95년은 통일을 향한 힘찬 발걸음으로 나아가자

김형대 북한연구소 1995 北韓 Vol.- No.277

[수세장병 수기] 방황끝에 찾은 길

김형대 새가정사 1973 새가정 Vol.- No.-

테프론 코팅 전열관 표면으로의 열 및 물질 전달 특성에 관한 실험적 연구

김형대,이장호,김정배,김무환 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.8

* 포항공과대학교 대학원 기계공학과†책임저자, 회원, 포항공과대학교 기계공학과E-mail: mhkim@postech.ac.krTEL: (054)279-2165, FAX: (054)279-3199The heat and mass transfer on two kinds of tube surfaces (bare stainless steel tube and Teflon coated tube) in steam-air mixture flow are experimentally studied to obtain design data for the heat exchanger of the latent heat recovery from flue gas. In the test section, 3-tubes are horizontally installed, and steam-air mixture is vertically flowed from the top to the bottom. The pitch between tubes is 67mm, the out-diameter of tube is 25.4mm, and the thickness is 1.2mm; blockage factor (cross sectional tube area over the cross sectional area of the test section) is about 0.38. All of sensors and measurement systems (RTD, pressure sensor, flow-meter, relative humidity sensor, etc.) are calibrated with certificated standard sensors and the uncertainty for the heat transfer measurement is surveyed to have the uncertainty within 7%. As experimental results, overall heat transfer coefficient of the Teflon (FEP) coated tube is degraded about 20% compared to bare stainless tube. The degradation of overall heat transfer coefficient of Teflon coated tube comes from the additional heat transfer resistance due to Teflon coating. Its magnitude of heat transfer resistance is comparable to the in-tube heat transfer resistance. Nusselt and Sherwood numbers on Teflon (FEP) coated surface and bare stainless steel surface are discussed in detail with the contact angles of the condensate. 기호설명A : 면적 [m2]Cp : 정압 비열 [kJ/kg-K] D : 확산계수 [m2/s]F : 노즐면적을 포함한 유량계수 hs : 현열 열전달 계수 [w/m2.K]hm : 물질 전달 계수 [kg/m2.sec]K : 열전도율 [W/m.K]Kq : 막힘 비율 (blockage factor)m : 질량유량 [kg/s]Nu : Nusselt 수 (식 (14)) P : 노즐차압 [Pa]Q : 열전달량 [W]Re : 최소 흐름 면적에서의 Reynolds 수 (udo/μ) Sc : Schmidt 수 ( / D)Sh : Sherwood 수 (식 (15))t, : 두께 [m]R : 열저항 [K/W]T : 온도 [K or oC]U : 불확실성 Pr : Prandtl 수 u : 유속 [m/s]

EXPERIMENTAL STUDY ON CHF CHARACTERISTICS OFWATER-TIO2 NANO-FLUIDS

김형대,김무환,JEONGBAE KIM 한국원자력학회 2006 Nuclear Engineering and Technology Vol.38 No.1

CHF characteristics of nano-fluids were investigated with different volumetric concentrations of TiO2 nanoparticles. Poolboiling experiments indicated that the application of nano-fluids, instead of pure water, as a cooling liquid significantlyincreased the CHF. SEM (scanning electron microscope) observations subsequent to the pool boiling experiments revealedthat nanoparticles were coated on the heating surface during pool boiling of nano-fluids. In order to investigate the roles ofnanoparticles in CHF enhancement of nano-fluids, pool boiling experiments were performed using (a) a nanoparticle-coatedheater, prepared by pool boiling of nano-fluids, immersed in pure water and (b) a nanoparticle-coated heater immersed innano-fluids. The results demonstrated two different roles of nanoparticles in CHF enhancement using nano-fluids: the effectof nanoparticles coated on the heater surface and the effect of nanoparticles suspended in nano-fluids.

태권도선수의 시합 전 생리적 반응

김형대,오연풍,이석준 대한구강악안면병리학회 2011 대한구강악안면병리학회지 Vol.35 No.2

Exercise training effciency depends on the training load, as well as on the athlete's ability to tolerate it. Taekwondo has been recognized as an Olympic sport in the 2000 Sydney Olympic games. Taekwondo competitions are regularly organized at the regional, national and international level according to the athlete's age and skill level. An integrated psychobiological stress-related measurement during a Taekwondo competition could be of considerable interest for studies on athlete performanc and behavior. The aim of this study was to evaluate the effects of an official Taekwondo competition on the heart rate(HR) and galvanic skin response(GSR) which represent stress score. each 5 male and female Taekwondo athletics were participated in this experiment. All persons were raised GSR and HR during competition and punching or kicking on opposite athletics. The results were statistically significant. It was suggested that all athleics had stress about competition

