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871.
The effect of interactions between individual fronds in a bed of the large intertidal seaweed Durvillaea antarctica, when forced by breaking waves, is studied using a computational model. The model simulates the response of a seaweed bed using a sequence of connected oscillators which are excited by a propagating forcing function representing a breaking ocean wave. Two new facets of the interplay between seaweeds and hydrodynamics are considered: (i) wave forcing due to breaking waves is often not sinusoidal in the rocky intertidal zone and (ii) a frond interaction term is included. The addition of frond interaction reduces the maximum loading on individuals within the bed by around 30% using estimated biomechanical parameters. The rate of change of the loading on the holdfast (equivalent to the “jerk”) is affected in a similar or greater fashion. 相似文献
872.
Most EU member states and the European Commission regard the PPP as an important tool to attract additional financial resources for high priority investments such as transport. The objective of this paper is to delineate the EU panorama of PPP markets and investigate the impacts of EU institutions in the development and success of this type of financial arrangement for the transport sector in Europe. We examine how the scope of the PPP in Europe is based on the flexibility and adaptability of the contract to the features of the project and to the economic and institutional environment. These issues are illustrated through a number of examples in the transport sector. We conclude by observing that the market for PPPs, although still fragmented nationally, is developing a European dimension and attracting resources from a variety of players. 相似文献
873.
874.
Establishment of Model for Tire Steady State Cornering Properties using Experimental Modal Parameters 总被引:2,自引:0,他引:2
Guan Dihua Shang Jin L. H. Yam 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2000,34(1):43-56
Modeling of tire cornering properties using experimental modal parameters is studied. With tire lateral experimental modal parameters, the distribution of side force and lateral deformation under total adhesive and sliding conditions are obtained. Side force, self-aligning, cornering stiffness and relaxation length under different loads and friction coefficients are also calculated. The calculated results are in correspondence to experimental results in the references qualitatively. The non-dimensional side force obtained from the calculated results is compared with the Fiala model, its modified expression by experiments and also the widely used empirical Magic Formula model. The calculated results tally well with the fitted results obtained using Magic Formula model. It can be seen that the tire steady state cornering model using experimental modal parameters proposed in this paper is better for an in-depth study of tire natural characteristics, and the labored experimental work can be avoided. 相似文献
875.
876.
Stphane Lafortune Raja SenguptaDavid E. Kaufman Robert L. Smith 《Transportation Research Part B: Methodological》1993,27(6)
We propose a new mathematical formulation for the problem of optimal traffic assignment in dynamic networks with multiple origins and destinations. This problem is motivated by route guidance issues that arise in an Intelligent Vehicle-Highway Systems (IVHS) environment. We assume that the network is subject to known time-varying demands for travel between its origins and destinations during a given time horizon. The objective is to assign the vehicles to links over time so as to minimize the total travel time experienced by all the vehicles using the network. We model the traffic network over the time horizon as a discrete-time dynamical system. The system state at each time instant is defined in a way that, without loss of optimality, avoids complete microscopic detail by grouping vehicles into platoons irrespective of origin node and time of entry to network. Moreover, the formulation contains no explicit path enumeration. The state transition function can model link travel times by either impedance functions, link outflow functions, or by a combination of both. Two versions (with different boundary conditions) of the problem of optimal traffic assignment are studied in the context of this model. These optimization problems are optimal control problems for nonlinear discrete-time dynamical systems, and thus they are amenable to algorithmic solutions based on dynamic programming. The computational challenges associated with the exact solution of these problems are discussed and some heuristics are proposed. 相似文献
877.
A reasonable response to increasing traffic congestion may come from the rapidly developing traveler information systems. Such systems may be successful if they effectively influence drivers' enroute decisions; in this regard, a critical factor may be commuters' willingness to divert from their regular route in response to information about traffic congestion. This study evaluates the effects of real-time traffic information along with driver attributes, roadway characteristics and situational factors on drivers' willingness to divert.The empirical portion of this study is based on a survey of downtown Chicago automobile commuters. The stated preference approach was used to study commuters' diversion propensity. Drivers expressed a higher willingness to divert if expected delays on their usual route increased, if the congestion was incident-induced as opposed to recurring, if delay information was received from radio traffic reports compared with observing congestion, and if trip direction was home-to-work rather than work-to-home. Respondents were less willing to divert if their alternate route was unfamiliar, unsafe or had several traffic stops. Socioeconomic characteristics were also significant in predicting willingness to divert. 相似文献
878.
879.
I. L. Buxton 《Maritime Policy and Management》1991,18(2):105-112
Little has been written about the ship demolition market, an essential element in the supply/demand balance for shipping. Either technical or economic obsolescence may be the cause for scrapping a ship, where the latter is strongly influenced not only by anticipated freight market levels, but the rate at which more efficient ships are being introduced. The scrap value of a ship is a function both of the realizable value of the materials within the ship and cost of demolition. Both are strongly influenced by the cost structures prevailing in the likely country of demolition. The paper explores not only the fundamentals of the ship demolition market, but the trends from the 1960s to the present. The shipbreaking market has moved in that time from being West European-centred to Asian-centred, concentrating for some years in Taiwan, but now shifting to the Indian subcontinent. 相似文献
880.
Semi-Active Heave and Pitch Control for Ground Vehicles 总被引:1,自引:0,他引:1
Donald L. Margolis Associate Professor 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1982,11(1):31-42
A model is presented which includes both the heave and pitch motions of a vehicle traversing a roadway. Provision is made for testing totally passive, totally active, and semi-active secondary suspensions. Control strategies are developed for the totally active case and vehicle isolation is demonstrated. These active controllers are then modified to be semi-active, i.e., no power is provided from the controller to the vehicle. The semi-active isolation is shown to be comparable to the totally active system and much superior to the passive suspension. 相似文献