• 한국자동차공학회논문집
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• 제3권6호
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• pp.188-198
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• 1995

Turbulent flow characteristics of a lean-burn engine were qualitatively studied in order to obtain the optimum design parameters. 3-D lean-burn model engine was made up of an intake port, an intake valve and a cylinder. Computational grids were generated using PATRAN which was a FEM grid-generation software and numerical calculations were performed using STAR-CD. The predicted results showed that swirl and tumble structures were significantly changed by the valve lifts.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 정기총회 및 추계학술대회 논문집
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• pp.1594-1600
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• 2011

본 연구에서는 가장 최근에 NIST(National Institute of Standards and Technology)에서 LES(large eddy simulation)기법을 사용하여 개발한 3D 화재유동 해석용 FDS5의 중요한 기능 중 Werner-Wengle wall law의 성능을 평가하기 위하여 평행 평판에서의 유동을 조사하였다. 격자 형성을 위하여 $y^+$ 값은 11 이상으로 유지하도록 하였으며, 총 사용격자는 $32{\times}32{\times}32$를 사용하였다. 입구와 출구에서는 반복(periodic) 경계조건이 주어졌고, 양측면에서는 대칭(symmetry) 경계조건이 주어졌다. 충분히 발달된 난류에서의 유동조건을 조사하기 위하여 Re=10,700을 사용하였다. 시뮬레이션으로 구하여진 결과는 DNS(Direct Numerical Simulation) 결과 및 이론값과 비교하여 분석하였다. 또한 FDS 결과를 RANS의 난류 유동 해석 결과와도 비교하였다.

• 대한기계학회논문집B
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• 제22권4호
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• pp.428-439
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• 1998

Fluid flow and heat transfer have been numerically investigated for an oscillating flow in a tube with a regenerator. The regenerator is placed between hot and cold spaces which are heated and cooled at uniform temperature. An oscillating flow is generated by the piston motion at both ends of a tube. The time dependent, two-dimensional Navier-Stokes equations and energy equation are solved by using the finite-volume and moving grid method. The regenerator is adopted as Brinkmann-Forchheimer extended Darcy model. Numerical results are obtained for the flow and temperature fields, and described the effects of the oscillating frequency and amplitude ratio by the piston motion as well as the aspect ratio. The numerical results obtained indicate that the heat transfer between the tube wall and oscillating flow is increased as the oscillating frequency, amplitude ratio and the aspect ratio are increased.

• 대한조선학회논문집
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• 제48권2호
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• pp.147-157
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• 2011

A RANS(Reynolds averaged Navier-Stokes) based numerical method is developed for the evaluation of ship resistance and self-propulsion performances. In the usability aspect of CFD for the hull form design, the field grid around practical hull forms is generated by solving a grid Poisson equation based on the hull surface grid generated from station offsets and centerline profile. A body force technique is introduced to model the effects of the propeller in which the propeller loads are obtained from potential flow analysis using an unsteady lifting surface method. The free surface is captured by using a two-phase level-set method and the realizable $k-{\varepsilon}$ model is used for turbulence closure. The hull attitude in vertical plane, i.e., trim and sinkage, is calculated by using a quasi-steady method and then considered in the computation by translating and rotating the grid system according to the values. For the validation of the proposed method, the numerical results of resistance tests for KCS, KLNG, and KVLCC1 and of self-propulsion test for KCS are compared with experimental data.

• International Journal of Computer Science & Network Security
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• 제22권4호
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• pp.1-12
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• 2022

In order to overcome the power fluctuation issues in photovoltaic (PV) smart grid-connected systems and the inverter nonlinearity model problem, an adaptive backstepping command-filter and a double second order generalized Integrators (DSOGI) controller are designed in order to tune the AC current and the DC-link voltage from the DC side. Firstly, we propose to present the filter mathematical model throughout the PV system, at that juncture the backstepping control law is applied in order to control it, Moreover the command filter is bounded to the controller aiming to exclude the backstepping controller differential increase. Additionally, The adaptive law uses Lyapunov stability criterion. Its task is to estimate the uncertain parameters in the smart grid-connected inverter. A DSOGI is added to stabilize the grid currents and eliminate undesirable harmonics meanwhile feeding maximum power generated from PV to the point of common coupling (PCC). Then, guaranteeing a dynamic effective response even under very unbalanced loads and/or intermittent climate changes. Finally, the simulation results will be established using MATLAB/SIMULINK proving that the presented approach can control surely the smart grid-connected system.

