• The Journal of the Acoustical Society of Korea
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• v.12 no.6
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• pp.77-84
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• 1993

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.447-450
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• 2004

선박에서 발생하는 소음 가운데 수중 추진기 소음은 가장 우세한 소음이다. 추진기 소음은 소나에 의해 적을 탐지하는 군용 선박에 경우 생존과 직결된 문제가 되며 쾌적함과 정숙성을 요구하는 여객선의 경우에서도 중요한 문제로 대두되고 있다. 이러한 중요성과 필요성에 따라, 본 연구에서는 수중 추진기의 비공동 및 공동 소음을 수치적으로 해석하였다. 수중 추진기 소음 해석을 위해 유동 해석이 선행되어야 하며 이는 포텐셜을 기반으로 한 패널법을 이용하여 해석한다. 소음 해석은 시간 영역 음향상사법을 이용하였으며, 공동 소음은 홀극 음원으로 모사하여 해석하였다. 또한 향후 수중 추진기의 날개 끝 볼텍스 캐비테이션 해석을 위한 기초연구로서 Eulerian-Lagrangian 접근법을 이용하여 수중익에서의 날개 끝 볼텍스 캐비테이션의 거동과 소음을 예측하였다.

• Proceedings of the Acoustical Society of Korea Conference
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• 1998.08a
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• pp.281-286
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• 1998

ETRI에서 개발 중인 대화체 음성언어번역 시스템에 대하여 기술한다. 현재, ETRI는 DAM성언어번역 국제 공동 연구콘서시움인 C-STAR에 핵심참가기관으로 참여하여, 한일, 한영음성언어번역 시스템을 개발하고 있으며 1999년 국제 공동시험을 계획하고 이？. 최근의 연구 진행상황을 간추리면, 먼저 음성인식분야에서 유무성음 및 묵음정보를 미리 추출하여 이를 탐색에 활용하였으며, 음향모델 규모의 설정을 위한 교차 엔트로피 기반 변이음 군집화 알고리즘이 구현되었다. 또한 대상어휘의 확장을 위하여 의사형태소의 개념을 도입하였다. 언어번역분야에서는 이전과 같은 개념기반의 번역을 시도하고 있으며, C-STAR 회원기관과 공동으로 중간언어 규격을 정의하고 있다. 음성합성분야에서는 훈련형 합성기를 개발하여 합성데이타베이스 구축기간을 현저하게 줄였다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.399-402
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• 2009

Acoustic design parameters of a Helmholtz resonator are studied experimentally and numerically for acoustic stability in a model acoustic tube. According to standard acoustic-test procedures, acoustic-pressure signals are measured. Quantitative acoustic properties of sound absorption coefficient are evaluated and thereby, the acoustic damping capacity of the resonator is characterized. Helmholtz resonator on spring-damper system use were understanding for acoustic damping. The length of orifice and the volume of cavity of resonator are selected as design parameters for tuning of the resonator. Acoustic- damping capacity of the resonator increases with its cavity volume. And orifice length as increases with acoustic damping capacity was decreased.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.254-257
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• 2010

Acoustic design parameters of a Helmholtz resonator are studied experimentally and numerically for acoustic stability in a model acoustic tube. Acoustic damping is quantified by the amplitude of the fluid velocity in mass-spring-damper system. The length of an orifice, the volume of a cavity, and the diameters of an orifice and a cavity in the resonator are selected as design parameters for tuning of the resonator. It is found that acoustic damping capacity is increased by shorter orifice and longer cavity in the resonator. As the ratio of the orifice diameter to the cavity diameter increases in the resonator, the damping capacity decreases.

