Flow Of Electrorheological Fluid Research Articles

Existence of Steady Solutions for a Model for Micropolar Electrorheological Fluid Flows with Not Globally log-Hölder Continuous Shear Exponent

In this paper, we study the existence of weak solutions to a steady system that describes the motion of a micropolar electrorheological fluid. The constitutive relations for the stress tensors belong to the class of generalized Newtonian fluids. The analysis of this particular problem leads naturally to weighted variable exponent Sobolev spaces. We establish the existence of solutions for a material function {hat{p}} that is log -Hölder continuous and an electric field textbf{E} for that vert textbf{E}vert ^2 is bounded and smooth. Note that these conditions do not imply that the variable shear exponent p={hat{p}}circ vert textbf{E}vert ^2 is globally log -Hölder continuous.

A novel bending microactuator with integrated flexible electro-rheological microvalves using an alternating pressure source for multi-actuator systems

This paper presents a novel bending microactuator with integrated flexible electro-rheological microvalves (FERVs) using an alternating pressure source for multi-actuator systems. The proposed bending microactuator is a fluidic elastomer actuator that has two fluidic chambers inside and can bend with the chamber pressures controlled by the integrated FERVs, each of which has a flexible structure and changes a flow of electro-rheological fluid (ERF) through its viscosity change due to an applied electric field. The utilization of the FERVs in the actuator reduces the overall size, while the benefits of the alternating pressure source are reduction of the number of pipes in a multi-actuator system and removal of the fluid reservoir tank. The mathematical models were demonstrated and utilized for optimizing and designing the dimensions of the actuator to obtain the maximum bending angle, the fast response, and the highest output force. The designed actuator was successfully fabricated using MEMS technologies and experiments were conducted to investigate the bending angle and the response time of the successfully fabricated actuator. The results showed good agreement between the experimental results and the simulation results, which proved the validity of the proposed models. Comparing with the previously proposed microactuator with an FERV, the proposed actuator had 4.5 times larger bending angle. From the results, the optimized actuator showed the feasibility for use in e.g. micro gripper application.

Design, modeling, and evaluation of a slim haptic actuator based on electrorheological fluid

Realistic haptic feedback is needed to provide information to users of numerous technologies, such as virtual reality, mobile devices, and robotics. For a device to convey realistic haptic feedback, two touch sensations must be present: tactile feedback and kinesthetic feedback. Although many devices today convey tactile feedback through vibrations, most neglect to incorporate kinesthetic feedback. To address this issue, this study investigates a haptic device with the aim of conveying both kinesthetic and vibrotactile information to users. A prototype based on electrorheological fluids was designed and fabricated. By controlling the electrorheological fluid flow via applied electric fields, the device can generate a range of haptic sensations. The design centered on an elastic membrane that acts as the actuator’s contact surface. Moreover, the control electronics and structural components were integrated into a compact printed circuit board, resulting in a slim device suitable for mobile applications. The device was tested using a dynamic mechanical analyzer to evaluate its performance. The device design was supported with mathematical modeling and was in agreement with experimental results. According to the just-noticeable difference analysis, this range is sufficient to transmit distinct kinesthetic and vibrotactile sensations to users, indicating that the electrorheological fluid–based actuator is capable of conveying haptic feedback.

Operational durability of a giant ER valve for Braille display

The compact configuration of giant ER (electrorheological) valves provides the possibility of realizing a full-page Braille display. The operational durability of ER valves is a key issue in fulfilling a Braille display. A giant ER valve was used to investigate the variations in pressure drops and critical pressure drops of the valves over a long period under some typical operational parameters. The results indicate that neither the pressure drops nor critical pressure drops of giant ER valves show apparent deterioration over a long period. Without ER fluid exchange, a blockage appears in the channel of the valve because the ER structures induced by an external electric field cannot be broken by the Brownian motion of hydraulic oil molecules when the external electric field is removed. Forcing ER fluid flow is an effective and necessary method to keep the channel of the valve unblocked. Thus the operational durability of the valve using giant ER fluids is able to meet the demands of Braille display.

