• 한국자동차공학회논문집
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• 제7권8호
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• pp.150-159
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• 1999

Exhaust system is composed of several parts. Among, them , design of muffler system strongly influences on engine efficiency and noise reduction. So , through comprehension of flow characteristics inside muffler is necessary . In this study , three-dimensional steady and unsteady compressible flow analysis was performed to understand the flow characteristics, pressure loss and amplitude variation of pulsating pressure. The computational grid generation was carried out using commercial preprocessor ICEM CFD/CAE. And the three-dimensional fluid motion inside the muffler was analyzed by STAR-CD, the computational fluid dynamics code. RNG k-$\varepsilon$ tubulence model was applied to consider the complexity of the geometry and fluid motion. The steady and unsteady flow field inside muffler such as velocity distribution, pulsating pressure and pressure loss was examined. In case of unsteady state analysis, velocity of inlet region was converted from measured pulsating pressure. Experimental measurement of pressure and temperature was carried out to provide the boundary and initial condition for computational study under three engine operating conditions. As a result of this study, we could identify the flow characteristics inside the muffler and obtain the pressure loss, amplitude variation of pulsating exhaust gas.

• 대한전기학회논문지:전력기술부문A
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• 제51권8호
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• pp.379-384
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• 2002

In the competitive electricity market, various pricing methods are developed and practiced in many countries. Among these pricing methods, marginal loss factor(MLF) can be applied to reflect the marginal cost of network losses. For the calculation of MLF, power flow method has been used to calculate system loss deviation. However, this power flow method shows some shortcomings such as necessity of regional reference node, and absence of an ability to consider network constraints like line congestion, voltage limit, and generation output limit. The former defect might affects adversely to the equity of market participants and the latter might generate an inappropriate price signals to customers and generators. To overcome these defects, the utilization of optimal power flow(OPF) is suggested to get the system loss deviation in this paper. 30-bus system is used for the case study to compare the MLF results by the power flow and the OPF method for 24-hour dispatching and pricing, Generator payment and customer charge are compared with these two methods also. The results show that MLF by OPF reflects the power system condition more faithfully than that of by the conventional power flow method

• 대한기계학회논문집
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• 제12권6호
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• pp.1407-1414
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• 1988

본 연구에서는 저자들에 의해 이미 개발된 경계유선수정법에 의한 B-B 유동계 산을 통해 익열의 편차각을 계산하고 기존의 예측방법에 의한 결과와 비교 검토하여 압축성 및 3차원 비축대칭성의 효과를 검토하였다.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2006년 제4회 한국유체공학학술대회 논문집
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• pp.161-164
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• 2006

Three-dimensional flow and aerodynamic loss in the tip-leakage flow region of a high-turning first-stage turbine rotor blade with a squealer tip have been measured with a straight miniature five-hole probe for the tip gap-to-chord ratio, h/e, of 2,0%. This squealer tip has a indent-to-chord ratio, $h_{st}/c$, of 5.5%. The results are compared with those for a plane tip ($h_{st}/c\;=\;0.0%$). The squealer tip tends to reduce the mass flow through the tip gap and to suppress the development of the tip-leakage vortex. Therefore, it delivers lower aerodynamic loss in the near-tip region than the plane tip does. At the mid-span, however, the aerodynamic loss has nearly the same value for the two different tips.

• 한국화재소방학회논문지
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• 제16권4호
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• pp.59-64
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• 2002

버터플라이 밸브의 압력손실과 캐비테이션에 대한 유동특성 연구를 수행하였다. 밸브의 열림각에 대한 압력손실계수는 Carnot 방정식을 응용하여 수식화하였다. 캐비테이션(캐비테이션의 발단, 슈퍼 캐비테이션, 캐비테이션 손상, 초킹 캐비테이션과 같은)은 밸브의 압력손실계수로부터 예측되었다. 압력손실과 캐비테이션 예측은 밸브의 열림각에 대한 두께 비의 변화에 따라 수행하였다. 예측 데이터는 버터플라이 밸브를 개발하는데 필요한 엔지니어링 데이터로 활용하고자 한다.

