• Journal of Mechanical Science and Technology
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• v.17 no.7
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• pp.1095-1103
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• 2003

The Holographic Particle Velocimetry system can be a promising optical tool for the measurements of three dimensional particle velocities. In this study, the holographic particle velocimetry system was used to measure the sizes and velocities of droplets produced by a commercial full cone spray nozzle. As a preliminary validation experiment, the velocities of glass beads on a rotating disk were measured with uncertainty analysis to identify the sources of all relevant errors and to evaluate their magnitude. The error of the particle velocity measured by the holographic method was 0.75 ㎧, which was 4.5% of the known velocity estimated by the rotating speed of disk. The spray droplet velocities ranged from 10.3 to 13.3 ㎧ with average uncertainty of ${\pm}$ 1.6 ㎧, which was ${\pm}$ 14% of the mean droplet velocity. Compared with relatively small uncertainty of velocity components in the normal direction to the optical axis, uncertainty of the optical axis component was very high. This is due to the long depth of field of droplet images in the optical axis, which is inherent feature of holographic system using forward-scattering object wave of particles.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.10
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• pp.184-193
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• 2001

In vector control technique, stator currents of an induction motor are transformed to equivalent d-q currents in a reference frame consist of d and q axis, each of which is coincide with flux and torque direction respectively. Since the current in q-axis is related to the torque in a synchronously rotating frame, torque is estimated as a function of q-axis current and flux. In this paper, a method to estimate torque of an induction motor based on the measurement of 3-phase currents and rotating velocity of a rotor is presented. Graphic-programming is used to measure signals, to estimate the torque and to show the result in the form of user friendly graph in window environment. To stabilize the fluctuation of estimated torque caused from the small measurement error of the rotor velocity, the stator current is reconstructed in a program based on measured signals. The experimental results executed under the velocity of 500 rpm, 1500 rpm without load and 1500 rpm with load show that the proposed method estimates the torque very well.

• Journal of Wind Energy
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• v.9 no.4
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• pp.9-15
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• 2018

In a previous study, a technique for measuring wind speed and direction by using a roll-rotating three-axis ultrasonic anemometer was proposed and verified by wind tunnel tests. In the tests, instead of a roll sensor, roll angle was trimmed to make no up flow in the transformed wind speeds. Verification was done in point of the residual error of the rotation effect treatment. In this study, roll angle was measured from the roll motor encoder and the transformed wind speed and direction on the test section axis were compared with the ones provided to the test section. As a result, up to yaw $20^{\circ}$ at a wind speed of 12 m/sec or over, the RMS error of wind speed was within the double of the ultrasonic anemometer error. But at yaw $30^{\circ}$, it was over the double of the ultrasonic anemometer error. Regardless of wind speed, at yaw $20^{\circ}$ and $30^{\circ}$, the direction error was within the double of the ultrasonic anemometer error. But at yaw $10^{\circ}$ or less, it was within the error of the ultrasonic anemometer itself. This is a very favorable characteristic to be used for wind turbine yaw control.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10a
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• pp.315-318
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• 1996

In this paper a new positioning method for cylindrical work pieces on rotating supports is studied. A work piece on a rotating axis is positioned by an impact drive mechanism (IDM) whose driving parameters are steadily updated by observing the object movement. The application of this actuator and the use of a multi-functional PC board for all necessary input and output operations such as e.g. data acquisition or wave form generation allow an alignment with a precision of less than 1.mu.m in a relatively short time and at low cost compared to conventional methods.

• 한국가시화정보학회:학술대회논문집
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• 2004.11a
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• pp.36-39
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• 2004

In this study, we present the theoretical, numerical and experimental results of the sink flow from a rotating, circular tank Strikingly enough, when the upper free surface was set with no-slip boundary conditions, the Ekman boundary-layer develops not only above the bottom surface but under the free surface. The sink fluid is coming from the two Ekman layers, and the mass transfer from the bulk, inviscid region is dependent on the rotational speed. It is also remarkable to see that all the fluid gathered along the axis flows through a rapidly rotating fluid column with almost the same size as the hole.

• Journal of Magnetics
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• v.22 no.1
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• pp.122-132
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• 2017

This study dealt with the design process of the 78 kW permanent magnet synchronous generator for engines. After the calculation of the basic dimensions through a theoretical method in the process of initial model design, FEA (finite-element analysis) and a d,q-axis equivalent circuit were used to identify the generator characteristics depending on the number of poles. With the use of the space harmonic analysis method, the back-EMF (electromotive force) and THD were checked, and then the number of slots was determined. In addition, the most optimized generator dimensions were determined through a sizing optimization technique. Based on this, the optimum model with enhanced efficiency, material costs, and temperature characteristics was derived, and the availability of the design method was confirmed through a comparative analysis of the initial and optimum models.

• Journal of Magnetics
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• v.22 no.1
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• pp.65-68
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• 2017

This paper reports simulation and evaluation of the magnetic flux density (MFD) of a rotating Halbach magnet (RHM) composed of a rotating inner Halbach cylinder (HC) and a fixed outer HC. We first chose the dimension of a single HC, then determined the dimensions of an inner and outer HC to get MFD = 2 T. Simulation results were used to guide fabrication of an RHM; its magnetic field in the central axis direction agreed well with simulated values.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.349-350
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• 2009

Superconducting magnetic bearing and rotating system were developed by utilizing the high magnetization YBaCuO superconductor. The pellets prepared by quasi-melt process had a high magnetic levitation force and a high magnetic attractive force. The shaft also could be moves its position and orientation of the rotating axis freely. Is is essential to enhance the materials properties and to improve the system design for the application of the system to industrial purpose.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.809-813
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• 2006

We have studied the optical properties of the biaxial film such as fast axis, retardance and the change of polarization state between crossed polarizer using dual rotating retarder polarimeter. We have developed a novel simulation model, which could explain well the experimental results, and found that it could be used to optimize the compensation film in LCD for improving wide-viewing property.

• Tribology and Lubricants
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• v.30 no.3
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• pp.131-138
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• 2014

This study investigates the effects of the slopes of the rotational axis and bearing preloads on the natural frequencies and onset speeds of the instability of a rotor supported on gas foil bearings (GFBs). The predictive model for the rotating system consists of a rigid rotor supported on two gas foil journal bearings (GFJBs) and a pair of gas foil thrust bearings (GFTBs). Each GFJB supports approximately half the rotor weight. As the slope of the rotational axis increases from $0^{\circ}$(horizontal rotor operation) to $90^{\circ}$(vertical rotor operation), the applied load on the GFJB owing to the rotor weight decreases. The predictions show that the natural frequency and onset speed of instability decrease significantly with an increase in the slope of the rotational axis. In a parametric study, the nominal radial clearance and preload for the GFJB were changed. In general, a decrease in the nominal radial clearance lead to an increase in the natural frequency and onset speed of instability. For constant assembly clearance, the decrease in the preload changed the natural frequency and onset speed of instability with insignificant improvements in the rotordynamic stability. The present predictions can be used as design guidelines for GFBs for oil-free high-speed rotating machinery with improved rotordynamic performance.