• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2006년 제4회 한국유체공학학술대회 논문집
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• pp.415-421
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• 2006

The unsteady flow calculation around the proprotor of Smart UAV was conducted. Using the flight scenario of SUAV which composed of hover, transition, and airplane mode, the aerodynamic analysis of proprotor were performed for the variation of collective pitch, rpm, forward speed, and tilt angle. The unsteady compressible Navier-Stokes equations were used for the calculation and the dynamic overset grid technique was applied for the rotating proprotor. The aerodynamic performance of proprotor calculated in this way were validated by comparing with the performance data obtained from the blade element momentum method.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.929-929
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• 2005

In this study, computational demonstrations for the flutter suppression are presented for the 3-DOF airfoil system with oscillating flap. Advanced computational methods such as computational fluid dynamics (CFD) and computational structural dynamics (CSD) are used and a simultaneous coupling method has been developed to accurately conduct flutter analyses. In addition, optimal control theory is integrated into the CFD based flutter analysis method to construct the coupled aeroservoelastic analysis system for the airfoil with oscillating flap. For a well-defined typical section model, fundamental unsteady aerodynamics and flutter characteristics are investigated. Finally, to show the effectiveness of flutter control the physical aeroelastic responses are directly compared between the open loop and the closed loop systems.

• Nuclear Engineering and Technology
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• 제38권2호
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• pp.147-154
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• 2006

Thermal fatigue of the coolant circuits of PWR plants is a major issue for nuclear safety. The problem is especially accute in mixing zones, like T-junctions, where large differences in water temperature between the two inlets and high levels of turbulence can lead to large temperature fluctuations at the wall. Until recently, studies on the matter had been tackled at EDF using steady methods: the fluid flow was solved with a CFD code using an averaged turbulence model, which led to the knowledge of the mean temperature and temperature variance at each point of the wall. But, being based on averaged quantities, this method could not reproduce the unsteady and 3D effects of the problem, like phase lag in temperature oscillations between two points, which can generate important stresses. Benefiting from advances in computer power and turbulence modelling, a new methodology is now applied, that allows to take these effects into account. The CFD tool Code_Saturne, developped at EDF, is used to solve the fluid flow using an unsteady L.E.S. approach. It is coupled with the thermal code Syrthes, which propagates the temperature fluctuations into the wall thickness. The instantaneous temperature field inside the wall can then be extracted and used for structure mechanics computations (mainly with EDF thermomechanics tool Code_Aster). The purpose of this paper is to present the application of this methodology to the simulation of a straight T-junction mock-up, similar to the Residual Heat Remover (RHR) junction found in N4 type PWR nuclear plants, and designed to study thermal striping and cracks propagation. The results are generally in good agreement with the measurements; yet, in certain areas of the flow, progress is still needed in L.E.S. modelling and in the treatment of instantaneous heat transfer at the wall.

• 한국해양환경ㆍ에너지학회지
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• 제12권1호
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• pp.9-14
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• 2009

2차원 비정상의 RANS 방정식을 이용하여 피치가 고정된 3개 혹은 4개의 날개(hydrofoil)를 가지는 조류발전용 수직축 터빈주위의 비정상 유동장 해석을 수행하였다. 상용수치해석코드인 Fluent를 이용하여, 균일류에 놓인 $NACA65_3$-018날개에 대하여 받음각(angle of attack)의 변화를 주며 계산되는 유체력을 실험값과 비교하였고, 이를 바탕으로 대표적인 수직축 조류발전 터빈의 특성을 2차원적으로 고찰하였다. 사용된 수치해법은 대상 유동을 효과적으로 모사할 수 있음을 확인 하였고, 터빈의 최적 효율은 날개수 및 유속 대비 회전수 등의 적절한 조합으로 실현 될 수 있음을 파악하였다.

