Buyung Kosasih

An application of nonlinear feature extraction - A case study for low speed slewing bearing condition monitoring and prognosis

This paper presents the application of four nonlinear methods of feature extraction in slewing bearing condition monitoring and prognosis: these are largest Lyapunov exponent, fractal dimension, correlation dimension, and approximate entropy methods. Although correlation dimension and approximate entropy methods have been used previously, the largest Lyapunov exponent and fractal dimension methods have not been used in vibration condition monitoring to date. The vibration data of the laboratory slewing bearing test-rig run at 1 rpm was acquired daily from February to August 2007 (138 days). As time progressed, a more accurate observation of the alteration of bearing condition from normal to faulty was obtained using nonlinear features extraction. These findings suggest that these methods provide superior descriptive information about bearing condition than time-domain features extraction, such as root mean square (RMS), variance, skewness and kurtosis.

Thin film lubrication of hexadecane confined by iron and iron oxide surfaces: A crucial role of surface structure

A comparative analysis of thin film lubrication of hexadecane between different iron and its oxide surfaces has been carried out using classical molecular dynamic simulation. An ab initio force-field, COMPASS, was applied for n-hexadecane using explicit atom model. An effective potential derived from density functional theory calculation was utilized for the interfacial interaction between hexadecane and the tribo-surfaces. A quantitative surface parameterization was introduced to investigate the influence of surface properties on the structure, rheological properties, and tribological performance of the lubricant. The results show that although the wall-fluid attraction of hexadecane on pure iron surfaces is significantly stronger than its oxides, there is a considerable reduction of shear stress of confined n-hexadecane film between Fe(100) and Fe(110) surfaces compared with FeO(110), FeO(111), Fe2O3(001), and Fe2O3(012). It was found that, in thin film lubrication of hexadecane between smooth iron and iron oxide surfaces, the surface corrugation plays a role more important than the wall-fluid adhesion strength.

Friction and anti-wear property of aqueous tri-block copolymer solutions in metal forming

Friction and anti-wear property of aqueous symmetrical tri-block normal PEOm-PPOn-PEOm and re-verse PPOn-PEOm-PPOn copolymer solutions have been studied. The study focuses on the effect of the solution bulk temperatures and the copolymer block structures. It was found that the concentration and the length of the copolymer blocks affect the solution cloud points, friction and anti-wear property. When solution was supplied at bulk temperature above their cloud point, aqueous copolymer solutions were not able to develop effective adsorbed film resulting in high friction and severe wear. When the bulk temperatures were below the cloud point, the anti-wear property improved significantly and the dynamic friction is lower than that when the temperatures were above the cloud point. This demonstrates the importance of the supply temperature of this type of lubricant in metal forming. However by adding ethyl phosphate ester to the copolymer solutions further improved friction reducing property of the solutions was observed and the friction and anti-wear property of the lubricant become insensitive to bulk temperature. In the effort to understand the lubrication mechanism of the aqueous solutions, wear tracks were studied using scanning electron microscope (SEM) and atomic force microscope (AFM), and the surface wetting ability via contact angle measurements.

Degradation Trend Estimation and Prognosis of Large Low Speed Slewing Bearing Lifetime

In many applications, degradation of bearing conditions is usually monitored by changes in time-domain features. However, in low speed (< 10 rpm) slewing bearing, these changes are not easily detected because of the low energy and low frequency of the vibration. To overcome this problem, a combined low pass filter (LPF) and adaptive line enhancer (ALE) signal pre-conditioning method is used. Time-domain features such as root mean square (RMS), skewness and kurtosis are extracted from the output signal of the combined LPF and ALE method. The extracted features show accurate information about the incipient of fault as compared to extracted features from the original vibration signal. This information then triggers the prognostic algorithm to predict the remaining lifetime of the bearing. The algorithm used to determine the trend of the non-stationary data is auto-regressive integrated moving average (ARIMA).

Investigation on mechanical properties of high speed steel roll material by nanoindentation

Abstract The hardness and elastic module of carbides and matrix of a high speed steel (HSS) roll material have been characterised by nanoindentation in the force range of 5–10 mN. It has been found that a different correlation needs to be applied to convert nanohardness to micro-Vickers hardness for the carbides and matrix. The pile-up phenomenon occurs significantly at the edge of the indent on the HSS matrix after nanoindentation, which resulted in a slight overestimation of the hardness. The nanohardness of the MC carbides, M2C/M7C3 carbides and HSS matrix is ∼20·0, 12·6 and 9·2 GPa, which are in good agreement with the reported values by micro-Vickers test.

