Faramarz Gordaninejad

Flow Analysis of Field-Controllable, Electro- and Magneto-Rheological Fluids Using Herschel-Bulkley Model

The Bingham plastic constitutive model has been widely used to predict the post-yield behavior of electro- and magneto-rheological fluids (ER and MR fluids). However, if these fluids experience shear thinning or shear thickening, the Bingham plastic model may not be an accurate predictor of behavior, since the post-yield plastic viscosity is assumed to be constant. In a recent study, it was theoretically and experimentally demonstrated that the Herschel-Bulkley fluid model can be successfully employed when evaluating non-Newtonian post-yield behavior of ER and MR fluids. In this paper, we extend our previous work and adopt the Herschel-Bulkley model to include a detailed analysis of ER and MR fluid dynamics through pipes and parallel plates. Simplified explicit expressions for the exact formulation are also developed. It is shown that the proposed simplified model of the Herschel-Bulkley steady flow equations for pipes and parallel plates can be used as an accurate design tool while providing a convenient and generalized mathematical form for modeling ER and MR fluids. Theoretical and experimental analyses are presented for a MR fluid damper, which is designed, developed, and tested at the University of Nevada, Reno (UNR).

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.

Fail-safe magneto-rheological fluid dampers for off-highway, high-payload vehicles

This paper presents the study of a field-controllable, semi-active magneto-rheological fluid (MRF) shock absorber for high-payload, off-highway vehicles. A MRF damper is developed that is tailored for ground vehicles which undergo a wide range of dynamic loading. The MRF damper also has the capability for different rebound and compression characteristics. The new MRF shock absorber emulates the original equipment manufacture shock absorber behavior in its passive-off mode. Theoretical and experimental studies are performed to examine this MRF damper. The Bingham Plastic theory is employed to model the nonlinear behavior of the MRF. A fluid-mechanics-based theoretical model along with a three-dimensional finite element electromagnetic analysis is utilized to predict the MRF damper performance. The theoretical and experimental results are demonstrated to be in good agreement.

Flow Analysis and Modeling of Field-Controllable, Electro- and Magneto-Rheological Fluid Dampers

This study combines a fluid mechanics-based approach and the Herschel-Bulkley constitutive equation to develop a theoretical model for predicting the behavior of field-controllable, magneto-rheological (MR), and electro-rheological (ER) fluid dampers. The goal is to provide an accurate theoretical model for analysis, design, and development of control algorithms of MR/ER dampers. Simplified explicit expressions for closed-form solution of the pressure drop across a MR fluid valve are developed. The Herschel-Bulkley quasi-steady flow analysis is extended to include the effect of fluid compressibility to account for the nonlinear dynamic behavior of MR/ER fluid dampers. The advantage of this model is that it only depends on geometric and material properties of the MR/ER material and the device. The theoretical results are validated by an experimental study. It is demonstrated that the proposed model can effectively predict the nonlinear behavior of field-controllable fluid dampers.

A New MR Fluid-Elastomer Vibration Isolator

In this study, the performance of a new design concept utilizing a magnetorheological (MR) fluid composite material is examined through encapsulating a MR fluid into an elastomer. A prototype MR Fluid-Elastomer (MRF-E) Vibration Isolator is built and its dynamic behavior is studied in oscillatory compressions for a wide range of frequencies under various applied magnetic fields. The experimental results show that both the stiffness and the damping capability of the MRF-E Vibration Isolator is a function of the displacement amplitude and magnetic field strength, and only weakly dependent upon the frequency of excitation. This demonstrates that the new vibration isolator, whose mechanical properties can be controlled by an applied magnetic field, has potential in applications where tuning vibration characteristics are desired.

Sensing Behavior of Magnetorheological Elastomers

A magnetorheological elastomer (MRE) is comprised of ferromagnetic particles aligned in a polymer medium by exposure to a magnetic field. The structures of the magnetic particles within elastomers are very sensitive to the external stimulus of either mechanical force or magnetic field, which result in multiresponse behaviors in a MRE. In this study, the sensing properties of MREs are investigated through experimentally characterizing the electrical properties of MRE materials and their interfaces with external stimulus (magnetic field or stress/strain). A phenomenological model is proposed to understand the impedance response of MREs under mechanical loads and magnetic fields. Results show that MRE samples exhibit significant changes in measured values of impedance and resistance in response to compressive deformation, as well as the applied magnetic field.

