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Short-term traffic safety forecasting using Gaussian mixture model and Kalman filter
Sheng Jin, Dian-hai Wang, Cheng Xu, Dong-fang Ma
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2013, 14(4): 231-243.
https://doi.org/10.1631/jzus.A1200218
In this paper, a prediction model is developed that combines a Gaussian mixture model (GMM) and a Kalman filter for online forecasting of traffic safety on expressways. Raw time-to-collision (TTC) samples are divided into two categories: those representing vehicles in risky situations and those in safe situations. Then, the GMM is used to model the bimodal distribution of the TTC samples, and the maximum likelihood (ML) estimation parameters of the TTC distribution are obtained using the expectation-maximization (EM) algorithm. We propose a new traffic safety indicator, named the proportion of exposure to traffic conflicts (PETTC), for assessing the risk and predicting the safety of expressway traffic. A Kalman filter is applied to forecast the short-term safety indicator, PETTC, and solves the online safety prediction problem. A dataset collected from four different expressway locations is used for performance estimation. The test results demonstrate the precision and robustness of the prediction model under different traffic conditions and using different datasets. These results could help decision-makers to improve their online traffic safety forecasting and enable the optimal operation of expressway traffic management systems.
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Investigation of the hydro-mechanical behaviour of fouled ballast
Yu-jun Cui, Trong Vinh Duong, Anh Minh Tang, Jean-Claude Dupla, Nicolas Calon, Alain Robinet
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2013, 14(4): 244-255.
https://doi.org/10.1631/jzus.A1200337
In this study, a fouled ballast taken from the site of Sénissiat, France, was investigated. For the hydraulic behaviour, a large-scale cell was developed allowing drainage and evaporation tests to be carried out with monitoring of both suction and volumetric water content at various positions of the sample. It was observed that the hydraulic conductivity of fouled ballast is decreasing with suction increase, as for common unsaturated soils. The effect of fines content was found to be negligible. For the mechanical behaviour, both monotonic and cyclic triaxial tests were carried out using a large-scale triaxial cell. Various water contents were considered. The results were interpreted in terms of shear strength and permanent axial strain. It appeared that the water content is an important factor to be accounted for since any increase of water content or degree of saturation significantly decreases the shear strength and increases the permanent strain. Constitutive modelling has been attempted based on the experimental results. The model in its current state is capable of describing the effects of stress level, cycle number and water content.
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Coupled elasto-plasticity damage constitutive models for concrete
Qiang Xu, Jian-yun Chen, Jing Li, Gang Xu
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2013, 14(4): 256-267.
https://doi.org/10.1631/jzus.A1200196
The paper is to design and construct a coupled elasto-plasticity damage constitutive model for concrete. Based on the energy dissipation principle, the Hsieh-Ting-Chen four-parameter yield function is used. The model can reflect different strength characteristics of concrete in tension and compression, and reduce the limitation and lacuna of the traditional damage constitutive models for concrete. Furthermore, numerical test for concrete stress-strain relation under uniaxial tension and compression is given. Moreover, the damage process of concrete gravity dam is calculated and analyzed in seismic load. Compared with other damage constitutive models, the proposed model contains only one unknown parameter and the other parameters can be found in the Hsieh-Ting-Chen four-parameter yield function. The same damage evolution law, which is used for tension and compression, is good for determining stress-strain constitutive and damage characteristics in complex stress state. This coupled damage constitutive models can be applied in analyzing damage of concrete gravity dam and arch dam.
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3D analysis for pit evolution and pit-to-crack transition during corrosion fatigue
Xiao-guang Huang, Jin-quan Xu
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2013, 14(4): 292-299.
https://doi.org/10.1631/jzus.A1200273
This paper presents a deterministic model to predict the pit evolving morphology and crack initiation life of corrosion fatigue. Based on the semi-ellipsoidal pit assumption, the thermodynamic potential including elastic energy, surface energy and electrochemical energy of the cyclically stressed solid with an evolving pit is established, from which specific parameters that control the pit evolution are introduced and their influence on the pit evolution are evaluated. The critical pit size for crack nucleation is obtained from stress intensity factor criterion and the crack nucleation life is evaluated by Faraday’s law. Meanwhile, this paper presents a numerical example to verify the proposed model and investigate the influence of cyclic load on the corrosion fatigue crack nucleation life. The corrosion pit appears approximately as a hemisphere in its early formation, and it gradually transits from semicircle to ellipsoid. The strain energy accelerates the morphology evolution of the pit, while the surface energy decelerates it. The higher the stress amplitude is, the smaller the critical pit size is and the shorter the crack initiation life is.
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7 articles
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