Numerical modeling of breaking waves generated by a ship’s hull

A new model for the simulation of spilling breaking waves in naval flows is presented. The hydrostatic pressure is used in order to mimic the weight of the breaker on the underlying flow, as in the model of Cointe and Tulin, whereas the algorithm for detecting the breaking inception and the definition of its geometry are completely new and are suitable for the simulation of three–dimensional flows around shipsrc="/content/530e51el9lev1ry2/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0"> hulls. The model has been implemented in a finite-volume code developed for naval flows, and its performances have been validated against experimental data for a submerged profile, an S60 hull in drift motion, and the US Combatant DTMB 5415 model on a straight course.     

Wave forecasts and small-vessel safety: A review of operational warning parameters

Traditionally most meteorological offices forecast height, direction and period of wind sea and swell based on phase-averaged wave models. In recent years, there has been special interest in whether it is possible to produce better forecasts, which include information about high-risk situations that are not resolved by the traditional wave parameters. Here we will review and discuss sea-state parameters and safety warning-indices that have been suggested and investigated in recent years. In this review we particularly focus on parameters that are important for small vessels. Some of the findings are:

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A current trend in marine forecasts, going beyond the usual parameters, is tailoring of the product to the end users. The extent to which wave forecasts are tailored to small vessels differs quite a lot among meteorological offices.

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Single wave and crest heights are adequately described by first- and second-order theory, respectively. Present understanding of mechanisms behind abnormally high single waves suggests that modulational instability is limited to almost unidirectional seas.

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Combining wave height and steepness or calculating the risk of synchronous waves is useful, especially in relation to safety of smaller vessels.

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Ship accident statistics suggest that the H_m0 value of sea state is not as important as whether this value is unexpected, due to rapid development or compared to local wave climate.

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Severe waves can occur in areas where strong currents oppose the waves, and operational warnings exist for some areas.

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The best way to communicate the directional composition of the wave field still seems to be a division of the sea state into wind sea and swell.

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In spite of incomplete physics, the predicted level of wave dissipation can be used to highlight potentially dangerous seas in some areas.

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Local experience-based warnings are necessary if dangerous sea states can occur that are not resolved by prognostic wave models.

     

Incorporating Logistics in Freight Transport Demand Models: State-of-the-Art and Research Opportunities

Freight transport demand is a demand derived from all the activities needed to move goods between locations of production to locations of consumption, including trade, logistics and transportation. A good representation of logistics in freight transport demand models allows us to predict the effects of changes in logistics systems on future transport flows. As such it provides better estimations of the costs of interaction and allows to predict changes in spatial patterns of freight transport flows more accurately. In recent years, the attention for freight modelling has been growing and new research work has appeared aimed at incorporating logistics in freight models. In this paper we review the state of the art in the representation of logistics considerations in freight transport demand models. Our focus is on the service and cost drivers of changes in logistics networks and how these affect freight transport. Our review proceeds along a conceptual framework for modelling that goes beyond the conventional 4-step modelling approach. We identify promising areas for freight modelling that have an integrative function within this framework, such as spatial computable general equilibrium models, supply chain choice models and hypernetwork models.     

The urban road pricing scheme to curb pollution in Milan,Italy: Description,impacts and preliminary cost–benefit analysis assessment

Starting from January 2008 Milan implemented a charging scheme to enter an 8 km² area of the city centre. The term used to denote the scheme is Ecopass, conveying the stated political objective of the scheme: a pass to improve the quality of the urban environment (ECO). The charge depends on the Euro emission standard of the vehicle. The paper illustrates the main features and impacts of the Milan Ecopass scheme, and presents a preliminary cost–benefit analysis. The scheme has been effective in curbing not only pollution emissions, but also congestion, and the result has been achieved with low implementation costs and without major political opposition. The cost–benefits analysis presents an overall net benefit. The identification of the winners and losers of the policy is conditioned by penalty payments. Without including the penalties, the surface public transport users and the society at large are the main winners, whereas car and especially freight vehicle users are net losers.     

The influence of three-way catalysts on harmful emission production

This article deals with the influence of three-way catalysts on the production of basic emissions, such as carbon monoxide, unburned hydrocarbons and nitrogen oxides from spark-ignition engines. A virtual simulation of the new European driving cycle is used. Characteristics of components in emissions in the front and back of the catalyst are measured on the test bed to form the basis of the simulation. The results relate to emissions for 1 km travelled.