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In this research, an attention-based feature fusion network (AFFNet), with a backbone residual network (ResNet101) enhanced with two attention mechanism modules, is proposed for automatic pixel-level detection of concrete crack. In particular, the inclusion of attention mechanism modules, for example, the vertical and horizontal compression attention module (VH-CAM) and the efficient channel attention upsample module (ECAUM), is to enable selective concentration on the crack feature. The VH-CAM generates a feature map integrating pixel-level information in vertical and horizontal directions. The ECAUM applied on each decoder layer combines efficient channel attention (ECA) and feature fusion, which can provide rich contextual information as guidance to help low-level features recover crack localization. The proposed model is evaluated on the test dataset and the results reach 84.49% for mean intersection over union (MIoU). Comparison with other state-of-the-art models proves high efficiency and accuracy of the proposed method.

Magnetorheological (MR) grease, which is a type of magneto-sensitive smart material, exhibits complex viscoelastic behavior under different magnetic fields. Storage and loss moduli from oscillatory test are commonly used to characterize such field-dependent viscoelastic behavior. However, they are not able to represent the higher harmonic nonlinearity appeared in oscillatory responses under large amplitude oscillatory (LAOS) shear. In this paper, an investigation is conducted on the characterization of the filed-dependent nonlinearity of MR grease under LAOS by utilizing of Fourier transform (FT)-Chebyshev analysis. To capture the higher harmonic nonlinearity for the modeling and analysis, a comprehensive test program has been conducted. Firstly, MR grease with 70% weight percentage of carbonyl iron particles (MRG-70) is prepared and the stress response of MRG-70 under the oscillatory shear from small to large strain amplitudes with different magnetic field are measured. Then the higher harmonics in stress response signal are used to detect the intercycle nonlinearity of MRG-70 and compare with the traditional analysis method of dynamic modulus. Further, the elastic and viscous measures from FT-Chebyshev analysis are obtained to capture the inter-/intracycle nonlinear behaviors, that is, strain stiffening/softening, shear thickening/thinning, of MRG-70 under LAOS. It is found that, in the presence of magnetic fields, the onset of the intercycle nonlinearities of MRG-70 is originated from shear thickening of MR grease. With the further increase of the shear strain, MRG-70 exhibits the nonlinearities with different combinations of strain stiffening/softening and shear thickening/thinning.

In this paper, to improve the heat dissipation efficiency of a radiator for focal plane assemblies, a topology optimization method is introduced into the design process. For the realization of the optimization, an objective of maximal thermal stiffness concerning the radiator is formulated. The topology optimization is performed under the same mass constraint of 2.05 kg as the initial design. To improve the manufacturability of topology optimization result, an inverse design is conducted to reconstruct a new model. In transient thermal simulation, the average maximal temperature on focal plane assemblies with a reconstructed radiator is 8.626 °C, while the average maximal temperature with the initial design is 9.793 °C. Compared to the initial design, a decrease of 1.167 °C on maximal temperature is achieved. As the heat dissipation efficiency of the proposed radiator design is improved compared to the initial design, it is meaningful in future applications.

In this paper, a “smart” base isolation strategy is proposed in this study utilising a semi-active magnetorheological elastomer (MRE) isolator whose stiffness can be controlled in real-time and reversible fashion. By modulating the applied current, the horizontal stiffness of the MRE isolator can be controlled and thus the control action can be generated for the isolated structure. To overcome the inherent nonlinearity and hysteresis of the MRE isolator, radial basis function neural network based fuzzy logic control (RBF-NFLC) was developed due to its inherent robustness and capability in coping with uncertainties. The NFLC was optimised by a non-dominated sorting genetic algorithm type II (NSGA-II) for better suited fuzzy control rules as well as most appropriate parameters for the membership functions. To evaluate the effectiveness of the proposed smart base isolation system, four scenarios are tested under various historical earthquake excitations, i.e. bare building with no isolation, passive isolated structure, MRE isolated structure with Bang-Bang control, MRE isolated structure with proposed NFLC. A three-storey shear building model was adopted as the testing bed. Through the testing results, limited performance of passive isolation system was revealed. In contrast, the adaptability of the proposed isolation strategy was demonstrated and it is proven that the smart MRE base isolation system is able to provide satisfactory protection for both structural and non-structural elements of the system over a wide range of hazard dynamic loadings.

Tuned inerter damper (TID) has recently gained increasing attention as a new structural control mechanism for seismic protection of structures. Currently, theoretical investigations are undertaken by researchers to reveal its fundamentals and to understand its underline principles in altering the structural performances of structures against dynamic loadings. However, the comprehensive study of optimization design of TID for undamped structures is lacking and the majority of the research focuses on the optimization of TID for structures without any damping. This research evaluates the [Formula: see text] and [Formula: see text] optimal designs of TIDs on the structures with damping. Using SDOF structure as an example, the frequency response function of the system equipped with TID underground motion excitation is obtained. The [Formula: see text] and [Formula: see text] designs of TID for structures without damping are derived considering various response parameters using analytical method. A numerical search method is utilized for the [Formula: see text] and [Formula: see text] designs of TID for structures with damping; meanwhile, a set of explicit formulae are obtained by curve-fitting for convenience in the application. Finally, the relative motion response of the inerter is explored, and an optimal design formula of TID which can reduce the displacements of primary mass and inerter simultaneously, is proposed.

