Cable vibration and monitoring the cable maintenance are inevitable parts of cable bridges. To integrate both problems, the electromagnetic (EM) devices are proposed to self-power damper and studied in various ways. The conventional EM devices have a lack of damping performance that additional damping is needed to mitigate the cable vibration. Therefore, the regenerative hybrid electrodynamic damper (RHED) is developed to increase the damping performance which can mitigate the cable vibration properly while electrical energy is generated. In this study, experiments for mechanical damping of RHED and vibration induced electrical energy are conducted to investigate the RHED configuration. The applied damper has various characteristics that can be used in civil engineering such as high induced voltage and variation of damping force. The damping force is varying according to external resistance and condition of excitation. The characteristics of RHED are considered to produce the energy harvesting circuit. This study increases the harvesting energy and charges the rechargeable battery through the proposed circuit. Besides, the proposed harvesting circuit perform more than 70% efficiency in certain excitation. As the result, energy harvesting and damping mechanism can be utilized simultaneously by grasping the relationship between the RHED and a circuit.
Magnetorheological elastomer (MRE)-based base isolation system has been proposed to compensate for the drawbacks of the existing passive-type base isolation system. MRE is one of smart material with magnetorheological (MR) effect that can change the stiffness and damping ratio in real time when the magnetic field is applied. The conventional MREbased base isolation system has inter-place between MRE and electromagnetic system. This is determined in consideration of the deformation of MRE, resulting in loss of magnetic flux density and excessive volume of MRE-based base isolation system. Since the strain of the MRE should be considered to be 100 % as base isolation system, the size of the base isolation system becomes large and the practical applicability is remarkably reduced. In addition, the loss of the magnetic flux density increases according to the size of the inter-space between MRE and electromagnetic system. Therefore, a new type of electromagnetic system is proposed to address these problems. In this study, an electromagnetic system which can move with MRE by separating it to the laminated type is proposed. MRE-based base isolation system with the laminated electromagnetic system occupies a small volume compared to the conventional MRE-based base isolation system and can form magnetic closed loop which can minimize the loss of the magnetic flux density. The numerical simulation was performed to compare the proposed electromagnetic system and the conventional MRE-based base isolation. From the numerical simulation, the lab-scale experiment was carried out and the proposed method can be utilized to improve the reality of MRE-based base isolation system.
Bridge cables should always be equipped with vibration mitigation measures and monitoring techniques. The proposed electromagnetic damper was developed to reduce vibration of the cable and utilize induction current as the power source of the wireless sensor. Major parameters for the design of the damper were derived. Then, the cable experiment was carried out under the conditions of free vibration and force vibration. For free vibration conditions, the change of damping ratio according to the acceleration amplitude evaluation point was analyzed through Hilbert transform. As a result, the damping performance of the passive electronic damper applying the external resistance under the free vibration condition was improved to 2.18% of the maximum damping ratio and 1.88% of the average damping ratio. Under the sinusoidal forced vibration conditions, it was found that the acceleration and frequency domain response at each measurement point of the cable decreased by 30% to 50% or more, and the RMS displacement response decreased by 45% to 49% under the excitation with 1st to 3rd natural frequencies. In addition, it has been confirmed that effective damping performance is exhibited in the 2nd and 3rd natural frequency, which are the main response conditions of the cable. Hybrid simulation was carried out to evaluate the energy harvesting performance of the electromagnetic damper. As a result, the output power was 174.6mWh at the mean wind speed of 5.4 m/s. Even if the sensor and the battery loss were considered, enough power was generated to operate the wireless sensor.
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