P.B. Kosasih

Development of an MR-brake-based haptic device

This paper describes the design, testing and modelling of a magneto-rheological (MR) fluid brake as well as its application in a haptic device. The MR device, in disc shape, is composed of a rotary shaft and plate, an electromagnetic coil, MR fluids, and casings. The working principle of the actuator is discussed and the transmitted torque equation employed by using the Bingham plastic model. The optimal dimensions of the actuator were obtained by finite-element analysis using the COSMOSEMS package. Following manufacturing and fabrication of the actuator prototype, the steady-state performance of the MR actuator was measured using a force gauge. The experimental results show that the actuator exhibits hysteresis behaviour. A sub-hysteresis model was then proposed and the model parameters were identified. Example applications of this actuator in virtual reality are demonstrated.

MRE Properties under Shear and Squeeze Modes and Applications

Magnetorheological elastomers (MREs) are smart materials whose mechanical properties, like their modulus and elasticity, can be controlled by an external magnetic field. This feature has resulted in a number of novel applications, such as adaptive tuned dynamic vibration absorbers for suppressing unwanted vibrations over a wide frequency range. MRE-based devices operate in different modes, such as shear mode and squeeze mode; however, the study of mechanical performances of MREs under squeeze mode is very rare. This article aims to investigate MRE performances under both shear and squeeze modes. Experimental studies and simulations were conducted to analyze the MR effect in both modes. These studies indicate a different working frequency ranges for both modes. In a case study, a MRE-based vibration absorber was built up in a simulation and its mechanical performances were analyzed, which demonstrated good capabilities in reducing vibrations.

Magnetorheological fluids based haptic device

This paper presents the development of a haptic device working with magnetorheological (MR) fluids. The computer screen is portioned in various segments and the controllable software monitors the attributed values of the voltage to the screen. The motion of a cursor on the computer screen is controlled by the MR actuator. A resistance force, the strength of which depends on the cursor position, would be generated and perceived by the user. The performance of the device is tested and verified with finite element analysis.

An investigation into the thermal mixing in journal bearings

Abstract Flows in the thermal mixing zone of a journal bearing are investigated using the computational fluid dynamics (CFD) approach. The complexity and inertial effect of the flows inside the supply region of different configurations are considered. It is shown that these flows are highly recirculating but have almost negligible effects on the thermal mixing. The turbulent flow inside the supply region is modelled using the k-ω turbulence model. Most parts of the supply region are filled with recirculation zones and most of the injected cold oil does not immediately enter the oil film. For all configurations considered the extent of the thermal mixing zone is not confined to just above the supply groove. This zone extends some distance beyond the pockets/grooves and in some cases extends for almost the whole bearing length in the axial direction. The length of the supply region and supply pressure governs the extent of the mixing zones. To investigate the effect of various groove dimensions, locations and bearing operating conditions on the bush temperature, the supply region and oil film were considered as separate domains. This allows the difference in length scales to be resolved. The results are presented quantitatively in terms of bush temperatures and maximum temperature. A flow field inside a pocket is compared with available experimental flow visualizations.

Learning Finite Element Methods by Building Applications

This paper describes how programming projects are used to help students understand the theory of finite element (FE) methods in the authors class. The implementation of FE theory in FE-based commercial software is made clearer through programming simple FE analysis codes. From the experience gained in the coding, students have a better understanding of the theory and numerical processes used in FE commercial software. As a result, they have more confidence in using commercial software, knowing that the computer programs are not simply ‘black boxes’ that process data and produce colourful results. More importantly, they understand the limitations of the programs, how to use them correctly and interpret the generated output correctly. Two projects are described in which students develop codes and then compare the results with those from commercial software.

Linear Viscoelasticity of MR Fluids: Dependence on Magnetic Fields

The paper presents investigation of dynamic properties of MR fluids by using a rheometer with parallel-plate geometry. The sample is reduced iron powder based MR suspensions. Linear viscoelastic properties of such sample, which can be variably controlled using a magnetic field, are obtained and summarized based on oscillatory tests. Four field-induced regimes, I, II, III, and IV, are found in the system, which are defined by three critical field strengths: BC1 < BC2 < BC3. MR fluids in regime I through IV experience four typical structural convolutions: coexisting of particles and random chains; coexisting of chains and random clusters; coexisting of clusters and chains; stable clusters. Such results are in good accord with experimental results achieved by Lius group using light scattering techniques.

