Simulations of roughness growth on rails - results from a 2D non-Hertzian, non-steady contact model

A new model for simulating rail roughness growth on tangent track is presented in this paper. The model consists of three relatively independent components: (1) a time-domain vehicle/track interaction model; (2) a 2D non-Hertzian and non-steady wheel/rail contact model; and (3) a wear model. Wheel/rail contact forces for a given initial roughness obtained from the vehicle/track interaction model are used by the contact model to calculate the contact patch size, normal pressure and tangential stresses with material removal assumed to be linearly proportional to the friction work in the contact patch. The roughness profile is updated and fed back into vehicle/track interaction model. The 2D contact model is initially compared with a 3D model for various wavelength of initial sinusoidal roughness. Long term roughness growth is then simulated with the 2D contact model. Simulation shows that all initial sinusoidal roughness of wavelengths between 20-100 mm are levelled out. The wavelength-fixing mechanism, that has previously been used to explain the cause of corrugation, is not found in the present investigations.     

Effects of household structure and selected travel characteristics on trip chaining

This paper analyzes trip chaining, focusing on how households organize non-work travel. A trip chaining typology is developed using household survey data from Portland, Oregon. Households are organized according to demographic structure, allowing analysis of trip chaining differences among household types. A logit model of the propensity to link non-work trips to the work commute is estimated. A more general model of household allocation of non-work travel among three alternative chain types — work commutes, multi-stop non-work journeys, and unlinked trips — is also developed and estimated. Empirical results indicate that the likelihood of linking work and non-work travel, and the more general organization of non-work travel, varies with respect to household structure and other factors which previous studies have found to be important. The effects of two congestion indicators on trip chaining were mixed: workers who commuted in peak periods were found to have lower propensity to form work/non-work chains, while a more general congestion indicator had no effect on the allocation of non-work trips among alternative chains.     

The Influence of the Suspension System on Motorcycle Weave-mode Oscillations

The vertical motions of a large motorcycle on its tyres and suspension system are analysed, and the possibility of one of the natural frequencies being close to that of the lateral oscillation, the weave mode, is demonstrated. Interactions between the vertical and lateral modes, and the implications for motorcycle design and development are discussed.     

Modelling of high speed gas quenching

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Cost-benefit analysis,government policy and the British railway network

In 1963 the Beeching Report on Britain's railways proposed the closure of a substantial part of the railway network (British Railways Board, 1963). Although many services were withdrawn, disquiet at the Report's failure to analyse the social benefits of rail passenger services eventually led to the application of the technique of cost-benefit analysis to the problem of unremunerative rail services. However, although such studies revealed that the retention of many rural rail services could not be justified on social grounds, these services were not withdrawn. This paper outlines briefly the history of attempts to deal with the question of the optimal size of the rail passenger network. Secondly, it considers the social cost-benefit case for reducing the present size of the network in Britain and the quantifiable benefits from such a reduction. The problem of joint costs is discussed. Finally, it attempts to explain the failure of successive Governments to apply the results of cost-benefit studies in practice, and suggests how the decision-making process might be altered to facilitate a more rational approach towards public transport problems in Britain.     

Shallow water processes govern system-wide phytoplankton bloom dynamics: A modeling study

A pseudo-two-dimensional numerical model of estuarine phytoplankton growth and consumption, vertical turbulent mixing, and idealized cross-estuary transport was developed and applied to South San Francisco Bay. This estuary has two bathymetrically distinct habitat types (deep channel, shallow shoal) and associated differences in local net rates of phytoplankton growth and consumption, as well as differences in the water column's tendency to stratify. Because many physical and biological time scales relevant to algal population dynamics decrease with decreasing depth, process rates can be especially fast in the shallow water. We used the model to explore the potential significance of hydrodynamic connectivity between a channel and shoal and whether lateral transport can allow physical or biological processes (e.g. stratification, benthic grazing, light attenuation) in one sub-region to control phytoplankton biomass and bloom development in the adjacent sub-region. Model results for South San Francisco Bay suggest that lateral transport from a productive shoal can result in phytoplankton biomass accumulation in an adjacent deep, unproductive channel. The model further suggests that turbidity and benthic grazing in the shoal can control the occurrence of a bloom system-wide; whereas, turbidity, benthic grazing, and vertical density stratification in the channel are likely to only control local bloom occurrence or modify system-wide bloom magnitude. Measurements from a related field program are generally consistent with model-derived conclusions.     

