Youyun Zhang

Concentration Measurement of Dilute Pulverized Fuel Flow by Electrical Capacitance Tomography

In order to eliminate the effects of flow regimes on phase concentration measurements, electrical capacitance tomography (ECT) was employed to improve the measurement accuracy. The solid particle distribution in the flow pipelines were characterized by measuring capacitance to obtain flow patterns. An improved offline iteration online reconstruction (OIOR) algorithm was proposed as the image reconstruction for the ECT system and a method of two-dimension maximum entropy threshold image segmentation was used for further image processing. Dynamic experiments were carried out for gas/solid two-phase flows. First, the flow regime was identified by the ECT, and the results were used to trace the fluctuation of the dynamic two-phase flow online. The volume concentrations were then calculated based on the reconstructed results. The experimental results indicate that the average relative error of the concentration measurements was about 1.5% over a pulverized coal volume concentration range 0.96–4.97%.

Intelligent Fault Diagnosis of Rolling Element Bearing Based on SVMs and Statistical Characteristics

In this paper, the statistical characteristics of time, frequency and time-frequency domain are applied to discriminate various fault types and evaluate various fault conditions of rolling element bearing, and the classification performance of them is evaluated by using SVMs. Experimental results showed that the statistical characteristics Mean, Variance, Root, RMS and Peak of the 25 sub frequency bands in frequency domain obtain higher classification accuracy rate on all the fault datasets than the statistical characteristics in the whole time and frequency domain. Wavelet packet decomposition is an efficient time-frequency analysis tool, and it can decompose the original signal into independent frequency bands. Experiment on the statistical characteristics of the 5th level wavelet packet decomposition showed that the statistical characteristics Variance, Root, RMS and Peak can discriminate various fault types and evaluate various fault conditions well on all the datasets. Compared with the statistical characteristics of sub frequency bands in frequency domain, the classification performance of the statistical characteristics of the wavelet packet transform is a little lower than that of the statistical characteristics of sub frequency bands in frequency domain.© 2007 ASME

Experimental study of the transient thermal effect and the oil film thickness of the equalizing thrust bearing in the process of start-stop with load

It was important to note the load could not be distributed equally over the thrust pads when the thrust bearing was in operation, especially at the stage of start-up and stop with load. An experimental study that investigated the transient thermal effect and the oil film thickness of the equalizing thrust bearing in the process of start-stop with load was presented in this article. Four static loads and three supplied oil pressures were used in this study. The transient thermal effect and the oil film thickness were simultaneously obtained from a horizontal thrust-bearing test rig. It was shown in experimental results that the transient thermal effect and the oil film thickness varied rapidly at the stage of start-up and stop, and had an unobvious variance when the rotational speed was constant. The structure of the equalizing thrust bearing allowed it to work well at the stage of start-up and stop with load.

A method to achieve uniform clamp force in a bolted rotor with curvic couplings

The preloading process is essential for circumferential bolted rotors with curvic couplings and preloading effects determining the rotor performance. A nonuniform clamp load of each bolt will destroy the periodicity of the rotor and affect its strength, stiffness, and stability. In this paper, the finite element method was adopted, the influence of elastic interaction on two types of preload methods (one by one and group) was investigated and the mechanism about elastic interaction was analyzed, and a method to achieve a uniform clamp force of spindle bolts was proposed. This method is based on displacement, and by ensuring equal relative displacements of each bolt and nut during the preloading process, the uniform clamp force can be obtained. The validity of the proposed method is experimentally verified.

Analysis of the contact stresses in curvic couplings of gas turbine in a blade-off event

The contact pressure distribution of the curvic couplings in a heavy duty gas turbine under a blade-off load condition is investigated in a three-dimensional finite element model. Several blade-off positions on each stage disk may develop the different characters on the contact pressure distributions of the curvic couplings during the application of a blade-off load. Both the position and magnitude of the applied blade-off load and the distribution of the spindle bolts have an effect on the contact pressure distribution of the curvic couplings. Further the contact stress on the left and right sides of the teeth develops different characters during the application of torque load following not only a normal centrifugal load but also a blade-off load which produces a unbalanced equivalent bending force. Furthermore the stiffness of the connection body part of the rotor between the compressor end and the turbine end associated with its section thickness is crucial in deciding the contact stress distribution on the curvic couplings. This analysis shows a change in the magnitude of contact stress of each set of the curvic couplings.

