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121.
Knut Veisten Stefan Flügel Luis I. Rizzi Juan de Dios Ortúzar Rune Elvik 《Research in Transportation Economics》2013
Stated choice studies have been applied regularly to the valuation of time savings and other attributes of travelling as perceived by individuals. In such experiments, respondents often provide reference levels for the attributes and the hypothetical choices presented to them are pivoted around actual behaviour. However, most individuals are not able to provide reference levels for the number of casualties on the road they travel. Thus, if valuation of this important element is attempted, it is the researcher who must provide casualty risk reference levels to the respondents. Some studies have applied route choice experiments including a safety attribute but the majority has been limited to only one particular road section with a common baseline risk for all respondents. 相似文献
122.
In this paper, a tramp ship routing model of fleet deployment in a hub-and-spoke network is presented. This model simultaneously determines the selection of hubs, the assignment of spokes to hubs, the deployment of feeder-containerships as well as containership routing between spokes and spokes, hubs and spokes, and hubs and hubs. Even though some parts have been studied, this complex combination of shipping problems has never been addressed. Because the problem is NP-hard, a genetic algorithm (GA) with local search is proposed. In the algorithm, a cut-off procedure is applied to fleet deployment in a sub-route strategy. A number of randomly generated problem instances are solved by both a mathematical program and the GA with local search. A simple but realistic heuristic algorithm is also developed. Both the GA with local search and the heuristic algorithm are used to solve a number of real case instances. A comparison of the results shows the efficiency of the GA with local search. The developed model can be used as a route-decision support tool for shipping companies that provide long-haul shipping services in a hub-and-spoke network. 相似文献
123.
Chong Wu Xin‐ying Zhang I‐Cheng Yeh Fei‐yu Chen Jacob Bender Tie‐nan Wang 《先进运输杂志》2013,47(7):619-634
With the development of a national market economy, the Chinese aviation industry is now confronted with international competition. Therefore, it is necessary to research the competitive status of Chinese national aviation, as well as advice on how to enhance the competitiveness of the Chinese aviation industry. The main objective of this paper is to propose FAHP as an effective solution for resolving the uncertainty and imprecision in the evaluation of airlines' competitiveness. In this paper, we review the research of industrial international aviation competitiveness at both home and abroad, discuss a theoretical framework for the study of aviation competitiveness, establish an index system with five first‐order indicators and 17 second‐order indicators, set up a Chinese aviation competitiveness model based on simple fuzzy numbers from the fuzzy analytic hierarchy process, and evaluate the competitiveness of five major Chinese airlines. The results showed that this model and these indicators are scientific and practical, with a wide range of application prospects for the purpose of improving and increasing Chinese airline competitiveness in the international market. The effective approach presented in this paper is especially applicable when subjective judgments on performance ratings and attribute weights are not accessible or reliable, or when suitable decision makers are not available. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
124.
Hydraulically damped rubber mount (HDM) can effectively attenuate vibrations transmitted between an automotive powertrain
and body/chassis and reduce interior noise in the car compartment. Predicting the dynamic characteristics of a HDM faces challenges
due to fluid-structure interactions between the rubber spring and fluid in the chambers, nonlinear material properties of
the rubber parts and turbulent flow in the chambers and fluid track linking chambers. In this paper, an experimental analysis
and hydrostatic finite element (FE) modeling technique are integrated in a numerical simulation approach to modeling the dynamic
characteristics of a HDM with a lumped-parameter HDM model. The dynamic characteristics of a typical HDM with a fixed decoupler
are predicted and compared with experimental results, which verify the effectiveness of the proposed approach. Moreover, a
parametric effect analysis is performed to demonstrate parameter influence on dynamic characteristic, which provides a concise
design guideline for the parameter adjustments necessary for a HDM to meet the vibration isolation requirements of a powertrain
mount system. 相似文献
125.
Effect of various LPG supply systems on exhaust particle emission in spark-ignited combustion engine
J. W. Lee H. S. Do S. I. Kweon K. K. Park J. H. Hong 《International Journal of Automotive Technology》2010,11(6):793-800
The particle size distribution and particle number (PN) concentration emitted by internal combustion engine are a subject
of significant environmental concern because of their adverse health effects and environmental impact. This subject has recently
attracted the attention of the Particle Measurement Programme (PMP). In 2007, the UN-ECE GRPE PMP proposed a new method to
measure particle emissions in the diluted exhaust of automotive engines and a regulation limit (<6.0×1011 #/km, number of particles). The specific PN regulation of spark-ignited combustion engine will be regulated starting on September
1, 2014 (EURO 6). In this study, three types of LPG supply systems (a mixer system and a multi-point injection system with
gas-phase or liquid-phase LPG fuel) were used for a comparison of the particulate emission characteristics, including the
nano-sized particle number density. Each of the three LPG vehicles with various LPG injection systems contained a multi-cylinder
engine with same displacement volumes of 2,000 cm3 and a three-way catalytic converter. The test fuel that was used in this study for the spark-ignited combustion engine was
n-butane basis LPG fuel, which is primarily used for taxi vehicles in Korea. The characteristics of nano-particle size distribution
and number concentration of particle sizes ranging from 20 to 1,000 nm (aerodynamic diameter) that were emitted from the three
LPG vehicles with various LPG supply systems were investigated by using a condensation particle counter (CPC), which is recommended
by the PMP under both the NEDC and FTP-75 test modes on a chassis dynamometer. The experimental results indicate that the
PN emission characteristics that were obtained by the CPC system using the PMP procedure are sufficiently reliable compared
to other regulated emissions. Additionally, the sources of PN emissions in ascending order of magnitude are as follows: mixer
type, gas-phase LPG injection (LPGi) and liquid-phase LPG injection (LPLi) passenger vehicles. The liquid-phase LPG injection
system produced relatively large particle sizes and number concentrations compared to the gaseous system, regardless of the
vehicle driving cycle. This phenomenon can be explained by unburned micro-fuel droplets that were generated due to a relatively
short homogeneous fuel-air mixture duration in the engine intake manifold. Also the particle number emissions from the LPG
vehicle were influenced by the vehicle driving cycle. 相似文献
126.
