While most aggregate studies of transit ridership are conducted at either the stop or the route level, the present study focused
on factors affecting Metro ridership in the Seoul metropolitan area at the station-to-station level. The station-to-station
analysis made it possible to distinguish the effect of origin factors on Metro ridership from that of destination factors
and to cut down the errors caused by the aggregation of travel impedance-related variables. After adopting two types of direct-demand
patronage forecasting models, the multiplicative model and the Poisson regression model, the former was found to be superior
to the latter because it clearly identified the negative influences of competing modes on Metro ridership. Such results are
rarely found with aggregate level analyses. Moreover, the importance of built environment in explaining Metro demand was confirmed
by separating built environment variables for origin and destination stations and by differentiating ridership by the time
of day. For morning peak hours, the population-related variables of the origin stations played a key role in accounting for
Metro ridership, while employment-related variables prevailed in destination stations. In evening peak hours, both employment-
and population-related variables were significant in accounting for the Metro ridership at the destination station. This showed
that a significant number of people in the Seoul metropolitan area appear to take various non-home-based trips after work,
which is consistent with the results from direct household travel surveys. 相似文献
The total economic value for a transportation service consists of use, option, and non-use value. The use benefit is based
on a traveler’s willingness to pay for usual consumption of the service. The optional value, on the other hand, is related
to the possible use of the service for trips not yet anticipated or currently accommodated by other travel modes. The non-use
value, however, is derived from the intrinsic merit of the service, even though a trip-maker never actually or potentially
depends on the mode. A closed-ended contingent valuation method is considered for the quantification of the option and non-use
values. A survey of single- and double-bounded dichotomous choices is conducted with a case study of South Korean bus operations.
A logistic regression model and a survival analysis for the single- and double-bounded approaches, respectively, are applied.
The estimation result is examined according to the statistical property required and the behavioral validity expected. In
particular, three issues from the output are discussed. First, the results help to show the preferable framework between single-
and double-bounded surveys for addressing an individual’s option and non-use values. Second, the differences in the absolute
values of option and non-use values are compared. Thirdly, the relationship between trip-makers’ willingness to pay and the
level of service of their primary travel modes are investigated. In conclusion, the summary of research and the possibilities
for future studies are given. 相似文献
Turbulent overturning on scales greater than 10 m is observed near the bottom and in mid-depth layers within the Gaoping (formerly spelled Kaoping) Submarine Canyon (KPSC) in southern Taiwan. Bursts of strong turbulence coexist with bursts of strong sediment concentrations in mid-depth layers. The turbulence kinetic energy dissipation rate in some turbulence bursts exceeds 10− 4 W kg− 1, and the eddy diffusivity exceeds 10− 1 m2 s− 1. Within the canyon, the depth averaged turbulence kinetic energy dissipation rate is ~ 7 × 10− 6 W kg− 1, and the depth averaged eddy diffusivity is ~ 10− 2 m2 s− 1. These are more than two orders of magnitude greater than typical values in the open ocean, and are much larger than those found in the Monterey Canyon where the strong turbulent mixing has also been. The interaction of tidal currents with the complex topography in Gaoping Submarine Canyon is presumably responsible for the observed turbulent overturning via shear instability and the breaking of internal tides and internal waves at critical frequencies. Strong 1st-mode internal tides exist in KPSC. The depth averaged internal tidal energy near the canyon mouth is ~ 0.17 m2 s− 2. The depth integrated internal tidal energy flux at the mouth of the canyon is ~ 14 kW m− 1, propagating along the axis of the canyon toward the canyon head. The internal tidal energy flux in the canyon is 3–7 times greater than that found in Monterey Canyon, presumably due to the more than 10 times larger barotropic tide in the canyon. Simple energy budget calculations conclude that internal tides alone may provide energy sufficient to explain the turbulent mixing estimated within the canyon. Further experiments are needed in order to quantify the seasonal and geographical distributions of internal tides in Gaoping Submarine Canyon and their effects on the sediment flux in the canyon. 相似文献
