• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1223-1228
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• 2001

We have been developing the pantograph for Korean High Speed Train for the last five years. To fulfil the following requirements at designed speed of 350km/h ： 1) contact loss less than 1 ％, 2) aerodynamic noise less than 91dB, 3) average uplift force less than 200N, the pantograph has been modified two times since the first prototype pantograph was manufactured, By means of the following up characteristic test, low speed wind tunnel test, and high speed wind tunnel test for the prototype pantographs, we found that the aerodynamic uplift force did not exceed l60N at speed up to 350km/h and the aerodynamic noise was less than 88dB, that the following up characteristics of the prototype pantograph was excellent.

• International Journal of Fluid Machinery and Systems
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• v.4 no.2
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• pp.289-306
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• 2011

In the development of very high head pumped storage projects, one of the critical problems is the strength of pumpturbine runners. Data obtained by stress measurements of high head pump-turbine runners indicated that dynamic stress due to the vibration of runner might be detrimental, possibly to cause fatigue failure, if the runner were designed without proper consideration on its dynamic behaviour. Numerous field stress measurements of runners and model tests conducted with hydrodynamic similarity revealed that the hydraulic excitation force developed by the interference of rotating runner blades with guide vane wakes sometimes would induce such heavy vibration of runner. Theoretical and experimental investigations on both the hydraulic excitation force and the natural frequencies of runner have been conducted to explore this forced vibration problem.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.7 s.112
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• pp.697-703
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• 2006

This article proposes a new technique for the reduction of vibration and noise in the geared system by adjusting the distance between gear shafts. The vibration and noise may be produced by the abnormal force applied to the tooth face. And the force may be the cause of ununiform velocity in the driven shaft. If the velocity is obtained to be uniform by adjusting the distance between shafts. the vibration and noise may be reduced to some extent. In order to review, a dynamic analysis model for the gear train used in a mill turret and a test rig are developed. The velocities in the driven shaft are calculated by dynamic simulations for the model and noises in the test rig are measured with varying of the distance between shafts. The comparison of simulation and test data shows that the distance between shafts at the most uniform velocity has the lowest level of noise.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.9 s.90
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• pp.837-845
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• 2004

A variable friction damper for vehicle driveline has been proposed. This new torsional damper system uses a solenoid as an actuator to vary friction force of the damper. To verify the idea of using a solenoid in a variable damper system, the test fixture and the dampers are made and tested. Also, to find out the range of damper friction forces that influence the vehicle driveline vibration, a mathematical model of the driveline had been developed and simulated. Test and simulation results show that, within electric current used in the vehicle electric system, the solenoid can develop enough friction force that will surpass resonance in the driveline of 1.5 L Gasoline engine vehicle during acceleration.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.381-386
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• 2007

This paper presents vibration control performances of a commercial magnetorheological (MR) suspension via new control strategy considering hysteresis of the field-dependent damping force of MR damper. A commercial MR damper which is applicable to high class passenger vehicle is adopted and its field-dependent damping force is experimentally evaluated. Preisach hysteresis model for the MR damper is identified using experimental first order descending (FOD) curves. Then, a feed-forward compensation strategy for the MR damper is formulated and integrated with a linear quadratic regulation (LQR) feedback controller for the suspension system. Control performances of the proposed control strategy for the MR suspension is experimentally evaluated with quarter vehicle test facility.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.3
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• pp.315-322
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• 2008

This paper presents vibration control performances of a commercial magnetorheological(MR) suspension via new control strategy considering hysteresis of the field-dependent damping force of MR damper. A commercial MR damper which is applicable to high class passenger vehicle is adopted and its field-dependent damping force is experimentally evaluated. Preisach hysteresis model for the MR damper is identified using experimental first order descending(FOD) curves. Then, a feed-forward compensation strategy for the MR damper is formulated and integrated with a linear quadratic regulation(LQR) feedback controller for the suspension system. Control performances of the proposed control strategy for the MR suspension is experimentally evaluated with quarter vehicle test facility.

• Proceedings of the KIEE Conference
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• 1999.07a
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• pp.55-57
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• 1999

SRM Drives generate large vibration and acoustic noise because it is rotated by step pulse mmf and switching commutation mechanism. The main vibration source of SRM Drive is generated by rapidly variation of radial force when phase winding current is extinguished for commutation action. So the rapidly variation of radial force is repressed firstly to reduce vibrating force of SRM Drive. This paper suggests the vibration reduction method that SRM Drive with unidirect-short compensation winding is excited by a two stage commutation method at commutation period. This reduction effect of vibration is verified with the result obtained in the test of prototype machine.

• Wind and Structures
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• v.9 no.2
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• pp.109-124
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• 2006

This paper describes the characteristics of the fluctuating lift forces when a circular cylinder vibrates in the cross-flow direction. The response characteristics on elastically supported the circular cylinder was first examined by a free-vibration test. Next, flow-induced vibrations obtained by the free-vibration test were reproduced by a forced-vibration test, and then the characteristics of the fluctuating lift forces, the work done by the fluctuating lift, the behavior of the rolling-up of the separated shear layers were investigated on the basis of the visualized flow patterns. The main findings were that (i) the fluctuating lift forces become considerably large than those of a stationary circular cylinder, (ii) negative pressure generates on the surface of the circular cylinder when the rolling-up of separated shear layer begins, (iii) the phase between the fluctuating lift force and the cylinder displacement changes abruptly as the reduced velocity $U_r$ increases, and (iv) whether the generating cross-flow vibration becomes divergent or convergent can be described based on the work done by the fluctuating lift force. Furthermore, it was found that the generation of cross-flow vibration can be perfectly suppressed when the small tripping rods are installed on the surface of the circular cylinder.

• Journal of KSNVE
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• v.7 no.2
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• pp.247-254
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• 1997

In the case of a precision equipment, it requires a vibration free environment to provide its proper function. Especially, lithography and inspection devices, which have sub-nanometer class high accuracy and resolution, have come to necessity for producing more improved giga class semiconductor wafers. This high technology equipments require very strict environmental vibration standard in proportion to the accuracy of the manufacturing, inspecting devices. The vibration criteria are usually obtained either by the real vibration exciting test on the equipment or by the analytical calculation. This paper proposes a new method to solve this problem at a time. The permissible vibration level to a precision equipment can be easily obtained by analyzing a process of Frequency Response Function. This paper also demonstrates its effectiveness by applying the proposed method to finding the vibration criteria of a Computer Hard Disk Driver by Impact Test.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.775-780
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• 2011

This paper represents the study on the development of semi-active bicycle suspension system. The road vibration and transmissibility of front suspension are obtained by driving test on proving ground. The numerical simulation is evaluated by dynamic system modeling and equation of motion. The numerical simulation are performed to estimate the optimal damping force for minimal vibration transmission. And oscillating displacement is calculated and analyzed. Therefore the stoke which convert the damping characteristics is suggested from the driving test and numerical simulation.