The dielectric properties and flow of electrorheological fluids based on polymer-coated nanodispersed barium tetraacetate titanyl particles upon a dynamic shear in electric fields

The shear stress in flowing electrorheological fluids consisting of PMS-20 poly(dimethylsiloxane) filled with nanodispersed barium tetraacetate titanyl particles coated with polymers (polyethyleneimine, poly(ethylene glycol), and polyethyloxazoline) has been studied as depending on the strengths of direct- and alternating-current (f = 50 Hz) electric fields. Results of analyzing the dielectric spectra of electrorheological fluids in a frequency range of 25–106 Hz have been presented. The values of the shear stress in the flowing fluids as depending on the nature of a polymer adsorbed on the particle surface decrease in a series corresponding to a reduction in the Maxwell–Wagner relaxation times of the suspensions. The current-voltage characteristics of the electrorheological fluids at high voltages (up to 5 kV) indicate the realization of the mechanism of currents limited by the space charge. The influence of an adsorbed polymer on the magnitude of the electrorheological effect is reduced to blocking polar groups on the particle surface and variations in the conductivity, effective dielectric permittivity, and loss tangents of filler materials. An increase in the contribution from these factors leads to a gradual decrease in the magnitude of the electrorheological effect.

Existence of steady solutions for micropolar electrorheological fluid flows

In this paper we study the existence of weak solutions to a steady system describing the motion of micropolar electrorheological fluids. The constitutive relations for the stress tensors belong to the class of generalized Newtonian fluids. The analysis of the problem leads naturally to weighted Sobolev spaces. The emphasis of the paper is devoted to the study of the degenerate problem. Using the Lipschitz truncation and the L∞-truncation we derive various lower bounds, depending also on the electric field, ensuring the existence of solutions.

Electro-capillary effects in capillary filling dynamics of electrorheological fluids.

The flow of electrorheological fluids is characterized by an apparent increase in viscosity manifested by the yield stress property of the fluid, which is a function of the applied electric field and the concentration of the suspended solute phase within the dielectric medium. This property of electrorheological fluids generally hinders flow through a capillary if the imposed shear stress is lower than the induced yield stress. This results in a plug-like zone in the flow profile, thus giving the fluid Bingham plastic properties. In the present work, we study such influences of the yield stress on the capillary filling dynamics of an electrorheological fluid by employing a rheologically consistent reduced order formalism. One important feature of the theoretical formalism is its ability to address the intricate interplay between the surface tension and viscous forces, both of which depend sensitively on the electric field. Our analysis reveals that the progress of the capillary front is hindered at an intermediate temporal regime, which is attributable to the increase of the span of the plug-zone across the channel width with time. With a preliminary understanding on the cessation of the capillary front advancement due to the yield stress property of the electrorheological fluids, we further strive to achieve a basic comparison with an experimental study made earlier. Reasonable agreements with the reported data support our theoretical framework. Comprehensive scaling analysis brings further insight to our reported observations over various temporal regimes.

Structure evolution in electrorheological fluids flowing through microchannels

Enhanced knowledge of the transient behavior and characteristics of electrorheological (ER) fluids subject to time dependent electric fields offers the potential to advance the design of fast actuated hydraulic devices. In this study, the dynamic response of electrorheological fluid flows in rectilinear microchannels was investigated experimentally. Using high-speed microscopic imaging, the evolution of particle aggregates in ER fluids subjected to temporally stepwise electric fields was visualized. Nonuniform growth of the particle structures in the channel was observed and correlated to field strength and flow rate. Two competing time scales for structure growth were identified. Guided by experimental observations, we developed a phenomenological model to quantitatively describe and predict the evolution of microscale structures and the concomitant induced pressure gradient.

Flow of an electrorheological fluid between eccentric rotating cylinders

Electrorheological fluids have numerous potential applications in vibration dampers, brakes, valves, clutches, exercise equipment, etc. The flows in such applications are complex three-dimensional flows. Most models that have been developed to describe the flows of electrorheological fluids are one-dimensional models. Here, we discuss the behavior of two fully three-dimensional models for electrorheological fluids. The models are such that they reduce, in the case of simple shear flows with the intensity of the electric field perpendicular to the streamlines, to the same constitutive relation, but they would not be identical in more complicated three-dimensional settings. In order to show the difference between the two models, we study the flow of these fluids between eccentrically placed rotating cylinders kept at different potentials, in the setting that corresponds to technologically relevant problem of flow of electrorheological fluid in journal bearing. Even though the two models have quite a different constitutive structure, due to the assumed forms for the velocity and pressure fields, the models lead to the same velocity field but to different pressure fields. This finding illustrates the need for considering the flows of fluids described by three-dimensional constitutive models in complex geometries, and not restricting ourselves to flows of fluids described by one-dimensional models or simple shear flows of fluids characterized by three-dimensional models.