• 한국농공학회:학술대회논문집
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• 한국농공학회 1999년도 Proceedings of the 1999 Annual Conference The Korean Society of Agricutural Engineers
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• pp.606-611
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• 1999

Recently , the hydraulic fill method is commonly used in many reclamation projects due to lack of fill materialss. The method of hydraulic fill i recalmation is executed by transporting the mixture of water -soil particles into a relcaimed land through dredging pipes, then the dredged soil particels settle down in thewater orflow over an out flow weir with the water. The amount of the volume reductions of dredged soil is considered the sum of the overall settlement by descication shrinkage and self-weigth consolidation and the loss of soil particles flow over a weir. In the present study, hydrometer analysis was performed with the soil samples obtained bofore and after dredging to estimate the amount of soil particles residual at reclaimed area and the loss of soil particles , then it was suggested the method of determining the loss ratio of dredged soils from the tests results. The hydrometer analysis of in-situ soil samples showed that the loss ratio of dredged soils is lowest at the nearest point to dredge pipe and highest at the nearest point of out flow weir.

• 대한전기학회논문지
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• 제44권1호
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• pp.21-24
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• 1995

The larger and the more complicated the system size and configuration grow, the more serious the system loss problem becomes. Exessive system loss causes severs system voltage depression, which even may result in system voltage collapse. This paper proposes an effective tool for minimizing the system power loss by optimal re-location of the static condenser based on the system loss sensitivity index .lambda.$_{Q}$. It is possible to determine the optimal location and amount of VAR investment for minimizing the system loss by priority of .lambda.$_{Q}$ index given for each bus. Several computational techniques for avoiding divergency of the load flow solution are proposed. The loss sensitivity index .lambda.$_{Q}$ uses information of normal power flow equations and their Jacobians. Two case studies proved the effectiveness of the algorithm proposed.posed.

• 대한기계학회논문집B
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• 제21권9호
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• pp.1185-1197
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• 1997

Three-dimensional flow within a film-cooling hole, which is normally oriented to the main flow, has been measured by using a straight five-hole probe for the blowing ratios of 1.0 and 2.0. The length-to-diameter ratio of the injection hole is fixed to be 1.0 throughout the whole experiments. The result shows that the secondary flow within the hole is strongly affected by the main flow and flow separation at the hole inlet. The higher blowing ratio provides less influence of the main flow on the injectant flow. The three-dimensional flow at the hole exit is considerably altered due to the strong interaction between the injectant and main flow. The aerodynamic loss produced inside the injection hole is mainly attributed to the inlet flow separation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1975-1980
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• 2004

The three-dimensional flow in a turbine nozzle guide vane passage causes large secondary loss through the passage and increased heat transfer on the blade surface. In order to reduce or control these secondary flows, a linear cascade with a contoured endwall configuration was used and changes in the three-dimensional flow field were analyzed and discussed. Measurements of secondary flow velocity and total pressure loss within the passage have been performed by means of five-hole probes. The investigation was carried out at fixed exit Reynolds number of $4.0{\times}10^5$. The objective of this study is to document the development of the three-dimensional flow in a turbine nozzle guide vane cascade with modified endwall. The results show that the development of passage vortex and cross flow in the cascade composed of one flat and one contoured endwalls are affected by the flow acceleration which occurs in contoured endwall side. The overall loss is reduced near the flat endwall rather than contoured endwall.

• Membrane and Water Treatment
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• 제13권6호
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• pp.313-320
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• 2022

Theoretical calculation results are presented for the enhancement of the water mass flow rate through the hydrophobic micro/nano pores in the membrane respectively on the micrometer and nanometer scales. The water-pore wall interfacial slippage is considered. When the pore diameter is critically low (less than 1.82nm), the water flow in the nanopore is non-continuum and described by the nanoscale flow equation; Otherwise, the water flow is essentially multiscale consisting of both the adsorbed boundary layer flow and the intermediate continuum water flow, and it is described by the multiscale flow equation. For no wall slippage, the calculated water flow rate through the pore is very close to the classical hydrodynamic theory calculation if the pore diameter (d) is larger than 1.0nm, however it is considerably smaller than the conventional calculation if d is less than 1.0nm because of the non-continuum effect of the water film. When the driving power loss on the pore is larger than the critical value, the wall slippage occurs, and it results in the different scales of the enhancement of the water flow rate through the pore which are strongly dependent on both the pore diameter and the driving power loss on the pore. Both the pressure drop and the critical power loss on the pore for starting the wall slippage are also strongly dependent on the pore diameter.