• Wind and Structures
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• v.6 no.5
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• pp.387-402
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• 2003

In the past decades, much effort has been made towards the study of single-mode-based vibration controls with dynamic energy absorbers such as single or multiple Tuned Mass Dampers(TMDs). With the increase of bridge span length and the tendency of the bridge cross-section being more slender and streamlined, multi-mode coupled vibrations as well as their controls have become very important for large bridges susceptible to strong winds. As a simple but effective device, the TMD system especially the semi-active one has become a promising option for such coupled vibration controls. However, despite various studies of optimal controls of single-mode-based vibrations with TMDs, research on the corresponding controls of the multi-mode coupled vibrations is very rare so far. For the development of a semi-active control strategy to suppress the multi-mode coupled vibrations, a comprehensive parametric analysis on the optimal variables of this control is substantial. In the present study, a multi-mode control strategy named "three-row" TMD system is discussed and the general numerical equations are developed at first. Then a parametric study on the optimal control variables for the "three-row" TMD system is conducted for a prototype Humen Suspension Bridge, through which some useful information and a better understanding of the optimal control variables to suppress the coupled vibrations are obtained. This information lays a foundation for the design of semi-active control.

• Smart Structures and Systems
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• v.19 no.4
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• pp.341-350
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• 2017

Based on the super elastic properties of the shape memory alloy (SMA) and the inverse piezoelectric effect of piezoelectric (PZT) ceramics, a kind of hybrid semi-active control device was designed and made, its mechanical properties test was done under different frequency and different voltage. The local search ability of genetic algorithm is poor, which would fall into the defect of prematurity easily. A kind of adaptive immune memory cloning algorithm(AIMCA) was proposed based on the simulation of clone selection and immune memory process. It can adjust the mutation probability and clone scale adaptively through the way of introducing memory cell and antibody incentive degrees. And performance indicator based on the modal controllable degree was taken as antigen-antibody affinity function, the optimization analysis of damper layout in a space truss structure was done. The structural seismic response was analyzed by applying the neural network prediction model and T-S fuzzy logic. Results show that SMA and PZT friction composite damper has a good energy dissipation capacity and stable performance, the bigger voltage, the better energy dissipation ability. Compared with genetic algorithm, the adaptive immune memory clone algorithm overcomes the problem of prematurity effectively. Besides, it has stronger global searching ability, better population diversity and faster convergence speed, makes the damper has a better arrangement position in structural dampers optimization leading to the better damping effect.

• Earthquakes and Structures
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• v.11 no.2
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• pp.347-369
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• 2016

The main objective of this paper is the robust multi-objective optimization design of semi-active tuned mass damper (STMD) system using genetic algorithms and fuzzy logic. For optimal design of this system, it is required that the uncertainties which may exist in the system be taken into account. This consideration is performed through the robust design optimization (RDO) procedure. To evaluate the optimal values of the design parameters, three non-commensurable objective functions namely: normalized values of the maximum displacement, velocity, and acceleration of each story level are considered to minimize simultaneously. For this purpose, a fast and elitist non-dominated sorting genetic algorithm (NSGA-II) approach is used to find a set of Pareto-optimal solutions. The torsional effects due to irregularities of the building and/or unsymmetrical placements of the dampers are taken into account through the 3-D modeling of the building. Finally, the comparison of the results shows that the probabilistic robust STMD system is capable of providing a reduction of about 52%, 42.5%, and 37.24% on the maximum displacement, velocity, and acceleration of the building top story, respectively.

• Earthquakes and Structures
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• v.17 no.5
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• pp.463-475
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• 2019

In this paper, a procedure to develop fragility curves of structures equipped with semi-active tuned mass dampers (SATMDs) considering multiple failure criteria has been presented while accounting for the uncertainties of the input excitation, structure and control device parameters. In this procedure, Latin hypercube sampling (LHS) method has been employed to generate 30 random SATMD-structure systems and nonlinear incremental dynamic analysis (IDA) has been conducted under 20 earthquakes to determine the structural responses, where failure probabilities in each intensity level have been evaluated using Monte Carlo simulation (MCS) method. For numerical analysis, an eight-story nonlinear shear building frame with bilinear hysteresis material behavior has been used. Fragility curves for the structure equipped with optimal SATMDs have been developed considering single and multiple failure criteria for different performance levels and compared with that of uncontrolled structure as well as structure controlled using passive tuned mass damper (TMD). Numerical analysis has shown the capability of SATMDs in significant enhancement of the seismic fragility of the nonlinear structure. Also, considering multiple failure criteria has led to increasing the fragility of the structure. Moreover, it is observed that the influence of the uncertainty of input excitation with respect to the other uncertainties is considerable.

• Journal of the Earthquake Engineering Society of Korea
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• v.26 no.4
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• pp.157-164
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• 2022

The TMD has a simpler structure than other vibration control devices and shows excellent control performance for the standardized vibration occurring in the structure. However, when the vibration cycle of the structure coincides with the vibration cycle of the TMD due to the sudden external loads, the off-tuning occurs, which threatens the structure while increasing the vibration width of the TMD. Therefore, Electromagnetic Tuned Mass Damper (ETMD) was developed as a semi-active TMD that prevents off-tuning while exhibiting excellent control performance like TMD. To verify the control performance of the developed ETMD, the bending behavior control performance evaluation experiment using a simple beam bridge was performed. The experimental method compared the mutual control power by experimenting with the existing TMD method and the developed ETMD under nine excitation frequency conditions. As a result, it was confirmed that the control effect of ETMD was about 4.85% higher than that of TMD at 3.02Hz, which generates the maximum displacement in the simple beam bridge. Also, the off-tuning occurred in some excitation conditions when using TMD, although the off-tuning did not occur when using ETMD. Therefore, the excellent control performance of the ETMD developed in this study was verified.

