• Wind and Structures
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• 제38권6호
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• pp.427-443
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• 2024

By using a computational program of three-dimensional aerostatic and aerodynamic stability analysis of long-span bridges under skew wind, the dynamic characteristics and structural stability(including the aerostatic and aerodynamic stability) of a three-tower cable-stayed-suspension hybrid bridge with main span of 1 400 meters are investigated numerically under skew wind, and the skew wind and aerostatic effects on the aerostatic and aerodynamic stability of three-tower cable-stayedsuspension hybrid bridge are ascertained. The results show that the three-tower cable-stayed-suspension hybrid bridge is a longspan structure with greater flexibility, and it is more susceptible to the wind action. The aerostatic instability of three-tower cable-stayed-suspension hybrid bridges is characterized by the coupling of vertical bending and torsion of the girder, and the skew wind does not affect the aerostatic instability mode. The skew wind has positive or negative effects on the aerostatic stability of the bridge, the influence is between -5.38% and 4.64%, and in most cases, it reduces the aerostatic stability of the bridge. With the increase of wind yaw angle, the critical wind speed of aerostatic instability does not vary as the cosine rule as proposed by the skew wind decomposition method, the skew wind decomposition method may overestimate the aerostatic stability, and the maximum overestimation is 16.7%. The flutter critical wind speed fluctuates with the increase of wind yaw angle, and it may reach to the minimum value under the skew wind. The skew wind has limited effect on the aerodynamic stability of three-tower cable-stayed-suspension hybrid bridge, however the aerostatic effect significantly reduces the aerodynamic stability of the bridge under skew wind, the reduction is between 3.66% and 21.86%, with an overall average drop of 11.59%. The combined effect of skew and static winds further reduces the critical flutter wind speed, the decrease is between 7.91% and 19.37%, with an overall average decrease of 11.85%. Therefore, the effects of skew and static winds must be comprehensively considered in the aerostatic and aerodynamic stability analysis of three-tower cable-stayed-suspension hybrid bridges.

• 해양환경안전학회지
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• 제25권7호
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• pp.982-990
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• 2019

최근 점점 더 많은 연구자와 정부에서 해양에너지 자원 개발에 대한 관심이 고조되고 있다. 장죽수도는 조류에너지 밀도가 높아 조류 발전소를 건설하기에 적합한 잠재적 후보지 중 하나이다. 따라서 본 연구에서는 ADCIRC 모델을 이용하여 장죽수도의 조류자원의 잠재량을 평가하기 위한 수치적 접근방식을 제시하고, 내부 코드를 이용하여 조석 특성을 입력 매개변수로 활용하여 1 MW급 규모의 조류에너지 변환장치를 대상으로 4개의 레이아웃으로 배열하고 후류 효과로 인한 연간 에너지 생산량에 관한 수치해석을 수행하였다. 그 결과 효율이 가장 좋은 배치는 연간 최대 12.96 GWh/year의 에너지를 생성할 수 있으며, 이 값은 후류 효과로 인한 에너지 손실을 고려하면 연간 0.16 GWh씩 감소될 수 있음을 보였다. 또한, 창낙조 때 터빈 요 각도를 변경함으로써 이 요소가 에너지 추출에 미치는 영향을 분석하였으며, 터빈 배열은 터빈 요 각도가 346°와 164°(북쪽에서 시계 방향으로)일 때 대조기와 소조기에서 차례로 최대 조류 에너지를 얻을 수 있었다.

• 오토저널
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• 제14권4호
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• pp.90-96
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• 1992

The effect of base cavities on the drag of a simplified tractor-trailor model for Re=4.1*10$^{5}$ is investigated experimentally. Three different types of base cavities are studied in this work. They are solid-wall, slitted-wall, and slotted-wall cavities. Slotted-wall cavity is found to be most effective for drag reduction. A maximum of 11% reduction in the zero-yaw drag coefficient is achieved with the slotted wall cavity.

• 한국해양공학회지
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• 제13권1호통권31호
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• pp.18-22
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• 1999

One of the problem areas in designing a barge is its resistance and corese stability when it is towed by a tugboat. In this paper, as a part of design of a incinerating vessel, the results of some experimental studies on the effect of various kinds of anti-yawing skegs to the course keeping stability and on the additional resistance caused by them were summarized.

