Dan Guo

Using genetic algorithms and finite element methods to detect shaft crack for rotor-bearing system

Shaft crack is a very dangerous and frequent fault in rotating machine, but how to locate and configure it is just an inverse problem and not easy to tackle. In this paper, a genetic algorithms based method for shaft crack detection is proposed and described, which formulates the shaft crack detection as an optimization problem by means of finite element method and utilizes genetic algorithms to search the solution. Using genetic algorithms avoids some of the weaknesses of traditional gradient based analytical search methods including the difficulty in constructing well-defined mathematical models directly from practical inverse problems. The numerical experiments suggest that good predictions of the shaft crack locations and configuration are possible and the proposed method is feasible. The study also indicates that the proposed method has the potential to solve a wide range of inverse identification problems in a systematic and robust way.

RETRACTED: Using genetic algorithms to detect and configure shaft crack for rotor-bearing system

This article has been retracted at the request of the Editors. n n nReason: The above mentioned article was published in virtually identical form in another journal prior to appearing in Computer Methods in Applied Mechanics and Engineering. Papers submitted to the journal are required to be original works and, therefore, should not be submitted elsewhere. The duplication occurred without the knowledge of the editors, and they wish to withdraw the article from publication. The original article by Yongyong He, Dan Guo and Fulei Chu, entitled “Using genetic algorithms and finite element methods to detect shaft crack for rotor-bearing system”, was published in Mathematics and Computers in Simulation, 57 (2001) 95–108.

Vibration Analysis of Rotor With Transverse Surface Cracks

The vibration of cracked rotor is investigated by numerical method. The FEM is used to model the rotor with cracks. Six degrees of freedom are considered in each elemental node. Full 6×6 flexibility matrix is deduced by Papadopoulos and Dimarogonas’ method, and 12×12 stiffness matrix of cracked element is derived. The influence of one or more cracks on the natural frequencies and different modals (including bending modal, torsion modal and longitudinal modal) of cracked rotor is explored. Vibration responses of rotor with open cracks or breathing crack loading by eccentric force and rotor gravity force are obtained and analyzed by numerical integer method and spectral technology. The coupling of lateral, longitudinal and torsion vibrations due to transverse surface crack is studied. It is concluded that the above research is useful in detecting crack in rotor.Copyright

Wavelet Multifractal Approaches for Singularity Analysis of Vibration Signals

For rotating machinery, there may exist many kinds of malfuncti o s that will influence the normal operation, such as oil whirl, coupling misalignment, rub-i mpact etc, whose vibration signals often have different singularity properties. The multifr actal spectrum, also called singularity spectrum, calculated by the wavelet transform modulus-maxima (W TMM) method is a comprehensive reflection of the distribution of the singularities of signals. I this paper, the WTMM method for multifractal spectrum is introduced, and the multifractal spectra are used to analyze the experimental data of rub-impact, oil whirl, coupling misalignment and imbalance faults. The results show that the vibration signals of the rub-impact have the strongest singularity; the signals of the coupling misalignment are the next and the signals of the imbalanc e have the weakest singularity. It means that some features can be extracted from the multifractal spectr a for fault diagnosis.

Life Damage of Shaft and Spider in Hydraulic Generator Unit Based on Vibration Signal

As we know, more and more systems of condition monitoring for hydro-turbi ne generator units have been put into practice all over the world. Among all the systems, the functions are often limited on the aspects of stability tracking, signal capturin g, data saving, signal analysis and fault diagnosis, etc., the most important problems that operators on field conc erned directly, for example, the life damage of key components, are not solved well up to now. In this paper, the life damage has been researched for two key components, the turbine shaft and spider, in a hydraulic generator unit. Firstly, the outer exciting loads and normal stresses are anal yzed. Then how to determine the critical plane in the turbine shaft caused by transverse vibration is descri b d, and several different calculating cases are given. Based on deeply processing of vibration signals, a concept of 3dimensional database is proposed, in which the relationship between normal stress in the critical plane and vibration signals, including amplitude and frequency components, at measurable locations is determined. Finally, a programmable algorithm is proposed to calc ulate the life damage of a turbine shaft. And by simplifying, an application of life damage c alculation for the spider is given in the end. Introduction It is well known that problems on fatigue life estimation for mec hanical components, various life estimation methods have been widely reported. But these methods are almost completed according to the empirical or semi-empirical formulas obtained from fati gue experiments in laboratory or computer simulation. For the mechanical structures, e.g., bridge, oi l platform in the sea, even the high and low pressure rotors in gas turbine generator unit, etc., the life analysis on these kinds of structure have been widely explored, which is not a new topic today [1,2]. But, problems on life damage analysis for the turbine shaft and other key components, such a s the spider, in a hydraulic generator unit were just proposed in recent years. Up to now, there are little researches on the life damage of key components in hydraulic generator units in the world. The traditional methods for the life prediction of mechanical structure is to stick strain g auge transducers on special locations on the structures considered, but the measuring accuracy is very low, a nd which cannot meet the demand of on-line analysis. However, in recent years, with the development of l arge and middle scale hydraulic power plant and increasing of hydraulic power in the national power net work, China, the hydraulic power industry is facing such two problems: One is the life damage estimation and residual life prediction of key components in old hydraulic generator units. In some hydraulic power plants Key Engineering Materials Online: 2003-07-15 ISSN: 1662-9795, Vols. 245-246, pp 537-546 doi:10.4028/www.scientific.net/KEM.245-246.537

