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41.
The effects of the temperature, salinity, and fluid type on the acoustic characteristics of turbulent flow around a circular cylinder were numerically investiga... 相似文献
42.
In contrast with reviews of values of time and price elasticities, the literature contains little by way of detailed reviews
of travel time based choice and demand elasticities. This paper reports the most extensive meta-analysis of time-based demand
elasticities yet undertaken, supplemented with a review of literature not previously in the public domain. The meta-analysis
is based upon 427 direct elasticities covering travel time, generalised journey time (GJT) and service headway and drawn from
69 UK studies. The elasticities are found to vary, as expected, across attributes, and quite strong effects have been detected
according to distance. We provide interesting insights into the relationship between long and short run elasticities and elasticities
obtained from static models and choice models based on actual and hypothetical preferences. Significantly, the results seem
to indicate that the duration for the long run demand impact to work through depends upon the periodicity of the model estimated.
There is little variation apparent by journey purpose, source of the evidence, nor over time or by region/flow type, whilst
travel time elasticities for high speed rail are not materially different from conventional contexts. The findings support
some official elasticity recommendations and conventions but challenge others, and can be used to provide time-based elasticities
where none exist or to assess new empirical evidence. 相似文献
43.
It has been over fifteen years since the Morgantown PRT system went into passenger service. Its start was marked by cost overruns, high operating costs and poor reliability. However over time, these initial problems and difficulties have been overcome, and today the system provides an extremely important and reliable service that links downtown Morgantown with three campuses of West Virginia University. It is still running. This paper provides background on the development of the system and current operating characteristics of this famous transit demonstration project. 相似文献
44.
Edward W. Walbridge 《运输规划与技术》2013,36(4):221-231
An information system is presented which identifies the transportation technologies suited to any one transportation need situation lying in a broad range of such situations. The system is concerned with people movement rather than goods movement. The user of the system specifies the nature and extent of demand, as well as certain service requirements. A transportation technology is identified as suited to a particular need situation when the technology meets the demand and the service requirements, and does so at reasonable cost. The technologies identified by the system as suited to a need situation must be examined to select the one best alternative. This final selection process is not part of the system. This system consists of two tables. Their use is described and examples are given. The procedure used to develop the tables is discussed. The system identifies new transportation technologies (PRT, AGT, etc.) as well as old. 相似文献
45.
There is a large class of problems in the field of fluid structure interaction where higher-order boundary conditions arise for a second-order partial differential equation. Various methods are being used to tackle these kind of mixed boundary-value problems associated with the Laplace’s equation (or Helmholtz equation) arising in the study of waves propagating through solids or fluids. One of the widely used methods in wave structure interaction is the multipole expansion method. This expansion involves a general combination of a regular wave, a wave source, a wave dipole and a regular wave-free part. The wave-free part can be further expanded in terms of wave-free multipoles which are termed as wave-free potentials. These are singular solutions of Laplace’s equation or two-dimensional Helmholz equation. Construction of these wave-free potentials and multipoles are presented here in a systematic manner for a number of situations such as two-dimensional non-oblique and oblique waves, three dimensional waves in two-layer fluid with free surface condition with higher order partial derivative are considered. In particular, these are obtained taking into account of the effect of the presence of surface tension at the free surface and also in the presence of an ice-cover modelled as a thin elastic plate. Also for limiting case, it can be shown that the multipoles and wave-free potential functions go over to the single layer multipoles and wave-free potential. 相似文献
46.
This paper proposes a new method for ship recognition and classification using sound produced and radiated underwater. To do so, a three-step procedure is proposed. First, the preprocessing operations are utilized to reduce noise effects and provide signal for feature extraction. Second, a binary image, made from frequency spectrum of signal segmentation, is formed to extract effective features. Third, a neural classifier is designed to classify the signals. Two approaches, the proposed method and the fractal-based method are compared and tested on real data. The comparative results indicated better recognition ability and more robust performance of the proposed method than the fractal-based method. Therefore, the proposed method could improve the recognition accuracy of underwater acoustic targets. 相似文献
47.
