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Liu C.-W.,Beijing Institute of Technology | Zhao Y.-D.,Beijing Institute of Technology | Zhao Y.-D.,Research Institute of Army Aviation | Liang W.,Beijing Institute of Technology
Beijing Ligong Daxue Xuebao/Transaction of Beijing Institute of Technology | Year: 2012

A novel spatio-temporal patch based background modeling (STPBM) approach was proposed. Spatio-temporal patches (bricks) are utilized to characterize both the appearance and motion information of objects in videos. It was observed that, under all possible illumination conditions, all the bricks at a given background position lie in a low dimensional background subspace. In contrast, bricks with moving foreground are uniformly distributed in original space. Then an efficient online subspace learning method for capturing the background subspace was presented, and the incoming bricks with moving foreground could be detected according to their distance to the background subspace. Experimental results demonstrate that, compared with traditional pixel-wise or block-wise methods, our approach is more insensitive to drastic illumination changes and capable of detecting dim foreground objects under low contrast. Source

Dai S.-J.,PLA Air Force Aviation University | Xiao Y.,PLA Air Force Aviation University | Xiao Y.,Research Institute of Army Aviation | He L.-M.,PLA Air Force Aviation University | And 4 more authors.
International Journal of Heat and Mass Transfer | Year: 2015

This paper presents a new way to improve film-cooling performance by using surface dielectric barrier discharge actuators installed downstream from film-cooling hole. Results provide insight into the flow field characteristic and film-cooing effectiveness of both primary cylindrical hole with and without actuator, and a comparison is made. The velocity field near the test surface is found to be significantly changed under the effect of actuator, resulting in a new pair of vortexes of which the rotating direction is opposite to that of counter rotating vortex pair. Under the effect of new vortex pair, the trend of hot main flow pushing jet flow up is impeded and the jet flow is induced to flow along spanwise direction. A better jet flow adherent performance and greater jet flow coverage are achieved by installing actuator downstream from cylindrical hole than from primary hole, providing an increment in the film-cooing effectiveness. The effects of each location parameter of the actuator on the film-cooling effectiveness are studied in detail. The results indicate that under different blow ratio, the actuator location parameter has various levels of influence on film-cooing effectiveness. This is mainly due to the strength of counter rotating vortex pair in the primary cylindrical hole and the induced ability of surface dielectric barrier discharge actuators. © 2015 Elsevier Ltd. All rights reserved. Source

Dai S.-J.,PLA Air Force Aviation University | Xiao Y.,PLA Air Force Aviation University | Xiao Y.,Research Institute of Army Aviation | He L.-M.,PLA Air Force Aviation University | And 4 more authors.
AIP Advances | Year: 2015

The present paper is performed on the effect of plasma aerodynamic actuation on a round jet in cross flow field with a low Reynolds number by using smoke visualization. The actuator is constituted by an electrode pair separated by a dielectric Al2O3 sheet. Several AC supply conditions are utilized. The experimental result shows a closing-in tendency of the jet flow toward the wall after being induced by plasma aerodynamic actuation, and such tendency is increasingly intensified as the actuation voltage increases. Numerical simulation is also performed. The simulation results show that an induced vortex pair is generated by plasma aerodynamic actuation near the wall flow field. The rotation direction of the induced vortex pair reverses against the counter-rotating vortex pair generated by a round jet in a cross flow without plasma aerodynamic actuation. Then the strength and structural size of the counter-rotating vortex pair are significantly reduced, resulting in the intensified near-wall effect of the jet flow. Three electrode-typed actuators (straight, 150°-elliptic arc and 180°-elliptic arc with the same streamwise extent) are placed at the exit of round jet to research the influence of electrode structure on jet in cross flow. The result shows that the longer the arc electrode surrounding the hole, the stronger the induced jet that flow near the wall is. © 2015 Author(s). Source

Dai S.-J.,PLA Air Force Aviation University | Xiao Y.,PLA Air Force Aviation University | Xiao Y.,Research Institute of Army Aviation | He L.-M.,PLA Air Force Aviation University | And 4 more authors.
AIP Advances | Year: 2015

An investigation on film cooling holes with plasma actuators are performed for circular hole, expansion-shaped hole and fan-shaped hole on the surface of flat plate. The results are compared with those obtained from the same combination of varied shaped holes without plasma actuator. Computational results suggest that plasma-induced body force mitigates the intensity of the counter rotating vortex pair by creating a new pair of vortexes, thereby providing greater coolant-surface attachment for each hole shape, resulting in the improvement of film cooling effectiveness. As for the holes of varied shapes with plasma actuator, the expansion-shaped hole shows superior laterally averaged film cooling effectiveness to that of the circular hole. Comparing with the abovementioned two shaped holes, the fan-shaped one performs worse in terms of laterally averaged film cooling effectiveness at low blow ratios, and better at high blow ratios. The fan-shaped hole also provides the best uniformity of film cooling effectiveness among all cases. © 2015 Author(s). Source

Guo X.,PLA Logistical Engineering University | Jiang M.,PLA Logistical Engineering University | He Z.,Lanzhou Petrochemical Company | Sun Y.,PLA Logistical Engineering University | Deng C.,Research Institute of Army Aviation
Shiyou Xuebao, Shiyou Jiagong/Acta Petrolei Sinica (Petroleum Processing Section) | Year: 2010

Self-repairing properties of two kinds of particle materials were investigated in lithium based grease by using a four-ball friction tester, based on the mass losses of the tribomates. Deposit and self-repairing conditions of the two additives were analyzed by way of XPS and EDS, and the spot surfaces were contrastingly analyzed applying the SEM. The experimental results showed that the self-repairing performances of rare earth fluoride and layered silicate were remarkable and their tribological properties were excellent. Their anti-wear and self-repairing mechanisms were also studied. Source

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