• Journal of the Earthquake Engineering Society of Korea
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• v.26 no.4
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• pp.149-156
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• 2022

Magneto-Rheological Fluid (MRF) is a functional fluid in which flow characteristics change into magnetic force due to its magnetic particles. When the semi-active control device does not use MRF for a long time, precipitation of magnetic particles and abnormal control force occur. Thus, Electro Magneto-Rheological Fluid (EMRF), which improves the precipitation of magnetic particles for MRF and exhibits existing control performance, was developed in this study. First, the optimal mix proportion ratio was selected by conducting a precipitation experiment and a controlled force test by varying the content of grease based on the existing MRF components. Also, EMRF was applied to the shear-type damper to evaluate the control performance when applied to the control device. The cylinder-type damper was developed to apply to the structure, and control performance evaluation was conducted. The result confirmed that the precipitation of the magnetic particles was improved, while the damper using EMRF exhibited excellent control performance.

• Smart Structures and Systems
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• v.16 no.6
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• pp.1003-1021
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• 2015

MR dampers have been proposed for the control of cable vibration of cable-stayed bridge in recent years due to their high performance and low energy consumption. However, the highly nonlinear feature of MR dampers makes them difficult to be designed with efficient semi-active control algorithms. Simulation study has previously been carried out on the cable-MR damper system using a semi-active control algorithm derived based on the universal design curve of dampers and a bilinear mechanical model of the MR damper. This paper aims to verify the effectiveness of the MR damper for mitigating cable vibration through a full-scale experimental test, using the same semi-active control strategy as in the simulation study. A long stay cable fabricated for a real bridge was set-up with the MR damper installed. The cable was excited under both free and forced vibrations. Different test scenarios were considered where the MR damper was tuned as passive damper with minimum or maximum input current, or the input current of the damper was changed according to the proposed semi-active control algorithm. The effectiveness of the MR damper for controlling the cable vibration was assessed through computing the damping ratio of the cable for free vibration and the root mean square value of acceleration of the cable for forced vibration.

• Structural Engineering and Mechanics
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• v.19 no.6
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• pp.721-747
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• 2005

The strong need of verifying theories formulated for semi-active control through applications to real structures is due to the fact that theoretical research on semi-active control systems is not matched by a corresponding satisfactory experimental activity. This paper shows how a smart system including magnetorheological devices as damping elements can be implemented in a large-scale structural model, by describing in detail the kind of electronics (dedicated hardware and software) adopted during the experimental campaign. It also describes the most interesting results in terms of reduction of the seismic response (either experimental or numerical) of the semi-actively controlled structure compared to a passive operating control system, and in terms of the evaluation criteria proposed in the benchmark for seismically excited controlled buildings. The paper also explains how to derive from the classical theory of optimal control the adopted control logic, based on a clear physical approach, and provides an exhaustive picture of the time delays characterizing the control sequence.

• Journal of Korean Association for Spatial Structures
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• v.15 no.4
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• pp.81-89
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• 2015

Damped outrigger systems have been proposed as a novel energy dissipation system to protect tall buildings from severe earthquakes and strong wind loads. In this study, semi-active damping devices such as magnetorheological (MR) dampers instead of passive dampers are installed vertically between the outrigger and perimeter columns to achieve large and adaptable energy dissipation. Control performance of semi-active outrigger damper system mainly depends on the control algorithm. Fuzzy logic control algorithm was used to generate command voltage sent to MR damper. Genetic algorithm was used to optimize the fuzzy logic controller. An artificial earthquake load was generated for numerical simulation. A simplified numerical model of damped outrigger system was developed. Based on numerical analyses, it has been shown that the semi-active damped outrigger system can effectively reduce both displacement and acceleration responses of the tall building in comparison with a passive outrigger damper system.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.278-281
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• 2003

The focus of this research is to realize the function which is equivalent to the active suspension system, with controlling semi-active suspension through the attenuation of power variable damper in lower cost and smaller energy. Actually some semi-active suspension systems have been adopted, but they are not sufficient in performance. The authors intended to develop more effective and practical system and applied the optimal control technique. The results of experiments with practical suspension system showed a degree of improvement of comfortableness.

