• 한국환경과학회지
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• 제16권7호
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• pp.771-778
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• 2007

This study has been conducted to achieve the following objectives: First, in order to understand the horizontal propagation and attenuation characteristics for the railroad traffic noise, we selected areas within 100 meters away from the railroad and then selected Saemaul-ho and Mugoongwha-ho as the subjects for our experiment. In this way, we analyzed the horizontal propagation and attenuation characteristics for the traffic noise occurring in diversified areas. Second, in order to understand the vertical propagation and attenuation characteristics for the railroad traffic noise, we measured and analyzed the distributional characteristics of vertical sound pressure levels on each floor of multi-storied apartment buildings according to changes of traffic load and types, and the existence or nonexistence of soundproof walls. For the case of the railroad traffic noise, we also selected Samaul-ho and Mugoongwha-ho as the subjects for our experiment, and we measured and analyzed the different noise levels on each floor of multi-storied apartment buildings from the soundproof wall. The results of Horizontal propagation and attenuation characteristics for the railroad traffic noise are as follows: In cases of the flat land, cutting land, and bridge area, as distance increases, the sound pressure level steadily decreases. The sound pressure level for the bridge area is higher than that of the flat land with a measurement of $5.5{\sim}10.2\;dB(A)$. Vertical propagation and attenuation characteristics for the railroad traffic noise are as follows: The amount of sound pressure level decrease is $14.2{\sim}14.8\;dB(A)$ for Samaul-ho and $13.5{\sim}14.3\;dB(A)$ for Mugoongwha-ho when measuring the vertical sound pressure levels at heights lower than 4.5 m, which indicates a fairly large decrease. At 6 m, the amount of decrease is 8.6 dB(A) for Samaul-ho and 8.2 dB(A) for Mugoongwha-ho, which indicates a small decrease.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2011년도 전기공동학술대회 논문집
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• pp.188-188
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• 2011

This paper describes the propagation characteristics of acoustic signals as a function of distance from the location of partial discharge(PD) occurrence to analyze correlation between discharge magnitude and acoustic signal in insulation oil. We fabricated a decoupler and an amplifier to measure acoustic signals produced by PD. The amplifier has the gain of 40 dB and the frequency bandwidth of 1.6 kHz~1.6 MHz. After a comparative calibration by a standard pulse generator and a coupling capacitor, we analyzed the propagation characteristics of acoustic signals in insulation oil as a function of distance.

• 대한기계학회논문집A
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• 제20권11호
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• pp.3463-3473
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• 1996

The characteristics of wave propagation along a catenary depend on various impedance conditions; i.e., spatial impedance of catenary, impedance of boundaries. In this study, wave propagation along a simple catenary system is studied with arbitrary impedance conditions such as impedance of pantograph, boundary, catenary etc. Seven coupled equations which determine the characteristics of wave propagation along catenary system have been derived and numerically solved. Results demonstrate the role of each impedance condition in the dynamics of catenary system, i.e. the way in which the conditions affect waves on catenary as well as contact force of pantograph. The formulation and suggested solution method can be certainly used for desinging an optimal catenary system for a given pantograph.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1998년도 봄 학술발표회 논문집
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• pp.406-413
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• 1998

The distinct element method is improved to consider the charateristics of stress wave propagation in media involving the discontinuous faces. The distinct element method has many advantages to analyse the characteristics of the reflection, refraction and deflection of the waves in nonhomogeneous media. The double-suing connection system is adopted instead of the single-spring connection system because the distinct element cannot be used for analysing the contact behavior between the different materials by only one contact spring. For the verification of the improved code, the results of the numerical analysis are compared with that of the photoelastic experiments which are one or two dimensional wave propagation problem of the nonhomogeneous media including the different accoustic impendence material or voids. It is shown that the characteristics of the stress wave propagation in nonhomogeneous media can be simulated appropriately using the improved distinct element method.

• 한국해안·해양공학회논문집
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• 제20권3호
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• pp.268-276
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• 2008

오키나와 트러프에서 발생되는 잠재 지진해일의 한반도 남서외해에서의 전파특성을 규명하기 위한 수치모의를 수행하였다. 동중국해 대륙붕의 얕은 수심과 오키나와 트러프의 깊은 수심은 이 지역에서 발생하는 지진해일의 전파특성에 중요한 역할을 한다. 전파특성은 전파 단계에 따라 두 가지로 분류된다. 첫 단계는 수심이 깊은 트러프를 따라서 북동과 남서방향으로 전파해가는 과정이고, 두 번째 단계는 등수심선과 직각방향으로 동중 국해의 대륙붕으로 진입하는 과정이다. 수치모의 결과 오키나와 트러프에서 발생하는 지진해일파는 남서외해의 특수한 해저지형의 영향으로 우리나라 남해안과 서해안에 미치는 영향이 매우 작은 것으로 나타났다.

