• 한국연소학회:학술대회논문집
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• 2000.05a
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• pp.142-151
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• 2000

Dump combustor is a combustor having a dump plane to make coherent structures. A non-premixed flame dump combustor of simple geometry was constructed. We conducted basic experiments such as frequency response on the combustor to confirm the characteristics of the phenomena as a typical dump combustion and unsteady combustion. Furthermore we visualized the flame front behavior by CH chemiluminescence and high speed motion analysis. In spite of the lack of another data such as velocity, species concentration and temperature, the results showed not only the periodic motion of flame front but the ignition process of vortex ring flame. Also we could check out Rayleigh criterion by combining the visualization data with the pressure data.

• Proceedings of the KSRS Conference
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• v.2
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• pp.954-957
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• 2006

Satellite data (thermal and color imagery) show that offshore flowing filaments off the west coasts of North America, North and South Africa can influence significantly the cross-frontal mixing in the coastal upwelling zones. To evaluate this role, we investigated structure, dynamics and behavior of surface filaments in the Canary and Benguela upwelling regions on the base of daily satellite IR and VIS imagery (AVHRR NOAA, MODIS-Aqua). It was found that seasonal variability of the filaments location depends on intra-annual shift of general upwelling intensity along the coast. The main statistical characteristics of filaments - length, width, temperature anomaly and estimates of velocity were obtained. Estimates of cross-frontal water exchange due to filamentation based on the statistical data show that these coherent structures play a major role in the water and particle exchange between coastal zone and the open ocean in both upwelling regions.

• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.5
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• pp.716-723
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• 1990

Transmission electron microscopy (TEM) and anger electron microscopy(AES) studies of GaAs/AlxGa1-xAs(x=0.58) quantum wells grown by low pressure metalorganic chemical vapor deposition(LP-MOCVD) are carried out. Isolated quantum well structure having the well width as small as 15 \ulcornerand multiquantum well structure, which consisted of 51 alternating layers with each thickness of 10\ulcorner were suscessfully grown. TEM analyses have shown that their interfaces were almost completely coherent without any structural disorder, alloy clustering and crystal defect. AES depth resolution have shown the compositional periodicity of superlattice structure.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.177-178
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• 2006

Digital holographic particle tracking velocimetry (HPTV) is developed by single high-speed camera and single continuous laser with long coherent length. This system can directly capture 4000 hologram fringe images for 1 second through a camera computer memory. The 3D particle location is made of the reconstruction by using a computer hologram algorithm. This system can successfully be applied to instantaneous 3D velocity measurement in the water flow inside a micro-tube. The average of 100 instantaneous velocity vectors is obtained by reconstruction and tracking with the time of evolution of recorded fringes images. In the near future, we will apply this technique to measure 3D flow information inside various micro structures.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1801-1805
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• 2003

The intermittent characteristics of fluid particle accelerations near the wall are investigated with the higher-order statistics and the probability density functions (PDF) by using a direct numerical simulation of turbulent channel flow. Also, the behaviors of acceleration associated with the coherent structures are discussed. The flatness factor of wall-normal acceleration is extremely high near the wall and it exceeds the previously reported value obtained in isotropic turbulence. The presence of the wall seems to make the accelerations more intermittent and the associated mechanism is explained with the PDFs. The skewness factor of wall-normal acceleration indicates that accelerations are associated with the streamwise vortices.

• 한국데이터정보과학회:학술대회논문집
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• 2004.04a
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• pp.91-101
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• 2004

The turbulent flow is of fundamental interest because the conservation equations for thermodynamics, mass and momentum are linked together. This turbulent flow consists of some coherent time- and space-organized vortical structures. Research has already shown that some dynamic systems and experimental models still cannot provide a good nonlinear analysis of turbulent time series. In the real turbulent flow, very complicated nonlinear behaviors, which are affected by many vague factors are present. In this paper, a kernel-based machine for fuzzy nonlinear regression analysis is proposed to predict the nonlinear time series of turbulent flows. In order to show the practicality and usefulness of this model, we present an example of predicting the near-wall turbulence time series as a verifiable model and compare with fuzzy piecewise regression. The results of practical applications show that the proposed method is appropriate and appears to be useful in nonlinear analysis and in fuzzy environments to predict the turbulence time series.

• Wind and Structures
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• v.17 no.6
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• pp.589-608
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• 2013

A model is proposed to analyse the along-wind dynamic response of upwind turbines with horizontal axis under service wind conditions. The model takes into account the dynamic coupling effect between rotor blades and supporting tower. The wind speed field is decomposed into a mean component, accounting for the well-known wind shear effect, and a fluctuating component, treated through a spectral approach. Accordingly, the so-called rotationally sampled spectra are introduced for the blades to account for the effect of their rotating motion. Wind forces acting on the rotor blades are calculated according to the blade element momentum model. The tower shadow effect is also included in the present model. Two examples of a large and medium size wind turbines are modelled, and their dynamic response is analysed and compared with the results of a conventional static analysis.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.6
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• pp.120-127
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• 2000

This study is concerned with evaluating the effects of acoustic excitation on the development of two stream mixing layer generated by split plate. The ratios of two velocities U1 and U2 either side of the splitter plate were such that $U_1/U_2$=1.0 (uniform flow) or $U_1/U_2$<1.0(shear flow). The mixing layers were disturbed acoustically through the edge of split plate. Quantitative data were obtained with hot-wire anemometry. Flow visualization with smoke-wire was also employed for qualitative study. the results show that the large scale structures of mixing layers are strongly affected by excitation frequency and amplitude in both uniform and shear flows. The maximum streamwise and vertical turbulent intensities of the excited flow fields are apt to be decreased as compared with those of without excitation. The flow characteristics of uniform flow are more influenced by acoustic excitation than those of shear flow.

• Transactions of the Korean Society of Automotive Engineers
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• v.2 no.4
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• pp.1-8
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• 1994

이 논문에서 우리는 발전하는 전단층의 2차원 Wave Mode에 대한 비선형 상호작용에 대한 문제를 다루었다. 총 위상각은 Wave Mode ij와 k$\ell$의 상응하는 에너지와 위상 상호작용을 조절한다. 그러므로 이 논문의 목적은 전단층에서 Lange-Scale 구조의 초기 위상각의 효과를 조사하고자 하는 것이다. 이 연구에서 우리는 Subharmonic의 존재는 전단층의 성장에 상당한 영향을 준다는 것을 알았고 Entrainment에서도 증가하는데 영향을 준다는 것을 알았다. 우리는 또한 Mean Flaw와 Fundamental의 다른 초기 위상각의 효과는 Subharmonic이 성장하는 먼 Downstream 영역에서 보여지기 시작한다는 것을 알았다.

• Proceedings of the Optical Society of Korea Conference
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• 2001.02a
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• pp.54-55
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• 2001

Recently, there has been much interests in InGaN/GaN multiple-quantum-well (MQW) structures due to their applicability as optoelectronic devices such as light-emitting diodes (LEDs) and laser diodes [1]. Their ultrafast and physical properties are also of significant interests. Anomalously large acoustic phonon oscillations have been observed using ultrafast lasers in InGaN MQWs [2]. In this study, we have peformed femtosecond pump-probe experiments in the reflection geometry on 5 periods InGaN/GaN MQW LED structure with well width of 20$\AA$ and barrier width of 100$\AA$ at room temperature. (omitted)