• Journal of Magnetics
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• 제20권4호
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• pp.460-465
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• 2015

The paper presents methodologies and results concerning one- and two-dimensional numerical modeling of radio frequency oscillations in a coaxial transmission line fed with a short pulse of electric current. The line is partially filled with a ferrite material, magnetized longitudinally close to saturation. The 2D model has permitted analyzing, for the first time in the art, the spatial structure and dynamics of the wave field within the radially non-uniform cross-section planes of the non-linear and dispersive guiding structure. This opens ways for optimizing size parameters of the line and the extent to which it is filled with the ferromagnetic material, thus increasing the line's electric strength and intensity of the r.f. oscillations.

• ETRI Journal
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• 제39권6호
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• pp.813-819
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• 2017

A slotted rectangular nameplate antenna design with a patch bearing the name of the first author is presented. A $6.8mm{\times}26mm{\times}1.6mm$ substrate of FR-4 epoxy material having a relative permittivity of 4.4 and a dielectric loss tangent of 0.02 is used. Additionally, the feeding technique used is a coaxial mechanism. The standard antenna design parameters, including the reflection coefficient, bandwidth, radiation pattern, gain, directivity, and voltage standing wave radio (VSWR) for the proposed prototype are analyzed using a high-frequency structure simulator (HFSS) v-15, and are compared to the measured results. The designed structure may be considered for different satellite- and radio-determination applications at the respective resonant frequencies.

• 대한기계학회논문집B
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• 제20권7호
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• pp.2326-2336
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• 1996

So most practical combustor is considered to the swirl flame, it is very important to examinate swirl flame structure and combustion characteristics. Recently, attention has been paid to the flame diagnostic by radical luminous intensity. For swirl flame structure and combustion characteristic, reverse flow boundary, temperature, ion current and radical luminous intensity were measured in the double-coaxial swirl combustor which was used principle of multi-annular combustor. This study had three experimental condition, S-type, C-type, SC-type. S-type and C-type flames were formed recirculation zone, but SC-type flame wasn't formed. C-type flame had two recirculation zone. The position with maximum value of ion current and CH-radical, temperature and OH-radical had similarity distribution almost. Therefore, it is possible that the macro structure of flame was measured by radical luminous intensity in the high intensity of turbulent combustion field which was formed by swirl.

• 대한기계학회논문집B
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• 제20권3호
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• pp.1028-1039
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• 1996

This study was focused on the examination of the flame structure and the combustion characteristics of diffusion flame which was formed the turbulent shear flow of a double coaxial air jet system. The shear flow was formed by the difference velocity of surrounding air jet(U$\_$s/) and center air jet (U$\_$c/). So experimental condition was divided S-type flame (.lambda. > 1) and C-type flame (.lambda. < 1) by velocity ratio .lambda. (=U$\_$s//U$\_$c/). For examination of the flame structure and the combustion characteristics in diffusion flame, coherent structure was observed in flame by schlieren photograph method. We measured fluctuating temperature and ion current simultaneously and accomplished the statistical analysis of its. According to schlieren photograph, the flame was stabilized in the rim of the direction of lower velocity air jet, coherent eddy was produced and developed by higher velocity air jet. The statistical data of fluctuating temperature and ion current was indicated that reaction was dominated by higher velocity air jet. The mixing state of burnt gas and non-burnt gas was distributed the wide area at Z = 100 mm of C-type flame.

• 한국추진공학회지
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• 제23권6호
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• pp.28-38
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• 2019

액체로켓엔진용 동축 와류형 분사기에서의 화염 구조와 연소 동특성간의 관계를 파악하기 위해 기체메탄과 기체산소를 사용하여 연소실험을 수행하였다. 리세스 길이/오리피스 직경과 같은 분사기 형상과 당량비/산화제 질량유량과 같은 유동조건을 변화시키며, CH* 라디칼과 압력섭동을 동시에 측정하였다. 분사기 형상은 추진제 유속과 혼합에 영향을 주기 때문에 이에 따른 화염 구조의 변화를 알 수 있었다. 주파수 분석 결과 유동조건과 분사기 형상에 따라 연소 동특성이 변화하였으며, 특정 리세스 길이/유동조건에서 연소불안정이 발생함을 확인하였다.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 춘계학술발표대회
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• pp.26.1-26.1
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• 2011

