Katsuaki Sunakoda

Development of Large Capacity Semi-Active Seismic Damper Using Magneto-Rheological Fluid

In recent years, there has been increasing research in several industrial fields for development of semi-active vibration control devices. In particular, devices using magneto-rheological (MR) fluid have been attracting great research interest because they can realize high performance as capacity-variable dampers. MR fluids are controllable fluids that respond to applied magnetic fields. Applied magnetic fields drastically change the viscosity ofMR fluids from an oily state to a semi-solid state. This paper describes a study on a large capacity device using an MR fluid, i.e., an MR damper This developed MR damper provides a maximum damping force of 300 kN. Various tests were carried out and the dynamic characteristics, force-displacement hysteresis loops and controllable forces were investigated. These tests verified that the MR damper provides a technology that enables effective semi-active control of large-scale structure systems, i.e., real buildings and civil engineering structures.

Dynamic Characteristics of Magneto-Rheological Fluid Damper

Two kinds of Magneto-rheological fluid damper (MRF damper) have been designed and manufactured. One has a nominal capacity of 2kN and the other 20kN. A bypass flow system is adopted for both dampers and each has the same capacity of electromagnet attached to the bypass portion. The effective fluid orifice is the rectangular space and the magnetic field is applied from the outside. A test was performed by applying different magnetic fields to the orifice portion of the rectangular space. The damping force and the force- displacement loop were evaluated. The test results yielded the following: (1) Two types of dampers functioned by using one unit of the electromagnet under an appropriate electrical current control. (2) The magnitude of the damping force depends on the input magnetic field, but it has an upper limit. (3) Without an applied magnetic field, the MRF damper exhibits viscous-like behavior, while with a magnetic field it shows friction-like behavior. A mechanical model of the damper is estimated by taking account of the force-displacement loop. It is clarified that MRF dampers provide a technology that enables effective semi-active control in real building structures.

Development of 400kN magnetorheological damper for a real base-isolated building

A 400kN magnetorheological damper (MR damper) for a real base-isolated building was developed and its dynamic characteristics were verified by experimental tests. The MR damper has 950mm (+/-475mm) stroke and by-pass flow potion. A new type of Magneorheological fluid is also developed in order to apply to the MR damper. MR fluid had a property of the settlement of particles in dampers. Authors developed a new MR fluid, which keeps the particles in the fluid adequately enough for usual use of MR damper. Analytical model was discussed in this paper. The force by the bingham visco-plastic model was compared with the results of experimental tests. It was found that this analytical model is useful to predict the capacity of the MR damper.

STUDY ON VIBRATION CONTROL DEVICE USING POWER GENERATOR

In this paper, the authors propose a vibration control device using power generator in order to develop a small damper which is suitable for structural vibration control in space. The vibration control device consists of a ball screw, piston, ball nut, gear, power generator, and rod ends. The linear motion of the piston is converted into a rotary motion by the ball screw, and then the electric power is generated as dissipation of energy. A very low sinusoidal input displacement is applied to the device, and the characteristics of the damping force are examined with open circuit and short circuit of the generator. Experimental results are compared with theoretical results. Numerical simulation is applied to a flexible structure, by using sinusoidal input motion, and random motion.Copyright

Vibration Tests of a Cut-off System Using Water and Functional Fluids

In the previous paper, the authors proposed a new Cut-off system for vibration control using water and/or functional fluid which acts as a series inertia mass. In this paper, frequency response vibration tests of the Cut-off system installed in one degree of freedom vibration system are carried out using a shaking table. Transmissibility between main mass and base is measured and evaluated. The Cut-off system consists of a piston cylinder, by-pass pipe, and the fluid. It is clarified that the series mass has a large inertia effect which is proportional to the forth power of the inner diameter of the piston cylinder. The experimental results are compared with the numerical analysis, and the effects of vibration isolation are confirmed.

Simultaneous Optimal Design of the Lyapunov-Based Semi-Active Control and the Semi-Active Vibration Control Device: Inverse Lyapunov Approach

We address a simultaneous optimal design problem of a semi-active (SA) control law and design parameters in a semi-active control device for civil structures. The vibration control device (VCD) that is being developed by authors is used as the semi-active control device. The VCD is composed of a ball screw with a flywheel for the inertial resistance force and an electric motor with an electric circuit for the damping resistance force. A new bang–bang type semi-active control law referred to as inverse Lyapunov approach is proposed. In the inverse Lyapunov approach, the Lyapunov matrix in the bang–bang type semi-active control based on the Lyapunov function is searched so that the control performance of the semi-active control system is optimized. Design parameters to determine the Lyapunov function and those of the VCD are optimized with the genetic algorithm (GA). The effectiveness of the proposed approach is presented with simulation studies.

