수직 동심 환형관 내부유동에서 과냉 유체의 비등 시작 열유속에 관한 표면 볼록 곡률의 영향

변정환,이승홍,Byun, Jung-Hwan,Lee, Sung-Hong 대한기계학회 2002 大韓機械學會論文集B Vol.26 No.11

Effect of Convex Surface Curvature on the Onset of Nucleate Boiling of Subcooled Fluid Flow in Vertical Concentric Annuli An experimental study has been carried out to investigate the effect of the transverse convex surface curvature of core tubes on heat transfer in concentric annular tubes. Water is used as the working fluid. Three annuli having a different radius of the inner cores, Ri=3.18mm, 6.35mm, and 12.70mm with a fixed ratio of Ri/Ro=0.5 are used over a range of the Reynolds number between about 40,000 and 80,000. The inner cores are made of smooth stainless steel tubes and heated electrically to provide constant heat fluxes throughout the whole length of each test section. Experimental result shows that heat flux values on the onset of nucleate boiling of the smaller inner diameter model is much higher than that of the larger size test model.

겨울철 규조류 대발생 제어를 위한 Naphthoquinone 유도체 Nq 4-6의 적용 가능성

변정환,주재형,김백호,한명수,Byun, Jung-Hwan,Joo, Jae-Hyoung,Kim, Baik-Ho,Han, Myung-Soo 응용생태공학회 2015 Ecology and resilient infrastructure Vol.2 No.3

겨울철 한강과 낙동강에서 규조 Stephanodiscus hantzschii에 의한 조류발생이 빈번하게 일어나며, 이로 인한 수자원의 질적변화와 정수과정에 많은 경제적 손실을 주고 있다. 본 연구진은 조류대발생의 원인종인 S. hantzschii을 제어할 수 있는 naphthoquinone (Nq) 화합물을 개발하였다. 본 연구는 개발된 Nq 화합물 중 가장 친환경적인 화합물을 선정하기 위한 실험으로 물질의 살조범위 실험과 낙동강 현장수를 이용한 10 L 규모의 미소생태 실험을 수행하였다. 그 결과 Nq 4-6 화합물의 살조범위는 원반형 규조류에 특이적으로 나타났으며, 남조류 및 녹조류에 대해 살조 활성이 나타나지 않았다. 미소생태 실험 결과, 대조구에서 S. hantzschii가 지속적으로 세포밀도가 증가한 반면, Nq 4-6 화합물을 접종한 처리구에서는 처리 7일째 대조구 대비 S. hantzschii가 94.4% 감소하였으며, S. hantzschii를 제외한 나머지 규조류 및 녹조류에서는 Nq 4-6 화합물 처리 후 살조활성이 관찰되지 않았다. 식물플랑크톤 군집 분석 결과 대조구에 비해 처리구에서 우점도는 낮게 나타났으며, 다양도, 풍부도, 균등도 등은 처리구에서 높게 나타났다. 물리화학적요인 (용존산소, pH, 영양염) 및 미소생물 (heterotrophic nanoflagellates, 섬모충, 박테리아) 등에서도 Nq 4-6 화합물 처리 후 특이적인 변화는 나타나지 않았다. 따라서 본 연구에서 개발된 Nq 4-6 화합물은 생태독성이 낮고, 겨울철 국내 하천에서 매년 대발생을 일으키는 규조 S. hantzschii만을 특이적으로 제어함을 확인하였으며, 적용 시 식물플랑크톤 종 다양성을 증진시키는 친환경적인 조류제어제로 판단된다. We conducted the algicidal activity screening tests using 10 L microcosm to investigate the possibility of the field application of naphthoquinone derivative Nq 4-6 compound as an algicide. We determined its application range to assess its algicidal effects on the phytoplankton and to evaluate the response of the planktonic community and the water environment to this chemical. From results of the microcosm experiments, Nq 4-6 compound showed high algicidal activity on the centric diatoms such as Stephanodiscus hantzschii and Cyclotella meneghiniana, but it had no effect on other phytoplankton. The abundance of S. hantzschii continuously increased in the control, but its cell density decreased 1 day after the Nq 4-6 treatment. In particular, Nq 4-6 showed algicidal activity of 94.4% against S. hantzschii 7 days after the treatment. The dominance index of phytoplankton community was lower in the treatment than in the control. The diversity index, richness index and evenness index of phytoplankton community was higher in the treatment. Environmental factors and biological factors did not show specific changes after the Nq 4-6 compound treatment. Therefore, the results of this study demonstrates that Nq 4-6 is an effective agent for the control of S. hantzschii blooms, and that the microcosm tests play a crucial role when assessing field application.