• Smart Structures and Systems
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• v.13 no.3
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• pp.435-451
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• 2014

In this paper, we investigate the vibration control of multimodal structures and present an efficient control law that requires less energy supply than active strategies. This strategy is called modal global semi-active control and is designed to work as effectively as the active control and consume less power which represents its major limitation. The proposed law is based on an energetic management of the optimal law such that the controller follows this latter only if there is sufficient energy which will be extracted directly from the system vibrations itself. The control algorithm is presented and validated for a cantilever beam structure subjected to external perturbations. Comparisons between the proposed law performances and those obtained by independent modal space control (IMSC) and semi-active control schemes are offered.

• Smart Structures and Systems
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• v.5 no.3
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• pp.261-277
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• 2009

A fuzzy-sliding mode controller is presented to control the dynamics of semi-active suspension systems of vehicles using magneto-rheological (MR) fluid dampers. A full car model is used to design and evaluate the performance of the proposed semi-active controlled suspension system. Four mixed mode MR dampers are designed, manufactured, and integrated with four independent sliding mode controllers. The siding mode controller is designed to decrease the energy consumption and maintain robustness. In order to overcome the chattering of the sliding mode controllers, a fuzzy logic control strategy is merged into the sliding mode controller. The proposed fuzzy-sliding mode controller is designed and fabricated. The performance of the semi-active suspensions is evaluated in both the time and frequency domains. The obtained results demonstrate that the proposed fuzzy-sliding mode controller can effectively suppress the vibration of vehicles and improve their ride comfort and handling stability. Furthermore, it is shown that the "chattering" of the sliding mode controller is smoothed when it is integrated with a fuzzy logic control strategy. Although the cost function of the fuzzy-sliding mode control is a slightly higher than that of a classical LQR controller, the control effectiveness and robustness are enhanced considerably.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.4
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• pp.135-143
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• 2003

In this study, a real-time simulation model was developed for tracked vehicles with in-arm type semi-active hydro-pneumatic suspension unit using MATLAB S-functions. Since the vehicle model uses relative coordinates and massless link elements, the developed model has an enhanced analytic time performance. Through the comparison of simulation results with multi-body software(DADS), the vehicle model is verified. A controller using on-off skyhook control algorithm is designed with the pilot-centre]led proportional valve based on conventional damper characteristics. Exploiting the developed tracked vehicle model with other subsystem model such as a controller model, a suspension unit model, and a test road model, computer simulations are carried out. Control simulation results with the developed tracked vehicle model show that the semi-active suspension control system has a better performance than the conventional suspension system.

• Smart Structures and Systems
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• v.24 no.1
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• pp.141-155
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• 2019

This work evaluates the influence of negative stiffness on the performances of various vehicle suspension systems, and proposes a re-centering negative stiffness device (NSD). The re-centering NSD consists of a passive magnetic negative stiffness spring and a positioning shaft with a re-centering function. The former produces negative stiffness control forces, and the latter prevents the amplification of static spring deflection. The numerical simulations reveal that negative stiffness can improve the ride comfort of a vehicle without affecting its road holding abilities for either passive or semi-active suspension systems. In general, the improvement degree of ride comfort increases as negative stiffness increases. For passive suspension system, negative stiffness brings in negative stiffness feature in the control forces, which is helpful for the ride comfort of a vehicle. For semi-active suspensions, negative stiffness can alleviate the impact of clipped damping in semi-active dampers, and thus the ride comfort of a vehicle can be improved.

• Journal of Mechanical Science and Technology
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• v.14 no.8
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• pp.807-815
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• 2000

In this paper, modified discrete time preview control algorithms for active and semi-active suspension systems are derived based on a simple mathematical 4 DOF half-car model. The discrete time preview control laws for ride comfort are employed in the simulation. The algorithms for MIMO system contain control strategies reacting against body forces that occur at cornering, accelerating, braking, or under payload, in addition to road disturbances. Matlab simulation results for the discrete time case are compared with those for the continuous time case and the appropriateness of the discrete time algorithms are verified by the of simulation results. Passive, active, and semi-active system responses to a sinusoidal input and an asphalt road input are analysed and evaluated. The simulation results show the extent of performance degradation due to numerical errors related to the length of the sampling time and time delay.