• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.5
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• pp.734-741
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• 2003

This paper addresses the vibration mode shape Measurement technique utilizing a Continuous Scanning Laser Doppler Vibrometer (CSLDV). The continuous scanning capability is added to the conventional discrete Laser Doppler Vibrometer by reflecting the laser beams on the surface of the object using two oscillating mirrors. The bow scanning resulted from the proposed scanning method is eliminated by feedback control. The velocity output signal from the CSLDV is modulated to give the spatial velocity distribution in terms of coefficients which are obtained from the Fast Fourier Transformation of the time dependent velocity signal. Using the Chebyshev series from, the analysis of the vibration mode shape techniques for straight line scanning and 2 dimensional scanning are presented and discussed. The performance of the proposed SLDV is presented using the experimental results of the vibration mode shape of a cantilever and plate

• Journal of ILASS-Korea
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• v.26 no.3
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• pp.149-156
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• 2021

In this study, the behavior of the droplet colliding with parallel wires was analyzed by time-delay photography. The impact behavior modes and the critical capture speed were analyzed by changing fluids, the droplet velocity, the wire diameter and the distance between wires. Seven typical modes of impacting droplet on parallel wires were observed. The tendency of mode change was generally similar when the wire diameter was changed, but the increase of the wire diameter caused the increase of the droplet velocity at which the mode changed. The modes at the highest droplet velocity were the splitting mode when the wires were closest, the passing and splitting mode in the middle, and the passing mode when the wires were farthest apart. The critical capture speed increased as the wire diameter increased and the distance between wires decreased. The ethanol droplet showed the lowest critical capture speed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.6
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• pp.521-530
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• 2016

Weather radar is observation equipment that transmits electromagnetic waves and receives backscattered signals from the targets. The weather radar systems of the Korea Meteorological Administration have a doppler mode that can extract the target's radial velocity. However, the radial velocity over the maximum unambiguous velocity(${\nu}_m$) for which is in a trade-off relationship with the maximum unambiguous range is folded. Therefore, a dual PRF mode of which transmits and receives signals using two different PRFs(high and low) must be used to extend the vm while maintaining the maximum unambiguous range. Using a dual PRF mode, vm can be extended to the amount of lowest common denominator of two observed vm from high and low PRF. For this extension, we have developed a velocity unfolding algorithm of which uses several criteria for classification considering observed velocity differences between high and low PRF and their error boundary. Then, correction factors are calculated for each class and are applied to unfold radial velocity. The developed algorithm was applied to the Yong-In Testbed(YIT) radar and the generated better performance of radial velocity extraction than those of the previous system.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.2
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• pp.69-79
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• 1996

Dynamic stress intensity factors are derives when the crack is propagating with constant velocity under longitudinal shear stress in orthotropic disk plate. General stress fields of crack tip propagating with constant velocity and least square method are used to obtain the dynamic stress intensity factor. The dynamic stress intensity factors of GLV/GTV=1(=isotropic material or transversely isotropic material) which is obtained in out study nearly coincides with Chiang's results when mode Ⅲ stress is applied to boundary of isotropic disk. The D.S.I.F. of mode Ⅲ stress is greater when α(=angle of crack propagation direction with fiber direction) is 90° than that when α is 0°. In case of a/D(a:crack length, D:disk diameter)<0. 58, the faster crack propagation velocity, the less D.S.I.F. but when crack propagation velocity arrive on ghear stress wave velocity, the D.S.I.F. but when crack propagation velocity arrive on shear stress wave velocity, the D.S.I.F. unexpectedly increases and decreases to zero.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.1
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• pp.51-57
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• 2011

Information of the lateral velocity and the sideslip angle in a vehicle is very useful in many active vehicle safety applications such as yaw stability control and rollover prevention. Because cost-effective sensors to measure the lateral velocity and the sideslip angle are not available, reliable algorithms to estimation them are necessary. In this paper, a sliding mode observer is designed to estimate the lateral velocity. The side slip angle is estimated using the recursive least square with the disturbance observer and the pseudo integral. The estimated parameters from the combined estimation method are updated recursively to minimize the discrepancy between the model and the physical plant, and any possible effects caused by disturbances. The performance of the proposed monitoring system is evaluated through simulations and experiments.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.12
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• pp.1206-1212
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• 2012

The brake squeal propensity due to the friction-velocity curve is numerically investigated. The finite element models for the disc and pad are correlated with the modal test. In the friction-engaged system modeling, the friction function is linearized at the equilibrium. The damping term induced by friction-velocity slope is incorporated into the equations of motion. In the complex eigenvalue analysis, it is found that the pad shear mode is very sensitive to the friction curve. The results shows that the squeal propensity of the pad shear mode can be controlled by the design parameters such as pressure and stiffness.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.11 no.3
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• pp.93-101
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• 2002

The effect of nonlinear friction in the low velocity is dominant in precise controlled mechanisms and it is difficult to identify the friction effect. The friction model which Canudas suggested so called, LuGre model is well expressed the friction effect as Streibeck in the law velocity. But it\`s model parameters were estimated continuously in operation for precise control. This paper suggests the sliding mode controller and observer for compensating the friction effect. Experimental results for a ball-screw system show that the proposed method has a good performance especially in the low velocity.

• The Transactions of the Korean Institute of Power Electronics
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• v.3 no.3
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• pp.240-245
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• 1998

This paper presents an improved sliding mode controller design for induction motor. In place of the discontinuous control inputs, continuous inputs are proposed in order to remove the undesirable chattering phenomena, which represent major drawbacks of the sliding mode controller. The design strategy is illustrated with a microprocessor based implementation for the velocity control of an induction motor. An induction motor is operated under sling mode control such that the motor angular velocity follows a predetermined trajectory. The experimental results confirm the validity of the proposed method.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.50 no.5
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• pp.238-242
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• 2001

In this paper, we extracted design parameters for re-entrant mode microstrip directional coupler using FE(finite element) calculations. The microstrip directional coupler suffers from a poor directivity due to effect of the inhomogeneous dielectric including both dielectric substrate and air in microstrip transmission lines. Thus, the phase velocity of even mode is not equal to that of odd mode. In order to improve the directivity of microstrip directional coupler, a novel re-entrant mode microstrip directional coupler was employed. In microstrip configuration, the high directivity can be reached by matching the even- and odd-mode effective phase velocities. Through the values of capacitance obtained from 2-dimensional FE calculations, the phase velocities for each mode and the design parameter were extracted for the proposed parallel coupled-line configuration. Based on the extracted design parameter with phase matching condition, we designed and fabricated a 30dB directional coupler at 0.85GHz. Experimental results show good performance with excellent, isolation and directivity.

• Transactions of the Society of Information Storage Systems
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• v.1 no.1
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• pp.99-107
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• 2005

According to recent trend, hard disk drive(HDD) has been smaller and less weight. Therefore, it needs new method of writing position information. In this thesis, a new controller that is suitable for SSW is proposed. The controller accepted SSW technology that is used to write position information in current HDD industry. The important condition to perform SSW is to reach constant velocity decided from the head velocity profile as fast as possible. The constant velocity decides the positional accuracy of spiral pattern and setup time decides the capacity of HDD. The head velocity profile as a reference signal must be designed not to cause resonance mode. The proposed controller was designed with consideration of these 3 elements, and it properly works for SSW. The velocity profile designed with SMART control not only minimizes the jerk, but also does not cause the resonance mode of a plant. After designing a conventional PID controller, it compared with electrical spring technique and ZPET technique.