Performance of radial-type metal foam diesel particulate filters

An analytical study of the performance of a radial-type, metal foam diesel particulate filter is reported. A mathematical model for the filtration and regeneration of soot in a metal foam filter was developed. Nickel foam was selected for the filter medium due to its large specific area, high porosity, and high thermal resistance. For various metal foams, the filtration efficiency and the pressure drop through the filter were calculated, as was the deposition of soot. The results from the analytical model were compared with experimental data. In comparison with a conventional wall flow filter, the metal foam diesel particulate filter (DPF) is effective in utilizing the volume of material, due to the porous structures. As the size of the metal foam pores in the DPF increases from 580 μm to 800 μm, the filtration efficiency decreases from 90% to 50%, and the pressure drop decreases from 380 mbar to 20 mbar. The metal foam DPF with a large pore size is effective in utilizing the volume of material with a small pressure drop. The regeneration is completed within four minutes by the flow of hot exhaust gases under full load conditions.     

Effects of residual stresses on the static and fatigue strength of laser-welded lap joints with different welding speeds

This study was conducted to determine whether the different residual stresses caused by different welding speeds affect the static and fatigue strength of laser-welded lap joints. Residual stresses in STS301L laser-welded lap joints of different thicknesses under two laser-welding speed conditions, 4.1 m/min and 5.1 m/min, were evaluated with the incremental hole-drilling strain gage method at the middle of the heat-affected zone (HAZ). Then, static and fatigue tests were performed. The results show that higher static and fatigue strengths were obtained from the specimens welded with a 4.1 m/min welding speed than from the specimens welded at 5.1 m/min. The main difference was due to the compressive principal residual stress magnitude and its orientation near the HAZ. Also, the micro-hardness profile along the failure interface was measured to verify the static and fatigue failure behavior.     

Optimum SUV bumper system design considering pedestrian performance

Until recently, passenger cars have primarily interested in pedestrian protection performance. Nowadays, however, it is important for a sport-utility vehicle (SUV) to meet the bumper system standards for pedestrian safety. For a SUV bumper system, there are some difficulties in attaining a high level of pedestrian performance for the lower legform. An SUV has a high bumper position from the ground level, and the bumper approach angle must also be secured, which has an effect on car insurance fees. Due to these reasons, it is difficult to meet the pedestrian performance of the lower legform for an SUV. In this paper, a comparative study was performed on various SUV bumper systems, and a concept model for a SUV bumper system was developed, which is expected to meet the pedestrian performance by using the Pugh method. The design control factors were defined to affect the bumper pedestrian performance through the experiences of tests and analyses. For the noise factor to affect the pedestrian performance, the deviation of the impactor position was selected at the moment of impact. The design control factors were optimized by using the Taguchi optimization technique. For the Taguchi method, an L18 orthogonal array table of design control factors was used in the optimization process. Particularly, for the optimization of the bumper corner region, an optimization analysis was performed three times to meet pedestrian performance. Based on the results of the Taguchi optimization method, the sensitivity of the bumper design parameters was studied, and a new SUV bumper system is proposed that satisfies the pedestrian performance of the lower legform. The optimized bumper system should obtain a full Euro-NCAP score of 6 points for the bumper test. The pedestrian performance of the optimized bumper system is validated by using a CAE (Computer Aided Engineering) analysis, which has been proven to be in accurate. A comparison between the test and analysis results is shown for the validation of accuracy. By using the optimized bumper system, the tests and development costs of a bumper can be reduced.     

Experimental investigation of the valvetrain friction in actual engine operation conditions

Recently, the demands for improved fuel economy have been continually rising because of environmental protection policies, legislative pressures on emissions and increases in the price of oil. Reducing the friction power loss in a production engine may be regarded as one of the most effective technologies for improving fuel economy because the technology is cost effective and applicable to a great number of vehicles. This paper describes attempts to measure the torque needed to drive a camshaft and to examine the sources of the torque fluctuations in order to analyze the friction in valvetrains. The measurements were performed through a cam sprocket-type torquemeter, which was able to measure the torque of the valvetrain under actual engine operating conditions. In the cam torque measured, the fluctuations were mainly dependent on the primary oscillations caused by cam events and the secondary oscillations caused by the valvetrain natural frequency. The range of the fluctuations became greater at high speed because of the inertial mass. The resulting FMEP (friction mean effective pressure) of the valvetrain decreased, and the effective peak tension increased with an increase in the engine speed.     

