Using methods established in earlier work, calculations are carried out to reveal the influence of actuator bandwidth on the performance capabilities of a class of active suspension system for automobiles. The suspension consists of an actuator in series with a spring, the combination being in parallel with a passive damper, and the system is modelled as a single wheel station traversing a random road. The results indicate that a system with a 3 Hz bandwidth actuator and variable damping will have excellent ride performance qualities over a wide range of road roughness conditions. Since such a system can be expected to be easily adaptable to the running conditions, to provide good static and dynamic attitude control, to be capable of contributing to good steering control responses and to be inexpensive in terms of capital and energy consumption costs compared with most of the active systems which have previously been discussed, it is suggested that it is a prime candidate for further study and practical development. 相似文献
The idea of a passive safety belt operated solely by the motor car's door has been rigorously analysed on a mathematical model. By calculation methods, an optimal configuration of the device was produced and a working model built, based on the analytically obtained design specifications. The model proved the feasibility and advantages of the proposed system, which is based on the conventional 3-point safety-belt design and utilises existing car structures. 相似文献
Transportation - In Canada, transportation regulation has evolved in response to the country's unique economic and demographic conditions—a land mass larger than that of the U.S.A. with... 相似文献
This paper examines the growth of world trade in the period 1960-70 and its characterization by two indices, the Maritime Potential Index and the Maritime Dependence Index. 相似文献
This is the second of two papers on cargo handling productivity presenting the results of the model developed int he first [1] which had been designed to test a productivity measurement method with cross-sectional empirical data. Four productivity measures were employed. Two related cargo handling to time, with labour brought into the analysis as an independent variable. The third productivity measure expressed total throughput as an aspect of labour productivity, while the final measure was a full productivity index developed by relating output to both capital and labour.
The productivity measurement technique demonstrated that this method can be used for cross-sectional studies and can cope with and allow for variation in non-controllable extraneous factors, thus proving useful for policy decision-makers in shipping lines and/or port authorities.
This paper presents the results of the prodictivity analysis for which the analytical design was decribed in Part 1. The first section briefly restates the productivity indices developed. The principal results and tests on these measures are present in Section 2 with conclusion following in Section 3. 相似文献
The ‘simple double-elliptical contact’ (SDEC) approach by Piotrowski et al. [The Kalker book of tables for non-Hertzian contact of wheel and rail. Vehicle Syst Dyn. 2017;55:875–901] generates a-symmetrical contact patches in an elegant way. This allows to extend the table-based approach for the wheel–rail creep force calculation towards non-Hertzian contact geometry. This is an important line of research, because FASTSIM is intricate for non-Hertzian contacts, whereas CONTACT requires long calculation times.
Here, we comment on the further motivation that's provided for the approach. According to the authors, ‘the spin creepage generates longitudinal creep force in non-symmetric, non-elliptical contacts’, which is ‘completely lost’ when using elliptical regularisation. We demonstrate that this mainly depends on the choice of contact origin, and that the interaction is much reduced if different choices are made. This suggests that elliptical regularisation may be viable still, if the details are properly worked out. Furthermore, we introduce the spin center and the free-rolling position as means to extend the table-based approach towards more general non-Hertzian circumstances. 相似文献
There have been a number of studies of the effectiveness of vehicle scrappage programs, which offer incentives to accelerated
scrappage of older vehicles often thought to be high emitters. These programs are voluntary and aimed at replacement of household
vehicles. In contrast, there is a gap in knowledge related to the emissions benefits of government fleet replacement (retirement)
programs. In this study, the efficacy of a fleet replacement program for a local government agency in Northern Illinois, the
Forest Preserve of DuPage County (FPDC), is examined using a probabilistic vehicle survival model that accounts for time-varying
covariates such as vehicle age and gasoline price. The vehicle lifetime operating emissions are calculated based on the estimated
vehicle survival probabilities from the survival model and compared with those derived using the EPA default fleet used in
MOBILE6 and the fleet represented by the Oak Ridge National Laboratory (ORNL) survival curve. The results suggest that while
there may be short term emission benefits of the FPDC fleet replacement plan, the long-term emission benefits are highly sensitive
to economic factors (e.g., future gasoline price) and exhibit a decreasing trend. This indicates that an adaptive multi-stage
replacement strategy as opposed to a fixed one is preferable to achieve optimal cost effectiveness.
Debbie A. NiemeierEmail:
Dr. Jie Lin (Jane)
is an assistant professor in Department of Civil and Materials Engineering and a researcher with the Institute for Environmental
Science and Policy at University of Illinois at Chicago. Her current research is focused on transportation sustainability
through holistic modeling of energy consumption and emissions associated with private, freight, and public transportation
activities.
Dr. Cynthia Chen
is an assistant professor in the civil engineering department at City College of New York. Her research expertise and interests
cover travel behavior analysis, land use and transportation, transportation safety, and environmental analysis.
Dr. Deb Niemeier
is a professor at UC Davis and her current research focus is on the nexus between transportation, land use and climate change,
particularly how land use and transportation decisions affect energy consumption and contribute to climate change. She is
considered an expert on transportation-air quality modeling and policy and sustainability. 相似文献