Wheel/Rail Non-linear Interactions With Coupling Between Vertical and Lateral Directions

Summary A theoretical model is developed to explore the high frequency wheel/rail interaction with coupling between the vertical and lateral directions. This coupling is introduced through the track dynamics due to the offset of the wheel/rail contact point from the rail centre line. Equivalent models of the railway track in the time domain are developed according to the rail vibration receptances in the frequency domain. The wheel is represented by a mass in each direction with no vertical-lateral coupling. The vertical wheel/rail interaction is generated through a non-linear Hertzian contact stiffness, allowing for the possibility of loss of contact between the wheel and rail. The lateral interaction is represented by a contact spring and a creep force damper in series and their values depend on the vertical contact force. The vibration source is the roughness on the wheel and rail contact surfaces which forms a relative displacement excitation in the vertical direction. Using the combined interaction model with this relative displacement excitation, the wheel/rail interactions with coupling between the vertical and lateral vibrations are simulated. It is found that the lateral interaction force caused by the offset is usually less than thirty percent of the vertical dynamic force. The lateral vibration of the rail is significantly reduced due to the presence of the lateral coupling, whereas the vertical interaction is almost unaffected by the lateral force.     

Force Control in Electrohydraulic Active Suspensjons

For a simple vehicle active suspension system complete optimality and zero steady state body displacements may be achieved if the axle and body accelerations, and other easily measured quantities, are included in the performance index. Apart from not requiring an observer, this also allows the optimal feedback gains to be determined for an arbitrary body spring rate. In a theoretical example, model parameters matching those of an experimental test rig are employed. The results of computer simulations, with and without an electrohydraulic servovalve and actuator, are compared to demonstrate the effects of inner loop gain on force control. Aspects of the system behaviour including lockup are commented upon.     

Physically Realisable Feedback Controls for a Fully Active Preview Suspension Applied to a Half-Car Model

An optimal preview type active suspension with feedback control based on easily measured relative displacements, velocities and accelerations is proposed. Measurements relative to the road, except by the preview sensor, are not required and the front and rear spring rates are quite arbitrary. Also, state estimators or observers are unnecessary and as a practical alternative the body accelerometers may be replaced by load cells. The effects of preview on the performance, for a theoretical step type road input and an analogous random road input, are described. The definition of the optimum preview function, and its consequent effects on performance, receives attention and an example is given.     

An Active Suspension with Optimal Linear State Feedback

In this paper modern optimal control theory is applied to the design of an active suspension system for a motor vehicle. The road profile is assumed to be continuous and random with a power spectral density (P.S.D.) which varies inversely with the square of the frequency. The quadratic integral type performance index employed is a weighted sum of the integral squares of body acceleration, dynamic tyre deflection and relative body-to-axle displacement. A solution is obtained for the infinite time case which is both computationally and physically realizable as an active suspension in which the only continuous measurements required are the body absolute velocity and the body displacement relative to the road. The performance is compared with that of a conventional type passive suspension and found to be significantly better in practically all respects.     

Modeling access to public transport in urban areas

It is important to measure public transport accessibility to help improve the sustainability of transport systems in metropolitan areas. Although many studies have defined different approaches for measuring public transport accessibility, there have been limited methods developed for measuring accessibility levels that incorporate spatial aspects. Population density is an important distributional indicator that has also been ignored in previous methods developed for quantifying accessibility. This paper outlines the research context for measurement of public transport accessibility and then describes a methodology developed as well as an application the Public Transport Accessibility Index in Melbourne area, Australia. Using the Victorian Integrated Survey of Travel and Activity dataset, we applied separate‐ordered logit regression models to examine how the new index performs with a series of predictor variables compared with two existing approaches. Key findings indicate that there is a higher probability of public transport patronage in areas with higher levels of accessibility. Furthermore, it was found using statistical modelling that the new index produces better results compared with previous approaches. Copyright © 2016 John Wiley & Sons, Ltd.     

