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291.
由于在模拟密集网络、宏观问题和方案阶段中的优势,连续性模拟方法应用到交通模型的模拟中,正在得到越来越多的关注。此论文意在为二维连续模拟方法的发展和应用提供综合的概括。首先讨论的是理论的发展和对特殊的或多变领域机理的模拟,然后再针对连续模拟方法应用到工厂选址、道路选择、人行道的规划、政策和社会经济分析进行评论。最后,预测其未来研究的前景。 相似文献
292.
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
293.
Predictive control of a vehicle trajectory using a coupled vector with vehicle velocity and sideslip angle 总被引:2,自引:0,他引:2
In this paper, a predictive algorithm for vehicle trajectory control using the vehicle velocity and sideslip angle is proposed.
Since the driving state of a vehicle generates nonholonomic constraint equations, it is difficult to control the trajectory
with a conventional control algorithm. Furthermore, control vectors such as vehicle velocity and sideslip angle are coupled
together; hence, a separate control for each variable is not suitable. In this study, a coupled control vector that combines
the velocity and sideslip angle is proposed for the predictive control of vehicle trajectory. Since the coupled control vector
is derived from the status of the vehicle’s motion, it is easy to generate a feedback control vector for the predictive controller.
The coupled vector cannot be directly used as input to the vehicle systems; therefore, the vehicle input vector should be
calculated from the control vector using a nonlinear function. Since nonlinear functions are not inserted in the control loop,
they are calculated by the controller. Therefore, this method does not require a linearization process in the control logic,
which enhances the stability and accuracy of the predictive controller. 相似文献
294.
H. S. Kook S. R. Shin K. D. Ih D. B. Kim D. H. Yu 《International Journal of Automotive Technology》2009,10(1):55-63
The large-scale shear flows over the sunroof opening of a mid-sized SUV measured using a PIV system were investigated. The
shear flows were measured for five different cases of deflector protrusion (one case was the baseline test without deflector)
at two different free stream flow velocities below the critical velocity where the buffeting noise level reached a maximum.
The structures of the shear flows were observed to differ, apparently depending on whether the radiated buffeting noise is
relatively strong or not. For strongly buffeting experimental cases, the momentum thicknesses of the shear layers were observed
to grow rapidly and saturated at a station near the downstream edge of the sunroof opening, where the saturation of the transverse
velocity fluctuations was also observed, and where the vortex coalescence process was presumably completed. On the other hand,
no discrete large-scale vortex structures were observed for none-buffeting or weakly buffeting cases. Streamwise growth of
the velocity fluctuations was found to be well predicted by a linear hydrodynamic instability analysis for the strongly buffeting
cases. Numerical results obtained from a linear inviscid instability analysis using a hyperbolic tangent mean velocity profile
were used to calculate the amplification factors with the initial momentum thickness and the streamwise fluctuation wavenumber.
The shear flows were found to form large-scale discrete vortices when the linear inviscid amplification factors exceeded a
threshold amplification factor. 相似文献
295.
G. S. Jung Y. H. Sung B. C. Choi M. T. Lim 《International Journal of Automotive Technology》2009,10(1):1-7
Compression ignition of homogeneous charges in internal combustion (IC) engines is expected to offer high efficiency of DI
diesel engines without high levels of NOx and particulate emissions. This study is intended to find ways of extending the
rich limit of HCCI operation, one of the problems yet to be overcome. Exhaust emissions characteristics are also explored
through analyses of the combustion products. DME fuel, either mixed with air before induction or directly injected into the
combustion chamber of a rapid compression and expansion machine, is compressed to ignite under various conditions of compression
ratio, equivalence ratio, and injection timing. The characteristics of the resulting combustion and exhaust emissions are
discussed in terms of the rate of heat release computed from the measured pressure, and the concentrations of THC, CO, and
NOx are measured by FT-IR and CLD. The experimental data to date show that operation without knock is possible with mixtures
of higher equivalence ratio when DME is directly injected rather than when it is inducted in the form of a perfectly homogeneous
fuel-air mixture. Although fuel injected early in the compression stroke promotes homogeneity of the DME-air mixture in the
cylinder, it causes the mixture to ignite too early to secure good thermal efficiency and knock-free operation at high loads.
Low temperature reactions occur at about 660K regardless of the fueling methods, fuel injection timing and equivalence ratio.