Phase Behavior and Lubricity of Aqueous PEO-PPO-PEO and PPO-PEO-PPO Triblock Copolymer Solutions

ABSTRACT Aqueous triblock copolymer solutions are potential low-cost, eco-friendly lubricants. However, as a solution, their phase changes with copolymer concentration and solution temperature, raising the question, “Does the phase change affect the formation of adsorbed layer and the lubrication performance?” This article studies the copolymer solution phase behavior and lubricity in response to the copolymer structure, concentration, and solution temperature. Four different triblock copolymers, two normal PEO-PPO-PEO and two reverse PPO-PEO-PPO composed of PEO poly(ethylene oxide) and PPO poly(propylene oxide), have been investigated. From cloud point and surface tension measurements, phase change and micellization are shown to depend on copolymer type, number of hydrophilic PEO blocks, and temperature. Furthermore it is found that the phase and the presence of micelles lead to significant variation in adsorbed copolymer mass and lubricity. Based on the observed phase behaviors, the lubricity of copolymer solutions is discussed with regard to aggregation and adsorption on the solid–liquid interface.

The Effect of Molecular Structure on the Adsorption of PPO-PEO-PPO Triblock Copolymers on Solid Surfaces

This paper investigates the adsorption behavior of triblock copolymer Poly (propylene oxide)-poly (ethylene oxide)-poly (propylene oxide), PPO-PEO-PPO on silicon and iron surfaces by using the contact angle goniometer, spectroscopic ellipsometer and atomic force microscopy (AFM). After adsorption, the decrease of water contact angle was observed on each surface; and a larger reduction of water contact angle occurred on the surface covered by the copolymer film with longer and higher weight percent of hydrophilic PEO block. This means that the PEO block may be on the top of the adsorbed copolymer film. The film thickness measurement shows that the copolymer with longer and higher weight percent of PPO block forms a thicker film on the hydrophobic surface, which suggests that the hydrophobic PPO block of the copolymer in the aqueous solution plays the main role during the adsorption of PPO-PEO-PPO onto the hydrophobic surface. It has been found from the AFM results that the roughness of the surface decreased after adsorption and the smoother topography was observed on the surface adsorbed by a thicker adsorbed film.

Analysis of Interference Factors of Air Turbine Cascades

Abstract This paper reports viscous compressible aerodynamics analysis of two-dimensional cascades (arrays of aerofoils). The study elucidates the effect of cascade parameters such as solidity, σ and angle of attack, α, on the interference between blades. Understanding the interference behaviour is important in the performance analysis of air turbines such as Wells turbine commonly used in oscillating water column (OWC) - wave energy converter (WEC) system. The present analysis shows that isolated two-dimensional lift coefficient modified by interference factors, ko, based on inviscid flow theory is acceptable for low solidity cascades, i.e. σ ≤ 0.5, and that stall occurs at lower angle of attack in cascade compared to isolated aerofoil. When σ > 0.5, ko is shown to depend on both α and σ especially in the post-stall flow. The result suggests that interference factors that is applicable for wide range of flow conditions as in Wells turbines should also include the α effect in the modifier.

Particle Trajectories in Dilute Phase Pneumatic Conveying

A nonintrusive cross-correlation method to measure the particle velocities in dilute phase pneumatic conveying is described. The cross-correlation function generated gives information about the time it takes for a particle to travel between two optimally placed measurement planes. Experiments and CFD simulations are used to estimate an optimal inter-plane distance for various flow conditions.

A Study of Abrasive Wear on High Speed Steel Surface in Hot Rolling

In hot rolling, the thermal cyclic of work rolls causes a superficial oxide scale, which plays an important role on the contact friction and wear. The asperities of oxidised strip surface and wear debris slide over the High Speed Steel (HSS) work roll surface which comprises of hard carbides within an iron matrix under high pressure and velocity. Abrasive wear occurs and the particles will be removed from HSS surface. The current study introduces the Discrete Element Method (DEM) to investigate this abrasive wear phenomenon. The model successfully provides a physically based abrasive roll wear predication of HSS work roll with the consideration of carbides and oxide layers. It has been found that the carbide shape in the HSS roll affects the wear significantly, which has not been reported by previous numerical simulations and is the main focus of this research.