• Journal of KSNVE
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• v.7 no.4
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• pp.621-629
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• 1997

For computer aided design and costruction of low noisy power plants, indoor and outdoor noise prediction program has been developed. The program utilizes the predefined data of noise sources and building materials and has the faculty to estimate the source level using the empirical formula in case of the measured data not being available. In the noise prediction, the mutual noise propagation between indoor and outdoor sites are considered. The outdoor noise source in the calculation of geometric divergence effects is modelled as the omni-directional finite line or planar source according to the source geometry and the receiving points. Outdoor noise prediction is carried out to consider the diffraction effect due to plant structures as well as the attenuation effect due to atmospheric absorption and soft ground. The results of indoor and outdoor noise prediction for a recently constructed diesel engine power plant show good agreement with the measured.

• Proceedings of the Korea Concrete Institute Conference
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• 1995.04a
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• pp.164-169
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• 1995

Cracks in the concrete structure are known to develope by various mechani는, including an alkali-aggregate reaction. The alkali-silicate reaction between aggregates and cement is studied using polarized microscope, electron probe microanalyser and electron microscope. Metamorphosed, biaxial quartz and feldspars grains appear to have reacted readily with alkali from cement. For a given mineral, fine-grained minerals tend to react readily over the coarse-grained ones. A chemical analysis shows that the elements K, Na, Ca, and Si migrated, in most cases, fro the portion of h호 concentration to the low, Some clay minerals, including smectite and illite are newly formed as one of the reaction products. The continual expansion and shrinkage of the expandible clay minerals, probably due to repeated absorption and loss of water within the structure, plays an important role in the development of cracks within the concrete structure.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.604-607
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• 2004

Concrete structures in the marine environment often deteriorate in the early stage of their service life because of contact with various aggressive conditions. In recent years, the study on the concrete in the marine environment are carried out to increase their service life. In this experimental study, the concrete specimens were prepared with various adding contents of inorganic antifouling agent$(0\~3.0wt\%)$ composed to some fluosilicate solution. For evaluatin of the physical and chemical properties of concretes containing inorganic antifouling agent, various tests such as setting time, slump loss, compressive strength, water absorption rate, freezing and thawing resistance and SEM micrographs of concrete, were conducted. As the results, physical and chemical properties of concretes were improved with an adding of inorganic antifouling agent. From the results of various tests, the optimal adding contents of antifouling agent was $1.0wt\%$.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1994.10a
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• pp.323-330
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• 1994

본 연구에서는 다공질 흡음재료 중 closed cell 구조를 갖는 발포수지재료(Foamed Material)에 음(sound)이 입사할 때 발생하는 흡음현상을 보다 정확히 예측하기 위해서 다공질 흡음재료에 대한 Biot 이론에 근거한 Allard의 모델링기법[4]을 이용하여 해석 프로그램을 개발하였고, 이를 이용하여 다공질 흡음재료가 단층(single layer)일 때 이 재료의 Surface Impedance와 흡음률(Absorption Coefficient)을 예측하고, 물성치(parameters)변화에 따른 다공질 흡음재료의 흡음특성을 분석하였으며, 이 재료가 자동차 제조시 사용되는 압연강판(rolled steel piate)에 부착되었을 때의 투과손실(Transmission Loss)을 예측하였고, 또한 다공질 흡음재료는 중고주파 대역의 음에 대한 흡음특성은 좋지만 저주파 대역의 음에 대한 흡음특성은 좋지 않으므로 흡음 재료의 저주파 대역의 흡음특성을 향상시키기 위해서 2층(two layers)으로 하였을 때의 흡음특성을 분석하였다. 본 논문의 연구결과는 자동차 제조시 사용되어지는 다공질 흡음재료는 물론 산업용기계나 건축용등 여러 분야에서 사용되어지는 다공질 흡음재료의 흡음특성 분석에 응용될 수 있으리라 기대된다.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.7
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• pp.679-684
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• 2009

Low frequency exhaust noise of marine diesel engine is one of the most important noise sources in vessels. However, conventional absorptive silencers are ineffective to control exhaust noise because of low absorption in the low frequency range. In the paper, exhaust noise control of marine diesel engine was studied by using the hybrid silencer, which was composed of virtually divided array of concentric hole-cavity resonators and conventional absorptive silencer. A series of tests including field tests were performed to investigate the acoustic performance of the hybrid silencer. Consequently, its high performance of 5${\sim}$10 dB noise reduction in the low frequency range was confirmed and it is expected to be very helpful in reducing the exhaust noise of marine diesel engine.