• 한국통신학회논문지
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• 제36권3B호
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• pp.297-304
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• 2011

무선통신 임베디드시스템 및 MIMO 전파특성 예측을 위해 실내 및 실외 전파 예측 프로그램을 통합하여 하나의 시뮬레이터를 통해 실내 외 전파 예측이 가능하다. 이러한 해석 기법 개발을 통하여 여러 송신기간의 간섭 문제 및 최대 송신거리 문제, 주파수 이용 효율 등 여러 가지 문제에 대한 분석 및 예측이 가능해진다. 본 예측 기술 개발에서는 기존의 Walfish-Ikegami 방법 등 간략화된 모델보다 정확도 높으면서도 환경적 특성을 잘 고려 할 수 있는 광선추적법을 구현한 모의해석 소프트웨어를 개발하고 효율적인 광선 추적이 가능하도록 고안된 광선 추적 기법과 추적된 광선 정보를 이용하여 전파 특성 해석 기술을 접목시켜 효율적이면서도 이론적 특성을 잘 반영한 전파 특성 예측 기술을 확보하였다. 또한 주파수 확보를 위한 국내 임베디드시스템 및 IMT-Advanced용 신규대역 확보를 위한 주파수 특성 및 IMT-Advanced용 주파수인 3-5GHz대역 전파특성을 규명하여 국내 무선통신 기술 개발에 필요한 기반 기술 확보 및 전파간섭등 주파수 관리 기술 확보를 위하여 검증 및 실험을 통하여 확인 하였다.

• Journal of Mechanical Science and Technology
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• 제16권12호
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• pp.1710-1718
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• 2002

The effect of fuel concentration gradient on the propagation characteristics of tribrachial (or triple) flames has been investigated experimentally in both two-dimensional and axisymmetric counterflows. The gradient at the stoichiometric location was controlled by the equivalence ratios at the two nozzles; one of which is maintained rich, while the other lean. Results show that the displacement speed of tribrachial flames in the two-dimensional counterflow decreases with fuel concentration gradient and has much larger speed than the maximum speed predicted previously in two-dimensional mixing layers. From an analogy with premixed flame propagation, this excessively large displacement speed can be attributed to the flame propagation with respect to burnt gas. Corresponding maximum speed in the limit of small mixture fraction gradient was estimated and the curvefit of the experimental data substantiates this limiting speed. As mixture fraction gradient approaches zero, a transition occurs, such that the propagation speed of tribrachial flame approaches stoichiometric laminar burning velocity with respect to burnt gas. Similar results have been obtained for tribrachial flames propagating in axisymmetric counterflow.

• 한국해양공학회지
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• 제9권1호
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• pp.132-141
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• 1995

The purpose of the present study is to investigate the statistical characteristics of m and C in the fatigue crack propagation law, da/dN=C(.DELTA.K)/sup m/ and to studies on the randomness of fatigue crack propagation and retardation behavior. Fatigue tests were perfomed on 32 CT specimens of SPV50 steel under the same one condition. First, the value of m and C were determined for each specimen, and all the data were analyzed statistically. second, the material's resistance to fatigue crack propagation is modeled as a stchastic process, which varies randomly along the crack path. The statistical analysis of the material resistance is performed with the data obtained by constant load controlled tests. Finally, retardation behavior was examined experimentally by using a CT specimen, and a retardation parameters were analyzed statistically.

• Journal of Advanced Marine Engineering and Technology
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• 제33권4호
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• pp.466-475
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• 2009

A numerical analysis of reactive flow in a liftoff flame is accomplished to elucidate the characteristics of flame propagation velocity and volume integral of reaction rate with the variation of fuel injection velocity at the fuel rich region, fuel lean region and diffusion flame region. The increase of fuel injection velocity enhances flame propagation velocity, but its effect on the flame propagation velocity is not much greater under 4%. The increase of fuel injection velocity affects directly and linearly on the flame surface area in the fuel rich region and so enhances volume integral of reaction rate to accommodate the increment of fuel.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.835-840
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• 2000

The objective of the present study is to investigate the characteristics of pressure wave propagation of viscous fluid flow in a circular pipe line. The goal of this study is to select the best frequency of each control factor of a circular pipe. We intend to approach a formalized mathematical model by a very exact and reasonable polynomial for fluid transmission lines. and we computed this mathematical model by computer. The results show that the oil viscosity decreased as the length of the circular pipe increases. and The energy of pressure wave propagation decreased as the pipe diameter decreases. The factor is that density of oil was changed resonant frequency. It has been found the viscosity characteristics is changed largely by length of hydraulic pipe and volume of cavity tank.