Key Engineering Materials Vols. 293-294

Abstract: A quantitative identification procedure for local rubbing fault in rotor systems based on a hybrid model is proposed. The hybrid model combines finite element model of rotor and rigid discs, online identified oil film stiffness and elastic supports. The identification algorithm of oil film parameters is stated in detail. The hybrid model based diagnosis process for local rubbing fault is described with assumption of periodic rubbing forces. With the help of modal expansion technique, the estimated rubbing forces at each node along rotor are checked for the rubbing position. The estimated rubbing forces at ascertained position are then used in fault severity assessing quantitatively next. These approaches have been tested successfully on a test rig with single rotor double discs.

Abstract: The steam turboset is the key equipment of the electric power system. Thus, it is very important and necessary to monitor and diagnose the running condition and the faults of the steam turboset for the safe and normal running of the electric power system. In this paper, the Internet/Intranet based remote condition monitoring and fault diagnosis scheme is proposed. The corresponding technique and methods are discussed in detail. And a real application system is developed for the 300MW steam turboset. In this scheme, the system is built on the Internet/Intranet and the Client/Server construction and Web/Server model are adopted. The proposed scheme can guarantee real-time data acquisition and on-line condition analysis simultaneously. And especially, the remote condition monitoring and fault diagnosis can be implemented effectively. The developed system has been installed in a power plant of China. And the plant has obtained great economic benefits from it.

Abstract: In this paper, a novel intelligent fault diagnosis method based on empirical mode decomposition (EMD), fuzzy feature extraction and support vector machines (SVM) is proposed. The method consists of two stages. In the first stage, intrinsic mode components are obtained with EMD from original signals and converted into fuzzy feature vectors, and then the mechanical fault can be detected. In the second stage, these extracted fuzzy feature vectors are input into the multi-classification SVM to identify the different abnormal cases. The proposed method is applied to the classification of a turbo-generator set under three different operating conditions. Testing results show that the classification accuracy of the proposed model is greatly improved compared with the multi-classification SVM without feature extraction and the multi-classification SVM with extracting the fuzzy feature from wavelet packets, and the faults of steam turbo-generator set can be correctly and rapidly diagnosed using this model.

Abstract: This paper describes initial results from a project expanding the field of rotor health monitoring by using Active Magnetic Bearings (AMBs) as actuators for applying a variety of known force inputs to a spinning rotor in order to monitor and evaluate response signals resulting from these inputs on-line. Similar to modal analysis and other nondestructive evaluation (NDE) techniques which apply input signals to static structures in order to monitor responses; this approach allows for the measurement of both input and output response in a rotating system for evaluation. However, unlike these techniques, the new procedure allows for multiple forms of force input signals to be applied to a rotating structure. This technique is being developed for use on rotating equipment supported in conventional bearings where an AMB actuator is added to a system for improved health monitoring. This paper presents initial results from this project including a demonstration of the system identification capability of the procedure during the commissioning of a test rig, and a summary of a technique developed for identifying breathing-cracks in rotors using the new technique.

Abstract: Presented have been the methods of modelling of the selected materials and operational imperfections (defects) like rotor cracks and hydrodynamic instability in rotating machines. Despite abundant information on this topic, there are still numerous problems to be solved. This regards primarily to the analysis of characteristic symptoms of such defects in the form of e.g. nonlinear vibrations and coupled forms of lateral, axial and torsional vibrations. The paper presents also author’s opinions concerning the one of the most intriguing operational imperfections, namely the formation of oil whirls and oil whips in slide bearings of a rotating machine. Coupled forms of vibration are generally a result of different kinds of couplings taking place in the system and interactions between construction and material imperfections.

Abstract: In this paper, a simplified finite element model of the cracked crankshaft is proposed, and a new method for simulating the nonlinear vibration of operating crankshaft with several cracks is presented. For crankshaft, cracks occur frequently in the parts of crankpin-web fillet region and the edge of oil aperture because of fatigue or damage. According to the characteristic of those cracks, the cracked parts are modeled by the corresponding cracked spatial finite elements respectively, and two cracked elements are discussed in this study. The other, un-cracked, crankshaft parts are modeled by spatial Timoshenko beam elements. Flywheel and front pulley are simplified as lumped mass elements, and main bearings are simulated by equivalent linear springs and dashpots. In order to find the dynamic response of crankshaft-bearing system, a right-handed rotating coordinate system attached to crankshaft is applied. Based on the proposed finite element model, the breathing behavior of cracks in operating crankshaft is studied, and the nonlinear motion equation with variational stiffness is formed. Finally, a four-in-line crankshaft is taken as an example, and its vibration response corresponding to different kinds of crack are calculated and analyzed. Some conclusions are drawn, and a foundation is laid for diagnosing crack fault of crankshaft.

Abstract: In any high-performance turbo-machinery, instability and damage are commonly occurring problems. The aim of this paper is to present a stability analysis of a fully-bladed flexible rotor. The flexural vibrations of the blades as well as those of the shaft are considered; the energetic approach used includes the effect of the rotational inertia. A stability detection method, bringing loci separation phenomena and coalescence, in case of an asymmetric rotor, to the fore, is made in order to determine a parametric domain where turbomachinery cannot encounter damage. Moreover, extensive parametric studies including for instance the length and the stagger angle of the blades are presented in order to obtain robust criteria for stable and unstable areas prediction. Finally, rotor/stator contact is introduced and the effect of the radial load acting on the blades when rubbing against a casing is considered.

Abstract: The rubbing fault is a very serious and frequent malfunction in rotating machinery, and the determination of the rubbing location is very important in actual fault diagnosis. In this paper, a method based on genetic algorithms to detect the rubbing location is presented. The finite element model of the rubbing rotor is established with the rubbing location, the stator stiffness, the clearance between stator and rotor, the damping coefficient and the friction coefficient as the fault parameters, and the rubbing location determination is transferred into the parameter identification problem. The genetic algorithm is then utilized to search the solution. Using genetic algorithms avoids some of the weaknesses of traditional parameter identification methods such as local minimum problem in nonlinear system identification. The experimental results suggest that the rubbing location can be effectively determined when the rubbing occurs.

Abstract: In the paper presented are course and results of investigations of the influence of slide bearing bush and shaft mutual skewness on the dynamic properties of the 200 MW 13K215 turboset. The defect was simulated by means of numerical model of the turboset. Simulation was performed for each bearing individually in both, horizontal and vertical planes. Maximum values of the skewness angle were calculated for each bearing at both planes. The influence of the defect on dynamic properties of turboset was presented. Basing on the results of the simulation multiple defect-symptom diagnostic relations were built. Diagnostic relations were used as learning and testing data sets for a knowledge base of an expert system based on the inverse diagnostic model. This expert system is implemented at the unit 7 at the Kozienice Power Station as a first domestic diagnostic system.

Abstract: The paper presents the procedure and the results of determination of acceptable dislocation for particular bearings of the large power turbine set. The ranges have been evaluated by numerical analysis of the turbine set model. Acceptable dislocations of the bearings were calculated in horizontal and vertical direction separately in regard to criterion of permissible bearing vibration and in regard to permissible bearing load. The results have been presented graphically in the form of areas of acceptable dislocations, which allow the comparison considering both criteria. The paper contains exemplary trajectory graphs for all bearings corresponding to maximum acceptable dislocations. The investigations revealed asymmetry of areas of acceptable dislocations, which suggests that the constructional kinetostatic line of rotors is not optimal.