• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2005년도 춘계 학술대회논문집
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• pp.128-134
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• 2005

In the CFD area, the numerical analysis of high Mach number flow over a blunt-body poses many issues. Various numerical schemes have been developed to cover the issues, but the traditional schemes are still used widely due to the complexities of new schemes and intricacy of modifying the established codes. In the present study, the well-known Roe's FDS based on TVD-MUSCL scheme is used for the solution of very high Mach number three-dimensional flows posing carbuncle and non-physical phenomena in numerical analysis. A parametric study was carried out to account for the effects of the entropy fixing, grid configurations and initial condition. The carbuncle phenomena could be easily overcome by the entropy fixing, and the non-physical solution could be eliminated by the use of the modified initial condition regardless of entropy fixing and grid configurations.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.514-519
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• 2003

A computational study is performed to clarify the characteristics of supersonic moist air jet issuing from a simple sonic nozzle. The effects of the initial supersaturation on the Mach disk diameter and location, the barrel shock wave and jet boundary structures are investigated in details. The axisymmetric, compressible, Navier-Stokes equations, coupled with droplet growth equation, are solved using a third-order MUSCL type TVD finite-difference scheme. It is found that the Mach disk diameter increases with an increase in relative humidity of moist air. while its location is not significantly dependent on the relative humidity. As the relative humidity increases, the barrel shock wave and jet boundary are more expanded due to the local static pressure rise of nonequilibrium condensation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.562-567
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• 2003

A computational study is performed to clarify the characteristics of supersonic moist air jet issuing from a simple sonic nozzle. The effects of the initial supersaturation on the Mach disk diameter and location, the barrel shock wave and jet boundary structures are investigated in details. The axisymmetric, compressible, Navier-Stokes equations, coupled with droplet growth equation, are solved using a third-order MUSCL type TVD finite-difference scheme. It is found that the Mach disk diameter increases with an increase in relative humidity of moist air. while its location is not significantly dependent on the relative humidity. As the relative humidity increases, the barrel shock wave and jet boundary are more expanded due to the local static pressure rise of nonequilibrium condensation.

• International Journal of Aeronautical and Space Sciences
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• 제5권2호
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• pp.18-27
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• 2004

An axisymmetric supersonic jet is simulated at a Mach number 2.1 and a Reynolds numberof 70000 to identify the mechanism of Mach wave generation and radiation from the jet. In orderto provide the near-field radiated sound directly and resolve the large-scale vortices highly.high-resolution essentially non-oscillatory(ENO) scheme, which is one of the ComputationalAeroAcoustics(CAA) techniques, is newly employed. Perfectly expanded supersonic jet is selectedas a target to see pure shear layer growth and Mach wave radiation without effect of change injet cross section due to expansion or shock wave generated at nozzle exit. The sound field ishighly directional and dominated by Mach waves generated near the end of potential core. Thenear field sound pressure levels as well as the aerodynamic properties of the jet, such asmean-flow parameters are in fare agreement with experimental data.

• 한국인터넷방송통신학회논문지
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• 제11권4호
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• pp.141-145
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• 2011

마크-젠더 변조기와 광 필터를 사용하여 광 듀오바이너리 신호를 생성하는 광 듀오바이너리 송신기의 분산 내성을 이론적으로 분석하였다. 송신기의 전송 성능은 마크-젠더 변조기와 광 간섭계를 사용하고 구동 전압 조정으로 최적화하여 분산 내성을 향상 시킨 광 듀오바이너리 송신기와 비교하였다. 그 결과 광 필터를 사용한 광 듀오바이너리 송신기는 좁은 스펙트럼 대역폭을 유지하면서 광 간섭계를 사용한 광 듀오바이너리 송신기보다 개선된 수신 감도와 더 높은 분산 내성을 나타냈다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.26-33
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• 2004

In this study, a boundary-layer bleeding and a two-staged fuel injection were applied to a scramjet engine for suppressing unstart transition and improving the thrust performance under Mach 6 flight conditions. With the boundary-layer bleeding, the engine could operate without unstart transition around at the fuel equivalence ratio of unity ($\Phi$ = 1). The thrust increment from the no fuel condition (dF) increased to 2460 N, which was about 1.4 times as large as that of the case without the bleeding and maximum in our Mach 6 tests. It was confirmed that the boundary-layer bleeding suppressed the separation during the engine operation. The two-staged fuel injection was less effective for improving the thrust performance com-pared with the single-staged one with the bleeding at Mach 6.

• 한국통신학회논문지
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• 제17권10호
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• pp.1092-1099
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• 1992

본 논문은 광섬유 가속도기를 이용한 중력가속도$(0{\sim}1G)$의 감도를 보였다. 단일모드 광섬유 Mach-Zehnder 간섭계가 약 1 그람 정도의 probe mass를 이용하여 광섬유 내의 스트레인에 의해 발생된 광로정 변화를 감지하는데 이용 되었다. 본 시스템의 기준 통로내 PZT 원통의 위상 변환 이득은 0.88rad./v로 측정 되었다.

• 한국추진공학회지
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• 제23권1호
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• pp.61-70
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• 2019

0.4 MW 급 고 엔탈피 초음속 아크 가열 플라즈마 풍동에서 발생된 팽창 유동에 대한 기초연구를 실험적으로 완료하였다. 노즐 출구로부터의 마하 디스크의 직경과 위치는 전체 압력비가 200에서 30까지 측정되었다. 마하 디스크 직경과 위치에 대한 경험적인 상관관계는 실험결과와 매우 일치하는 결과를 얻었다.

• 천문학회보
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• 제44권1호
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• pp.44.1-44.1
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• 2019

Davis-Chandrasekhar-Fermi (DCF) method is a tool that is widely used to obtain the strength of the mean magnetic field projected on the plane of the sky. When there are independent eddies along the line of sight, the variation of polarization angle will decrease by the averaging effect. Therefore, the measured strength of the magnetic field can be overestimated. Cho & Yoo (2016) proposed a modified DCF method considering such effect. By using this, we quantitatively compared the results from the conventional DCF and the modified DCF methods for various sonic Mach numbers and driving schemes (the solenoidal and compressive driving). Here, we present that the modified DCF method does not show a strong dependence on the sonic Mach number or driving schemes either, while the conventional DCF method depends on the sonic Mach number for the compressive driving scheme.

• 한국광학회:학술대회논문집
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• 한국광학회 2007년도 하계학술발표회 논문집
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• pp.357-358
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• 2007