• 한국지구과학회지
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• 제34권4호
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• pp.336-344
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• 2013

이 연구는 북서태평양에서 여름철(7-9월) 동안 발생하는 태풍 빈도를 예측하기 위한 다중회귀모델을 4가지 원격패턴을 이용하여 개발하였다. 이 패턴은 4-5월 동안 동아시아 대륙에서의 시베리아 고기압 진동, 북태평양에서의 북태평양 진동, 호주근처의 남극진동, 적도 중앙태평양에서의 대기순환으로 대표된다. 이 통계모델은 이 모델로부터 예측된 높은 태풍발생빈도의 해와 낮은 태풍발생빈도의 해 사이에 차를 분석함으로써 검증되었다. 높은 태풍발생빈도의 해에는 다음과 같은 4가지의 아노말리 특성을 나타내었다: i) 동아시아 대륙에 고기압성 순환 아노말리(양의 시베리아 고기압진동), ii) 북태평양에 남저북고의 기압계 아노말리, iii) 호주 근처에 저기압성 순환 아노말리(양의 남극진동), iv) 봄부터 여름 동안 니뇨3.4 지역에 저기압성 순환 아노말리. 따라서 적도 서태평양에서 무역풍 아노말리는 양반구의 아열대 서태평양에 위치한 저기압성 순환 아노말리에 의해 약화되었다. 결국, 이러한 기압계 아노말리의 공간분포는 열대 서태평양에 대류를 억제하는 대신 아열대 서태평양에 대류를 강화시켰다.

• 한국유체기계학회 논문집
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• 제13권5호
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• pp.22-28
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• 2010

A study has been made of cool-down process on an incompressible fluid contained in a periodically oscillating cylinder when an abrupt cooling of wall temperature is imposed. Characteristics of flow and heat transfer are investigated along the variations of oscillating frequency and amplitude. One found the flow regimes are divided into 4-modes : 1 thermal island mode, 2 thermal island mode, 4 thermal island mode and asymmetry mode. Comprehensive analysis for each mode are given with a physical mechanism on cool-down process.

• 소음진동
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• 제9권5호
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• pp.1005-1011
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• 1999

Generation of hole-tones and the instability of circular impinging jets are investigated based on the frequency characteristics and the radiated sound field. The experiment is carried out with varying hole sizes, jet speeds and impinging distances. It is found that hole-tones occur by both the low-speed laminar jet and the high-speed turbulent jet, but not by the transient jet, while plate-tones without holes are produced only in the high-speed turbulent impinging jet. When the diameter ratio of the hole to the nozzle is nearly one, hole-tones occur most easily. At low speed, it is found that hole-tones are due to the symmetrical unstable jet and the impinging distance decreases with jet speed. And the Strouhal number and the sound pressure level increase with jet speed. At high speed, hole-tones show the same characteristics as plate-tones. It is found that the ratio of the convection speed varies with the Strouhal number and the jet speed.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1997년도 춘계학술대회논문집; 경주코오롱호텔; 22-23 May 1997
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• pp.608-614
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• 1997

2차원 압축성 오일러 방정식을 지배 방정식으로 하여 음향학적 문제를 직접 수치 계산하였다. Roe의 개략적인 리만해(Approximate Riemann Solver)에 의거하여 대류항을 구성하였고 높은 정확도를 유지하기 위해 Vanleer의 MUSCL 방법을 사용하여 공간을 이산화하였다. 시간 적분으로는 2차의 Runge-Kutta 방법을 사용하였다. Resonance tube 내의 음향학적 문제 해석을 위해 최근까지 제시된 음향 경계 조건들을 비교하였고 각 경계 조건들이 갖는 물리적 의미를 고찰하였다. 이들을 통하여 압력파의 물리적인 행태를 모사하였고 실험과 비교하였다. 계산결과들을 통하여 사용된 방법은 전형적인 압축성 유동 해석 문제 뿐만 아니라 선형, 비선형의 음향학적 문제들을 적절한 경계 조건과 결합하여 해석할 수 있음을 알 수 있었고 resonance tube와 같은 공학적으로 실제적인 문제들에 대한 응용이 기대된다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2248-2253
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• 2008

A numerical study on oscillatory thermocapillary flow in half-zone has performed to understand the effect of axial rotation. 2d unsteady code is developed to observe the onset of oscillation. 2cs Silicone oil with Prandtl number of 26.5 is used as a working fluid. The critical temperature difference at onset of oscillation is investigated under the different aspect ratios and rotation modes. It is shown that the onset of oscillation is delayed when aspect ratio reduces and rotating speed increases. The oscillatory flow is strongly reduced under top rotation and co-rotation modes, while it is augmented under bottom rotation and counter-rotation modes. It is thought that interaction between return flow and bottom wall is important to explain the oscillatory flow.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.915-918
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• 2005

