• 한국초전도ㆍ저온공학회논문지
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• 제12권2호
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• pp.13-16
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• 2010

The superconducting synchronous motor or generator mostly has high permeability iron only around outer yoke portion. Therefore, if excitation voltage (Back E.M.F) is calculated from 2 dimensional magnetic field distributions, it can be largely different from actual value due to additional voltage originated from end coils. In order to calculate the excitation voltage more accurately, 3 dimensional magnetic field calculation is necessary for including the end coil effect from large air-gap structure. The excitation voltage can be calculated by stator (armature) coil linkage flux originated from rotor (field) coil excitation, but it is difficult to calculate the flux linkage exactly because of complicated structure of the stator coil. This paper shows a method to calculate the excitation voltage from 3 dimensional magnetic energy that can be calculated directly from volume integration of magnetic flux density and field intensity scalar product through FEM (Finite Element Method) analysis software.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2005년도 추계 학술대회논문집
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• pp.131-134
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• 2005

Conventional high order interpolation schemes are limitative in several aspects mainly because they need data of neighboring cells at the reconstruction step. However, discontinuous Galerkin method and spectral volume method, two high order flux schemes which will be analyzed and compared in this paper, have an important benefit that they are not necessary to determine the flow gradients from data of neighboring cells or elements. These two schemes construct polynomial of variables within a cell so that even near wall or discontinuity, the high order does not deteriorate.

• International Journal of Aerospace System Engineering
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• 제2권2호
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• pp.40-43
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• 2015

A hybrid mesh based finite volume compressible flow code (PolySim) has been developed recently. Instead of the simple average method for the gradients of variables at each face, the volume average is applied for the calculation of the viscous flux. What is more, an improved Green Gauss method for the calculation of the gradient is also presented. These two techniques will improve both the accuracy and robustness of the code. The aerodynamic performance of this in-house cell centered code is examined by several widely-used bench-mark test cases. These cases include flows over flat plate and RAE 2822 etc. The comparisons on results between calculation and experiment are conducted. They show that the code can produce good numerical results which agree well with the corresponding experiment data.

• 한국수자원학회논문집
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• 제46권2호
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• pp.139-153
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• 2013

고르지 않은 바닥을 지나는 천수 흐름을 해석하기 위해 천수방정식의 흐름률 경사항과 바닥 경사 생성항에 대해 HLLL 기법과 DFB(Divergence Form for Bed slope source term) 기법을 각각 적용하여 유한체적 모형을 구성하였다. 또한, PSC(Partially Submerged Cell)의 고려를 위해 VFR(Volume/Free-surface Relationship)도 이용하였다. MUSCL에서 WSDGM(Weighted Surface-Depth Gradient Method)을 보다 단순하게 고쳐도 원래의 방법과 정확도가 동등함을 1차원 정상 흐름에 대해 확인하였다. 1차원 PSC에 대한 VFR를 통해 흐름률 경사항과 바닥 경사 생성항의 선평형성이 정확하게 충족됨을 입증하였다. 2차원 PSC에서 DFB 기법으로는 지배방정식의 선평형성이 충족되지 않은 문제를 삼각형 격자에 대한 VFR를 이용하여 해소하였다. 삼각형 턱과 둥근 융기를 지나는 2차원 댐 붕괴 흐름에 대한 모의에서 실험실 실험 결과와 잘 부합됨을 확인하였다. 또한, 부분 댐 붕괴 흐름에 대한 모형의 적용에서 경사면은 물론 불규칙 바닥에서도 요철의 잠김이 성공적으로 모의되었다. 따라서 고르지 않은 실제 하천 지형에 대한 이 모형의 적용성이 기대된다.

• 대한기계학회논문집B
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• 제24권11호
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• pp.1428-1436
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• 2000

The absorption of vapor involves simultaneous heat and mass transfer in the vapor/liquid system. In this paper, a numerical study for vapor absorption process into LIBr-H$_2$O solution film flowing over helical absorber has been carried out. Axisymmetric cylindrical coordinate system was adopted to model the helical tube and the transport equations were solved by the finite volume method. The effects of operating conditions, such as the cooling water temperature. the system pressure, the film Reynolds number and the solution inlet concentration have been investigated in view of the absorption mass flux and the total absorption mass flux and the total absorption rate. The results for the temperature and concentration profiles, as well as the local absorption mass flux at the helical absorber are presented. It is shown that solution inlet concentration affected other than operation conditions for a mass flux.

• Journal of international Conference on Electrical Machines and Systems
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• 제1권1호
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• pp.32-39
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• 2012

With the aid of genetic algorithm (GA), global optimization with multiple geometry parameters is feasible in the design of switched flux permanent magnet (SFPM) machines. To investigate the advantages of global optimization over individual optimization, which has been used extensively for the design of SFPM machines, a comparison between the two approaches is carried out for the case of fixed copper loss and volume. In the case of individual parameter optimization, the sequence in which the individual parameters are optimized is very important. In the global optimization a better design can always be achieved although the corresponding torque density is found to be only slightly better than that of individually optimized with correct design sequence. By using the obtained global optimization results, the performance in machines having two types of stator and rotor pole combinations, i.e. 12/10 and 12/14, are compared, and it is shown that higher torque is exhibited in the 12/14 SFPM machine. Finally, this paper also demonstrates that global optimization, with the restriction of equal pole width, magnet thickness and slot opening, can maximize the torque density without significantly sacrificing other performance, such as cogging torque and overload capability.

