• 한국자동차공학회논문집
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• 제7권9호
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• pp.158-164
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• 1999

In this paper a simple measurement technique for mechanical-acoustic transfer functions is proposed . The mechanical-acoustic transfer functions, generally , are measured through mechanical excitations ; impact hammers or shakers. Recently , by virtue of vibro-acoustical reciprocity principle, they are measured through acoustic excitations : loudspeakers. This kind of test needs to measure the volume velocity , the radiation characteristics of a sound source. Because the volume velocity of the sound source is changed by driving signal , it is difficult to measure it. However , the new method in this paper needs not to measure the volume velocity of a sound source by combination of mechanical and acoustic excitations. Moreover, this method has the methodological advantages, such as usage of a general loudspeaker for the reciprocal excitation, no sptatial limitations for measurements of mechanical-acoustic transfer functions.

• 한국기계가공학회지
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• 제20권6호
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• pp.82-91
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• 2021

We compared the heat transfer characteristics of the parallel and the counterflow flow in the concentric double tube of the Al₂O₃/water nanofluids using numerical methods. The high- and low-temperature fluids flow through the inner circular tube and the annular tube, respectively. The heat transfer characteristics according to the flow direction were compared by changing the volume flow rate and the volume concentration of the nanoparticles. The results showed that the heat transfer rate and overall heat transfer coefficient improved compared to those of basic fluid with increasing the volume and flow rate of nanoparticles. When the inflow rate was small, the heat transfer performance of the counterflow was about 22% better than the parallel flow. As the inflow rate was increased, the parallel flow and the counterflow had similar heat transfer rates. In addition, the effectiveness of the counterflow increased from 10% to 22% rather than the parallel flow. However, we verified that the increment in the friction factor of the counterflow is not large compared to the increment in the heat transfer rate.

• 한국인터넷방송통신학회논문지
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• 제14권4호
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• pp.107-112
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• 2014

본 연구에서는 다중 사용자 환경의 볼륨 가시화(Volume Rendering)에서 변환 함수(Transfer Function)의 최적화 방안을 연구한다. 볼륨 데이터에 따라 필요한 변환 함수의 형태가 다르기 때문에 여러 번의 시행착오를 겪어야 필요한 변환 함수를 얻을 수 있는데, 이를 방지하기 위해 크라우드 소싱 기법을 이용하여 변환 함수의 파라미터를 최적화 하는 방안을 제안한다. 다중 사용자 환경에서 각 사용자마다 신뢰도에 따른 레벨을 지정하여 가중치로 사용한다. 이전 사용자가 사용했던 변환 함수 파라미터는 가중치만큼 다음 사용자에게 제공되기 때문에 다음 사용자는 변환 함수의 최적 파라미터를 찾기 위한 시도횟수를 줄일 수 있다.

• Journal of Advanced Marine Engineering and Technology
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• 제26권3호
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• pp.320-327
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• 2002

An experimental study of heat transfer from hot flat surface to water sprays was conducted in high temperature region. Heat transfer measurements for hot flat surface were made by 4 sheathed C-A thermocouples. Droplets volume flux were also measured-independently at a position in spray field. The test conditions included variations in droplets volume flux, subcooling of cooling water of $1.565\times10^{-3} to 14.089\times10^{-3}m^3/m^2s and 80 to $20^{\circ}C$ respectively. The effects of inclination angle on heat transfer were investigated and changes in inclination angle of hot flat surface affected heat transfer coefficients of high temperature region.

• Journal of Advanced Marine Engineering and Technology
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• 제24권5호
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• pp.25-32
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• 2000

In this paper, experiments investigating the high-temperature region heat transfer coefficients for the spray cooling of hot flat plates were performed by down spray water using flat spray nozzles. The heat transfer surface is made of copper and is 100mm in length and 40mm in width and 15mm in thickness. The experimental condition of spray are as follows: temperatures of the water droplets are T=20~$80^{\circ}C$ and droplets volume fluxes are D=0.001565~0.010438$m^3/m^2s$. Next, correlating equations for the heat transfer characteristics of spray cooling in the high temperature region are developed from the effects of droplets volume flux and the surface temperature of heat transfer plate.

