• 대한기계학회논문집A
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• 제35권8호
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• pp.905-912
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• 2011

견마로봇이 야지 노면에서 주행할 때 로봇에 설치되어 있는 각종 장비의 보호를 위하여 주행 안정성을 높이는 것이 중요하다. 견마로봇의 주행 안정성을 평가하는 데에 있어서 차체의 수직 가속도, 롤 각가속도, 피치 각가속도의 영향이 지배적이다. 가속도가 발생한다는 의미는 차체에 그만큼의 힘이 가해진다는 것을 의미한다. 따라서 차체에 작용하는 힘의 크기를 조절함으로써 차량의 안정성을 향상시킬 수 있다. 차량의 안정성을 높이기 위한 하나의 방법으로 MR 댐퍼와 스카이 훅 제어기법을 적용할 수 있다. 본 연구에서는 $6{\times}6$ 견마로봇에 대하여 MR 댐퍼에 스카이 훅 제어기법을 적용하였으며, 수직 가속도 및 롤, 피치 각가속도를 줄이는 방향으로 제어하여 차량의 주행 안정성을 향상시켰다.

• 한국산학기술학회논문지
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• 제21권1호
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• pp.774-779
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• 2020

본 논문에서는 RNN 순환 신경망 (Recurrent Neural Network) 모델을 사용하여 스마트 중간층 면진 시스템의 지진 응답 제어 성능을 수치 해석을 통하여 검토하였다. 이를 위해서 지진 하중을 받는 건물의 동적 지진 응답 예측을 위한 RNN 모델을 개발하였다. 보다 실제적인 연구를 위하여 중간층 면진 시스템이 설치된 실존하는 건물인 시오도메 스미토모 건물을 예제 구조물로 선택하였다. 스마트 중간층 면진 시스템은 기존의 납 댐퍼를 대신하여 MR (Magnetorheological) 댐퍼를 사용하여 구성하였다. 그 외 고무 베어링이나 강재 댐퍼는 그대로 사용 하였다. 수치 해석을 통하여 개발된 RNN 모델이 기존의 FEM (Finite Element Method) 모델과 비교해서 매우 정확한 응답을 예측하는 것을 확인할 수 있었다. RNN 모델을 사용하면 자유도가 많은 FEM 모델을 사용한 경우에 비하여 해석 시간을 대폭 줄일 수 있다. 개발된 RNN 모델을 사용한 수치 해석 결과 스마트 중간층 면진 시스템이 기존의 수동 중간층 면진 시스템에 비하여 구조물의 지진 응답을 대폭 저감시킬 수 있는 것을 확인할 수 있었다.

• 한국산학기술학회논문지
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• 제15권3호
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• pp.1247-1252
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• 2014

본 연구에서는 온도조건에 따른 MR 유체의 물리적 특성을 연구하고자 침전 및 전단응력실험을 수행하였다. MR 댐퍼에 사용되는 MR 유체는 자성 파우더를 포함하고 있어 침전현상이 발생하므로 침강성과 인가전류에 의한 전단응력 변화를 상온과 고온조건에서 실험하였다. 침강특성을 조사하기 위하여 강제 대류형 오븐을 인가전류에 의한 전단응력을 측정하기 위하여 점도계를 사용하였다. 실험결과로부터 MR 유체는 시간과 온도에 따른 침강 특성이 다름을 그리고 교반시간이 큰 경우에 MR 유체의 분산성이 2배 이상 우수하였다. 전단률이 증가할수록 전단응력은 로그함수의 증가분포를 인가전류를 증가할수록 2차 함수의 증가분포를 그리고 MR 유체의 전단응력은 상온보다 고온에서 6-18% 낮은 분포를 보였다.

