Transportation - Commercial vehicles are more likely to park close to their destinations than passenger vehicles even though sometimes parking violations are inevitable for their freight or service... 相似文献
Much of the literature in recent years has examined the vulnerability of transportation networks. To identify appropriate and operational measures of nodal centrality using connectivity in the case of heavy rail systems, this paper presents a set of comprehensive measures in the form of a Degree of Nodal Connection (DNC) index. The DNC index facilitates a reevaluation of nodal criticality among distinct types of transfer stations in heavy rail networks that present a number of multiple lines between stations. Specifically, a new classification of transfer stations—mandatory transfer, non-mandatory transfer, and end transfer—and a new measure for linkages—link degree and total link degree—introduces the characteristics of heavy rail networks when we accurately expose the vulnerability of a node. The concept of partial node failure is also introduced and compare the results of complete node failure scenarios. Four local and global indicators of network vulnerability are derived from the DNC index to assess the vulnerability of major heavy rail networks in the United States. Results indicate that the proposed DNC indexes can inform decision makers or network planners as they explore and compare the resilience of multi-hubs and multi-line networks in a comprehensive but accurate manner regardless of their network sizes.
Transportation - This article discusses results of a study on turn taking behavior in escorting children in dual-earner households. Using a multinomial logit model, the probability of different... 相似文献
Normally, Maglev (magnetic levitation) vehicles run on elevated guideways. The elevated guideway must satisfy various load conditions of the vehicle, and has to be designed to ensure ride quality, while ensuring that the levitation stability of the vehicle is not affected by the deflection of the guideway. However, because the elevated guideways of Maglev vehicles in South Korea and other countries fabricated so far have been based on over-conservative design criteria, the size of the structures has increased. Further, from the cost perspective, they are unfavourable when compared with other light rail transits such as monorail, rubber wheel, and steel wheel automatic guided transit. Therefore, a slender guideway that does have an adverse effect on the levitation stability of the vehicle is required through optimisation of design criteria. In this study, to predict the effect of various design parameters of the guideway on the dynamic behaviour of the vehicle, simulations were carried out using a dynamics model similar to the actual vehicle and guideway, and a limiting value of deflection ratio of the slender guideway to ensure levitation control is proposed. A guideway that meets the requirement as per the proposed limit for deflection ratio was designed and fabricated, and through a driving test of the vehicle, the validity of the slender guideway was verified. From the results, it was confirmed that although some increase in airgap and cabin acceleration was observed with the proposed slender guideway when compared with the conventional guideway, there was no notable adverse effect on the levitation stability and ride quality of the vehicle. Therefore, it can be inferred that the results of this study will become the basis for establishing design criteria for slender guideways of Maglev vehicles in future. 相似文献
The appearance and exterior precision of passenger cars aesthetics has become an important factor in the automotive industry. During vehicle assembly, the curvature of the roof can change slightly and create cosmetic defects that affect the exterior appearance. The critical factor causing curvature change on the roof is the thermally driven expansion of an elastomer-based mastic sealer which is applied between the exterior roof panel and support rail during the frame assembly process. Therefore the expansion of the mastic sealer was modeled to predict the curvature change in the roof panel. In order to evaluate the causes and predict the curvature change quantitatively, a Finite Element (FE) simulation of the oven heating and mastic curing was performed. Validation of the simulation model was performed by comparing the local deformation and amount of the curvature change on the roof obtained from the actual process. In order to minimize the curvature change, the Taguchi method was used in conjunction with the FE model where a total of eight factors were chosen to perform a sensitivity analysis. In order to exclude the deformation due to residual stress resulting from the oven process, it was selected as a noise factor. Response was taken as the maximum curvature change calculated by a flexural function which was used to distinguish absolute curvature that is not affected by the horizontal or vertical movement of roof panel. A total of 18 cases were analyzed with length of each sealer, pitch of sealer, and rail location being identified as the most influential factors affecting the curvature change. Using the optimum values, the amount of curvature change in the roof panel was reduced by 12 percent. 相似文献
This paper describes a pressure-model-based coordinated control method of a variable geometry turbine (VGT) and dual-loop exhaust gas recirculation (EGR) in a diesel engine air-path system. Conventionally, air fraction or burnt gas fraction states are controlled for the control of dual-loop EGR systems, but fraction control is not practical since sensors for fractions are not available on production engines. In fact, there is still great controversy over how best to select control outputs for dual-loop EGR systems. In this paper, pressure and mass flow states are chosen as control outputs without fraction states considering the availability and reliability of sensors. A coordinated controller based on the simple control-oriented model is designed with practical aspects, which is applicable for simultaneous operations of high pressure (HP) EGR, low pressure (LP) EGR, and VGT. In addition, the controller adopts the method of input-output linearization using back-stepping to solve the chronic problems of conventional pressure-based controllers such as coupling effects between operations of HP EGR, and VGT. The control performance is verified by simulation based on the proven GT-POWER model of a heavy-duty 6000cc diesel engine air-path. 相似文献