Acoustic holography uses Kirchhoff·Helmholtz integral equation and Green's function which satisfies Dirichlet boundary condition Applications of acoustic holography have been taken to the sound field neglecting the effect of flow. The uniform flow, however, changes sound field and the governing equation, Green's function and so on. Thus the conventional method of acoustic holography should be changed. In this research, one possibility to apply acoustic holography to the sound field with uniform flow is introduced through checking for the plane wave in a duct. Change of Green's function due to uniform flow and one method to derive modified form of Kirchhoff·Heimholtz integral is suggested for 1-dimensional sound field. Derivation results show that using Green's function satisfying Dirichlet boundary condition, we can predict sound pressure in a duct using boundary value.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 추계학술대회 논문집
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• pp.821-832
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• 2011

Recently, the noise of vehicle is the one of the key factors for customers to purchase a vehicle and the most important part which is related to the noise is the exhaust system. Thus, car makers have their own ways to assess this exhaust noise not only to decrease the level of noise but to enhance the feeling of it. Typically, to do these things in the early stage of development, the tuning code of the exhaust system has to be made by CAE tool, which is very reliable but expensive, and the prototype parts of this code would be made for the validation test. Then this process can be iterated to meet the target of the performance. In this study, a new algorithm which adapts the '3 dimensional convective sound wave theory 'and 'Doppler effect' has been developed. With this new algorithm, a brand new system for the calculation of tail pipe noise has been developed and validated by acoustic wind tunnel test. As a result of this study, various comparisons and have been carried out, for example, the comparison with other CAE tool has been performed for the validity and the improvement of the new calculation code could be achieved.

• 대한기계학회논문집
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• 제17권9호
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• pp.2304-2314
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• 1993

Natural convective flow and heat transfer in a two-dimensional square enclosure fitted with a horizontal partition are investigated numerically. The enclosure was composed of the lower hot and the upper cold horizontal walls and the adiabatic vertical walls, and a partition was situated perpendicularly at the one vertical insulated wall. The governing equations are solved by using the finite element method with Galerkin method. The computations were carried out with the variations of length, position and thermal conductivity of the partition, and Rayleigh number based on the temperature difference between two horizontal walls and the enclosure height with water(Pr=4.95). As the results, an oscillatory motion of natural convection is resulted in a sudden rise of overall heat transfer, but the increase of length of partition is significantly restrained the increase of Nusselt number. The maximum heat transfer was shown just before the transition of the direction of oscillating flow. An oscillatory motion of flow was perfectly shown the stability with the decrease of the length of partition and Rayleigh number. Also, the heat transfer was raised with the increase of the thermal conductivity in proportion to the increase of the length of partition. The stability and oscillation of flow are affected by the position of partition.

• 대한기계학회논문집B
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• 제20권7호
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• pp.2397-2408
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• 1996

A numerical study was made of the control of transient oscillatory flow modes in Czochralski convection. The reduction of temperature oscillation was achieved by changing the rotation rate of crystal rod, .OMEGA.$_{S}$=.OMEG $A_{S0}$(1+ $A_{S}$sin(2.pi. $f_{S}$/ $t_{p}$t)). The temporal behavior of oscillation flow was scrutinized over broad ranges of two parameters, i.e., the rotation amplitude( $A_{S}$.leq.0.5) and the nondimensional frequency (0.9.leq. $f_{S}$.leq.1.5). The mixed convection parameter was ranged 0.225.leq.Ra/PrR $e^{2}$.leq.0.929, which encompassed the buoyancy-and forced-dominant convection regimes. Computational results revealed that the temperature oscillations could be reduced effectively by a proper adjustment of the control parameters. The uniformity of temperature distribution near the crystal rod was examined. The control of oscillatory flow modes was also made for a realistic, low value of Pr.

• 설비공학논문집
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• 제7권3호
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• pp.528-537
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• 1995

Natural convective flow and heat transfer characteristics in a partially opened enclosure fitted with a horizontal divider are investigated numerically. The enclosure is composed of a lower hot and a upper cold horizontal walls and adiabatic vertical walls. A divider is attached perpendicularly to the vertical insulated wall. The governing equations are solved by using the finite element method with Galerkin method. The computations have been carried out by varying the length of divider, the opening size, and the Rayleigh number based on the temperature difference between two horizontal walls and the enclosure height for air(Pr=0.71). As result, when the opening size is fixed, the intensity of the secondary flow is weaken as the length of divider increases. The maximum heat transfer rate over the upper cold wall occurs at a position bounded on the opening. However, when the length of divider is increased considerably, its maximum occurs at the right wall. The stability and frequency of oscillation are affected by the Rayleigh number and length of divider. The Nusselt number is increased with the increase of the opening size and the increase of Rayleigh number.