Dong-Doo Jang

Seismic Performance Analysis of A Smart Base-isolation System Considering Dynamics of MR Elastomers

This article investigates a smart base-isolation system using magnetorheological (MR) elastomers, which are a new class of smart materials whose elastic modulus or stiffness can be adjusted depending on the magnitude of the applied magnetic field. The primary goals of this study are to develop a smart base-isolation model that represents the field-dependent dynamic behaviors of MR elastomers, to design and construct a scaled smart isolation system and a scaled building structure for a proof of concept study and to investigate the dynamic performance of the smart base-isolation in mitigating excessive vibrations of the scaled building structure under earthquake loadings. To this end, a dynamic model of an MR elastomer was first obtained based on characteristic test results of MR elastomers in shear mode. The dynamic model was then incorporated in a shear building model. Its effectiveness was validated by comparing the test results of a small-scale, single-story building structure coupled with the MR elastomer under harmonic excitations. After validating the MR elastomer-based base-isolation system, a further numerical study was performed to evaluate its effectiveness under seismic excitations. The results show that the proposed MR elastomer base-isolation system with the fuzzy logic control algorithm outperforms the conventional passive-type base isolation system in reducing the responses of the building structure for the seismic excitations considered in this study. The results further suggest that the feasibility of using MR elastomers as variable stiffness elements for enhancing the performance of conventional base-isolation systems.

Dynamic Characterization of Magneto-Rheological Elastomers in Shear Mode

The paper presents dynamic shear properties of magneto-rheological elastomers (MREs) under various loading conditions. It particularly focuses on characterization of MREs under compression-shear type combined loading, as it represents realistic loading conditions in various engineering systems and structures. In this study, MRE samples were fabricated by curing a two component elastomer resin with 30% content of 10 mum sized iron particles by volume. In order to vary the magnetic field during shear testing, a test fixture was designed and fabricated in which two permanent magnets could be variably positioned on either side of the specimen. By changing the distance between the magnets, the fixture allowed for varying the magnetic field that passes uniformly through the sample. Using this test setup and a dynamic test frame, a series of shear tests of MRE samples was performed by varying the magnetic field and frequency of loading. The results show the MR effect (percent increase in the materials ldquostiffnessrdquo) increases as the magnetic field increases and loading frequency increases within the range of the magnetic field and input frequency considered in this study. The results further show that the elastic modulus of the precompressed MREs increases as compared with that of MREs without precompression.

Numerical investigation of smart base isolation system employing MR elastomer

This paper evaluates the dynamic performance of a newly proposed smart base isolation system employing Magneto-Rheological Elastomers (MREs). MREs belong to a class of smart materials whose elastic modulus or stiffness can be adjusted by varying the magnitude of the magnetic field. The base isolation systems are considered as one of the most effective devices for vibration reduction of civil engineering structures in the event of earthquakes. The proposed base isolation system strives to enhance the performance of the conventional base-isolation system by using controllable MREs. To validate the effectiveness of the MRE-based isolation system, an extensive simulation study has been performed using a five degree-of-freedom structure under several historical earthquake excitations. The results show that the proposed system outperformed the conventional system in reducing the responses of the structure in all the seismic excitations considered in the study.

Experimental Evaluation of a ‘Self-Sensing’ Capability of an Electromagnetic Induction System Designed for MR Dampers

