Dynamic stability in following seas: predictive and experimental approaches

This article presents work based on the development of a performance-based stability assessment method. It describes a numerical method used to determine the survival limit for a dynamic intact stability assessment procedure. The numerical method utilises a time-domain vessel motion program to assess the limit for a range of vertical centres of gravity (KG). The appropriateness of the numerical predictions was examined through comparison with model experiment results. Free-running model tests were conducted in regular following waves at discrete KGs. A comparison between the survival limits determined through the numerical and experimental methods is presented. The current International Maritime Organisation (IMO) stability criteria are also evaluated against the numerical and experimental dynamic performance-based stability assessment methods.     

Cost analysis of bulk cargo containerization

ABSTRACT

Bulk cargo containerization (BCC) involves changes in the transportation mode of container shipping for cargo that uses bulk carriers without packing. This topic has recently attracted considerable attention as an alternative transportation method for container cargo. BCC is advantageous because it can address imbalances in the amount of cargo conveyed between the main and back hauls, thereby improving efficiency. A previous survey among companies involved in cargo shipping revealed that in addition to ocean freight, vanning and devanning, and customs clearance costs, consignees’ decisions were the key factor in selecting transport modes. The present study aims to clarify the cost competitiveness of container shipping and identify cost reductions that may increase the use of BCC. To quantitatively check the results of the survey employed in this study, we constructed a model based on consignees’ and container shipping companies’ costs to determine the choice of transport mode for back-haul trade, then examined the incentives for consignees and shipping companies. We found that BCC can be realized by cost reduction on the part of the consignee and profit improvement on the part of the container shipping company for some routes and goods. Although reducing the freight rate would effectively promote BCC, reducing other costs would not have the same effect.     

如何在治堵大环境下进行公交线路提速

2013年浙江省各市开展全面治堵工作,其中提高公共交通的服务水平是交通治堵的重点工作,也是城市交通可持续发展的必经之路。公交服务水平的提高不仅追求量的发展,还要保证质的提升,而对公交线路进行提速就是提升公交服务品质的途径之一。本文在城市交通治堵的大环境下,利用治堵的压力和动力,借机调动大量资源,从公交系统内和公交系统外全面、系统、科学地对温州运量最大的前20条线路进行提速。通过方案的逐步落实,3条提速线路效果明显,城市交通也得到进一步改善。     

The importance of being early

This research quantifies the relationship between the cost of earliness and lateness by empirically observing commute trips from two different sources. The first empirical analysis uses individual level travel survey data from six metropolitan regions while the second analysis uses traffic data from the Twin Cities freeway network. The analysis conducted in this research provides a method to estimate the ratio of the costs of earliness to lateness for different datasets. This can be a useful tool for traffic engineers and planners, to assist them in the development and implementation of improved control strategies for congested cities. The results also corroborates the hypothesis of earliness being less expensive than lateness and show that the finding holds steady over time and across different regions and levels.     

Financial lessons from Asian experience in constructing and operating high speed train networks

A serious interest in high speed train has been increasing all over the world. However, recent experiences in Asian countries show that high speed rail projects are not financially viable even in areas seemingly favorable to rail operations. Considering the existing intensive highway and airline network, putting public subsidies to high speed rail projects are barely justifiable from a purely economic point of view. What is required of any government which contemplates high speed rail construction as a policy option is to show taxpayers the cost/revenues difference between constructing a high speed rail line and expanding a capacity of other means, before proceeding.     

Uncertain benefits: Application of Bayesian melding to the Alaskan Way Viaduct in Seattle

Uncertainty is inherent in major infrastructure projects, but public decision-making for such projects ignores it. We investigate the uncertainty about the future effects of tearing down the Alaskan Way Viaduct in downtown Seattle, using an integrated model of housing, jobs, land use and transportation, on outcomes including average commute times. Our methodology combines the urban simulation model UrbanSim with the regional transportation model. We assess uncertainty using Bayesian melding, yielding a full predictive distribution of average commute times on 22 different routes in 2020. Of these routes, 14 do not include the viaduct and eight do. For the 14 base routes that do not include the viaduct, the predictive distributions overlap substantially, and so there is no indication that removing the viaduct would increase commute times for these routes. For each of the eight routes that do include the viaduct, the 95% predictive interval for the difference in average travel times between the two scenarios includes zero, so there is not strong statistical support for the conclusion that removing the viaduct would lead to any increase in travel times. However, the median predicted increase is positive for each of these routes, with an average of 6 min, suggesting that there may be some measurable increase in travel time for drivers that use the viaduct as a core component of their commute.     

Wave impact underneath horizontal decks

The problem of water impact on a fixed horizontal platform deck from regular incident waves was studied. Two-dimensional potential flow was assumed, and the resulting boundary-value problem was solved by three alternative numerical methods, a method based on a generalization of the impact theory by Wagner, and two different nonlinear boundary-element methods. The Wagner-based method used a von Karman approach during the water exit phase, i.e., when the wetted surface decreases. Experiments of the impact on an idealized platform deck have been performed to validate the theory. Comparisons show that the Wagner-based method yields good results for the water entry phase, when the wetted deck area increases, but poor results when the wetted area diminishes. The boundary-element methods compare well with experiments for the entire impact process. A Kutta condition is necessary at the aft body–free surface intersection during water exit and when the flow separates from the aft edge. Gravity effects matter for the water exit phase.     

Evaluation of marine radar as an ocean-wave-field detector through full numerical simulation

The importance of ocean waves parameters (propagation direction, mean period, significant wave height, etc.) is related to several aspects of a ships safety, efficiency in operation, routing, design, and maintenance. However, some available methods for obtaining those parameters have data limitations and inconvenient aspects. In severe weather conditions, an ocean-wave-field detector is necessary. This can provide two-dimensional ocean-wave-field information directly. Among other conventional methods, ship-borne wave radar has the ability to function as such a detector, and some researchers have tried to develop practical systems. A numerical approach using plan position indicator (PPI) images from conventional marine radars is proposed to retrieve valuable information from the ocean waves. A three-dimensional Fourier transform is applied to a set of consecutive radar PPI images to perform spectrum analysis. The removal of undesired elements in the spectrum is achieved by applying a hi-pass filter to remove static components, and by comparing the data with the expected dispersion shell to correct for nonocean-wave power. Numerical experiments under controlled conditions using simulated PPI images were performed through numerical simulations based on theoretical ocean-wave equations. The results include a comparison between the original wave parameters used in the simulation and the values retrieved from the spectrum analysis.     

Author Index Volume 30 2003

Authors Index

Author Index Volume 30 2003