Rational structural design of ships or offshore platforms against collisions requires prediction of the extent of damage to stiffened plates generated by lateral impact. In predicting the extent of collision damage, most researchers employ numerical analysis methods using commercial software packages. Like other structural problems, any nonlinear dynamic analysis methods should be substantiated with relevant test data prior to being employed for design. Unfortunately, full-scale collision tests on marine structures are very rare. Still, results from collision tests on marine structural elements can help to substantiate theoretical methods for collision analyses. Lateral collision test data for unstiffened plates are available, but it is difficult to find results from tests on stiffened plates in the open literature. In this paper, the results of lateral collision tests on 33 stiffened plates are reported. A simplified analytical method is developed for the prediction of the extent of damage to stiffened plates due to lateral collisions and this method is substantiated with the test results. Also proposed is a simple criterion with which the occurrence of crack damage can be judged. 相似文献
This paper examines ship-speed performance based on acomputational method. The computations are carried out under identical
model conditions, i.e., resistance and self-propulsion tests, to predict the speed-power relationship. The self-propulsion
point is obtained from the self-propulsive computational results of two propeller rotative speeds. The speed-power relationship
in full scale is obtained through analyzing the computational results in model scale according to the model-ship performance
analysis method of ITTC’78. The object ship is a VLCC. The limiting streamlines and the distribution of the pressure coefficient
on the hull, the wake characteristics on the propeller plane, and the wave characteristics around a model ship are also investigated.
After completing the computations, a series of model tests are conducted to evaluate the accuracy of the predictions by comparing
the computational results with the experimental results. 相似文献
The rapid development of autonomous vehicles (AV) in recent years has drawn the attention of numerous countries in terms of its feasibility for use and deployment as individually-owned vehicles or for large-scale fleet planning and deployment as a mobility-on-demand (MOD) service. Singapore is no exception to this global trend and in her pursuit to be smart and car-lite, numerous efforts are made to have AV trials in place and test out their potential deployment in the city state. As one of the many prerequisites of AV planning, public perception on AV plays a vital role when designing any potential AV deployment scheme. As such, a stated preference survey comprising both online survey and field interviews/surveys, was performed island-wide to understand how commuters in Singapore perceive about different AV-based MOD modes. The logit kernel model is adopted to determine how different preference attributes and key demographic indicators can affect the use of AV-based MOD services over other existing first- and last-mile connection modes. The model results have identified how demographics such as gender, age, housing type, education level and income level can influence the travel mode choice. Also, the impacts brought by individuals’ stated preferences over convenience, privacy and familiarity of ride-hailing apps are also investigated. Such findings can provide useful insight in planning future car-lite towns and implementing AV-based MOD services in these towns.
A knowledge-based flow process is presented for large injection-molded body technology (LIMBT). Injection molding of a large body is a difficult technique because of the many factors and their interactions during the molding process. The proposed flow process can support LIMBT through integration of CAE(Computer-Aided Engineering), CAI (Computer-Aided Inspection), and monitoring systems. CAE and DOE (Design of Experiment) are used to construct an optimal mold design in terms of gates and runners and to identify working conditions for the molding process. CAI and monitoring systems with temperature sensors and pressure sensors can be used to inspect the physical molding process and the molded parts. The flow process of a large body is systematically planned and constructed using a knowledge-based flow process with DOE and computer-aided technologies. The proposed flow process is implemented for the molding process of an automobile front bumper fascia. 相似文献
This paper proposes a lateral control system for an unmanned vehicle that is designed to improve the responsiveness of the system with the use of a PD control. The vehicle heading error can be stabilized, and the transient response characteristics can be improved using the proposed controller. A mathematical model of the vehicle dynamics using two degrees of freedom was developed for the controller design. The waypoint tracking method for autonomous navigation was tested with incorporation of the Point-to-Point algorithm with position and heading measurements received from GPS receivers via Kalman filtering. The performance of the designed controller was verified through experiments with a real vehicle. 相似文献