• Elastomers and Composites
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• 제51권2호
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• pp.113-121
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• 2016

Magneto-rheological elastomer (MRE) is a material which shows reversible and various modulus under magnetic field. Comparing to conventional rubber vibration isolator, MREs are able to absorb broader frequency range of vibration. These characteristic phenomena result from the orientation of magnetic particle (i.e., chain-like formation) in rubber matrix. In this study, silicone rubber was used as a matrix of MREs. Carbonyl iron particle (CIP) was used to give magnetic field reactive modulus of MRE. The surface of the CIP was modified with chemical reactants such as silane coupling agent and poly(glycidyl methacrylate), to improve interfacial adhesion between matrix and CIP. The mechanical properties of MREs were measured without the application of magnetic field. The results showed that the tensile strength was decreased while the hardness was increased with the addition of CIP. Also, surface modification of CIP resulted in the improvement of physical properties of MRE, but the degree of orientation of CIP became decreased. The analysis of MR effect was carried out using electromagnetic equipment with various magnetic flux. As the addition of CIP and magnetic flux increased, increment of MR effect was observed. Even though the surface modification of CIP gave positive effect on the mechanical properties of MRE, MR effect was decreased with the surface modification of CIP due to decrease of CIP orientation. Throughout this study, it was found that the loading amounts of CIP affected the mechanical properties of MRE, and surface property of CIP was an important factor on MR effect of MRE.

• 한국지진공학회논문집
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• 제10권1호
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• pp.51-62
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• 2006

다양한 원인에 의해서 발생하는 구조물의 동적응답을 감소시키기 위하여 현재까지 여러 가지 형태의 동조질량감쇠기(Tuned Mass Damper; TMD)가 개발되었고 이에 대한 많은 연구가 수행되어 왔다. 본 연구에서는 구조물의 응답에 따라서 실시간으로 TMD의 감쇠를 변화시킬 수 있는 준능동 TMD(Semi-active TMD; STMD)의 제어성능을 다양한 형태의 하중을 적용하여 해석적으로 검토하였다. STMD를 구성하는 준능동 감쇠기의 감쇠력을 조절하기 위하여 skyhook 제어알고리즘을 이용하였다. 조화하중 및 임의의 동적하중을 직접가력하중과 지반진동하중 형태로 단자유도 구조물에 가하여 STMD와 일반적인 TMD의 제어성능을 비교하였다. 또한, 주구조물의 질량의 변화에 따른 TMD 및 STMD의 제어성능의 견실성을 비교하였다. 그리고, 가변감쇠장지 뿐만 아니라 MR 감쇠기를 사용한 STMD의 제어성능도 평가하여 새로운 진동제어장치로서의 활용가능성을 검토하였다. 수치해석을 수행한 결과 STMD는 TMD에 비하여 조화하중 및 임의의 동적하중에 대해서 매우 뛰어난 제어성능을 보이는 것을 확인할 수 있었다.

• 한국공간구조학회논문집
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• 제18권3호
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• pp.37-44
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• 2018

A base isolation system is widely used to reduce seismic responses of low-rise buildings. This system cannot be effectively applied to high-rise buildings because the initial stiffness of the high-rise building with the base isolation system maintains almost the same as the building without the base isolation system to set the yield shear force of the base isolation system larger than the design wind load. To solve this problem, the mid-story isolation system was proposed and applied to many buildings. The mid-story isolation system has two major objectives; first to reduce peak story drift and second to reduce peak drift of the isolation story. Usually, these two objectives are in conflict. In this study, a hybrid mid-story isolation system for a tall building is proposed. A MR (magnetorheological) damper was used to develop the hybrid mid-story isolation system. An existing building with mid-story isolation system, that is "Shiodome Sumitomo Building" a high rise building having a large atrium in the lower levels, was used for control performance evaluation of the hybrid mid-story isolation system. Fuzzy logic controller and genetic algorithm were used to develop the control algorithm for the hybrid mid-story isolation system. It can be seen from analytical results that the hybrid mid-story isolation system can provide better control performance than the ordinary mid-story isolation system and the design process developed in this study is useful for preliminary design of the hybrid mid-story isolation system for a tall building.

• Structural Engineering and Mechanics
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• 제24권3호
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• pp.375-393
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• 2006

