Among all environmental forces acting on ocean structures and marine vessels, those resulting from wave impacts are likely to yield the highest loads. Being highly nonlinear, transient and complex, a theoretical analysis of their impact would be impossible without numerical simulations. In this paper, a pressure-split two-stage numerical algorithm is proposed based on Volume Of Fluid (VOF) methodology. The algorithm is characterized by introduction of two pressures at each half and full cycle time step, and thus it is a second-order accurate algorithm in time. A simplified second-order Godunov-type solver is used for the continuity equations. The method is applied to simulation of breaking waves in a 2-D water tank, and a qualitative comparison with experimental photo observations is made. Quite consistent results are observed between simulations and experiments. Commercially available software and Boundary Integral Method (BIM) have also been used to simulate the same problem. The results from present code and BIM are in good agreement with respect to breaking location and timing, while the results obtained from the commercial software which is only first-order accurate in time has clearly showed a temporal and spatial lag, verifying the need to use a higher order numerical scheme. 相似文献
Formal safety assessment (FSA) is a formal, structured and systematic methodology, aimed at enhancing maritime safety, including protection of life, property and marine environment, by using risk and cost–benefit assessments. For the application of this methodology to the rule-making process, the International Maritime Organization (IMO) presented the Interim Guidelines, which describe procedures of FSA and inputs/outputs of each procedure in detail. This paper basically deals with an application of FSA methodology according to the IMO's Interim Guidelines to the hatchway watertight integrity of bulk carriers, which was carried out as a cooperative research between Korean Register of Shipping and Seoul National University. As results of this application study, 18 hazards are identified and 32 risk control measures are devised to reduce the associated risks. Potential risks, costs and benefits when some Risk Control Options are introduced are evaluated in monetary unit of US $. Finally, some discussions and recommendations based on experiences are also given for both future work and better application of this FSA methodology to the rule-making process. 相似文献
1 Introduction1 The sensor array and the correlative signal processing methods have been adopted for the ability improvement of detection and orientation in modern sonar systems, and beamforming is a widely used tool in sensor array signal processing for … 相似文献
This paper studies the impact of removing the level crossing, which constitutes traffic hazard to the society, on house prices by conducting a quasi-natural experiment using the Level Crossing Removal Project (LXRP) implemented by the Victoria state government in Australia since 2015. Using a difference-in-differences method, we analyzed the changes in housing prices due to the improvement of transportation infrastructure, gauging the LXRP’s impact on house and unit submarkets separately. We found that the prices for house and unit markets increased significantly after the removal of level crossings, with the value uplift decreasing with distance from the removal site. This paper contributes to the existing literature by adding an empirical study related to the enhancement of infrastructure aiming to improve the traffic safety in the urban context. Unlike previous studies, this study examines the effect of improvement projects for existing infrastructure and provides relevant implications to improve the efficiency of investing public resources in infrastructure improvement.
This paper looks at the first and second best jointly optimal toll and road capacity investment problems from both policy
and technical oriented perspectives. On the technical side, the paper investigates the applicability of the constraint cutting
algorithm for solving the second best problem under elastic demand which is formulated as a bilevel programming problem. The
approach is shown to perform well despite several problems encountered by our previous work in Shepherd and Sumalee (Netw.
Spat. Econ., 4(2): 161–179, 2004). The paper then applies the algorithm to a small sized network to investigate the policy implications of the first and second
best cases. This policy analysis demonstrates that the joint first best structure is to invest in the most direct routes while
reducing capacities elsewhere. Whilst unrealistic this acts as a useful benchmark. The results also show that certain second
best policies can achieve a high proportion of the first best benefits while in general generating a revenue surplus. We also
show that unless costs of capacity are known to be low then second best tolls will be affected and so should be analysed in
conjunction with investments in the network.
Agachai SumaleeEmail:
Andrew Koh
Prior to joining the Institute for Transport Studies in December 2005, Andrew was employed for number of years as a consultant
in highway assignment modelling. He is an economist with wide ranging research interests in transport economics as well as
evolutionary computation heuristics such as genetic algorithms, particle swarm optimisation and differential evolution.
Simon Shepherd
At the Institute for Transport Studies since 1989, he gained his doctorate in 1994 applying state-space methods to the problem
of traffic responsive signal control in over-saturated conditions. His expertise lies in modelling and policy optimisation
ranging from detailed simulation models through assignment to strategic land use transport models. Recently he has focussed
on optimisation of road user charging schemes and is currently working on optimal cordon design and system dynamics approaches
to strategic modelling.
