Abstract

We consider the assignment of gates to arriving and departing flights at a large hub airport. This problem is highly complex even in planning stage when all flight arrivals and departures are assumed to be known precisely in advance. There are various considerations that are involved while assigning gates to incoming and outgoing flights (such a flight pair for the same aircraft is called a turn) at an airport. Different gates have restrictions, such as adjacency, last-in first-out gates and towing requirements, which are known from the structure and layout of the airport. Some of the cost components in the objective function of the basic assignment model include notional penalty for not being able to assign a gate to an aircraft, penalty for the cost of towing an aircraft with a long layover, and penalty for not assigning preferred gates to certain turns. One of the major contributions of this paper is to provide mathematical model for all these complex constraints that are observed at a real airport. Further, we study the problem in both planning and operations modes simultaneously, and such an attempt is, perhaps, unique and unprecedented. For planning mode, we sequentially introduce new additional objectives to our gate assignment problem that have not been studied in the literature so far(i) maximization of passenger connection revenues, (ii) minimization of zone usage costs, and (iii) maximization of gate plan robustnessand include them to the model along with the relevant constraints. For operations mode, the main objectives studied in this paper are recovery of schedule by minimizing schedule variations and maintaining feasibility by minimal retiming in the event of major disruptions. Additionally, the operations mode models must have very, very short run times of the order of a few seconds. These models are then applied to a functional airline at one of its most congested hubs. Implementation is carried out using Optimization Programming Language, and computational results for actual data sets are reported. For the planning mode, analyst perception of weights for the different objectives in the multi-objective model is used wherever actual dollar value of the objective coefficient is not available. The results are also reported for large, reasonable changes in objective function coefficients. For the operations mode, flight delays are simulated, and the performance of the model is studied. The final results indicate that it is possible to apply this model to even large real-life problems instances to optimality within short run times with clever formulation of conventional continuous time assignment model. Copyright (c) 2013 John Wiley & Sons, Ltd. Document type: Report

Abstract

Purpose : the aim of this study is to estimate monetary abatement values for road and rail traffic noise that can be used for policy purposes. However, a main objective is to critically discuss the assumptions necessary to convert the monetary values elicited in willingness to pay (WTP) studies to values than can be use for policy purposes. Methods : we employ the hedonic regression technique on Swedish data to elicit individuals’ preferences for noise abatement. Our elicited values are then converted to policy values and critically examined based on findings from a literature review. Results : we show that WTP for road and rail not only differs in levels but also that the relationship between the noise level and the marginal value differs between the two sources. We also show that a health cost component added to the WTP estimate, based on the assumption of uninformed property buyers, will be small but not negligible and that also modest differences in the assumption of the discount rates will have a significant effect on the estimated values. Conclusions : the main implications from this study are: (i) WTP for road and railway noise abatement differs not only on absolute but also marginal levels, (ii) Even small differences in the chosen discount rate, which is necessary to convert WTP values from a hedonic price study to policy values, have large effects on the policy values, and (iii) We show how to add a health cost component to the WTP estimates in order for the monetary estimates to reflect the total social cost. However, we argue that the motivation for doing so is weak and that more research is needed on this issue. Document type: Preprint

Abstract

Purpose: This study compared road safety and related factors in the U.S. with those in Sweden, the United Kingdom, and the Netherlands (which are among the best-performing countries), in order to identify actions most likely to produce casualty reductions in the U.S. Method: The reviewed topics were basic country statistics, road fatalities and various fatality rates, and selected road-safety issues. Results: The main differences concerned structural and cultural factors (such as vehicle distance driven), and procedural factors (such as alcohol-impaired driving, exceeding speed limits, and use of seat belts). Conclusions: The main recommendations for improving road safety in the U.S. are as follows: (1) lower states' BAC limits, and encourage the use of alcohol ignition interlocks (2) reexamine the current speed-limit policies and improve speed enforcement, (3) implement primary seat-belt-wearing laws in each state that would cover both front and rear occupants, and reward vehicle manufacturers for installation of advanced seat-belt reminders, and (4) reconsider road-safety target setting so that the focus is on reducing fatalities and not on reducing fatality rate per distance driven, and (5) consider new strategies to reduce vehicle distance driven. Document type: Article

