Harish Hirani

Magnetic Bearing Configurations: Theoretical and Experimental Studies

A radial magnetic bearing, consisting of two permanent magnets, is an attractive choice because of its zero wear, negligible friction, and low cost, but it suffers from low load capacity, low radial stiffness, lack of damping, and high axial instability. To enhance the radial load and radial stiffness, and reduce the axial thrust, we have made a theoretical and experimental study of various radial configurations, including hydrodynamic lubrication to improve dynamic performance of the magnetic bearing. We developed an experimental setup to investigate the performance of bearing configurations under different operating conditions. The motion of a rotating shaft is mapped by two displacement sensors with a data acquisition system and personal computer. The first critical speed of each configuration is determined experimentally and verified through frequency analysis. We present a polar plot of displacement data.

Optimization of Eight Pole Radial Active Magnetic Bearing

In the current paper, studies carried out to design an eight pole electromagnetic bearing have been presented. The magnetic levitation force, accounting the copper and iron losses, was maximized for the given geometric constraints. Derivation of winding constraint equation in terms of wire diameter, number of turns, and dimensions of pole has been presented. Experiments were conducted to establish the constraints related to temperature rise. Finally, the dimensions of the electromagnet for maximizing the force obtained using numerical optimization have presented. [DOI: 10.1115/1.4029073]

Development of Analytical Equations for Design and Optimization of Axially Polarized Radial Passive Magnetic Bearing

In the present research work, analytical equations have been developed for design and optimization of radial axial polarized passive magnetic bearing (PMB) with single layer for facilitating easy and quick solution, obviating the need of costly software. Seven design variables: eccentricity, rotor width, stator width, rotor length, stator length, clearance, and mean radius were identified as the main factors affecting the design and were thus considered in the development of analytical equations. The results obtained from the developed analytical equations have been validated with the published results. The optimization of the bearing design, with minimization of magnet volume as the objective function, was carried out to demonstrate the accuracy and usefulness of the developed equations. [DOI: 10.1115/1.4028488]

Design of a squeeze film magnetorheological brake considering compression enhanced shear yield stress of magnetorheological fluid

A magnetorheological brake, consisting of rotating disks immersed in a MR fluid and enclosed in an electromagnet, is proposed to replace the conventional heavy weight low response hydraulic disk brake. The frictional characteristics of the proposed brake can be controlled by regulating the yield stress of the MR fluid as function of magnetic field and normal compressive force. The controllable yield stress retards the surfaces of rotating disks, thus MR fluid can be used as a brake lining material. The present research work attempts designing a squeeze film MR brake by accounting compression enhanced shear yield stress of magnetorheological fluid. Theoretical calculations indicate that the estimated braking torque of the six plate squeeze film MR brake, under compression, is in the order of 600Nm. To validate the theoretical design and its findings, a prototype of single-plate squeeze film MR disk brake has been developed. Experimental test setup helps to illustrate braking torque under different control currents (0.0 to 1.25 A).

An Analytical Approach to Evaluate Dynamic Coefficients and Nonlinear Transient Analysis of a Hydrodynamic Journal Bearing

The objective of this work is the development of analytical expressions for accurate evaluation of dynamic coefficients and prediction of post whirl orbits (transient journal center motion above instability critical speed) by computation of nonlinear journal trajectory for a cylindrical journal bearing.

Effect of Particle Size on Shear Stress of Magnetorheological Fluids

Magnetorheological fluids (MRF), known for their variable shear stress contain magnetisable micrometer-sized particles (few micrometer to 200 micrometers) in a nonmagnetic carrier liquid. To avoid settling of particles, smaller sized (3–10 micrometers) particles are preferred, while larger sized particles can be used in MR brakes, MR clutches, etc. as mechanical stirring action in those mechanisms does not allow particles to settle down. Ideally larger sized particles provide higher shear stress compared to smaller sized particles. However there is need to explore the effect of particle sizes on the shear stress. In the current paper, a comparison of different particle sizes on MR effect has been presented. Particle size distributions of iron particles were measured using HORIBA Laser Scattering Particle Size Distribution Analyser. The particle size distribution, mean sizes and standard deviations have been presented. The nature of particle shapes has been observed using scanning electron microscopy. To explore the effect of particle sizes, nine MR fluids containing small, large and mixed sized carbonyl iron particles have been synthesized. Three concentrations (9%, 18% and 36% by volume) for each size of particles have been used. The shear stresses of those MRF samples have been measured using ANTON PAAR MCR-102 Rheometer. With increase in volume fraction of iron particles, the MR fluids synthesized using “mixed sized particles” show better shear stress compared to the MR fluids containing “smaller sized spherical shaped particles” and “larger sized flaked shaped particles” at higher shear rate.