복합형 이동로봇의 동력학적 모델링 및 제어

김형대,권대갑 대한기계학회 1991 대한기계학회논문집 Vol.15 No.5

본 로봇은 wheeled type과 legged type의 장점을 함께 가지고 있으므로 주행 속도가 빠르며 환경적응력이 좋다. 기존 로봇과 비교할때 Y.Icihkawa등이 개발한 HLV와 가장 유사하지만 모터 3개로 6개의 바퀴-다리 유닛을 구동하므로 모터15개로 5개의 바퀴-다리유닛을 구동하는 Ichikawa HLV와 동력전달구조에서 많이 상이하다. 뿐만아니라 본 로봇은 3개의 모터만 사용했기 때문에 주행제어가 훨씬 간단하고 제작 비가 저렴하며 장애물 및 계단승강시 걸음새가 훨씬 간단하다.(Ichikawa HLV 경우 뒷 쪽 2개의 다리를 동시에 들 수 없기 때문에 계단 승강시 몸체 회전을 적절하게 섞어야 한다.)

소규모학교 활성화를 위한 법적 제도적 지원방안

김형대 한국교육재정경제학회 2013 한국교육재정경제학회 학술대회 자료집 Vol.2013 No.62

지속가능한 에너지 정책을 위한 예비 연구: 에너지원별 정치-사회-경제적 영향 예측

김형대 한국정책학회 2018 한국정책학회 춘계학술발표논문집 Vol.2018 No.-

블록체인 합의 방해요인 제거를 위한 Adaptive Consensus Bound PBFT 알고리즘 설계

김형대,윤주식,고윤영,정종문 한국인터넷정보학회 2020 인터넷정보학회논문지 Vol.21 No.1

With the rapid development of block chain technology, attempts have been made to put the block chain technology into practical use in various fields such as finance and logistics, and also in the public sector where data integrity is very important. Defense Operations In addition, strengthening security and ensuring complete integrity of the command communication network is crucial for operational operation under the network-centered operational environment (NCOE). For this purpose, it is necessary to construct a command communication network applying the block chain network. However, the block chain technology up to now can not solve the security issues such as the 51% attack. In particular, the Practical Byzantine fault tolerance (PBFT) algorithm which is now widely used in blockchain, does not have a penalty factor for nodes that behave maliciously, and there is a problem of failure to make a consensus even if malicious nodes are more than 33% of all nodes. In this paper, we propose a Adaptive Consensus Bound PBFT (ACB-PBFT) algorithm that incorporates a penalty mechanism for anomalous behavior by combining the Trust model to improve the security of the PBFT, which is the main agreement algorithm of the blockchain. 블록체인 기술이 급속도로 발전하고 있음에 따라 금융·물류 등 다양한 분야에서 블록체인 기술을 실용화하려는 시도들이 진행되고 있으며, 데이터 무결성이 매우 중요한 공공분야 또한 마찬가지이다. 국방분야 또한 네트워크 중심 작전환경(NCOE) 하에 작전운영을 위해서는 지휘통신 네트워크의 보안성 강화 및 완전무결성 확보가 매우 중요하다. 이를 위해 블록체인 네트워크를 적용한 지휘통신네트워크 구축이 필요하나, 현재까지의 블록체인 기술은 51% 공격 등의 보안 이슈들을 해결하지 못하고 있어, 국방에 접목하기어려운 것이 현실이다. 특히, 현재 블록체인에서 많이 사용되고 있는 Practical Byzantine fault tolerance (PBFT)알고리즘은, 악의적인행동을 하는 노드들에게 penalty 요소가 없고, 합의를 방해하는 노드가 전체 노드의 33%이상만 차지해도 합의 실패를 만드는 문제점이 있다. 본 논문에서는 블록체인의 주요 합의 알고리즘인 PBFT의 보안성 향상을 위해, Trust 모델을 접목하여 비정상 행위에 대한penalty 메커니즘이 적용된 Adaptive Consensus Bound PBFT (ACB-PBFT) 합의 알고리즘을 제안한다.

인터넷 교육망을 이용한 ICT 활용학습에 관한 연구

金炯大,李大勳 충주대학교 산업대학원 2002 大學院論文輯 Vol.3 No.-

The materials in this research deal with as many as 22 classes of the first semester of the 4th grade of social studies in the 7th elementary school curriculum, and were created for the internet-using teaching as so called 'the teaching and learing aids of the beautiful Chung-chong North Province'. After using the data in the class I also made verification tools for the ICT-using ability in order to check the effects of the classes. The tools are a checking sheet of ICT-using abilities and another sheet that checks the changes of interests on the ICT using abilities. Especially, because of the characteristics of the internet-based teaching and learning aids applied to this research, students' learning efficiency was shown high at three areas of (ⅰ)the area of understanding of information and ethics, (ⅱ)the area of computer communication, (ⅲ)the area of general activities, and revealed that they approached to the tarket levels on the chart of the ICT-using abilities. And the types of interests to the ICT using abilities were also shown positive. I could find that these internet-based 'teaching and learning aids' had been very efficient. Besides, the ICT-using ability applied to the pair cooperatioal learning models with a structural view, the wide educational use of internet data and educational effects using various study programs are expected.