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221.
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
222.
The experimental results of the collapse of three box girders subjected to pure bending moment are presented. The structures are made of high tensile steel of 690 MPa of nominal yield stress reinforced with bar stiffeners of the same material. The moment curvature curves are presented covering the pre- and post-collapse regions. The modes of collapse for each box girder are discussed considering the variation on the panel's slenderness. The concept of efficiency of high tensile steel structures is introduced. The concept is very useful to identify the governing parameters affecting the ultimate strength of 3D structures under predominant bending moment. 相似文献
223.
224.
满堂支架法作为一种成熟的施工技术手段,目前被大量应用于城市桥梁现浇主梁的施工项目中.具有施工方便、周转时间短和辅助设备少的优点.但对于直腹板现浇箱梁,尤其是主梁较窄的现浇箱梁,由于混凝土侧压力、倾倒混凝土产生的水平荷载以及振捣产生的水平荷载存在,使得腹板处支架存在较大的水平推力,导致整个结构处于危险状态.以某工程项目为依托,提出了两种解决方案,通过调整斜撑布置形式对结构受力状态进行改善.结果 表明,两种方案均可有效降低水平推力作用下造成结构局部应力集中的现象,有利于不利荷载均匀向整个支架结构传递. 相似文献
225.
Tao Feng Junyi Zhang Akimasa Fujiwara Harry J.P. Timmermans 《Transportation Research Part D: Transport and Environment》2010,15(5):263-274
This paper presents an integrated model system for mobility maximization based on a quantified specification of environmental capacity, and evaluates policy interaction and effectiveness by simulating a number of policy scenarios. The system is designed to specify the maximum level of car ownership and number of trips by private and public modes subject to an environmental capacity constraint defined as the frontier emission under maximum system efficiency. Four types of hypothetical policies (population change, urban sprawl, land-use pattern and network improvement) are designed and the effects of 13 policy scenarios are simulated using data of Dalian City, China. Results reveal that the integrated model system reacts sensitively to policy interventions. The urban sprawl reflected in a changing residential distribution from central to suburban areas is most instrumental from the perspective of pollution alleviation. If the goal is to simultaneously reduce emissions while accommodating mobility, two combinational policy scenarios outperform all others. 相似文献
226.
Panagiotis Ch. Anastasopoulos Raymond J.G.M. Florax Samuel Labi Mathew G. Karlaftis 《Transportation Research Part A: Policy and Practice》2010,44(3):136-146
Highway agencies around the world strive to improve practices for infrastructure maintenance and rehabilitation, using project delivery policies that range from total ‘in-house’ responsibility to complete privatization, with a number of flexible contracting policies such as performance-based contracting, variants of design-build-maintain, and lane rentals among others between these two extremes. In this paper, we present a methodology that duly accounts for underlying spatial effects and estimates the expected cost savings of innovative contracting policies for highway maintenance and rehabilitation relative to in-house execution of these activities. Spatial econometric modeling is used to analyze highway contract data from 49 countries. We also investigate the marginal effects of key explanatory variables on contract cost savings using spatial multipliers. Our findings show that there are significant relationships between cost savings and contract characteristics, and that there is an apparent direct relationship between the average cost savings of contracts in a country and contract average cost savings and contract sizes in neighboring countries. 相似文献
227.
A. E. Ismail A. K. Ariffin S. Abdullah M. J. Ghazali 《International Journal of Automotive Technology》2011,12(2):225-232
An assessment was carried out herein to study the eccentricity of cracks subjected to mixed-mode loadings. Several loading
locations relative to a central line were selected to induce mixed-mode loadings, which were computed using a finite element
method. An adaptive meshing technique was adopted during the simulation of crack propagation to ensure the singularity of
stress at the tip of the crack. The stress intensity failure criterion was used and programmed, and the node splitting technique
was used when the stress intensity factor reached the fracture toughness of the material to simulate crack propagations. It
was found that large variations in the stress intensity factor were observed when off-set cracks were used, and that K
II
decreased when loading distance increased, but increased when the off-set crack distance was increased. Both crack eccentricity
and loading distance played important roles in producing mixed-mode loading, compared to the influence of central cracks.
Correction factors were introduced to modify the calculation of stress intensity factors under mixed-mode loadings. Simulations
of crack propagation were also conducted to study the effects of crack eccentricities and loading distances. It was found
that the crack length, the loading distance relative to the central crack and the crack eccentricity dominated calculations
of the integrity of cracked structures. 相似文献
228.
C. -H. Lee 《International Journal of Automotive Technology》2008,9(3):317-322
High speed and sport utility vehicles with large joint articulation angle demand lower friction in automotive driveshaft joints
to meet noise and vibration comfort levels. Thus a more thorough understanding of internal friction characteristics and mechanisms
is required. In this paper, a friction model in automotive driveshaft joints was developed through the use of test data from
an instrumented Constant Velocity (CV) joint friction apparatus with actual driveshaft assemblies. Experiments were conducted
under different realistic operating conditions of oscillatory speeds, CV joint articulation angles, lubrication, and torque.
The experimental data was used to develop a physics-based semi-empirical CV joint internal friction model as a function of
different CV joint operating parameters. It was found that the proposed friction model captures the experimental results well.
Also the friction model estimates the generated axial force (GAF) in tripod CV joints well, which is the main source of force
that causes vehicle vibration problems. 相似文献
229.
Development of a low-noise cooling fan for an alternator using numerical and doe methods 总被引:1,自引:0,他引:1
W. Kim W. -H. Jeon N. Hur J. -J. Hyun C. -K. Lim S. -H. Lee 《International Journal of Automotive Technology》2011,12(2):307-314
An alternator, which converts mechanical rotational energy into electrical energy, is an important component of a vehicle.
Alternators operate over a broad range of rotational speeds, typically from 3,000 RPM to 18,000 RPM, which demands a cooling
fan producing sufficient airflow, ideally with a minimum of noise. In the current study, an optimized alternator-cooling fan
was developed through a linked DOE(Design OF Experiment) process and numerical analysis. The SC/Tetra and FlowNoise S/W programs were used to calculate flow rates and noise levels, respectively, for the newly developed fan. Compared with
original model, the numerical results predicted a 3 dBA noise reduction; the measured reduction was 4 dBA. 相似文献
230.
H. G. Zhang E. H. Wang B. Y. Fan M. G. Ouyang S. Z. Xia 《International Journal of Automotive Technology》2011,12(2):173-182
Variable Nozzle Turbocharger (VNT) was invented to solve the problem of matching an ordinary turbocharger with an engine.
VNT can harness exhaust energy more efficiently, enhance intake airflow response and reduce engine emissions, especially during
transient operating conditions. The difficulty of VNT control lies in how to regulate the position of the nozzle at different
engine working conditions. The control strategy designed in this study is a combination of a closed-loop feedback controller
and an open-loop feed-forward controller. The gain-scheduled proportional-integral-derivative (PID) controller was implemented
as the feedback controller to overcome the nonlinear characteristic. As it is difficult to tune the parameters of the gain-scheduled
PID controller on an engine test bench, system identification was used to identify the plant model properties at different
working points for a WP10 diesel engine on the test bench. The PID controller parameters were calculated based on the identified
first-order-plus-dead-time (FOPDT) plant model. The joint simulation of the controller and the plant model was performed in
Matlab/Simulink. The time-domain and frequency-domain performances of the entire system were evaluated. The designed VNT control
system was verified with engine tests. The results indicated that the real boosting pressure traced the target boosting pressure
well at different working conditions. 相似文献