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전충호(Chung Ho Jeon),이창열(Chang Yeol Lee),윤현식(Hyun-Sik Yoon) 한국해양공학회 2010 韓國海洋工學會誌 Vol.24 No.5
The flow around a two-dimensional; rectangular cylinder that is freely falling in a channel was simulated using the immersed boundary method with direct forcing to determine the interactions between the fluid and the structure. The results of the present study were in good agreement with previous experimental results. Regardless of the H/L ratio (where H and L are the height and width of the rectangular cylinder, respectively), the flow structures had essentially the same pattern as the two symmetrical circulations that form about the horizontal center of the cylinder, with those centers located at each lateral position near the wake. When the cylinder approaches ve교 close to the bottom, a jet-like flow appeared between the bottom of the rectangular cylinder and the channel. When the jet-like flow goes through the channel, surrounding fluids are sucked into this jet, forming the secondary vortices.
전충호(Chung Ho Jeon),박종엽(Jong Yeob Park),이효삼(Hyo Sam Lee),윤성호(Sung Ho Yun),김상수(Sang Su Kim),최일중(Il Jung Choi) 한국마린엔지니어링학회 2009 한국마린엔지니어링학회 학술대회 논문집 Vol.2009 No.-
The technology for our country's Diving Systems has lagged behind Europe & USA. There are many problems on maintenance or operation because most of diving equipments have been introduced to ROK Navy from Europe & USA. The Gas Mix Maker that is developed by KR-AMC first time in domestic is boarding to the naval rescue vessel for the mixed-gas diving. It will be a base for the technology of our deep diving systems.
이상 유동에서의 유체-구조 연성해석을 위한 Direct Forcing/Ficititious Domain-Level Set Method
전충호(Chung Ho Jeon),윤현식(Hyun-Sik Yoon),정재환(JaeHwan Jung) 한국해양공학회 2011 韓國海洋工學會誌 Vol.25 No.4
In the present paper, a direct forcing/fictitious domain (DF/FD) level set method is proposed to simulate the FSI (fluid-solid interaction) in two-phase flow. The main idea is to combine the direct-forcing/fictitious domain (DF/FD) method with the level set method in the Cartesian coordinates. The DF/FD method is a non-Lagrange-multiplier version of a distributed Lagrange multiplier/fictitious domain (DLM/FD) method. This method does not sacrifice the accuracy and robustness by employing a discrete δ (Dirac delta) function to transfer quantities between the Eulerian nodes and Lagrangian points explicitly as the immersed boundary method. The advantages of this approach are the simple concept, easy implementation, and utilization of the original governing equation without modification. Simulations of various water-entry problems have been conducted to validate the capability and accuracy of the present method in solving the FSI in two-phase flow. Consequently, the present results are found to be in good agreement with those of previous studies.
$SF_6 Gas$를 용해시킨 변압기 절연유의 고주파 전기 특성의 향상
전충생,Jeon, Chung-Saeng 한국재료학회 1994 한국재료학회지 Vol.4 No.3
이 논문은 절연유를 정제하여 $SF_6$ 가스를 용해시켰을 때 절연유의 수십 MHz대의 고주파 절연파괴 전압과 유전특성에 관해서 연구한 것이다. 1)절연유에서의 고주파 전류는 전압의 1/2승에 거의 비례하여 증가한다. 2)전원주파수가 증가함에 따라 고주파 절연파괴는 주파수의 제곱에 역비례하여 감소하는 현상을 나타내고 AC절연파괴의 전압때보다 약 35%정도가 감소한다. 3) 용해된 기체의 압력을 증가시킴에 따라 고주파 절연파괴 전압은 원만하게 증하한다. 4)전원주파수의 증가에 따른 유전정접(tan $\delta$)은 거의 지수 함수적으로 증가하고 유전률($\varepsilon$)은 [0.6% MHZ]의 기울기로 삼소하는 경향을 나타낸다. 5) $SF_6$ 가스를 용해시켰을때 절연파괴 특성은 Air 또는 Ar을 용해시켰을 때 보다 약 25% 정도 향상되는 특성을 나타낸다. In this paper the breakdown and dielectric characteristics of purified transformer oil dissolved with $SF_6$ Gas are investigated with a few decade MHz frequency voltage. The results are as follows. 1) High frequency current is a approximately proportional to the square root of high frequency voltage in purified transformer oil. 2) As frequency increase breakdown voltage decrease inversely proportional to the square root of frequency and the high frequency breakdown voltage is lower about 35 percentage than that of AC 3) The breakdown voltage of high frequency has a little increase with the pressure increase of dissolved $SF_6$, Air and Ar Gas. 4) As voltage freguency increases the value of the dielectric loss tangent has increased almost exponentially and the dielectric constant ($\varepsilon$) has tended to decrease with a slope[0.6% MHz]. 5) When dissolved with $SF_6$ Gas, oil electrical characteristics has more increased about 25% than in Air or Ar gas with high voltage frequency.