• 한국안광학회지
• /
• 제11권3호
• /
• pp.201-206
• /
• 2006

본 연구에서는 조절마비제 점안 후(CR상태) 정시가 된 소아(6~13세)들의 현성굴절상태(MR상태)와 나안시력을 측정해 봄으로써 조절마비 효과를 알아보고자 하였다. 시력검사와 교정을 원하여 내원한 소아 중에서 CR상태의 값이 등가구면굴절력(SE값) ${\pm}0.50D$ 이하이며 난시도수가 ${\pm}1.00D$ 미만인 경우를 정사안으로 간주하여, CR상태 정시안 소아 105안을 대상으로 MR상태와 CR상태에서 각각 자동굴절검사기(NIDEK ARK-700)를 이용하여 굴절검사를 실시하였다. CR상태 정시안의 MR상태 굴절이상량은 남자는 -0.67D, 여자는 -0.92D로 CR과 MR의 차이는 남자 0.5D, 여자 0.81D 전체는 0.69D로 여자가 약간 높게 나타났으며, 나안시력은 남자는 0.82, 여자는 0.74 전체는 0.77로 나타났다. 연령별로는 평균 0.69D였고 13세에서 1.1D로 CR과 MR의 차이가 가장 많았다. 시력은 10세에서 0.86으로 가장 높게 측정되었다. CR상태 정시안의 조절마비제 효과는 $0.69D{\pm}0.79$, 나안시력은 $0.77{\pm}0.21$ 정도임을 알 수 있었다. 조절마비제를 사용할 수 없는 안경사들은 소아의 초기 안경착용을 처방할 경우 MR상태에서 -0.75D 이하의 근사상태인 경우와 시력이 0.77 이상인 경우에는 불필요한 안경처방과 근시의 과교정 처방을 주의해야 할 것으로 사료된다.

• 한국재료학회:학술대회논문집
• /
• 한국재료학회 2001년도 추계 학술발표강연 및 논문개요집
• /
• pp.41-41
• /
• 2001

• Smart Structures and Systems
• /
• 제10권6호
• /
• pp.557-572
• /
• 2012

This paper focuses on the vibration control of long-span reticulated steel structures under multi-dimensional earthquake excitation. The control system and strategy are constructed based on Magneto-Rheological (MR) dampers. The LQR and Hrovat controlling algorithm is adopted to determine optimal MR damping force, while the modified Bingham model (MBM) and inverse neural network (INN) is proposed to solve the real-time controlling current. Three typical long-span reticulated structural systems are detailedly analyzed, including the double-layer cylindrical reticulated shell, single-layer spherical reticulated shell, and cable suspended arch-truss structure. Results show that the proposed control strategy can reduce the displacement and acceleration effectively for three typical structural systems. The displacement control effect under the earthquake excitation with different PGA is similar, while for the cable suspended arch-truss, the acceleration control effect increase distinctly with the earthquake excitation intensity. Moreover, for the cable suspended arch-truss, the strand stress variation can also be effectively reduced by the MR dampers, which is very important for this kind of structure to ensure that the cable would not be destroyed or relaxed.

• 한국구조물진단유지관리공학회 논문집
• /
• 제13권2호통권54호
• /
• pp.165-171
• /
• 2009

본 논문에서는 건설구조물의 스마트 제어를 위해 오리피스 구간의 갭(gap) 조건을 달리한 2개의 준능동 MR 감쇠기를 개발하고, 동하중 실험을 통해 갭 조건에 따른 감쇠성능을 비교 평가하였다. 여기서, MR 감쇠기는 그 특성상 재료적 및 기계적인 다양한 변수들로 인해 그 감쇠성능이 크게 좌우될 수 있으나, 특히 MR 감쇠기의 오리피스 구간에 대한 갭 크기의 영향은 MR감쇠장치의 설계 시 핵심적인 요소 중에 하나이다. 따라서 본 논문에서는 오리피스 구간의 갭 조건을 1.0mm와 2.0mm로 각각 설계하였으며, 인가전류 조건을 달리한 동하중 실험을 통해 발생 감쇠력을 획득하였다. 이들 획득결과는 힘-변위 이력곡선과 힘-전류 관계곡선으로부터 최대 최소 감쇠력 및 동적범위로 분석 평가되었다. 이상의 결과로부터, 갭의 조건에 따른 MR감쇠장치의 감쇠성능 변화를 규명하였으며, 본 연구에서 개발된 2개의 MR 감쇠기는 인가전류셑 및 코일 권선수 등의 추가핵심설계요소를 효과적으로 고려함으로써 건설구조물의 스마트 제어를 위해 유용하게 활용될 수 있는 가능성을 제시하였다.

