• Energy Research
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• Hong Kong Polytechnic University close

Abstract In this paper, the characteristics of a hybrid regenerative electromagnetic (EM) damper are first determined and experimentally examined. The main idea is to have two modes of operation for the EM damper, namely passive energy harvesting and semi-active modes. In the passive mode, the vibrational energy of an underlying structure is harvested and stored in a rechargeable battery. The harvested energy can then be employed in the semi-active control mode to supply the power demand for the required sensors and microcontroller. This hybrid damper would thus be capable of realizing the characteristics of a self-powered EM damper. A prototype of the damper was designed and tested under different harmonic excitations. The mechanical and electrical characteristics of both passive and semi-active modes were investigated and verified. The average harvested power and current were measured, and the efficiency of the different elements of the damper is determined. Next, for tuning the semi-active mode, a sliding mode control algorithm was proposed which considers the inherent nonlinear parasitic force of the EM damper. The proposed algorithm aims to track the response of an optimally controlled structure, by having knowledge of the bound of the nonlinear parasitic force. Finally, the effects of the proposed damper and sliding mode controller for vibration mitigation of a small-scale structure is demonstrated through a series of shake table tests, under harmonic and random excitations.

Abstract In this paper, the characteristics of a hybrid regenerative electromagnetic (EM) damper are first determined and experimentally examined. The main idea is to have two modes of operation for the EM damper, namely passive energy harvesting and semi-active modes. In the passive mode, the vibrational energy of an underlying structure is harvested and stored in a rechargeable battery. The harvested energy can then be employed in the semi-active control mode to supply the power demand for the required sensors and microcontroller. This hybrid damper would thus be capable of realizing the characteristics of a self-powered EM damper. A prototype of the damper was designed and tested under different harmonic excitations. The mechanical and electrical characteristics of both passive and semi-active modes were investigated and verified. The average harvested power and current were measured, and the efficiency of the different elements of the damper is determined. Next, for tuning the semi-active mode, a sliding mode control algorithm was proposed which considers the inherent nonlinear parasitic force of the EM damper. The proposed algorithm aims to track the response of an optimally controlled structure, by having knowledge of the bound of the nonlinear parasitic force. Finally, the effects of the proposed damper and sliding mode controller for vibration mitigation of a small-scale structure is demonstrated through a series of shake table tests, under harmonic and random excitations.

Abstract The present paper investigates the axial splitting and curling behaviour of circular metal tubes. Mild steel and aluminum circular tubes were pressed axially onto a series of conical dies each with different semi-angle. By pre-cutting eight 5 mm slits which were distributed evenly at the lower end of each tube, the tube split axially and the strips curled outward. Experiments showed that this mechanism results in a long stroke and a steady load. An approximate analysis is presented which successfully predicts the number of propagated cracks, the curling radius and the force applied. This analysis takes into account ductile tearing of the cracks, plastic bending/stretching and friction. Effects of tube dimensions, semi-angle of the die and friction are discussed in detail.

Abstract The present paper investigates the axial splitting and curling behaviour of circular metal tubes. Mild steel and aluminum circular tubes were pressed axially onto a series of conical dies each with different semi-angle. By pre-cutting eight 5 mm slits which were distributed evenly at the lower end of each tube, the tube split axially and the strips curled outward. Experiments showed that this mechanism results in a long stroke and a steady load. An approximate analysis is presented which successfully predicts the number of propagated cracks, the curling radius and the force applied. This analysis takes into account ductile tearing of the cracks, plastic bending/stretching and friction. Effects of tube dimensions, semi-angle of the die and friction are discussed in detail.

Abstract The primary objective of this research is to extend energy balance concept in seismic behavior evaluation of low-to-medium rise frame systems with energy dissipation fuses dominated by racking deformations. At its core, energy demand indices under ground motions considering both peak responses and cumulative responses are quantified to develop a dual-energy-demand-indices-based procedure for damage-control behavior evaluation. Firstly, based on the experimentally validated hysteretic feature and representative ground motion ensembles, a parametric study is conducted considering the demand indices of the energy factor and the cumulative ductility. Results of the indices distribution and dispersion are presented in detail. Subsequently, a stepwise procedure that accounts for the peak demand and the cumulative demand is constructed. Then, the procedure is applied in prototype structures for validation. Results indicate that the consideration of dual energy demand indices is necessary for evaluation of systems with fuses, and these indices are influenced by structural nonlinear parameters and ground motions properties. The procedure based on the dual energy demand indices can be used to evaluate the structural damage-control behavior with satisfactory accuracy considering the peak response, the cumulative response, and the energy distribution along stories.

