• Journal of KSNVE
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• v.8 no.5
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• pp.914-921
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• 1998

Combusion instability due to thermoacoustic feedback in a ducted combustor usually excites severe noise and vibration, which could lead to result in the failure of the system or environmental dispute. In the present study, an active noise control(ANC) method with an adaptive algotithm is hired to suppress instability which has very discrete behavior in the frequency domain. Especially a feedback system is composed to evade hot environment of the combustor, and as a preliminary, the performance and stability of the controller is chekced by simulating the real situation with harmonic waves. Application to the real combustor showed serious reductions in sound pressure level by 20∼30 dB. It was also shown that the selected control system was very stable and effective.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.3
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• pp.190-197
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• 2006

For enhancement of flaw detactability using array transducers, focusing of ultrasonic waves on a target in an inhomogeneous medium or through a complex geometry is important. But focusing can be strongly degraded by geometrical distortion of field radiated by the array transducers or by sound speed fluctuations in the propagating medium. In recent years, the time reversal technique has been proposed. Thus, in this paper, we describe the basic principal of the time reversal technique for focusing. Then, the implementation results of the time reversal technique for ultrasonic inspections using bulk waves and guided waves generated by array transducers are presented.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.562-565
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• 2008

Measuring system for piezo inkjet droplet and ink jetting status was developed. In order to measure the jetting performance, two different approaches have been used. One is to use the self-sensing capability of the piezo actuator in the printhead. The other is to use the droplet image from a CCD camera. The software as well as hardware using two approaches was developed. The self-sensing signal as well as meniscus motion was shown to be useful in monitoring jetting conditions. Furthermore, ink properties such as viscosity and speed of sound, which is related to jetting performance, can be understood.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.882-888
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• 2008

The increase in logistics and the emergence of high speed vehicles are aggravating the noise problem, and disturbing large numbers of people. Therefore, growing attention is being paid to the creation and utilization of a noise map in order to grasp and predict the influence of noise, and to establish a policy that effectively reduces noise. However, so far there has been little progress in developing a predictive formula for railway noise, and a noise prediction program suitable for the domestic environment. Therefore, there is a need for a method to apply the overseas prediction formula to domestic railway vehicles. This study evaluated the prediction method, the result of which is similar to that of a real measurement, using a noise map. It also employed a commercial software program, SoundPlan, to predict noise.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.210-213
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• 1999

수동소나체계에서 음원의 위치와 관련된 매개변수를 산출하기 위해 정합장처리(Matched Field Processing)가 이용된다 본 연구에서는 수직선배열센서를 이용한 정합장처리에서 음원 위치추정에 영향을 미치는 다양한 요인 중, 수직음속분포 오정합(mismatch)에 의한 영향을 MV 프로세서 (Minimum Variance Processor)를 이용하여 모의실험함으로써 그 결과를 분석하였다. 천해 모의환경에서 동일한 기울기로 증감하는 수직음속분포 오정합은 음원 위치추정에서 거리성분의 오차를 가지며, 상이한 기울기를 갖는 수직음속분포 오정합은 거리와 수심 성분의 오차가 유발됨을 확인할 수 있었다. 심해 모의 환경에서 수직음속분포 오정합은 거리와 수심 성분의 오차가 유발되고, 거리추정의 전반적인 경향은 천해의 동일한 기울기를 가지는 경우와 유사함을 확인할 수 있었다.

• Journal of Ship and Ocean Technology
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• v.11 no.4
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• pp.29-54
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• 2007

Systematic sensitivity analysis of smoothed particle hydrodynamics method (SPH), a gridless Lagrangian particle method, was carried out in this study. Unlike traditional grid-based numerical schemes, systematic sensitivity study for computational parameters is very limited for SPH. In this study, the effect of computational parameters in SPH simulation is explored through two-dimensional dam-breaking and sloshing problem. The parameters to be considered are the speed of sound, the type of kernel function, the frequency of density re-initialization, particle number, smoothing length and pressure extraction method. Through a series of numerical test, detailed information was obtained about how SPH solution can be more stabilized and improved by adjusting computational parameters.

• Journal of the Semiconductor & Display Technology
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• v.8 no.4
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• pp.83-88
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• 2009

In this paper TRIZ was used to solve noise and dust reduction related to cable carrier chain system. On modern machines in a clean room, the contradictions arose due to increase noise and dust for the high speed were eliminated with 40 principles and seperation rules. As the results, the sound pressure level of the new carrier chain system was reduced to below 40 dB(A), and cleanroom classifications was satisfied with ISO class 4. In these successful results, TRIZ showed its usefulness in solving the design problems even with severe constraints.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.2
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• pp.95-104
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• 2004

Leaks in underground pipelines can cause social, environmental and economical problems. One of relevant countermeasures against leaks is to find and repair of leak points of the pipes. Leak noise is a good source to identify the location of leak points of the pipelines. Although there have been several methods to detect the leak location with leak noise, such as listening rods, hydrophones or ground microphones, they have not been so efficient tools. In this paper, accelermeters aroused to detect leak locations which could provide an easier and more efficient method. Filtering, signal processing and algorithm of raw input data from sensors for the detection of leak location are described. A 120m-long and a 70m-long experimental pipeline systems are installed and the results with the systems show that the algorithm with the accelerometers offers accurate pinpointing for leaks location detection. Theoretical analysis of sound wave propagation speed of water in underground pipes, which is critically important in leak locating, is also described.

• Journal of KSNVE
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• v.9 no.1
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• pp.113-120
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• 1999

A perforated tube nozzle as an exhaust noise suppressor of a high-speed civil transport(HSCT) is proposed. The experimental results for the near and far field sound. the visualization of jet structures and the static pressure distributions in the jet passing through a perforated tube are presented and discussed in comparison with those for a simple tube. It is shown that the perforated tube has an excellent performance to greatly reduce the shock-associated noise and that also the turbulent mixing noise is reduced in the range of a limited jet pressure ratio. This considerable noise reduction is due to the pressure relief caused by the through-flow through the perforated holes. Such a pressure relief results in the transformation of normal shock waves into weak Mach waves of X -type and increases the thrust force of the perforated tube nozzle.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.9
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• pp.593-598
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• 2015

In this paper, the silencer for large caliber gun to reduce the propagation of gun-generated noise was studied. The results of structural analysis and firing test were described. Structural analysis was conducted by using a commercial program, ANSYS, and showed that there was not any structural problem. The sound pressure level was diminished about 10 dB by the silencer adapted in front of the gun and the soundness of the material was verified from the internal pressure measurement. The reduction of weight, improvement of durability and speed-up of actuating device have to be studied later to improve the usability of silencer for large caliber gun.