Triangulation of two methods measuring the impacts of a free-floating carsharing system in Germany

This article reports on two different methods applied in the same survey (N = 1881) to measure the impact of the carsharing system car2go on other transportation modes in Ulm, Germany. The first method calculated how the mobility behavior of respondents would hypothetically be at the present time if car2go was not available. The second method determined the respondents’ past mobility behavior before using car2go. Confounding circumstances were corrected in both approaches through different mechanisms. Comparable methods calculating carsharing impacts have only been applied individually in past studies. This is the first study applying two measurement methods within the same survey, which enables a triangulation. As other influencing parameters were equal (e.g. sampling frame, nonresponse bias, mode of asking, point in time of the survey), the deviating results are assumed to have resulted from the different measurement techniques. The findings indicate a primacy effect (disproportionally high selection of first answer options) having influenced the first measurement and an overestimation of the impact on total kilometers travelled in the second measurement. The comparative findings of this dual-measurement could contribute to research designs of greater precision in future work on carsharing impacts.     

The changes of activity-travel participation across gender,life-cycle,and generations in Sweden over 30 years

Transportation - This study utilised the Swedish national travel survey covering a period of over 30 years. We investigated the long-term trends in activity-travel patterns of individuals...     

Weaving marine food webs from end to end under global change

Marine food web dynamics are determined by interactions within and between species and between species and their environment. Global change directly affects abiotic conditions and living organisms, impinging on all trophic levels in food webs. Different groups of marine researchers traditionally study different aspects of these changes. However, over medium to long time scales perturbations affecting food webs need to be considered across the full range from nutrients to top predators. Studies of end-to-end marine food webs not only span organism sizes and trophic levels, but should also help align multidisciplinary research to common goals and perspectives. Topics are described that bridge disciplinary gaps and are needed to develop new understanding of the reciprocal impacts of global change on marine food webs and ocean biogeochemistry. These include (1) the effects of nutrients on biomass and production, (2) the effects of varying element ratios on food web structure and food quality, (3) bulk flows of energy and material in food webs and their efficiencies of transfer, (4) the ecological effects of species richness and the roles of microbial organisms, (5) the role of feeding behaviour in food web dynamics and trophic controls, (6) the spatial dynamics of communities and links between different food webs, (7) the combined effects of body size and behaviour in determining dynamics of food webs, and (8) the extent to which the ability of marine organisms (and communities) to adapt will influence food web dynamics. An overriding issue that influences all topics concerns the time and space scales of ecosystem variability. Threads link different nodes of information among various topics, emphasizing the importance of tackling food web studies with a variety of modelling approaches and through a combination of field and experimental studies with a strong comparative approach.     

Parametric roll mitigation using rudder control

Severe roll angles can be developed by parametric excitation in relatively moderate weather without any apparent pre-warning for the crew onboard. In this study the prospect of using rudder control to mitigate parametric roll was investigated using multi-degree of freedom simulations. A typical modern Pure Car and Truck Carrier was considered and modelled by coupling a roll model with a planar motion manoeuvring model. The combined model was calibrated using in-service, full-scale trials and model tests. Irregular variations of the metacentric height were applied to simulate recorded, full-scale events of parametric roll that have occurred with the considered design. These simulations with rudder roll control showed promising results and demonstrate that the approach could be very efficient for mitigation of parametric roll.     

An algorithm for the combined distribution and assignment problem

Much interest has recently been shown in the combination of the distribution and assignment models. In this paper we adopt a generalized Benders' decomposition to solve this combined problem for a system optimized assignment with linear link costs and explicit capacity constraints on link flows. The master problem which is generated is used to show that the combined problem can be viewed as a modified distribution problem, of gravity form, with a minimax instead of a linear objective function. An algorithm for solving the master problem is discussed, and some computational results presented.     

ESI,专业化的虚拟仿真技术推动数字化造船

在工程仿真领域,有一家以提供专业化的仿真解决方案享誉业界的公司引起了记者的注意,这家公司何以能在激烈的全球CAE行业中赢得越来越多的市场?其解决方案的特点是什么?其未来发展和技术研发方向是什么?面对中国技术创新的巨大机遇,以及中国已成为造船大国并向造船强国转型的时机下,该公司如何布局中国的CAE市场?其仿真技术和方案能给中国船舶工业转型过程技术创新带来什么益处?带着这些问题,在一个初冬的早晨,本刊记者对这家的全球运营官ChristopherSt.John博士进行了专访。     

Predicting freight flows in a globalising world

In this paper we suggest a methodology to predict commodity specific transportation flows that brings together data in value and in quantity terms in a consistent way. The approach is based on the modern gravity formulation. There are three driving forces of the transport flows dynamics: economic growth, the ongoing globalization (reduction of trade barriers), and the changing commodity composition of trade, whereby the evolution of value-to-weight ratios is explicitly taken into account. The methodology is applied to forecast the interregional trade flows in Europe.     

Sail-assisted motor vessels weather routing using a fuzzy logic model

In this study sail-assisted motor vessels weather routing is investigated to establish the most economical route by applying available information of the ship's behavior regarding the encountered sea-conditions. To derive the vessel’s fuel use on a route, a fuzzy logic model is constructed through an automated identification process. Only data collected from actual integrated bridge measurements systems is used. Fuzzy modeling is a framework providing a flexible and transparent mathematical structure to describe the physical relationships in a vessel's behavior. This consumption model is integrated into a determinist weather-routing optimization workflow based on a systematic meshing scheme of the sailing area. Pareto-optimization with a multi-objective genetic algorithm is used to maximize fuel economy in a limited or optimum time. The benefits of the developed decision helping tool in sail-assisted motor vessel routing are highlighted on a westbound north Transatlantic journey.     

Forecasting Freight Flows

Trade patterns and transport markets are changing as a result of the growth and globalization of international trade, and forecasting future freight flow has to rely on trade forecasts. Forecasting freight flows is critical for matching infrastructure supply to demand and for assessing investment. This article models long-term dynamic physical trade flows and estimates a dynamic panel data model for foreign trade for the EU15 and two countries from the EFTA (European Free Trade Association) 1967–2002. The analysis suggests that a dynamic three-way-effects gravity equation is the best-fitted econometric model. The analysis uses a structural relationship to explain the structure of the exchange of the goods—a relationship that can be used in the year of forecast. This article also provides a new methodology for converting monetary aggregates into quantity aggregates. The resulting commodity growth rates constitute a valuable input to freight models for forecasting future capacity problems.     

Disaggregate Path Flow Estimation in an Iterated Dynamic Traffic Assignment Microsimulation

This article describes the first application of a novel path flow and origin/destination (OD) matrix estimator for iterated dynamic traffic assignment (DTA) microsimulations. The presented approach, which operates on a trip-based demand representation, is derived from an agent-based DTA calibration methodology that relies on an activity-based demand model (Flötteröd, Bierlaire, & Nagel, 2011). The objective of this work is to demonstrate the transferability of the agent-based approach to the more widely used OD matrix-based demand representation. The calibration (i) operates at the same disaggregate level as the microsimulation and (ii) has drastic computational advantages over conventional OD matrix estimators in that the demand adjustments are conducted within the iterative loop of the DTA microsimulation, which results in a running time of the calibration that is in the same order of magnitude as a plain simulation. We describe an application of this methodology to the trip-based DRACULA microsimulation and present an illustrative example that clarifies its capabilities.