The effect of rigid bed proximity on flow parameters and hydrodynamic loads in offshore pipelines exposed to turbulent flow is investigated numerically. The Galerkin finite volume method is employed to solve the unsteady incompressible 2D Navier–Stokes equations. The large eddy simulation turbulence model is solved using the artificial compressibility method and dual time-stepping approach. The proposed algorithm is developed for a wide range of turbulent flows with Reynolds numbers of 9500 to 1.5×104. Evaluation of the developed numerical model shows that the proposed technique is capable of properly predicting hydrodynamic forces and simulating the flow pattern. The obtained results show that the lift and drag coefficients are strongly affected by the gap ratio. The mean drag coefficient slightly increases as the gap ratio increases, although the mean lift coefficient rapidly decreases. The vortex shedding suppression happen at the gap ratio of less than 0.2. 相似文献
A major issue that State Departments of Transportation (DOTs) in the US face relates to financing future transportation investments. Questions of interest to State DOT officials relate to the suitability and revenue potential of alternative financing approaches. This paper presents a methodology to estimate the potential levels of revenue associated with the use of selected combinations of financing approaches and to assess the adequacy of these revenues vis-a-vis various levels of investments being considered by decision-makers. The methodology is designed to accommodate a wide array of inputs such as major policy objectives and initial assumptions that may vary significantly from State to State in order to provide a greater flexibility of implementation. The application of this methodology is demonstrated with an illustrative example for Massachusetts. This paper should be of interest to State DOTs seeking an acceptable combination of financing approaches to support future transportation investments. 相似文献
Despite the increasing popularity of including attitudinal and perceptual indicators within discrete choice models, debate endures as to whether there exists a causative relationship between attitudes and behaviour, resulting in what has been termed the attitude behaviour gap. In attempt to understand its origins, attitudes have been categorised as global or localised according to whether or not they are related to a specific time, context and action. Under this framework, global attitudes (GA) typically result in poor predictions of specific overt behaviours, whilst attitudes toward behaviour, or localised attitudes (LA), tend to be better predictors of actual outcomes. Also, attitude strength, measured as the accessibility in memory, plays a determinant role in reducing the gap between attitudes and behaviour, with “memory-based” attitudes having a better prediction of overt behaviours than short-term attitudes constructed “on the spot”. The specific focus of the current paper is to examine the temporal stability and the nature of attitudes, being it critical to transportation planning and research considering the controversial link between attitudes and behaviour. An in depth analysis of the different types of attitudes towards satisfaction for train trips reveals that GAs and LAs provide moderately different outcomes. Also, a memory effect has been found, suggesting the connection between attitudes created on the spot and those stored in memory. Further, both GAs and LAs impact significantly on individual preferences. Finally, the omission of LAs, which are rarely employed within transport literature, may potentially lead to inconsistent estimates, as their contribution in explaining the choice will be absorbed by the error term.
In September of 2000 the UK experienced a blockade of oil refineries in response to rising fuel prices. These protests resulted in severe fuel supply disruptions that intensified over the course of about one week. During the peak of the crisis, travel activity by car was curtailed. This paper analyzes survey data collected about two months after the crisis utilizing the recent memory of respondents as to how they would expect this sort of disruption to affect their participation in daily activities. Specifically, we focused on a variety of non-discretionary and discretionary activities and examined what factors are associated with respondents expecting disruption to those activities. Statistical models were developed to analyze how demographic factors, commute mode selection, vehicle characteristics, and various other factors can explain how individuals expect disruption to their activities. Results suggest that the majority of individuals do not expect major disruptions, although for more car-dependent individuals, disruption was expected to be substantial, especially for work-related trips. These results have implications for the potential success and benefits of an integrated transport policy. 相似文献
A model is presented that relates the proportion of bicycle journeys to work for English and Welsh electoral wards to relevant
socio-economic, transport and physical variables. A number of previous studies have exploited existing disaggregate data sets.