Design of eight pole radial active magnetic bearing using monotonicity

In the present research, studies have been carried out to design an eight-pole electromagnetic bearing considering copper- and iron- losses. The magnetic lévitation force was maximized for the given geometric constraints using (i) numerical optimization and (ii) monotonicity analysis. The dimensions of the electromagnet using both the methods has been presented and compared.

Optimization of Magnetorheological Brake

Quick response and rheological properties as a function of magnetic field are well known features of MR fluids which inspire their usage as brake materials. Controllable torque and minimum weight of brake system are the deciding functions based on which the viability of the MR brake against the conventional hydraulic brake system can be judged. The aim of this study is to optimize a multi-disk magneto-rheological brake system considering torque and weight as objective functions and geometric dimensions of conventional hydraulic brake as constraints. The electric current accounting magnetic saturation, MR gap, number of disk, thickness of disk, and outer diameter of disk have been considered as design variables. To model the behavior of MR Fluid, Bingham and Herschel Bulkley models have been compared. To implement these models in estimating the braking torque a modification in shear rate dependent component has been proposed. The overall design of MR brake has been optimized using a hybrid (Genetic algorithm plus gradient based) optimization scheme of MATLAB software.© 2011 ASME

Development of a magnetorheological brake with a slotted disc

A conventional disc wears out and the brake pollutes the environment. Brake pad dust is reported to be the largest source of environment pollution1. The particles emanating because of wear of the brake pad pollute the environment2,3,4. In addition to pollution caused by wear particles, the friction-induced noise between the brake pad and the disc is also a major concern5. Also, localized heating occurs in a conventional disc brake. To tackle both of these problems, conventional disc brakes can be replaced with manetorheological fluid brakes. Magnetorheological fluids are materials having a shear yield stress which is a function of the magnetic field. On the application of a magnetic field, magnetorheological particles become aligned and increase the shear resistance between relatively moving surfaces. The friction between the stator and the rotor increases and fulfils the braking function, which means that magnetorheological fluids can be used as brake friction materials. A magnetorheological brake consists of a rotating disc or discs immersed in a magnetorheological fluid and enclosed in an electromagnetic casing. The torque characteristics of the magnetorheological brake in the shear mode are controlled by regulating the yield stress of the magnetorheological fluid. An increase in the yield stress increases the braking torque, which means that, the higher the yield strength of the magnetorheological fluid, the better is the performance of the magnetorheological brake. However, the major disadvantage of the shear-mode-based magnetorheological brake is its high resisting torque even in the off-state viscosity, and such magnetorheological brakes cannot be recommended for automotive applications. To obtain the performance of a conventional disc brake, experimental studies on a conventional disc brake were performed using a full-scale dynamometer. In addition to wear particles, localized heating of the disc was observed. The disc–pad interfaces were modelled to simulate the disc temperature. The values of the maximum temperature, which were obtained from simulations as well as experiments, were compared. The simulations were extended to hypothetical 360° pads, and a significant reduction in the maximum temperature was noted. Based on the idea of 360° pads, a magnetorheological brake subjected to shearing was analysed. To perform experiments on a small-scale magnetorheological brake, a test set-up was designed and developed, and it was confirmed that a magnetorheological brake subjected to shearing provides a better torque than does a conventional disc brake of the same size. An ideal magnetorheological brake should exert a zero frictional torque in the off-state condition and a controllable frictional torque in the on-state condition. An attempt was made to design such a magnetorheological brake. To overcome the disadvantage of the shear-mode-based magnetorheological brake, a new design of magnetorheological brake with a slotted disc was proposed. The design and development of the proposed magnetorheological brake, incorporating the compression-assisted shear mode, was detailed. The results of the braking torque, the temperature distribution and the off-state viscosities were plotted. Finally, comparison between the proposed magnetorheological brake and a small-scale disc brake was presented. The results show that, with an increase in the braking pressure (from 2 bar to 6 bar), the maximum value of temperature rises because of enhancement of the localized heating in the disc. The temperature rise is less in the case of the extended brake pad (360°), which was used in the magnetorheological brake. The surface temperature of the magnetorheological brake increases with increasing magnetic field. The magnetorheological fluid with 50 wt % iron particles has a less viscous torque in the off-state condition and a high-field torque under the compression mechanism in the magnetorheological brake, which fulfils the criterion for an ideal magnetorheological brake to replace a conventional disc brake of the same size.

An Overview of Passive Magnetic Bearings

This paper describes different passive magnetic bearing configurations and associated pros and cons. It details the techniques used by different inventors to overcome the limitations of passive magnetic bearing, such as low damping, low stiffness and its inherent instability. To overcome these limitations different hybridization techniques used by different researchers have been illustrated. Finally, a new hybrid bearing configuration invented by the authors has been described.Copyright