Abstract

Traffic is the most widespread source of environmental noise. Railway noise has become increasingly common in urban areas in the past few decades. Therefore environmental requirements for railway operations regarding noise are becoming very strict and will become even tighter in future. In the present paper we present actual track- based field test performed on Slovenian Railways. The significant noise reduction (up to 30dBA) was achieved by the application of CHFC material on the rail using CL-E1 top anti noise system. Der Verkehr ist die am weitesten verbreitete Quelle von Umgebungslärm. Eisenbahnlärm nahm in den letzten Jahrzehnten in städtischen Gebieten immer mehr zu. Aus diesem Grund wurden die Umweltanforderungen für den Bahnverkehr bezüglich des Lärms immer strenger und werden in der Zukunft noch höher. In der vorliegenden Arbeit stellen wir den tatsächlichen Track-basierten Feldversuch auf der Slowenischen Bahn dar. Die deutliche Lärmreduzierung (bis 30 dBA)wurde durch die Anwendung von CHFC-Material auf der Schiene mithilfe des Cl-E1 Antirauschsystems erreicht. Document type: Article

Abstract

This study presents the results from detailed experiments of the two-phase pressurized flow behavior during the rapid filling of a large-scale pipeline. The physical scale of this experiment is close to the practical situation in many industrial plants. Pressure transducers, water-level meters, thermometers, void fraction meters, and flow meters were used to measure the two-phase unsteady flow dynamics. The main focus is on the water–air interface evolution during filling and the overall behavior of the lengthening water column. It is observed that the leading liquid front does not entirely fill the pipe cross section; flow stratification and mixing occurs. Although flow regime transition is a rather complex phenomenon, certain features of the observed transition pattern are explained qualitatively and quantitatively. The water flow during the entire filling behaves as a rigid column as the open empty pipe in front of the water column provides sufficient room for the water column to occupy without invoking air compressibility effects. As a preliminary evaluation of how these large-scale experiments can feed into improving mathematical modeling of rapid pipe filling, a comparison with a typical one-dimensional rigid-column model is made. Keywords: Experimentation, Large-scale pipeline, Unsteady flow, Two-phase flow, Air–water interface, Flow-regime transition

Abstract

The motion of liquid filling a pipeline is impeded when the gas ahead of it cannot escape freely. Trapped gas will lead to a significant pressure build-up in front of the liquid column, which slows down the column and eventually bounces it back. This paper is an extension of previous work by the authors in the sense that the trapped gas can escape through a vent. Another addition is that the driving pressure is not kept constant but fluctuating. The obtained analytical and numerical solutions are utilized in parameter variation studies that give deeper insight in the system’s behavior.

Abstract

Fluid-structure interaction (FSI) due to water hammer in a pipeline which has viscoelastic wall behaviour is studied. Appropriate governing equations are derived and numerically solved. In the numerical implementation of the hydraulic and structural equations, viscoelasticity is incorporated using the Kelvin-Voigt mechanical model. The equations are solved by two different approaches, namely the Method of Characteristics - Finite Element Method (MOCFEM) and full MOC. In both approaches two important effects of FSI in fluid-filled pipes, namely Poisson and junction coupling, are taken into account. The study proposes a more comprehensive model for studying fluid transients in pipelines as compared to previous works, which take into account either FSI or viscoelasticity. To verify the proposed mathematical model and its numerical solutions, the following problems are investigated: axial vibration of a viscoelastic bar subjected to a step uniaxial loading, FSI in an elastic pipe, and hydraulic transients in a pressurized polyethylene pipe without FSI. The results of each case are checked with available exact and experimental results. Then, to study the simultaneous effects of FSI and viscoelasticity, which is the new element of the present research, one problem is solved by the two different numerical approaches. Both numerical methods give the same results, thus confirming the correctness of the solutions. Keywords: water hammer; fluid transient; pressure surge; fluid-structure interaction; pipe vibration; plastic pipe; viscoelasticity

Abstract

The main theme in this article is the description of time-based traffic management procedures that have been proposed to increase the capacity of the air traffic system by the beginning of the next century. However, the article starts with a brief description of today's air traffic control systems. Their shortcomings are identified and the need for improved systems and procedures is discussed. The new technologies which will enable us to overcome the limitations of the present communication, navigation and surveillance systems by providing higher quality and improved efficiency, are briefly discussed. Because terminal area management certainly is one of the most critical aspects of overall air traffic management, the main focus in this article is on this issue. Finally, current research efforts towards improved trajectory optimization and control for flight operations in an extended terminal area are described in some detail.