This study uses UK 2001 census data, is based on a logistic regression model and provides complementary evidence based on
aggregate data for the determinants of cycle choice. It suggests a saturation level for bicycle use of 43%. Smaller proportions
cycle in wards with more females and higher car ownership. The physical condition of the highway, rainfall and temperature
each have an effect on the proportion that cycles to work, but the most significant physical variable is hilliness. The proportion
of bicycle route that is off-road is shown to be significant, although it displays a low elasticity (+0.049) and this contrasts
with more significant changes usually forecast by models constructed from stated preference based data. Forecasting shows
the trend in car ownership has a significant effect on cycle use and offsets the positive effect of the provision of off-road
routes for cycle traffic but only in districts that are moderately hilly or hilly. The provision of infrastructure alone appears
insufficient to engender higher levels of cycling.
Matthew PageEmail:
John Parkin
joined academia after a career in consultancy. He has experience of all stages of the promotion of transport infrastructure,
from planning and modelling to design and implementation. His specialises in transport engineering with an emphasis on design
innovation, sustainability principles and community benefit.
Mark Wardman
has been involved in transport research for over 20 years. His main research interests are in behavioural response models
in general and stated preference in particular. Areas of application have included public transport, notably rail, with several
novel applications to cycling and environmental issues.
Matthew Page
research interests include transport policy and how it has developed, the environmental impacts of transport, the impacts
of transport on climate change, and walking and cycling. 相似文献
Objective On the basis of developing a new animal model for oxyhemoglobin (OxyHb) injection into subarachnoid space in mice, this research was to explore the temporal dependence and spatial distribution of OxyHb- induced apoptosis in the mouse brain cells in vivo and the mechanism of neurocyte injury induced by OxyHb. Methods The animal model for OxyHb injection into subarachnoid space in mice was developed. Mice were divided randomly into the experimental group (n=40) and the control group (n= 35). The control group received saline injection (50 μL ) and the experimental group received OxyHb injection (50 μL ), both into the subarachnoid space. The mice of the two groups were subdivided according to different postoperative time (3 h, 6 h, 12 h, 24 h and 48 h). The apoptosis or necrosis of cells was distinguished with microscopy (HE staining), transmission electron microscopy and TUNEL method. Results The distribution of apoptosis was mainly in the ipsilateral neocortex and bilateral hippocampal gyrus. The apoptotic mouse brain cells showed morphological changes in the experimental group by HE staining and transmission electron microscopy. The count of TUNEL-positive cells showed substantial increase in the experimental group, and there was a significant difference between the control and experimental groups, and the number of OxyHb- induced apoptotic cells decreased with time. Conclusion OxyHb in subarachnoid space in mice can induce apoptasis, but not necrosis of mouse brain cells in viro. The apoptotic brain cells show the pattern of temporal dependence and spatial distribution. It is suggested that the early treatment should be the method of first choice for treating the hemorrhagic brain injury. 相似文献
Abstract An essential aspect of economic analysis associated with planning efforts is identifying the composition of existing economic activity and understanding historical trends in economic change. The shift‐share model is a useful and inexpensive tool for this purpose. Shift‐share analysis evaluates changes in local economic activities relative to changes in a reference area (usually the state or nation). Economic change is separated into a reference area component, an industry mix component, and a local share component. These measure, respectively, the effect on the local economy due to changes in the reference area, factors specific to the local mix of industries, and the changing competitive position of the local area relative to the reference area. A shift‐share analysis of Florida's coastal counties reveals that all grew much faster over the 1965–1975 period than did the national economy. This rapid growth is primarily a result of a net shift of economic activity toward the study area relative to the nation. However, a few coastal counties did exhibit a mix of slow‐growing industries. Specific industry results for Florida counties at the eighty‐industry level reveal that many industries showed significant shifts toward Florida's coastal counties. The performance of individual industries in the coastal counties generally exceeded that of the same industries in noncoastal counties. 相似文献