• Journal of Korea Foundry Society
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• v.1 no.3
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• pp.19-29
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• 1981

An emphasis has been placed on the importance of selecting a sand for furan sand process, which ie affected by the properties of sand. Investigations have been carried out to use the domestic artificial sands for the furan sand process. For laboratory investigations, the sands have been prepared and tested for chemical analysis, loss on ignition, sieve analysis, AFS grain fineness number, grain shape, PH value, acid demand, surface shape, theoretical surface area, moisture absorption, crushing durability and compressive strength and S. S. I. of molding sands. Most commercial sands have been found to be able to be used. The main requirement of the sands has been shown to be that 3 or 4 screen sands, AFS no.40-70 (or 100), of low acid demand, good surface area and good grain shape require less resin and catalyst to give an adequate strength.

• Journal of the Korean Ceramic Society
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• v.36 no.9
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• pp.923-929
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• 1999

The cause of optical nonlinearity induced in thermally poled silica glass is believed to be the space charge polarization. Since the second order optical nonlinearity (electro-optic effect) can be used in optical switches the optical nonlinearity in silica glass has drawn a large attention. Space charge polarization occurs when an ionic conducting material is subjected to dc electric field by the blocking electrode. Thermal poling performed to induce the optical nonlinearity in silica glass is basically identical to the process generating space charge polarization. As a first step to understand the mechanism of space charge polarization in silica glass hence the induced optical nonlinearity the absorption currents as functions of time were measured for various types of silica glasses and analyzed by the theory of space charge polarization. It was found that the electrical relaxation exhibited a step by the space charge polarization in the relatively long time range and dielectric loss peak showed a maximum at a specific temperature which is depending on type of silica glass. It was turned out that this relaxation might be a cause of nonlinearity in electrical conductivity of silica glass.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.8
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• pp.678-686
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• 2002

This paper presents the effects of accumulation of surface charges on hydrophobic level and the changes of surface potential decay with various artificial environment treatments on high temperature vulcanized (HTV) silicone rubber used for outdoor insulating material. For this study, the charging apparatus by corona discharge, in which grid electrode was installed between the main corona and ground electrode, was used. From this study, it was found that the accumulation of surface charges above a critical surface potential on silicone insulating materials could lead to the temporary loss of surface hydrophobicity. In addition, corona stress and water absorption stress increase the decay rate of surface charges of HTV silicone rubber, while ultraviolet (UV) stress causes longer decay time. We could conclude that the effects of surface charges on hydrophobicity level and the changes of surface state by various artificial treatments were found through a trend of surface potential decay.

• Journal of the Korean Ceramic Society
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• v.32 no.1
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• pp.25-30
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• 1995

The frequenc dependence of magnetic permeability($\mu$r) and dielectric constant($\varepsilon$r) in MHz-GHz frequency range and their relationships with microwave absorbing properties were investigated in sintered and composite Ni-Zn ferrites, respectively. It was confirmed that zero reflection condition was required the real parts of permeability and permittivity in sintered specimen, and the complex permeability, permittivity and dielectric loss tangent in composite specimen. The real part of permittivity varied with the replacement of nickel by manganese in sintered Ni-Zn ferrite. Therefore, we could control the matching frequency and matching thickness.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.449-455
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• 2001

도로교통소음의 저감을 위해 설치되는 방음벽의 성능평가를 위해서는 흡음률 및 투과손실과 같은 음향성능에 대한 평가뿐만 아니라, 풍압 및 충격하중과 같은 구조성능과 방음판 제작에 사용되는 재질에 관한 성능평가도 수반되어야 한다. 따라서, 본 논문에서는 이러한 방음벽의 성능평가를 위한 음향 구조 및 재질에 관한 시험 및 평가방법을 제시하였다.