Magnetorheological elastomer (MRE) base isolations have attracted considerable attention over the last two decades thanks to its self-adaptability and high-authority controllability in semi-active control realm. Due to the inherent nonlinearity and hysteresis of the devices, it is challenging to obtain a reasonably complicated mathematical model to describe the inverse dynamics of MRE base isolators and hence to realise control synthesis of the MRE base isolation system. Two aims have been achieved in this paper: i) development of an inverse model for MRE base isolator based on optimal general regression neural network (GRNN); ii) numerical and experimental validation of a real-time semi-active controlled MRE base isolation system utilising LQR controller and GRNN inverse model. The superiority of GRNN inverse model lays in fewer input variables requirement, faster training process and prompt calculation response, which makes it suitable for online training and real-time control. The control system is integrated with a three-storey shear building model and control performance of the MRE base isolation system is compared with bare building, passive-on isolation system and passive-off isolation system. Testing results show that the proposed GRNN inverse model is able to reproduce desired control force accurately and the MRE base isolation system can effectively suppress the structural responses when compared to the passive isolation system.

Adaptive negative stiffness device is one of the promising seismic protection devices since it can generate seismic isolation effect through negative stiffness when it is mostly needed and achieve similar vibration mitigation as a semi-active control device. However, the adaptive negative stiffness device generally combined with linear viscous damping underpins the drawback of degrading the vibration isolation effect during the high-frequency region. In this paper, a modified adaptive negative stiffness device (MANSD) with the ability to provide both lateral negative stiffness and nonlinear damping by configuring linear springs and linear viscous dampers is proposed to address the above issue. The negative stiffness and nonlinear damping are realised through a linkage mechanism. The fundamentals and dynamic characteristics of a SDOF system with such a device are analyzed and formulated using the Harmonic Balance Method, with a special focus on the amplitude–frequency response and transmissibility of the system. The system with damping nonlinearity as a function of displacement and velocity has been proven to have attractive advantages over linear damping in reducing the transmissibility in the resonance region without increasing that in the high-frequency region. The effect of nonlinear damping on suppressing displacement and acceleration responses is numerically verified under different sinusoidal excitations and earthquakes with different intensities. Compared with linear damping, the MANSD with nonlinear damping could achieve additional reductions on displacement and acceleration under scaled earthquakes, especially intensive earthquakes.

Stretchable and lightweight polymer composite material possessing tunable microwave absorption (MA) properties under thermal radiations remain a significant challenge. Here, we proposed a facile strategy to fabricate stretchable, magnetic composite skeletons by incorporating the tadpole-like CNTs@Fe3O4 nanoparticles into self-foaming polyurethane (PU) matrix and the electromagnetic responsive of CNTs@Fe3O4/PU composite foams with different CNTs contents under heating−cooling cycle in a temperature range of 253 −333 K were carefully investigated. Enhanced complex permittivity and shifting peak frequency were observed at elevated temperatures. For instance, the 70-CNTs@Fe3O4/PU sample with 15 wt% loading content at 333 K exhibits excellent MA properties including a minimum reflection loss (RLm) of −66.9 dB and ultrabroad effective frequency bandwidth (RL ≤ −20 dB) of 9.98 GHz at the thickness of 1.58−3.37 mm. Meanwhile, great recoverability in terms of RL-f profile was achieved in the process of thermal cooling back to 253 K. Such adjustable MA property was attributed to the well-matched impedance and dramatic attenuation ability, benefiting from the temperature-dependant electrical conductivity, abundant interfacial polarization and interior microcellular structures. Besides, the rising temperature increased the sample elongation and electrical conductivity with a slight sacrifice of maximum tensile strength. This stretchable PU skeleton with a unique assembly of CNTs and Fe3O4 nanoparticles are expected to be promising candidates as smart absorbers for application in the harsh environments.

© Institution of Mechanical Engineers 2016. This paper presents the design and multi-physics optimization of a novel multi-coil magnetorheological (MR) damper with a variable resistance gap (VRG-MMD). Enabling four electromagnetic coils (EMs) with individual exciting currents, a simplified magnetic equivalent circuit was presented and the magnetic flux generated by each voltage source passing through each active gap was calculated as vector operations. To design the optimal geometry of the VRG-MMD, the multi-physics optimization problem including electromagnetics and fluid dynamics has been formulated as a multi-objective function with weighting ratios among total damping force, dynamic range, and inductive time constant. Based on the selected design variables (DVs), six cases with different weighting ratios were optimized using Bound Optimization BY Quadratic Approximation (BOBYQA) technique. Finally, the vibration performance of the optimal VRG-MMD subjected to sinusoidal and triangle displacement excitations was compared to that of the typical multi-coil MR damper.

Magnetorheological gel (MRG) excels in the material properties in term of adjustability and sedimentation performance, which could upgrade the performances of the current magnetorheological fluid based adjustable devices for structural control and vibration mitigation. However, the characterization and modelling of the stress-strain hysteresis responses of MRG has not been reported in the past, which are fundamental steps towards engineering applications. In this study, the stress-strain hysteresis of polyurethane based MRG sample with 60% carbonyl iron particle weight fraction was characterized under sinusoidal shear excitations with broad ranges of strain amplitude (5%–100%), excitation frequency (0.1 Hz–2 Hz) and magnetic fields (0–0.91 T). Significant stress overshooting phenomenon were observed under the application of low magnetic fields (0.27 T). A structurally-simple and accurate phenomenological model has been established to capture this unique nonlinearity. By validating the experimental results, the proposed model accurately predicts the hysteretic behaviour and the overshoot of the MRG under the excitation scenarios and the magnetic fields considered. Finally, the support vector machine (SVM) was implemented to provide the solution to the model generalization. The SVM-assisted model showed good agreement with the experimental data and can benefit the efficiency and viability in developing controllable MRG-based devices and system.