Damping force prediction of electrorheological fluid damper using an analytical dynamic model

This work proposes a new analytical approach for dynamic modelling of the Electrorheological (ER) damper for accurate prediction of the hysteresis behaviour. In the proposed dynamic model, both the compressibility of ER fluid in the upper and lower chambers and the dynamics of ER fluid flow in the annular duct of the ER damper are considered. In order to demonstrate the effectiveness of the proposed model, a comparative work between simulation and experiment is undertaken at various piston motions with different excitation magnitude and frequency. The effects of the fluid compressibility, initial pressure and gas volume in the accumulator on the hysteresis of the ER damper are investigated.

A new approach for dynamic modeling of an electrorheological damper using a lumpedparameter method

This work proposes a new method for dynamic modeling of an electrorheological (ER)damper using a lumped parameter method. After describing the configuration andoperating principle of the ER damper, quasi-static modeling of the damper isconducted on the basis of the Bingham model of ER fluid. Subsequently, the lumpedparameter models of ER fluid flows in the damper are established and the integratedlumped model of the whole damper system is obtained by taking into account thedynamic motions of the annular duct, upper chamber, lower chamber and connectingpipe. In order to demonstrate the effectiveness of the proposed dynamic model, acomparative work between the simulation and the experiment is undertaken. This isperformed under various piston motions with different excitation magnitudesand frequencies. In addition, the effect of ER fluid compressibility and initialpressure in the accumulator on the hysteresis of the ER damper is investigated.

Unsteady flow modeling of an electrorheological valve system with experimentalvalidation

This paper presents an unsteady flow modeling of an electrorheological (ER) valve systemand verifies its effectiveness through experimental investigation. After designing acylindrical ER valve, a dynamic model for unsteady flow of ER fluid is derived byconsidering the fluid inertia. The field-dependent pressure drop of the unsteady flow isthen calculated and validated with the experimental result. In order to clearlyobserve the difference between the unsteady flow model and the steady model, theflow rate of the ER valve is analyzed under low frequency and high frequencysinusoidal inputs. In addition, in order to demonstrate the effectiveness of theproposed unsteady flow model, a position control system activated by ER valves isconstructed. The dynamic model of the control system is formulated on the basis of theunsteady flow analysis, and control responses such as flow rate, pressure dropand displacement are compared between the unsteady flow and the steady flowmodels.

A study on flow characteristics of electrorheological fluid in a damper model

PurposeThe purpose of this paper is to investigate flow behavior of electrorheological (ER) fluid in a closed piston–cylinder system.Design/methodology/approachA basic study of flow characteristics of ER fluid in a damper model is conducted experimentally and numerically. The electric field is applied between inner wall of the cylinder and outer wall of the piston, and the pressure difference between upper and lower chamber of the cylinder is measured. A numerical prediction of ER fluid flow in the damper model system is performed in order to study the ER fluid flow characteristics. Visualization experiment is also made and used to qualitatively verify the numerical formulation.FindingsThe agreement between the numerical predictions and experimental results is encouraging, and the ER fluid flow patterns under different piston aspect ratios, movement speeds and applied electric field strengths are presented. The results show that the piston aspect ratio has much smaller influence on the ER flow pattern than other influencing factors. Increasing piston movement speed or reducing the electric field applied is helpful to reduce the pressure response time period, which is an important indicator showing sensitiveness of the damper. It is also seen that the pressure difference between the upper and lower chamber of the cylinder increases with the electric field strength and the piston movement speed.Originality/valueFirst time the detailed investigation into the hydrodynamics behavior in such working models of engineering applications for ER fluid.

Dynamic modeling of an electrorheological damper considering the unsteady behavior ofelectrorheological fluid flow

In this study, dynamic modeling of an electrorheological (ER) damper is performedconsidering the unsteady behaviors of ER fluid flow through the annular duct of thedamper. After describing the configuration of the ER damper, quasi-static modeling ofthe damper is conducted on the basis of the Bingham model of ER fluid. Thepressure drop of the unsteady ER fluid flow through the annular duct between theelectrodes of the damper with a known variation of flow rate is then obtained bysolving the momentum equation of the ER fluid flow using the Laplace transformtechnique. Based on the proposed unsteady flow solution, the simulated results areobtained and compared with measured ones in order to evaluate the effectivenessof the proposed model. In addition, in order to reduce the computation load, asimplified solution of the dynamic damping force is proposed with validation.