Modeling stochastic perception error in the mean-excess traffic equilibrium model

In this paper, we extend the α-reliable mean-excess traffic equilibrium (METE) model of Chen and Zhou (Transportation Research Part B 44(4), 2010, 493-513) by explicitly modeling the stochastic perception errors within the travelers’ route choice decision processes. In the METE model, each traveler not only considers a travel time budget for ensuring on-time arrival at a confidence level α, but also accounts for the impact of encountering worse travel times in the (1 − α) quantile of the distribution tail. Furthermore, due to the imperfect knowledge of the travel time variability particularly in congested networks without advanced traveler information systems, the travelers’ route choice decisions are based on the perceived travel time distribution rather than the actual travel time distribution. In order to compute the perceived mean-excess travel time, an approximation method based on moment analysis is developed. It involves using the conditional moment generation function to derive the perceived link travel time, the Cornish-Fisher Asymptotic Expansion to estimate the perceived travel time budget, and the Acerbi and Tasche Approximation to estimate the perceived mean-excess travel time. The proposed stochastic mean-excess traffic equilibrium (SMETE) model is formulated as a variational inequality (VI) problem, and solved by a route-based solution algorithm with the use of the modified alternating direction method. Numerical examples are also provided to illustrate the application of the proposed SMETE model and solution method.     

Global optimization method for mixed transportation network design problem: A mixed-integer linear programming approach

This paper proposes a global optimization algorithm for solving a mixed (continuous/discrete) transportation network design problem (MNDP), which is generally expressed as a mathematical programming with equilibrium constraint (MPEC). The upper level of the MNDP aims to optimize the network performance via both expansion of existing links and addition of new candidate links, whereas the lower level is a traditional Wardrop user equilibrium (UE) problem. In this paper, we first formulate the UE condition as a variational inequality (VI) problem, which is defined from a finite number of extreme points of a link-flow feasible region. The MNDP is approximated as a piecewise-linear programming (P-LP) problem, which is then transformed into a mixed-integer linear programming (MILP) problem. A global optimization algorithm based on a cutting constraint method is developed for solving the MILP problem. Numerical examples are given to demonstrate the efficiency of the proposed method and to compare the results with alternative algorithms reported in the literature.     

The economics of parking provision for the morning commute

In this paper, we study the economics of parking provision for the morning commute, where all the parking lots are owned and operated by private operators. The parking capacity allocations, parking fees and access times are considered in a parking market. First we solve the parking market equilibrium without regulatory intervention, revealing four types of competitive equilibrium. Only one of the four types of equilibrium, however, is found to be stable and realistic, and under it each parking area is preferred by the commuters during certain time periods. Compared to the case without parking choice, provision of parking through a competitive market is able to reduce commuters’ travel cost and queuing delay, but it does not necessarily lead to the most desirable market outcome that minimizes social cost or commuter cost. This issue can be addressed through market regulations, such as price-ceiling, capacity-floor or capacity-ceiling, and a quantity tax/subsidy regulation. It is found that both price-ceiling and quantity tax/subsidy regulations can efficiently reduce both the system cost and commuter cost under certain conditions, and help ensure the stability of the parking market. Numerical examples are also provided to illustrate these findings and furthermore, how a price ceiling or a quantity tax/subsidy should be set in a parking market under realistic model parameters.     

Road transport and climate change: Stepping off the greenhouse gas

Transport is Australia’s third largest and second fastest growing source of greenhouse gas (GHG) emissions. The road transport sector makes up 88% of total transport emissions and the projected emissions increase from 1990 to 2020 is 64%. Achieving prospective emission reduction targets will pose major challenges for the road transport sector. This paper investigates two targets for reducing Australian road transport greenhouse gas emissions, and what they might mean for the sector: emissions in 2020 being 20% below 2000 levels; and emissions in 2050 being 80% below 2000 levels. Six ways in which emissions might be reduced to achieve these targets are considered. The analysis suggests that major behavioural and technological changes will be required to deliver significant emission reductions, with very substantial reductions in vehicle emission intensity being absolutely vital to making major inroads in road transport GHG emissions.     

Transport policy for London in 2001 The case for an integrated approach

The paper reports the results of a series of studies conducted to enable the London Planning Advisory Committee to provide advice on strategic transport policy for London. The analytical approach combined the use of an area-based, multi-modal strategic model (LAM) and professional judgment. The performance of LAM as a basis for providing rapid advice on complex issues in transport policy is assessed.The resulting policy advice advocated a coherent approach, involving new infrastructure, particularly for rail; improved management of the road and public transport networks; the use of subsidy to enhance public transport service levels; and road user charges to reduce the impact of private vehicles on congestion and the environment. Road user charges emerged as the pivotal issue in the policy; the paper discusses their role, and the questions which still need to be resolved before they can be implemented.The main message of the study is that no one element of transport policy can tackle London's problems alone; an integrated policy in which infrastructure provision, management and pricing are used to complement one another is shown to be far more effective.     

Port pricing: a cost axiomatic approach

The earlier port pricing literature argued that port prices should be based uponk marginal cost pricing. However, recent literature suggests that a conflicts would arise between marginal cost pricing and full cost recovery at ports. Further, problems arise in determining or estimating marginal costs. A price structure that addresses the problems of port marginal cost pricing is cost axiomatic pricing, given the goals, objectives and constraints of ports. Fairness and cost efficiency cost axioms for ports are considered. A methodology for determining cost axiomatic prices for a marine container terminal is presented.