• Structural Engineering and Mechanics
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• 제87권2호
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• pp.151-164
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• 2023

The latest earthquake's costly repairs and economic disruption were brought on by excessive residual drift. Self-centering systems are one of the most efficient ways in the current generation of seismic resistance system to get rid of and reduce residual drift. The mechanics and behavior of the self-centering system in response to seismic forces were impacted by a number of important factors. The amount of post-tensioning (PT) force, which is often employed for the standing posture after an earthquake, is the first important component. The energy dissipater element is another one that has a significant impact on how the self-centering system behaves. Using the damper as a replaceable and affordable tool and fuse in self-centering frames has been recommended to boost energy absorption and dampening of structural systems during earthquakes. In this research, the self-centering steel moment frame connections are equipped with cushion flexural dampers (CFDs) as an energy dissipator system to increase energy absorption, post-yielding stiffness, and ease replacement after an earthquake. Also, it has been carefully considered how to reduce permanent deformations in the self-centering steel moment frames exposed to seismic loads while maintaining adequate stiffness, strength, and ductility. After confirming the FE model's findings with an earlier experimental PT connection, the behavior of the self-centering connection using CFD has been surveyed in this study. The FE modeling takes into account strands preloading as well as geometric and material nonlinearities. In addition to contact and sliding phenomena, gap opening and closing actions are included in the models. According to the findings, self-centering moment-resisting frames (SF-MRF) combined with CFD enhance post-yielding stiffness and energy absorption with the least amount of permeant deformation in a certain CFD thickness. The obtained findings demonstrate that the effective energy dissipation ratio (β), is increased to 0.25% while also lowering the residual drift to less than 0.5%. Also, this enhancement in the self-centering connection with CFD's seismic performance was attained with a respectable moment capacity to beam plastic moment capacity ratio.

• 한국태양에너지학회 논문집
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• 제27권3호
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• pp.117-125
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• 2007

This study proposes a CFD(Computational Fluid Dynamics) analysis as a method of verification of the designed-data and a supplement of the insufficient experiences in geothermal system, which shows a rapid growth among the renewable energies. The followings are the results. FLUENT 6.2.12 is used as a CFD tool on this study, with the equations of continuity, motion, energy for unsteady flow through pipes and k-epsilon turbulent model. S-type model which has one borehole with diameter 12m by depth 206m and T-type model which has 3 boreholes with $12m{\times}20m{\times}206m$ are proposed, and also the boundary conditions are described. The temperature differences between temperatures by CFD analysis and by on-site measurement are less than 1.5%, this shows a high reliability of CFD analysis process which this study proposes. After 11 days simulation operated 12 hours interval On/Off mode, it is clearly predicted that the outlet temperatures of geothermal pipes are increased by $1.2^{\circ}C$, and $2.2^{\circ}C$ after 4 months. And the outlet temperatures of geothermal pipes increased with increase of the mass flow rates through the pipes. T-type model shows that the 4m distance between boreholes are reasonable because the temperatures at 2m and 6m from boreholes are nearly same.

• 대한조선학회논문집
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• 제50권5호
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• pp.355-363
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• 2013

Panel methods are essential tools for analyzing a fluid-flow problem around complex three dimensional bodies, but they lack ability to solve viscous effects. On the other hand, CFD methods are considered as powerful tools for analyzing fluid-flow characteristics including viscosity. However, they also have short falls, requiring more computing time and showing different results depending on the selection of turbulence models and grid systems. In this paper a hybrid scheme combining a panel method and a CFD method is suggested. The scheme adopts a panel method for far-field solution where viscous effects are negligible and a CFD method for the solution of RANS equations in near-field where viscous effects are relatively strong. The intermediate region between the far-field and near-field is introduced where the calculated field point velocities by the panel method are given as boundary velocities for the CFD method. To verify the scheme, calculated results, by a panel method, a CFD method and the hybrid scheme, for a two dimensional foil section are compared. The suggested hybrid scheme gives reasonable results, while computation time and memory can be dramatically reduced. By using the hybrid scheme efforts can be concentrated for the local flow near the leading and trailing edges, by providing more dense grid system, where detailed flow characteristics are required.

