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이현호,황준영,정석호,이원남,Lee, Hyeon-Ho,Hwang, Jun-Yeong,Jeong, Seok-Ho,Lee, Won-Nam 대한기계학회 1997 大韓機械學會論文集B Vol.21 No.1
Flame oscillation phenomena in a co-flow diffusion flame was experimentally studied with periodic fuel supply using a solenoid valve. The degree of excitation was controlled by changing the volume flux of fuel passing through the valve. Flame oscillation frequencies were measured utilizing a photodiode, a spectrum analyzer, video and high speed movies. Laser planar visualization was employed to study the correlation between the flame oscillation and the toroidal vortices. Observed are three regimes of flame oscillation, where the oscillation frequencies are for the multiples of excitation, the excitation itself and the flame natural oscillation. Both periods of natural oscillation and of excitation induced oscillation exist over one cycle of the excitation in the frequency multiplied regime. It is considered as an effect of balancing the influence of buoyancy driven vortex with that of excitation induced vortex near the excitation rate of 0.2. Flame shapes are become monotonous as increasing the excitation frequency to the range of over two fold of the natural oscillation. The flame oscillation can be modulated to the frequency of either multiples of excitation or excitation itself under certain conditions. This implies that the flame oscillation could be modulated to avoid the resonance frequency of the combustor, and shows the possibility of active control of the flame oscillation.
이현호,Lee, Hyeon-Ho 한국데이터베이스진흥원 2002 디지털콘텐츠 Vol.5 No.-
지난 호에서는 정적 SQL(Static SQL)의 장점과 Oracle8i에서 도입된 analytic function이라는 새로운 기능을 이용해서 부분범위처리가 가능한 효율적인 게시판 구현에 대해서 살펴보았다. 이번 호에서는 analytic function, FBI(Function Based Index), 순환관계(connect by ㆍㆍㆍstart with)를 이용한 응답글(속칭 리플)이 있는 게시판의 부분범위처리에 대해서 살펴보고, 게시판의 총글수나 사용자별 마일리지합 정보 등 집계성이나 항상 사용자가 온라인상에 보고자하는 정보들을 효율적으로 관리하기 위해 materialized view를 적용하는 방법에 대해서 알아보겠다.