• 대한조선학회논문집
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• 제43권1호
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• pp.59-67
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• 2006

Evolution of the unsteady three-dimensional tip vortex in the wake field of a rectangular NACA 0012 hydrofoil in pitching motion is investigated. Measurements were made in CWC using PIV. A hydrofoil has an aspect ratio of 5 with chord length of 1 Oem. Pitching angle and mean angle of attack were set to $\pm$ $5^{\circ}$ and $10^{\circ}$, respectively. Frequency of oscillation was varied from 0.1 Hz to 1 Hz in order to study the effect of unsteadiness imposed by various frequencies, which correspond to the reduced frequency of K=0.1, 0.21, 0.52 and 1.05. Reynolds number based on chord length and free-stream velocity was $30\times$$10^{4}$ Phase-averaging technique was employed. Unsteadiness and variation of the size and characteristics of tip vortex at different reduced frequency were discussed.

• 한국전산유체공학회지
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• 제8권2호
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• pp.24-32
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• 2003

In this work, we propose a new idea of flapping airfoil design for optimal aerodynamic performance from detailed computational investigations of flow physics. Generally, flapping motion which is combined with pitching and plunging motion of airfoil, leads to complex flow features such as leading edge separation and vortex street. As it is well known, the mechanism of thrust generation of flapping airfoil is based on inverse Karman-vortex street. This vortex street induces jet-like flow field at the rear region of trailing edge and then generates thrust. The leading edge separation vortex can also play an important role with its aerodynamic performances. The flapping airfoil introduces an alternative propulsive way instead of the current inefficient propulsive system such as a propeller in the low Reynolds number flow. Thrust coefficient and propulsive efficiency are the two major parameters in the design of flapping airfoil as propulsive system. Through numerous computations, we found the specific physical flow phenomenon which governed the aerodynamic characteristics in flapping airfoil. Based on this physical insight, we could come up with a new kind of airfoil of tadpole-shaped and more enhanced aerodynamic performance.

• 한국해양공학회지
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• 제28권2호
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• pp.119-125
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• 2014

A vertical planar motion mechanism(VPMM) test was used to increase the prediction accuracy for the maneuverability of an underwater glider model. To improve the accuracy of the linear hydrodynamic coefficients, the analysis techniques of a pure heave test and pure pitch test were developed and confirmed. In this study, the added mass and damping coefficient were measured using a VPMM test. The VPMM equipment provided pure heaving and pitching motions to the underwater glider model and acquired the forces and moments using load cells. As a result, the hydrodynamic coefficients of the underwater glider could be acquired after a Fourier analysis of the forces and moments. Finally, a motion control simulation was performed for the glider control system, and the results are presented.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 춘계학술대회 논문집
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• pp.1321-1326
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• 2011

THE RAILWAY VEHICLE IS CONSISTS OF CARBODY, BOGIE AND WHEELSETS, EACH OF COMPONENTS IS CONNECTED WITH RIGID MASS, SPRING AND DAMPER. EACH OF COMPONENTS HAS TRANSLATION MOTIONS OF LONGITUDINAL (X AXIS), LATERAL (Y AXIS) AND VERTICAL (Z AXIS) DIRECTIONS, ROTATION MOTIONS OF X, Y, Z AXIS WHICH ARE NAMED ROLLING, PITCHING AND YAWING. THE VIBRATION MODE OF RAILWAY VEHICLE IS DIFFICULT TO FIND THE CHARACTERISTICS OF MOTION DURING THE OPERATION ON THE TRACK BECAUSE THESE HAPPEN TO INDEPENDENCE OR DUPLICATION MOTION CAUSED BY VEHICLE, WHEEL/RAIL AND TRACK IRREGULARITY ETC. IT IS NAMED AN ABNORMAL VIBRATION THAT THE VIBRATION, WHICH WAS PASSED THE PRIMARY AND SECONDARY SUSPENSION, IS AFFECTED TO THE PASSENGER WITHOUT DAMPING. THIS PAPER DESCRIBES AN EXPERIENCE EVALUATION TO FIND THE CAUSE OF AN ABNORMAL VIBRATION WHICH WAS HAPPEN AT OPERATING SPEED 60KPH ZONE DURING THE MAINLINE TEST.

