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Ashley, United Kingdom

Wang J.,Atkins | Shi Q.,Tsinghua University
Transportation Research Part C: Emerging Technologies | Year: 2013

Based on the previous literature review, this paper builds a short-term traffic speed forecasting model using Support Vector Machine (SVM) regression theory (referred as SVM model in this paper). Besides the advantages of the SVM model, it also has some limitations. Perhaps the biggest one lies in choice of the appropriate kernel function for the practical problem; how to optimize the parameters efficiently and effectively presents another one. Unfortunately, these limitations are still research topics in current literature. This paper puts an effort to investigate these limitations. In order to find the effective way to choose the appropriate and suitable kernel function, this paper constructs a new kernel function using a wavelet function to capture the non-stationary characteristics of the short-term traffic speed data. In order to find the efficient way to identify the model structure parameters, this paper uses the Phase Space Reconstruction theory to identify the input space dimension. To take the advantage of these components, the paper proposes a short-term traffic speed forecasting hybrid model (Chaos-Wavelet Analysis-Support Vector Machine model, referred to as C-WSVM model in this paper). The real traffic speed data is applied to evaluate the performance and practicality of the model and the results are encouraging. The theoretical advantage and better performance from the study indicate that the C-WSVM model has good potential to be developed and is feasible for short-term traffic speed forecasting study. © 2012 Elsevier Ltd. Source


Winer H.S.,Atkins
Journal of Coastal Research | Year: 2011

An environmentally sound concept of maximizing the benefits of the Mississippi River sediment load is proposed by allowing the river to naturally change its course to the Atchafalaya while maintaining navigation and flood control in the present channel of the Mississippi. A sediment lean, minimum necessary flow is determined for the lower Mississippi River to insure navigation and freshwater needs. Some of the political and economic ramifications are anticipated and discussed. The need for a new engineering study is addressed. Finding an effective way to utilize the sediment load of the Mississippi River is essential if the coastal wetland ecology of southern Louisiana is to survive and flourish. Allowing the river to naturally change its course is ultimately the only viable option. The short comings of other means of using the river sediment load are discussed. © 2011 Coastal Education and Research Foundation. Source


Sia A.H.I.,Atkins | Sia A.H.I.,Loughborough University | Dixon N.,Loughborough University
Geosynthetics International | Year: 2012

Numerical modelling techniques can be used to examine the serviceability limit states of landfill side-slope lining systems in response to waste placement. A study has been conducted in which the variability of significant model input parameters have been investigated within a probabilistic framework using Monte Carlo simulation. Key model parameters are treated as random variables, and the statistical information required to describe their distributions has been derived from a laboratory repeatability testing programme, a literature survey and an expert consultation process. Model outputs include relative shear displacements between lining components, and tensile strains in the geosynthetic layers that occur in response to staged placement of waste against the side slope. It was found that analyses including input parameter variability were able to identify mechanisms influencing liner performance and their probability of occurrence. These mechanisms include large (i.e. ≫100 mm) relative displacements at interfaces that can generate post-peak strengths, and mobilised tensile strains in the geomembrane and geotextile layers. Additionally, it was found that relative displacements at the controlling (i.e. weakest) liner interface are greater for landfills with a steep side slope, for stiffer waste and thicker waste lifts, while tensile strains in the geosynthetic elements are greater for steep side slopes, more compressible waste and thinner waste lifts. Outputs from probabilistic analyses such as that used in this study can guide engineers regarding geometries and materials that could produce waste-settlement-generated serviceability limit state failures, and hence can be used to support more reliable designs. © 2012 Thomas Telford Ltd. Source


Fenna A.,Atkins
Proceedings of the Institution of Civil Engineers: Engineering and Computational Mechanics | Year: 2012

A strategic flood risk management (SFRM) study was undertaken for the heavily urbanised reaches of the River Medlock through Manchester, UK. Many of the buildings and structures on this reach date back to the Victorian era and the industrial revolution, when rapid growth of cities often focused on areas around sources of water for industrial and transportation needs. Key structures on the modelled reach include the Medlock Cloughs, a group of structures designed by Victorian engineers to actively manage water levels in the Bridgewater Canal and the Medlock. Further downstream at Potato Wharf, Giants Basin allows overflow from the canal to spill back into the river. A one-dimensional hydrodynamic model to represent the study reaches was built. Hydraulic modelling of the Medlock Cloughs and Giants Basin proved challenging for several reasons. It was not possible to verify existing survey data or to obtain new survey data because of health and safety issues. The study team was also unable to establish maintenance procedures on the structures or determine whether they now operate as intended by the Victorian engineers who built them. These obstacles were overcome by using old survey drawings, historic data and photographs in modelling the structure. The Medlock Cloughs component of the model proved crucial to obtaining accurate level and flow results for the modelled reaches, as the split in flows between the canal and river controlled the water levels upstream. The lessons learnt from this study may have application in assessing flood risk in other similar situations, and included the requirement for credible, accurate data for structures, and the importance of accurately representing, in a computational model, old structures that are no longer operating as intended. Source


Huang D.,Atkins | Huang D.,Fuzhou University
Journal of Bridge Engineering | Year: 2012

The purpose of this study is to investigate the dynamic behavior of steel deck-arch bridges with side-by-side multiple vehicle loadings moving over a rough deck. A brief description of analytical theory is provided, including vehicle model, bridge model, and numerical methods. Both vehicle and bridge are treated as three-dimensional models. The effectiveness of mode superposition and Newmark numerical methods are investigated. Most of the important factors that affect the dynamic response of bridges are considered in this study. The effects of the deck, column and arch boundary conditions are also studied, and the analytical impact factors of deck, column, and arch rib are compared with those determined on the basis of current American Association of State Highway and Transportation Officials (AASHTO) specifications. Study results are useful for both bridge engineers and bridge engineering researchers. © 2012 American Society of Civil Engineers. Source

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