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Flow structure of conical distributed multiple gas jets injected into a water chamber
Jiajun Zhao,Yonggang Yu 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.4
Based on an underwater gun firing project, a mock bullet with several holes on the head was designed and experimented to observe the combustion gas injected into a cylindrical water chamber through this mock bullet. The combustion gas jets contain one vertical central jet and 4 to 8 slant lateral jets. A high speed camera system was used to record the expansion of gas jets in the experimental study. In numerical simulations, the Euler two-fluid model and volume of fluid method were adopted to describe the gas-liquid flow. The results show the backflow zone in lateral jet is the main factor influencing the gas-liquid turbulent mixing in downstream. On cross sections, the gas volume fraction increased with time but the growth rate decreased. With a change of nozzle structure, the gas fraction was more affected than the shock structure.
Jiajun Tao,Xiaoshuang Ding 한국중국어교육학회 2022 중국어교육과연구 Vol.- No.37
开展来华研究生学术汉语需求调查研究是构建学术汉语教学与研究体系的起点和基础。本研究采用深度访谈法,对20名来华研究生的学术汉语需求进行了调查。访谈对象包括11名硕士生和9名博士生,所学专业涉及经济学、法学、教育学、文学及管理学等多个学科。访谈结果显示,来华研究生普遍存在学术汉语能力有限、难以胜任学术研究的情况;其对学术汉语存在较大需求,亟需开设相关的学术汉语课程,尤其是学术汉语写作课程。针对留学生的需求以及存在的问题,本文建议完善汉语水平考试(HSK)体系,增设学术类汉语水平考试;鼓励高校分专业开展学术汉语诊断性评估测试;适当增设学术汉语相关课程。
Research on the Application of BIM in the Construction Industry
Jiajun Huang 보안공학연구지원센터 2016 International Journal of Smart Home Vol.10 No.8
BIM is a major innovation in the past ten years, it has had a broad and far-reaching impact in the construction industry. Based on the research and analysis of the application value and application status of BIM, this paper forecasts the application prospect of BIM, and puts forward the application scope and application mode of BIM in the construction industry. In this paper, the author participate in B IM projects, he details BIM’s Technology of Application in the green building design and analysis process; he explore the using BIM Technology for green building design and simulation analysis, finally ,he summarizes the technical advantages.
Jiajun Feng,Cleone I Pardoe,Ashley Manuel Mota,Christopher Hoe-Kong Chui,Bien-Keem Tan 대한성형외과학회 2016 Archives of Plastic Surgery Vol.43 No.2
Background The aim of unilateral breast reconstruction after mastectomy is to craft a naturallooking breast with symmetry. The latissimus dorsi (LD) flap with implant is an established technique for this purpose. However, it is challenging to obtain adequate volume and satisfactory aesthetic results using a one-stage operation when considering factors such as muscle atrophy, wound dehiscence and excessive scarring. The two-stage reconstruction addresses these difficulties by using a tissue expander to gradually enlarge the skin pocket which eventually holds an appropriately sized implant. Methods We analyzed nine patients who underwent unilateral two-stage LD reconstruction. In the first stage, an expander was placed along with the LD flap to reconstruct the mastectomy defect, followed by gradual tissue expansion to achieve overexpansion of the skin pocket. The final implant volume was determined by measuring the residual expander volume after aspirating the excess saline. Finally, the expander was replaced with the chosen implant. Results The average volume of tissue expansion was 460 mL. The resultant expansion allowed an implant ranging in volume from 255 to 420 mL to be placed alongside the LD muscle. Seven patients scored less than six on the relative breast retraction assessment formula for breast symmetry, indicating excellent breast symmetry. The remaining two patients scored between six and eight, indicating good symmetry. Conclusions This approach allows the size of the eventual implant to be estimated after the skin pocket has healed completely and the LD muscle has undergone natural atrophy. Optimal reconstruction results were achieved using this approach.
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.
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.
The Fabrication of Floating Gate CMUT with Multi Cantilevers and Its Failure Analysis
Jiajun Liu,Benxian Peng,Fengqi Yu 대한전자공학회 2021 Journal of semiconductor technology and science Vol.21 No.1
In order to realize soft grasp of robot manipulator, distance sensors need to be installed in the robotic fingers. CMUT (Capacitive Micromachined Ultrasonic Transducer), which owns advantages of extra small size and excellent dielectric impedance matching, meets the demand very well. However there are some difficulties in design and fabrication of a CMUT device. In this paper we propose a novel CMUT design technique based on the integration of standard 0.18 um CMOS process and MEMS process. The design and post processing of CMUT is explained in detail. The fabricated CMUT is tested. It is found that the signal is not detected from some devices. Therefore, the failure analysis of CMUT is carried out in some aspects. Finally, fatigue failure is determined as the cause of the failure.