Numerical analysis of crack under compression by 3D displacement discontinuity method

A 3D displacement discontinuity method is applied to solve the fracture mechanics problems of the mixed mode crack under compression. Friction between the surface of the closed crack is considered by establishing a simple and efficient iterative algorithm based on method of contact resistance mitigation. On the surfaces of the closed crack, the Mohr-coulomb rule is satisfied by iteration when the crack is in condition of sliding. The stress intensity factors are obtained using displacement fitting method. It is shown that the numerical results agree with the experimental results well and that friction plays an important role in resisting crack propagation.     

Experimental study on the liquid slug of cryogenic slug flow in inclined tubes

An experimental study was carried out to understand the phenomena of the boiling flow of liquid nitrogen in inclined tubes with closed bottom by using a high speed motion analyzer.The experimental tubes are 0.018 and 0.014 m inner diameter(ID) and 1.0 m in length.The range of the inclination angle is 45°-90° from the horizontal.The experimental observation on the liquid slug was carried out along the tubes.Statistical method was employed to analyze the experimental data.The experiment analyzed the influences of the inclination angle and the tube diameter on the liquid slug length and velocity.The results show the liquid slug propagation velocity increases with the decrease of inclination angle θ.For all cases,the maximum values of the mean liquid slug lengths were obtained at θ = 60°.The mean liquid slug lengths were greater for large tube at higher tube position.These conclusions provide a basis for further study liquid slug of cryogenic two-phase undeveloped slug flow.     

Linking an activity-based travel demand model with traffic emission and dispersion models: Transport’s contribution to air pollution in Toronto

This paper describes the development of an integrated approach for assessing ambient air quality and population exposure as a result of road passenger transportation in large urban areas. A microsimulation activity-based travel demand model for the Greater Toronto Area – the Travel Activity Scheduler for Household Agents – is extended with capabilities for modelling and mapping of traffic emissions and atmospheric dispersion. Hourly link-based emissions and zone-based soak emissions were estimated. In addition, hourly roadway emissions were dispersed at a high spatial resolution and the resulting ambient air concentrations were linked with individual time-activity patterns derived from the model to assess person-level daily exposure. The method results in an explicit representation of the temporal and spatial variation in emissions, ambient air quality, and population exposure.     

“Turn on the radio,bust out a song”: the experience of driving to work

Though driving to and from work has become a prevalent experience in the lives of individuals in every metropolitan region in the US, much remains to be learned about the activity from the perspective of the drivers. To increase our understanding of the motivation for certain travel behaviors, we must first know something about what those drivers experience. The existing literature explains much, but the application of new methodologies could improve our ability to explain the willingness of individuals to choose to drive through increasingly congested road networks. The results of this study of oral histories of 12 women commuters underscore the idea that commute should be seen as a set of subjective behaviors that contradict some existing assumptions about why individuals commute.     

Threshold controlled scheme of difference expansion techniques for reversible watermarking

Since Tian Jun proposed the difference expansion embedding technique, based on which, many reversible watermarking techniques were proposed. However, these methods do not perform well when the payload is high. In this paper, we proposed an expandable difference threshold controlled scheme for these three methods. Experiments show that our scheme improves the performance of these three methods for heavy payload.     

The utilisation and user characteristics of Uber services in London

ABSTRACT

Ridesourcing services such as Uber are nowadays a common feature within available transport options of many cities around the world (E.g. London & San Francisco). There has been much publicity about the potential impacts of ridesourcing services and how (or if) they should be managed or regulated without an objective understanding of who uses these services and why, as well as its current and future implications for public transport (PT).

Ridesourcing is part of a broader tech-driven, mobile app-based sharing phenomenon – the ‘sharing economy’ – which has disrupted traditional market models and industries, for example, the transport industry, where new players such as Uber have emerged and have quickly become part of the urban transport landscape. Uber has been at the forefront in disrupting the transport sector since its first launch in 2010 (San Francisco, USA). Since its launch, Uber has generated extensive media coverage and debate among policymakers, transport planners and transport authorities on how these services are affecting traditional transport modes such as buses and taxis. However, without objective empirical data – in terms of impacts on trip making characteristics, PT ridership and congestion – policymakers and transport regulators are yet to fully understand the real impacts ridesourcing services are having on the transport network.