A comparative study of thermal behavior of iron and copper nanofluids

Nanofluids consist of nanoparticles dispersed in heat transfer carrier fluid and are typically used for enhancing thermal conductivity in devices and systems. This study investigated the synthesis of iron and copper nanoparticle-based thermal fluids prepared using a two-step process. Chemical precipitation was used for the synthesis of the powders, and ultrasonic irradiation was used to disperse the nanoparticles in the carrier fluid (ethylene glycol). The size distributions of the nanopowders in the carrier fluid were determined using dynamic light scattering resulting in average particle sizes of around 500 nm. The crystallite sizes of the powders were below 20 nm. Thus, both types of nanofluids are comparable with regard to crystallite size, particle size, and morphology resulting in a direct comparison of material properties and their effect on thermal conductivity of the nanofluids. A guarded hot parallel-plate method and dynamic tests were used to compare the thermal conductivities of the nanofluids. It was shown that thermal conductivity can be enhanced by up to 70% for copper nanofluids. It was also demonstrated that for a given particle concentration, copper nanofluids are superior in thermal conductivity compared to iron nanofluids.Nanofluids consist of nanoparticles dispersed in heat transfer carrier fluid and are typically used for enhancing thermal conductivity in devices and systems. This study investigated the synthesis of iron and copper nanoparticle-based thermal fluids prepared using a two-step process. Chemical precipitation was used for the synthesis of the powders, and ultrasonic irradiation was used to disperse the nanoparticles in the carrier fluid (ethylene glycol). The size distributions of the nanopowders in the carrier fluid were determined using dynamic light scattering resulting in average particle sizes of around 500 nm. The crystallite sizes of the powders were below 20 nm. Thus, both types of nanofluids are comparable with regard to crystallite size, particle size, and morphology resulting in a direct comparison of material properties and their effect on thermal conductivity of the nanofluids. A guarded hot parallel-plate method and dynamic tests were used to compare the thermal conductivities of the nanofluids...

Temperature Dependence of Magneto-rheological Materials

The properties of magneto-rheological (MR) materials are temperature dependent. Compared to MR fluids, MR greases (MRGs) are more sensitive to temperature due to their inherent behavior of carrier materials. In this study, MRGs are studied to examine the temperature effect on their yield stress and apparent viscosity. Experimental data are obtained for magnetic fields ranging from 0.14 T to 0.53 T and temperatures ranging from 10°C to 70 °C. It is observed that temperature has a significant effect on the field-induced yield stress of MRGs. A new yield stress model, based on an extended Herschel—Bulkley constitutive relation, in which the shear yield stress is a function of magnetic field and temperature, is proposed. Excellent agreement between the theoretical results and experimental data is obtained.

Lyapunov-based control of a bridge using magneto-rheological fluid dampers

This study focuses on the effect of semi-active magneto-rheological fluid (MRF) dampers in reducing the response of a scaled bridge structure subjected to a random loading. A fluid-mechanics based model that can characterize the nonlinear dynamic behavior of MRF dampers is employed. A state-variable model for an integrated system of a scaled, two-span bridge and two MRF dampers is established. A feedback on-off control law is employed based on Lyapunov approach that guarantees the system stability for uncertain bounded input disturbances. An output feedback Lyapunov controller is implemented in the experimental study to verify the presented method. Both the theoretical and experimental studies show that the Lyapunov based control systems can effectively reduce the relative displacement between the deck and the abutment of the bridge when subjected to various input motions. In addition, when comparing to the experiment results, it is demonstrated that the proposed analytical model can predict the response of the system, accurately.

A new theory for bending of thick sandwich beams

Abstract Classical sandwich theory incorporates stretching and bending action in the facings and transverse shear deformation in the core. The theory presented here is intended for sandwich beams with relatively thick facings and moderately stiff cores of either bimodular material (which has different elastic moduli in tension and compression) or ordinary materials. Thus, transverse shear deformation in the facings as well as stretching and bending action in the core are also considered. Both analytical and finite-element results are presented and compared with the existing classical sandwich theory, which is shown to be unconservative in its predictions of both deflections and maximum shear stresses.