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김기만,차일환,Kim, Gi-Man,Cha, Il-Hwan 한국음향학회 1996 韓國音響學會誌 Vol.15 No.6
실제 환경에서 배열은 비정상적으로 동작하는 소자를 가질 확률이 높다. 결함 소자는 출력이 없거나 정상인 것에 비해 크게 감소된 이득을 갖는다. 이는 빔의 부엽 레벨을 높이고, 적응 빔 형성기에서 간섭 신호를 제거하지 못하도록 한다. 이 논문에서는 결함 소자들을 갖는 배열을 위한 빔 형성 방법을 제안하였다. 이상적인 경우 배열 출력 자료들로부터 계산된 자기 상관 행렬은 Toeplitz 행렬이다. 그러나 결함 소자를 갖는 배열로부터 게산된 자기 상관 행렬은 결함 행렬이다. 따라서 이 행렬의 대각항들을 평균하여 얻어진 값들로 새로운 자기 상관 행렬을 구성하고, 새로 구성된 자기 상관 행렬을 빔형성 방법에 적용한다. 제안된 방법의 성능을 고찰하기 위해 컴퓨터 시뮬레이션을 수행하였다. 그 결과 제안된 방법은 기존의 부분 처리 기법의 단점이었던 자유도 문제를 해결할 수 있었다. An array often has faulty elements in real operation. The faulty elements, producing no output or highly reduced gain than other normal elements, cause an elevated sidelobe level and fail to reject the interference signals in an adaptive beamformer. In this paper we have presented the beamforming algorithm for arrays with faulty elements. In the ideal case, an autocorrelation matrix computed from array output data is the toeplitz. However, the inverse of the autocorrelation matrix computed from array with faulty elements can not be obtained due to deficient values of matrix. To overcome this problem, an adaptive beamforming algorithm using the average values of the diagonal terms of matrix is proposed. The computer simulations have been performed to study the performance of the presented method. We have been able to solve the degrees-of-freedom problem that is the drawback of the previous subaperture processing technique.
김기만(Gi Man KIM),최성대(Seong Dae CHOI) 한국기계가공학회 2010 한국기계가공학회지 Vol.9 No.5
In this paper, the dynamic response of a CNC 5 Axles machining center was analyzed and then controlled passively by using the dynamic absorber. For the simplification of the theoretical approach, the CNC 5 Axles machining center was modeled as a flexible beam(Bed) having a point mass(Column), two discrete systems(a Table-set and a dynamic absorber). Specifically by using the dynamic absorber, the dynamic response of a Table-set which be caused by the vibration of a flexible beam, was reduced down to the infinitesimal level. The optimal design factors of the dynamic absorber were obtained from the minimization of the cost function. It was found that the natural frequencies of a UT-380 machining center be varied due to the movement of the Table-set. In view of the dynamic response of a Table-set, the larger spring stiffness and mass of the dynamic absorber were found to give the greater reduction.
이산계와 탄성 지지보의 동응답 및 진동 인텐시티 저감을 위한 목적함수 해석
김기만(Kim, Gi-Man),최성대(Choi, Seong-Dae) 한국소음진동공학회 2010 한국소음진동공학회 논문집 Vol.20 No.1
In this paper, the feasibility of the cost function having two control factors were discussed in compared to two others which has one different control factor respectively. As of the control factors, the dynamic response of a discrete system and the vibrational intensity at the reference point which is the connecting point of a discrete system to a flexible beam were controlled actively by the control force obtained from the minimization of the cost function. The method of feedforward control was employed for the control strategy. The reduction levels of the dynamic response of a discrete system and the vibrational intensity at a reference point, and also the input power induced by the control force were evaluated numerically in cases of the three different cost functions. In comparison with the results obtained from the cost functions of one control factor, which is the dynamic response or the vibrational intensity, in most cases of the cost function of two control factors the better or similar results were obtained. As a conclusion, it is surely noted that both the dynamic response and the vibrational intensity of the vibrating system be controlled up to the expected level by using the single cost function having two control factors.
저온 열원으로부터 최대 동력을 생산하기 위한 유기랭킨사이클(ORC)에 관한 연구
김경훈(Kim Kyoung-Hoon),한철호(Han Chul-Ho),김기만(Kim Gi-Man) 한국태양에너지학회 2011 한국태양에너지학회 논문집 Vol.31 No.3
ORC(organic Rankine cycle) has potential of reducing consumption of fossil fuels and has many favorable characteristics to exploit low-temperature heat sources. This work analyzes performance of ORC with superheating using low-temperature energy sources in the form of sensible energy. Maximum mass flow rate of a working fluid relative to that of a source fluid is considered to extract maximum power from the sources. Working fluids of R134a, iC₄H<SUB>10</SUB> and C?H?, and source temperatures of 120℃, 200℃ and 300℃ are considered in this work. Results show that for a fixed source temperature thermal efficiency increases with evaporating temperature, however net work per unit mass of source fluid has a maximum with respect to the evaporating temperature in the range of low source temperature. Results also show that the maximum power extraction is possible with R134a for the source temperature of 120℃, with iC₄H<SUB>10</SUB> for 200℃, and with C?H? for 300℃.
선형 제한 조건을 갖는 광대역 빔 형성기의 출력 SINR
곽병재,김기만,차일환,윤대희,Gwak, Byeong-Jae,Kim, Gi-Man,Cha, Il-Hwan,Yun, Dae-Hui 한국음향학회 1994 韓國音響學會誌 Vol.13 No.e2
본 논문에서는 벡터적 접근 방법을 이용하여 noncoherent 상황에서 선형 제한 조건을 갖는 광대역 빔 형성기의 출력 SINR식을 도출하였다. 여기서 입사되는 광대역 신호들은 평탄한 스펙트럼을 갖는다고 가정하였다. In this paper, we derive expressions for the output signal-to-interference plus noise ratio(SINR) of the linearly constrained broadband beamformer in noncoherent situations using a vector approach. The incoming broadband signals are assumed to have flat spectra.
양세영,최성대,김기만,전재목,공병채,Yang, Se-Young,Choi, Seong-Dae,Kim, Gi-Man,Jun, Jea-Mok,Gong, Byeong-Chae 한국생산제조학회 2010 한국생산제조학회지 Vol.26 No.2
The general way to process the surface by means of the laser was heat treatment for strengthening the surface hardness. They have used the laser for changing the property of the surface, especially for metal. Generally, it is recent increasing tendency to use the thin plate panel for making things smaller and lightweight. However, thin plate should be strengthened or let the thin plate panel have moment of inertia by means of engraving the groove or wave on them for lightweight and strengthening. Therefore it is expected that the thin plate panel can be harder and more stable through processing the metal surface by laser beam irradiation and the hardness of thin plate possibly can be also changed how many parts of them are harden. Through this research, it can be grasped how the hardness and mechanical characteristic changes according to width and depth of groove by laser affect the max stress by the ratio of $A_H/A_T$ (hardening area/total area) and characteristic of displacement and structural characteristic for making the thin plate harder by the strengthening metal surface of thin plate by laser through the experiment and analysis of FEA can be presented.