• Nuclear Engineering and Technology
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• 제52권10호
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• pp.2353-2360
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• 2020

An anodic electrophoretic deposition (EPD) technique is used to create a uniform TiO₂ thin film coating on boiling thin steel plates (1.1 mm by 90 mm). All of the effective parameters except time of the EPD method are kept constant. To investigate the effect of gamma irradiation on the critical heat flux (CHF), the test specimens were irradiated in a gamma cell to different doses ranging from 100 to 300 kGy, and then SEM and BET analysis were performed. For each coated specimen, the contact angle and capillary length were measured. The specimens were then tested in a boiling pool for CHF and boiling heat transfer coefficient. It was observed that irradiation significantly decreases the maximum pore diameter while it increases the porosity, pore surface area and pore volume. These surface modifications due to gamma irradiation increased the CHF of the nano-coated surfaces compared to that of the unirradiated surfaces. The heat transfer coefficient (HTC) of the nano-coated surfaces irradiated at 300 kGy increased from 83 to 160 kW/(㎡ K) at 885 kW/㎡ wall heat flux by 100%. The CHF of the irradiated (300 kGy) and unirradiated surfaces are 2035 kW/㎡ and 1583 kW/㎡, respectively, an increase of nearly 31%.

• 대한기계학회논문집B
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• 제32권6호
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• pp.429-445
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• 2008

Two-phase compressible flow fields of air-water are investigated numerically in the fixed Eulerian grid framework. The phase interface is captured via volume fractions of each phase. A way to model two phase compressible flows as a single phase one is found based on an equivalent equation of states of Tait's type for a multiphase cell. The equivalent single phase field is discretized using the Roe‘s approximate Riemann solver. Two approaches are tried to suppress the pressure oscillation phenomena at the phase interface, a passive advection of volume fraction and a direct pressure relaxation with the compressible form of volume fraction equation. The direct pressure equalizing method suppresses pressure oscillation successfully and generates sharp discontinuities, transmitting and reflecting acoustic waves naturally at the phase interface. In discretizing the compressible form of volume fraction equation, phase interfaces are geometrically reconstructed to minimize the numerical diffusion of volume fraction and relevant variables. The motion of a projectile in a water-filled tube which is fired by the release of highly pressurized air is simulated presuming the flow field as a two dimensional one, and several design factors affecting the projectile movement are investigated.

• 한국해안·해양공학회논문집
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• 제26권4호
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• pp.253-266
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• 2014

광양만 권역의 해수 순환 양상과 섬진강 하천수 유입으로 발생하는 밀도류 이동 양상을 3차원 수치모델링 실험을 통해 연구하였다. $120m^3/s$의 섬진강 연평균 유량을 부과하여 실험을 진행하였다. 조위와 유속장, 염분장에 대해 각각 스킬분석(skill analysis)을 이용하여 모델을 검증하였으며, 그 결과 대부분 90%가 넘는 재현율을 보였다. 모델은 조류, 담수유입에 의한 염분장의 변화를 잘 재현하였다. 창낙조시의 유속장의 분포는 1~2.5 m/s의 범위를 보였다. 특히 노량과 대방, 그리고 창선수로에서 2.0 m/s 이상의 강한 흐름이 발생하는 것으로 나타났다. 지형적 요인에 의해 좌우되는 조석잔차류의 크기는 1~21 cm/s의 범위를 보였고, 섬진강 담수 유입으로 인해 형성된 표층의 밀도류는 여수해만으로 진행하는 12 cm/s의 이하의 남향류와 노량수로로 진행하는 4 cm/s 이하의 동향류가 발생한다. 특히 여수해만에서의 밀도류 흐름은 서쪽 해안에 편향되어 남하하는 양상을 보였다. 모델 내 경계면에서의 체적 수송량과 밀도류 분포를 분석한 결과, 평수기시 섬진강으로부터 광양만 권역에 유입된 담수는 $97.4m^3/s$ (81.5%)가 여수해만으로 유입되며 $22.1m^3/s$ (18.5%)가 진주만으로 유입되는 양상을 보였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.3418-3422
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• 2007

The neutron imaging technique was used to investigate the water discharge characteristics at PEMFC. Prior to investigation of water discharge characteristics, the linear attenuation coefficient for water at Neutron Radiography Facility (NRF) was calibrated. The feasibility test apparatus was consisted of pressurized air and water in order to simulate the actual operating PEMFC. The feasibility tests have been performed at 1-parallel serpentine type with 100 $cm^2$ active area and different air flow rate (1, 2, and 4 lpm). The total water volume variations at each condition were calculated from the neutron images. The water at channel is well discharged as soon as supplying the pressurized air into the PEMFC. However, because the water at MEA isn't removed the total water volume is constant after 150. Therefore more effective method is needed in order to discharge water at MEA, and the neutron imaging technique is helpful for it.