We investigated the atomic layer deposition (ALD) process for nitrogen doped ZnO and the application for n-ZnO : N/p-Si (NW) coaxial hetero-junction photodetectors. ALD ZnO:N was deposited using diethylzinc (DEZ) and diluted $NH_4OH$ at $150^{\circ}C$ of substrate temperature. About 100~300 nm diameter and 5 um length of Si nanowires array were prepared using electroless etching technique in 0.108 g of $AgNO_3$ melted 20 ml HF liquid at $75^{\circ}C$. TEM images showed ZnO were deposited on densely packed SiNW structure achieving extraordinary conformality. When UV (360 nm) light was illuminated on n-ZnO:N/p-SiNW, I-V curve showed about three times larger photocurrent generation than film structure at 10 V reverse bias. Especially, at 660 nm wave length, the coaxial structure has 90.8% of external quantum efficiency (EQE) and 0.573 A/W of responsivity.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2011년도 제37회 추계학술대회논문집
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• pp.74-77
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• 2011

고성능 다단연소방식 액체 로켓엔진에 사용되는 기체 중심 스월 동축형 분사기의 리세스 길이 변화에 따른 혼합특성을 수치해석을 통해 연구를 수행하였다. 실제 추진제의 상(phase)은 기체(산화제)-액체(연료)형이지만, 모사조건을 통해 기체-기체로 고려하였다. 추진제의 확산각도를 측정하기 위해 분사기 출구에서의 속도 분포 및 추진제의 분무형상을 분석하였다. 리세스 길이가 증가함에 따라 축방향 속도는 증가하는 반면, 탄젠셜 방향 속도는 감소하였다. 이 결과 확산각도가 감소하는 정성적인 특징을 확인하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2009년도 제33회 추계학술대회논문집
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• pp.49-53
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• 2009

본 논문은 액체로켓용 이중 와류 동축 분사기의 유량 특성에 대한 실험적 연구 결과를 수록하였다. 분사기의 추진제 유량 공급 특성은 매우 중요한 로켓엔진 연소장치 설계 인자이다. 분사기 유량 특성 파악을 위해 상온시험은 물을, 연소시험은 액체산소와 케로신을 사용하였다. 상온 시험 결과와 달리 연소시험 유량 계수는 혼합비, 리세스 비 변경에 따라 변화하며 그 변화 정도는 분사기 형상과 작동 조건에 따라 다르다. 연소시험 산화제 측 유량 계수 변동 원인은 물성값 변화에 따른 화염 구조 변화에 의한 것으로 판단된다.

• 대한기계학회논문집B
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• 제28권2호
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• pp.223-229
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• 2004

Combustion using oxygen enriched air is known as a technology which can increase thermal efficiency due to increase of the flame temperature. Flame shapes, schlieren photos, OH radical chemiluminescence and local flame temperature were examined as a function of OEC(Oxygen Enriched Concentration) in a coaxial non-premixed jet. With increase of OEC, flame length and width decreased, but its brightness increased significantly, and the size of vortices in the flame also increased. Especially, the reaction around the flame surface became active. The strong OH intensity appeared to be made and moved from middle stream to upper one with increase of OEC, which shows combustion reaction in the upper stream becomes more dominant In addition, the temperature distributions of the flames showed similar tendency with OH radical intensities. A flame with high temperature and strong stability was obtained with increasing OEC of the coflow.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.320-329
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• 2008

The influence of thermodynamic transition associated with transcritical nitrogen injection upon the flow structure was investigated to explore numerical simulation of the injectant dynamics of oxygen/hydrogen coaxial jet in liquid rocket engines. Single and coaxial nitrogen jets were treated by comparing the transcritical and perfect-gaseous conditions, wherein the numerical model was accommodative to the real-fluid thermodynamics and transport properties at supercritical pressures. The model was in the first place validated by comparing the results of transcritical nitrogen injection between calculations and available experiments. For a single jet under the transcritical condition, the nitrogen kept a relatively high density up to its pseudo-critical temperature inside the mixing layer, since it remains less expanding until heated up to its pseudo-critical temperature. Numerical analysis revealed that cryogenic jets exhibit strong dependence of specific enthalpy profile upon the associated density profile that are both dominated by turbulent thermal diffusion. In the numerical model, therefore, exact evaluation of turbulent heat fluxes becomes very important for simulating turbulent cryogenic jets under supercritical pressures. Concerning the coaxial jets due to transcritical/gaseous nitrogen injections, the density profile inside the mixing layer was again affected by the thermodynamic transition of nitrogen. However, hydrodynamic instability modes of the inner jet did not show significant differences by this thermodynamic transition, so that further study is needed for the mixing process downstream of the near injection position.