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RISS 인기검색어
- 검색키워드
- 저자 : Jiajun He (검색결과 4 건)
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Numerical simulation on aerodynamic characteristics of moving van under the train-induced wind
Jiajun He,Huoyue Xiang,Wenyuan Ren,Yong-Le Li 한국풍공학회 2021 Wind and Structures, An International Journal (WAS Vol.33 No.1
Constructing combined highway–railway bridge brings concerns regarding the aerodynamic interference between train and road vehicle. Research on the interaction mechanism can help calculate the vehicle response for the assessment of travelling safety. In this work, computational fluid dynamics (CFD) verified by a moving model test was applied on researching the aerodynamic characteristics of a moving van under the influence of train-induced wind. Two processes - encounter process (train and van drive towards each other) and chase process (train surpasses the van), are compared. The aerodynamic forces and pressure distribution of the van as well as the flow fields around the vehicles during the interaction are analyzed coherently. The results reveal that the adjacent positive and negative pressure zones around the nose and tail of the train bring moving and centralized high-pressure zone on the van’s flank and generate significant aerodynamic variations, each variation contains at least two peak/valley values, and the middle carriage provide a stable transition between. Different superposition effect of the pressure zones results in difference between the encounter process and chase process, the variation trend of drag force and lift in the two processes are similar while the encounter has larger variation amplitude, in terms of pitching moment and yawing moment, more inversions of force happen in the encounter process but the variation amplitude is smaller. When the van runs near the nose of the train in the encounter, it gets the largest variation of drag force, lift force and rolling moment, while the largest variation of yawing moment and pitching moment happens when it runs near the nose of the train in the chase process.
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Jiajun He,Jin Zhu,Huoyue Xiang,Botao Zhang,Yongle Li,Bing Han 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.8
Single-level rail-cum-road steel box girder is a relatively new form of bridge superstructure that accommodates railway and highway in the same level. The wind flow pattern over the bridge deck is quite complex and a new issue of aerodynamic interference between vehicles also rise up. This paper conducted an in-depth investigation on the aerodynamic characteristics of vehicles on a single-level rail-cum-road bridge as well as the aerodynamic interference among vehicles. The results reveal that the bridge deck makes the aerodynamic coefficients of vehicles on windward lanes vary a lot with respect to vehicle location and vehicle type, while it also well protects the train and leeward road vehicles from large wind load. Among all the vehicles, the van gets several of the largest aerodynamic coefficients and is considered as a critical vehicle. In terms of the vehicles’ interference, the upstream truck trailer brings significant aerodynamic variation for the overtaking vehicle, but its inadequate shelter effect yields fluctuation in the variation. An upstream truck trailer brings significant rise for the aerodynamic load of the train, larger distance between the train and the truck trailer will bring larger increase on the train’s aerodynamic load.
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( Guoqiang Zhao ),( Hao Wu ),( Li Li ),( Jiajun He ),( Zhichao Hu ),( Xinjian Yang ),( Xiangxue Xie ) 한국축산학회 2021 한국축산학회지 Vol.63 No.6
This study investigated the effects of applying cellulase and starch on the fermentation char acteristics and microbial communities of Napier grass silage after ensiling for 30 d. Three groups were studied: No additives (control); added cellulase (Group 1); and added cellulase and starch (Group 2). The results showed that the addition of cellulase and starch decreased the crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF) and pH significantly (p < 0.05) and increased water-soluble carbohydrate (WSC) content (p < 0.05). The addition of additives in two treated groups exerted a positive effect on the lactic acid (LA) content, lactic acid bacteria (LAB) population, and lactic acid / acetic acid (LA/AA) ratio, even the changes were not significant (p > 0.05). Calculation of Flieg’s scores indicated that cellu lase application increased silage quality to some extent, while the application of cellulase and starch together significantly improved fermentation (p < 0.05). Compared with the control, both additive groups showed increased microbial diversity after ensiling with an abundance of favorable bacteria including Firmicutes and Weissella, and the bacteria including Proteobac teria, Bacteroidetes, Acinetobacter increased as well. For alpha diversity analysis, the com bined application of cellulase and starch in Group 2 gave significant increases in all indices (p < 0.05). The study demonstrated that the application of cellulase and starch can increase the quality of Napier grass preserved as silage.
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Guoqiang Zhao,Hao Wu,Yangyuan Li,Li Li,Jiajun He,Xinjian Yang,Xiangxue Xie Asian Australasian Association of Animal Productio 2024 Animal Bioscience Vol.37 No.1
Objective: The objective of this study was to investigate how cellulase or/and lactic acid bacteria (LAB) affected the fermentation characteristic and microbial community in wet brewer's grains (WBG) and corn stover (CS) mixed silage. Methods: The WBG was mixed thoroughly with the CS at 7:3 (w/w). Four treatment groups were studied: i) CON, no additives; ii) CEL, added cellulase (120 U/g fresh matter [FM]), iii) LAB, added LAB (2×10<sup>6</sup> cfu/g FM), and iv) CLA, added cellulase (120 U/g FM) and LAB (2×10<sup>6</sup> cfu/g FM). Results: All additive-treated groups showed higher fermentation quality over the 30 d ensiling period. As these groups exhibited higher (p<0.05) LAB counts and lactic acid (LA) content, along with lower pH value and ammonia-nitrogen (NH<sub>3</sub>-N) content than the control. Specifically, cellulase-treated groups (CEL and CLA) showed lower (p<0.05) neutral detergent fiber and acid detergent fiber contents than other groups. All additives increased the abundance of beneficial bacteria (Firmicutes, Lactiplantibacillus, and Limosilactobacillus) while they decreased abundance of Proteobacteria and microbial diversity as well. Conclusion: The combined application of cellulase and LAB could effectively improve the fermentation quality and microbial community of the WBG and CS mixed silage.
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