암호화폐공개(ICO) 투자 참여의도 영향요인 분석

변정환(Jung-Hwan Byun),성행남(Haengnam Sung),정대을(Dae-Yul Jeong) 한국인터넷전자상거래학회 2021 인터넷전자상거래연구 Vol.21 No.5

ICO(Initial Coin Offering) based on Blockchain technology is in the spotlight as a method of investing funds for early start-ups. ICO is an investment method like as Angel Investment or Venture Capital, but it has unique characteristics that are different from other investment methods because it raises fund from the people who have enough fund, but most of them are not specialist in investment. This study analyzes the intention of investment and influencing factors in ICO. The theoretical model was built based on TAM(Technology Acceptance Model). To test, hypotheses, measurement model and structural model was verified with a survey of 187 samples who are potential investors to ICO. The research model was enough to find influence factors to ICO investment intention with the samples. The structural model showed the strong relationship among the perception of easy to use, usefulness, attitude, and intention to invest on ICO, but the quality of investment information about the offering company did not affect the usefulness of ICO. Concludingly, traditional TAM approach is enough to find influence factors on ICO investment intention like another technology based services.

전동실린더의 동기제어시스템 구축

변정환(Jung Hwan BYUN) 전남대학교 수산과학연구소 2010 수산과학연구소논문집 Vol.18 No.2

A motor cylinder is widely used as an apparatus for transportation of a small scale load. It is, however, difficult for only one motor cylinder to transfer a large scale load such as a weir. The large scale load is transferred by two motor cylinders which are mounted on right and left of load itself. In this case, the displacement difference generated between two motor cylinders, namely, the synchronous error has a bad influence on the transportation. In this study, a synchronous control system is designed to restrain synchronous error caused by disturbance. the control system is composed of two disturbance observers and one synchronous controller. Each disturbance observer is designed to restrain the disturbance. And the synchronous controller is designed to achieve accurate synchronization. Finally, the simulation results show that the designed control system is effective for the disturbance which lead to synchronous error.

3위치 솔레노이드 밸브를 이용한 소형선박의 선수각 제어에 관한 연구

변정환(Jung Hwan BYUN),양주호(Joo Ho YANG) 전남대학교 수산과학연구소 2008 수산과학연구소논문집 Vol.17 No.2

The electro-hydraulic servo valve is broadly used in rudder control of a large ship. But, this valve is not compatible with a small ship for offshore fisheries, because a great cost is demanded. And, if a solenoid valve of on-off type is used in a small ship, there exists offset such that a good control performance can not be achieved. In this study, the rudder control algorithm to get over demerits of solenoid has been developed. The proposed controller which is designed to suit for long sample time is constituted of software timer, relay, and switch. And, the controller generates PWM wave as a control input signal. The validity of the controller is proved through heading angle control system which is composed of hydraulic steering gear, electro magnetic compass, micro processor, and etc.

