| 1. |
- Wang, Weixing, et al.
(författare)
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Pavement crack image acquisition methods and crack extraction algorithms : A review
- 2019
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Ingår i: Journal of Traffic and Transportation Engineering (English Edition). - : KEAI PUBLISHING LTD. - 2095-7564. ; 6:6, s. 535-556
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Forskningsöversikt (refereegranskat)abstract
- The extraction of pavement cracks is always a hard task in image processing. In airport and road construction, cracking is the main factor for pavement damage, which can decrease the quality of pavement and affect transportation seriously. Cracks also exist in other artificial or natural objects, such as buildings, bridges, tunnels, etc. Among all the object images, pavement crack images are the most complex, so the image processing and analysis for them is harder than other crack images. From the early image acquisition based on photography technology to the current 3D laser scanning technology, the pavement crack image acquisition technology is becoming more convenient and efficient, but there are still challenges in the automatic processing and recognition of cracks in images. From the early global thresholding to deep learning algorithms, the research for crack extraction has been developed for about 40 years. There are many methods and algorithms that are satisfactory in pavement crack applications, but there is no standard until today. Therefore, in order to know the developing history and the advanced research, we have collected a number of literature in this research topic for summarizing the research artwork status, and giving a review of the pavement crack image acquisition methods and 2D crack extraction algorithms. Also, for image acquisition methods and pavement crack image segmentation, more detailed comparison and discussions are made.
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| 2. |
- Liu, Mingyang, et al.
(författare)
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A numerical study of snow accumulation on the bogies of high-speed trains based on coupling improved delayed detached eddy simulation and discrete phase model
- 2019
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Ingår i: Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit. - : SAGE Publications. - 0954-4097 .- 2041-3017. ; 233:7, s. 715-730
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Tidskriftsartikel (refereegranskat)abstract
- A numerical simulation method based on the improved delayed detached eddy simulation coupled with a discrete phase model is used to study the influence of the snow on the performance of bogies of a high-speed train running in snowy weather. The snow particle trajectories, mass of snow packing on the bogie, and thickness of snow accumulation have been analyzed to investigate the flow mechanisms of snow accumulation on different parts of the bogies. The results show that the snow accumulation on the first bogie of the head vehicle is almost the same as that of the second bogie, but the total accumulated snow on the top side of the second bogie is more than 74% higher than that of the first bogie. Among all the components of the bogies, the motors were found to be strongly influenced by the snow accumulation. The underlying flow mechanisms responsible for the snow accumulations are discussed.
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| 3. |
- Wang, Jiabin, et al.
(författare)
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Impact of rotation of wheels and bogie cavity shapes on snow accumulating on the bogies of high-speed trains
- 2019
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Ingår i: Cold Regions Science and Technology. - : Elsevier BV. - 0165-232X. ; 159, s. 58-70
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Tidskriftsartikel (refereegranskat)abstract
- The snow accumulation on the bogies of a high-speed train was studied using the unsteady Reynolds-Averaged Navier-Stokes simulations (URANS) coupled with the Discrete Phase Model (DPM). The effects of the rotation of wheels, shape of bogie fairings and length of bogie cavities on the flow characteristics and snow accumulation around bogie regions are discussed. The results show that the rotation of wheels significantly affects the flow characteristic and snow distribution around rear plates and the snow accumulation on the top surface of bogies. The shape of bogie fairings has been found to have large influence on the velocity profiles at the inlet and the outlet of bogie cavity, and thereby on the snow accumulation. The bogies without fairing have been found to be less influenced by the snow in the flows without crosswinds. The length of the bogie's cavity was found to have dominant role on the distribution of particle concentration and snow accumulation on the bogie surface. The total mass of snow accumulation on the bogie surface was shown to decrease with the shorter bogie cavity. Finally, the shorter bogie cavity is recommended for the design of the high-speed trains running under the circumstances permitted by the vehicle gauge.
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| 4. |
- Wang, Jiabin, 1993, et al.
(författare)
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The effect of bogie fairings on the slipstream and wake flow of a high-speed train. An IDDES study.
- 2019
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 191, s. 183-202
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Tidskriftsartikel (refereegranskat)abstract
- In this study, an improved delayed detached eddy simulation (IDDES) method based on shear-stress transport k-ω turbulence model has been used to investigate the slipstream and wake flow around a high-speed train with different bogie fairings at Re = 1.85 × 10^6. The accuracy of the numerical method has been validated by wind tunnel experiments and full-scale field tests. Further, the train slipstream, underbody flow and wake structures are compared for three cases. The results show that the bogies covered by full size bogie fairings significantly decrease the train slipstream velocity and weaken the pressure fluctuation around the high-speed train, especially near the bogie regions. Compared to the maximum slipstream velocity at trackside position in Case 2 (half size fairings), it increases by 15.2% in Case 1 (no fairing) and decreases by 16.1% in Case 3 (full size fairings), respectively. The larger size fairings are found to reduce the scale of longitudinal vortices and decrease the streamwise vorticity level in the wake region, thereby lowering the slipstream velocity distribution in the wake. Finally, the larger bogie fairings are recommended to improve the train aerodynamic performance as well as to improve the safety of trackside workers and passengers standing on the platform.
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| 5. |
- Zhang, Jie, 1987, et al.
(författare)
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Detached eddy simulation of flow characteristics around railway embankments and the layout of anemometers
- 2019
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 193
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Tidskriftsartikel (refereegranskat)abstract
- Anemometers are usually set up along railway embankments to monitor wind speeds, and the layout for them has to be investigated. This work used an improved delayed detached eddy simulation (IDDES) approach to explore the flow properties around railway embankments, and then a proposal was put forward for the layout of anemometers. The numerical method was validated against previous wind tunnel tests on the speed-up ratios of the flow around a 1/300 scale two-dimensional embankment with the slope gradient of 1:2. The effects of inlet velocity profiles, i.e., uniform velocity and atmospheric boundary layer velocity profiles, on the speed-up ratios around a 5 m high railway embankment were compared. The study indicates that using a uniform velocity profile to assess the operational safety of trains running across strong wind regions could be favourable, especially when complex local terrains contribute to different wind characteristics. The anemometers should be set upstream, i.e., at a well defined distance in locations with sufficient extent of open ground and on the electrification masts along railway lines. This is not in line with the anemometer layout of the existing SWEWS (Strong Wind Early Warning Systems), the difference being due to the speed-up effect of the railway embankment, which is usually not considered explicitly. Formulas have been developed on the basis of regression of the simulation results to express the relationships between e.g. top wind speed over the embankment (located in an area where it is not possible to install anemometers) and measured wind speeds. In this way it is possible to take into account the speed-up effect encountered by the wind passing over the embankment, which needs to be considered in the operational rules in order to ensure safe operations.
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