A Tool to Estimate the Wheel/Rail Contact and Temperature Rising Under Dry, Wet and Oily Conditions

In this paper, finite element method (FEM) has been applied to evaluate the wheel/rail contact stress under different contact conditions. The elastic-plastic model coded in ANSYS/LS-DYNA includes a whole wheel, 680 mm of the canted rail, and sub-components of the track (railpads, sleepers, and ballast). The three values of friction coefficient 0.4, 0.2 and 0.07 have been chosen to model the dry, wet and oily environmental contacts, respectively. The high mechanical stresses exerted at the contact area will cause the temperature to rise, which results in decreasing of the yield strength of the wheel/rail. The growth of temperature is a major source of the various microstructure changes that occurs on the rail surface, especially the formation of White Etching Layer (WEL). Therefore, a theoretical calculation of heat generation has also been implemented in the current research. The output data from the FEM models have been considered as the input for the theoretical thermal model to examine temperature rising on and beneath the rail surface. The combination of finite element method for contact stress and theoretical thermal method for temperature variation would provide a better understanding about wheel/rail contact under a variety of contact conditions (dry, wet, and oily). Various scenarios of damage mechanisms of rail have been considered in the paper. The obtained results from the model have revealed that the influence of environmental conditions on normal contact stress, pressure and contact area is negligible.

Condition Monitoring of Low Speed Slewing Bearings Based on Ensemble Empirical Mode Decomposition Method

Vibration condition monitoring at low rotational speeds is still a challenge. Acoustic emission (AE) is the most used technique when dealing with low speed bearings. At low rotational speeds, the energy induced from surface contact between raceway and rolling elements is very weak and sometimes buried by interference frequencies. This kind of issue is difficult to solve using vibration monitoring. Therefore some researchers utilize artificial damage on inner race or outer race to simplify the case. This paper presents vibration signal analysis of low speed slewing bearings running at a low rotational speed of 15 rpm. The natural damage data from industrial practice is used. The fault frequencies of bearings are difficult to identify using a power spectrum. Therefore the relatively improved method of empirical mode decomposition (EMD), ensemble EMD (EEMD) is employed. The result is can detect the fault frequencies when the FFT fail to do it.

An analysis of sector-shaped thrust bearings operating in the transition regime

Abstract The purpose of this study was twofold: (i) to introduce a modified mixing length expression of Reynolds stress in transition and turbulent lubrication theory; (ii) to determine the performance characteristics of sector-shaped thrust bearings when operated in the transition regime taking into account the inertia effects. A new model of Reynolds stresses for transition-turbulent theory is proposed. The approach relies on Prandtls mixing length theory and a modified Van Driest mixing length formula which accounts for the effect of the shear stress gradient in thin film lubrication. The mixing length model is used to analyse turbulent planar and non-planar flows. Turbulent coefficients obtained from the non-planar cases are used to analyse the sector-shaped thrust bearing in the transition region, taking into account the convective inertia forces and centrifugal forces. Bearing performance characteristics such as pressure distribution, load carrying capacity, pressure centre and inlet flow rate are calculated.

MRE properties under shear and squeeze modes and applications

Magnetorheological elastomers (MREs) belong to the group of so called smart materials. Due to an applied magnetic field the MREs change their material properties like the stiffness. This feature has resulted in a number of novel applications, such as adaptive tuned dynamic vibration absorbers (ATDVA) for suppressing unwanted vibrations over a wide frequency range. MRE based devices operate in different modes, such as shear mode and squeeze mode but the study of mechanical performances of MREs under squeeze mode is very rare. This paper aims to investigate MRE performances under both shear and squeeze modes. Both experimental and simulation studies were conducted to analyze the MR effect in both modes. These studies indicate that MRE working in squeeze mode would result in higher MR effects. As a case study, a MRE based ATDVA was analyzed, which demonstrated good capabilities in reducing vibrations.