• Proceedings of the IEEK Conference
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• 2002.07a
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• pp.9-11
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• 2002

We improve the free-space optical interconnection efficiency by using circular aperture computer-generated hologram (CGH). In free-space optical interconnection system using CGH, the single CGH is composed of sub-CGHs, which can change the direction of input beams to desired output positions, by Fourier transform. Each sub-CGH is rectangular shape, so the input beams through each sub-CGH are transformed to sinc functions in output plane. The side lobes of each sinc function are superimposed in output plane and they result in detection error in output plane, so the detection efficiency is low. We use the circular shaped sub-CGHs in order to reduce the side lobe value in output plane instead of rectangular shaped sub-CGHs. The each input beam is transformed to first-order Bessel functions through circular shaped sub-CGHs in output plane. The side lobes of first-order Bessel functions us low values compared with side lobes of sinc function, so we can improve the detection efficiency in output plane. We use binary phase modulated CGH, and confirm this improvement results by simulation.

• Journal of the Society of Naval Architects of Korea
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• v.44 no.3 s.153
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• pp.219-227
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• 2007

A stereo-PIV (particle image velocimetry) technique is used to investigate the vortical structure of the wake behind a rotating propeller in the present study. A four bladed propeller is tested in a cavitaion tunnel without any wake screen. Hundreds of instantaneous velocity fields are phase-averaged to reveal the three dimensional spatial evolution of the flow behind the propeller. The results of conventional 2-D PIV are also compared with those of the stereo-PIV to understand the vortical structure of propeller wake deeply. The variations of radial and axial velocities in the 2-D PIV results seem to be affected by the out-of-plane motion. generating a little perspective error in the in-plane velocity components of the slipstream. The strong out-of-plane motion around the hub vortex also causes the perspective error to vary the axial velocity component a little at the near wake region. The out-of-plane velocity component had the maximum value of about 0.3U0 in the tip vortices and continued its magnitude in the wake region.

• Progress in Superconductivity
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• v.11 no.2
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• pp.112-117
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• 2010

We examine phase transition of the spin density wave and $\pi$ phase shifted superconductivity in the Fe pnictide superconductors. The phase diagram is described in the plane of the temperature T and the doping x with the combination of Ginzburg-Landau expansion of the free energy near the multi-critical temperature $T_c$ and the self-consistent numerical iterations of the gap equations. The phase separation or coexistence is determined by computing the 4-th order terms of the free energy which is confirmed by the numerical calculations. We can show the phase coexistence when the spin density wave is incommensurate. And the first order phase transition is observed near the boundary between commensurate and incommensurate spin density wave.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.421-424
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• 2002

The 3-D measurement using a sinusoidal grating pattern projection is very attractive because of its high measuring speed and high sensitivity. When a sinusoidal amplitude grating was projected on an object, the surface-height distribution of the object is translated into a phase distribution of the deformed grating image. The phase-acquisition algorithms are so sufficiently simple that high-resolution phase maps using a CCD camera can be generated in a short time. The PMP technique is discussed, and the analysis of the systematic errors, the calibration procedure designed to determined the optimal setting of the measurement parameters is illustrated. Results of measurements and calibrations on the measurement plane objects are described.

• International Journal of Automotive Technology
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• v.7 no.7
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• pp.821-826
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• 2006

This paper describes a rollover index (RI)-based rollover mitigation control (RMC) system. A rollover index which indicates an impending rollover has been developed by a roll dynamics phase plane analysis. The rollover index is calculated using the roll angle, the roll rate, the lateral acceleration and time to wheel lift (TTWL). A differential braking control law based on a 2-D bicycle model has been designed using the direct yaw control (DYC) method. An RMC threshold has been determined from the rollover index. The performance of the RMC scheme and the effectiveness of the proposed rollover index are illustrated using a vehicle simulator.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.11
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• pp.1249-1255
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• 2009

Cord-rubber composites widely used in tires show very complicated mechanical behavior such as nonlinearity and large deformation. Three-phase(cord, rubber and the interface) modeling has been used to analyze the stress distribution in the cord-rubber composites more accurately. In this study, finite element methods were performed using two-dimensional generalized plane strain element and plane strain element to investigate the stress distribution and effective modulus of cord-rubber composites. Neo Hookean model was used for rubber property and several interface properties were assumed for various loading directions. It was found that the interface properties affect the effective modulus and the distributions of shear stress.

• The Journal of the Korea institute of electronic communication sciences
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• v.1 no.1
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• pp.49-55
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• 2006

Applied by periodic Stimulating Currents in Bonhoeffer -Van der Pol(BVP) model, chaotic and periodic phenomena occured at specific conditions. The conditions of the chaotic motion in BVP comprised 0.7182< $A_1$ <0.792 and 1.09< $A_1$ <1.302 proved by the analysis of phase plane, bifurcation diagram, and lyapunov exponent. To control the chaotic motion, two methods were suggested by the first used the amplitude parameter A1, $A1={\varepsilon}((x-x_s)-(y-y_s))$ and the second used the temperature parameterc, $c=c(1+{\eta}cos{\Omega}t)$ which the values of ${\eta},{\Omega}$ varied respectlvly, and $x_s$, $y_s$ are the periodic signal. As a result of simulating these methods, the chaotic phenomena was controlled with the periodic motion of periodisity. The feasibilities of the chaotic and the periodic phenomena were analysed by phase plane Poincare map and lyapunov exponent.

• Aerospace Engineering and Technology
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• v.11 no.1
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• pp.145-157
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• 2012

The novel limit cycle analysis of the attitude control system using jet thrusters was presented based on a phase plane method by paper. It was shown in the software simulation results that the analysed results of the limit cycle was more accurate than those of the Haloulakos' method. But it was not verified in the real system. The proposed method is verified in the reaction control system for KSLV-I via an real time hardware in the loop simulation. It can be shown in this test that analyzed result of the limit cycle is very accurate.

• Transactions of The Korea Fluid Power Systems Society
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• v.1 no.1
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• pp.17-22
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• 2004

The goal of this paper is to improve the position control performance of pneumatic rotary actuator with variable brake using Magneto-Rheological Fluid. The air compressibility and the lack of damping of the pneumatic actuator bring the dynamic delay of the pressure response and cause the oscillatory motion. In this study, a variable rotary brake comprising Magneto-Rheological Fluid is equipped to the joint of a pneumatic manipulator. Experiments of step response have proved that the transient response of the manipulator could be improved compared with that of the conventional control algorithm by using a phase plane switching control algorithm.

• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.5
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• pp.195-201
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• 2005

In conventional Vehicle Stability Control (VSC) System, a control threshold is designed by average driver characteristics. Despite the stabilizing effort, VSC causes redundancy to an expert driver. An advanced VSC which has flexibility on its control property is proposed in this study. By using lateral velocity estimator, a control threshold is determined on side slip angle and angular velocity phase plane. Vehicle planar motion model based sliding controller is modified with respect to various control thresholds. The performance of the proposed VSC algorithm has been investigated by human-in-the-loop simulation using a vehicle simulator. The simulation results show that the control threshold has to be determined with respect to the driver steering characteristics. A VSC with variable control thresholds would provide an improvement compared to a VSC with a constant threshold.