Abstract The primary objective of this research is to extend energy balance concept in seismic behavior evaluation of low-to-medium rise frame systems with energy dissipation fuses dominated by racking deformations. At its core, energy demand indices under ground motions considering both peak responses and cumulative responses are quantified to develop a dual-energy-demand-indices-based procedure for damage-control behavior evaluation. Firstly, based on the experimentally validated hysteretic feature and representative ground motion ensembles, a parametric study is conducted considering the demand indices of the energy factor and the cumulative ductility. Results of the indices distribution and dispersion are presented in detail. Subsequently, a stepwise procedure that accounts for the peak demand and the cumulative demand is constructed. Then, the procedure is applied in prototype structures for validation. Results indicate that the consideration of dual energy demand indices is necessary for evaluation of systems with fuses, and these indices are influenced by structural nonlinear parameters and ground motions properties. The procedure based on the dual energy demand indices can be used to evaluate the structural damage-control behavior with satisfactory accuracy considering the peak response, the cumulative response, and the energy distribution along stories.

Abstract Over the past decades, the research on structural vibration control has mainly focused on ‘energy dissipation’ strategy using various dampers for hazard mitigation. This paper proposes a novel application of linear motion electromagnetic (EM) devices, termed linear EM dampers hereinafter, for both vibration damping and energy harvesting. The kinetic energy caused by earthquakes, wind or traffic loads is not only dissipated by EM dampers, but also stored by energy-harvesting electric circuits connected to EM dampers. The green and regenerative energy output may provide an alternative power supply to portable and wireless devices at remote sites. This paper presents a theoretical and experimental study of linear EM dampers connected with four representative circuits. The dynamic characteristics of linear EM dampers, including parasitic damping, EM damping, energy conversion efficiency and output power, are modeled and discussed systematically in each case. The modeling is further verified by a series of dynamic testing of a small-scale linear EM damper, which is cyclically tested on a MTS machine at different frequencies and amplitudes. A good match between the modeling and testing results clearly demonstrates that the described model can predict the performance of the linear EM damper and energy harvesting circuit very well. The promises and challenges of using EM dampers in future civil infrastructure for both vibration damping and energy harvesting are discussed based on the outcome of this study.

Abstract Over the past decades, the research on structural vibration control has mainly focused on ‘energy dissipation’ strategy using various dampers for hazard mitigation. This paper proposes a novel application of linear motion electromagnetic (EM) devices, termed linear EM dampers hereinafter, for both vibration damping and energy harvesting. The kinetic energy caused by earthquakes, wind or traffic loads is not only dissipated by EM dampers, but also stored by energy-harvesting electric circuits connected to EM dampers. The green and regenerative energy output may provide an alternative power supply to portable and wireless devices at remote sites. This paper presents a theoretical and experimental study of linear EM dampers connected with four representative circuits. The dynamic characteristics of linear EM dampers, including parasitic damping, EM damping, energy conversion efficiency and output power, are modeled and discussed systematically in each case. The modeling is further verified by a series of dynamic testing of a small-scale linear EM damper, which is cyclically tested on a MTS machine at different frequencies and amplitudes. A good match between the modeling and testing results clearly demonstrates that the described model can predict the performance of the linear EM damper and energy harvesting circuit very well. The promises and challenges of using EM dampers in future civil infrastructure for both vibration damping and energy harvesting are discussed based on the outcome of this study.

Abstract This paper presents the energy factor of trilinear single-degree-of-freedom (SDOF) systems representing low-to-medium rise damage-control buildings equipped with energy dissipation fuses under near-fault earthquake ground motions, and the focus is given to the ultimate stage of the systems. The hysteretic behaviour of a damage-control building structure with energy dissipation fuses is firstly idealised by the trilinear kinematic model, and the rationality of the trilinear idealisation is validated by the test result of a representative damage-control structure. Subsequently, the hysteretic law is assigned to SDOF systems and the seismic demand of the systems quantified by the energy factor is examined through extensive nonlinear dynamic analyses with an ensemble of near-fault earthquake ground motions as input excitations. Based on the statistical investigations of more than twenty-one (21) million inelastic spectral analyses of SDOF systems subjected to ground motions, the effect of the post-yielding stiffness ratios and the corresponding inelastic deformation range of the multiple yielding stages on the energy factor of the trilinear SDOF systems are examined in detail, and the corresponding empirical expressions for quantifying the energy factor demand are also developed. The observations of this work show that the energy factor of trilinear SDOF systems subjected to near-fault earthquake ground motions is appreciably influenced by the hysteretic parameters in multiple yielding stages, and engineers have sufficient flexibility to modulate the seismic energy balance of the system by adjusting these influential parameters. The proposed empirical expressions offer a practical tool for estimating the energy factor of a low-to-medium rise damage-control buildings equipped with energy dissipation fuses subjected to near-fault ground motions in the preliminary design phase.