As an essential and critical step, magnetic circuit model is usually implemented in the design of efficient and compact magnetorheological (MR) devices, such as MR dampers and MR elastomer isolators. Conventional magnetic circuit analysis simplifies the analysis by ignoring the magnetic flux leakage and magnetic fringing effect. These assumptions are sufficiently accurate in dealing with less complicated designs, featuring short magnetic path lengths such as in an MR damper. However, when dealing with MR elastomer devices, such simplification in magnetic circuit analysis results in inaccuracy of dimensioning and performance estimation of the devices due to their sophisticated design and complex magnetic paths. Modelling permanent magnets also imposes challenges in the magnetic circuit analysis. This work proposes an improved approach to include magnetic flux fringing effect in magnetic circuit analysis for MR elastomer device. An MRE-based isolator containing multiple MRE layers and both a permanent magnet and an exciting coil is used in this paper as a case study. The results are compared to those of conventional magnetic circuit modeling and finite element analysis to demonstrate the effectiveness of the proposed approach.

© The Author(s) 2015. In the past decades, base isolation techniques have become increasingly popular for seismic protection of civil structures owing to its capability of decoupling buildings from harmful ground motion. However, it has been recognised recently that the traditional passive base isolation technique could encounter a serious problem during earthquakes due its incapability in adjusting the isolation frequency to cope with the unpredictability and diversity of earthquakes. To address this challenge, a great deal of research efforts have been conducted to improve traditional base isolation systems, most of which focused on hybrid supplementary devices (passive, active and semi-active types) for the isolators to control displacement or to dissipate seismic energy. On the other hand, the most effective approach to address the aforementioned challenge should lay on varying isolator stiffness in real-time to achieve real-time spontaneous decoupling. A recent advance of the development of an adaptive magneto-rheological elastomer base isolator has brought such idea to reality as the new magneto-rheological elastomer base isolator is capable to alter its stiffness significantly in real-time. In this article, an innovative smart base isolation system employing such magneto-rheological elastomer isolator is proposed and a novel frequency control algorithm is developed to shift the fundamental frequency of the structure away from the dominant frequency range of earthquakes. Such design enables the building to avoid resonant state in real-time according to the on-coming spectrum of the earthquakes. Extensive simulation has been conducted using a five-storey benchmark model with the isolation system, and testing results indicate that the proposed control system is able to significantly suppress both the floor accelerations and inter-storey drifts simultaneously under different earthquakes.

© SAGE Publications. Available magnetorheological elastomer devices normally consist one to two layers of small-size magnetorheological elastomer materials. To be used in large-scale structures, magnetorheological elastomer devices with multiple larger magnetorheological elastomer materials are expected. This article addresses the critical issue in designing a large-scale device with multiple layers of low magnetic conductive magnetorheological elastomer materials, that is, magnetic circuit design. The primary target in magnetic circuit design for magnetorheological elastomer devices is to provide sufficient and uniform magnetic field to all magnetorheological elastomer layers in the device. In this article, finite element investigations are conducted. An innovative magnetic circuit design is proposed for magnetorheological elastomer base isolator with multi-layer of magnetorheological elastomer materials. In the design, laminated magnetorheological elastomer and steel structure is adopted as part of the magnetic core together with two steel blocks. Cylindrical steel tube is used as the yoke of the magnetic circuit. Two plates are placed on the top and bottom of the device to form enclosed magnetic path in the device. Finite element results showed that such innovative magnetic design is able to provide sufficient and uniform magnetic field to all magnetorheological elastomer layers, that is, 25 magnetorheological elastomer layers with thickness of 1 mm and diameter of 120 mm in this case. Finally, the influence of lateral deformation of the magnetorheological elastomer base isolator on the magnetic field is investigated. It is found that the magnetic field in magnetorheological elastomer materials deteriorates when the deformation of the device increases.

© SAGE Publications. Laminated magnetorheological elastomer base isolator is regarded as one of the most promising candidates for realizing adaptive base isolation for civil structures. However, the intrinsic hysteretic and nonlinear behavior of magnetorheological elastomer base isolators imposes challenge for adopting the device to accomplish high-accuracy performance in structural control. Therefore, it is essential to develop an accurate model for symbolizing this unique characteristic before designing a feedback controller. So far, some classical parametric models, such as Bouc-Wen, Dahl, and LuGre, have been proposed to depict the hysteretic response of magnetorheological devices, that is, magnetorheological damper, which may also be used for describing the nonlinear behavior of magnetorheological elastomer base isolator. However, the parameter identification is difficult to implement due to the nonlinear differential equations existing in these models. Considering this problem, this article proposes a nonparametric model, that is, an artificial neural network-based model with 3 input neurons, 18 hidden neurons, and 1 output neuron, to predict the magnetorheological elastomer isolator behavior. In this model, the ant colony algorithm is employed for model training to obtain the optimal weights based on the force-displacement/velocity data sampled from the magnetorheological elastomer isolator. Finally, experimental data are used to validate the effectiveness of the proposed artificial neural network-based model with the good forecasting results.