This paper is part of broader research that aims to provide insights and empirical-based evidence on how Uber services are used (UberX and Uberpool) in London. A comprehensive survey was undertaken using a detailed questionnaire, issued to UberX and Uberpool users in London to gather detailed data on who uses the Uber services, why they use it and what are the trip purposes, in order to understand Uber user demographics and what effects (if any) Uber services are having on PT usage and trip making characteristics in London. The final findings provide important insights on Uber user demographics, trip purposes, types of trips replaced, impact on car ownership and why travellers use Uber services.     

Wind-induced mesoscale circulation off the Ebro delta, NW Mediterranean: a numerical study

It is well known that the general circulation on the Catalan continental slope is dominated by a quasi-permanent southwestward geostrophic jet associated to the so-called Catalan front [Millot, C., 1987. Circulation in the western Mediterranean sea. Oceanol Acta 10, 143–149; Font, J., Salat, J., Tintoré, J., 1988. Permanent features of the circulation in the Catalan Sea. Oceanol. Acta 9, 51–57]. On the continental shelf, however, the flow is modified by the action of friction which enhances also other nonlinear interactions. Several authors have hypothesized that the shelf circulation is anticyclonic north of the Ebro delta [Salat, J., Manriquez, M., Cruzado, A., 1978. Hidrografia del golfo de Sant Jordi. Campaña Delta (Abril 1970). Investigación Pesquera 42 (2), 255–272; Ballester, A., Castellví, J., 1980. Estudio hidrográfico y biológico de las plataformas continentales españolas: I. Efecto de los efluentes de una planta de energía nuclear en el Golfo de San Jorge (Febrero 1975–Octubre 1976). Informes Técnicos del Instituto de Investigaciones Pesqueras 76, 70 pp.]. A quasi-3D finite element code based on the shallow-water equations has been used to explore the effect of several mechanisms which might be responsible for such a local circulation pattern, and in particular of wind. The obtained numerical results suggest that the basic anticyclonic structure of the mean flow is controlled by the bathymetry and that the clockwise-rotating mean flow pattern is not a permanent circulation feature. It is seen that the characteristic local wind stress fields—computed through interpolation of the records of a local network of meteo stations—may ‘enhance' or ‘delete' the anticyclonic gyre depending on the sign of their relative vorticity. According to the analysis of a 2-yr record of local wind data, the net contribution of wind events with a duration longer than 24 h is to reinforce the anticyclonic circulation (over 70% of these wind fields supply negative relative vorticity to the study area).     

Load-leveling suspension system with a magnetorheological damper

In this paper, a load-leveling suspension system with a magnetorheological (MR) damper is investigated. In this suspension system, the MR damper is connected to a spring to form a load-leveling suspension system. The system effective stiffness and damping can be adjusted by controlling the MR damper. The characteristics of a load-leveling suspension system are studied first. When the linear damper is replaced with an MR damper, the averaging method is adopted to obtain the steady-state response of the nonlinear system. A comparison demonstrates that the results of the averaging method are in good agreement with those obtained by numerical simulations. The analytical results are then verified experimentally. The load-leveling suspension system studied here is able to adjust both suspension stiffness and damping and, hence, it may provide more effective vibration control in a wider frequency range, when the damper is controlled.     

闪急沸腾喷雾研究的现状与展望

阐述了闪急沸腾喷雾的基本原理,通过比较分析闪急沸腾喷雾与传统喷雾的差异,指出闪急沸腾喷雾是一种极具潜力的燃油喷射方式;论述了近年来国内外对过热燃油和溶气燃油闪急沸腾喷雾研究的进展与现状,介绍了过热液体闪急沸腾喷雾的数学模型及其发展,并从理论上分析了影响闪急沸腾喷雾的因素;展望了闪急沸腾喷雾的应用前景以及进一步研究的发展方向。