Majid Behrooz

Performance of a new magnetorheological elastomer isolation system

This paper presents the performance of a new magnetorheological elastomer-based semi-active/passive variable stiffness and damping isolator (VSDI) in a scaled building system. The force of the VSDI can be controlled in real time by varying the applied magnetic field. To demonstrate the performance of the VSDI, four prototypes are built and utilized in a scaled three-story building. A Lyapunov-based control strategy is employed and it is demonstrated that it works well for the scaled building system under the scaled El Centro earthquake motion. Experimental results show that the VSDIs significantly reduce the acceleration and relative displacement of the building floors.

Behavior of magnetorheological elastomers with coated particles

Iron particle coating can improve the behavior of magnetorheological elastomers (MREs) by inhibiting iron particle rusting; however, such a process can change physical properties of MREs such as oxidation resistance, shear modulus, and stiffness change due to an applied magnetic field. In this study, MRE samples are fabricated with regular and polymerized iron particles. To investigate the possibility and extent of these changes, polymerized particle MRE samples are made using a combination of reversible addition fragmentation chain transfer and click chemistry. Shear test sample MREs with pure elastomer and 50 wt% MRE with and without polymerization are fabricated. To observe the effect of oxidation on shear properties of MREs, pure elastomer and 50 wt% coated and non-coated samples are oxidized using accelerated oxidation procedure. Experimental results show that oxidation significantly reduces the shear modulus of the elastomer matrix. The coating process of iron particles does not significantly change the shear modulus of resulting MREs but reduces the loss of shear modulus due to oxidation.

Control of structures featuring a new MRE isolator system

This study is focused on control of a scaled building structure using a new semi-active Variable Stiffness and Damping Isolator (VSDI). The proposed VSDI system consists of a traditional steel-rubber vibration absorber, and a magnetorhelogical elastomer (MRE) with a controllable stiffness and damping behavior. To demonstrate the feasibility of using VSDIs a 1:16 scaled, three-story building is constructed and installed on a shake table and its base is supported by four prototype VSDIs. The VSDIs can be regulated in real time by varying the applied magnetic field through a controller. A phenomenological model is proposed and implemented on VSDI devices. The scaled El Centro earthquake excitation is applied to the system, and the vibration mode is controlled by a Lyapunov-based control strategy. Results show that the a significant reduction in structural response can be achieved for both displacement and acceleration.

A self-sensing magnetorheological elastomer-based adaptive bridge bearing with a wireless data monitoring system

This study presents an adaptive bridge bearing that can sense structural loads and tune its properties to mitigate structural vibrations. The bearing utilizes magnetorheological elastomer (MRE) layers which allow for an increased stiffness induced with a magnetic field. The system also features a MRE-based sensing system for sensing the structural wind and traffic load. The sensing system is capable of transmitting data wirelessly to a central logging computer for monitoring bridge performance and sending alerts in the case of a major event. The capability of the MRE-based sensing system for sensing structural loads and wireless transmission of data were investigated. The adaptive bridge bearing incorporates a closed-loop magnetic circuit that results in an enhanced magnetic field in the MRE layers. Results show the sensitivity of the MRE-based sensors and the performance of the wireless system, as well as the design and analysis of the tunable bridge bearing.

A flexible micro fluid transport system featuring magnetorheological elastomer

This study presents a flexible magnetically-actuated micro fluid transport system utilizing an isotropic magnetorheological elastomer (MRE). Theoretical modeling and analysis of this system is presented for a two-dimensional model. This fluid transport system can propel the fluid by applying a fluctuating magnetic field on the MRE. The magneto-fluid-structure interaction analysis is employed to determine movement of the solid domain and the velocity of the fluid under a controllable magnetic field. The effects of key material, geometric, and magnetic parameters on the behavior of this system are examined. It is demonstrated that the proposed system can propel the fluid unidirectionally, and the volume of the transported fluid is significantly affected by some of the design parameters.

Seismic Control of Base Isolated Structures Using Novel Magnetorheological Elastomeric Bearings

This paper presents the performance of a novel semi-active variable stiffness magnetorheological elastomer (MRE) bearing for seismic mitigation of civil structures. The proposed MRE bearing consists of a traditional steel-rubber vibration absorber, as the passive element, and a MRE with a controllable stiffness behavior. The controllability of the prototype MRE bearing is investigated experimentally under quasi-static and dynamic shear tests. The behavior of the MRE bearings is modeled using a phenomenological method which includes Bouc-Wen hysteresis element. The results show that both the single MRE bearing and an integrated system with four MRE bearings can increase the stiffness, damping, and hysteresis effect with a control input electric current. In addition, to demonstrate the feasibility of utilizing the MRE base isolation for seismic control of structures, a 1:16 scaled, three-story building supported by four MRE bearings, is constructed. A feedback control system is used to validate the effectiveness of the controlled MRE bearing in reducing structural responses. The scaled El-Centro seismic earthquake excitation is applied to the isolated building. The response of the controlled building shows significant reduction in displacement and acceleration compared to those of passive and on-state conditions.Copyright

Modeling of a new magnetorheological elastomer-based isolator

A variable stiffness and damping isolator (VSDI) is designed, developed and tested using a magnetorheological elastome (MRE). A double lap shear test is performed to characterize the MRE-based VSDI under the quasi-static shear loading. A phenomenological model that can capture the behavior of the VSDI is developed and related parameters are identified using experimental data.

Behavior of a flexible controllable micropump

This study presents a theoretical investigation of a flexible, electromagnetically controlled microchannel transport system (i.e., controllable micropump) utilizing a soft magnetorheological elastomer. A two-dimensional time-dependent model using a coupled fluid-solid-magnetic analysis is developed to conduct a parametric study on a system which consists of a flexible channel and valves. Effect of different geometric, magnetic and mechanical properties on the performance of the system is investigated through the net generated flow. It is demonstrated that the microchannel diameter, elastic foundation constant, elastic modulus of the microchannel and the valves, fluid viscosity, and the applied magnetic field have significant effect on the net generated flow.

Behavior of an adaptive bio-inspired spider web

The goal of this study is to demonstrate the feasibility of an artificial adaptive spider web with comparable behavior to a real spider web. First, the natural frequency and energy absorption ability of a passive web is studied. Next, a control system that consists of stepper motors, load cells and an Arduino, is constructed to mimic a spider’s ability to control the tension of radial strings in the web. The energy related characteristics in the artificial spider web is examined while the pre-tension of the radial strings are varied. Various mechanical properties of a damaged spider web are adjusted to study their effect on the behavior of the web. It is demonstrated that the pre-tension and stiffness of the web’s radial strings can significantly affect the natural frequency and the total energy of the full and damaged webs.

A flexible magnetically-controllable fluid transport system

The goal of this study is to understand the mechanics of a flexible magnetically-controllable fluid transport system. A two-dimensional time-dependent model using a coupled fluid-solid and magnetic model is developed. The flow of fluids through sinusoidal wall is modeled, numerically analyzed and compared with an analytical solution, for the passive case (i.e., zero applied magnetic field). The modeling and analysis are extended to include a magnetic field that is applied to the wall of the flexible tube in order to produce the one-way forward movement of the fluid. Results demonstrate the fluid transportation capabilities of the one-way transport system.