Under high velocity, pulse type near source earthquakes semi-active control systems are very effective in reducing seismic response base isolated structures. Semi-active control systems can be classified as: 1) independently variable stiffness, 2) independently variable damping, and 3) combined variable stiffness and damping systems. Several researchers have studied the effectiveness of independently varying damping systems for seismic response reduction of base isolated structures. In this study effectiveness of a combined system consisting of a semi-active independently variable stiffness (SAIVS) device and a magnetorheological (MR) damper in reducing seismic response of base isolated structures is analytically investigated. The SAIVS device can vary the stiffness, and hence the period, of the isolation system; whereas, the MR damper enhances the energy dissipation characteristics of the isolation system. Two separate control algorithms, i.e., a nonlinear tangential stiffness moving average control algorithm for smooth switching of the SAIVS device and a Lyapunov based control algorithm for damping variation of MR damper, are developed. Single and multi degree of freedom systems consisting of sliding base isolation system and both the SAIVS device and MR damper are considered. Results are presented in the form of nonlinear response spectra, and effectiveness of combined variable stiffness and variable damping system in reducing seismic response of sliding base isolated structures is evaluated. It is shown that the combined variable stiffness and variable damping system leads to significant response reduction over cases with variable stiffness or variable damping systems acting independently, over a broad period range.

• 한국기계가공학회지
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• 제16권5호
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• pp.85-90
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• 2017

Mica-glass ceramics has features such as micro-sized crystals, high strength, chemical resistance, semitransparent optical properties, etc. Due to its superior material properties, mica glass ceramics have increasing applications in dental and medical components, insulation boards, chemical devices, etc. In many applications, especially for dental and medical components, ultra-precise polishing is required. However, it is known to be a very difficult-to-grind material because of its high hardness and brittle properties. Thus, in this study, a newly developed ultra-precise polishing method is applied to obtain nano-level surface roughness of the mica glass ceramics using magnetorheological (MR) fluids and nano abrasives. Nano-sized ceria particles were used for the polishing of the mica glass ceramics. A series of experiments were performed under various polishing conditions, and the results were analyzed. A very fine surface roughness of Ra=6.127 nm could be obtained.

• Tribology and Lubricants
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• 제31권2호
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• pp.62-68
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• 2015

A magnetorheological (MR) fluid is a smart material whose rheological behavior can be controlled by varying the parameters of the applied magnetic field. Because the damping force and shear force of an MR fluid can be controlled using a magnetic field, it is widely employed in many industrial applications, such as in vehicle vibration control, powertrains, high-precision grinding processes, valves, and seals. However, the characteristics of friction caused by iron particles inside the MR fluid need to be understood and improved so that it can be used in practical applications. Surface process technologies such as polytetrafluoroethylene (PTFE) coatings and diamond-like carbon (DLC) coatings are widely used to improve the surface friction properties. This study examines the friction characteristics of an MR fluid with different surface process technologies such as PTFE coatings and DLC coatings, by using a reciprocating friction tester. The coefficients of friction are in the following descending order: MR fluid without any coating, MR fluid with a DLC coating, and MR fluid with a PTFE coating. Scanning electron microscopy is used to observe the worn surfaces before and after the experiment. In addition, energy dispersive X-ray spectroscopy is used to analyze the chemical composition of the worn surface. Through a comparison of the results, the friction characteristics of the MR fluid based on the different coating technologies are analyzed.

• Smart Structures and Systems
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• 제7권5호
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• pp.379-392
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• 2011

This paper presents a multi-functional system, consisting of a magnetorheological (MR) damper and an electromagnetic induction (EMI) device, and its applications in stay cables. The proposed system is capable of offering multiple functions: (1) mitigating excessive vibrations of cables, (2) estimating cable tension, and (3) harvesting energy for wireless sensors used health monitoring of cable-stayed bridges. In the proposed system, the EMI device, consisting of permanent magnets and a solenoid coil, can converts vibration energy into electrical energy (i.e., induced emf); hence, it acts as an energy harvesting system. Moreover, the cable tension can be estimated by using the emf signals obtained from the EMI device. In addition, the MR damper, whose damping property is controlled by the harvested energy from the EMI device, can effectively reduce excessive cable vibrations. In this study, the multi-functionality of the proposed system is experimentally evaluated by conducting a shaking table test as well as a full-scale stay cable in a laboratory setting. In the shaking table experiment, the energy harvesting capability of the EMI device for wireless sensor nodes is investigated. The performance on the cable tension estimation and the vibration mitigation are evaluated using the full-scale cable test setup. The test results show that the proposed system can sufficiently generate and store the electricity for operating a wireless sensor node twice per day, significantly alleviate vibration of a stay cable (by providing about 20% larger damping compared to the passive optimal case), and estimate the cable tension accurately within a 2.5% error.