Macroscopic modeling of lane‐changing for two‐lane traffic flow

We propose a macroscopic model of lane‐changing that is consistent with car‐following behavior on a two‐lane highway. Using linear stability theory, we find that lane‐changing affects the stable region and the propagation speeds of the first‐order and second‐order waves. In analyzing a small disturbance, our model effectively reproduces certain non‐equilibrium traffic‐flow phenomena—small disturbance instability, stop‐and‐go waves, and local clusters that are affected by lane‐changing. The model also gives the flow‐density relationships in terms of the actual flow rate, the lane‐changing rate, and the difference between the potential flow rate (the flow rate that would have occurred without lane‐changing) and the actual flow rate. The relationships between the actual flow rate and traffic density and between the lane‐changing rate and traffic density follow a reverse‐lambda shape, which is largely consistent with observed traffic phenomena.     

Empowering Stakeholders to Manage Stinging Jellyfish: A Perspective

A global challenge is dealing with the risk of envenomation by the stinging jellyfish. Those who are affected include: the people stung, tourist providers; diving and adventure operations, beach and park authorities, life guards, commercial marine operators as well as local and centralized government; we focus on tourism. There is a diversity of jellyfish that pose a risk and they vary greatly in their ecology. Here, we propose five eco-groups of jellyfish to assist in prioritizing estimates of the risks to a broad clientele. Eco-groups are: (1) “Pulse species” that impact on beaches for short well-defined periods; (2) “Shelf-wide species;” (3) “Nearshore species;” (4) “Drifter species” and (5) “Deep sea species.” Great spatial variation and strong seasonality in the occurrence and abundance of jellyfish is the rule, rather than the exception, and this indicates that local knowledge and preventative action is the key to reducing the risk of envenomation. Managers can take control by getting involved in: predicting risk, detecting the presence of jellyfish and advising on/or providing barriers and protection, first responses and treatment of sting victims. Good communication and record keeping is critical within the stakeholder chain.     

Interference resistance of pentamaran ship model with asymmetric outrigger configurations

An experimental investigation is performed to assess the relation of interference performance on the total resistance of a pentamaran model advancing in calm water. For this motivation, the total drag of the ship is performed for several values of asymmetric outrigger configuration and hull separation, altering the Froude number in the range 0.3–0.9. Our results indicate that remarkable changes in resistance require notable changes in transverse distance values (hull separation) when wave interference may occur. In addition, there is no single configuration that consistently outperforms the other configurations across the entire speed range and the optimum interference factor ?0.2 appears at a Froude number of 0.45 in S/L=0.33 with the outrigger outer position: asymmetric outboard for A3 configuration.     

Numerical Simulation of Shield Tunnelling Under a Historic Building Based on the Local Stiffness Correction Method (DMSM)北大核心CSCD

The district modified stiffness method (DMSM) considers the effect of joints and hand holes on the stiff-ness of the lining ring, assuming the stiffness around the joint and hand hole is to be reduced and the stiffness else-where is not changed. Considering the stiffness reduction of the lining ring caused by the segment’s circumferential joint, the internal force of the lining structure, the ground surface settlement and the displacement response of the surrounding soil body induced by shield driving are analyzed by an HS small strain constitutive model, and a 3D FEM model is established to analyze the interactions among the tunnel, soil body and building to apply to the dou-ble-line running tunnel of Shanghai Metro Line 11, which crosses under a historic building. In contrast, a 3D numeri-cal model based on the routine method (RMM) is set up and a comparison with the site measured data is conducted,with results indicating that they agree very well. The simulation results show that the existing building not only changes the surface settlement trough but also largely reduces horizontal displacement at the corresponding measuring points of the settlement trough; the distortion values of the existing building are related to the positions of the tunnel face and the location of the building; and the final distortion doesn’t decrease after completion of tunnel construction, but major residual distortion remains. This simulation method provides a reference for the control of disturbances during shield construction in soft rock. © 2018, Editorial Office of "Modern Tunnelling Technology". All right reserved.