부영양 신갈지에서 천연물질 혼합제(PMC)의 수질개선능: 현장수온의 영향

변정환 ( Jung Hwan Byun ),황수옥 ( Su Ok Hwang ),문선기 ( Sun Ki Mun ),황순진 ( Soon Jin Hwang ),김백호 ( Baik Ho Kim ) 한국하천호수학회 2013 생태와 환경 Vol.46 No.2

We examined the effect of different field temperatures on water quality improvement (WQI) of natural domestic plant-mineral composites (PMCs). This method was previously used by Kim et al. (2011), to monitor the restoration of water quality of a eutrophic lake, Lake Shingal (Korea). Results indicate that PMCs on phytoplankton, BOD and phosphorus showed more than 70% WQI below 20°C, and less than 40% WQI over 25°C, respectively. The WQIs of PMCs on blue-green algae were gradually decreased with the increase of temperature, whilst diatoms exhibited more than 90% higher WQIs, regardless of water temperature. Additionally, the WQIs on bacterial biomass and total nitrogen were low at all temperatures. These results collectively indicate that water quality improvement activity of plant-mineral composites was dependent on the water temperature, and that the field application of above chemical during temperatures over 25°C, would be less effective in treating a cyanobacteria bloom dominated by Microcystis aeruginosa, than by diatoms.

기술수용모델을 이용한 창업기업의 신규코인상장(ICO) 참여의사 분석

변정환(Jung-Hwan Byun),정대율(Dae-Youl Jeong) 한국창업학회 2018 한국창업학회 Conferences Vol.2018 No.2

본 연구는 창업기업의 신규코인상장(ICO) 참여에 대한 의사결정 요인에 대해 분석 한다. ICO는 암호화폐에 대한 폭발적 관심과 함께 블록체인 기술을 이용한 응용분야 로 크라우드펀딩과 같이 창업기업 초반에 온라인 플랫폼을 통해 불특정 다수를 대상 으로 투자자를 모집한다. 현재, 한국을 비롯한 중국 등 ICO를 금지하고 있는 국가도 있는 반면에 ICO를 새로운 사업분야로 육성하기 위한 스위스나 싱가포르 같이 적극 적으로 유치하고 장려하는 국가도 있다. 연구를 위한 첫 번째 단계로 ICO의 개념을 정의하고 창업기업의 자금조달 방법인 크라우드펀딩과 IPO간의 비교를 통해 유사점 을 찾는다. 그리고 ICO의 기업 참여수와 모금금액에 대한 통계자료와 함께 국가별 ICO 및 사업분류별 조사자료를 검토한다. 창업기업의 ICO 참여의사를 분석하기 위해 기술수용모델(Technology Acceptance Model)을 이용하고, 연구모형을 구축하기 위해서는 기존 연구결과를 토대로 기업정보 공개, 사회적 영향, 성과기대에 대한 요소를 검토한다. This study analyzes the determinants of Initial Coin Offering(ICO) participation in start-up entrepreneurship. ICO is an application area using block chaining technology with explosive interest in crypto-currency. It attracts investors to an unspecified number of people through an online platform like crowd funding at the beginning stage of a startup company. Currently, there are some countries that prohibit ICO, such as Korea and China, while some countries actively attract and encourage ICO such as Switzerland and Singapore to foster new business areas. And find similarities by comparing the funding methods of entrepreneurs with crowd funding and IPO. This study reviews business classification of ICO participants, along with statistical data on ICO fundraising. The Technology Acceptance Model(TAM) is used to analyze the entrepreneurial intention of the ICO. In order to construct a research model, this study examines the elements of corporate information disclosure, social impact, and performance expectation based on existing research results.

창업 투자 모금을 위한 ICO(Initial Coin Offering)의 수용도에 대한 집단간 차이 분석

변정환(Jung Hwan Byun),성행남(Haengnam Sung),정대율(Dae Yul Jeong) 한국창업학회 2021 한국창업학회지 Vol.16 No.5

