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711.
This paper presents a detailed exploratory analysis of joint activity participation characteristics using the American Time
Use Survey (ATUS). As a very large nationwide survey that explicitly elicited information on both household and non-household
companions for each activity episode, the ATUS is ideally suited for this analysis. Several intuitive and interesting results
are obtained. Joint episodes are found to be of longer durations, significantly likely to take place at the residence of other
people, and often confined to certain time periods of the weekday. In addition, important differences in these characteristics
are also observed based on activity purpose, companion type, and the day of the week. These findings are intended to provide
the basis for the justification of detailed collection of joint activity–travel participation information in household activity–travel
surveys, and also as a stimulant for further empirical analysis and modeling of joint activity participation behavior.
相似文献
Chandra R. BhatEmail: |
712.
D. H. Koo J. C. Kim W. H. Yoo T. W. Park 《Transportation Research Part D: Transport and Environment》2002,7(6)
Wheel/rail interaction is a major source of railway noise. A low-noise wheel structure is developed and its effect on noise reduction is investigated. This low-noise wheel employs a rubber material inserted into the steel rim or mounted on the wheel surface. The low-noise wheel has low stiffness and a high-damping ratio compared to a solid wheel. Measurement shows that it reduces rolling and squealing. It turns out that a subway line with the proposed wheel could reduce its interior noise level by 4–5 dB(A) and vehicle vibration level by 7–8 dB. While the proposed structure seems promising in noise reduction for railway vehicles, the endurance and cost effectiveness of the low-noise wheel are yet to be verified. 相似文献
713.
为了提高山区公路抗水灾能力,在实地调查、研究基础之上,详细阐明了山区公路水灾害评价中危险性、易损性、损失、风险、减灾效益等基本概念。提出了山区公路水灾害评价系统应由危险性评价、易损性评价、风险评价及减灾效益评价4部分构成,而对于路网水灾害评价应由点、线、面构成,首次建立了完整的三维评价体系。指出对已有公路的防排水与抗水毁能力的工程评价,是水毁防治工程投资决策的重要依据,应作为重点进行研究。对于路网水灾害评价,应侧重于点(点单元)评价,适当考虑线评价。最后,从致灾因子、承灾体、灾情及防灾减灾4个方面构建了公路水灾害评价基本模型。 相似文献
714.
715.
Fuel economy comparison of conventional drive trains series and parallel hybrid electric step vans 总被引:1,自引:0,他引:1
S. B. Han Y. H. Chang Y. J. Chung E. Y. Lee B. Suh A. Frank 《International Journal of Automotive Technology》2009,10(2):235-240
A hybrid electric vehicle (HEV) is a vehicle that combines a conventional propulsion system with an on-board rechargeable
energy storage system to achieve better fuel economy than a conventional vehicle HEVs do not have limited ranges like battery
electric vehicles, which use batteries charged by an external source. The different propulsion power systems may have common
subsystems or components. The objective of this study is to compare the fuel economies of a conventional step van, a series
hybrid electric step van (HESV), and a parallel HESV by calculating the fuel consumption using the ADVISOR software by NREL.
We also showed the results of the vehicles in different driving cycles including the Central Business District bus cycles,
the New York City Cycle, and the US EPA City and Highway cycles. 相似文献
716.
In this work a two-stroke scooter engine was modified to work with semi-direct injection of gasoline at a pressure of 8 bar
from an injector in the cylinder barrel pointed toward the cylinder head. The influence of injection timing, injection pressure,
spark plug location and air-fuel ratio, on performance, emissions and combustion characteristics has been investigated. In
addition, a comparison has been made with manifold injection of gasoline on the same engine at a given speed and various outputs.
A significant reduction in HC emissions and fuel consumption with no adverse effects on NOx emissions and combustion stability
was observed. A small drop in power and increase in CO emission were observed disadvantages of the new injection system. Injection
timing was found to be the most important factor and a balance between reduction in shortcircuited fuel by late injection,
and time for mixture preparation by advancing the injection, was found to be essential. 相似文献
717.
