• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.145-147
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• 2009

The benefits of hydroforming technology are known as weight and cost savings through part consolidation and reduced post-forming processes such as welding and piercing. Hydroforming technology has some weaknesses in terms of process cycle times. But, as the hydraulic system and process designs are continuously developed, the cycle time is also reduced to acceptable and competitive levels. Hot air bulging is one of recently developed hydroforming techniques. Hot air bulging in order to further extend the forming degrees of Al lightweight material is investigated. A heated tube is placed in a heated die and sealed at the ends by sealing cylinders. The tube is subsequently expanded against the die cavity wall by internal pressure provided by air medium. The result of this study shows that axial feeding speed and air pressure have an effect on formability of Al air bulging at elevated temperature.

• 한국컴퓨터정보학회논문지
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• 제23권9호
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• pp.27-34
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• 2018

Personal media centered on blogs, Twitter, and Facebook has opened up a personal broadcasting area while meeting platforms such as YouTube and Africa TV. Due to the many advantages and disadvantages of personal broadcasting, a study on it was necessary and statistical survey was conducted. The study conducted opinion survey of 118 university students on personal broadcasting. As a result, we are getting news using smartphones and mainly watching videos through YouTube, and watching videos type in the order of games, music videos and sports. Satisfaction rate of video was 72.4%, 80.2% of survey did not use paid services, experiences about personal broadcasting was 96.6% and 90.5% of survey the prospect of person broadcasting of the opinion that "it will be expanded". The first thing we want to be improved in personal broadcasting is the prevention of abusive language and hate speech. Second, we were reluctant to sensational content. Third, the survey results are the improvement of excessive advertising.

• 한국항공우주학회지
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• 제32권10호
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• pp.112-117
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• 2004

본 연구는 공기역학적 운동에너지를 이용하여 점화장치를 구성하는데 따른 해석과 실험에 관한 연구로써 공기역학 점화기는 크게 노즐과 공명관으로 구성되어 있다. 압축가스가 노즐을 통과하여 공명관으로 유입되며, 이때 노즐과 공명관사이에 압력맥동이 발생한다. 이러한 압력맥동에 의한 운동에너지는 일정한 조건하에 공명관 내부에서 열에너지로 변화하게 된다. 본 연구에서는 음속노즐과 초음속 노즐을 두개의 각기 다른 공명관에서 실험과 수치해석을 실시하였으며, 노즐표면의 마찰손실과 공기역학 손실을 최소화하는 초음속 노즐의 최적형상을 제시하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.734-738
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• 2017

본 연구에서는 가스다이내믹 공진 점화시스템 (Gas-dynamic Ignition System)의 온도상승 지배인자를 파악하고, 공진관으로의 질량유입 패턴의 영향에 대해 연구하였다. OpenFOAM 프로그램을 이용하여 세 가지 Case에 대한 전산해석을 수행하였으며, RhoCentralFoam을 적용하였다. 해석결과로, 작동유체의 가열이 공기열역학적 현상에 의한 것임을 밝히고, 공진관으로의 원활한 질량유입이 온도 상승에 중요한 지배인자임을 확인하였다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1993년도 추계학술대회 논문집
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• pp.666-671
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• 1993

Fatigue life prediction under multi-axial variable load were performed for Aluminium 7075-T651 alloy using SAE Notched specimen & Torque tube shaft component specimen. When variable multiaxial load is applied to material, maximum damaged plane(critical plane) change. To clarify the situation, experiment is performed on two different changing load path. For multiaxial fatigue life prediction, miner rule is expanded to critical plane theory. Shear based parameter and Elliptical parameter give better correlation. This suggests that miner rule can be applicable on multi-axial variable load.

• 한국광학회:학술대회논문집
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• 한국광학회 1989년도 제4회 파동 및 레이저 학술발표회 4th Conference on Waves and lasers 논문집 - 한국광학회
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• pp.76-80
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• 1989

Spatial filters were designed for 1 TW high power phosphate glass laser development. Laser beam should be expanded from 1 mm diameter to 200mm diameter. Pin hole size should be determined and most of incident energy should be transmitted through out to final spatial filter. Each pin hole size is determined by calculating encircled energy for Gaussian beam from the oscillator. The optical tube length of each spatial filter is corrected to have the best collimating quality by scew raytracing through the total system.

