• International Journal of Fluid Machinery and Systems
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• v.10 no.3
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• pp.188-196
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• 2017

The objective of this paper is to investigate the flow-induced vibration of a flexible hydrofoil in cavitating flows via combined experimental and numerical studies. The experiments are presented for the modified NACA66 hydrofoil made of POM Polyacetate in the closed-loop cavitation tunnel and the numerical investigations are performed using a hybrid coupled fluid structure interaction model. The results showed that with the decreasing of cavitation number, the vibration magnitude increases dramatically for the cloud cavitation and declines for the supercavitation. The cloud cavitation development strongly affects the vibration response, with the main frequency of the vibration being accordance with the cavity shedding frequency and other two frequencies corresponding to the bending and twisting frequencies.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.867-871
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• 1996

Recently many studies have been carried out to predict the characteristics of vehicle noise and to reduce the noise for enhancing the ride quality. In this study, the structural-acoustic coupling theory and the acoustic finite element theory were reviewed, and the structural acoustic coupling analysis was applied to an automobile. Because of nonuniformed lateral shape of a compartment cavity, the acoustic modes were calculated with 3-D finite element modeling. The structural modes were measured with the modal testing. Using the structural-acoustic cooling analysis, the modes which strongly coupled to the interior noise were identified and the boundary regions which could reduce noise level efficiently by structural modification were predicted.

• Proceedings of the Optical Society of Korea Conference
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• 2000.08a
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• pp.82-83
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• 2000

굴절율이 외부보다 큰 실린더 (cylinder)나 스피어 (sphere)는 경계면에서의 전반사에 의해 손실이 매우 적은 high-Q 공진기가 될 수 있음이 잘 알려져 있다. 크기가 수 십 $mu extrm{m}$ 되는 실린더나 스피어에서의 공명모드는 편광(TM, TE), 모드 수 (mode number) n, 모드 순서 (mode order) l에 의해 정의되고 WGM (whispering gallery mode)라고도 불리워진다$^{(1)}$ . 모드 수n 이 클수록 모드 순서 l이 작을수록 공명모드의 Q 값은 큰 경향을 가진다. 액체 방울이나 액체 제트와 같이 열적 섭동에 민감한 마이크로 공진기 (micro-cavity)의 경우 Q값이 $10^{7}$ 정도로 제약되나, 실리카 마이크로 스피어 (micro-sphere)와 같은 고체 구에서 측정된 Q값은 약 $101^{10}$ 정도로 손실이 매우 적은 공진기가 될 수 있다$^{(2)}$ . 이와 같은 마이크로 공진기 특성을 이용하여 다양한 형태의 마이크로 공진기 레이저 대한 연구가 진행되어 왔다. 색소가 첨가된 고체구, 액체 방울, 액체 제트 등에서 기본적인 실험이 이루어졌고 반도체마이크로 스피어 구조에서 WGM 레이저$^{(3)}$ , polymer disc laser$^{(4)}$ , 광양자테 (photonic quantum ring)$^{(5)}$ 특성 연구 등이 실용가능성을 목표로 진행되고 있다. (중략)

• Journal of the Optical Society of Korea
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• v.19 no.2
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• pp.154-158
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• 2015

We experimentally demonstrated a novel wavelength-swept laser using a cascaded Raman gain around 1310 nm. A 1064/1310 wavelength division multiplexing (WDM) coupler and coupled fiber Bragg gratings mirrors at 1064, 1117, 1175, 1240 nm are effectively used to increase the power efficiency in a laser ring cavity with highly non-linear fiber (HNLF) of 2 km. Linear wavelength sweeping is demonstrated with the 100 Hz triangular driving signal to fiber Fabry-Perot tunable filter (FFP-TF) around the 1310 nm region. The measured sweeping range and output power were 27 nm and 2.1 mW, respectively, which are suitable for optical coherence tomography (OCT) imaging.

• Journal of Industrial Technology
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• v.9
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• pp.87-99
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• 1989

It is desirable to predict the noise and vibration problems of a passenger car in its design stage for a better ride quality. Dominant frequencies of the noise inside a car range from about 50 Hz to 300 Hz and these are frequently caused by the coupling of the acoustic normal modes of the compartment cavity and structural modes of the body. In this paper, car interior noise problem is investigated in view of vibration-acoustic modes coupling and numerical simulation is performed on the interior noise. In the simulation, experimental modal data of the vehicle structure are utilized to improve the accuracy of the analysis. The results are in good agreement with those of experiment on a half scaled vehicle compartment model. Especially, strongly coupled modes can be predicted, which give useful informations to solve noise problems of real car at design stage.

