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991.
R. S. Sharp lecturer C. J. Jones research student 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1980,9(1):45-57
A simple system capable of wheel shimmy is analysed in three different ways and the results are compared. The tyre in each case is taken to be representable by a “taut string”, and the three ways involve (a) developing a digital tyre simulation which operates sequentially with a digital simulation of the mechanical system, (b) representing the tyre responses by linear constant coefficient differential equations derived empirically to match the string responses, and (c) as in (b) but employing fundamentally derived equations which approximate the exact string responses. The approximations are shown to give good results at reduced frequencies typical of the wheel shimmy phenomenon. 相似文献
992.
A model was developed to forecast the duration of emergency shut downs of the Morgantown People Mover. An extensive data base of downtime events for a 2 1/2 year period were analyzed. Analysis of Variance (ANOVA) methods were applied to determine the significance of five variables which were hypothesized to influence downtime duration, including physical sub-system, restartablity, location of failure, number of vehicles in the system, and level of demand. Results of the analysis enable MPM system operators to provide improved information to system users during downtime events. The forecasting methodology also enables operators to evaluate alternative user management strategies during downtimes. 相似文献
993.
994.
R. S. Sharp 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1982,11(1):43-61
A mathematical model for the representation of longitudinal oscillations which can occur in car/trailer systems in braking, when the trailer brakes are applied through compression of the towing hitch, is described. The model is used to show how the trailer braking system parameters affect the steady deceleration performance of the vehicle combination, and the stability, in the linear system sense, of the steady motions. The sensitivity of the stability to other system design parameters is also examined.
Digital simulation of the motions occurring in response to a step input of car braking torque is reported, with the results confirming the predictions of the linear stability analysis, and also showing the influence of backlash in the trailer brake actuating mechanism.
The system is shown to be capable of self-excitation in a “shunting” mode, in which the car and trailer motions are in antiphase, with the stability/damping property critically dependent on drawbar damping, and only weakly dependent on other system parameters. The characteristic frequency of the “shunting” mode oscillations is shown to be controllable via the stiffness of the trailer brake linkage, but this frequency is closely related to the steady drawbar deflection which occurs in uniform deceleration.
The model behaviour described provides a basis for the design of relevant systems whose longitudinal dynamic characteristics will be satisfactory. 相似文献
Digital simulation of the motions occurring in response to a step input of car braking torque is reported, with the results confirming the predictions of the linear stability analysis, and also showing the influence of backlash in the trailer brake actuating mechanism.
The system is shown to be capable of self-excitation in a “shunting” mode, in which the car and trailer motions are in antiphase, with the stability/damping property critically dependent on drawbar damping, and only weakly dependent on other system parameters. The characteristic frequency of the “shunting” mode oscillations is shown to be controllable via the stiffness of the trailer brake linkage, but this frequency is closely related to the steady drawbar deflection which occurs in uniform deceleration.
The model behaviour described provides a basis for the design of relevant systems whose longitudinal dynamic characteristics will be satisfactory. 相似文献
995.
996.
Modelling the temporal response of travellers to transport policy interventions has rapidly emerged as a major issue in many
practical transport planning studies and is recognised to hold particular challenges. The importance of congestion and its
variation over the day, together with the emergence of time-dependent road user charging as a policy tool, emphasise the need
to understand whether and how travellers will change the timing of their journeys. For practical planning studies, analysts
face a major issue of relating temporal changes to other behavioural changes that are likely to result from policy or exogenous
changes. In particular, the relative sensitivity of time and mode switching has been difficult to resolve. This paper describes
a study undertaken to determine the relative sensitivity of mode and time of day choice to changes in travel times and costs
and to investigate whether evidence exists of varying magnitudes of unobservable influences in time of day switching. The
study draws on data from three related stated preference studies undertaken over the past decade in the United Kingdom and
the Netherlands and uses error components logit models to investigate the patterns of substitution between mode and time of
day alternatives. It is concluded that the magnitude of unobserved influences on time switching depends significantly on the
magnitudes of the time switches considered. With time periods of the magnitude generally represented in practical modelling,
i.e. peak periods of 2–3 hours, time switching is generally more sensitive in these data than mode switching. However, the
context of the modelling and the extent to which relevant variables can be measured will strongly influence these results. 相似文献
997.
A.B. Chelani S. Devotta 《Transportation Research Part D: Transport and Environment》2007,12(8):596-600
This study evaluates the potential of nonlinear time series analysis based methods in predicting the carbon monoxide concentration in an urban area. To establish the functional relationship between current and future observations, two models based on local approximations and neural network approximations are used. To compare the performance of the models, an autoregressive integrated moving average model is also applied. The multi-step forecasting capabilities of the models are evaluated. 相似文献
998.
999.
1000.
A proportional shares model of daily time allocation is developed and applied to the analysis of joint activity participation between adult household members. The model is unique in its simultaneous representation of each decision maker's decisions concerning independent activity participation, allocation of time to joint activities, and the interplay between individual and joint activities. Further, the model structure ensures that predicted shares of joint activity outcomes be the same for both decision makers, an improvement over models that do not make interpersonal linkages explicit. The empirical analysis of travel diary data shows that employment commitments and childcare responsibilities have significant effects on tradeoffs between joint and independent activities. In addition, evidence is presented for the continued relevance of gender-based role differences in caring for children and employment participation. 相似文献