美国铁路车钩缓冲装置的发展(待续)

介绍美国铁路车钩缓冲装置的发展过程、结构特点及运用情况。     

Modelling forward freight rate dynamics—empirical evidence from time charter rates

The purpose of this paper is to investigate the dynamics of forward freight rate dynamics. We specify our model in a Heath–Jarrow–Morton framework. This model was originally developed for interest rate markets and, in subsequent work, the model has been applied to various commodity markets. We analyse ten years of weekly time charter (TC) rates for a Panamax 65,000?dwt bulk carrier. Our data set consists of 6-, 12- and 36-month TC rates. We use this data to construct, each day, a forward rate function using a smoothing algorithm. We use the smooth data to investigate the factors governing the dynamics of the forward freight rate curve. We find a strange volatility structure in the data. Out results show that the volatility of the forward curve is bumped, with volatility reaching a peak for freight rates with roughly one year to maturity. Also, correlations between different parts of the term structure are in general low and even negative.     

The applicability of hydrofoils as a ship control device

Centrifugal forces are commonly created when ships turn, which may cause a ship to capsize in a critical situation. A mathematical model has been developed to optimize the stability coefficients for ship, with the aim to prevent capsizing and to increase ship maneuverability in high-speed water craft. This model can be used to develop algorithms for control system improvement. The mathematical model presented in this paper optimized the use of multipurpose hydrofoils to reduce heeling and the trimming moment, maintaining an upright ship’s position and lessening the resistance via transverse force. Conventionally, the trimming and heeling of a ship are controlled using ballast water; however, under variable sea conditions it is sometimes difficult to control a ship’s motion using ballast water. In this case, a hydrofoil would be more stable and maneuverable than a ballast tank controlled vessel. A movable hydrofoil could theoretically be adapted from moveable aerofoil technology. This study proves the merit of further investigation into this possibility.     

Dynamic adaptive finite element analysis of acoustic wave propagation due to underwater explosion for fluid-structure interaction problems

In this paper, an investigation into the propagation of far field explosion waves in water and their effects on nearby structures are carried out. For the far field structure, the motion of the fluid surrounding the structure may be assumed small, allowing linearization of the governing fluid equations. A complete analysis of the problem must involve simultaneous solution of the dynamic response of the structure and the propagation of explosion wave in the surrounding fluid. In this study, a dynamic adaptive finite element procedure is proposed. Its application to the solution of a 2D fluid-structure interaction is investigated in the time domain. The research includes: a) calculation of the far-field scatter wave due to underwater explosion including solution of the time-depended acoustic wave equation, b) fluid-structure interaction analysis using coupled Euler-Lagrangian approach, and c) adaptive finite element procedures employing error estimates, and re-meshing. The temporal mesh adaptation is achieved by local regeneration of the grid using a time-dependent error indicator based on curvature of pressure function. As a result, the overall response is better predicted by a moving mesh than an equivalent uniform mesh. In addition, the cost of computation for large problems is reduced while the accuracy is improved.     

Dependability as a measure of on-time performance of personal rapid transit systems

A comprehensive method for calculating and measuring Dependability of Personal Rapid Transit systems is derived and compared with the more common measure called Availability. Availability is the percentage of all revenue trips that are completed without interruption. It does not take into account the duration of delays of the passengers because of the diffiiculty of gathering the necessary information in conventional transit systems. In PRT systems, vehicle-hours of travel and of delay relate in a statistically simple way to person-hours of travel and of delay. Therefore, in such systems, it is practical to use the performance measure called Dependability that takes into account the inconveince of people as a result of delays. To form a bridge to present practice, it is recommended that both measures be calculated and compared in forthcoming PRT systems. With today's computer systems, this is easily accomplished.     

Quantitative assessment of effect of enforcement intensity on violation rates of vehicle weight and dimension regulations

A theory of upper bound limit describing the relationship between maximum possible violation rate as a function of the intensity of enforcement of vehicle weight and dimension regulations and indeed other transport administrative regulations is postulated. The model is an exponential function that determines the maximum violation rate for given inspection capacity. The constant of the function depends on the method of enforcement. The theory is demonstrated to be valid. It has potential for facilitating important policy issues relating to enforcement of transport administrative regulations and within the framework of infrastructure management to be addressed.

The relative effectiveness of enforcement methods is quantified by two parameters namely, the effectiveness index and the truckers’ relative perceived probability of detection. These parameters facilitate evaluation of the performance of various enforcement methods and operation strategies. It is found that patrol teams are, on average, 30 times as effective in detecting violations as continuously operated permanent weigh scales. High perceived detection probabilities are associated with high inspection capacities. To increase the perceived detection probability (reduce violation rates) therefore implies increasing the inspection capacity.     

A cost performance analysis of transport infrastructure construction in Slovenia

Due to limited data availability only a few studies have been able to provide statistically significant evidence on cost overruns in transport infrastructure investments and their systematic nature, and fewer still for road infrastructure investments. The body of available evidence refers to the most economically developed countries, while very little evidence was found regarding other countries. In this article the authors focus on cost performance of road infrastructure constructed through the National Motorway Construction Programme in Slovenia. Methodologically the study departs from other studies in this field by building on detailed expenditure data and not aggregate reports from the relevant institution. This enabled the analysis of four individual project cost categories (construction cost, land acquisition damages and others) and comparably more accurate results. A representative sample of randomly selected completed projects in the period 1995–2007 revealed that the cost overruns (19%; SD = 46.10%) in the entire period studied do not appear to be higher than in other comparable studies. At the same time the study results showed that cost overruns were unstable, i.e. much higher for older projects.     

Oil spill risk analysis of routeing heavy ship traffic in Norwegian waters

Norwegian authorities have for a long time been concerned about the risk of oil spills outside the Norwegian coast. One of the key measures adopted has been to reduce the risk of ship accidents by imposing sailing routes for heavy ship traffic (over 5,000 gross tonnages) with high environmental risk potential farther away from part of the coast. This article is based upon two reports which conducted risk assessments of imposing such sailing routes outside the entire Norwegian coast. These routes were proposed by an expert group consisting of relevant stakeholders. Data of traffic pattern and number of sailing were collected for the year 2008 using the universal Automatic Identification System (AIS). The proposed route was compared with 2008 traffic pattern in regard to the accident frequencies and the expected oil spills per year. An accident and oil spilling simulation program called MARCS was used to simulate these results. After conducting a traffic forecast for the year 2025, the simulation was again run and the results compared with the year 2008. In total, the proposed route is expected to reduce oil spills by 590 t per year in 2008 and by 3670?t in 2025. The main reason for this substantial reduction is that the number of groundings is reduced because of the distance from the shore being increased. The reduction was particularly strong for tankers.