Abstract

div"Due to recent advances in sensor technology and the exponential increase in computation power of electronic control units (ECUs) along with their increasing affordability, active safety and vehicle automation have become major trends in the commercial vehicle industry. New regulations for increased safety are also a major driver behind the industry's increased interest in that topic. As a result, being a crucial part of vehicle automation, steering systems had to be adapted to enable Active Steering. Consequently, commercial vehicle steering designers introduced the concept of torque and angle overlay using an electric motor in series with the conventional hydraulic steering system. However, despite the fact that these systems are becoming more prevalent in the market, they still suffer from inefficiencies intrinsic to the conventional hydraulic steering system still being used. These inefficiencies are a result of"/div""div"flow metering losses due to the use of control valves to regulate the pump flow output, as well as inside the steering gear with the use control valves to build assistance pressure."/div""div""br""/div""div""div"In this research project, we investigate the potential use of the proven pump Displacement Control (DC) technology in steering on-highway commercial vehicles. DC pumps have been shown to signicantly improve system efficiency as they allow the removal of control valves typically used to regulate "/div""div"ow [1]. Instead, the displacement of the pump can be directly controlled to vary the pump's flow rate and direction,"/div""div"and thus eliminating throttling losses. The DC technology has been successfully used in a steer-by-wire conguration for an articulated frame steering vehicle and has been shown to signicantly improve efficiency and productivity, as well as result in a reduction in fuel consumption [2]."/div""/div""div""br""/div""div""div"In this work, we propose a steer-by-wire system, using DC pump technology, for on-highway commercial vehicles, and present the dierent possible congurations in which it can be implemented. Moreover, the benets and drawbacks of the steer-by-wire system are researched and identied. Subsequently, the system is designed and validated in simulation, on laboratory test setup, as well as on a test vehicle to prove its feasibility."/div""/div""div""br""/div""div""div"Chief among the drawbacks of the steer-by-wire system is potential failures that can lead to the complete loss of the steering function of the vehicle. As a result, different possible fail-safe mechanisms are researched from which the most suitable ones are proposed to allow the steer-by-wire system to fail safely. Moreover, two of the proposed fail-safe mechanism are implemented onto the test vehicle to prove and validate their feasibility."/div""/div""div""br""/div""div""div"Furthermore, an alternative way of using displacement controlled pumps for active steering is be proposed. For this concept, we investigate the possibility of actively controlling the driver's steering effort by varying the pump displacement while maintaining the mechanical link between the steering wheel and the road wheels. If successful, this method will allow for a more efficient way of providing steering assistance as it does away with the conventional control valves used to build pressure and regulate pump flow, and thus eliminating throttling losses. This method has also the advantage of having an intrinsic fail-safe mechanism with manual steering being always possible should the hydraulic or electric systems fail."/div""/div

