• 대한공업교육학회지
• /
• 제33권2호
• /
• pp.248-258
• /
• 2008

현재 인터넷은 응용계층에서 HTTP를 사용하고 트랜스포트 계층에서는 TCP를 사용하여 서비스를 제공하고 있다. 새롭게 제안된 전송 계층 프로토콜인 SCTP(Stream Control Transmission Protocol)는 슬로우 스타트 기간 동안에 초기 윈도우의 값 등을 제외하고는 TCP와 유사한 혼잡 제어 메커니즘을 사용한다. 본 논문에서는 이 점에 주목하여 슬로우 스타트 기간 동안에 HTTP over SCTP의 평균 전송 시간을 구하는 수학적 모델을 제시하고 이를 기존의 HTTP over TCP와 비교한다. 비교 결과는 HTTP over SCTP의 평균 전송 시간이 HTTP over TCP의 그것보다 평균 11 % 우수함을 보여준다.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2008년도 춘계학술대회논문집
• /
• pp.109-112
• /
• 2008

In this work, a mathematical heat transfer model of a walking-beam type reheating furnace that can predict the formation and growth of the scale layer, which is produced due to oxidative reaction between the furnace oxidizing atmosphere and the steel surface in the reheating furnace, has been developed. The model can also predict the heat flux distribution within the furnace and the temperature distribution in the slab and scale throughout the reheating furnace process by considering the heat exchange between the slab and its surroundings in the furnace, including radiant heat transfer among the slabs, the skids, the hot gases and the furnace wall as well as the gas convection heat transfer in the furnace. Using the model developed in this work, the effects of the scale layer on the heat transfer characteristics and temperature behavior of the slab is investigated. A comparison is also made between the predictions of the present model and the data from an in situ measurement in the furnace, and a reasonable agreement is founded.

• 신재생에너지
• /
• 제18권2호
• /
• pp.73-81
• /
• 2022

This study was aimed at designing a condenser, as a component of the organic Rankine cycle system for ships. The condenser was manufactured through press molding to achieve a bent shape to enhance the heat transfer performance, considering the shape of the heat transfer plate used in a brazing plate heat exchanger. The heat transfer plate was made of copper-nickel alloy. The required heat transfer rate for the condenser was 110 kW, and the maximum number of layers was set as 25, considering the characteristics of high-temperature brazing. Computational fluid dynamics techniques were used to perform the thermal fluid analysis, based on the ANSYS CFX (v.18.1) commercial program. The heat transfer rate of the condenser was 4.96 kW for one layer (width and length of 0.224 and 0.7 m, respectively) of the heat transfer exchanger. The fin efficiency pertaining to the heat transfer plate was approximately 20%. The heat flow analysis for one layer of the heat exchanger plate indicated that the condenser with 25 layers of heat transfer plates could achieve a heat transfer rate of 110 kW.

• 대한기계학회논문집B
• /
• 제24권2호
• /
• pp.298-305
• /
• 2000

The flow characteristics and the heat transfer rate on a surface by interaction of a pair of vortices were studied experimentally. The test facility consisted of a boundary-layer wind tunnel with a vortex introduced into the flow by half-delta wings protruding from the surface. In order to control the strength of the longitudinal vortices, the angles of attack of the vortex generators were varied from - 20 degree to - 45 degree, but spacings between the vortex generators were fixed to 4 cm. The 3-dimensional mean velocity measurements were made using a five-hole pressure probe. Heat transfer measurements were made using the thermochromatic liquid to provide the local distribution of the heat transfer coefficient. Unlike common flow down, common flow up vortices moved toward the centerline as they developed and interacted strongly with each other but not with the boundary layer. Spanwise profiles of Stanton number were similar for ${\beta}=-20^{\circ}\;and\;-35^{\circ}$, but not similar for ${\beta}=-45^{\circ}$. The case of ${\beta}=-20^{\circ}\;and\;-35^{\circ}$ showed the two peak Stanton number, but the case of ${\beta}=-45^{\circ}$ showed the only one peak Stanton number.

• 태양에너지
• /
• 제13권2_3호
• /
• pp.120-132
• /
• 1993

본 연구의 목적은 터어빈 회전차를 모델로한 복합회전형 히이트파이프의 전열특성을 실험과 유한요소의 해석법에 의하여 연구한 것이다. 입열량과 회전수에 따른 Nu, Re, Pr 그리고 무차원 응축액막두께가 변수로 사용되었다. 해석과 실험치는 거의 유사한 경향으로 일치하였으며, 연구결과는 복합히이트파이프 성능예측을 하는데 도움을 주었다. 복합회전형 히이트파이프에서의 열저항은 응축액막두께가 감소함에 따라 응축부의 열전달은 급격히 증가하였고, 응축액막두께는 복합회전형 히이트파이프의 전열 특성에 가장 큰 영향을 주었다. 주어진 Pr에서 Re가 변화함에 따라 무차원 응축액막두께가 일정한값으로 나타났고,무차원 응축액막두께는 회전수의 역수의 제곱근에 비례하였다. 본 연구의 해석적 방법에 의해서 Nu=A$({\delta}({\omega}/v)^{-1/2}Re^B)$라는 식을 구했고, 이때 A=0.963, B=0.5025의 값을 얻었다.

