• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2006년도 추계학술대회 논문집
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• pp.78-85
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• 2006

Flows around two oscillating cylinders in side-by-side arrangement at Re=185 are simulated using immersed boundary method. The cylinders oscillate vertically with prescribed sinusoidal function in opposite directions in uniform cross-flow. Flow patterns and drag & lift forces are described by varying distance between two cylinders and oscillating frequency. Time series of flow patterns are investigated along with corresponding drag k lift coefficients.

• Journal of Astronomy and Space Sciences
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• 제25권4호
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• pp.415-424
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• 2008

곽영실 등(2008)의 연구로부터 고위도 하부 열권의 평균 수평바람 형태는 발산적인 흐름보다는 회전적인 흐름에 더 강하게 지배된다는 것이 확인되었다. 이 연구에서는, 곽영실 등(2008)의 연구의 연장으로, 회전적인 흐름의 척도인 소용돌이도(vorticity)를 유지시켜주는 강제(forcing)항들을 정량화하고 서로 비교 분석함으로써, 고위도 하부 열권에서의 전체 수평 바람장의 강한 회전 흐름을 유발시키는 주된 물리적인 과정을 규명하였다. 이 연구를 위하여 미 국립대기연구소(NCAR)의 열권-이온권 전기역학적 대순환 모델(Thermosphere-ionosphere Electrodynamic General Circulation Model, TIEGCM)을 이용하였다. 고위도 하부 열권의 소용돌이의 변화를 결정하고 유지시켜 주는 주된 강제항은 이온항력(ion drag)항과 수평 이류(horizontal advection)항으로 확인되었다. 늘림(stretching)항 또한 뚜렷한 기여를 하는 것으로 확인되었다. 소용돌이도 강제에 대한 IMF의 영향이 고도 105-110km부근까지 뚜렷하게 나타남이 확인되었다.

• 한국해안·해양공학회논문집
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• 제23권5호
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• pp.369-382
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• 2011

본 연구에서는 육상구조물에 작용하는 지진해일파력해석을 위하여 Navier-Stokes slover에 기초한 3차원 혼상류수치해석법을 적용하여 검토하였다. 여기서, 대상구조물을 육상저유탱크와 육상가옥으로 하여 호안과 육상구조물간의 이격거리에 따라 육상구조물에 작용하는 지진해일파력을 검토하였다. 또한 육상구조물에 작용하는 지진해일 파력의 추정을 위하여 항력만을 고려한 방법과 항력 및 관성력을 동시에 고려한 방법을 각각 적용하여 얻은 결과와 수치해석결과 및 설계기준에 의한 결과치를 비교 분석하였다. 이로부터 항력 및 관성력을 동시에 고려하여 추정한 지진해일파력이 항력만을 고려한 경우 보다 수치해석결과에 더 근접하는 것을 확인하였다.

• 한국해안해양공학회지
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• 제5권1호
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• pp.25-38
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• 1993

해양구조물의 케이블 반응 분석을 위한 다방향 파람 스펙트라의 수치모델이 조사되었다. 여러 형태의 전파모델을 파랑으로 인한 물입자의 흐름과 계류시스템을 예측하기 위해 사용하였다. 케이블에 작용하는 수동역학적 파력은 케이블의 경사에 평행한 방향과 접선방향에서의 항력과 관성력을 고려한 Morison 공식에 의해 평가되었다. 변위와 속도, 궤적, 위상면의 반응, 그리고 장력을 고려한 다방향 불규칙 파랑의 수치해석에 의하여 부체의 tether pc와 anchor point에서 계류시스템 케이블의 반응을 나타내었다. 서로 다른 항력 계수와 다양한 유의 파고, 그리고 선택된 파랑계수들이 이 분석에 고려되었다. 예제에서 고려된 특정 시스템을 통하여 파랑의 전파함수계수와 항력계수 뿐만 아니라 파랑의 주기와 높이가 케이블-부체시스템의 동적반응에 중요한 영향을 미침을 알 수 있었다.