• 한국소음진동공학회논문집
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• 제15권7호
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• pp.788-798
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• 2005

The monopole theory has long been used to model air-pumped effect from the elastic cavities in car tire. This approach models the change of an air as a Piston moving backward and forward on a spring and equates local air movements exactly with the volume changes of the system. Thus, the monopole theory has a restricted domain of applicability due to the usual assumption of a small amplitude acoustic wave equation and acoustic monopole theory This paper describes an approach to predict the air-pumping noise of a car tyre with CFD/Kirchhoff integral method. The tyre groove is simply modeled as piston-cavity-sliding door geometry and with the aid of CFD technique flow properties in the groove of rolling car tyre are acquired.'rhese unsteady flow data are used as a air-pumping source in the next CFD calculation of full tyre-road geometry. Acoustic far field is predicted from Kirchhoff integral method by using unsteady flow data in space and time which is provided by the CFD calculation of full tyre-road domain. This approach can cover the non-linearity of acoustic monopole theory with the aid of Non-linear governing equation in CFD calculation. The method proposed in this paper is applied to the prediction of air-pumping noise of simply modeled car tyre and through the predicted results, the influence of nonlinear effect on air-pumping noise propagation is investigated.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2007년도 정기총회 및 학술발표대회
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• pp.449-453
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• 2007

After over a century of effort by researchers and engineers, the problem of bluff body flow, in particular vortex shedding frequency, remains almost entirely in the empirical, descriptive realm of knowledge. Computational methods have been systematically applied for vortex-induced vibrations of the cable-stayed bridge with steel composite deck by unsteady wind loadings due to vortex-shedding. The focus of this paper is to predict the vortex-induced vibration of the cable-stayed bridge with steel composite deck based computational fluid dynamics(CFD).

• EDISON SW 활용 경진대회 논문집
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• 제6회(2016년)
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• pp.27-34
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• 2016

본 연구에서는 EDISON CFD의 2D_Incomp_P 해석자를 이용하여 0.16부터 1,000,000까지 다양한 레이놀즈수에서 실린더의 유동 특성을 연구하였다. 임계 레이놀즈수 이하에서 실험값과 유사한 압력분포도를 제작하여 해석 결과의 타당성을 검증하였다. 레이놀즈수에 따른 항력계수의 그래프를 제작하여 항력계수의 값이 레이놀즈수의 변화에 대해 선형적으로 변화하는 것을 연구하였다. 같은 속도장일 때 특성길이에 따른 유동장의 차이점도 연구하기 위하여 특성길이에 변화를 주어 해석을 진행하였고, 특성길이가 길수록 박리가 빠르게 발생하는 것을 알게 되었다.

• 한국항공우주학회지
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• 제37권5호
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• pp.425-432
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• 2009

본 연구에서는 오일러 CFD코드에서 얻은 데이터를 이용하여 2차원 익형의 비정상 공력하중을 모델링하고 예측할 수 있는 신경망의 능력을 확인하였다. 신경망 모델은 감독자 관리 학습을 기반으로 하여 르벤버그-마쿼트 알고리즘, 그리고 여기에 유전알고리즘을 결합시킨 혼합형 유전알고리즘을 사용하여 구성하고 각 경우에 대하여 그 효율성을 비교 분석하였다. 복잡한 시스템을 모사하는 신경망을 학습시키는 데는 혼합형유전알고리즘이 더 효율적이라는 것을 보였으며 신경망모델에 의한 2차원 익형의 비정상공력하중 예측결과 실제 수치결과와 비교적 정확하게 일치하여 신경망 모델이 축소모델로서의 기능을 발휘하는 것을 입증하였다.

• 한국항해항만학회지
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• 제27권3호
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• pp.253-258
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• 2003

To evaluate the unsteady motion in laterally berthing maneuver, it is necessary to grasp very clearly the magnitude and properties of the hydrodynamic forces acting on ship hull in shallow water. In this study, numerical calculation was made to investigate quantitatively the hydrodynamic force according to the water depth for Wigley model using the CFD (Computational Fluid Dynamics) technique. Comparing the computational results to the experimental ones, the validity of the CFD method was verified. The numerical solutions evaluated the hydrodynamic force with good accuracy, and then captured the features of the flow field around the ship in detail. The transitional lateral force in a state ranging from rest to uniform motion is modeled by using the concept of the circulation.

• 수산해양교육연구
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• 제27권5호
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• pp.1303-1309
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• 2015

The behavior and flow characteristics of the floating wave energy converter were analyzed by using CFD in this study. The average significant wave height was confirmed as 0.5~2.0m from the Korean coastal sea area. This study was carried out by selecting a range of 1.0~1.6m in the wave height to simulate the operations of realistic wave energy converter system. The principle of a piston wave maker was applied in order to produce periodic wave. The behavior of the wave energy converter and the state of the wave overtopping according to the generated periodic wave were confirmed through the unsteady three-dimensional flow analysis. It was found that the wave overtopping rate according to the generated periodic wave was in range of the 11.6~30.0 kg/s.