This article presents a sensing capability of an electromagnetic induction (EMI) system that is incorporated in a vibration control system based on an MR fluid damper. The EMI system, consisting of permanent magnets and coils, converts reciprocal motions (kinetic energy) of the MR damper into electrical energy (electromotive force or emf). The EMI system was previously studied as an alternative power source for the MR damper control system, eliminating the need of external power sources, such as a battery. The primary goal of the current study, however, is to study a sensing capability of the EMI with an aim to eliminate a conventional velocity sensor being used to implement control policies for MR damper based vibration control systems. According to the Faraday’s law of electromagnetic induction, the emf signal, produced from the EMI, is an alternating voltage signal, and it is proportional to the velocity of the motion. As such, the induced voltage (emf) signal of the EMI can sufficiently provide necessary measurement information (i.e., relative velocity across the damper) to some of the well-known control methods designed for MR damper systems (such as skyhook and maximum energy dissipation algorithm). This is because such control methods only require the sign change of the velocity signal (or phase of the velocity), rather than the exact magnitude and phase of the velocity signal. In order to evaluate the proposed concept of the EMI sensor, an EMI system was constructed. The EMI was designed to be augmented to a large-scale MR damper system (MR-EMI). The MR-EMI system was then mounted on a hydraulic servo controlled shaking table. Both harmonic and scaled historic earthquake inputs were used in a series of shaking table tests. The emf signals generated by the EMI were compared with the velocity signals (derivative of the reference input displacements). The results show that the induced emf voltage signal coincided with the phase of the velocity signal, indicating that the EMI can act as a relative velocity sensor for common control methods for MR damper systems.

Feasibility study on a hybrid mount system with air springs and piezo-stack actuators for microvibration control

This article proposes a new hybrid mount system with air springs and piezo-stack actuators that can deliver excellent performance in the microvibration control of high-tech facilities. Air springs are one of the most popular products for vibration isolation and deliver good performance in general. Piezo-stack actuators are capable of controlling micro- and nanolevel displacement with a fast response. In order to fully utilize the isolation and leveling performances of an air spring as a passive part, it is serially connected with a piezo-stack actuator serving as an active part. As a control logic for the hybrid mount, the filtered-X least-mean-square algorithm is applied. A hybrid mount system with four hybrid mounts is configured in order to confirm the performance of the hybrid mount and its performance is verified through a series of experimental tests.

Experimental verification of sensing capability of an electromagnetic induction system for an MR fluid damper-based control system

This paper investigates the sensing capability of an Electromagnetic Induction (EMI) system that is incorporated in a vibration control system based on MR fluid dampers. The EMI system, consisting of permanent magnets and coils, converts reciprocal motions (kinetic energy) of MR damper into electrical energy (electromotive force or emf). According to the Faradays law of electromagnetic induction, the emf signal, produced from the EMI, is proportional to the velocity of the motion. Thus, the induced voltage (emf) signal is able to provide the necessary measurement information (i.e., relative velocity across the damper). In other words, the EMI can act as a sensor in the MR damper system. In order to evaluate the proposed concept of the EMI sensor, an EMI system was constructed and integrated into an MR damper system. The emf signal is experimentally compared with the velocity signal by conducting a series of shaking table tests. The results show that the induced emf voltage signal well agreed with the relative velocity.

Integrated design method of MR damper and electromagnetic induction system for structural control

Magnetorheological (MR) dampers are one of the most advantageous control devices for civil engineering applications to natural hazard mitigation due to many good features such as small power requirement, reliability, and low price to manufacture. To reduce the responses of a structural system by using MR dampers, a control system including a power supply, control algorithm, and sensors is needed. The control system becomes complex, however, when a lot of MR dampers are applied to large-scale civil structures, such as cable-stayed bridges and high-rise buildings. Thus, it is difficult to install and/or maintain the MR damper-based control system. To overcome the above difficulties, a smart passive system was proposed, which is based on an MR damper system. The smart passive system consists of an MR damper and an electromagnetic induction (EMI) system that uses a permanent magnet and a coil. According to the Faraday law of induction, the EMI system that is attached to the MR damper can produce electric energy and the produced energy is applied to the MR damper to vary the damping characteristics of the damper. Thus, the smart passive system does not require any power at all. Besides the output of electric energy is proportional to input loads such as earthquakes, which means the smart passive system has adaptability by itself without any controller or sensors. In this paper, the integrated design method of a large-scale MR damper and Electromagnetic Induction (EMI) system is presented. Since the force of an MR damper is controllable by altering the input current generated from an EMI part, it is necessary to design an MR damper and an EMI part simultaneously. To do this, design parameters of an EMI part consisting of permanent magnet and coil as well as those of an MR damper consisting of a hydraulic-type cylinder and a magnetic circuit that controls the magnetic flux density in a fluid-flow path are considered in the integrated design procedure. As an example, a smart passive control system for reducing stay cable responses is considered in this investigation and it will be fabricated and tested through experiment in the future.