• 한국공작기계학회논문집
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• 제11권5호
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• pp.7-14
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• 2002

In order to achieve high precision machine tools, the research for performance enhancement of feed drive systems is required. Development of the high speed feed drive system has been a major issue for the past few decades in machine tool indestries. Because table levitation system decrease the table weight, an effect of reaction by weight is minimized and lost motion can be removed at maximum. In case fled system is designed with drive motor, ball screw and support bearing load capacity selection, an effect of decrease of the table weight exist. So, the table weight through an effect of decrease call it into the realization of cost down. Stick-slip friction has a great influence on the contouring accuracy of CNC machine tools. In this paper table levitation system has been developed for the stick-slip in a fled drive systems.

• Wind and Structures
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• 제29권6호
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• pp.457-469
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• 2019

In this paper, a numerical solution is presented for supersonic flutter analysis of cantilever non-symmetric functionally graded (FG) sandwich plates. The plate is considered to be composed of two different functionally graded face sheets and an isotropic homogeneous core made of ceramic. Based on the first order shear deformation theory (FSDT) and linear piston theory, the set of governing equations and boundary conditions are derived. Dimensionless form of the governing equations and boundary conditions are derived and solved numerically using generalized differential quadrature method (GDQM) and critical velocity and flutter frequencies are calculated. For various values of the yaw angle, effect of different parameters like aspect ratio, thickness of the plate, power law indices and thickness of the core on the flutter boundaries are investigated. Numerical examples show that wings and tail fins with larger length and shorter width are more stable in supersonic flights. It is concluded for FG sandwich plates made of Al-Al₂O₃ that increase in volume fraction of ceramic (Al₂O₃) increases aeroelastic stability of the plate. Presented study confirms that improvement of aeroelastic behavior and weight of wings and tail fins of aircrafts are not consistent items. It is shown that value of the critical yaw angle depends on aspect ratio of the plate and other parameters including thickness and variation of properties have no considerable effect on it. Results of this paper can be used in design and analysis of wing and tail fin of supersonic airplanes.

• International Journal of Aeronautical and Space Sciences
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• 제1권1호
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• pp.70-80
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• 2000

The attitude knowledge error model is formulated for specifically KOMPSAT attitude determination system using the Lefferts/Markley/Shuster method, and the attitude determination(AD) error analysis is performed so as to investgate the on-board attitude determination capability of KOrea Multi-Purpose SATellite(KOMPSAT) using the covariance analysis method. Analysis results show there is almost no initial value effect on Attitude Determination (AD) error and the sensor noise effects on AD error are drastically decreased as is predicted because of the inherent characteristic of Kalman filter structure. However, it shows that the earth radiance effect of IR-sensor(earth sensor) and the bias effects of both IR-sensor and fine sun sensor are the dominant factors degrading AD error and gyro rate bias estimate error in AD system. Analysis results show that the attitude determination errors of roll, pitch and yaw axes are 0.056, 0.092 and 0.093 degrees, respectively. These numbers are smaller than the required values for the normal mission of KOMPSAT. Also, the selected on-orbit data of KOMPSAT is presented to demonstrate the designed AD system.

• International Journal of Fluid Machinery and Systems
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• 제1권1호
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• pp.47-56
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• 2008

The flow behind the variable area nozzle which corresponds to the flow at the leading edge of the impeller was measured with a 3-hole yaw probe and calculated with CFD. Two nozzle throat-areas were investigated. One is the smallest and the other is the largest opening for the variable nozzle. Test results agreed with the calculated results qualitatively. The leakage flow through the tip clearance of the nozzle vane significantly affected the flow field downstream of the nozzle vane with the smallest opening. However, the effect on leakage flow on the flow field downstream of the nozzle vane with the largest opening was very weak and the effect of wake is dominant.

• 대한기계학회논문집
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• 제8권6호
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• pp.526-535
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• 1984

본 연구에서는 개인용 컴퓨터 정도를 사용하여서도 각 성능을 계산할 수 있고 또 실제 상황이 비교적 잘 반영될 수 있는 모델을 채택하였다. 한편으로 이 모델의 적합성 여부도 검토하여 해석 결과의 적용한계를 추측하고져 하였다.

• 제어로봇시스템학회논문지
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• 제11권3호
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• pp.246-253
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• 2005

An experimenal study on flight control of high-speed AEV(Aero-levitation Electric Vehicle) scale model in wind-tunnel is conducted. The AEV is to fly at very low altitude in predesigned track so that it is always under the wing-in-ground effect. The experiment is intended to fly the scale model to follow the predesigned altitude schedule while holding its attitude (pitch, roll, and yaw). Especially, the altitude changes for climb, cruise, and descent with constant pitch angle are most important maneuvers. The experiment shows that the required mission flights can be performed with appropriate sensors, processors, and actuators.