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Jihwan Ahn,Geonryul Lee,Keeman Lee 한국연소학회 2021 KOSCOSYMPOSIUM논문집 Vol.2021 No.11
In this study, the combustion instability characteristics of low swirl model gas turbine combustor was investigated. In addition, Flame transfer function(FTF) measurements performed to develop low swirl combustor combustion instabilities prediction tool. For more accurate prediction, wide range of combustor length and forcing frequency condition were investigated. Also l-D numerical analysis were performed, and numerical data were compared to experimental data. Numerical analysis conducted by open-source code OSCILOS. According to analysis experimental data, several flame models were derived and used for numerical analysis. From the results, eigenfrequency and growth rate were inferred, and multiple instability models can be prediction. Numerical prediction unstable regime is not exactly correct for experimental results. Nevertheless, the numerical prediction data were considered reliable.
Compact Spiral Element for Wideband Beam-Steering Arrays
Ahn, Jihwan,Cha, Seung Hun,Cha, Seung Gook,Yoon, Young Joong IEEE 2017 IEEE antennas and wireless propagation letters Vol.16 No.-
<P>In this letter, a compact spiral element is proposed for wideband beam-steering arrays. The extremely limited element spacing and size to prevent the occurrence of grating lobes at high frequency range are the most critical issues in designing wideband phased arrays. Two miniaturization techniques are simultaneously applied to an Archimedean spiral radiator to reduce the area of the proposed spiral. This spiral radiator is designed with a reflector plane instead of an absorber and cavity to realize low-profile characteristics and achieve unidirectional pattern without power loss. A wideband balun that operates simultaneously as a wideband impedance transformer is also miniaturized to be integrated between the radiator and reflector plane. The proposed element consists of these three components, and its size is 0.25 lambda(L) x 0.25 lambda(L) x 0.13 lambda(L,) where lambda(L) is the wavelength at 2 GHz, the lowest frequency of interest. This compact spiral element with a simple structure and design procedure can achieve wideband beam steering without grating lobes and be employed in numerous applications, such as conformal arrays.</P>
모델 가스터빈 연소기에서 인젝터 형태에 따른 종-방향 불안정성 특성에 관한 실험적 연구
안지환(Jihwan Ahn),강연세(Yeonse Kang),이기만(Keeman Lee) 한국추진공학회 2021 한국추진공학회지 Vol.25 No.2
In this study, the combustion instability characteristics of low-swirl injector and high-swirl injector is compared by model gas turbine combustor. To compare of unstable behavior in high-swirl injector and low-swirl injector, we performed lots of measurement of combustion instability, with variable of equivalence ratio, combustor length and injector type. The results shown that longitudinal instability occur dominantly in model gas turbine combustor. In addition, it was found that high-swirl injector has more wide range of unstable regime than low-swirl injector. The blockage ratio what one of a parameter in low-swirl injector has not much effected in aspects of overall combustor behavior. Also, revealed that combustion instability occurred in the same combustor length has same properties, regardless of the injector type.
고출력 전자기파 발생 장치용 소형화 된 원뿔 계단형 COBRA
안지환(Jihwan Ahn),이상흔(Sang Heun Lee),윤영중(Young Joong Yoon),김준연(Junyeon Kim),이우상(Woo Sang Lee),소준호(Joonho So),한인희(In Hee Han) 한국전자파학회 2008 한국전자파학회논문지 Vol.19 No.9
본 논문에서는 고출력 전자기파 발생 장치에 사용될 소형화 된 원뿔 계단형 COBRA(Coaxial Beam-Rotating Antenna)를 제안하였다. COBRA는 혼 안테나와 렌즈로 구성되는데, 일반적인 방법으로 설계할 경우 정전 파괴방지를 위해 그 크기가 매우 커지게 된다. 소형화를 위해 안테나의 길이만 줄일 경우 위상 오류의 증가로 인해 안테나의 이득이 줄어들게 되는데, 이를 방지하기 위해 COBRA 렌즈를 원뿔 계단형으로 변형시켜 개구면에서의 위상 오류가 보정되도록 하였다. 시뮬레이션 결과, 1,300 ㎜ 길이의 안테나를 600 ㎜로 줄였음에도 불구하고 제안된 안테나는 더 높은 이득을 보였으며, 제작하고 측정된 원뿔 계단형 COBRA의 이득은 26.2 ㏈i로 나타났다. In this paper, miniaturized conically stepped COBRA is proposed. In order to prevent electrical breakdown, COBRA, which consists of horn and lens, has to get bigger if it is designed with conventional method. Because of the phase error increase, shortening the length of the antenna without changing the aperture size leads to the reduction of the antenna gain. To avoid this, the phase error at the aperture is compensated by transforming the COBRA lens into conically stepped form. The simulations result shows that the proposed antenna has higher gain than the conventional COBRA in spite of the size reduction from 1,300 mm to 600 mm. The fabricated and measured COBRA has the gain of 26.2 ㏈i.
A Survey on Characteristics and Trends of the WEEE Discharge in Korea
( Jihwan Park ),( Insang Jung ),( Sudong Kim ),( Chimoon Ahn ),( Wonheechoi ) 한국폐기물자원순환학회(구 한국폐기물학회) 2019 ISSE 초록집 Vol.2019 No.-
Since 2003, Extended Producer Responsibility (EPR) system has been continuously applied in the context of collection and recycling of Waste Electrical and Electronic Equipment (WEEE). This system has contributed to design the WEEE management directives and infra-structures for WEEE collecting and recycling in Korea. As an example, Ministry of Environment (MOE) achieved WEEE collection performance that approximately 297,610t of WEEE was collected in formal sector from the all nationwide in 2018. MOE takes this achievement a step further, encourage to expand the formal sector for the more WEEE collection and recycling performance. In this study, we investigate the current status of WEEE discharging trends and user behavior as well as systematical strategies that how to expand the formal sector in WEEE discharging step. A survey interviews were implemented using the telephone survey with computer-assisted telephone interviewing (CATI) method targeting the number of 2,000 interviewees. Survey results showed that 31.50% (n=630) of total respondents have the WEEE discharging experience within recent one year, and the most discharged item was refrigerator (n=221, 35.08%) from the interviewees. From the whole interviewee’s perspective, the top three discharge channels preferred were Local Authority (39.00%), Take-back (37.30%), and Personal Recyclers (10.20%). On the other hand, respondents who have responded had discharge experience within recent one year preferred the Local Authority (27.50%), Take-back (26.80%), and Door-to-Door service (18.7%) respectively. Result for survey on whether interviewees holding or not the end-of-life appliances which was potentially needed showed that the 38.05% (n=761) of the whole respondents have and hold the end-of-life appliances in their house. The most type of end-of-life appliances which held in their inhabitancy were refrigerator (48.10%), washing machine (16.03), television (9.46%), and computer (4.20%). This study can be utilized as a basic data for establishing more effective WEEE collecting strategies by the MOE based on WEEE discharge experience, routes, and potential item to be discharged.