• 전기화학회지
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• 제18권4호
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• pp.172-181
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• 2015

고체산화물 연료전지는 다양한 응용분야에서 대체에너지로서 각광받고 있다. 본 논문은 평판형 anode 전극으로 들어가는 공기유량에 따른 SOFC의 I-V 그래프 특성에 대해 연구하였다. 본 연구를 위해, Butler-Volmer 반응속도 식이 상용 CFD코드인 FLUENT에 적용되었다. CFD로부터 얻어진 결과값은 문헌으로부터 참고한 실험데이터와 0.4 V ~ 1 V 범위에서 I-V 분극곡선이 잘 맞는 것을 보여줌으로써 그 유효성을 확인하였다. 연료전지의 수치적 계산은 각각 다른 유량조건 하에서 3D 구조를 이용하여 수행하였다. 결과는 수소, 산소 그리고 물의 농도 분포의 항목으로 제시하였다. 전산모사와 그 결과들은 Butler-Volmer 방정식을 사용자 정의 함수로 적용한 CFD기법이 공기 유량과 비표면적에 대한 조건을 확인하는데 사용될 수 있고, 작동조건 연구를 위한 지침이 됨으로써 연료전지 시스템의 성능을 향상시킬 수 있음을 보여준다.

• 전기화학회지
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• 제19권3호
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• pp.114-121
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• 2016

본 연구에서는 리튬이온전지의 충방전시 발생하는 발열특성을 CFD 모델링하고, 발열에 따른 충방전 특성을 해석하였다. 리튬이온전지는 직교 파우치형 구조로서 두께방향으로의 1차원계로 설정하여, 전류밀도 방정식, 열 및 물질전달 지배방정식을 도입하였다. Cut-off 전압이 3 V에서 충방전 전류밀도가 1C($17.5A/m^2$), 3C($52.5A/m^2$) 와 5C($87.5A/m^2$)에 대하여, 298K의 등온계와 충방전 전류밀도 별 발열계로 각각 설정하였다. 등온계와 발열계에서 모두 충방전 전류밀도가 높을수록 전지의 용량은 감소되는 것으로 나타났다. 등온계에 비하여 발열계에서 충방전 시간이 증가하였으며, 이는 발열에 의한 온도의 증가로 인해 전극의 평형전위가 감소하고, 리튬이온의 확산계수가 증가하기 때문인 것으로 고려된다. 또한, 리튬이온전지의 충전과 방전에 의한 열 발생 영향을 제어하기 위한 냉각효과를 분석하였다.

• 대한원격탐사학회지
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• 제38권5_1호
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• pp.471-484
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• 2022

본 연구는 전산유체역학 모델을 이용하여 기상청에서 운용하는 종관기상관측소(automated synoptic observing system, ASOS) 10개 지점을 대상으로 ASOS 주변 지형과 건물이 기온과 바람(풍속, 풍향) 관측 환경에 미치는 영향을 분석하였다. ASOS에서 최근 10년간 8월의 관측 자료를 기반으로 전산유체역학(computational fluid dynamics, CFD) 모델의 초기·경계 자료를 구축하였다. 실제 토지 피복을 고려한 경우와 모든 피복을 초지로 가정한 경우에 대해, 관측 고도에서 초기 기온 대비 기온 변화율을 비교함으로써 기온 관측 환경을 분석하였다. 기온 관측 환경은 관측 지점 주위의 토지 피복에 의한 영향을 많이 받았다. ASOS 주변에 지표면 온도가 높은 건물과 도로가 밀집한 경우에 기온 변화율이 크게 나타났다. 반면, 모든 토지 피복을 초지로 가정한 경우에는 초기 기온 대비 기온 변화율이 작았다. 실제 토지 피복을 고려하여 관측 고도의 유입류 대비 풍속 변화율과 풍향 변화를 비교함으로써 풍속과 풍향 관측 환경을 분석하였다. 풍속과 풍향은 ASOS 주변에 관측 고도보다 높거나 비슷한 높이의 지형과 건물 영향을 크게 받았으며, 원거리에 위치한 장애물에 의한 영향도 나타났다. 본 연구 결과는 종관기상관측소의 이전과 신설 단계에서 관측 환경 평가에 활용될 것이다.