• 대한기계학회논문집B
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• 제27권8호
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• pp.1142-1149
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• 2003

The present study describes a numerical analysis for simulation of the sloshing of flows with free-surface which contained in a rectangular tank moving in harmonic or pitching motion. The VOF function, representing the volume fraction of a cell occupied by the fluid, is calculated for each cells, which gives the location of the free-surface filling any some fraction of cells with fluid. The time-dependent changes of free-surface height are used for visualization subject to several conditions such as fluid height, horizontal acceleration, sinusoidal motion, and viscosity. The free-surface heights were used for comparing wall-force, which is caused by sloshing of flows. Damping effects by baffles were extensively investigated for various conditions in terms of baffle shape and position.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2002년도 춘계학술대회 논문집
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• pp.161-166
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• 2002

Recently, researches on precision machining of nato-order, especially in the field of optical components and semi-conductors have been under development very actively. A accuracy of machining and positioning in a critical issue in ultra-precision machining. This paper proposes a new positioning system which can give excellent dynamic characteristics and reduce errors in horizontal, vertical, pitching, and yawing motions. In this paper, we suggest a connecting mechanism (the couplings) to reduce motion errors such as chatter and runout while preserving the positioning accuracy. We verified the good performance in the new connecting systems with various coupling types, which we classified into the fixed type, the spring type, the aeroctatic-nozzle type, and the aeroctatic-porous type according to the way of reducing the chatter and error.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1996년도 한국자동제어학술회의논문집(국내학술편); 포항공과대학교, 포항; 24-26 Oct. 1996
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• pp.410-414
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• 1996

A visual servoing algorithm is proposed for a robot with a camera in hand. Specifically, novel image features are suggested by employing a viewing model of perspective projection to estimate relative pitching and yawing angles between the object and the camera. To compensate dynamic characteristics of the robot, desired feature trajectories for the learning of visually guided line-of-sight robot motion are obtained by measuring features by the camera in hand not in the entire workspace, but on a single linear path along which the robot moves under the control of a, commercially provided function of linear motion. And then, control actions of the camera are approximately found by fuzzy-neural networks to follow such desired feature trajectories. To show the validity of proposed algorithm, some experimental results are illustrated, where a four axis SCARA robot with a B/W CCD camera is used.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2004년도 추계학술대회 논문집
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• pp.14-17
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• 2004

A purpose of this visual experiment is to investigate the effect of reduced frequency qualitatively by examining wake pattern change for insect flying motion. Insect is composed of two pair wing with forewing and hindwing, flying motion of insect is performed pitching and plunging so it makes a separation over the wings. The separation affects at the wake pattern and changed wake pattern has an influence on lift, drag and propulsion. This experiment is conducted by using a smoke wire technique and a camera is fixed at hindwing to take a photograph of wake. An electronic device is mounted below test section to find exact the mean positional angle of wing. The reduced frequency in experiment is 0.15, 0.3 and 0.45. We obtained the result which that reduced frequency is closely related to wake pattern that determines flight efficiency.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2010년도 춘계학술대회 논문집
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• pp.30-35
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• 2010

The railway vehicle is a multi-body system running on the track which consists of carbody, bogie and wheelset, each of components is connected with rigid mass, spring and damper. each of components has translation motions of longitudinal (X axis), lateral(Y axis) and vertical(Z axis) direction, and rotation motions of X, Y, Z axis which are named Rolling, Pitching and Yawing. The vibration mode of railway vehicle is difficult to find the characteristics of motion during the operation on the track because these happen to independence or duplication motion caused by vehicle, wheel/rail and track irregularity etc. This paper presents the result of ramp test to show the bounce, roll, pitch and yaw mode frequency of the railway vehicle.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1998년도 Proceedings ICPE 98 1998 International Conference on Power Electronics
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• pp.119-124
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• 1998

This paper proposes a new repulsive-Maglev vehicle in which a vertical type PM linear synchronous motor (LSM) can levitate and propel simultaneously, independently of the vehicle speeds. A compact control method is developed which is based on the concept of controlling individually the levitation system by armature-current and the propulsion system by mechanical load-angle. The levitation-motion control experiments have carried out successfully together with positioning at standstill. The pitching motion has been compensated for very well by using the zero-phase-current control method proposed here.