• 비파괴검사학회지
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• 제30권4호
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• pp.359-366
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• 2010

램파를 구조물 안전진단(structural health monitoring, 이하 SMH) 기법에 효과적으로 적용하기 위해서 구조물의 손상과 램파간의 물리적 특성 및 상호관계를 정확히 이해하는 것이 중요하다. 본 연구에서는 modal decomposition 방법을 이용하여 비대칭 불연속면에서 램파의 투과와 반사, 모드 변이를 모사하고, 그 진폭 비율을 불연속면의 깊이에 따라 예측하였다. 또한 이론적으로 예측된 결과를 압전센서(PZT)를 모사한 유한요소법(FEM) 모델과 실험을 통해 검증하였다. 그 결과, modal decomposition 방법을 이용한 이론적 예측이 압전센서를 이용한 유한요소 해석 및 실험 결과와 근접한 것을 확인하였으며, 불연속면의 깊이에 따른 램파의 반사와 투과, 모드 변이의 양을 이용하여 손상의 크기를 정량적으로 측정할 수 있는 방법을 제안하였다.

• Journal of Advanced Research in Ocean Engineering
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• 제3권2호
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• pp.75-82
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• 2017

With the development of computational fluid dynamics (CFD), studies on shipbuilding and maritime issues including free-surface wave flow have been conducted. Although the volume of fluid (VOF) and level-set methods are widely used to study the free-surface wave flow, disadvantages exist. In particular, it takes a long time to obtain solutions. In this study, a free-surface capturing code is developed for ship and offshore structures. The developed code focuses on accuracy and computation time. Open source CFD libraries, termed OpenFOAM, are used to develop the code. The results obtained using the developed code are compared with those obtained using interFoam. The results show that the developed code could be used to capture the free-surface wave flow without numerical diffusion; moreover, the accuracy of the developed code is largely the same as that of interFoam.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2015년도 제51회 KOSCO SYMPOSIUM 초록집
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• pp.107-108
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• 2015

The acoustic optimization of a swirl coaxial jet injector mounted upstream a combustion chamber is investigated to tackle combustion instabilities. The least damped modes are extracted with the help of the dynamic mode decomposition (DMD). The sensitivity of the heat release perturbation to the velocity perturbation for the second longitudinal mode is investigated by combining the Crocco's equation and the inhomogeneous wave equation and computing the flame transfer function (FTF). DMD and FTF results agree in terms of the optimized injector length.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2008년도 정기총회 및 학술발표대회
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• pp.241-244
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• 2008

The decomposition of incident and reflected wave on the two-dimensional experimental flume is very important to elucidate the phenomena between waves and coastal structure such as submerged breakwater or rubble-mound breakwater. In generally, two or three point methods are widely used to decompose waves. Even though three point method gives more accurate result, it requires more wave gauge to install than two point method. Sometimes, this causes economic or measurement problems. In this study, therefore, the applicability of two point method was investigated by using Eigenfunction expansion method.

• 한국입자에어로졸학회지
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• 제13권3호
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• pp.127-132
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• 2017

In this paper, the effect of the irradiation of the median-frequency of ultrasonic wave on the aqueous solution have been investigated. In addition, the decomposition ability of radical species was observed using phytoncide oil of 0.1 wt %. By observing the degree of decomposition while maintaining magnetic stirring, the unirradiated aqueous solution maintained turbid condition and the particle size of the oil was the same as the initial size. On the other hand, the irradiated aqueous solution presented that the transparency degree became good after 3 days and became to the same as the original purified water after one week. The particle size of the after 3 days was about 0.1 to $0.5{\mu}m$. From these results it could be demonstrated that when a medium frequency (about 400 kHz) is applied to the aqueous solution, decomposition ability of radical species are formed and the medium frequency irradiation system can be possible to purify the turbid aqueous solution.

• Journal of Ship and Ocean Technology
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• 제7권1호
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• pp.13-18
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• 2003

The control performances for active re-reflecting wave control suggested in the previous paper have been verified in cases of regular and irregular waves in a real two dimensional wave basin. For regular waves, the control performances are investigated in terms of reflection coefficients, expected amplitudes of propagating waves and wave absorbing capabilities after cessation of wave generation, compared with those of no-control cases. For irregular waves similar verification procedures were adopted. Though there are certain constraints due to the geometrical non-linearity of wave maker and certain nonlinear characteristics due to the near field and gravity waves these experiments show that the control logic could be useful in realizing re-reflecting wave control in conditions of real wave basin.

• 한국음향학회:학술대회논문집
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• 한국음향학회 1997년도 영남지회 학술발표회 논문집 Acoustic Society of Korean Youngnam Chapter Symposium Proceedings
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• pp.75-77
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• 1997

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2006년도 PARALLEL CFD 2006
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• pp.63-65
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• 2006

• 대한원격탐사학회지
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• 제26권6호
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• pp.681-691
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• 2010

LiDAR waveform decomposition plays an important role in LiDAR data processing since the resulting decomposed components are assumed to represent reflection surfaces within waveform footprints and the decomposition results ultimately affect the interpretation of LiDAR waveform data. Decomposing the waveform into a mixture of Gaussians involves two related problems; 1) determining the number of Gaussian components in the waveform, and 2) estimating the parameters of each Gaussian component of the mixture. Previous studies estimated the number of components in the mixture before the parameter optimization step, and it tended to suggest a larger number of components than is required due to the inherent noise embedded in the waveform data. In order to tackle these issues, a new LiDAR waveform decomposition algorithm based on the sequential approach has been proposed in this study and applied to the ICESat waveform data. Experimental results indicated that the proposed algorithm utilized a smaller number of components to decompose waveforms, while resulting IMP value is higher than the GLA14 products.

• 한국음향학회지
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• 제34권6호
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• pp.493-498
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• 2015

물로 채워진 음향 펄스 튜브 내에는 가진 조건들에 따라 복잡한 형태의 음향 신호들이 형성될 수 있다. 이는 펄스 튜브를 이용해 저주파수 대역에서 평면파 반사계수를 측정하는 것을 어렵게 한다. 본 연구에서는 COMSOL Multiphysics를 이용하여 튜브 벽이 가진되는 경우 펄스 튜브 내에 평면파 뿐 아니라 비평면파 모우드의 복잡한 음장이 발생됨을 보였다. 모우드 분리 방법인 이차원 푸리에 필터링으로 입사 또는 반사하는 평면파 모우드만을 각각 분리할 수 있었다. 이에 시간 게이팅을 적용하므로 음향 시편의 평면파 반사계수를 보다 정확하게 결정할 수 있게 하였다.