Over the past few decades, wireless sensor networks have been widely used in the field of structure health monitoring of civil, mechanical, and aerospace systems. Currently, most wireless sensor networks are battery-powered and it is costly and unsustainable for maintenance because of the requirement for frequent battery replacements. As an attempt to address such issue, this article theoretically and experimentally studies a compression-based piezoelectric energy harvester using a multilayer stack configuration, which is suitable for civil infrastructure system applications where large compressive loads occur, such as heavily vehicular loading acting on pavements. In this article, we firstly present analytical and numerical modeling of the piezoelectric multilayer stack under axial compressive loading, which is based on the linear theory of piezoelectricity. A two-degree-of-freedom electromechanical model, considering both the mechanical and electrical aspects of the proposed harvester, was developed to characterize the harvested electrical power under the external electrical load. Exact closed-form expressions of the electromechanical models have been derived to analyze the mechanical and electrical properties of the proposed harvester. The theoretical analyses are validated through several experiments for a test prototype under harmonic excitations. The test results exhibit very good agreement with the analytical analyses and numerical simulations for a range of resistive loads and input excitation levels. © 2014 The Author(s).

This paper presents the design and evaluation of a novel permanent magnet (PM) energy harvesting system for scavenging electrical energy from ambient vibrations. A two-phase tubular linear PM vibration energy harvester consisting of a mover attached with permanent magnets and a slotted stator with built-in two-phase electromagnetic coils is proposed to convert vibrational kinetic energy into electrical energy. Aiming at maximizing the efficiency of vibrationto-electrical energy conversion under designated vibration and limited space requirement, a systematic research, including innovative device design, theoretical modelling and analysis, and finite element evaluation on the PM vibration energy harvester will be presented in this paper. In addition, the methodology of winding the two-phase coils in slotted stator is explicated in order to fully utilize the harvested electrical energy. A two-phase rectifier circuit is developed to convert the alternative voltage generated by the PM harvester into DC voltage that can be used directly by the external resistive load. Simulation results indicate that the proposed linear PM vibration energy harvesting system is able to generate about 100 watt DC electrical power under the vibration with the velocity of 0.4 m/s and the output electrical power is proportional to the levels of vibration excitations.

Self-sensing concrete combines electrically conductive filler material and conventional building material together, and is able to realise a sensing function that by measuring the change of electrical properties of the composite under external loading, the stress, deformation and damage could be monitored. It has the advantages of high sensitivity, long service period, excellent compatibility, durability and mechanical strength, and low maintenance cost, and can be potentially applied in structure health monitoring, weight in motion, traffic detection, parking management and many other fields. This paper overviews the details of the composition and role of each component, the fabrication method and the mechanism of the self-sensing concrete. The future prospects are discussed at the end of the paper.

© 2016 The Korean Society of Rheology and Springer. In this paper, a comprehensive review of the present literature on energy generated magnetorheological (MR) fluid based damper, modeling and applications of the MR damper are presented. The review starts with an introduction of the basic of MR fluid and their different modes, consequences with different types of MR fluids based devices, and their relevant applications. Besides, various forms of MR damper and its applications are presented. Following this, the modeling of the MR fluids and the modeling of the MR fluid based damper are deliberated according to arrangement and configurations. Finally, the review ends with the design and advancement issues, performance analysis matters, and analytical modeling of energy generated magnetorheological fluid damper systems.

© The Author(s) 2015. A magnetorheological absorber is capable of actively adapting any gun recoil condition by means of controlled Coulomb force. The objective of multi-coil magnetorheological absorber with individual input currents is to mitigate the peak force transferred to the buffer structure during bullet firing, and thus to increase the structural fatigue life. This article investigates various cases by applying random combinations of input currents to the magnetic coils. The impact tests were conducted by obtaining and analyzing the force, displacement, and velocity. As a reference, input currents with equivalent magnitude are considered statistically, in terms of average peak force and occurrence time. The experimental results show that separately controlled multi-coils contribute to the magnitude and occurrence time of peak force significantly. Furthermore, to reduce peak forces, a simple open-loop control strategy was proposed and validated effectively by the experimental results.

In this article, an MRD50 type of large-scale magnetorheological shock absorber was designed and manufactured in Smart Materials and Structures Laboratory of Nanjing University of Science and Technology. Upon providing a brief background on magnetorheological dampers, the detailed structure of this developed large-scale magnetorheological shock absorber was depicted. A suit of hardware-in-the-loop simulation platform under high impact load excitation was introduced for a weapon system. A series of tests were conducted to establish the dynamic behaviors of magnetorheological shock absorber under impact loads. The test results show that the inertia damping force should not be ignored like a common magnetorheological damper because of the large acceleration from the impact load. Based on the theory model and the experimental data, index parameters of magnetorheological fluid and other structural parameters in Herschel-Bulkley-Inertia model were identified by using the least square algorithm. In order to evaluate the controllability of large-scale magnetorheological shock absorber applied into high impact loads, three control algorithms, including on-off control, proportional-integral-derivative control, and fuzzy control algorithm, were used in tests to control the dynamic behavior of magnetorheological shock absorber, and some results of the controllability tests were exhibited in this article. In conclusion, the results indicated that the developed large-scale magnetorheological shock absorber was indeed able to effectively control the recoil dynamics. © The Author(s) 2012.

A safety and arming (S&A) device keeps the fuze of a projectile unarmed during shipping, handling and storage, while arming the firing section at a proper time by sensing external conditions such as pressure, position, etc. With the increasing need for smaller S&A devices, a miniature design with a compact configuration and high reliability is in demand. This paper proposes a miniaturized timing trigger as the S&A device for a spinning projectile by utilizing the 'locking' and 'unlocking' properties of magnetorheological (MR) grease with/without the presence of a magnetic field. First, the design and arming mechanism of the timing trigger are introduced, in which the MR grease is locked by a magnetic field generated by two permanent magnets (PMs). Under sufficient firing acceleration, the PMs disengage to unlock the contraction flow of the MR grease, which enables its triggering function. A theoretical analysis was conducted to interpolate the delay time against the geometry of the device, the shear/extensional characteristics of MR grease and the spinning rate of a projectile. A series of tests have been conducted to measure the delay times by tuning the physical parameters, including particle concentration, spinning rate and orifice diameter etc. The experimental results showed that this theoretical model is capable of calculating well the delay time of a MR grease timing trigger.