Development of hybrid type pneumatic vibration isolation table by piezo-stack actuator and filtered-X LMS algorithm

Recently, vibration requirements are getting stricter as precise equipments need more improved vibration environment to realize their powerful performance. Though the passive pneumatic vibration isolation tables are frequently used to satisfy the rigorous vibration requirements, the specific vibration problem, especially continuous sinusoidal or periodic vibration induced by a rotor system of other precise equipment, a thermo-hygrostat or a ventilation system, is still left. In this research, the application procedure of Filtered-X LMS algorithm to pneumatic vibration isolation table with piezo-stack actuators is proposed to enhance the isolation performance for the continuous sinusoidal or periodic vibration. In addition, the experimental results to show the isolation performance of proposed system are also presented together with the isolation performance of passive pneumatic isolation table.

MR damper-based semiactive control system using electromagnetic induction device

Magnetorheological (MR) damper-based semiactive control systems can be considered as one of the most advantageous control systems for natural hazard mitigation in the field of civil engineering because MR dampers have many good features such as small power requirement, reliability, and low price to manufacture. Those systems require feedback control and power supply parts to efficiently reduce the structural responses. The control system becomes complex when a lot of MR dampers are applied to large-scale civil structures, such as cable-stayed bridges and high-rise buildings, resulting in difficulties in its implementation and maintenance. To overcome the above difficulties, a new-class MR damper-based control system was recently proposed by replacing feedback control and power supply parts with an electromagnetic induction (EMI) part consisting of permanent magnets and a coil. According to the Faradays law of electromagnetic induction, an EMI part produces electrical energy (i.e., electromotive force or induced voltage) from mechanical energy (i.e., reciprocal motions of an MR damper), which is proportional to the rate of the change of the movement of a damper. From this characteristic of an EMI part, it might be used as a response sensing device as well as an alternative power supply. In addition, some control algorithms used in the MR damper-based semiactive control systems require the measurement information on the response related to the relative velocity of the damper. In this study, the sensing capability of an EMI part is preliminarily examined for an application to the MR damper-based semiactive control system. To this end, experimental tests are carried out using the real-scale stay cable employing an MR damper with an EMI part. It is demonstrated from the tests that an EMI part could exactly extract the dynamic characteristics of the stay cable so that it might be used as a sensing device for estimating the tension force of the stay cable. In addition, numerical simulations are performed to verify the control performance of the MR damper-based semiactive control system adopting an EMI part as a power supply as well as a velocity sensor and the maximum energy dissipation algorithm, which requires the information on the relative velocity, as a control algorithm. The numerical result validates that the proposed control system can reduce the vibration of the stay cable effectively.

Smart Damping System Based on MR Damper and Electromagnetic Induction Device for Suppressing Vibration of Stay Cable

This paper investigates the effectiveness of a smart damping system consisting of a magnetorheological (MR) damper and an electromagnetic induction (EMI) device in reducing cable vibrations. The smart damping system incorporates an EMI device to reduce complexity of conventional MR damper based semi-active control system by eliminating external power sources. This is because the EMI part in the system generates electrical energy (i.e., induced voltage) from mechanical energy (i.e., reciprocal motions of an MR damper), which can be used as a power source for the MR damper. The primary goal of this experimental study is to evaluate the performance of the proposed smart damping system using a full-scale, 44.7 meters long, high-tension cable. To this end, free vibration responses and damping of the proposed smart damping system were compared with those of an equivalent passive control system. The experimental results show that the smart damping system shows better control performance than all the passive control cases.Copyright