Model uncertainty and the management of a system of infrastructure facilities

The network-level infrastructure management problem involves selecting and scheduling maintenance, repair, and rehabilitation (MR&R) activities on networks of infrastructure facilities so as to maintain the level of service provided by the network in a cost-effective manner. This problem is frequently formulated as a Markov decision problem (MDP) solved via linear programming (LP). The conditions of facilities are represented by elements of discrete condition rating sets, and transition probabilities are employed to describe deterioration processes. Epistemic and parametric uncertainties not considered within the standard MDP/LP framework are associated with the transition probabilities used in infrastructure management optimization routines. This paper contrasts the expected costs incurred when model uncertainty is ignored with those incurred when this uncertainty is explicitly considered using robust optimization. A case study involving a network-level pavement management MDP/LP problem demonstrates how explicitly considering uncertainty may limit worst-case MR&R expenditures. The methods and results can also be used to identify the costs of uncertainty in transition probability matrices used in infrastructure management systems.     

RECENT RESEARCH AND DEVELOPMENT OF POLYMER OPTICAL FIBRES

ＲＥＣＥＮＴＲＥＳＥＡＲＣＨＡＮＤＤＥＶＥＬＯＰＭＥＮＴＯＦＰＯＬＹＭＥＲＯＰＴＩＣＡＬＦＩＢＲＥＳ＊ＧＤＰｅｎｇ（彭刚定）ＰＬＣｈｕ（朱柏濂）（ＳｃｈｏｏｌｏｆＥｌｅｃｔｒｉｃａｌＥｎｇｉｎｅｅｒｉｎｇ，Ｕｎｉｖ．ｏｆＮｅｗＳｏｕｔｈＷａｌｅｓ，Ｋ...     

A Simplified Framework for String Stability Analysis of Automated Vehicles*

Automated vehicles traveling in platoons must exhibit stability both individually and as a group, a property referred to as “string stability”. We propose a new framework for evaluating the longitudinal string stability properties of platoons of automated vehicles. In this framework, the platoon is considered to be a mass-spring-damper system with linear characteristics. The resulting closed-loop representation yields transfer functions and impulse responses that can be analyzed to determine the string stability properties of the platoon. This framework facilitates qualitative comparisons of the effects of various controller characteristics, such as time headway and intervehicle communication, on string stability.     

National-flag shipping: An appraisal of policy options from a Canadian perspective

In this paper the author reviews recent developments in Canadian government policy with regard to national-flag shipping. In response to criticism from various marine interest groups that successive governments have done little to encourage the development of national-flag shipping, federal administrations have taken a more active part in the debate. This has been manifest in several reports produced under the auspices of Transport Canada, which discuss the desirability of using selective tax or fiscal incentives to promote investment in Canadian shipping. The author outlines the arguments for expanding national-flag shipping, relating these to the greater question of what effect these proposed financial measures might have on the use of capital and other resources. He concludes that selective preferential taxation may be justified by the repatriation of shipping activities now offshore and avoidance of further shifts of manpower and capital offshore.     

A simulation study for the logistics planning of a container terminal in view of SCM

This paper aims to apply a supply-chain modelling and its analysis framework to the supply chain in the port industry. The simulation approach serves two purposes: to model a supply-chain network in quantity approach and to evaluate its supply-chain performance based on proposed strategies. Through the modelling works to improve the performance, components of simulation model, such as input model, strategy model, operational policy model and performance model, in the port supply chain were identified. The effects of various strategies can guide the way to administrate the supply chain in the different objectives.     

Long-memory characteristics of urban roadside air quality

Carbon monoxide is a major contributor to air pollution in urban cities, particularly at the roadside. Hourly, monthly and seasonal mean carbon monoxide concentration data are collected from a roadside air monitoring station in Hong Kong over 7-years. The station is a few metres from a major intersection surrounded by tall buildings. In particular, hourly patterns of concentrations on different days of the week are investigated. The data show that hourly carbon monoxide concentrations resemble the traffic pattern of the area and tend to be lower in the summer. Using a seasonal autoregressive integrated moving average models shows that the daily traffic cycle strongly influences concentrations. Further, it is found that urban roadside carbon monoxide monitoring data exhibits a long-memory process, suggesting that a model incorporating long memory and seasonality effects is needed simulate urban roadside air quality.     

Experimental study on mobility of a vehicle with CTIS in soft soil

Recently, the domestic military vehicles currently being developed are installed with a central tire inflation system (CTIS) to control the pressure of tires to increase the contact area between the tires and the ground and improve mobility on soft soils. On the other hand, it is difficult to find technical data based on experiments for designing a CTIS. In this study, to obtain the technical data to set proper pressures according to road conditions a range of mobility tests were performed on soft soil roads, such as sand and clay, according to the CTIS operating modes to obtain the technical data to set proper pressures according to the road conditions. The characteristics of the mobility and its correlation with the tire pressures in each operating mode were analyzed. The results confirmed that a wheeled vehicle with a CTIS showed better performance on soft soil than a vehicle without a CTIS.