Magnetorheological elastomer (MRE) isolator has been proved as a promising semi-active control device for structural vibration control. For its engineering application, developing an accurate and robust model is definitely necessary and also a challenging task. Most of the present models, belonging to parametric models, need to identify various model parameters and sometimes are not capable of perfectly capturing the unique characteristics of the device. In this work, a novel nonparametric model is proposed to characterize the inherent dynamics of the MRE isolator with the features of hysteresis and nonlinearity. Initially, dynamic tests are conducted to evaluate the performance of the isolator under various loading conditions, including harmonic, random, and seismic excitations. Then, on the basis of the captured experimental results, a hybrid learning method is designed to forecast the nonlinear responses of the device with known external inputs. In this method, a type of single hidden layer feed-forward network, called extreme learning machine (ELM), is developed to forecast the nonlinear responses (shear force) of the device with captured velocity, displacement, and current level. To obtain optimal performance of the developed model, an improved binary-coded discrete cat swarm optimization (BCDCSO) method is adopted to select optimal inputs and neuron number in the hidden layer for the network development. The performance of the proposed method is verified through the comparison between experimental results and model predictions. Due to the noise influence in the practical condition, the robustness of the proposed method is also validated via adding noise disturbance into the supplying currents. The results show that the proposed method outperforms the standard ELM in terms of characterization of the MRE isolator, even though the captured responses are polluted with external measurement noises.

Hostile dynamic loadings such as severe wind storms, earthquakes, and sudden impacts can cause severe damage to many civil engineering structures. An intelligent structural system equipped with smart structural members that are controllable in real-time is an effective solution to structural damage and failure during such situations. Civil intelligent structures with controllable properties to adapt to any changes due to dynamic loadings can lead to effective protection of structures and their occupants. In this paper, design and testing of a semi-active magnetorheological (MR) pin joint, in which the moment resistance can be controlled in real-time by altering the magnetic field, is reported with the view of using it as a potential candidate for smart members in the development of intelligent structures. Design of prototype smart pin joints includes theoretical analysis related to the radius of the rotary plate, the property of MR fluids and the gap between the rotary plate and the casing based on the requirements of the dynamics of MR pin joints. FEM analysis was deployed to study the distribution of the magnetic field along the gap. It is found, from the theoretical analysis and experimental verification, that the MR pin joint with a diameter of 180 mm can produce a torque of up to 30 Nm, which meets requirements for semi-active members in a multi-storey prototype building model in the next stage of research and development. © Higher Education Press and Springer-Verlag 2009.

© 2015, Springer Science+Business Media Dordrecht. The recently-developed magnetorheological elastomer (MRE) base isolator can provide an instant change in the shear modulus and damping property under applied magnetic field, which makes it as an ideal device for the semi-active control in buildings and bridges. Previous studies show that this new device is featured with its nonlinear and hysteretic responses, and it is necessary to sufficiently understand its behaviour when adopting this device in control system. Although there are several models presented to predict the hysteresis of MRE base isolator, they are always suffered from some application limitations, e.g. high computation demand or complex model. To better interpret this complicated feature of the device, this work presents an improved LuGre friction model, which has been successfully used in modelling other magnetorheological device i.e. MR damper. In addition, an improved fruit fly optimization algorithm (IFFOA) is also proposed to identify the model parameters. In the improved algorithm, a transfer factor based on a self-adaptive step is added together with a three-dimensional searching space. This improvement can enhance the convergence rate of the algorithm and avoid the local optimum. Furthermore, to reduce the complexity of the model, the local and global parameter sensitivity analyses are conducted for model simplification. Eventually, the experimental measurements of device displacement, velocity and shear force are used to evaluate the performance of the proposed model and IFFOA.

Copyright © 2015 by ASME. This paper presents a recent research advance on the development of a novel adaptive seismic isolation system to be used in seismic protection of civil structures. A highly adjustable laminated magnetorheological elastomer (MRE) base isolator was developed and experimental results show that the prototypical MRE base isolator provides increase in lateral stiffness up to 1630%. To facilitate the structural control development using such adaptive MRE base isolator, an analytical model was developed to simulate its behaviors. Comparison between the analytical model and experimental data proves the effectiveness of such model in reproducing the behavior of MRE base isolator.

© SAGE Publications. This article presents a novel model to describe the nonlinear relationships between shear force and displacement/velocity in a magnetorheological elastomer base isolator. The proposed model, containing a strain stiffening element, is able to portray the distinct dynamic behaviors of magnetorheological elastomer base isolator. To identify the model parameters, an enhanced particle swarm optimization is used on force-displacement/velocity data sampled under different loading conditions. In this algorithm, a self-adaptive inertia weight replaces the general linear weight, enhancing the convergence rate of iteration process. Besides, the mutation operator in genetic algorithm is adopted for finding global optimum. Testing data of the device displacement, velocity and force from magnetorheological elastomer base isolator are utilized to validate the proposed model and corresponding parameter identification algorithm.