• Design & Manufacturing
• /
• 제13권3호
• /
• pp.12-18
• /
• 2019

Fluid jet polishing is a method of jetting a fluid to polish a concave or free-form surface. However, the fluid jet method is difficult to form a stable polishing spot because of the lack of concentration. In order to solve this problem, MR fluid jet polishing system using an abrasive mixed with an MR fluid whose viscosity changes according to the intensity of a magnetic field is under study. MR fluid jet polishing is not easy to formulate for precise optimal conditions and material removal due to numerous fluid compositions and process conditions. Therefore, in this paper, quantitative data on the factors that have significant influence on the machining conditions are presented using various simulations and the correlation studies are conducted. In order to verify applicability of the fabricated MR fluid jet polishing system by nozzle diameter, the flow pattern and velocity distribution of MR fluid and polishing slurry of MR fluid jet polishing were analyzed by flow analysis and shear stress due to magnetic field changes was analyzed. The MR fluid of the MR fluid jet polishing and the flow pattern and velocity distribution of the polishing slurry were analyzed according to the nozzle diameter and the effects of nozzle diameter on the polishing effect were discussed. The analysis showed that the maximum shear stress was 0.45 mm at the diameter of 0.5 mm, 0.73 mm at 1.0 mm, and 1.24 mm at 1.5 mm. The cross-sectional shape is symmetrical and smooth W-shape is generated, which is consistent with typical fluid spray polishing result. Therefore, it was confirmed that the high-quality surface polishing process can be stably performed using the developed system.

• 한국전기전자재료학회논문지
• /
• 제25권9호
• /
• pp.738-742
• /
• 2012

This paper conducted a study on how the heat radiation of light emitting diode(LED) luminaires affects the indoor temperature increase. The effect was compared with that of a 20 W compact fluorescent lamp(CFL) and a 50 W MR16 halogen lamp which are most widely used inside of cruises, a LED downlight and a 4W MR16 LED replacing each of them. We installed a luminarie inside a thermally shielded chamber, measuring the temperature changes under the same volume every 5 minutes and compared the result with theoretically calculated heat radiation. The temperature changes in the chamber was measured four times, on seven hours' period in order to keep sufficient time once the temperature reaches the thermal equilibrium state. The results showed that the temperature of the 20 W E26 CFL and the 10 W LED downlight increased by $21.1^{\circ}C$ and $10.4^{\circ}C$ respectively, while that of the 50 W halogen MR16 and the 4 W LED MR16 increased by $33.9^{\circ}C$ and $4.8^{\circ}C$ respectively. The experimental heat radiation were calculated from the results and the experimental heat radiation of the CFL and the LED downlight were 171.5 cal and 86.5 cal, and those of the halogen MR16 and the LED MR16 were 275.3 cal and 36.5 cal. Therefore, the heat radiation was reduced by 49.5% and 86.7%, respectively, by replacing conventional light source with LED. In conclusion, we can expect a reduction of power consumption in air condition system and the effect on indoor temperature increase by application of LED luminaires.

• 한국정밀공학회지
• /
• 제28권8호
• /
• pp.929-935
• /
• 2011

As a deterministic finishing process for the optical parts having complex surface, machining performance of the magnetorheological(MR) fluid jet polishing of optical glass are studied and compared with a general water jet polishing. First, design of the jet polishing system which has the special electromagnet-nozzle unit for stabilizing the slurry jet based on MR fluid and the change of jet shape as magnetic field is applied are explained. Second, for the BK7 glass, machining spot and its cross section profile are analyzed and the unique effect of MR fluid jet polishing is shown. Third, both material removal depth and surface roughness are explored in order to investigate the polishing performance of MR fluid jet. With the same ceria abrasives and amount in the polishing slurries, MR fluid jet shows superior machining performance compared to water jet and the difference of material removal mechanism and its resulting performance are described.

• 한국지진공학회:학술대회논문집
• /
• 한국지진공학회 2005년도 학술발표회 논문집
• /
• pp.421-428
• /
• 2005

In this paper, the performance of a toggle brace-MR damper system is evaluated for the control of the structure excited by earthquake load and the non-linearity of the toggle system is investigated. Considering that the control force of MR damper described by Bingham model is a function of velocity, velocity amplification factor by toggle brace system is calculated and the effect of toggle configuration on the amplification factor is also evaluated. Numerical results show that the control performance can be largely enhanced using toggle brace system especially for the case that the MR damper installed with conventional brace system such as Chevron and diagonal cannot provide enough control force under severe earthquake load.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2013년도 추계학술대회 논문집
• /
• pp.92-93
• /
• 2013

In this study, Shock Absorption performance of Magneto-rheological elastomer(MRE) is identified through the drop impact test. Magneto-rheological materials are divided into two groups by MR fluid in fluid state and MR elastomer in solid state like rubber. The stiffness characteristics of Magneto-rheological material can be changed as magnetic field is applied. The impact loads in MR elastomer were measured under weight of impactor. Experiment results are shown through the experiments to confirm the effect of shock absorption of MR elastomer. Thus, the MR elastomer can be applied to shock absorber used in area that shock occurs.

• Structural Engineering and Mechanics
• /
• 제41권6호
• /
• pp.791-803
• /
• 2012

Significant structural damages due to pounding between adjacent superstructures of multi-span reinforced concrete (RC) highway bridges have been observed in past earthquakes. Different methods have been proposed in the literature to mitigate the adverse seismic pounding effects. This paper presents an analytical investigation on the use of magnetorheological (MR) dampers in reducing seismic pounding effects of base-isolated multi-span RC highway bridges. It has been observed that MR damper can effectively reduce the seismic pounding effect. Three control strategies (passive off, passive on, and bang bang control) of MR damper have been investigated. Although all the control strategies are found to be effective, bang bang control has been observed to be the most effective.