Genetic Algorithms Based Rubbing Location Identification in a Rotor System

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.

Fault Detection in Rotor-Bearing System Using Measured Vibration Data

A general method for detecting fault of rotor-bearing system, by using of measured vibration data, is proposed and described in this paper. It formulates the fault detection as an inverse problem and the optimized method is used to solve it. The presented met hod needs merely on-line measured vibration data of several monitor points but not of whole nodes of r otor, and the machine need not to be stopped. This method can be applied to detect the multi-fault s of rotor system. Several experiments to detect depth and location of shaft transve se crack, size and angle of disk mass eccentricity and oil-film coefficients of rotor-bearing system have been implemented to illustrate the method. Introduction How to detect rotor faults, such as the size and location of shaft crack, the magnitude and position of mass eccentricity, the location of rub fault etc., has become inc r asingly an important research topic in connection with safety evaluation and damage assessment of rotor machine. Since the vary of parameters in a structure modifies the vibrati on behaviour of the structure, a strong interest has been developed within the last 20 years about the fa ul identification by means of the knowledge of vibrational behaviour of a structure. Among them, the model-based faul t detection method is one of the most important quantitative approaches. The modelbased method uses a simulated model of system or of the process to obtain the relation between output and fault parameters(fault type, location and severity). Among recent contribut ions in this field, Jiang,etc[1], Chen,etc[2], Zhang, etc.[3] reported their investigations for oil-film dynamic coefficients estimating by use of synchronous response or frequency response function of rotor sy stem. Markert etc.[4] and Platz etc. [5] present a model to generate a dynamic behaviour identical to the measured one of the damaged system. Krodkiewski,etc.[6], Shin,ect.[7], Edwards,etc.[8] prese nted model-based methods to determinate the configuration or unbalance of rotor system . A ore comprehensive approach has been introduced by Bachschmid and Pennacchi [9] to identify s veral different types of faults. Their method has been experimentally validated on different test-rigs and real machines Key Engineering Materials Online: 2003-07-15 ISSN: 1662-9795, Vols. 245-246, pp 527-536 doi:10.4028/www.scientific.net/KEM.245-246.527

Influence of bearing pre-load coefficient on shaft vibration and pad temperature in a hydroturbine generator unit: A case study

From data collected by an online condition monitoring and fault diagnosis system, a higher pad temperature at the upper guide bearing in a pumped storage power generator unit installed in Guangdong province(GPSPS), China, was found. And also a relatively intensive shaft vibration occurred at the lower guide bearing. By calculating the Reynolds equation and viscosity-temperature equation of the lubricant, a curve between the pre-load coefficient and the increment of pad temperature is obtained, which shows that the larger, the pre-load coefficient, the bigger, the increment of pad temperature. For a practical unit in GPSPS, by employing Transfer matrix method and Wilson-θ method to analyze shaft vibration at different pre-load coefficients of the whole bearing or pad pair bearings, the results show that the larger the pre-load coefficient is, the smaller the vibration amplitude is, the shorter the time for vibration to become steady is. And an uneven pre-load coefficient of the pad pair bearings will cause shaft orbit from a circle to an ellipse whose long axes is at the direction of the pad pair with the lowest pre-load coefficient. Finally, reasons of higher pad temperature of the upper guide bearing and larger shaft vibration at the lower guide bearing are due to the inconsistent relation of bearing assembling clearance or pre-load coefficient of the upper and lower guide bearing, and also due to the too small, uneven pre-load coefficient of pad pair bearings. After a scheme for adjusting the bearing clearance is given, data measured show that the analysis and simulation methods are correct and the adjustment scheme to the assembling clearance of the upper and lower guide bearings is feasible and can be used to guide the field maintenance conveniently.