Application of MR damper to base-isolated structures

This paper presents a comprehensive study on the application of the MR damper to base-isolated building structures. It first proposes a simple semi-active control algorithm for a base-isolated structure with an MR damper. The algorithm, in which the MR dampers hysteresis shape is controlled, aims to reduce the isolators displacement without increasing the acceleration responses of the upper structures. The second part of this paper covers the properties of an MR fluid and an MR damper developed for a base-isolated model structure. The damper has a nominal capacity of 40kN, which can be adjusted in accordance with the applied magnetic fields. In the test, the damper is subjected to cyclic sinusoidal displacements with different amplitudes, velocities and magnetic field intensities. The last part describes shaking table tests carried out using the MR damper and the base-isolated model structure. It is confirmed that the proposed semi-active control method is effective in reducing the isolators displacement without increasing the acceleration responses.

Experimental and analytical methods for predicting mechanical properties of MRF damper

First part of this paper covers experimental studies on mechanical properties of two types of magneto-rheological fluid (MRF) dampers. One is a commercial built-in-pass type damper and the other an original by-pass type damper. In the test, they are subject to cyclic sinusoidal displacements with different amplitudes, velocities and intensities of magnetic field. Not only their hysteretic properties but also their quickness to respond to the applied magnetic field are examined. In the second part, two analytical methods to represent the mechanical properties of the dampers are presented. One is a semi-empirical method making use of a Bingham Model to simulate the hysteretic properties of the damper. The other one, an analytical method based on the theory of non-Newtonian fluid. A design formula to predict the resistance of the damper is so obtained as to take into consideration the dampers dimensions, the properties of the fluid and the intensity of the magnet field applied.

Semi-Active Control of Civil Structures With a One-Step-Ahead Prediction of the Seismic Response

We propose a semi-active control of civil structures based on a one-step-ahead prediction of the seismic response. The vibration control device (VCD), which has been developed by authors, generates two types of resistance forces, i.e., a damping force proportional to the relative velocity and an inertial force proportional to the relative acceleration between two stories. The damping coefficient of the VCD can be changed with a command signal to an electric circuit connected to the VCD. In the present paper the command signal for changing the damping coefficient of each VCD is assumed to take two values, i.e., the command to take the maximum or minimum damping coefficient. The optimal command signal is selected from all candidates of command signals so that the Euclidean norm of the one-step-ahead predicted seismic response is minimized. As an example a semi-active control of a fifteen-story building with three VCDs is considered. The simulation results show that the proposed semi-active control achieves superior performance on vibration suppression compared with a passive control case where the damping coefficient of each VCD is fixed at its maximum value.Copyright

Semi-Active Control of Civil Structures Based on the Prediction of the Structural Response: Integrated Design Approach

Various methodologies for vibration control of civil structures have been proposed so far. The traditional scheme is passive vibration control, i.e., dissipation of the vibration energy to the outside of the structural systems with dampers or mass dampers etc.. Passive control is quite simple and popular still, however it has some limitations, e.g., insufficient performance and/or difficulty in tuning such devices for a case of multi-mode vibration control etc.. Active vibration control is a candidate for a breakthrough to overcome the above drawbacks of passive control and has been studied extensively these decades ((Spencer et al., 1998) and the references therein). Although many studies show that the active control methodology achieves the quite high control performance on vibration suppression, it requires a large energy source to produce the control force and this fact has been an obstacle in applying active methods to general vibration control problems. Semi-active control, which is not necessarily new (Karnop et al., 1974) either, can be recognized as an intermediate between passive and active schemes in the sense of not only the performance on vibration suppression but also the complexity of the control system. In most semi-active control vibration suppression is achieved by changing the damping coefficient of the semi-active damper. In civil structures semi-active control technique is getting more realistic recently (Casciati et al., 2006) along with the development of a large scale damper whose damping property is able to be changed (Sodeyama et al., 1997). In semi-active control, the damping coefficient of the semi-active damper is changed mainly based on the following two strategies: