For experimental studies on the production of MR fluid for MR dampers, MR fluid with a viscosity of 506 cP and a density of 2.6 g/cc was produced. In order for MR fluid to have suitable performance for MR dampers, it is important to select surfactants, magnetic particles, base oil, and characteristic additives to obtain high damping force and maintain physical and chemical properties. In order to investigate the redispersibility of MR fluid, viscosity, density, saturation magnetic flux density, dispersibility, and temperature effects were evaluated. A particle size distribution meter and a vibrating magnetometer were used, and a yield stress and redispersion device were developed to obtain the yield stress of the MR fluid. The recovery rate of MR fluid was approximately 97% at 0.2% succinic acid coating and 8% anti-settling agent. And when current is applied, the viscosity increases by more than 90% due to magnetic properties.

In order to understand the MR fluid flow in the MR damper core, the annular orifice path was simplified into a square channel and the electromagnetic flow was analyzed. For this purpose, the CFD-ACE+ program was used. The temperature and magnetic field of the MR fluid were based on room temperature and orifice wall data, and 2-D steady incompressible laminar flow was assumed. The inlet and outlet of the orifice channel are at atmospheric pressure, and the inflow velocity of the MR fluid is 0.1 m/s. After analyzing the magnetic field of the core, which is a simple model of the 1 stage MR damper, the electromagnetic flow analysis of the MR fluid flowing through the orifice channel was performed. From this, the magnetic field of the orifice channel and the electromagnetic flow of the MR fluid were observed. As the magnetic flux density increased, the flow distribution and velocity of the MR fluid in the channel core changed significantly.

본 논문에서는 미국토목학회(ASCE)의 사장교에 대한 첫번째 벤치마크 문제를 이용하여 제어-구조물 상호작용을 고려한 새로운 반능동제어 기법을 제안하였다. 이 벤치마크 문제에서는 2003년 완공 예정으로 미국 Missouri주에 건설 중인 Cape Girardeau 교를 대상 구조물로 고려하였다. Cape Girardeau 교는 New Madrid 지진구역에 위치하고, Mississippi 강을 횡단하는 주요 교량이라는 점 때문에 설계단계에서부터 내진 문제를 중요하게 고려하였다. 본 연구에서는 MR 유체 감쇠기를 제어 장치로 제안하였고, clipped-optimal 알고리듬을 제어 알고리듬으로 사용하였다. 또한, 대용량 MR 유체 감쇠기 실험 결과를 이용하여, Bingham 모델, Bouc-Wen 모델, 수정된 Bouc-HWen 모델과 같이 수치해석에 이용할 수 있는 다양한 동적 모델을 개발하였다. MR 유체 감쇠기는 제어가능한 에너지 소산장치이며 구조물에 에너지를 가하지 않기 때문에 제안된 제어기법은 한정입출력 안정성이 보장된다. 수치해석을 통해, MR 유체 감쇠기를 이용한 반능동제어 기법이 사장교의 응답 감소에 효과적인 방법임을 증명하였다