• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.67-70
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• 2002

This paper presents the property of the Squeeze Film Damper (SFD) using Magneto-Rheological fluid (MR fluid). The damping property of a SFD for a flexible rotor system varied according to vibration mode. MR fluid is known as a functional fluid with controllable apparent viscosity of the fluid by applied magnetic field strength. When the MR fluid is applied in the SFD, the SFD using MR fluid can effectively reduce vibrations of the flexible rotor in a wide range of rotating speed by control of the applied magnetic field strength. To investigate in detail the SFD using MR fluid, the SFD to support one mass was constructed and its performance was experimentally investigated in the present study. The damping property of the SFD using MR fluid has viscous damping by Newtonian fluid, but not Coulomb friction by Bingham fluid. Therefore, The system damped by the SFD can be considered as a linear system.

• 한국유체기계학회 논문집
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• 제7권4호
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• pp.24-31
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• 2004

The aim of this study is to provide fundamental information for the development of Semi-Active Damper Using Magnetic fluid. To achieve the aim, the damping effect of magnetic fluid is investigated by experiments that the diameter of inner circular bar and the input amplitude were varied in the magnetic field generated by the permanent magnet and the electromagnet coil. From the study, the following conclusive remarks can be made. As the diameter of inner circular bar and input amplitude increase, the damping effect is improved. This is explained by the fact that as the contact area between inner circular bar and magnetic fluid increases, the increase of friction lowers kinematic energy. If the magnetic field is generated, the damping effect is improved. This is explained the assumption that as the intensity of magnetic fluid particle increases, there is virtual mass phenomenon.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.184-187
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• 2005

The blade is an important part of rotating turbomachinery. The blade dynamic strength is of considerable importance as far as the reliability of operation and the life of the engine ate concerned. In this paper, blades are attached to a disk and coupled by means of damping wire. We assumes that the interfaces between the blade and disk dovetails are joined together, which means surface-to-surface contacts without friction. The damping wire is implemented using a beam element and temperature effect in the blade is neglected. Centrifugal forces ale applied by using an angular velocity to all elements in the system. The FEM results showed vibration characteristics in the blade disk system for the cases of a free-standing blade and blades with damping wire, respectively.

• 한국구조물진단유지관리공학회 논문집
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• 제17권2호
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• pp.54-61
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• 2013

사장교 케이블은 초기 큰 인장력으로 축강성이 매우 크지만, 횡방향 휨강성은 약하다. 풍하중이나 교통하중은 케이블을 심각하게 진동시켜 사장교의 사용성에 부정적 영향을 끼친다. 그러므로 장대교량에 감쇠장치를 설치하는 진동 저감 계획이 절실히 요구된다. 마찰댐퍼는 교통하중이나 풍하중과 같은 동적하중이 작용하는 케이블 진동에서 진폭과 지속시간을 대폭 감소시킬 수 있는 효과적인 장치임을 알 수 있다. 케이블 진동은 댐퍼제작방법과 설치위치 및 형상에 따라 효율이 달라질 수 있다. 그럼에도 불구하고 본 실험연구의 마찰댐퍼 설치전 후 제진성능효과 분석결과는 향후 사장케이블의 진동을 저감시키는 기본 자료로 활용할 수 있다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1993년도 추계학술대회 논문집
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• pp.363-368
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• 1993

Hilbert Transform has been used for detection of nonlinearity in modal analysis. HTD(Hilbert Transform Describers) are used to quantify and identify nonlinearity. Mottershead and Stanway method for identification of N-th power velocity nonlinear damping are extended to P-th power displacement stiffness, N-th power velocity damping and dry friction. Time domain and frequency domain data are used and HTD and Mottershead methods are combined for identification of nonlinear parameters in this paper. Computer simulations and experimental results are shown to verify nonlinear structure identification methods.

