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© 2019 Elsevier Ltd Magnetorheological elastomers (MRE) are emerging as smart materials for application in the field of the intelligent devices and structures. In order to design MRE-based vibration control devices, their dynamic behavior should be mathematically represented with respect to broadband excitation frequency, amplitude, and the applied magnetic field. In this study, a nonlinear MRE model consisting of three parts – a fractional viscoelasticity model, magnetic dipole model, and an adaptive smooth Coulomb friction model – is developed. The fractional Maxwell model with only three parameters was introduced to simulate the dynamic behavior of MRE in a wide frequency range. A magnetic interaction model for adjacent particles was investigated and the magnetic force corresponding to the particle volume was calculated. We found that the interaction force not only affects the shear modulus, but also affects slipping at the interface between the particle and matrix. The adaptive smooth Coulomb friction used to model the magnetic field-dependent properties of the MRE accurately described the behavior of the material over a wide range of amplitudes at different magnetic field strengths. The model parameters were estimated by a simple procedure and the proposed model was found to represent MRE characteristics accurately. Therefore, the new model is expected to be advantageous for designing MRE-based vibration devices.

© 2018 IOP Publishing Ltd. To increase output power for piezoelectric vibration energy harvesters, considerable attention has recently been focused on a self-powered synchronized switch harvesting on inductor (SSHI) technique employing an electrical and mechanical switch. However, there are two technical issues: in a medium or highly coupled harvester, the piezoelectric coupling force, which increases as the SSHI's voltage increases, will reduce the harvester's displacement and the resulting output power, and there are few reports comparing the performance of electrical switch SSHI (ESS) and mechanical switch SSHI (MSS) that include consideration of the piezoelectric coupling force. We developed a simulation technique that allows us to evaluate the output power considering the piezoelectric coupling force, and investigated the performance of stopper-based MSS and ESS, both numerically and experimentally. The numerical investigation predicted the following: (1) the output power for the ESS is lower than that for the MSS at acceleration lower than 3.5 m s-2; and (2) intriguingly, the output power for the MSS continues to increase, whereas the peak-peak displacement remains constant. The experimental results showed behaviour similar to that of the numerical predictions. The results are attributed to the different switching strategies: the MSS turns on only when the harvester's displacement exceeds the gap distance, while the ESS turns on at every maximum/minimum displacement.

© 2018 Elsevier Ltd The isolator based on magnetorheological elastomers (MREs) that is used with semi-active controllers has emerged as a kind of smart devices that could potentially improve vibration control in traditional systems. The nonlinear damping characteristics of the isolator make the controller design more difficult. Generally, the command current/voltage is determined according to the relative responses in conventional semi-active controllers. However, these controllers may exhibit unsatisfactory isolation performance and even cause instability owing to significant excitations or nonlinear effects. In this study, the design of the new semi-active controller for an MRE-based isolator was investigated to overcome the drawbacks of traditional controllers from two perspectives. Firstly, an inverse model is designed for the isolator so that it can be used to predict an appropriate electric current supplied to the electromagnet based on the desired control force. Secondly, a robust adaptive controller for semi-active control is proposed for a nonlinear system with unknown dynamic parameters. The control scheme consists of three parts: a standard adaptive linearizing controller, an adaptive sliding mode controller, and a single robust controller. The proposed method guarantees zero convergence of the displacement response and provides robust stability. In addition, the singularity problem that usually appears in standard adaptive control is eliminated. Simulations demonstrate that the proposed controller exceeds the performance of the passive system as assessed in the protection of a two-story shear building during seismic events.

© Published under licence by IOP Publishing Ltd. We proposed an autoparametric excitation harvester employing a microfabricated leaf spring for the base beam and a synchronized switch harvesting on inductor (SSHI) interface. Our harvester achieved miniaturization, low threshold acceleration of the autoparametric excitation, and increase in output power, compared with the previous work. The base beam for amplifying the excitation was microfabricated from a stainless steel film, through the photolithography followed by the wet-chemical etching. To trigger the autoparametric excitation, the main and the base beams are designed such that the resonance frequency for the base beam becomes twice higher than that for the main beam. The resonance frequencies obtained in experiment for the main and the base beams were 26.6 and 53.1 Hz, respectively. This study employed a self-powered parallel SSHI interface, which can increase the piezoelectric voltage and thus the output power, consuming only a small portion of the harvested energy. The harvester connected with the self-powered SSHI interface successfully displayed the autoparametric excitation at acceleration greater than 1.0 m/s2, and the output power showed 1.12 mW at the frequency of 53.1 Hz under the acceleration of 2.0 m/s2, which is 1.43-fold increase over the standard AC-DC interface.

© 2017 Elsevier Ltd In this paper, a magnetorheological elastomer (MRE) based isolator was investigated to mitigate excessive vibrations in structures during seismic events. The primary objectives of this research are to propose a numerical model that expresses viscoelastic behaviors of the MRE and predict operation process of the MRE-based isolator for future design of isolator systems for various technical applications. Despite the simplicity in parameter definition in comparison to the conventional models, the proposed model works efficiently in a wide range of frequencies and amplitudes. The model consists of the following components: viscoelasticity of host MRE, magnetic field-induced property, nominal viscosity as well as high stiffness in low excitation frequency that are modeled in analogy with a standard linear solid model (Zener model), a stiffness variable spring, and a smooth Coulomb friction, respectively. Furthermore, a semi-active fuzzy controller was designed to enhance the performance of the isolator in suppressing structural vibrations. The control strategy was built to determine the command applied current. The controller is completely adequate for handling the nonlinearity of the isolator and works independently with the building structure. The efficiency of the MRE-based isolator was evaluated by the responses of the scaled building under seismic excitation. Numerical and experimental results show that the isolator accompanied with a fuzzy controller remarkably reduces the relative displacement and absolute acceleration of the scaled building compared to passive-off and passive-on cases.