• 대한기계학회논문집
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• 제19권3호
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• pp.806-819
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• 1995

A study of radiative heat heat transfer has been done in the non-orthogonal coordinate system utilizing the finite volume method and the P.1 approximation. Radiation of absorbing, emitting and scattering media in a concentric annulus has been solved using the non-orthogonal coordinate and the calculations were compared with the existing results. The results obtained from the analysis using the finite volume method are in good agreement with the existing calculations for all optical thicknesses. It was also shown that for only optically thick cases, P-1 approximation can be used in a non-orthogonal coordinate. Convective heat transfer analysis has been carried out to obtain the temperature fields in a cross flow around a circular cylinder and the finite volume method was applied in the non-orthogonal coordinate system to analyze radiative heat transfer. Effects of the optical thickness, the ratio of the surface temperature of the cylinder tot he free stream temperature, and the scattering albedo on radiation have been presented.

• 대한토목학회논문집
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• 제38권5호
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• pp.693-701
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• 2018

수도권 도시철도의 환승통행은 '노선간환승'과 '역사환승'으로 구분된다. 역사환승은 1) 교통카드 Tag-In 단말기 운영노선과 초승열차 운영노선이 다른 경우와 2) 최종 하차열차 운영노선과 교통카드 Tag-Out 단말기 운영노선이 다른 경우에 발생한다. 기존연구에서 주로 교통카드자료를 이용한 환승량 추정은 '노선간 환승량'을 의미하며 '역사환승량'은 제외되어 환승통로를 이용하는 보행에 대한 과소추정의 원인이 되었다. 본 연구는 수도권 대중교통카드자료를 이용해서 역사환승량을 추정하는 방안을 제시한다. 이를 위해 승객의 경로선택모형에 역사환승량 산정에 적합하도록 변형된 Big-Node 기반 네트워크 구축기법과 자료구조 방법론을 제시한다. 1일 약 800만 건의 수도권 도시철도 이용카드자료를 대상으로 사례분석을 시행한다.

• 설비공학논문집
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• 제10권1호
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• pp.95-107
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• 1998

Natural convection and radiation heat transfer in a square enclosure containing absorbing, emitting, and isotopically scattering(participating) media is studied numerically using the finite volume method. Various numerical methods are employed to analyze the radiative heat transfer. However, it is very difficult to choose the proper method. In present study, a finite volume method(FVM) and a discrete ordinates method(DOM) are compared in rectangular enclosure. The SIMPLER algorithm is used to solve the momentum and energy equations. Thermal and flow characteristics are investigated according to the variation of radiation parameters such as optical thickness and scattering albedo. The result shows that the accuracy and the computing time of FVM are better than those of DOM in regular geometry.

• Journal of Mechanical Science and Technology
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• 제19권4호
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• pp.1006-1017
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• 2005

In this work, we developed an accurate and efficient radiative finite volume method applicable for the complex 2D planar and 3D geometries using an unstructured-grid finite volume method. The present numerical model has fully been validated by several benchmark cases including the radiative heat transfer in quadrilateral enclosure with isothermal medium, tetrahedral enclosure, a three-dimensional idealized furnace, as well as convection-coupled radiative heat transfer in a square enclosure. The numerical results for all cases are well agreed with the previous results. Special emphasis is given to the parallelization of the unstructured-grid radiative FVM using the domain decomposition approach. Numerical results indicate that the present parallel unstruc­tured-grid FVM has the good performance in terms of accuracy, geometric flexibility, and computational efficiency.

• Journal of Welding and Joining
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• 제15권3호
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• pp.47-55
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• 1997

Dynamic characteristics of the short circuit mode are investigated using the Volume of Fluid (VOF) method. When the initial molten drop volume, contact area and wire feed rate are given, rate change of the molten bridge profiles, pressure and velocity distributions are predicted. The electromagnetic force with proper boundary conditions are included in the formulation to consider the effects of welding current. It is found that the molten metal is transferred to the weld pool mainly due to the pressure difference caused by the curvatures in the initial stage, and electromagnetic force becomes dominant factor in the final stage of short circuit transfer. Necking occurs at the contact position between the molten drop and weld pool, and the initial molten drop volume and welding current have significant effects on break-up time.