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151.
Fast and predictive simulation tools are prerequisites for pursuing simulation based engine control development. A particularly
attractive tradeoff between speed and fidelity is achieved with a co-simulation approach that marries a commercial gas dynamic
code WAVE™ with an in-house quasi-dimensional combustion model. Gas dynamics are critical for predicting the effect of wave
action in intake and exhaust systems, while the quasi-D turbulent flame entrainment model provides sensitivity to variations
of composition and turbulence in the cylinder. This paper proposes a calibration procedure for such a tool that maximizes
its range of validity and therefore achieves a fully predictive combustion model for the analysis of a high degree of freedom
(HDOF) engines. Inclusion of a charge motion control device in the intake runner presented a particular challenge, since anything
altering the flow upstream of the intake valve remains “invisible” to the zero-D turbulence model applied to the cylinder
control volume. The solution is based on the use of turbulence multiplier and scheduling of its value. Consequently, proposed
calibration procedure considers two scalar variables (dissipation constant C
β
and turbulence multiplier C
M
), and the refinements of flame front area maps to capture details of the spark-plug design, i.e. the actual distance between
the spark and the surface of the cylinder head. The procedure is demonstrated using an SI engine system with dual-independent
cam phasing and charge motion control valves (CMCV) in the intake runner. A limited number of iterations led to convergence,
thanks to a small number of adjustable constants. After calibrating constants at the reference operating point, the predictions
are validated for a range of engine speeds, loads and residual fractions. 相似文献
152.
Using current meters and systematically repeated vessel mounted ADCP data legs, we describe the role of the semidiurnal and diurnal constituents in the tidal currents and investigate the mesoscale variability of the M2 tidal currents field along three cross-shelf legs over the Galician shelf. We found that the estimated values of the semi-major axes of the main semidiurnal tidal constituents are closely related to those obtained in previous research and that the tidal currents are predominantly semidiurnal. Amplitudes of the M2 and S2 semi-major axes constituents are comparable, and important fortnightly variability should thus be expected in the amplitude of the semidiurnal tidal currents. Vertical profiles of the semi-major axes of the main tidal constituents reveal that, in the absence of stratification, and far from the bottom frictional effects, the tidal currents are mostly barotropic. Over the slope, the tidal ellipses tilt from a north–south orientation toward the northeast–southwest direction and, as we go further into the shelf, their amplitude is increased, a feature that is reasonably explained by the transition from the dynamics of a Poincaré wave offshore to the dynamics of a northward alongshore propagating Kelvin wave over the shelf. The Ría de Vigo exerts a notable influence over the tidal currents, acting as an extension of the shelf and introducing a meridional variation in the orientation of the ellipses from the alongshore direction in the southern straight coast toward the northeast–southwest direction at the latitude of the Rías. Finally, the spatial fitting methods we tried have proved to be successful in VMADCP data detiding in this region. 相似文献
153.
Empirical approaches to combining revealed and stated preference data: Some recent developments with reference to urban mode choice 总被引:1,自引:0,他引:1
David A. Hensher 《Research in Transportation Economics》2008,23(1):23-29
This paper replaces the nested logit ‘trick’ used in estimation of a modal choice model, when stated preference (SP) and revealed preference (RP) data are pooled, with an error component mixed logit model that can (i) relax the IID condition attached to subsets of alternatives in nested logit models, (ii) accommodate correlated observations, and (iii) reveal the relevant scale parameter for subsets of alternatives. Such a model can also incorporate state dependence between data types and preference heterogeneity on observed attributes. An example of choice among bus, train and car modes illustrates the difference in empirical evidence, especially elasticity outputs. 相似文献
154.
In the present work, different ventilated disc brake rotor configurations were analysed to enhance the heat transfer rate and obtain the uniform temperature distribution in the rotor. CFD code used in this work was validated at using experimental results obtained by conducting experiments on a test rig. The experimental analysis was performed to calculate the mass flow rate and heat dissipation through the rotor. Further, different types of rotor configurations viz. straight radial vane (SRV), tapered radial vane (TRV), alternate long and short vane (ALSV), variable diameter circular pillars (VDCP) were considered for the analysis. A rotor segment of 20° was considered for the numerical analysis due to its rotational symmetry. CFD results were in good agreement with the experiments. The maximum deviation of the numerical results were about 12 % from the experimental results. It is found from the analysis that among the different types of rotor configurations; variable diameter circular pillars (VDCP) rotor gives better rate of heat dissipation with more uniform temperature distribution in the flow passages. Hence for modern high speed vehicles VDCP rotor may be more appropriate. 相似文献
155.
S. Lee 《International Journal of Automotive Technology》2008,9(4):429-436
This paper addresses the application of the perturbation/correlation method to optimizing the torque output of internal combustion
engines. This application was inspired by observations of the limitations in current techniques of the automotive performance
tuning industry. Performance issues such as errors from true optimum spark timing and fuel injector pulse width values as
well as convergence were considered for optimal tuning. The ability of the system to deal with engine cycle-to-cycle variations
and their effect on input parameters is also analyzed. 相似文献
156.