CHARACTERIZATION OF ELECTRO-RHEOLOGCIAL FLUIDS UNDER HIGH SHEAR RATE IN PARALLEL DUCTS

Electro-rheological (ER) fluid is a smart suspension which can be changed promptly from Newtonian to Bingham plastic material when subjected to a high-intensity electric field. This property of ER fluid makes it possible to be applied in adaptive energy absorbers. As the impact velocity encountered in applications could be very large, it is necessary to characterize the ERF under high shear rate. In this study, a capillary rheo-meter with parallel duct was designed and manufactured which is capable of producing a shear rate as high as 5000(1/s). Two giant ER fluids with mass concentration C = 51% and 44.5% and a commercial density-matched ER fluid with C = 37.5% were characterized. The experimental results show that when the ER fluids are free of electric field (E = 0 kV / mm ), they are Newtonian. However, for the former two ER fluids, the deposition effect is very remarkable and stirring has to be made continuously to keep the suspension stable. With the increase of the electric field intensity, the yield shear stresses of ER fluids increase exponentially but their viscosities do not change much. It is also found that within the parallel duct, the flow of ER fluids exhibits notable fluctuations, whose period increases with the increase of electric field intensity and is independent of the shear rate.

An experimental study of electrorheological fluid flow through a packed bed of glass beads

This paper shows that pressure drop-flow rate performance of an electrorheological (ER) fluid flowing through a packed bed of glass beads is consistent with a modified Ergun equation for yield stress flow through a packed bed. ER fluids are of scientific and engineering interest due to the sensitivity of their rheological properties on the applied electric field. As far as we know ER fluids have not been studied for flows through porous media. In this work a silica particle–silicone oil suspension is pumped through a rectangular packed bed of glass beads with applied electric fields. The silica particles are observed to form fibrous structures parallel to the electric field that stretch between the beads and extend between the electrodes. The pressure drop-flow rate performance agrees well with the expected performance calculated from a modified Ergun equation for a yield stress fluid flow through the packed bed with the viscosity and yield stress as functions of the applied electric field.

Problem on stationary flow of electrorheological fluids at the generalized conditions of slip on the boundary

General conditions of slip of a fluid on the boundary are derived anda problem on stationary flow of the electrorheological fluid in which the terms of slip are specifiedon one part of the boundary and surface forces are given on the otheris formulated and studied. Existence of a generalized (weak) solution of this problem is provedby using the methods of penalty functions, monotonicity and compactness.It is shown that the method of penalty functions and the Galerkinapproximations can be used for the approximatesolution of the problem under consideration. The existence and the uniqueness of the smooth classical solution of the problem is proved in the case that the conditions of slip are prescribed on the whole of the boundary.

Couette flow of electrorheological fluids between two concentric cylinders with wallslip

The Couette flow of electrorheological (ER) fluids between two concentric cylinders withwall slip is considered in the present paper. ER fluids can be closely approximated asBingham plastics. Based on the Navier slip model in the wall boundaries, thecharacteristics of slip flow, in particular the effects of velocity slip on the location of yieldsurface, are obtained by an analytical method. It is shown that the wall slip has a greateffect on the velocity distribution and the location of the yield surface. In the scope of theslip coefficient discussed, the wall slip velocity increases first with increasing slip coefficient;after reaching a maximum, the slip velocity then decreases on further increase of the slipcoefficient. The moments exerted by ER fluids on the walls decrease as the slip coefficientincreases.

Electrorheological Effects at High Shear Rate

Much attention has been given to electrorheological (ER) fluids because of the ER effect, which has been described by a large number of researchers as a notable increase in the apparent viscosity of a fluid upon the application of an electric field. The description of ER effects is, however, not accurate at high shear rates. To clarify the discrepancy, we analyze and compute the apparent viscosity as a function of shear rate for ER fluid flow between rotating coaxial cylinders in the presence of an electric field. The theoretical predictions show that the increase of electric intensity contributes little to the apparent viscosity enhancement at high shear rates, while ER effects for ER fluids with a higher polarization rate still exist and ER devices possess controllability in this regime. Description of the ER effect by the apparent viscosity leads to an unrealistic conclusion that ER effects disappear at high shear rates, because the apparent viscosity of ER fluids approaches the value for Newtonian fluids. Therefore, it is concluded that the proper description of ER effects, i.e., one that holds uniformly for any strain rate when ER effects exist, is manifested by a remarkable increase in the extra stress rather than in the apparent viscosity of ER fluids.

Flow of electrorheological fluid under conditions of slip on the boundary

We study a mathematical model describing flows of electrorheological fluids. A theorem of existence of a weak solution is proved. For this purpose the approximating-topological method is used.