Computational film cooling effectiveness of dual trench configuration on flat plate at moderate blowing ratios

In the present work, computational simulations was made using ANSYS CFX to predict the improvements in film cooling performance with dual trench. Dual-trench configuration consists of two trenches together, one wider trench and the other is narrow trench that extruded from the wider one. Several blowing ratios in the range (0.5:5) were investigated. The pitch-to-diameter ratio of 2.775 is used. By using the dual trench configuration, the coolant jet impacted the trench wall two times allowing increasing the spreading of coolant laterally in the trench, reducing jet velocity and jet completely covered on the surface. The results indicate that this configuration increased adiabatic effectiveness as blowing ratio increased. The spatially averaged adiabatic effectiveness reached 57.6% for at M= 2. No observed film blow-off at all blowing ratios. The adiabatic film effectiveness of dual trench case outperformed the narrow trench case, laidback fan-shaped hole, fan-shaped hole and cylinder hole at different blowing ratios.     

Does regional travel time unreliability influence mode choice?

Researchers and practitioners highlight the unreliability of travel as a potential weak link in the transportation system which may inhibit individuals’ accessibility and urban economic activity. With the trend towards increasing traffic congestion, the outlook suggests that travel conditions will become structurally less reliable over time, but that not all places will be equally affected. But is travel time unreliability a problem? This study uses global positioning systems travel survey data for Chicago to build a regional model of travel time unreliability. The results suggest that unreliability varies spatially during different time periods, but that the average overall network unreliability varies little across times in the day. Using the Chicago Metropolitan Agency for Planning (CMAP)’s 2007 Travel Tracker Survey, a household travel diary survey including both GPS and non-GPS components, we estimate a mode choice model for work trips to explore the influence of unreliability on travel behavior. The results suggest that unreliable auto travel conditions induce mode switching to transit and that the influence is strongest when service by train is already faster than by car. This further suggests that auto travel unreliability may have the strongest influence in metropolitan regions with highly-competitive transit systems. Nevertheless, the influence of travel unreliability is limited and is not the underlying driver of travel decision-making.     

Transport in developing and emerging nations

One perspective on the allocation of transport investments by public authorities is offered by the so‐called ‘pork barrel’ model, whereby politicians and political parties allocate public investment spatially in such a way as to gain electoral support from localities so benefited. The paper introduces this model and discusses its attractions and problems in the case of the transport sector. A review of the modest number of published examples of this approach is offered before a detailed case study considers the case of railway investment in Nelson, New Zealand.     

Vehicular pollution prediction modelling: a review of highway dispersion models

Air quality modelling plays an important role in formulating air pollution control and management strategies by providing guidelines for better and more efficient air quality planning. Several line source models, mostly Gaussian‐based, have been suggested to predict pollutant concentrations near highways/roads. These models, despite several assumptions and limitations, are used throughout the world, including in India, to carry out air pollution prediction analysis due to vehicular traffic near roads/highways. These models are being continuously upgraded and modified based on field experiments, and numerical and physical modelling results. An effort has been made in the present paper to review briefly the philosophy and basic features of most of the commonly used highway dispersion models. The paper also discusses various theories and techniques that led to the development and modification of these models along with the statistical analysis tools to evaluate the performance of these models. An attempt has also been made to summarize briefly the various line source models currently used in India and to highlight the difficulties being faced while using them in an Indian context.     

An international study on land‐use and transport interaction

This paper underlines the important role played by the interaction between transport and land use in the way cities develop and the need to use a fully integrated land‐use/transport model to assess the longer‐term impacts of urban policies. Since most of the models of this type had never been properly tested, the Transport and Road Research Laboratory in the early 1980s set up a collaborative study to examine critically their performance and to assess the impacts of a range of commonly applied policies.

The paper briefly describes the first phase of the study in which nine models from seven countries were subjected to a rigorous set of tests covering a variety of policies. For practical reasons each model was applied to the city on which it was originally calibrated. To overcome some of the problems of comparison, a second phase of the study was conducted in which some models were applied to several cities each so that the differences due to the particular characteristics of the cities could be identified. In carrying out this phase, some cities were examined by several models and discrepancies in the results analysed. The setting up of the second phase of the study is outlined in this paper, but not the results, which are given in later papers in this and subsequent issues of Transport Reviews.     

