• 한국전산유체공학회:학술대회논문집
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• 2003.08a
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• pp.152-157
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• 2003

As computer capacity has been progressed continuously, the studies of the flow characteristics have been performing by the numerical methods actively. Recent numerical simulation has a tendency to require the higher-order accuracy in time, as well as in space. This tendency is more true in LES and acoustic noise simulation. In this study, 3-dimensional unsteady Incompressible Navier-Stokes equation was solved by numerical method using the fractional step method with the fourth order compact pade scheme to achieve high accuracy To validate the present code and algorithm, 3D flow-field around a cylinder was simulated. The drag coefficient and lift coefficient were computed and, then, compared with experiment. The present code will be tailored to LES simulation for more accurate turbulent flow analysis.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.419-422
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• 2010

An unsteady numerical combustion analysis was performed to investigate the combustion characteristics of A Dual Combustion Ramjet(DCR) engine using a gas generator. According to a variance of the equivalence ratio of the gas generator, the flow pattern in the combustor was analyzed. A typical acoustic frequency in the combustor was observed by detail analysis of pressure fluctuation at each location of the combustor.

• Proceedings of the KSME Conference
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• 2001.06b
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• pp.210-215
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• 2001

CD-ROM Drives Rotating high speed as 10000 rpm cause serious noise and vibration problems. At the high speed, dominant noise is Air Borne Noise produced from high-speed airflow and Structure Borne Noise produced from structural vibration. In this research, vibration and sound characteristics in CD-ROM Drive were studied by the use of experimental analysis and computational simulation. Sound intensity techniques and ODS(Operational Deflection Shape) techniques are applied to identify the acoustic noise source of CD-ROM drive. And Computational simulation using SYSNOISE is conducted for describing the noise behavior.

• Journal of Mechanical Science and Technology
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• v.18 no.7
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• pp.1246-1257
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• 2004

The objective of this paper is to characterize dynamic pressure traces measured at self-excited combustion instabilities occurring in two combustion systems of different hardware. One system is a model lean premixed gas turbine combustor and the other a fullscale bipropellant liquid rocket thrust chamber. It is commonly observed in both systems that low frequency waves at around 300㎐ are first excited at the onset of combustion instabilities and after a short duration, the instability mode becomes coupled to the resonant acoustic modes of the combustion chamber, the first longitudinal mode for the lean premixed combustor and the first tangential mode for the rocket thrust chamber. Low frequency waves seem to get excited at first since flame shows the higher heat release response on the lower frequency perturbations with the smaller phase differences between heat release and pressure fluctuations. Nonlinear time series analysis of pressure traces reveals that even stable combustion might have chaotic behavior with the positive maximum Lyapunov exponent. Also, pressure fluctuations under combustion instabilities reach a limit cycle or quasi-periodic oscillations at the very similar run conditions, which manifest that a self-excited high frequency instability has strong nonlinear characteristics.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.3
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• pp.824-833
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• 1991

본 연구에서는 차체구조계의 진동모드 변수와 차실음향계의 음향모드변수들이 어떻게 관련되어 차실소음을 결정하는 가를 밝혔다. 그 결과, 수치해석 결과의 효용 성을 높이고 실내소음 평가방법을 체계화 시킬 수 있었으며, 효과적인 소음저감을 위 한 유용한 자료를 얻을 수가 있었다. 한편, 이제까지의 차실소음의 응답해석에서 가 장 큰 오차의 발생요인은 차체의 구조진동 모드데이타인데, 본 연구에서는 유한요소해 석 대신 모드시험 결과를 이용함으써, 유한요소 모델리이 어려운 경우의 소음 해석의 신뢰도를 높일수가 있었다.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.4
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• pp.55-60
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• 2005

In this study, vibration control of the enclosed plate which is typical two dimensional structure are performed by using intelligent control method and piezo ceramic as an actuator attached at the plate. The characteristics of the plate with piezo ceramic are examined to identify the natural frequencies. Then, the plate is controlled under the sinusoidal excitation by acoustic source and the reduction level of vibration is examined via frequency response and time sequence. The control result shows the effect of the intelligent control method as a control scheme compared with that of the previous filtered-X LMS algorithm.

• Proceedings of the KSR Conference
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• 2005.11a
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• pp.1223-1228
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• 2005

A lot of PSC railway bridges have been constructed in countries and, they are considered as cost-effective and less maintenance-demanded structures. However, recently several collapse of PSC bridges happened in Europe show that PSC bridges have some serious maintenance problems related to tendon corrosion and wire fractures. Furthermore, any reliable NDT method is not presented until recently. In this paper, AE techniques are investigated for detection of wire fractures in PSC beam. Using long-term monitoring AE techniques, two acoustic signals of wire fractures in a PSC beam are obtained. These data are compared to other noise signals. Based on the test results, the characteristics of the AE signals are classified and wire fracture signals are figured out among the other AE signals. As a result, AE techniques are certainly exposed to tendon fracture sound, and application of AE techniques are better than any other non-destructive method.

• International Journal of Railway
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• v.6 no.3
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• pp.125-130
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• 2013

Most of the test methods used for determining the acoustic performance of the noise barriers in Korean standards address the sound-proof panels but refer to noise barriers as a whole system or their in-situ performances less. Many new types of trains with different operating speeds have been developed and produced, and civil appeals against railway noise are becoming quite extensive. Considering these latest changes of circumstances, it is necessary to investigate the current standards and specifications pertaining to railway noise barriers. In this paper, criteria for the measurements and evaluations of noise barriers and sound-proof panels are examined and experimental studies are introduced. In order to suggest more efficient methods for reasonable evaluations of the noise barriers, frequency spectrums of the noise source, the power of the actual railway vehicles, are investigated and introduced.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.28B no.10
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• pp.822-830
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• 1991

In this paper, we propose a new process for ultrasonic B-mode image considering the sound field effects of a concave circuit focused transducer, and aim to remove the speckle pattern which cause the blurring on boundary in ultrasonic B-mode image. We discuss in detail the conception of speckle pattern generation, and the frequency compounding method which is applied to the process for getting a speckle reduced B-mode image. Through the computer simulation, we define the meaning of speckle region, and show the results of reduced speckle pattern. It is discovered in the results that the frequency compounding method is very effective for boundary detection and that the application of the method is limited by various conditions.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.365-368
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• 2002

수중에서와 같이 전자기파의 사용이 곤란한 환경에서 정보의 전달 방법으로 초음파를 사용하는 것이 일반적이다. 그러나 기존의 방법은 음파의 전파 경로 상에 있어서 잡음, 온도, 음속 등의 환경에 많은 영향을 받기 때문에 정확한 정보의 전달이 곤란한 경우가 있다. 본 연구에서는 전기적 용량으로 특성을 제어할 수 있는 2층 구조 압전 트랜스듀서에 있어서 전기적 용량 변화에 따른 공진 모드간의 효율 비의 변화를 이용하여 전파 경로 상의 환경 변화에 독립적인 원격 물리 계측법을 제안하고 그 가능성을 확인하였다.