The magnetorheological (MR) shock absorber is one of the most promising new devices for vibration reduction. Many investigations have been carried out on low velocity and frequency applications of MR devices. The use of the MR shock absorber under impact load is of great interest. The now widely used MR damper models, such as the Bingham model, cannot explain sufficiently the shear thinning behavior under impact loads. However, the Herschel–Bulkley model can be used to explain the same. The main purpose of this study is to analyze the behavior of the MR shock absorber under impact load and to verify the analytical conclusions and experiments. First, some dynamic simulations on the MR shock absorber under impact loads in Matlab and Simulink are carried out. The model describes the dynamic characteristics especially the shear thinning behavior of the shock absorber, based on this model, then analyzes the variations of piston acceleration and back cavity pressure of MR shock absorber at both same and different flow indices. A test rig is developed to test the characteristics of the long-stroke MR shock absorber under impact loads. Comparisons between the simulation and the test results are made to validate our conclusions. The results indicate that the peak acceleration value of the piston rod and the pressure of the back cavity are decided by the peak value and the duration of the impact force. The peak value of the acceleration and the cavity pressure cannot be changed, but the transitional time of the acceleration of the piston and the pressure of the back cavity of MR shock absorber can be controlled by changing the applied current in the electromagnetic coil. MR shock absorbers will be the most promising shock reduction device under an impact environment.

© 2014 IOP Publishing Ltd. During the last few decades, magnetorheological (MR) elastomers have attracted a significant amount of attention for their enormous potential in engineering applications. Because they are a solid counterpart to MR fluids, MR elastomers exhibit a unique field-dependent material property when exposed to a magnetic field, and they overcome major issues faced in magnetorheological fluids, e.g. the deposition of iron particles, sealing problems and environmental contamination. Such advantages offer great potential for designing intelligent devices to be used in various engineering fields, especially in fields that involve vibration reduction and isolation. This paper presents a state of the art review on the recent progress of MR elastomer technology, with special emphasis on the research and development of MR elastomer devices and their applications. To keep the integrity of the knowledge, this review includes a brief introduction of MR elastomer materials and follows with a discussion of critical issues involved in designing magnetorheological elastomer devices, i.e. operation modes, coil placements and principle fundamentals. A comprehensive review has been presented on the research and development of MR elastomer devices, including vibration absorbers, vibration isolators, base isolators, sensing devices, and so on. A summary of the research on the modeling mechanical behavior for both the material and the devices is presented. Finally, the challenges and the potential facing magnetorheological elastomer technology are discussed, and suggestions have been made based on the authors' knowledge and experience.

Magnetorheological (MR) pin joint is a novel device in which its joint moment resistance can be controlled in real-time by altering the applied magnetic field. The smart pin joint is intended to be used as a controllable connector between the columns and beams of a civil structure to instantaneously shift the structural natural frequencies in order to avoid resonance and therefore to reduce unwanted vibrations and hence prevent structural damage. As an intrinsically nonlinear device, modelling of this MR fluid based device is a challenging task and makes the design of a suitable control algorithm a cumbersome situation. Aimed at its application in civil structure, the main purpose of this paper is to test and characterise the hysteretic behaviour of MR pin joint. A test scheme is designed to obtain the dynamic performance of MR pin joint in the dominant earthquake frequency range. Some unique phenomena different from those of MR damper are observed through the experimental testing. A computationally-efficient model is proposed by introducing a hyperbolic element to accurately reproduce its dynamic behaviour and to further facilitate the design of a suitable control algorithm. Comprehensive investigations on the model accuracy and dependences of the proposed model on loading condition (frequency and amplitude) and input current level are reported in the last section of this paper. © 2014 Higher Education Press and Springer-Verlag Berlin Heidelberg.

This paper focuses on the development and experimental testing of a potential clean energy source for powering the remote equipment used in transportation infrastructure. Traditional power sources (i.e., power cables and batteries) are excessively expensive or infeasible in this type of application. A compression-based roadway energy harvester has been developed that can be embedded into pavement to scavenge electrical energy from traffic-induced vibrations. The proposed roadway harvester employs a group of piezoelectric harvesting units to convert traffic-induced vibrations into electrical energy, and each single harvesting unit contains three piezoelectric multilayer stacks. According to the linear theory of piezoelasticity, a two-degree-of-freedom electromechanical model of the piezoelectric harvesting unit was developed to characterize its performance in generating electrical energy under external excitations. Experimental testing in the laboratory was conducted to investigate the output power properties of the harvesting unit and shows good agreement with the theoretical analysis. Based on the testing results of the harvesting unit, the capability of the proposed roadway harvester has been theoretically evaluated and demonstrated that it has the ability to generate sufficient energy for driving common electrical equipment used in transportation infrastructure. © 2014 AIP Publishing LLC.

The nozzle/diffuser flow with different Reynolds number ranges and conical angles is analyzed first. It is found that the flow coefficients of nozzle/diffuser ξn and ξd vary with angle with different trends for large (> 105) and small (

Finding engineering applications for a new class of smart material, magnetorheological elastomer (MRE), has been a major task for researchers in this field. Novel MRE devices, such as vibration absorbers and vibration isolators, have been proposed and fabricated to pioneer its engineering applications. In civil engineering, the author has proposed a novel MRE based isolator to be used in the base isolation system for mitigating the devastating effects of earthquakes on civil structures. For any MRE-based device, electromagnetic coil is evitable involved to provide magnetic field for the MRE materials. Comparing with magnetic circuit design in magnetorheological fluid (MRF) device, i.e. MR damper, MRE devices normally need a larger coil to energize the MRE materials, particularly for a large-scale MRE device. Therefore, investigation of the solenoid on the magnetic field distribution is of great importance for the design and development of MRE based device. In particular, provision of sufficient and uniform magnetic field is essential towards the success in designing MRF/MRE devices. To understand the mechanism of magnetic field generation in a solenoid is the key for device design and optimization. The main objective of this paper is to analytically investigate and experimentally validate the magnetic field distribution in a solenoid. The theoretical investigation starts from the analysis on an ideally thin cylindrical solenoid in order to obtain analytical results. To stimulate the coil which can be used in the design of MRE device, theoretical investigation is to conduct on a thick-wall cylindrical solenoid. Finite element analysis is also used to examine the magnetic field distribution in the solenoid. In order to verify the theoretical findings, experimental testing is conducted to acquire the magnetic field distribution in a sample solenoid. Results from analytical solution, finite element analysis and experimental testing agree very well. The findings provide valuable information for the design and optimization of the MRE device in which a solenoid is inevitably involved. Copyright © 2013 by ASME.