• Journal of Biosystems Engineering
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• 제31권4호
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• pp.342-348
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• 2006

Aerial application using an unmanned agricultural helicopter became necessary for both labor saving and timely spraying. In the previous paper, a rotor system was developed and lift capability was evaluated. The experimental results were compared with simulated predictions using the CFD-ACE program. From the simulation, the relative velocity on the top surface of the blade airfoil increased, resulting in the pressure drop. The CFD analyses were revealed that a drag resistance on the leading edge of the airfoil, a wake at the trailing edge, and a positive pressure underneath the bottom surface were observed. As the results of the simulation, total lifts of 56.8, 74.4 and $95.0kg_f$ were obtained at the 6, 8 and $10^{\circ}$ of AAT (angle of attack), respectively. The simulation results agreed reasonably up to $10^{\circ}$ of AAT. However, at a greater AAT $(<12^{\circ})$ the simulated total lift continuously increased to $105kg_f$, comparing with a decreasing experimental total lift due to the lack of engine power. At a stiff angle of $18^{\circ}$ AAT, a wake was observed at the trailing edge of the airfoil. A rated operating condition determined from the previous paper was also verified through the simulation.

• 항공우주시스템공학회지
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• 제10권4호
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• pp.1-10
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• 2016

본 논문에서는 박막구조물 형태를 가진 풍력발전기 블레이드 패브릭스킨의 유체-구조연성해석을 수행하였다. 풍력발전기 블레이드는 5MW급의 중대형 풍력발전기로 선정하여 분석하였으며, 해석의 타당성을 높이기 위하여 다양한 참고문헌을 이용한 검증을 마쳤다. 본 해석에 앞서서, CFD해석과 모달해석을 나누어서 해석을 수행한 후 연성해석 진행하였다. CFD해석에서 나온 공기력 데이터를 장력으로 유지되는 박막구조물인 패브릭스킨에 적용시켜서 최종 구조물의 변형과 변형된 구조물로 인한 공기력의 변화를 확인하였다.

• 한국유체기계학회 논문집
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• 제17권6호
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• pp.109-114
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• 2014

After the Fukushima accident in 2011, it was revealed that nuclear power plant has the vulnerability to SBO accident and its extension situation without sufficient cooling of reactor core resulting core meltdown and radioactive material release even after reactor shutdown. Many safety systems had been developed like PAFS, hybrid SIT, and relocation of RPV and IRWST as a part of steps for the Fukushima accident, however, their applications have limitation in the situation that supply of feedwater into reactor is impossible due to high pressure inside reactor pressure vessel. The concept of hybrid heat pipe with control rod is introduced for breaking through the limitation. Hybrid heat pipe with control rod is the passive decay heat removal system in core, which has the abilities of reactor shutdown as control rod as well as decay heat removal as heat pipe. For evaluating the cooling performance hybrid heat pipe, a commercial CFD code, ANSYS-CFX was used. First, for validating CFD results, numerical results and experimental results with same geometry and fluid conditions were compared to a tube type heat pipe resulting in a resonable agreement between them. After that, wall temperature and thermal resistances of 2 design concepts of hybrid heat pipe were analyzed about various heat inputs. For unit length, hybrid heat pipe with a tube type of $B_4C$ pellet has a decreasing tendency of thermal resistance, on the other hand, hybrid heat pipe with an annular type $B_4C$ pellet has an increasing tendency as heat input increases.

• 한국수소및신에너지학회논문집
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• 제34권5호
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• pp.439-446
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• 2023

In this study, the computational fluid dynamics (CFD) simulations were conducted to verify the cooling capacity of the cryocooler used for pre-cooling of hydrogen gas. Based on the experimental results, the effect of the flow rate on a copper pipe attached to the bottom of the cryocooler was investigated. In this study, the temperature data was calculated through the change of boundary condition for heat flux in the copper pipe. In addition, the cooling capacity of the cryocooler for pre-cooling hydrogen gas was considered by calculating the cooling temperature according to the flow rate in the certified operating range. Consequently the pre-cooing system for hydrogen gas was validated with a reasonable accuracy through CFD simulations.