The inception of porpoising is theoretically predicted for planing vessels. Two different approaches are presented. First,
a linear stability analysis is applied to find the porpoising limits while the hydrodynamic coefficients, i.e. added mass
and damping coefficients, are determined by either a simplified method or a numerical method. Another approach is to seek
the porpoising limits by performing nonlinear time domain simulations. Either the simplified method or the numerical method
is used in the simulations. In the numerical method, a 2D+t theory together with a boundary element method is employed. The
trim angle limits for porpoising are determined by changing the longitudinal position of the centre of gravity (COG) of the
vessel and keeping the forward speed constant. The predicted porpoising limits are compared with Day and Haag’s (Planing boat
porpoising, Thesis, Webb Institute of Naval Architecture, 1952) experimental results. The influences of parameters such as the load coefficient, the vertical position of COG and the radius
of gyration of the ship are investigated by varying those parameters in the linear stability analysis. In the nonlinear time-domain
simulations, by trying different longitudinal position of COG, one can find the critical trim angle when the porpoising commences.
The obtained trim limits agree generally with those predicted by the linear stability analysis. Bounded oscillations for the
unstable cases near the critical trim angle can be seen in the time-domain simulations due to the nonlinear effects. 相似文献
48.
Rural seniors are highly dependent on their automobile to meet their trip making needs, yet the effects of aging can make
access to the vehicle difficult or impossible over time. The anticipated growth in the older person population, in concert
with limited travel data available to support rural transportation planning in Canada suggests a disconnect between what rural
older people may require for transportation and the availability of formal alternatives. Many will seek informal alternatives
to driving, such as depending on friends and family, to meet their travel needs, but the degree is not well understood in
the context of their actual vehicle usage and stated ability to adapt. This paper draws from a Global Positioning System (GPS)-based
multi-day travel diary survey of a convenience sample of 60 rural older drivers (29 men, 31 women, average age of 69.6 years)
from New Brunswick, Canada. Participants would rely on “friends and family” for 52% of all trips they undertook as driver
in the survey, “walk or bike” for 14% of trips, and “not take the trip” in 34% of trips if they did not have access to a vehicle.
The formal option of “Transit” was not selected as a viable alternative by any participant for any trip. “Medical trips”,
“Shopping” and “Personal Errands” were the least discretionary of all trip types, yet the most difficult for participants
to find alternate arrangements. This suggests the need to explore different models of service delivery, such as a community-supported,
member-based rural shuttle service with volunteer and paid drivers that build on informal social networks and can provide
service when friends and family are unavailable. 相似文献
49.
Inertia is related with effect that experiences in previous periods may have on the current choice. In particular, it has to do with the tendency to stick with the past choice even when another alternative becomes more appealing. As new situations force individuals to rethink about their choices new preferences may be formed. Thus a learning process begins that relaxes the effect of inertia in the current choice. In this paper we use a mixed dataset of revealed preference (RP)-stated preference (SP) to study the effect of inertia between RP and SP observations and to study if the inertia effect is stable along the SP experiments. Inertia has been studied more extensively with panel datasets, but few investigations have used RP/SP datasets. In this paper we extend previous work in several ways. We test and compare several ways of measuring inertia, including measures that have been proposed for both short and long RP panel datasets. We also explore new measures of inertia to test for the effect of “learning” (in the sense of acquiring experience or getting more familiar with) along the SP experiment and we disentangle this effect from the pure inertia effect. A mixed logit model is used that allows us to account for both systematic and random taste variations in the inertia effect and for correlations among RP and SP observations. Finally we explore the relation between the utility specification (especially in the SP dataset) and the role of inertia in explaining current choices. 相似文献
50.
The twin forces of rising affluence and population are altering coastal communities around the world. High amenity, environmentally sensitive areas—particularly attractive, non-metropolitan coastal environments—are witnessing a tidal wave of in migration from former urbanites. As a result, these communities are struggling to accommodate growing numbers of people with urban tastes and rural dreams in areas with governance structures and physical infrastructure designed for occasional tourists. This article looks at how governance frameworks in coastal Australia respond to the profound environmental, social, and cultural implications of this process. We offer a typology of non-metropolitan coastal growth settings—from exurban contexts to isolated coastal hamlets—and identify the main environmental, social, economic, and governance issues they face. We then outline the policy and legislative framework governing coastal areas in Australia and show how this framework is interpreted at the local level through an analysis of five local plans covering different coastal settings. 相似文献