This paper presents a recent research breakthrough on the development of a novel adaptive seismic isolation system as the quest for seismic protection for civil structures, utilizing the field-dependent property of the magnetorheological elastomer (MRE). A highly-adjustable MRE base isolator was developed as the key element to form smart seismic isolation system. The novel isolator contains unique laminated structure of steel and MRE layers, which enable its large-scale civil engineering applications, and a solenoid to provide sufficient and uniform magnetic field for energizing the field-dependent property of MR elastomers. With the controllable shear modulus/damping of the MR elastomer, the developed adaptive base isolator possesses a controllable lateral stiffness while maintaining adequate vertical loading capacity. Experimental results show that the prototypical MRE base isolator provides amazing increase of lateral stiffness up to1630%. Such range of increase of the controllable stiffness of the base isolator makes it highly practical for developing new adaptive base isolation system utilizing either semi-active or smart passive controls. To facilitate the structural control development using the adaptive MRE base isolator, an analytical model was developed to stimulate its behaviors. Comparison between the analytical model and experimental data proves the effectiveness of such model in reproducing the behavior of MRE base isolator, including the observed strain stiffening effect. Copyright © 2013 by ASME.

Following a successful experimental validation of a magnetorheological elastomer (MRE) base isolator, this study presents one of the major concerns, the heating of the magnetic coil, in the design and development of the adaptive MRE based isolator. In this research, the MRE materials, with a total thickness of nearly 150 mm, are placed as the magnetic core of the device to best utilize the magnetic energy provided by the coil. A series of tests are undertaken to investigate the magnetic fields inside the coil with or without the MRE materials. Thermocouples are used to monitoring the surface temperature of the coil when it is applied with various currents for 10 min. It is shown that the measurement of field inside the solenoid when no MRE is placed inside agrees with the theoretical analysis. It is also shown that the temperature of the coil increase dramatically when a current is applied. Cooling of the coil may takes even longer, about 4 h, till down to the room temperature. Dropping of the magnetic field is observed when the temperature goes high. © Published under licence by IOP Publishing Ltd.

