せん断型MRグリースダンパによる構造物のセミアクティブ制振

抄録

A magnetorheological (MR) fluid is a suspension of micron-sized magnetic particles in a carrier fluid. In the presence of a magnetic field, magnetic particles form the chain-like structure called “cluster” along the field. This phenomenon is MR effect. The clusters resist against the shear flow and the pressure flow. As a result, MR fluid generates the yield shear stress within few milliseconds by a magnetic field. The drastic change of the rheological property and the quick response to the external magnetic field enable the MR fluid to be used as a hydraulic oil of controllable dampers. However, conventional dampers using the MR fluid have two serious problems. One is the sedimentation, and the other is the narrow dynamic range. The sedimentation is the settlement of particles which arises from the density mismatch between the dispersed particles and the base oil. In order to keep the performance of the MR damper, its magnetic particles have to be held in the carrier fluid. On the other hand, the dynamic range is the ratio of the maximum damping force to the minimum damping force. The cylindrical-type dampers require the sealing elements to confine the MR fluid, thus the sliding friction between the sealing and the cylinder is inevitable. In order to suppress the vibration response in the high frequency range, the minimum damping force due to the sliding friction must be reduced. In this study, a shear-type MR grease damper was proposed to solve the sedimentation problem. The MR grease is a suspension of micron-sized magnetic particles in the grease, which is a lubricant composed of base oil, thickener, and additives. We hope that the particles in the MR grease might be held since the thickener is a three-dimensional network structure. Furthermore, the application of the MR grease to the shear-type damper can solve the problem of the narrow dynamic range. A shear-type damper doesn’t require sealing elements, thus the sliding friction is theoretically zero. As a result, the wider dynamic range is realized. Additionally, in order to verify its damping effect in the application to a structure, the vibration suppression test using a small structure model was carried out.