Application of the multi-kernel non-negative matrix factorization on the mechanical fault diagnosis

Although the computation amount involved in the image processing is very large, image information which is very intuitive and easy to be understood has attracted great many attentions in the fault diagnosis of machines. In order to extract useful features from the images accurately and perfectly, a novel mechanical fault diagnosis method was proposed by the combination of the multi-kernel non-negative matrix factorization and multi-kernel support vector machine. The genetic algorithm was used to optimize the parameters of both multi-kernel non-negative matrix factorization and multi-kernel support vector machine. Experiments were used to validate the efficacy of the proposed method. It is shown that the multi-kernel function combined with the polynomial kernel function and radial-based kernel function can describe the fault feature more perfectly in the kernel space than a single kernel function. Sound accuracy can be obtained in the application of the bearing fault diagnosis. Compared with the fault diagnosis method based on the sparse non-negative matrix factorization, the proposed method is more accurate in the condition identification of rotor.

Experimental Investigation on the Film Pressure Measurement in Microgap Water-Lubricated Hybrid Journal Bearing

ABSTRACT The film pressure of a microgap water-lubricated hybrid journal bearing (HJB) was investigated in this article. The pressure transmission system (PTS) formed by the flow exchange from clearance to the membrane of the sensor was also studied. Three static loads, five rotational speeds, and five water supply pressures were used in this study. The pressure was obtained from a microgap water-lubricated HJB test rig. The experimental results showed that the variation trend of the film pressure agreed with the theoretical results except that the pressure values were lower than the theoretical data. The experimental results should be corrected by the PTS to reflect the real film pressure. The influence of PTS should be considered to improve the precision of experimental results of microgap HJBs.

Influence of Thin-Wall Structure on Stress Distribution of Curvic Couplings

Abstract The objective of this paper is to investigate the influence of transition structure between curvic teeth and disk on stress distribution of curvic couplings, and provide data to help improving the design of curvic couplings. In this work, the three-dimensional finite element method was used, and Augmented Lagrange Algorithm was adopted to the contact algorithm during the analysis. According to the results of this paper, designing thin-wall structure reasonably can avoid detaching of contact interface at external diameter during preload process; reduce stress fluctuation of curvic teeth caused by circumferential bolts structure; and balance stress difference of each contact pair caused by different disk quality under the action of the centrifugal force.

The investigation of the temperature of high speed and heavy haul tilting pad journal bearing

Purpose – This paper aims to present the theoretical and experimental investigation of the temperature of high speed and heavy haul tilting pad journal bearing. Design/methodology/approach – The bearing is 152.15 mm in diameter with three slenderness ratios (L/D) and three clearance ratios. The equations that govern the flow and energy transport are solved by the finite difference method, and the experimental tests are conducted in a test rig of high speed and heavy haul tilting pad journal bearing. The shaft speed ranges from 3,000 to 16,500 r/min (the highest linear-velocity equals 131.4 m/s), and the three static loads are 10, 20 and 30 KN. Findings – The comparisons between numerical results and experimental results show better correlations. It is shown in the theoretical and experimental results that the temperature increases with static load and shaft speed and decreases with clearance ratio and L/D. Originality/value – The theoretical models presented in this paper can be used to predict the temper...

Nonnegative matrix factorization and artificial immune based classification for fault diagnosis of diesel valve train

To efficiently mine the classification model for machine fault diagnosis based on images, a hybrid classification algorithm, which inspired by combining nonnegative matrix factorization and artificial immune system, was put forward. In the algorithm, nonnegative matrix factorization was employed for dimensionality reduction of the time-frequency spectral images. An artificial immune based classification model was constructed by means of training of data samples mapped into low-dimensional space to recognize the machine conditions and diagnose faults. Experimental results on the fault classification of diesel valve train demonstrate the effectiveness of the algorithm. Compared with probabilistic neural network classifiers, the hybrid classifier achieves better fault diagnosis performance.