• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.377-384
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• 2014

The requirement of acoustic material which is used in underwater environment more increases. The material is used to reduce acoustic signature and radiate noise for underwater vehicle. Underwater acoustic material was made by viscoelastic material such as a rubber and a polyurethane etc. The mechanical and acoustic characteristics of these material change with hydrostatic pressure. In order to increase an acoustic performance according to hydrostatic pressure, several kinds of scatterers were added to viscoelastic material. In this paper, acoustic modelling and analysis techniques of underwater acoustic material with hydrostatic pressure were introduced and proposed. The specimens for pulse tube test were made and echo reductions were calculated and measured with hydrostatic pressure. Also the characteristics of echo reduction of the specimens with hydrostatic pressure were obtained and discussed.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.8
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• pp.684-694
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• 2004

Presented in this dissertation is a new method of identifying the critical speed of rotor-bearing systems without actually reaching at the critical speed itself. Using the method, it is possible to calculate the critical speed by measuring a series of rotor responses at much lower rotating speeds away from and without reaching at the critical speed of the system. In the course of the procedures illustrated, not only the critical speed but also the damping ratio and the eccentricity of the system can be identified at the same time. Test rotor was tested on the Rotor Dynamics Test Facility at the Korea Institute of Machinery ＆ Materials. Korea, and the theory has been confirmed experimentally. The method can be adopted to monitor changes of the dynamic characteristics of critical rotating machinery before and after overhauls, repairs, exchanges of various parts, or to detect trends or direction of subtle changes in the dynamic characteristic parameters over a long periods of time.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.358-362
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• 2006

Pyro-shock generally refers to the severe mechanical transients caused by the detonation of an ordnance device on a structure. Such device on a structure, including linear explosive, and point explosive are widely used to accomplish in-flight separation of structural elements on aerospace vehicle. And they are a significant cause of launch vehicle failures. The launch vehicle being developed in Korea also uses the explosive for separation events. In this paper, the isolator equipped to small satellite launch vehicle made of PTFE(Teflon) is developed to reduce the separation shock. The test to measure dynamic stiffness of PTFE isolator is performed. This test enables us to find the frequency range of PTFE isolator. And,, pyre-shock test using explosive to evaluate the performance of PTFE isolator is executed. from this study, the isolator conformed to frequency range and load requirement is developed using PTFE instead of rubber.

• Journal of Ocean Engineering and Technology
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• v.15 no.1
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• pp.19-25
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• 2001

Unlike structures in the air, the vibration analysis of a submerged or floating structure such as offshore structures or ships is possible only when the fluid-structure interaction is understood, as the whole or part of the structure is in contact with water. This paper introduces two methods to find natural frequency in consideration of fluid-structure interaction, direct coupled vibration analysis and fluid-structure modal coupled vibration analysis. The purpose of this study is to analyze the vibration characteristic of a submerged vehicle to obtain the anti-vibration design data, which could be used in the preliminary design stage. The underwater pressure hull of submerged vehicle is used as the model of this study. The F.E.M. model is meshed by shell and beam elements. Also, considering the inner hull weight, the mass element is distributed in the direction of hull length. Numerical calculations are accomplished by using the commercial B.E.M. code. The characteristics of natural frequency, mode shape and frequency-displacement response are analyzed.

• Journal of Sensor Science and Technology
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• v.2 no.1
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• pp.11-17
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• 1993

We have constructed an acceleration sensor which is based on the maximum magnetic induction changes of amorphous wire as a measurand. The frequency bandwith of the constructed sensor depends on the mass of a sensing element. For $Co_{72.5}Si_{12.5}B_{15}$ amorphous wire, the bandwith is DC-700 Hz for $1{\times}10^{-3}kg$ sensing element and DC-200 Hz for $5{\times}10^{-3}kg$. The linearity of the acceleration sensor was less than 1% within the acceleration of 5 g.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.11
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• pp.868-875
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• 2014

The requirement of acoustic material which is used in underwater environment more increases. The material is used to reduce acoustic signature and radiate noise for underwater vehicle. Underwater acoustic material was made by viscoelastic material such as rubber and polyurethane etc. The mechanical and acoustic characteristics of these material change with hydrostatic pressure. In order to improve an acoustic performance according to hydrostatic pressure, several kinds of scatterers were added to viscoelastic material. In this paper, acoustic modelling and analysis techniques of underwater acoustic material with hydrostatic pressure were introduced and proposed. The specimens for pulse tube test were made and echo reductions were calculated and measured with hydrostatic pressure. Also the characteristics of echo reduction of the specimens with hydrostatic pressure were obtained and discussed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.10a
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• pp.870-870
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• 2013