• Proceedings of the Acoustical Society of Korea Conference
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• 1994.06c
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• pp.275-276
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• 1994

본 발표에서는 한국전자통신연구소의 대화체 음성언어번역 연구방향을 기술한다. 한국전자통신연구소에서는 1979년 공중전화 관련 연구를 필두로, 음성분야의 연구를 시작하여 그간 음성인식, 자동통역 등을 연구하였다. 특히 1991년부터 KT와 공동연구체계를 수립하여 특정분야를 대상으로 음성언어번역 연구를 수행하는 중이다. 이러한 경험을 바탕으로 한국전자통신연구소에서는 국내외 공동연구를 통해 대화체 음성언어 번역 연구를 수행하고자 한다. 앞으로 다중매체통신이 더욱 보편화될 것일므로 다중매체 환경을 고려하여 연구를 수행할 계획이다. 아울러 연구의 부산물을 상용화 하는데에 노력을 경주할 계획이다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.10a
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• pp.658-663
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• 2013

A new formulation of the MNDIF method is introduced to extract highly accurate eigenvalues of concave acoustic cavities with arbitrary shapes. It is said that the MNDIF method cannot yield accurate eigenvalues for concave cavities. To overcome this weak point, a new approach of dividing a concave cavity into two convex domains is proposed. The validity of the proposed method is shown through a case study.

• The Journal of the Acoustical Society of Korea
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• v.42 no.3
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• pp.250-261
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• 2023

In this study, the noise contributions by the duct, stator and rotor, which are the propulsor components, are evaluated to identify the flow noise source in cavitation and non-cavitation conditions on pumpjet propulsion and the noise levels in both conditions are compared. The unsteady incompressible Reynolds averaged Navier-Stokes (RANS) equation based on the homogeneous mixture assumption is applied on the suboff submarine hull and pumpjet propeller in the cavitation tunnel, and the Volume of Fluid (VOF) method and Schnerr-Sauer cavitation model are used to describe the two-phase flow. Based on the flow simulation results, the acoustic analogy formulated by Ffowcs Williams and Hawkings (FW-H) equation is applied to predict the underwater radiated noise. The noise contributions are evaluated by using the three types of impermeable integral surface on the duct, stator and rotor, and the two types of permeable integral surface surrounding the propulsor. As a result of noise prediction, the contribution by the stator is insignificant, but it affects the generation of flow noise source due to flow separation in the duct and rotor, and the noise is predominantly radiated into the upward and right where the flow separations are. Also, the noise is radiated into the thrust direction due to pressure fluctuation between suction and pressure sides on the rotor blades, and the it can be seen that the cavitation effect into the noise can be considered through the permeable integral surface.

• The Journal of the Acoustical Society of Korea
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• v.39 no.2
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• pp.77-86
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• 2020

In this study, the Eulerian/Lagrangian one-way coupling method is proposed to predict flow noise due to Blade-Tip Vortex Cavitation (BTVC). The proposed method consists of four sequential steps: flow field simulation using Computational Fluid Dynamics (CFD) techniques, reconstruction of wing-tip vortex using vortex model, generation of BTVC using bubble dynamics model and acoustic wave prediction using the acoustic analogy. Because the CFD prediction of tip vortex structure generally suffers from severe under-prediction of its strength along the steamwise direction due to the intrinsic numerical damping of CFD schemes and excessive turbulence intensity, the wing-tip vortex along the freestream direction is regenerated by using the vortex modeling. Then, the bubble dynamics model based on the Rayleigh-Plesset equation was employed to simulate the generation and variation of BTVC. Finally, the flow noise due to BTVC is predicted by modeling each of spherical bubbles as a monople source whose strength is proportional to the rate of time-variation of bubble volume. The validity of the proposed numerical methods is confirmed by comparing the predicted results with the measured data.

• The Journal of the Acoustical Society of Korea
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• v.33 no.6
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• pp.358-365
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• 2014

When a ship propeller having wing type sections rotates at high speed underwater, local pressure on the blade decreases and various types of the cavitation inevitably occur where the local pressure falls below the vapor pressure. Fundamentally characteristics of the cavitation are determined by the shapes of the blade section and their operating conditions. Underwater noise radiated from a ship propeller is directly connected to the occurrence of the cavitation. In order to design low noise propeller, it is preferentially demanded to figure out key features: how the cavity is generated, developed and collapsed and how the effect of viscosity works in the process. In this study, we first perform inviscid analysis of the partial cavity generated on two dimensional hydrofoil. Secondly, viscous analysis using FLUENT with different turbulence and cavitation models are presented. Results from both approaches are also compared and estimated.