© Published under licence by IOP Publishing Ltd. In aiming to increase output power for piezoelectric vibration energy harvesters, a self-powered synchronized switch harvesting on inductor (SSHI) using an electrical or mechanical switch has considerable attention. However, the advantages and disadvantages of the two switching technique for the self-powered SSHIs remains unclear. In addition, for a harvester with a high electromechanical coupling coefficient k, the piezoelectric damping force, which enhances by the SSHI's voltage increase, is likely to reduce the harvester's displacement and thus lower the output power. We developed simulation technique, and numerically investigated the performance for the electrical switch SSHI (ESS) and for the mechanical switch SSHI (MSS) harvester, considering the feedback of the piezoelectric damping force. The numerical investigation revealed that, for the ESS, the piezoelectric damping force reduces the displacement every switching on at the maximum/minimum displacement, and thus lowers the output power. In contrast, the MSS, in which the switch turns on only when the displacement exceeds the gap distance, achieved a higher output power, and exhibited intriguing phenomena that the output power continues to increase, whereas the displacement is held constant. Therefore, for a harvester with high k, the MSS can outweigh the ESS.

© 2016, Springer Science+Business Media Dordrecht. A particle impact damper is a vibration absorber type that consists of a container attached to a primary vibrating structure. It also contains many particles that are constrained to move inside the container, whereby the damping effect can be obtained by collision between particles and the container. The discrete element method (DEM) has been developed for modeling granular systems, where the kinematics of each particle are calculated numerically using the equations of motion. However, the computational time is significant since the algorithm checks for particle contacts for all possible particle combinations. The use of a cellular automata (CA) modeling technique may provide increased computational efficiency due to the local updating of variables, and the discrete treatment of time and space. In this study, we propose a new approach combining DEM with CA for modeling a granular damper under a forced excitation. We use DEM to describe the particle motion according to the equations of motion, while CA is introduced for the particle contact checks in discrete space. We also investigate the effect of simplification in the contact force model, which allows the unit time step of numerical integration to become larger than that used in the strict model. It is shown that the suggested particle contact scanning method and the force approximation model contribute to the reduction of the computational time, and neither degenerates the calculation accuracy nor causes the numerical instability.

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Contains fulltext : 93823.pdf (publisher's version ) (Open Access)

Contains fulltext : 93823.pdf (publisher's version ) (Open Access)

Deciphering the influence of the interaction among the constituents of a complex system on the overall behaviour is one of the main goals of complex systems science. The model we present in this work is a 2D square cellular automaton whose of each cell is occupied by a complete random Boolean network. Random Boolean networks are a well-known simplified model of genetic regulatory networks and this model of interacting RBNs may be therefore regarded as a simplified model of a tissue or a monoclonal colony. The mechanism of cell-to-cell interaction is here simulated letting some nodes of a particular network being influenced by the state of some nodes belonging to its neighbouring cells. One possible means to investigate the overall dynamics of a complex system is studying its response to perturbations. Our analyses follow this methodological approach. Even though the dynamics of the system is far from trivial we could show in a clear way how the interaction affects the dynamics and the global degree of order. © 2008 Springer-Verlag Berlin Heidelberg.

he research context of this paper refers to bottom-up approaches to crowd dynamics that is, the study of how and where crowds form and move [1]. Several phenomena like crowd aggregation, dispersion and self-organized movement have been observed and studied by multiple disciplines interested to crowds (e.g. physics, sociology, ethology, social and behavioral psychology, building design, urban planning, security management, among others), each one with its specific viewpoint and ontological setting. SCA4CROWDS is an interdisciplinary research within this context that aims at contributing towards the development of a unifying ontology on crowds allowing the integration of contributions coming from several disciplines and that could be exploited for scientific and applicative issues (e.g. model comparison, validation, calibration). Potential exploitations of SCA4CROWDS results are towards the support of design and management of public crowded spaces and events to improve security, safety and comfort of people. SCA4CROWDS, in particular, aims at developing formal and computational tools to support the design, execution and analysis of crowds' behavior as effect of individual interactions (e.g. physical, social, emotional) according to Situated Cellular Agent (SCA) [2]. SCA is a modeling and simulation framework to model and study crowd dynamics phenomena with an approach based on Multi-Agent Systems (MAS) and Cellular Automata [3] principles. © 2008 Springer-Verlag Berlin Heidelberg.

This paper presents a research in the context of pedestrian dynamics according to Situated Cellular Agent (SCA), a Multi-Agent Systems approach whose roots are on Cellular Automata (CA). The aim of this work is to apply Genetic Programming (GP) approach, a well known Machine Learning method belonging to the family of Evolutionary Algorithms, to generate suitable behavioral rules for pedestrians in an evacuation scenario. The main contribution of this work is in the design of a testset of GP generated behaviors to represent basic behavioral models of evacuees populating a only locally known environment, a typical scenario for CA-based models. © 2008 Springer-Verlag Berlin Heidelberg.