The main components of hydrocarbon emissions turned out to be unburned fuel (DME), formaldehyde and methane. 相似文献
296.
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
297.
S. H. Jun T. K. Kim J. Y. Jang Y. Kidoguchi 《International Journal of Automotive Technology》2009,10(6):663-668
In an earlier study, the current authors showed that an unsteady-state lifted flame generated by an equivalence ratio conversion
system for a given fuel, was similar to a steady-state lifted flame in terms of the change characteristics from a premixed
flame to a critical flame and then to a triple flame with a diffusion flame positioned in the middle according to the concentration
difference. Therefore, this study used an OH-PLIF method to investigate the characteristics of a steady-state lifted flame
and an unsteady-state lifted flame created under conditions identical to the flames in the preceding study. PLIF (Planar laser
induced fluorescence) is practically effective for visualizing the concentration fields within a flame. The resulting OH-radical
measurements showed that an unsteady-state lifted flame created under the specific conditions used in this study showed similar
tendencies in terms of OH-radical distribution, fluorescence intensity, and liftoff height, to a steady-state lifted flame,
thereby confirming that the behavior of an unsteady-state lifted flame can be effectively predicted based on the behavior
of a steady-state lifted flame. 相似文献
298.
S. S. Merola P. Sementa C. Tornatore B. M. Vaglieco 《International Journal of Automotive Technology》2009,10(5):545-553
A low-cost solution based on fuel injection strategies was investigated to optimize the combustion process in a boosted port
fuel injection spark ignition (PFI SI) engine. The goal was to reduce the fuel consumption and pollutant emissions while maintaining
performance. The effect of fuel injection was analyzed for the closed and open valve conditions, and the multiple injection
strategies (MIS) based on double and triple fuel injection in the open-valve condition. The tests were performed on an optical
accessible single-cylinder PFI SI engine equipped with an external boost device. The engine was operated at full load and
with a stoichiometric ratio equivalent to that of commercial gasolines. Optical techniques based on 2D-digital imaging were
used to follow the flame propagation from the flame kernel to late combustion phase. In particular, the diffusion-controlled
flames near the valves and cylinder walls, due to fuel deposition, were studied. In these conditions, the presence of soot
was measured by two-color pyrometry, and correlated with engine parameters and exhaust emissions measured by conventional
methods. The open valve fuel injection strategies demonstrated better combustion process efficiency than the closed ones.
They provided very low soot levels in the combustion chamber and engine exhaust, and a reduction in specific fuel consumption.
The multiple injection strategies proved to be the best solution in terms of performance, soot concentration, and fuel consumption. 相似文献
299.
Fabian Walz Sören Hohmann 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2019,57(8):1126-1142
ABSTRACTSo far, longitudinal motion control has focused on situations like highway driving, where disturbances of the road profile can be neglected. In this paper, we show how the Two Point Tire Model can be used to derive a novel feed-forward control law for a vehicle's longitudinal motion that considers the effects of the road profile and can complement existing control approaches. For this purpose, we recapitulate the basic model assumptions and equations and briefly discuss how it can be used on arbitrary road profiles. Two approaches for implementation in a real vehicle are presented. Comparisons of these approaches in simulation and to a human driver of an experimental vehicle show that the controller can deal with stepped obstacles of up to 14?cm in height. However, the control performance is essentially limited by the actuator delay and human drivers outperform the controller due to their ability of sensing subtle vehicle motions. The results indicate that the control performance can be further improved by using a preview on the necessary drive torque, which can be provided by the solution that we propose. 相似文献
300.
Ocean transportation has been mainly studied from an economic and strategic point of view. This paper adopts an operations management approach aiming at the identification of the value-adding attributes that characterize the ocean transportation industry. This is achieved by using Johansson et al.'s 1 four value metrics—service, quality, cost, time—which are used for the identification of the contribution that different factors make to the total created value. In this paper, multi-attribute utility theory (MAUT) has been used to measure and compare the value of different processes of various sectors of the ocean transportation industry. The application of MAUT methodology is illustrated with an example from the four sectors of the industry: liner, dry bulk, liquid bulk and specialized. Results suggest that there is strong emphasis placed by ocean transportation companies on quality and that there is differentiating importance put on service and cost by different sectors. Time is seen as the lowest value contributor by all four sectors of the surveyed companies. 相似文献