Designing H∞/GH 2 static-output feedback controller for vehicle suspensions using linear matrix inequalities and genetic algorithms

This paper presents an approach to design the H_∞/GH ₂ static-output feedback controller for vehicle suspensions by using linear matrix inequalities (LMIs) and genetic algorithms (GAs). Three main performance requirements for an advanced vehicle suspension are considered in this paper. Among these requirements, the ride-comfort performance is optimized by minimizing the H_∞ norm of the transfer function from the road disturbance to the sprung mass acceleration, while the road-holding performance and the suspension deflection limitation are guaranteed by constraining the generalized H₂ (GH ₂) norms of the transfer functions from the road disturbance to the dynamic tyre load and the suspension deflection to be less than their hard limits, respectively. At the same time, the controller saturation problem is considered by constraining its peak response output to be less than a given limit using the GH ₂ norm as well. A four-degree-of-freedom half-car model with active suspension system is applied in this paper. Several kinds of H_∞/GH ₂ static-output feedback controllers, which use the available sprung mass velocities or the suspension deflections as feedback signals, are obtained by using the GAs to search for the possible control gain matrices and then resolving the LMIs together with the minimization optimization problem. These designed H_∞/GH ₂ static-output feedback controllers are validated by numerical simulations on both the bump and the random road responses which show that the designed H_∞/GH ₂ static-output feedback controllers can achieve similar or even better active suspension performances compared with the state-feedback control case in spite of their simplicities.     

Interaction of vehicle and steering system regarding on-centre handling

For the on-centre handling behaviour of vehicles the steering system is absolutely important. To investigate the interaction of the vehicle and steering system a validated, especially tailored simulation model was developed. Some meaningful vehicle and steering system parameters are altered to show the influence on steering wheel torque, steering feel and understeer. The results underline the importance of an accurate steering system model. Identified measures to improve the centre feel and steering response were a stiffer torsion bar, a higher cornering stiffness or a lower overall steering ratio. The steering response, however, suffers when the centre feel is improved by a higher trail. The steering rack friction reduces mainly the steering response while the steering column friction decreases the centre feel whereas a stiffer torsion bar lessens the understeer tendency.     

Methane release and coastal environment in the East Siberian Arctic shelf

In this paper we present 2 years of data obtained during the late summer period (September 2003 and September 2004) for the East Siberian Arctic shelf (ESAS). According to our data, the surface layer of shelf water was supersaturated up to 2500% relative to the present average atmospheric methane content of 1.85 ppm, pointing to the rivers as a strong source of dissolved methane which comes from watersheds which are underlain with permafrost. Anomalously high concentrations (up to 154 nM or 4400% supersaturation) of dissolved methane in the bottom layer of shelf water at a few sites suggest that the bottom layer is somehow affected by near-bottom sources. The net flux of methane from this area of the East Siberian Arctic shelf can reach up to 13.7 × 10⁴ g CH₄ km^− 2 from plume areas during the period of ice free water, and thus is in the upper range of the estimated global marine methane release. Ongoing environmental change might affect the methane marine cycle since significant changes in the thermal regime of bottom sediments within a few sites were registered. Correlation between calculated methane storage within the water column and both integrated salinity values (r = 0.61) and integrated values of dissolved inorganic carbon (DIC) (r = 0.62) suggest that higher concentrations of dissolved methane were mostly derived from the marine environment, likely due to in-situ production or release from decaying submarine gas hydrates deposits. The calculated late summer potential methane emissions tend to vary from year to year, reflecting most likely the effect of changing hydrological and meteorological conditions (temperature, wind) on the ESAS rather than riverine export of dissolved methane. We point out additional sources of methane in this region such as submarine taliks, ice complex retreat, submarine permafrost itself and decaying gas hydrates deposits.     

A decision support system for integrated hazardous materials routing and emergency response decisions

Hazardous materials routing constitutes a critical decision in mitigating the associated transportation risk. This paper presents a decision support system for assessing alternative distribution routes in terms of travel time, risk and evacuation implications while coordinating the emergency response deployment decisions with the hazardous materials routes. The proposed system provides the following functionalities: (i) determination of alternative non-dominated hazardous materials distribution routes in terms of cost and risk minimization, (ii) specification of the hazardous materials first-response emergency service units locations in order to achieve timely response to an accident, and (iii) determination of evacuation paths from the impacted area to designated shelters and estimation of the associated evacuation time. The proposed system has been implemented, used and evaluated for assessing alternative hazardous materials routing decisions within the heavily industrialized area of Thriasion Pedion of Attica, Greece. The implementation of the aforementioned functionalities is based on two new integer programming models for the hazardous materials routing and the emergency response units location problems, respectively. A simplified version of the routing model is solved by an existing heuristic algorithm developed by the authors. A new Lagrangean relaxation heuristic algorithm has been developed for solving the emergency response units location problem. The focus of this paper is on the exposition of the proposed decision support system components and functionalities. Special emphasis is placed on the presentation of the two new mathematical models and the new solution method for the location model.