• Structural Engineering and Mechanics
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• 제40권3호
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• pp.315-334
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• 2011

Seismic isolated building structures are examined in this study. The triple concave friction pendulum (TCFP) is used as a seismic isolation system which is easy to be manufactured and enduring more than traditional seismic isolation systems. In the TCFP, take advantage of weight which pendulum carrying and it's geometry in order to obtain desirable result of seismic isolation systems. These systems offer advantage to buildings which subject to severe earthquake. This is result of damping force of earthquake by means of their internal constructions, which consists of multiple surfaces. As the combinations of surfaces upon which sliding is occurring change, the stiffness and effective friction change accordingly. Additionally, the mentioned the TCFP is modeled as of a series arrangement of the three single concave friction pendulum (SCFP) bearings. A two dimensional- and eight- story of a building with and without isolation system are used in the time history analysis in order to investigate of the effectiveness of the seismic isolation systems on the buildings. Results are compared with each other to emphasize efficiency of the TCFP as a seismic isolation device against the other friction type isolation system like single and double concave surfaces. The values of the acceleration, floor displacement and isolator displacement obtained from the results by using different types of the isolation bearings are compared each other. As a result, the findings show that the TCFP bearings are more effective devices for isolation of the buildings against severe earthquakes.

• 대한기계학회논문집A
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• 제33권12호
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• pp.1417-1426
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• 2009

Various types of damper are usually applied to reduce noise and vibration for mechanical systems. Especially, for washing machines, the free-friction stroke damper is installed. The behavior of the free-friction stroke damper has nonlinear characteristics such as hysteresis and viscoelastic properties because of its foam material. First of all, the dynamic experiments were carried out by using a MTS machine to find characteristics of the free-friction stroke damper. And the simulation model of the free-friction stroke damper and characteristics of a foam material were evaluated by using optimization technique. To make a good simulation model which can show the dynamic characteristics, it is important to understand the working mechanism of the damper. The Finite Element Method (FEM) technique can help us instinctively understand the damping phenomenon under operating conditions, because we can observe the condition of damper at every step in the simulation by using it. Also, by changing factors, we can comprehend the variation of characteristics of damper. So, in this paper, a study on the dynamic characteristics of free-friction stroke damper by FEM is focused on. Finally, the possibility which physical experiments can be replaced into simulations is shown.

• 제어로봇시스템학회논문지
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• 제2권3호
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• pp.174-180
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• 1996

The friction is one of the nonlinearities to be considered in the precise position control of a system which has electromechanical components. The friction has complicated nonlinear characteristics and depends on the velocity, the position and the time. The conventional fixed friction compensator and the controller based on linear control theory may cause the steady state position error or oscillation. The plant to be controlled in this study is a positioning system with a linear brushless DC motor(LBLDCM). The system behaves like a 4th-order model including the compliance and the friction. In this study, the plant model is simplified to a 2nd-order model to reduce the computation in on- line estimation. Also, to reduce the computation time, only the friction is estimated on-line while the mass and the viscous damping coefficient are fixed to the values obtained from off-line estimation. The validity of the proposed scheme is illustrated with the computer simulation and the experiment where the friction is compensated by using the estimation.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.129.1-129.1
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• 2013

Atomically-thin graphene is the ideal model system for studying nanoscale friction due to its intrinsic two-dimensional anisotropy. Here, we report the reduced nanoscale friction of epitaxial graphene on SiC, investigated with conductive-probe atomic force microscopy/friction force microscopy in ultra-high vacuum. The measured friction on a buffer layer was found to be 1/8 of that on a monolayer of epitaxial graphene. Conductive probe atomic force microscopy revealed a lower conductance on the buffer layer, compared to monolayer graphene. We associate this difference in friction with the difference in total lateral stiffness. Because bending stiffness is associated with flexural phonons in two-dimensional systems, nanoscale frictional energy should primarily dissipate through damping with the softest phonons. We investigated the influence of hydrogen intercalation on the nanoscale friction. We found that the friction decreased significantly after hydrogen intercalation, which is related to loose contact between the graphene and the substrate that results in a lower bending stiffness.

• 한국항공우주학회지
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• 제40권10호
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• pp.894-900
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• 2012

본 연구의 목적은 풍동시험을 통해 회전발사체에서 발생하는 동적 롤댐핑 특성을 실험적으로 연구하는데 있었으며, 이를 위해 약 8,000 rpm으로 회전하는 회전발사체 실험모형에 작용하는 롤댐핑 특성의 측정을 위한 고속풍동시험을 국방과학연구소 삼중음속풍동에서 수행하였다. 실험시의 마하수는 0.6~0.9까지의 천음속 영역이었으며 이때의 받음각 구간은 최대 0~15 deg에 해당하였다. 측정된 공기역학적 댐핑 특성으로부터 회전체의 마찰 특성을 공제하기위한 베어링 마찰특성에 대한 평가도 함께 수행하였다.