喷油器波形与故障分析

我们剖开一只喷油器,就可以看清喷油器的内部结构,便可了解喷油器的工作原理。实际上,所谓的喷油器波形并不是什么特别高深的东西,它只不过是一组快照,记录了发生于一段时间内的电压或电流信号。     

汽车电子世界之窗——示波器

示波器能使你真正了解汽车电路的工作状态。更为重要的是,一旦这些电路工作不正常,它能帮助你找出故障的根源。     

旧金山-奥克兰海湾桥抗震安全设计

美国奥克兰海湾桥位于州际公路上,1936年通车.为上下行分离桥面,共10条车道,每天有超过28万辆车通过.Loma Prieta地震造成E9号墩上的两跨双向桥面部分坍塌.新建东跨奥克兰海湾桥项目由四个不同结构组成,第一部分从奥克兰到Yerba Buena岛,为奥克兰部分;第二部分以"高架桥"闻名,是一个平行的混凝土箱梁结构;第三部分为自锚式悬索桥,是当前在建的主要结构;最后一部分是一系列多室后张拉箱梁桥.本文将着重对东奥克兰海湾大桥新建项目为震后"生命线服务"进行的设计和施工进行论述.     

Turbulence in coastal fronts near the mouths of Block Island and Long Island Sounds

Measurements of turbulence were performed in four frontal locations near the mouths of Block Island Sound (BIS) and Long Island Sound (LIS). These measurements extend from the offshore front associated with BIS and Mid-Atlantic Bight Shelf water, to the onshore fronts near the Montauk Point (MK) headland, and the Connecticut River plume front. The latter feature is closely associated with the major fresh water input to LIS. Turbulent kinetic energy (TKE) dissipation rate, ε, was obtained using shear probes mounted on an autonomous underwater vehicle. Offshore, the BIS estuarine outflow front showed, during spring season and ebb tide, maximum TKE dissipation rate, ε, estimates of order 10^− 5 W/kg, with background values of order 10^− 6 to 10^− 9 W/kg. Edwards et al. [Edwards, C.A., Fake, T.A., and Bogden, P.S., 2004a. Spring–summer frontogenesis at the mouth of Block Island Sound: 1. A numerical investigation into tidal and buoyancy-forced motion. Journal of Geophysical Research 109 (C12021), doi:10.1029/2003JC002132.] model this front as the boundary of a tidally driven, baroclinically adjusted BIS flow around the MK headland eddy. At the entrance to BIS, near MK, two additional fronts are observed, one of which was over sand waves. For the headland site front east of MK, without sand waves, during ebb tide, ε estimates of 10^− 5 to 10^− 6 W/kg were observed. The model shows that this front is at the northern end of an anti-cyclonic headland eddy, and within a region of strong tidal mixing. For the headland site front further northeast over sand waves, maximum ε estimates were of order 10^− 4 W/kg within a background of order 10^− 7–10^− 6 W/kg. From the model, this front is at the northeastern edge of the anti-cyclonic headland eddy and within the tidal mixing zone. For the Connecticut River plume front, a surface trapped plume, during ebb tide, maximum ε estimates of 10^− 5 W/kg were obtained, within a background of 10^− 6 to 10^− 8 W/kg. Of all four fronts, the river plume front has the largest finescale mean-square shear, S² ~ 0.15 s^− 2. All of the frontal locations had local values of the buoyancy Reynolds number indicating strong isotropic turbulence at the dissipation scales. Local values of the Froude number indicated shear instability in all of the fronts.     

Environmental quality within an interorganizational matrix: A case study of the SOHIO project

Abstract

Urban coastal management is now part of a large, complex set of regional, state, and federal interorganizational arrangements. This emerging matrix consists of a loosely linked set of nearly independent decision points. Cities have little capacity within this matrix for independent action. Recent experience in the SOHIO project by the City and Port of Long Beach, California, illustrates the point to which external agencies have taken over decision‐making for use of coastal resources. Public bodies removed from city affairs and politics and with interests in other than coastal affairs have become dominant and have overridden local policy‐making. The public costs to citizens and local governments of the emerging interorganizational matrix are very high and may be excessive. As it is emerging, the matrix is a semi‐autonomous set of bureaucratic decision points which is unhinged from community values and regular political infrastructures.