• 한국초전도ㆍ저온공학회논문지
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• 제20권3호
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• pp.21-27
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• 2018

It is difficult to fabricate and maintain moving parts of expander at cryogenic temperature. This paper describes numerical analysis and experimental investigation on a cryogenic reciprocating expander without moving piston. An intake valve which takes high-pressure gas, and an exhaust valve which discharges low-pressure gas, are connected to a tube. The inside pressure of the tube is pulsated for work production. This geometric configuration is similar to that of pulse tube refrigerator but without regenerator. An orifice valve and a reservoir are installed to control the phase of the mass flow and the pressure. At the warm end, a heat exchanger rejects the heat which is converted from the produced work of the expanded gas. For the numerical analysis, mass conservation, energy conservation, and local mass function for valves are used as the governing equations. Before performing cryogenic experiments, we carried out the expander test at room temperature and compared the performance results with the numerical results. For cryogenic experiments, the gas is pre-cooled by liquid nitrogen, and then it enters the pulse tube expander. The experiments are controlled by the opening of the orifice valve. Numerical analysis also found the expander conditions that optimize the expander performance by changing the intake pressure and valve timing as well as the opening of the orifice valve. This paper discusses the experimental data and the numerical analysis results to understand the fundamental behavior of such a newly developed non-mechanical expander and elucidate its potential feature for cryogenic application.

• Clinics in Shoulder and Elbow
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• 제26권2호
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• pp.162-168
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• 2023

Background: Reverse shoulder arthroplasty (RSA) has evolved continuously over recent years, with expanded indications and better outcomes. YouTube is one of the most popular sources globally for health-related information available to patients. Evaluating the reliability of YouTube videos concerning RSA is important to ensure proper patient education. Methods: YouTube was queried for the term "reverse shoulder replacement." The first 50 videos were evaluated using three different scores: Journal of the American Medical Association (JAMA) benchmark criteria, the global quality score (GQS), and the reverse shoulder arthroplasty-specific score (RSAS). Multivariate linear regression analyses were conducted to determine the presence of a relationship between video characteristics and quality scores. Results: The average number of views was 64,645.78±264,160.9 per video, and the average number of likes was 414 per video. Mean JAMA, GQS, and RSAS scores were 2.32±0.64, 2.31±0.82, and 5.53±2.43, respectively. Academic centers uploaded the highest number of videos, and surgical techniques/approach videos was the most common video content. Videos with lecture content predicted higher JAMA scores whereas videos uploaded by industry predicted lower RSAS scores. Conclusions: Despite its massive popularity, YouTube videos provide a low quality of information on RSA. Introducing a new editorial review process or developing a new platform for patients' medical education may be necessary. Level of evidence: Not applicable.

• 에너지공학
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• 제23권2호
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• pp.149-157
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• 2014

원자력발전소의 증기발생기 전열관은 가동 중에 다양한 형태의 부식 손상이 발생한다. 전열관의 외면에 발생하는 응력부식균열은 2차측 응력부식균열이라 불리는데 주로 전열관의 확관천이지역에서 발생한다. 그 원인은 이 지역의 기하학적 특성과 관련된 슬러지의 침적에 의한 불순물의 농축과 증기 발생기 제작과정에서 확관에 의한 잔류응력이다. 특히 잔류응력은 확관방법에 따라 방향성 및 그 크기가 달라지는데 전열관에 발생하는 균열의 방향 및 발생빈도는 이와 관련이 있다. 현장 경험에 따르면, 폭발확관된 전열관은 수압확관된 전열관에 비해 확관천이 부위에서 원주방향 균열이 잘 발생하는 것으로 나타났다. 따라서 본 연구에서는 예민화된 증기발생기 전열관에 대한 응력부식균열 시험을 통해 확관법에 따른 특정방향 균열의 발생빈도 및 균열 크기를 비교하였다. 또한 균열이 발생된 전열관의 파단면 검사를 통해 균열 양상과 수화학 환경 중의 특정 성분의 영향을 관찰하였다.

• 해양환경안전학회지
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• 제17권2호
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• pp.173-178
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• 2011

선박에 사용되는 TEMA 열교환기 전열관의 확관 공정에서 발생되는 탄소성 응력과 변형량의 거동을 유한요소법으로 해석하였다. 열교환기의 관판 구명의 홈 깊이와 롤러 익스팬더의 작용압력을 변화시켜 해석한 결과, 전열관의 관판 구멍의 홈 깊이가 커지면 탄소성 압축응력은 감소하였고, 롤러 익스팬더 압력이 높을수록 관판 구멍의 홈 모서리 부분의 탄소성 응력이 증가되었다.