Abstract

Road transport contributes to approximately one quarter of all EU greenhouse gas emissions and is the leading cause of air pollution in cities. There are significant measures aimed at the reduction of use phase environmental impacts; in the EU, these strategies focus on the decarbonisation of road transport, such as through the prioritization of low- and zero-emission vehicles. Electric vehicles are seen as one of the primary measures for reducing road transport impacts. However, the introduction of new technology includes new challenges throughout the vehicle life cycle, such as the need for critical raw materials, high-energy manufacturing, charging electricity, and waste management; this, in turn, leads to a risk of impact shifts between life cycle phases and impact categories. Life Cycle Assessment (LCA) is one way to analyse environmental impacts. Applying LCA and life cycle thinking in research and industry allows for the detection of impact shifts and environmental sub-optimisation. A full LCA study is demanding in terms of both data collection efforts and user expertise requirements. The need to simplify the process and results of an assessment in order to support decision-making was identified in the early days of LCA development. There are numerous simplification approaches in LCA. Previously, the most prominent simplification terms were screening and streamlined LCA; now, a multitude of names and approaches have emerged. There is no consensus in the LCA community about LCA simplifications. In some cases, the line between what should be considered an LCA, simplified LCA or neither is fuzzy. The haphazard application of simplifications in LCA studies undermines the transparency and confidence in results. The aim of this thesis is to use the life cycle perspective guided by simplified LCA approaches to increase our understanding of the risk of impact shifts, resulting from measures to reduce vehicle environmental impacts. Four appended publications present five LCA studies of road vehicles. All appended studies are simplified using different approaches. The studies examine different impact reduction measures such as changing drivetrains, reducing particulate emissions from braking, and the scrapping of old vehicles. A fifth publication is a literature review that explores the common understanding of simplifications used in published LCA studies. The review identifies and investigates the types of simplifications used and discusses how these might be categorised. The appended LCA studies examine both impact shifts from one life cycle phase to another and between impact categories. It is difficult to determine whether a decrease in a life cycle phase or impact category could offset an increase in another and, therefore, to be able to determine if an impact shift is an acceptable compromise. New smart materials are expected to solve many environmental impact issues; however, there are risks associated with insufficient life cycle inventory data, limitations in knowledge about potential environmental impacts, and inefficient regulations covering new materials. The analysis of simplification approaches and case studies indicates that most simplifications are motivated by the lack of primary data. Additionally, study findings strengthen concerns about the significant inconsistency in LCA simplification terminology and how well approaches are described in individual studies. There is a need for a common simplification terminology and reporting standard. Due to the wide variety of purposes, scenarios, and products assessed, it is impossible to devise a one-size-fits-all approach for simplifications, especially if the aim is to identify potential impact shifts. Vägtransporter orsakar ungefär en fjärdedel av EUs totala utsläpp av växthusgaser och är den ledande orsaken till luftföroreningar i städer. Betydande åtgärder syftar till att minska användningsfasens miljöpåverkan. EUs strategier fokuserar på att minska vägtransporters koldioxidutsläpp, t.ex. genom att prioritera fordon med låga eller inga användning-utsläpp. Elektriska fordon ses som en av de främsta åtgärderna för att minska miljöpåverkan från vägtransport. Dock innebär introduktionen av ny teknik nya utmaningar längs fordonets livscykel, t.ex. behov av kritiska råmaterial, högenergiproduktion, ökad el-behov vid laddning och avfallshantering. Det finns en risk för förskjutning av miljöpåverkan mellan livscykelfaser och påverkanskategorier.   Livscykelanalys (LCA) är ett sätt att analysera miljöpåverkan. Möjligheten att upptäcka förskjutning av miljöpåverkan och ineffektiva åtgärder för miljön är en anledning till att tillämpa LCA och livscykeltänkande inom forskning och industri. En fullständig LCA-studie kräver både betydande datainsamlingsinsatser och krav på användarexpertis. Behovet av att förenkla processen och utvärderingsresultaten för att stödja beslut identifierades redan tidigt under utvecklingen av LCA.   Det finns en betydande mängd av LCA förenklingar. De mest framträdande förenklingstillvägagångssätten var tidigare ”screening” och ”streamlined” LCA, dessutom har en mängd andra namn och tillvägagångssätt dykt upp. Det finns ingen konsensus inom LCA-världen om hanteringen av LCA förenklingar. I vissa fall är gränsen luddig mellan vad som ska betraktas som en LCA, förenklad LCA och ingendera. Godtycklig tillämpning av förenklingar i LCA-studier undergräver transparensen och förtroendet för resultaten.   Syftet med denna avhandling är att öka förståelsen för risken för förskjutning av miljöpåverkan, vid åtgärder för att minska fordonens påverkan, genom att använda livscykelperspektivet stödd av förenklad LCA. De fyra publikationerna inkluderar fem LCA-studier av vägfordon och fordonskomponenter. Alla fem studierna är förenklade genom olika tillvägagångssätt. Studierna undersöker olika miljöåtgärder så som att byta drivlina, minska partikelutsläpp vid bromsning och skrotning av gamla fordon. En femte publikation undersöker också den gemensamma förståelsen för LCA förenklingar, genom en litteraturöversikt av publicerade LCA-studier. Litteraturöversikten identifierade och undersökte vilka förenklingar som används och hur dessa skulle kunna kategoriseras.   De inkluderade LCA-studierna exemplifierade både förskjutning av miljöpåverkan mellan livscykelfaser och påverkanskategorier. Det är svårt att avgöra om en minskning i en livscykelfas eller påverkanskategori kan kompensera för en ökning i en annan. Detta betyder att det är komplicerat att kunna avgöra om en förskjutning av miljöpåverkan är en acceptabel kompromiss. Nya smarta material förväntas vara lösningen för många miljöproblem. Det finns emellertid risker med otillräcklig LCI-data, kunskapsbegränsningar angående potentiella miljökonsekvenser och ineffektiva regler gällande nya material.   Analysen av förenklingstillvägagångssätt och fallstudier indikerade att de flesta förenklingar styrdes av brist på primärdata. Dessutom stärktes anledningen till oro gällande den betydande inkonsekvens i LCA-förenklingsterminologin och hur väl tillvägagångssätten beskrivs i enskilda studier. Det finns ett behov av en gemensam terminologi och rapporteringsstandard för LCA förenklingstillvägagångssätt. På grund av studiers varierande syften, scenarier och analyserade produkter är det omöjligt att utforma ett generellt tillvägagångssätt för alla LCA förenklingar, särskilt om syftet är att identifiera potentiella förskjutningar av miljöpåverkan.