W. Ryu N. Cho I. Yoo H. Song H. Kim 《International Journal of Automotive Technology》2009,10(1):115-121
In this study, the performance of a CVT clutch system for a hybrid electric vehicle was investigated. To analyzed the vehicle
performance at restart, the restart delay and driveshaft torque was investigated by simulations and experiments. It was found
from the simulation results that the vehicle restart response depends on the clutch pressure buildup time to the point where
the clutch torque begins to overcome the vehicle road load, and driving comfort at restart is directly related to the rate
change of the clutch pressure. 相似文献
127.
H. S. Wi Y. K. Lee J. I. Park J. H. Lee K. S. Park 《International Journal of Automotive Technology》2009,10(6):771-776
This paper focuses on fuel economy improvement according to the type of power steering system. Usually, a conventional power
steering system is directly driven by the crankshaft of the engine with a belt, known as HPS (hydraulic power steering). However,
there is some inefficiency with this system at high engine speeds. To improve this inefficiency, automobile makers have developed
two power steering systems: EHPS (electro-hydraulic power steering) and MDPS (motor-driven power steering) or EPS (electric
powered steering). However, there has been insufficient study of effects of the type of power steering system on fuel economy.
In this paper, the effect of the type of power steering system on fuel economy is studied experimentally, and calculations
of the effect on vehicle fuel economy are presenting using computer simulation with AVL cruise software. The results demonstrate
that a 1% vehicle fuel economy improvement can be achieved in a vehicle with an electro-hydraulic power steering system compared
to a vehicle with a hydraulic power steering system. In addition, a 1.7% vehicle fuel economy improvement can be achieved
using a full electric power steering system in a FTP-75 driving cycle. These results could be used to choose a power steering
system. 相似文献
128.
C. L. Myung K. H. Choi I. G. Hwang K. H. Lee S. Park 《International Journal of Automotive Technology》2009,10(2):161-166
In SI engines, valve events have a major influence on volumetric efficiency, fuel economy and exhaust emissions. Moreover,
swirl and tumble motions in the intake charge also improve combustion speed and quality by stratifying the mixture as well
as intensifying the mixing rate of air and fuel. This paper investigates the behaviors of an engine and the combustion phenomenon
for various intake valve timings and intake charge motions using CVVT system and port masking schemes. Test condition includes
a part load and a cold idle condition inclusive of a cold start of the engine. Time-resolved HC and NOx emissions were also
measured at an exhaust port to examine their formation mechanisms and behaviors with fast response HC/NOx analyzers. In conclusion,
the fast burning of fuel and improved combustion quality by enhanced charge motions reduced unburned HC emissions, and advancing
the intake valve opening reduced HC as well as NOx. Furthermore, HCs during the cold transient phase and idle conditions decreased
with recalibrated start parameters such as lean air-fuel ratio and spark retardation via the enhancement of intake charge
motions. 相似文献
129.
This paper introduces a methodology for the characterization of ports, employing specifically defined eco-efficiency indicators and combining typically available data (handled cargo, containers and passengers) with ship exhaust pollutants values (mainly NOx, SOx and PM) and anticipated external costs (ECs) due to emitted air pollutants to provide a collective overview of all port-related economic and environmental activities. The results from an applied case study allow a comparative evaluation of 16 selected ports based on 17 different evaluation criteria and denote that the employment of such an overall approach can allow port authorities to improve managerial aspects, potentially lower operational costs and promote reduced environmental effects. 相似文献
130.
戴雅康 《大连铁道学院学报》1989,10(3):61-68
本文通过对用铌磷半钢配制的中磷闸瓦的金相组织、力学性能、物理性能和摩擦-磨损特性的研究及其实际运行,证明:其质量指标和使用性能完全满足 TB1159-76标准,并超过普通中磷闸瓦的技术水平;可使中磷铸铁闸瓦的原材料成本降低10%左右. 相似文献