• 한국산학기술학회논문지
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• 제18권3호
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• pp.673-680
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• 2017

흡수정은 댐이나 저수지에 저장된 물을 흡입하여 사용하는 설비이다. 흡입한 다량의 물은 화력 및 원자력 등의 대형 발전소의 냉각시스템에 사용된다. 특징으로 흡입 유량과 흡수정의 비가 작으면 흡입구 주변에서 유속이 증가한다. 이로 인해 와류나 선회류의 불균형 유동이 발생된다. 불균형 유동은 흡수정의 성능을 저하나 고장의 원인이 된다. 해결하기 위한 다양한 방법이 고안되고 있으나 최저수위 일 경우 정확한 해결 방법을 찾지 못하고 있다. 가장 효율적인 해결방법으로는 AVD를 설치하거나 관로를 길게하는 방법이 있다. 이렇게 설치된 구조물이 유동의 흐름을 균일하게 만들어 주기 때문이다. 본 논문에서는 관로의 길이와 AVD의 형태 변화에 따른 흡수정 내의 유동특성을 수치해석으로 분석한다. 수치해석을 위하여 수정의 흡입부, 섬프, 펌프의 3단계로 분리하여 모델링하였다. 격자는 해석의 정확도를 위해 흡입부는 비조밀, 흡수정과 AVD는 조밀하게 하였다. ANSYS ICEM-CFD 14.5를 이용하여 120~150만개의 격자를 생성하였고 Tetra grid와 Prism grid를 혼용하였다. 해석을 위해 상용 CFD 프로그램인 ANSYS CFX14.5의 SST 난류모델을 선정하였다. 조건으로 H.W.L 6.0m, L.W.L 3.5, Qmax 4.000 kg/s, Qavg 3.500 kg/s Qmin 2.500 kg/s로 설정하였다. 보텍스 각도와 속도분포로 해석한 결과는 다음과 같다. Ext E-type의 AVD를 설치한 흡수정이 최고수위 일때 합격하였다. 추후, Ext E-type을 기본으로 하여 최저수위일 때 만족하는 연구가 필요하다.

• 한국전산유체공학회지
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• 제20권2호
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• pp.1-6
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• 2015

In this study, a numerical prediction on propulsive performance of a ducted propeller in open water condition was carried out by solving Reynolds averaged Navier-Stokes(RANS) equation using computational fluid dynamics(CFD). A configuration of propeller Ka-470 inside duct 19A was considered. Hexahedral grid system was generated by dividing whole computational domain into three separate regions; propeller, duct and outer flow region. A commercial CFD software, ANSYS-CFX was used for numerical simulations. Results were compared with experimental data and showed considerable improvement in accuracy, in comparison to those from surface panel method which is based on potential flow assumption. The results also exhibited the importance of grid system within the gap between the inner surface of duct and blade tip for accurate prediction of propulsive performance of ducted propeller.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.343-349
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• 2011

A loosely coupling method is adopted to combine a computational fluid dynamics (CFD) solver and the comprehensive structural dynamics (CSD) code, CAMRAD II, in a systematic manner to correlate the airloads, vortex trajectories, blade motions, and structural loads of the HART I rotor in descending flight condition. A three-dimensional compressible Navier-Stokes solver, KFLOW, using chimera overlapped grids has been used to simulate unsteady flow phenomena over helicopter rotor blades. The number of grids used in the CFD computation is about 24 million for the isolated rotor and about 37.6 million for the rotor-fuselage configuration while keeping the background grid spacing identical as 10% blade chord length. The prediction of blade airloads is compared with the experimental data. The current method predicts reasonably well the BVI phenomena of blade airloads. The vortices generated from the fuselage have an influence on airloads in the 1st and 4th quadrants of rotor disk. It appeared that presence of the pylon cylinder resulted in complex turbulent flow field behind the hub center.

• Nuclear Engineering and Technology
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• 제33권1호
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• pp.73-82
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• 2001

Pressurized water reactor(PWR) fuel rods. which are continuously supported by a spring system called a spacer grid(SG), are exposed to reactor coolant at a flow velocity of up to 6-8 m/s. It is known that the vibration of 3 fuel rod is generated by the coolant flow, a so-called flow-induced-vibration(FIV), and the relative motion induced by the FIV between the fuel rod and the SG can wear away the surface of the fuel rod, which occasionally leads to its fretting failure. It is, therefore, important to understand the vibration characteristics of the fuel rod and reflect that in its design. In this paper, vibration analyses of the fuel rod with two different SGs were performed using both analytical and experimental methods. Updating of the finite element(FE) model using the measured data was performed in order to enhance confidence in the FE model of fuel rods supported by an SG. It was found that the modal parameters are very sensitive to the spring constant of the SG.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2010년 춘계학술대회논문집
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• pp.109-114
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• 2010

Interface tracking of two phase is significant to analyze multi-phase phenomena. The VOF(Volume of Fluid) and level set are well known interface tracking method. However, they have limitations to solve compressible flow and incompressible flow at the same time. CIP(Cubic Interpolate Propagation) method is appropriate for considering compressible and incompressible flow at once by solving the governing equation which is divided up into advection and non-advection term. In this article, we analyze the droplet impingement according to various We number using improved CIP method which treats nonlinear term once more comparison with original CIP method. Furthermore, we compare spread radius after droplet impingement on the wall with the experimental data and original CIP original CIP method, and it reduces the mass conservation error which is generated in the numerical analysis comparison with original CIP method.