• Journal of the Korean Society of Propulsion Engineers
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• v.6 no.2
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• pp.9-17
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• 2002

For turbulent spray combustion flows a coupled numerical procedure was developed, This method was discretized by using generalized curvilinear coordinates to handle complex geometries. The preconditioning and eigenvalue rescaling techniques were employed to provide efficient convergences over a wide range of subsonic Mach numbers. The accuracy was validated by simulating the laminar cavity flow. The film cooling effect of a liquid rocket engine (KSR-III) were investigated by a spray combustion analysis. The film cooling showed a negative effect on the combustion efficiency. In the combustion chamber wall, the film cooling effect was revealed to be promoted by the production of fuel rich zone.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.411-411
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• 2010

Cavity mode Whistler wave를 사용하는 자화유도결합플라즈마 (Magnetized Inductively Coupled Plasma, MICP)의 제반 특성을 비등방성 수송계수를 가지는 Drift-Diffusion 근사, 에너지 보존 방정식 및 유도전자계를 self-consistent 하게 고려하여 계산하였다. 이러한 접근법은 비충돌성 전자가열현상을 고려하지 못하는 단점에도 불구하고, 반도체 장비설계에 필수적인 전자온도, 밀도, 플라즈마 전위, 시스템의 임피던스 특성에 대한 경향성 파악에 매우 유용하다. 뿐만 아니라 전자밀도분포가 공간내에 형성되는 R-wave mode에 미치는 영향을 분석할 수 있다. 직경 320 mm를 가지는 작은 반응기에서 시뮬레이션과 실험결과를 비교하여 본 모델링 방법의 타당성을 검증한 후, 450 mm wafer가공에 적합한 대면적 플라즈마 반응기에서 플라즈마 특성을 연구하였다. 수 mTorr의 공정압력에서 약 10 Gauss전후의 약한 자장이 인가됨으로서 반경방향의 전자밀도 균일성이 대폭 향상되었다. 플라즈마 및 안테나의 대면적화에 수반되는 높은 Q값이 자장의 인가로 큰 폭으로 감소함으로서 임피던스메칭의 안정성이 비약적으로 개선되었고 전력전달 효율 또한 크게 증가함을 알 수 있었다. 본 연구 결과는 차세대 450 mm 반도체 공정장비의 개발에 있어 자화유도결합플라즈마가 매우 유용하게 사용될 수 있음을 보여준다.

• Wind and Structures
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• v.16 no.2
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• pp.213-224
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• 2013

One of the key issues affecting the promotion of solar water heaters in Taiwan is the severe impact of typhoon each year. An experimental study was conducted to investigate the wind uplift characteristic of a solar collector model with and without a guide plate. The guide plate with different lengths and orientations with respect to wind direction was adopted. It is found that the wind uplift of a solar collector is associated with the tilt angle of the flat panel as expected. A cavity formed between the guide plate and the flat panel has a significant effect on the distributions of streamwsie and lateral pressure. Reduction in uplift is essentially coupled with the projected area of a guide plate on the lower surface of the tilt flat panel.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.5
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• pp.451-457
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• 2006

Conjugate heat transfer (CHT) is the simultaneous, coupled heat transfer within a fluid and an adjoining solid, and the interface treatment plays an important role in its analysis, particularly when using unstructured grid system. In the present paper a new solid-fluid interface treatment in CHT analysis is presented and applied to two typical CHT problems, i.e. natural convections in both concentric thick-walled cylinders and cavity with a centered solid body. The present interface treatment for unstructured mesh clearly demonstrates the same accuracy and robustness as that for typical structured mesh.

• Journal of the Korean Physical Society
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• v.73 no.11
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• pp.1663-1674
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• 2018

We propose the Poynting vector analysis of the air mode in a top-emitting organic light-emitting diode (OLED) by combining the transfer matrix method and dipole source term. The spatial profiles of the time-averaged optical power flow of the air mode are calculated inside and outside the multilayer structure of the OLED with respect to the thickness of the semi-transparent top cathode and capping layer (CPL). We elucidate how the micro-cavity effect controlled by the thickness variation of the semi-transparent top cathode or CPL affects the internal optical power and absorption loss inside the OLED multilayer and the external optical power coupled into the air. When the calculated absorption loss and external power obtained by the proposed Poynting vector and currently-used point dipole models are compared, two calculation results are identical, which demonstrates the validity of the two models.