본 연구의 목적은 창업기업의 초기 투자 모금 방법 중의 하나인 ICO(Initial Coin Offering)에 대해 일반투자자 집단의 특성에 따라 그 수용도에 차이가 있는가를 분석하기 위한 것이다. ICO는 암호화 기술을 이용한 토큰 발행을 통해 초기 창업기업의 투자자금을 조달하는 방식으로 투자 위험도가 매우 높은 반면, 법적인 제약이 적어 투자에 성공 시에 큰 수익을 얻을 수 있어 점차 혁신적인 창업기업의 자금조달 수단으로 자리를 잡아가고 있다. 본 연구에서는 기술기반의 ICO 투자 수용도에 있어 투자자 집단들 간에 차이가 있을 것으로 가정하고 잠재적일 투자자들을 대상으로 실증연구를 실시하였다. 연구 방법은 설문조사를 통해 일반투자자의 특성과 ICO 수용에 대한 자료를 수집하고, 카이제곱 분석을 통해 집단 간 차이분석을 실시하였다. 차이분석결과, 성별, 투자성향에 따라 유의적인 차이를 보였으나, 투자 경험은 그 종류에 따라 달리 나타났다. 본 연구는 일반투자자들도 블록체인과 같은 정보기술을 기반으로 하는 ICO가 창업기업의 새로운 투자수단으로 인식되고 있으며, 투자자의 특성에 따라 큰 차이가 있음을 검증하였다는데 그 의의가 있지만, 기존 선행 연구자료가 부족하고 ICO의 이용자가 국내에는 아직 극소수이기 때문에 일반화하기 어렵다는 한계점이 있다. 그럼에도 불구하고, 본 연구의 결과는 새로운 정보기술기반의 투자수단이나 투자플랫폼 개발과 ICO 투자대상자의 선정을 위한 타겟 마케팅 략수립에 유용한 정보를 줄 것으로 사료된다. The purpose of this study is to analyze the characteristics of general investors and technology acceptance factors for ICO, which is the initial stage investment method of blockchain-related startup companies. In this study, an empirical study was conducted on potential investors, assuming that there would be differences between investor groups in the technology acceptance in ICO. The research data on characteristics of general investors and ICO acceptance were collected through a survey, and differences between groups were analyzed through chi-square analysis. This paper verified that there were significant differences according to gender and investment propensity, but investment experience differed according to the investment types. This study is meaningful in that ICOs based on block chains are recognized as a new investment method for startups by general investors. In addition, the research results will provide useful information for the development of new information technology-based investment methods or investment platforms. As well, this paper will contribute to develope target marketing strategies for the selection of ICO investors.

2 자유도 제어기를 이용한 위어 제어시스템 설계

변정환(Jung Hwan BYUN),박일흠(Il Heum PARK) 전남대학교 수산과학연구소 2007 수산과학연구소논문집 Vol.16 No.-

The weir to regulate water level in a tide generation tank is above and below carried by two screw jacks which are mounted on right and left of weir itself. In this case, a movement difference between right jack and left jack causes unbalance, chattering and jamming of the weir. And then the weir can not be movable. In this study, a synchronous control system is developed to take accurate and quick equilibrium of the weir. The control system based on master-slave methodology consists of I-PD and two-degrees-of-freedom controller. The I-PD controller is designed in order that the left screw jack may follow the reference signal without overshoot and input saturation. And the two-degrees-of-freedom controller is designed to remove movement difference generated between right jack and left jack. The simulation results show that the weir can be smoothly transferred in equilibrium state by two screw jacks.

선박의 횡 동요 억제용 곡선레일의 위치제어

변정환(Jung Hwan BYUN),최명수(Myung Soo CHOI),여동준(Dong Jun YEO),양정규(Jung Kyu YANG),서정주(Jung Joo SUH) 전남대학교 수산과학연구소 2006 수산과학연구소논문집 Vol.14 No.1

A delivery ship is used to handle the cargo with the crane to/from the ships. The ship is inclined in the direction of a cargo which is hung on a crane. In this case, a arc shaped rail should be in the equilibrium state to get good anti-rolling performance. In this study, a device and control algorithm are developed to take accurate and quick equilibrium of the rail. The device is composed of a hinged immovable support and two screw jacks. And the control algorithm demands two controllers. One controller is designed such that the screw jack 1 and 2 follow the position reference signal generated by a tilt sensor. The other controller of is designed to remove the synchronous error occurred between jack 1 and jack 2. The simulation results show that the desirable control performance is achieved.