• 대한기계학회논문집B
• /
• 제23권5호
• /
• pp.567-576
• /
• 1999

An experimental study has been conducted to investigate the effects of the free stream turbulence intensity and Reynolds number on the heat transfer and flow characteristics In the linear turbine cascade. Profiles of the time-averaged velocity, turbulence intensity, and Reynolds stress were measured in the turbine cascade passage. The static pressure and heat transfer distributions on the blade suction and pressure surfaces were also measured. The experiments were made for the Reynolds number based on the chord length, Rec = $2.2{\times}10^4$ to $1.1{\times}10^5$ and the free stream turbulence intensity, $FSTI_1$ = 0.6% to 9.1 %. The uniform heat flux boundary condition on the blade surface was created using the gold film Intrex and the surface temperature was measured by liquid crystal, while hot wire probes were used for the flow measurements. The results show that the free stream turbulence promotes the boundary layer development and delays the flow separation point on the suction surface. It was found that the boundary layer flows on the suction surface for all Reynolds numbers tested with $FSTI_1$ = 0.6% are laminar. It was also found that the heat transfer coefficient on the blade surface increases as the free stream turbulence intensity increases and the flow separation point moves downstream with an increasing Reynolds number. The results of skin friction coefficients are in good agreement with the heat transfer results in that for $FSTI_1{\geq}2.6%$, the turbulent boundary layer separation occurs.

• 문화기술의 융합
• /
• 제10권2호
• /
• pp.465-470
• /
• 2024

인공지능(Artificial Intelligence, AI) 기반 이미지 생성 기술의 발달로 다양한 이미지가 생성되고 있으며, 이를 정확하게 판별하는 기술이 필요하다. 생성된 이미지 데이터의 양에는 한계가 있으며, 한정된 데이터로 높은 성능을 내기 위해 본 연구에서는 전이 학습(Transfer Learning)을 활용한 생성 이미지를 판별하는 모델을 제안한다. ImageNet 데이터 셋으로 사전학습 된 모델을 입력 데이터 셋인 CIFAKE 데이터 셋에 그대로 적용하여 학습의 시간 비용을 줄인 후, 3개의 은닉층과 1개의 출력층을 더해 모델을 튜닝한다. 모델링 결과, 최종 레이어를 조정한 모델의 성능이 높아짐을 확인하였다. 딥러닝에서 전이 학습을 통해 학습한 후 출력층과 가까운 레이어를 데이터의 특성에 맞게 추가 및 조정하는 과정을 통해 적은 이미지 데이터로 인한 학습 정확도 이슈를 줄이고 생성된 이미지 판별을 할수 있다는 데 의의가 있다.

• 한국전기전자재료학회논문지
• /
• 제27권6호
• /
• pp.377-382
• /
• 2014

We have investigated the effects of spacer layer inserted between blue and red doped emission layers on the emission and efficiency characteristics of phosphorescent OLEDs. N,N'-di-carbazolyl-3,5-benzene (mCP) was used as a host layer. Iridium(III)bis[(4,6-di-fluorophenyl)- pyridinato-N,$C^2$']picolinate (FIrpic) and tris(1-phenyl-isoquinolinato-$C^2$,N)iridium(III) [Ir(piq)3] were used as blue and red dopants, respectively. The emission layer structure was mCP (1-x) nm/mCP:$Ir(piq)_3$ (5 nm, 10%)/mCP (x nm)/mCP:FIrpic (5 nm, 10%). The thickness of mCP spacer layer was varied from 0 to 15 nm. The emission from $Ir(piq)_3$ and the efficiency of the device were dominated by energy transfer from mCP host and FIrpic molecules, and by diffusion of mCP host triplet excitons.

• Earthquakes and Structures
• /
• 제8권5호
• /
• pp.1241-1254
• /
• 2015

Spatially variable ground motions can be significant on the seismic response of a structure due to the incoherency of the incident wave. Incoherence of the incident wave is resulted from wave passage and wave scattering. In this study, wave passage effect on the response spectrum of a building structure built on a soft soil layer was investigated utilizing a finite element program of P3DASS (Pseudo 3-dimensional Dynamic Analysis of a Structure-soil System). P3DASS was developed for the axisymmetric problem in the cylindrical coordinate, but it is modified to apply anti-symmetric input earthquake motions. Study results were compared with the experimental results to verify the reliability of P3DASS program for the shear wave velocity of 250 m/s and the apparent shear wave velocities of 2000-3500 m/s. Studied transfer functions of input motions between surface mat foundation and free ground surface were well-agreed to the experimental ones with a small difference in all frequency ranges, showing some reductions of the transfer function in the high frequency range. Also wave passage effect on the elastic response spectrum reduced the elastic seismic response of a SDOF system somewhat in the short period range.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2002년도 추계학술대회 논문집
• /
• pp.599-602
• /
• 2002

A novel rapid prototyping (RP) process, an automated transfer type variable lamination manufacturing process (Automated VLM-ST) has been developed. In Automated VLM-ST, a vacuum chuck and linear moving system transfer the plate type material with two pilot holes to the rotation stage. A four-axis synchronized hotwire cutter cuts the material twice to generate Automated Unit Shape Layer (AUSL) with the desired width, side slopes, length, and two reference shapes in accordance with CAD data. Each AUSL is stacked on the stacking plate with two pilot pins using the pilot holes in AUSL and the pilot pins. Subsequently, adhesive is supplied to the top surface of the stacked AUSL by a bonding roller and pressure is simultaneously applied to the bottom surface of the stacked AUSL. Finally, three-dimensional shapes are rapidly fabricated. This paper describes the procedure for generating the cutting path data (AUSL data) f3r automated VLM-ST. The method for the generation of the Automated Unit Shape Layer (AUSL) in Automated VLM-ST was practically applied and fabricated for a various shapes.