운송수단은 시대별로 요구되는 성능과 기술 수준 그리고 사용 가능한 에너지의 형태에 따라서 변화되어 왔습니다. 1900년대 초 전기자동차의 고질적인 제한적 운행 거리 문제는 내연기관의 발명으로 인해서 쉽게 해결되었다. 이 후 내연기관의 급속한 보급과 도심 과밀화로 인해서 공해 문제가 대두되었는데, 공해 문제 역시 배기 가스 환원 촉매의 발달과 자동차 전자 제어 기술의 발달로 대부분 해결된 상태이다. 최근에는 사용 가능한 화석에너지의 절대량 측면에서 하나의 커다란 시대적 전환점에 서게 되었다. 즉 아직도 사용 가능한 석유의 절대적인 양적 측면에서는 적당한 공급이 이루어지고 있으나 그 가격 면에서는 급격한 상승이 이어지고 있으며 이는 석유의 채굴이 점점 어려워지고 있음에 기인한다. 에너지의 현황을 객관적으로 살펴 보기 위해서 자동차에 있어서 절대적인 오일을 중심으로 그리고 통계자료 위주로 문제를 분석해 본다. 그리고 수소 연료 전지와 전기자동차 등 여러 가지 대체 에너지 운송기술이 많이 거론되고 있으나 널리 대중화 되고 있지 못하는 근본적인 문제점들이 어디에 있는지 분석해 본다. 이어서 소위 대체 에너지들이 자동차에 있어서 석유의 대체 수단으로 적합하지 않다면 과연 에너지를 가장 많이 쓰는 영역중의 하나인 운송 분야의 현재와 미래의 나아갈 방향은 무엇인지 그 해법을 생각해 본다. 석유를 대체할 에너지의 공급 방안이 충분하지 않다면 마지막으로 생각할 수 있는 것은 에너지의 소비 측면이다. 다행히도 그간 소비 측면의 개선 방안이 많이 소홀하게 취급되어져 왔다. 즉 에너지의 효율을 향상시킬 수 있는 여력이 충분하고도 많이 있다는 희망적인 소식이다. 이에 따라 에너지 효율 향상에 유용하게 사용할 수 있는 다양한 제어 기술을 소개한다. 에너지와 운송수단의 문제를 거시적이고 동시에 현실적으로 바라볼 수 있는 안목을 갖게 되기를 기대한다.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.11
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• pp.199-205
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• 2000

The vibration and noise of gears is due to the vibration exciting force caused by the tooth stiffness which changes periodically as the mesh of teeth proceeds and by the transmission error, that is, the rotation delay between driving gear and driven gear caused by manufacturing error and alignment error in assembly and so on. The purpose of this study is to develop how to calculate simultaneously the optimum amounts of tooth profile modification, end relief and crowning by minimizing the vibration exciting force of helical gears. We estimate the vibration exciting force by the mesh analysis of gears. The constraints of this problem consist of contact ratio and strengths of gear teeth such as tooth fillet stress, surface durability and scoring. ADS(Automated Design Synthesis) is used as an optimization tool. And, since the aspect ratio is an important parameter of tooth modification, we investigate the relation between it and the optimum values of tooth modification. The proposed method can calculate the optimum amount of tooth modification automatically and is to be utilized to resolve the problem of vibration of helical gears.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.10a
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• pp.50-54
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• 1996

최근들어 전력수요와 상시 전력공급이 요구되는 시설이 증가함에 따라 독립적으로 전력을 공급할 수 있는 상용 또는 비상용발전기가 많이 이용되고 있는 추세이다. 이러한 소형 발전시스템에는 디젤엔진이나 터빈 엔진에 발전기를 연결하여 전력을 공급하는 코젠 시스템(co-generation system)이 주로 이용된다[1]. 일반적으로 코젠시스템은 운전중에 매우 높은 수준의 소음이 발생되므로 건물 주변이나 사람의 왕래가 잦은 곳에 설치되는 경우에 필히 소음저감을 위한 대책이 필요하게 된다[2,3]. 본 사례는 대형놀이시설의 전력공급용으로 설치된 옥내(발전실내)의 상용/비상용 발전기(3600 KW 디젤엔진 2대)에서 발생한 상당량의 소음이 놀이시설주변까지 전달되어, 소음원 및 그 전달경로를 규명하고 대책을 수립한 내용이다. 놀이시설의 개장을 앞두고 소음문제가 발생되었기 때문에 신속하고 현실적인 해결책의 적용이 요구되었으므로 발전기 및 발전실 주변의 소음레벨 및 주파수특성의 분석을 통하여 주소음원을 규명하는 방법을 택했다. 분석결과로부터 주 소음원은 엔진 배기구에서 발생되는 저주파수 특성을 갖는 소음으로 규명되었고, 그 주파수특성에 적합한 흡음 및 반사특성을 동시에 갖는 조합형 2차 소음기를 추가로 설치하여 발전실 주변소음레벨을 크게 저감할 수 있었다.

• Special Issue of the Society of Naval Architects of Korea
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• 2015.09a
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• pp.56-62
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• 2015

In ship structure, many parts are in contact with inner or outer fluid as stern, ballast and oil tanks. Fatigue damages are sometimes observed in these tanks which seem to be caused by resonance with exciting force of engine and propeller. Vibration characteristics of these tanks in contact with fluid are significantly affected by fluid coupling effect. Therefore it is important to exactly predict vibration characteristics of tank structure. In order to estimate the vibration characteristics, the fluid-structure interaction(FSI) problem should be solved precisely. But it is difficult to estimate exactly the magnitude of the fluid coupling effect because it has some problems such as a fluid-structure interaction, influence by the free surface, vibration modes of structural panels and depth of water. In this paper, with fluid coupling effect, the effect of structural constraint between panels on the vibration characteristics are investigated numerically and discussed.