Satsuya Soda

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.

Semi-active seismic response control of base-isolated building with MR damper

This study deals with a shake table test on a three-story base-isolated steel frame. The frame rests on four roller bearings for isolation and is equipped with four laminated rubbers as shear spring. An MR damper is used in the test to perform semi-active seismic response control. The basic control algorithm applied in the study is to simulate the load-deflection of an origin-restoring friction damper (ORFD) which is a sort of friction damper that looses its resistance when it moves toward the origin, making sure for the base-isolated system to minimize residual displacement even after an extremely strong ground motion. Also attempted is a hybrid type control that superposes viscous damping on the ORFD when the damper moves from the peak displacement toward the origin.

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.

Application of Magnetorheological Fluid to Semi-Active Control of Building Structures by BRI and Partners

This study was aimed at developing an application technology of magnetorhological (MR) fluid with improving the stability of MR fluid. Variable damper using MR fluid (MR damper) has been expected to control the response of building structures in recent years, because of its large force capacity and variable force characteristics. The MR damper changes the controlling force by adjusting the magnetic field with electric current, and can control the damping forces simply. The semi-active control using MR damper stabilizes the response of the building in earthquake better than the conventional passive control. Authors developed some MR dampers and conducted shaking table tests for the research to improve the performance of building structures against earthquake. A 40kN MR damper with 500mm (+/-250mm) stroke was constructed. Authors conducted a shaking table test of the three-story large-scale structure that has an isolated base using MR damper, and the effectiveness of MR damper was verified. Finally, a 400kN MR damper was constructed and installed in an actual base-isolated residential building in order to improve the performance of the building. Introduction The Building Research Institute (BRI) of Japan and the U.S. National Science Foundation (NSF) initiated the U.S.-Japan Cooperative Research Program on Auto-adaptive Media (Smart Structural Systems) in 1998 [1], under the aegis of the U.S.-Japan Panel on Wind and Seismic Effects of the U.S.-Japan Cooperative Program in Natural Resources. At the Joint Technical Coordinating Committee (JTCC) meeting, research items and plans were discussed in detail for three research thrusts: (1) structural systems, (2) sensing and monitoring technology, and (3) effecter technology. BRI conducted a series of large-scale tests to verify some smart systems developed in this project [2]. The effectiveness of “Semi-active control by MR dampers”, “Damage detection system” and “Rocking energy dissipation system” was confirmed. This paper outlines the development of MR fluid and MR damper, the large-scale test results of response control of base-isolated building by MR damper and the implementation of an MR damper to an actual residential building. Some researchers worked on semi-active control by MR damper [3, 4]. But such a large-scale test has not been conducted. Key Engineering Materials Online: 2004-08-15 ISSN: 1662-9795, Vols. 270-273, pp 2126-2133 doi:10.4028/www.scientific.net/KEM.270-273.2126

Introduction to Earthquake-Resistant Design of Nuclear Power Plants

The aim of the earthquake-resistant design of nuclear power plants is to retain three crucial functions, even in the event of a major earthquake and tsunami: to shut down the reactor (shut down), to cool down the reactor under a specified temperature and maintain a stable condition (cool down), and to confine so as to prevent radioactive materials from being released into the surrounding environment (confine). This chapter explains the mechanism of nuclear power generation and the safety assurance of nuclear power plants, and gives an overview of the earthquake-resistant design aiming to retain the three crucial functions, shut down, cool down, and confine. Furthermore, the damage to the Kashiwazaki-Kariwa Nuclear Power Plant caused by the 2007 Niigata-Ken Chuetsu-Oki earthquake and the catastrophic disaster that affected the Fukushima Daiichi Nuclear Power Plant as a result of the 2011 Great East Japan earthquake are described.

Earthquake-Resistant Design

Static methods and/or dynamic response analysis are applied to the earthquake-resistant design of nuclear facilities, buildings, foundation grounds, and surrounding slopes. In this chapter, the static methods, i.e., the seismic coefficient and modified seismic coefficient methods are described. For the dynamic response analysis of nuclear reactor buildings and other important structures, the methods used to prepare models for analysis, the procedure for evaluating restoring force and damping characteristics are explained. This chapter also explains the method used to examine the seismic safety of buildings and structures by dynamic response analysis as well as by the static method. Furthermore, this chapter introduces the response displacement method for underground structures of nuclear power plants, such as underground ducts for the emergency cooling water supply.

Future Technology for the Seismic Safety of Nuclear Power Facilities

Because earthquakes occur frequently in Japan, attention has been given to seismic safety in the design and construction of Japanese nuclear power facilities. A serious accident at the Fukushima Dai-ichi Nuclear Power Plant of the Tokyo Electric Power Company that was caused by the 2011 Great East Japan Earthquake prompted us to review measures to ensure structural safety against future earthquakes and tsunamis. In recent years, progress has been made in investigations and research on the earthquake-resistant design of nuclear power plants. This has contributed to the development of various new technologies based on the new findings. As examples of future technologies for the seismic safety of nuclear power facilities, this chapter describes structure control technologies for nuclear power facilities and technologies to allow for greater diversity in the siting of nuclear power plants.

Earthquake-Resistant Design of Building and Structure

A nuclear power plant comprises various buildings, such as the reactor building, turbine building, and exhaust stack. Such buildings and structures must continue to fulfill their functional requirements in the event of earthquakes to ensure that the nuclear power plant remains safe. This chapter discusses the earthquake-resistant design of buildings and structures at nuclear power plants. First, the flow of the earthquake-resistant design based on dynamic response analysis is explained. Focusing on the reactor building, the eternal loads considered in the earthquake-resistant design and their combinations with the stationary load are explained. In addition, static and dynamic design approaches are described. Dynamic response models of the buildings and the foundation ground for earthquake-resistant design, where the effects of the soil–structure interaction are taken into consideration, are explained. Furthermore, a method of verifying the earthquake resistance of facilities employing shaking table tests is described.