• 대한조선학회논문집
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• 제56권6호
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• pp.507-514
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• 2019

Computational studies of accelerating flow around 2D Circular Cylinder was performed to investigate characteristics of wake field and drag forces. Previous studies had revealed that drag on the cylindrical body in accelerating flow is much greater than that in the flow with constant velocity; however, the underlying physics on the drag increase has not been clearly investigated. In order to investigate the drag increase and its relationship with wake development, this study employed a finite-volume based CFD code, Fluent 13.0 with k-ω SST model for turbulence effects. Inflows are modeled with varied accelerations from 0.4905 to 9.81m/s². The drag computed in the present study is in good agreement with previous studies, and clearly shows the increase compared to the drag on the body in the flow with constant velocity. The results also show that drag crisis observed at high Reynolds number in the case of the flow with constant velocity is also found in the case of accelerating flow. The analysis for wake and recirculation length shows that conventional vortex shedding does not occur even at high Reynolds number and the drag increase is larger at higher acceleration.

• 생물환경조절학회지
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• 제2권1호
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• pp.46-52
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• 1993

The wind pressure distributions were analyzed through the wind tunnel experiment to provide fundamental criteria for the structural design on the three-span arched house according to the wind directions. In order to investigate the wind force distribution, the variation of the wind force coefficients, the mean wind force coefficients, the drag force coefficients and the lift force coefficients were estimated from the experimental data. The results obtained are as follows : 1. The variation of the wind force with the wind directions on the side walls was the greatest at the upwind edge of the walls. The change of pressure from the positive to the negative on the side walls occurred at the wind direction of 30$^{\circ}$ in the first house and 60$^{\circ}$ in the third house. 2. The maximum negative wind force along the length of the roof appeared at the length ratio of 0-0.2, when the wind directions were 90$^{\circ}$ in the first house, 60$^{\circ}$ in the second house and 30$^{\circ}$ in the third house. 3. The maximum negative wind force along the width of the roof appeared at the width ratio and the wind direction of 0.4 and 0$^{\circ}$ in the first house, 0.4-0.6 and 30$^{\circ}$ in the second house and 0.6 and 30$^{\circ}$ in the third house, respectively. 4. The maximum mean positive and negative wind forces occurred at the wind direction of 60$^{\circ}$ and 30$^{\circ}$, respectively, on the side walls of the first house, and the maximum mean negative wind force on the roof occurred at the wind direction of 30$^{\circ}$ in third house. 5. The maximum drag and lift forces occurred at the wind direction of 30$^{\circ}$, and the maximum lift force appeared in the third house. 6. The parts to be considered for the local wind forces were the edges of the walls, the edges of the x-direction of the roofs, and the locations of the width ratio of 0.4 of the first and third house and the center of the width of the second house for the y-direction of the roofs.

• 한국터널지하공간학회 논문집
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• 제17권3호
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• pp.403-413
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• 2015

본 논문은 복합지반에서 쉴드 TBM 커터헤드의 회전속도 제어에 관한 실험적 연구이다. 복합지반에서는 암반을 굴착하는 디스크커터와 더불어 커터비트의 절삭 성능이 매우 중요하다. 이 연구에서는 특히 풍화토와 풍화암으로 이루어진 복합지반의 커터비트의 성능평가에 초점을 두었다. 이 연구를 위하여 실험실용으로 개발된 쉴드 TBM 커터비트 평가 장비를 이용하여 실내시험을 실시하였다. 복합지반은 공학적 상사성을 고려하여 조성하였다. 조성된 복합지반에서 쉴드 TBM 커터헤드 회전속도를 2, 3, 4 rpm으로 적용하여 각 커터비트에 작용하는 절삭력을 측정하고 회전에 따른 절삭력의 변화를 분석하였다. 실험결과로 부터 커터비트에 작용하는 절삭력은 지반경계부에서 급상승하는 경향을 보여주었다. 또한 이러한 상승되는 절삭력의 크기는 쉴드 TBM 커터헤드의 회전속도가 클수록 크게 나타났다. 이러한 결과로부터 복합지반에서 쉴드 TBM 커터헤드의 회전속도를 빠르게 할 경우 커터비트에 가해지는 위험요소가 더 크다는 것을 보여주고 있다. 따라서 복합지반조건에 현장 TBM 굴착 시 회전속도의 제어가 필요한 것으로 나타났으며 감속시키는 것이 비트에 가해지는 리스크를 저감시킬 수 있을 것이다.