Base isolation is the most popular seismic protection technique for civil structures. However, research has revealed that the traditional base isolation system is vulnerable to both kinds of earthquakes, i.e. the near-fault and far-fault earthquakes, due to its passive nature. A great deal of effort has been dedicated to improve the performance of the traditional base isolation system for these two types of earthquakes. Controllable supplementary and energy-dissipation members, such as magnetorheological damper, friction damper or hydraulic fluid damper, have been proposed to reduce the seismic response of the building structures. However, with the introduction of additional control devices, the system complexity increases which results in difficulty in the system implementation and control system design. It would be ideal if a certain level of adaptability could be introduced into the base isolator while maintaining the traditional outfit. This paper addresses the challenge facing the current base isolation practice and proposes a novel adaptive base isolator as solution to the problem. A smart rubber, namely, magnetorheological elastomer (MRE), is utilised in this research for its magnetic field-sensitive material property as the main element in the novel device. The tradition base isolation design for a large-scale structure with laminated steel and MRE layers is adopted. To verify and characterise the performance of the MRE base isolator, experimental testing was conducted on UTS shake table facility. Experimental results show that after being energised with magnetic field, the maximum force and the stiffness of the novel device can increase by up to approximately 45% and 37%, respectively. With the field-dependent stiffness and damping, the proposed adaptive base isolator is very promising in meeting the challenges associated with the base isolation encountered in practice. of the building structures. Yang (Yang, Danielians and Liu, 1991) presented a hybrid control system in which a passive or active mass damper, connected with base isolation system, is used to alleviate the deformation of seismic isolators. Although numerical results showed that the proposed system worked effectively, the hybrid system is less practical since it is difficult to implement a mass damper, either passive or active, on the seismic isolators. Destructive potential of near-source earthquakes to flexible structures still remains a challenge and has received considerable attention within the earthquake engineering community. Another effort to augment the adaptability of base isolation system has been to combine passive isolators with semi-active or active actuators to develop hybrid base isolation systems. Spencer (Ramallo, Johnson and Spencer, 2002) proposed a smart base isolation system, composed of conventional low-damping elastomeric isolators and smart controllable dampers, such as MR damper, to protect structures against extreme earthquakes. Wongprasert (Wongprasert and Symans, 2005) experimentally evaluated a smart base isolation system consisting of spherical sliding bearings and variable fluid dampers for a multi-storey building frame. In the above-mentioned research, the proposed base isolation systems proved to be more effective than the traditional passive ones. However, those systems, termed hybrid systems, are either a combination of passive bearings/isolators (such as low-damping bearing or spherical sliding bearings) and semiactive actuators (MR damper or piezoelectric friction damper) or a mixture of passive bearings/isolators and active actuating system. The separated passive and semi-active/active actuator increases the complexity of the base isolation system, leading to many problems, such as instability, reliability, and the increasing difficulty in system installation. Moreover, the need for large power in active hybrid base isolation systems restricts their implementation in largescale structures. The advent of a kind of smart material, magnetorheological elastomer, offers a way forward to develop more effective and efficient semi-active base isolators than traditional passive ones, and will further lead to the development of intelligent selfadaptive base isolation systems. Magnetorheological elastomer (MRE) is a new generation of MR materials whose stiffness and damping can be changed by magnetic field in real-time. In the absence of magnetic field, MRE is similar to that of a soft rubber. While under magnetic field, MRE turns to be very stiff. The maximum relative change of the modulus of the MRE can be from about 50% (stiffer rubber carrier) to beyond 300% (soft rubber carrier, such as silicone gel) (Davis, 1999). Damping ratio of the MRE can differ from 10% to 32% depending on the types of rubber matrix and iron particles, and is more affected by the magnetic field when the MRE is driven at a lower frequency (Chen, Gong and Li, 2008). Other merits of MREs are their low power requirement and rapid response to the magnetic field. Normally, magnetic coils will be designed and utilised to supply the currents for the energisation and control of the MREs. The power supply needed by the magnetic coil is only 20-40 volts which can be easily achieved by normal batteries and accumulators. MREs also have rapid response to magnetic fields and the time of response is less than 10 ms (Li, Zhang, Du and Chen, 2006.). Although the research and development in MRE material has been emerging in recent years, research on MRE applications can rarely be found. Majority of research on new MRE devices are reported in mechanical engineering. Ginder (Ginder, Scholotter and Nichols, 2001) piloted a pioneer theoretical work that utilised MREs as variable-spring-rate elements to develop an adaptive tuned vibration absorber. Deng (Deng and Gong, 2008) developed an adaptive tuned vibration absorber. Experimental results indicated that its natural frequency can be tuned from 27.5Hz to 40Hz. In civil engineering, however, the idea of using MRE as the fundamental material to develop adaptive MRE seismic isolators is quite new and novel. Hwang (Hwang, Lim, and Lee, 2006) carried out a conceptual study on the application of MREs to base isolation system for building structures. Usman (Usman, et al, 2009) numerically evaluated the dynamic performance of a smart base isolation system employing MR elastomer, and the results show that the proposed system outperforms the conventional system in reducing the responses of the structures during seismic excitations. Despite the two publications addressing the potential of MRE based base isolation system, the critical question on how to incorporate MREs into the base isolation system is yet to be addressed. This paper aims to design and develop an adaptive base isolator using the new smart material, MR elastomer, for its controllable material properties, including shear modulus and damping. A novel MRE base isolator with similar laminated structure of passive rubber base isolator is prototyped with the aim to comply with the requirement in the base isolation practice. Experiments were designed and conducted to examine the adaptive performance of the MRE base isolator. 2 MR ELASTOMER AND THE ADAPTIVE BASE ISOLATOR

Inspired by its controllable and field-dependent stiffness/damping properties, there has been increasing research and development of magnetorheological elastomer (MRE) for mitigation of unwanted structural or machinery vibrations using MRE isolators or absorbers. Recently, a breakthrough pilot research on the development of a highly innovative prototype adaptive MRE base isolator, with the ability for real-time adaptive control of base isolated structures against various types of earthquakes including near- or far-fault earthquakes, has been reported by the authors. As a further effort to improve the proposed MRE adaptive base isolator and to address some of the shortcomings and challenges, this paper presents systematic investigations on the development of a new highly adjustable MRE base isolator, including experimental testing and characterization of the new isolator. A soft MR elastomer has been designed, fabricated and incorporated in the laminated structure of the new MRE base isolator, which aims to obtain a highly adjustable shear modulus under a medium level of magnetic field. Comprehensive static and dynamic testing was conducted on this new adaptive MRE base isolator to examine its characteristics and evaluate its performance. The experimental results show that this new MRE base isolator can remarkably change the lateral stiffness of the isolator up to 1630% under a medium level of magnetic field. Such highly adjustable MRE base isolator makes the design and implementation of truly real-time adaptive (e.g. semi-active or smart passive) seismic isolation systems become feasible. © 2013 IOP Publishing Ltd.

Magnetorheological fluid (MRF) has received significant attention lately and MRF based devices have been proposed for structural control applications in recent years. The unique characteristics of MR fluid lies in its abilities to reversibly, repeatedly and instantly change from a free flowing liquid to a semi-solid state when exposed to a magnetic field. The electric power required to drive the MR devices can be easily provided by a battery. Possessing such unique properties, MR fluid based devices, such as MR damper, have become promising candidates in the semi-active control for civil structure applications. However, most of the published research has focused on application of MR dampers instead of exploring other type of MR devices. In addition, MR based devices exhibit complex nonlinear hysteresis behaviour and thus making their modelling a challenging task. In this paper, a novel MR fluid based device, namely MR pin joint, is proposed as a smart structural member in development of an intelligent civil structure that can suppress unwanted vibrations to ensure safety and serviceability of the structure. After design and fabrication, experiments have been conducted to characterise dynamic behaviours of the new device under different harmonic excitations with various input currents. Response time of the MR pin joint is compared when the MR pin joint is driven under different applied currents and moving speeds. Test data shows that the MR pin joint possesses a unique behaviour in the moment-angular velocity plot. A hyperbolic hysteresis model is proposed to model such unique behaviour. The investigation presented in the paper explores dynamic performance of MR pin joint. Finally, a parametric model is developed following the investigation on the correlation of coefficients in the proposed model with the loading conditions and applied currents.