• The Journal of the Acoustical Society of Korea
• /
• v.33 no.3
• /
• pp.163-173
• /
• 2014

Sound propagation algorithm for a sonar simulator is required to run in real-time and should be able to model the range and depth dependence of the Korean ocean environments. Ray model satisfies these requirements and we developed an algorithm for range-dependent ocean environments. In this algorithm, we considered depth-dependence of sound speed through rays based on a rectangular cell method and layer method. Range-dependence of sound speed was implemented based on a split-step method in the range direction. Eigen-ray is calculated through an interpolation of ray bundles and Gaussian interpolation function was used. The received time signal of sonar was simulated by Fourier transform of eigen-ray solution in the frequency domain. Finally, for the verification of proposed algorithm, we compared the results of transmission loss with other validated models such as BELLHOP, SNUPE, KRAKEN and OASES, for the Pekeris waveguide, wedge, and deep ocean environments. As a result, we obtained satisfactory agreements among them.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2000.11a
• /
• pp.34-34
• /
• 2000

극초음속 공기 흡입 추진기관에 대한 기초연구로서 본 논문은 단순 구조의 초음속 제트 화염을 기반으로 하는 초음속 연소기내에서의 유동과 연소 특성에 대한 충격파의 역할을 고찰하였다. 기존에 수행된 실험 결과와 최근에 외국에서 발표될 계산 결과를 토대로 초음속 연소기내에서의 충격파 역할을 체계적으로 정리해 보고자 함이 본 연구 발표의 목적이다.(중략)

• Proceedings of the Acoustical Society of Korea Conference
• /
• spring
• /
• pp.203-206
• /
• 2004

본 논문에서는 중규모 해양음향 토모그래피의 선결문제 해결을 위한 방법을 제안하였다. 선결문제 해결을 위해 음속구조에 대한 군집분석 방법을 사용하였으며, 제안된 방법의 성능 검증을 위해 동해 중규모 해양환경 역산 모의실험을 수행하였다. 연구 결과 제안된 방법을 사용함으로써 중규모 해양음향 토모그래피 역산 성능이 향상됨을 확인하였다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 1998.10a
• /
• pp.14-14
• /
• 1998

램제트 엔진은 초음속에서 공기가 충격파를 통해 아음속으로 속도가 낮아지고 압력이 증가하는 램 압축 현상을 이용하되 압축기를 사용하지 않고 아음속 상태에서 연소하는 구조로 되어 있다. 따라서 각 부품의 성능은 독립적이지 않으며 전체적인 성능을 규명하기 위해서는 공기 흡입구와 연소실, 연료 분사체계 등의 상호작용을 고려하여 유동의 특성과 그에 따른 연소현상의 특성을 함께 고려해야만 한다. 본 연구에서는 속도 범위 Mach 5이내, 고도 30km이내의 운항조건을 갖는 유도 무기에 장착될 램제트 엔진 개발을 위한 연구의 첫 번째 단계로써, 램제트 연소실내의 유동장해석을 실험과 수치해석 두 분야로 나누어 수행하였다.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.18 no.5
• /
• pp.496-502
• /
• 2008

In this study, supersonic and hypersonic flutter characteristics have been analyzed for the various typical section shapes of missile fin configurations. Nonlinear flutter analyses are conducted considering the effect of moving shock waves. Computational fluid dynamic method is applied to accurately predict unsteady aerodynamic loads due to structural motions for the solution of aeroelastic governing equations. Commonly used typical section shapes of supersonic and hypersonic launch vehicles are considered in the present numerical study. Detailed flutter responses for four different typical section models are presented and the flutter characteristics are physically investigated.

• Proceedings of the KSME Conference
• /
• 2003.11a
• /
• pp.986-991
• /
• 2003

A turbulent wake generated by a cylinder in nozzle contraction affects to the jet flow characteristics. In this study, a computational work to investigate the effect of the turbulent wake on two-dimensional subsonic jet was carried out with three different kinds of nozzle. Computations are applied to the two-dimensional unsteady, Navier-Stokes equations. Several kinds of turbulent models and wall functions are employed to validate the computational predictions. It was known that the wake flow enhanced the spread of the jet flow, compared with no wake flow condition. It was also found that the jet core is shortened by the wake flow developed from a control cylinder.

• Proceedings of the Acoustical Society of Korea Conference
• /
• autumn
• /
• pp.101-104
• /
• 2000

본 논문은 중거리 수중표적이 고정 설치된 수신기에 접근 시 표적신호의 다중경로에 신호변형을 일으키며, 특히 신호의 변형 중 도플러효과를 변화정도를 신호모의를 동하여 분석하였다. 동해의 동계와 하계의 대표적인 음속구조에 따른 고유음선(eigenray)의 도플러 주파수를 계산하였다. 수중표적의 속도는 12노트, 주파수는 135Hz, 350Hz, 신호는 정현파로 가정하여 신호모의를 하였다. 그 결과 해저면 반사가 한번인 음선은 수신신호에 주로 Vp-doppler를 형성하였고 두 번인 음선은 주로 Down-doppler를 형성하였다.

• The Journal of the Acoustical Society of Korea
• /
• v.16 no.6
• /
• pp.100-105
• /
• 1997

To analyze the multipath propagation effects on the source bearing detection of HLA(Horizontal Line Array), the conversion mechanism of the multipath into the bearing is described, and the bearing is estimated from the multipath modeled with typical sound velocity structures of the East and the South Sea of Korea. The erroneous bearing is observed from the beamforming outputs simulated with the modeled multipath, and the erroneous phenomena are analyzed. In case of the East Sea, since the multipath propagation with a high receiving angle occurs due to strong inverse slope of the sound velocity structure, it is possible that the estimated source bearing is different from the real source bearing, and that the number of the source is misrecognized.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.7 no.3
• /
• pp.45-52
• /
• 2003

Detailed flowfield resulting from the secondary sonic gas injection into a divergent section of supersonic conical nozzle has been numerically investigated. The three-dimensional flowfield associated with the bow-shock/boundary-layer interaction inside the nozzle has been solved by Reynolds-averaged Navier-Stokes equations with an algebraic and $\kappa$-$\varepsilon$ turbulence model. The numerical results have been compared with the experimental results for the identical flow conditions, and it is shown that the comparison is satisfactory Effects of different injection pressures of the secondary jet on the shock/boundary-layer interactions and the overall flow structure inside the nozzle have been investigated. The vortex structures behind the shock interaction and wall pressure variations have also been studied.

• The Journal of the Acoustical Society of Korea
• /
• v.43 no.3
• /
• pp.314-323
• /
• 2024

Recently, a score-penalty method has been used for the acoustic passive tracking of marine mammals. The interesting aspect of this technique lies in the loss function, which has a penalty term representing the mismatch between the measured signal and the modeled signal, while the traditional time-domain matched-field processing is positively considering the match between them. In this study, we apply the score-penalty method into the depth estimation of a passive target with a known source waveform. Assuming deep ocean environments with uncertainties in the sound speed profile, we evaluate the score-penalty method, comparing it with the time-domain matched field processing method. We shows that the score-penalty method is more accurate than the time-domain matched field processing method in the ocean environment with weak mismatch of sound speed profile, and has better efficiency. However, in the ocean enviroment with strong mismatch of the sound speed profile, the score-penalty method also fails in the depth estimation of a target, similar to the time-domain matched-field processing method.