法.其基本思路是,停车问题不是一个单点问题,而是一个区域性问题.缓解停车紧张,可通过增加区域性停车能力.本文发现能力紧张的区域通常在大都市的郊区,反映出很多长途司机在此停车等待第二天往市区内送货的运作规律.研究结果与来自公路巡警方面的观察结果一致.     

Auction-Based Congestion Pricing

Abstract

Planners, engineers and economists have introduced various demand management methods in an attempt to reduce the fast growing traffic congestion. The basic idea behind various demand management strategies is to force drivers to travel and use transportation facilities more during off-peak hours and less during peak hours, as well as to increase the usage of underutilized routes. In this paper, a new demand management concept – Auction-based Congestion Pricing – is proposed and modeled.     

Evaluation of travel demand strategies: a microscopic traffic simulation approach

This research investigates the design and impact of a new travel demand management approach, namely the Downtown Space Reservation System (DSRS), using a microscopic traffic simulation approach executed in VISSIM. The DSRS is part of a Travel Demand Management strategy that is designed to mitigate traffic congestion in a downtown urban setting. The simulation is conducted according to an experimental design procedure for a revised road network representing downtown Boise, Idaho. The issues that are tested in the simulation include: (1) whether the DSRS improves traffic performance when compared with the case without the DSRS; (2) how the DSRS performs compared with a reservation system that uses a First Come First Serve principle; and (3) how the specific DSRS parameters (such as, the relative importance of throughput versus revenue generation) influence network system performance. Conclusions and future research recommendations are provided based on the insights from the simulation modeling work.