Reliability-based sensitivity analysis of vehicle components with non-normal distribution parameters
Techniques from the perturbation method, fourth moment method, reliability-based design theory, and sensitivity analysis approach
are employed to present a practical and efficient method for testing the reliability sensitivity of vehicle components with
non-normal distribution parameters. With the condition that the first four moments of original random variables are known,
the reliability sensitivity theory and cases are researched using the presented numerical method. The variation regularities
of reliability sensitivity are obtained and the effects of design parameters on reliability of the vehicle components are
studied. The sophisticated formulation provided in this paper is easily amenable to computational procedures. The respective
program can be used to obtain the reliability sensitivity of vehicle components with non-normal distribution parameters accurately
and quickly. The results obtained are perfect and the solutions compared very well with those from Monte Carlo simulation.
The method presents a theoretic basis for the reliability design of the vehicle components. 相似文献
718.
Model-based control system design in a urea-SCR aftertreatment system based on NH3 sensor feedback 总被引:1,自引:0,他引:1
M. Devarakonda G. Parker J. H. Johnson V. Strots 《International Journal of Automotive Technology》2009,10(6):653-662
This paper presents preliminary control system simulation results in a urea-selective catalytic reduction (SCR) aftertreatment
system based on NH3 sensor feedback. A four-state control-oriented lumped parameter model is used to analyze the controllability and observability
properties of the urea-SCR plant. A model-based estimator is designed via simulation and a control system is developed with
design based on a sliding mode control framework. The control system based on NH3 sensor feedback is analyzed via simulation by comparing it to a control system developed based on NOx sensor feedback. Simulation results show that the NH3 sensor-based strategy performs very similarly in comparison to a NOx sensor-based strategy. The control system performance metrics for NOx index, urea index, urea usage, and NH3 slip suggest that the NOx sensor can be a potential alternative to a NOx sensor for urea-SCR control applications. 相似文献
719.
W. B. Hou H. Z. Zhang R. F. Chi P. Hu 《International Journal of Automotive Technology》2009,10(2):175-180
The concept design phase is a critical step in auto-body design, as it has a great effect on later design work. This paper
describes the implementation of an auto-body structure design in the early stages of a new auto-body developing program. In
order to reduce the long design period and analysis error that plagues traditional auto-body concept design, an intelligent
CAE system has been successfully developed and implemented based on the UGS NX/API opening platform. This system, the so-called
ACD-ICAE (Auto-body concept design-intelligent computer aided engineering) System that means concept design-intelligent computer
aided engineering system, employs a fully parametrized template method to build the conceptual auto-body geometry model and
FEM model quickly and easily. It also integrates auto-body modeling, analysis and optimization on only one CAD platform via
a parametric variables database. Moreover, all parametric variables are shared and updated in different phases of the ACD-ICAE
System. A wizard User Interface (UI) based on knowledge of auto-body engineering was developed and used in this system. The
procedures implementing the functional diagram of the ACD-ICAE system are also provided. A typical example of a car body concept
design with four doors shows that the ACD-ICAE system is efficient and accurate. 相似文献
720.
In this study, a parallel flow condenser and laminated evaporator for an automotive air-conditioning system were modified
to improve performance. Gas-liquid separation type condensers, in which the condenser and receiver drier are integrated, and
one-tank laminated type evaporators were developed, and their performances were investigated experimentally using HFC-134a.
Heat transfer characteristics in the condenser are examined by means of air temperature, air velocity entering the condenser
and inlet pressure of the refrigerant; heat transfer characteristics in the evaporator are examined by means of air temperature,
relative humidity, flow rate of air, outlet pressure of refrigerant and superheat. Pressure drops for both evaporator and
condenser are also measured, and correlations for pressure drop are derived for the condenser and evaporator, respectively.
Air velocity and mass flow rate of the refrigerant have a significant effect on the overall heat transfer coefficient, and
flow pass is not significantly influenced by the cooling capacity of the condenser. The overall heat transfer coefficient
of the evaporator increases as air flow rate, air temperature and relative humidity increases. 相似文献