• Journal of the Korean Magnetics Society
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• v.8 no.2
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• pp.93-98
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• 1998

Magnetic fluids have been used in the commercial area, e. g damping, sealing and hydrodynamic bearing. In this study, magnetic fluid was made for damping in loudspeaker. The magnetic fluids were snthesized by dispersing the magnetite powder which was obtained by precipitation method in Yubase oil. When the magnetic fluid was applied to a 6 cm tweeter, improvements of damping, centering and heat transger in a loudspeaker were noted. Also we compared the performance of the magnetic fluid with 20 % magnetite in the oil and the one of APG-815 (Niphon Ferrofluidic Co.)

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.460-465
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• 2002

The nonlinear vibration of the CRT shadow mask is analyzed in consideration of the V-shaped tension distribution and the effect of wire impact damping. The reduced order FEM model of the shadow mask is obtained from dynamic condensation for the mass and stiffness matrices. Damping wire is modeled using the lumped parameter method to effectively describe its contact interactions with the shadow mask. The nonlinear contact-impact model is composed of spring and damper elements, of which parameters are determined from the Hertzian contact theory and the restitution coefficient, respectively. The analysis model of the shadow mask with damping wires is experimentally verified through impact tests of shadow masks performed in a vacuum chamber. Using the validated analysis model of the shadow mask with damping wires, the‘design of experiments’technique is applied to search fur the optimal damping wire configuration so that the vibration attenuation of the shadow mask is maximized.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.9
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• pp.731-737
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• 2002

Nonlinear vibration of the CRT shadow mask with impact damping wires is analyzed in consideration of the mask tension distribution and the effect of wire impact damping. A reduced order FEM model of the shadow mask is obtained from dynamic condensation of the mass and stiffness matrices, and damping wire is modeled using the lumped parameter method to effectively describe its contact interactions with the shadow mask. The nonlinear contact-impact model is composed of spring and damper elements, of which parameters are determined from the Hertzian contact theory and the restitution coefficient, respectively. The analysis model of the shadow mask with damping wires is experimentally verified through impact tests of shadow masks performed in a vacuum chamber.

• Electronics and Telecommunications Trends
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• v.13 no.6 s.54
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• pp.46-55
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• 1998

인텔사의 Xeon 프로세서 버스에 정합한 입출력 구동기를 선정하고자, Xeon 프로세서의 구동기술인 AGTL+를 조사하고 AGTL+와 GTL+ 구동기의 혼용 가능성을 분석하였다. GTL+(NTL)을 AGTL+와 함께 사용하고자 할 때 배선 토폴로지, 터미네이션, 댐핑저항 값에 따른 신호 및 시간 특성을 시뮬레이션 하였다. 시뮬레이션의 결과로 80 MHz 이하의 버스속도에서는 Xeon 프로세서 네 개와 GTL+(NTL) 구동기를 혼용하여 안정적으로 동작시킬 수 있음을 보였다.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1993.04a
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• pp.108-111
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• 1993

일반적으로 정수압 베어링은 저진동, 저마찰 및 높은 댐핑 특성을 가지며 하중 지지 용량도 커서 공작 기계, 측정 기구등에 광범위하게 하용된다. 특히 여러 산업이 발달함에 따라 점차 정밀 부품의 필요성이 증가되고 있고 공작 기계의 용량도 점차 대형화되는 추세에 있다. 이에 따라 공작 기계의 미끄럼 운동을 지지하는 베어링은 높은 강성 및 높은 하중 지지용량을 갖게할 필요가 있다. 본 논문에서는 능동적 급유 방식의 리스트릭터의 한 종류인 다이아프램 제어 밸브 (diaphram control valve)와 수동적 급유 방식의 리스트릭터의 한종류인 오리프스의 특성을 이론적으로 해석하고 실험을 통하여 이론 해석의 타당성을 검증하고 결과를 도시하고자 한다.

• The Journal of the Acoustical Society of Korea
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• v.5 no.2
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• pp.13-18
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• 1986

디지틀 데이터 전송시 수신기에서 또는 중계기에서 송신 데이터를 구하기 위해서는 타이밍 클럭 을 복원해야 한다. 대개의 실장된 경우에서는 PLL을 이용하는데, 이때 시스템/랜덤 지터가 발생되고 또 중계기가 늘어남에 따라서 생성된 지터가 누적되는데 이것을 해석하였다. 90 Mbps 광통신 시스템에 적 용하여 테이블 1,2,3,4와 같은 결과를 얻었으며, 시스템 지터가 랜덤 지터보다 더 급격히 누적됨을 알았 고, 또한 댐핑팩터가 커짐에 따라 지터 누적이 양화됨을 알았다.

• Journal of the Korean Wood Science and Technology
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• v.33 no.4 s.132
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• pp.15-22
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• 2005

The acoustic properties of various coatings for stringed musical instruments made were investigated. The applied coatings were urethane topcoat, oil stain, natural varnish, cashew and UV-curable epoxy coating. Acoustic properties of coatings inferred from a resonance frequency and a damping measured by FFT analyzer and tan ${\delta}$ measured by DMTA. Acoustic properties from resonance frequency and damping were analyzed. Optimum coating for stringed instruments was determined by viscoelastic properties and acoustic properties of coating.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.5
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• pp.385-394
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• 2012

A computer program that can estimate static, dynamic stability and control derivatives using a subsonic-supersonic panel method is developed. The panel method uses subsonic-supersonic source and elementary horse shoe vortex distributions, and their strengths are determined by solving the boundary condition approximated with a thin body assumption. In addition, quasi-steady analysis on the body fixed coordinate system allows the estimation of damping coefficients of aircraft 3 axes. The code is validated by comparing the neutral point, roll and pitch damping of delta wings with published analysis results. Finally, the static, dynamic stability and control derivatives of F-18 are compared with experimental data as well as other numerical results to show the accuracy and the usefulness of the code.

• Journal of the Korean Institute of Gas
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• v.19 no.5
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• pp.41-46
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• 2015

It is known that in aluminum 6061-T6, which is composed of $Mg_2Si$ and ${\beta}-Al_5FeSi$, void nucleation grows around ${\beta}-Al_5FeSi$ of Al606-T6. In this work, growth of voids was checked by scanning a 6061-T6 specimen with SEM observation. The effects of dislocation damping, coherency strain and voids on ultrasonic attenuation and nonlinearity parameters were experimentally measured. It was observed that a nonlinearity parameter increases until 75 percent of fatigue life and decreases after that. From the results, the authors inferred that dislocation damping and coherency damping increase nonlinearity parameters and void nucleation decreases them as ultrasonic scattering increases with void. The application of nonlinearity parameters in estimating degradation of materials with complex microstructures through fatigue process, therefore, should be carefully considered.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.4
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• pp.1813-1818
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• 2014

This paper presents the stability analysis of the haptic system including a human impedance using the Routh-Hurwitz criterion. The reflective force is computed from a virtual spring model and is transferred to a human operator using the first-order-hold method. The stability boundary conditions are induced and the relation among a virtual spring ($K_w$), the mass ($M_h$), the damping ($B_h$) and the stiffness ($K_h$) of a human impedance is analyzed. Hence the stability boundary of the virtual spring ($K_w$) is proposed as $K_w{\leq}54413{\sqrt{(M_h+M_d)(B_h+B_d)}}-0.486K_h$ when the sampling time is 1 ms. The average relative error is about 0.5% when the mathematical analysis results are compared with the results of the stability boundary model.