• Journal of Drive and Control
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• v.15 no.1
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• pp.38-49
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• 2018

This research describes the development model and testing of a hybrid damper which can be applicable to a vehicle suspension. The hybrid damper is devised to improve the performance of a conventional passive oil damper using a magneto-rheological (MR) accumulator which consists of a gas accumulator and a MR device. The level of damping is continuously variable by the means of control in the applied current in a MR device fitted to a floating piston which separates the gas and the oil chamber. A simple MR device is used to resist the movement of floating piston. At first a mathematical model which describes all flows within the conventional oil damper is formulated, and then a small MR device is also devised and adopted to a mathematical model to characterize the performance of the device.

• Structural Engineering and Mechanics
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• v.31 no.1
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• pp.39-56
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• 2009

Vibration is an undesirable phenomenon in a dynamic system like lightly damped aerospace structures and active vibration control has gradually been employed to suppress vibration. The objective of the current investigation is to introduce an active torsional magneto-rheological (MR) fluid based damper for vibration control of a typical nose landing gear. They offer the adaptability of active control devices without requiring the associated large power sources. A torsional damper is designed and developed based on Bingham plastic shear flow model. The numerical analysis is carried out to estimate the damping coefficient and damping force. The designed damper is fabricated and an experimental setup is also established to characterize the damper and these results are compared with the analytical results. A typical FE model of Nose landing gear is developed to study the effectiveness of the damper. Open loop response analysis has been carried out and response levels are monitored at the piston tip of a nose landing gear for various loading conditions without damper and with MR-damper as semi-active device. The closed-loop full state feedback control scheme by the pole-placement technique is also applied to control the landing gear instability of an aircraft.

• Journal of Biomedical Engineering Research
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• v.29 no.3
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• pp.179-186
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• 2008

This paper presents a portable tele-assessment system designed for remote evaluation of the hypertonic elbow joint of neurologically impaired patients. A patient's upper limb was securely strapped to a portable limb-stretching device which is connected through Internet to a portable haptic device by which a clinician remotely moved the patient's elbow joint and felt the resistance from the patient. Elbow flexion angle and joint torques were measured from both master and slave devices and bilaterally fed back to their counterparts. In order to overcome problems associated with the network latency, two different tele-operation schemes were proposed depending on relative speed of tasks compared to the amount of time delay. For slow movement tasks, the bilateral tele-operation was achieved in real-time by designing control architectures after causality analysis. For fast movement tasks, we used a semi-real-time tele-operation scheme which provided the clinicians with stable and transparent feeling. The tele-assessment system was verified experimentally on patients with stroke. The devices were made portable and low cost, which makes it potentially more accessible to patients in remote areas.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.1
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• pp.41-50
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• 2021

In this study, the flow path width (Gap Size), which is the flow path of fluid, was selected differently among various factors that determine the Ccontrol Force of MR damper, and the change of Control Force was confirmed accordingly. For this purpose, two MR dampers with a Gap Size of 1.0mm and 1.5mm were fabricated, respectively, and dynamic load experiments were conducted according to changes in applied current and vibration conditions The experimental results showed that the minimum Control Force was 3.2 times higher than 1.5mm in the case of 1.0mm Gap Size, and the maximum Control Force was 2.3 times higher than 1.5mm in the case of 1.0mm Gap Size. In addition, the increased width of the Control Force according to applied current was 34N for Gap Size 1.0mm, and 12.7N for Gap Size 1.5mm. As the gap Size increased, the overall Control Force and the increase in the Control Force by the applied current decreased. Next, the dynamic range, which is a performance evaluation index of the semi-active Control device, was 2.3 on average under 1.0mm condition and 2.8 on average under 1.5mm condition, confirming the possibility of utilization as a semi-active Control device.

• Journal of the Earthquake Engineering Society of Korea
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• v.6 no.2
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• pp.63-71
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• 2002

This paper examines the ASCE first generation benchmark problem for a seismically excited cable-stayed bridge, and proposes a new semi-active control strategy focusing on inclusion of effects of control-structure interaction. This benchmark problem focuses on a cable-stayed bridge in Cope Girardeau, Missouri, USA, for which construction is expected to be completed in 2003. Seismic considerations were strongly considered in the design of this bridge due to the location of the bridge in the New Madrid seismic zone and its critical role as a principal crossing of the Mississippi River. In this paper, magnetorheological(MR) fluid dampers are proposed as the supplemental damping devices, and a clipped-optimal control algorithm is employed. Several types of dynamic models for MR fluid dampers, such as a Bingham model, a Bouc-Wen model, and a modified Bouc-Wen model, are considered, which are obtained from data based on experimental results for full-scale dampers. Because the MR fluid damper is a controllable energy-dissipation device that cannot add mechanical energy to the structural system, the proposed control strategy is fail-safe in that bounded-input, bounded-output stability of the controlled structure is guaranteed. Numerical simulation results show that the performance of the proposed semi-active control strategy using MR fluid dampers is quite effective.