Agachai Sumalee
Agachai is currently an Assistant Professor at Department of Civil and Structural Engineering, Hong Kong Polytechnic University
(). He obtained a Ph.D degree with the thesis entitled “Optimal Road Pricing Scheme Design” at Leeds University in 2004. His
research areas cover transport network modeling and optimization, stochastic network modeling, network reliability analysis,
and road pricing. Agachai is currently an associate editor of Networks and Spatial Economics. 相似文献
With the recent increase in the deployment of ITS technologies in urban areas throughout the world, traffic management centers
have the ability to obtain and archive large amounts of data on the traffic system. These data can be used to estimate current
conditions and predict future conditions on the roadway network. A general solution methodology for identifying the optimal
aggregation interval sizes for four scenarios is proposed in this article: (1) link travel time estimation, (2) corridor/route
travel time estimation, (3) link travel time forecasting, and (4) corridor/route travel time forecasting. The methodology
explicitly considers traffic dynamics and frequency of observations. A formulation based on mean square error (MSE) is developed
for each of the scenarios and interpreted from a traffic flow perspective. The methodology for estimating the optimal aggregation
size is based on (1) the tradeoff between the estimated mean square error of prediction and the variance of the predictor,
(2) the differences between estimation and forecasting, and (3) the direct consideration of the correlation between link travel
time for corridor/route estimation and forecasting. The proposed methods are demonstrated using travel time data from Houston,
Texas, that were collected as part of the automatic vehicle identification (AVI) system of the Houston Transtar system. It
was found that the optimal aggregation size is a function of the application and traffic condition.
In Brazil, the explosion of informal transport activity during the past decade has had profound effects on formal public transport
systems and is a source of great controversy in the urban transportation sector. A variety of policies have been proposed
to manage the growth of the sector. This study seeks to understand how proposed policies will impact the users of these systems.
A corridor in Rio de Janeiro with substantial informal activity was used as a case study. Measures of welfare changes in a
discrete choice framework were used to estimate proposed policies’ impacts on users. Eleven candidate policies were evaluated,
ranging from the eradication of the informal modes and investment in formal modes, to the legalization of the informal modes.
Benefits were compared with costs and the distribution of benefits across income classes was explored. Net benefits from some
policies were found to be substantial. Legalizing the informal sector was found to benefit users slightly but further investments
in the sector are probably inefficient. Users benefited most from improvements in formal mass transit modes, at roughly 100–200
dollars per commuter per year. Finally, policies to foster a competitive environment for the delivery of both informal and
formal services were shown to benefit users about 100 dollars per commuter per year. Together, the regulation of the informal
sector and investments in the formal sector serve to reinforce the movement towards competitive concessions for services and
help reduce the impacts of cartelization and costly in-road competition.
The interactions among different types of vehicle ownership including car, motorcycle and bicycle are examined by developing
simultaneous vehicle ownership models in this study. Large scale person trip survey data for Osaka metropolitan area, Japan
and Kuala Lumpur, Malaysia are used for empirical analysis. The results suggest that population density at residential area
significantly and negatively affects car ownership for both areas, and that the effects are larger for Osaka metropolitan
area than for Kuala Lumpur. Also, bicycle ownership becomes higher at higher population density area for Osaka area, while
higher at lower population density area for Kuala Lumpur, which represents the different usage patterns of bicycle between
the two areas.
When a new public transport service is introduced it would be valuable for public authorities, financing organisations and
transport operators to know how long it will take for people to start to use the service and what factors influence this.
This paper presents results from research analysing the time taken for residents living close to a new guided bus service
to start to use (or adopt) the service. Data was obtained from a sample of residents on whether they used the new service
and the number of weeks after the service was introduced before they first used it. Duration modelling has been used to analyse
how the likelihood of starting to use the new service changes over time (after the introduction of the service) and to examine
what factors influence this. It is found that residents who have not used the new service are increasingly unlikely to use
it as time passes. Those residents gaining greater accessibility benefits from the new service are found to be quicker to
use the service, although the size of this effect is modest compared to that of other between-resident differences. Allowance
for the possibility that there existed a proportion of the sample that would never use the new service was tested using a
split population model (SPD) model. The SPD model indicates that 36% of residents will never use the new service and is informative
in differentiating factors that influence whether Route 20 is used and when it is used.
Kang-Rae MaEmail:
Kiron Chatterjee
has been a Senior Lecturer at the University of the West of England, Bristol, since 2003 and previously was at the University
of Southampton. Currently, a main focus of his research is on longitudinal analysis of travel behaviour to improve policy
analysis.
Kang-Rae Ma
received a PhD in Planning from University College London. He worked at the University of the West of England, Bristol, and
the Korea Transport Institute before he joined Chung-Ang University as an Assistant Professor. His research interests include
modelling of travel behaviour and urban excess commuting. 相似文献