• 설비공학논문집
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• 제13권3호
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• pp.194-199
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• 2001

The turbulent flow resistance of water solution with polymer is reduced as compared with that of pure water. This effects is named th drag reduction and offers the significant reduction of the pumping power and the energy consumption. But the intense shear forces and the high temperature experienced by the polymer solution when passing through the pipes cause the degradation a loss of drag reduction effectiveness. Especially, the degradation behavior is found to be strongly dependent on temperature. This mechanical and thermal degradation can be avoided by adding materials such as surfactant to the polymer solution, which enhance the bonding force between molecules. In the present study, Copolymer and SDS were utilized and they were mixed in 10 different mixture ratios, while total concentration was fixed as 100wppm. Degradation of Copolymer-SDS mixture solutions was investigated experimentally in closed loop at the temperature of $10^{\circ}C\; and\; 80^{\circ}C$ with various flow average velocities of 1.5 m/sec, 3.0m/sec, and 4.5m/sec. Degradation characteristics of polymer solution without surfactant show a radical loss of drag reduction effectiveness at high temperature. Degradation alleviation ability of surfactant is especially effective at high temperature. Consequently, this results show that the addition of surfactant to the polymer solution can control unfavorable degradation phenomena for high temperature systems.

• 한국가시화정보학회지
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• 제9권2호
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• pp.40-47
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• 2011

Tilt-rotor aircraft can be used in various fields because they have the capabilities of the vertical take-off and landing and the high-speed cruise flight. In the present study, the flow analysis of a tilt-rotor aircraft is conducted at various tilt angles. The lift and drag forces of the tilt-rotor aircraft are obtained and the wakes by the rotor-blade are visualized. The result shows that the rotor-blade affects the lift force in a hovering mode and the main wing has an influence on the lift force in a cruise mode. Additional thrust is required at the tilt angle of around 40 degree due to the least lift force. The drag force is dependent on the rotor-blade at overall tilt angles. The minus drag force appears between the tilt angles of 90 degree and 55 degree. Also, the drag force is dramatically increased at the other tilt angles. The wake by rotor-blade affects the flow around the fuselage of the tilt-rotor aircraft at the tilt angles of 75 degree and 60 degree.

• Wind and Structures
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• 제30권5호
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• pp.533-546
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• 2020

Large Eddy Simulation (LES) is used to study the effects of steady slot suction on the aerodynamic forces of and flow around a wall-mounted finite-length square cylinder. The aspect ratio H/d of the tested cylinder is 5, where H and d are the cylinder height and width, respectively. The Reynolds number based on free-stream oncoming flow velocity U_∞ and d is 2.78×10⁴. The suction slot locates near the leading edge of the free end, with a width of 0.025d and a length of 0.9d. The suction coefficient Q (= U_s/U_∞) is varied as Q = 0, 1 and 3, where U_s is the velocity at the entrance of the suction slot. It is found that the free-end steady slot suction can effectively suppress the aerodynamic forces of the model. The maximum reduction of aerodynamic forces occurs at Q = 1, with the time-mean drag, fluctuating drag, and fluctuating lift reduced by 3.75%, 19.08%, 40.91%, respectively. For Q = 3, all aerodynamic forces are still smaller than those for Q = 0 (uncontrolled case), but obviously higher than those for Q = 1. The involved control mechanism is successfully revealed, based on the comparison of the flow around cylinder free end and the near wake for the three tested Q values.