Geoffrey A. Boxshall 《Journal of Marine Systems》1998,15(1-4)
Parasitic copepods belonging to two orders, Siphonostomatoida and Poecilostomatoida, are frequently reported from fish hosts in the deep sea. Three families of copepods are most commonly encountered, Sphyriidae, Lernaeopodidae and Chondracanthidae, but members of another four families, Hatschekiidae, Pennellidae, Philichthyidae and Hyponeoidae, are occasionally recorded. These parasites utilise various deep demersal fishes as hosts, especially species of the most abundant families, Macrouridae, Moridae, Synaphobranchidae and Alepocephalidae. Host specificity levels are variable, as for shallow-water fishes. In contrast, few parasites are regularly reported from fishes inhabiting the pelagic water column away from the bottom and away from the near-surface zone. Only the pennellids Sarcotretes scopeli and Cardiodectes medusaeus appear common on pelagic fishes, in the Atlantic and Pacific respectively. Host specificity levels in these two pennellid species are relatively low. It is speculated that the difficulty of encountering a host in the vast pelagic biome has restricted the diversity of parasitic copepods that have successfully colonized pelagic fishes. 相似文献
157.
There is a growing literature that promotes the presence of a mix of compensatory and semi-compensatory processing strategies
in the way that individuals evaluate packages of attributes in real or hypothetical markets, and make choices. This paper
proposes a specification for the utility form in a choice model to test if, given a pair of attributes with a common-metric
(e.g., components of travel time or cost), the attribute with the dominating level defines the marginal (dis)utility that
is assigned to both attributes. We refer to this processing strategy as a parameter transfer rule. We use a stated choice
data set, in the context of car driving individuals choosing between tolled and non-tolled routes, to estimate a mixed logit
model which incorporates the presence of the parameter transfer rule and the conventional fully compensatory rule, both existing
up to a probability. We find that if this parameter transfer heuristic is part of the mix, the WTP is more than 30% higher,
on average, than when only a fully compensatory rule is imposed. We also contrast the parameter transfer rule with other semi-compensatory
heuristics which have been investigated in other papers, and show that the finding adds further support to the accumulating
evidence that a semi-compensatory attribute processing rules tend to result in higher mean WTP estimates compared to the fully
compensatory attribute processing rule. 相似文献
158.
Tudor D. Bodea Laurie A. Garrow Michael D. Meyer Catherine L. Ross 《Transportation Research Part A: Policy and Practice》2009,43(4):430-444
This paper explores the association of socio-demographic and built environment characteristics on the odds of being overweight and obese using data from the Atlanta SMARTRAQ travel survey. A new methodological framework based on a multinomial logit (MNL) model and an enhanced odds ratio plot is presented. The use of an MNL model overcomes limitations of many prior studies that employ a sequence of binary logit models to examine multiple weight categories. The use of an enhanced odds ratio plot provides important information into the relative importance of socio-demographic and built environment characteristics. Several new findings for the Atlanta area result from this study. Socio-demographic variables, including age and educational attainment, exhibit a non-linear relationship with the odds of being overweight or obese. Gender, age, ethnicity, and educational attainment are strongly associated with the odds of being overweight or obese, while income and number of students between 5 and 16 years old in the household have smaller effects. Built environment characteristics such as increased net residential densities and enhanced street connectivity are associated with reductions in the odds of being overweight and/or obese. Relative to socio-demographic variables, however, such built environment characteristics have a much smaller impact on describing the odds of being overweight or obese. 相似文献
159.
This paper examines the impact of policy changes in the funding of New Zealand public transit modes.These changes, introduced in 1983, are evaluated in terms of the net incidence of public transit subsidy assistance, taking into account its source of funding and the income class of those commuters benefiting from the subsidy. The general conclusion is that the net incidence of subsidy assistance remains progressive (i.e., a transfer from high to low income commuters) following the introduction of shared funding on the predominant public transit modes (rail and bus), sourced from income tax (central government) and property tax (regional/local government). However, because of the predominance of medium to high income commuters on rail vis-a-vis bus and the traditional source of funding on these modes in terms of income tax (a progressive tax source) and property tax (a regressive tax source), the degree of progressivity previously associated with public transit subsidies has now substantially reduced.The analysis and opinions expressed in this paper are the responsibility of the author alone and do not purport to represent the views of the Ministry of Transport. 相似文献
160.
Sibok Lee Raymond A. Krammes John Yen 《Transportation Research Part C: Emerging Technologies》1998,6(5-6)
This paper documents a fuzzy-logic-based incident detection algorithm for signalized urban diamond interchanges. The model is capable of detecting lane-blocking incidents whose effects are manifested by patterns of deterioration in traffic conditions that require adjustments in signal control strategies. As a component of a real-time traffic adaptive control system for signalized diamond interchanges, the algorithm feeds an incident report (i.e., the time, location, and severity of the incident) to the system's optimization manager, which uses that information to determine the appropriate signal control strategy.The performance of the model was studied using a simulation of an actual diamond interchange. The simulation study evaluated the model's performance in terms of detection rate, false alarm rate, and mean time to detect. The model's performance was encouraging, and the fuzzy-logic-based approach is considered promising. 相似文献