Key Engineering Materials Vols. 413-414

Abstract: The purpose of this paper is to investigate the influence of the presence of transverse cracks in rotors. The dynamic response of the cracked rotor is evaluated by expanding the changing stiffness of the crack (i.e. the breathing mechanism) as a truncated Fourier series and then using the Harmonic Balance Method. The crack detection is based on the use of the 2X and 3X super-harmonic frequency components of the non-linear dynamical behaviour at the associated sub-critical resonant peaks. Various parametric studies including the effects of the crack depth and location, and the crack–unbalance interaction on the dynamic of a crack rotor are undertaken. It will be illustrated that the emerging of super-harmonic frequency components and/or antiresonances can provide useful information on the presence of cracks and may be used on an on-line crack monitoring rotor system for small levels of damage.

Abstract: The use of structural health monitoring in the aerospace industry has many benefits including improved safety, reduced maintenance and extended aircraft lifecycles. A major focus of current research in this area is the development of wireless sensor 'nodes‘ which rely on batteries as a power source, severely limiting the product lifespan. This paper presents the results of work carried out to examine the feasibility of replacing or supplementing existing battery power supplies using thermoelectric energy conversion from ambient temperature differences in aircraft. An average power demand of 1mW over a typical sensor duty cycle is identified for current wireless sensor hardware. Temperature differentials between the wing fuel tanks and external air are determined and a theoretical model for thermoelectric energy harvesting potential is developed. Results indicate that average power outputs sufficient for the intended application of 6.6-22mW could be achieved during flight, based on a commercially available thermoelectric module of 30×30×4.1mm. An experimental investigation of the performance of this module when subjected to appropriate temperature conditions, using a Ranque-Hilshe vortex tube to generate easily controlled temperatures to -25°C is described. Excellent consistency is demonstrated between theoretical predictions and experimental results, confirming the accuracy of the theoretical model.

Abstract: Various research groups across the globe have developed models for engine condition monitoring and fault diagnosis based on the data from steady state performance measurements over the last two decade. However, these performance data are not amenable for easy collection in some situations and some of the data may show little performance deviation at the steady state conditions of operation. The aim of this study is to identify engine operating conditions and parameters that can be used to develop a diagnostic tool for internal combustion (CI) engine running on biodiesel blends fuel. Ricardo Wave Software was used to stimulate healthy and degraded engine. The degraded condition of operation was created by forcing one injector to work with 90%, 80% and 70% of the normal fuel flow efficiency. The measurable performance parameters such as brake power, brake torque and exhaust temperature and CO emission have been used to compare the deviations during steady and transient condition. From the comparison of the data obtained from transient and steady state simulation of the engine with and without injector fault, it can be concluded that the transient parameters show higher deviations and hence are better suited for condition monitoring and diagnostic modelling in engine working speed.

Abstract: The induction motor is the most common driver in industry and has been previously proposed as a means of inferring the condition of an entire equipment train, predominantly through the measurement and processing of power supply parameters. This has obvious advantages in terms of being non-intrusive or remote, less costly to apply and improved safety. This paper describes the use of the induction motor current to identify and quantify a number of common faults seeded on a two-stage reciprocating compressor. An analysis of the compressor working cycle leads to current signal the components that are sensitive to the common faults seeded to compressor system, and second- and third-order signal processing tools are used to analyse the current signals. It is shown that the developed diagnostic features: the bispectral peak value from the amplitude modulation bispectrum and the kurtosis from the current gives rise to reliable fault classification results. The low feature values can differentiate the belt looseness from other fault cases and valve leakage and inter-cooler leakage can be separated easily using two linear classifiers. This work provides a novel approach to the analysis stator current data for the diagnosis of motor drive faults.

Abstract: Rubbing between the rotor and the stator is the frequent fault and will cause very serious accident, even catastrophe, to rotating machinery. Therefore, timely detection of such rubbing is very important avoid severe consequences. Vibration based methods are very mature and traditional methods but not effective to detect incipient rubbing in rotating machinery. Rubbing between the rotor and the stator will cause elastic strain in the rubbing location and thus can produce acoustic emission (AE). Apparently, such AE contains direct and abundant information about the rubbing and can be used to detect and diagnose such fault effectively. In this paper, the AE based method is proposed for detecting and identifying the rubbing of the rotor-bearing system. An experimental study is presented to investigate the characteristics and features of rubbing AE using parameter analysis method. The results show that AE is very sensitive to the rubbing and AE parameters can reveal the characteristics and features of rubbing AE. Parameter analysis demonstrates that rubbing AE contains multiple modals, which will attenuate with propagation by negative exponent manner.

Abstract: This paper presents an initiative research work that applies cointegration testing method to the condition monitoring and fault diagnosis of nonstationary dynamic engineering systems. The cointegration testing method seeks a linear combination of a set of nonstationary system variables which describes the dynamic equilibrium relations among them. The fact that the cointegrational model could be violated on the occurrence of a fault is utilised to detect abnormal conditions. The model residuals are processed and analyzed to extract the fault features. In this paper it is demonstrated that the cointegration testing method is a power full means for condition monitoring for nonstationary engineering systems.

Abstract: The identification of non-linear systems is an important topic in structural health monitoring of structures undergoing non-stationary behavior. In general, a non-linear or hysteretic response is typical for buildings, bridges, dampers and structural elements not only as a consequence of strong excitations (i. e. earthquake), but also for low to medium loading levels, due to the constitutive behavior of structural elements or joints. This paper focuses on the non-linear identification of a RC beam-column joint, modeled as a SDoF system, subjected to non-stationary loading: the technique used entails the definition of proper instantaneous estimators of the system dynamic properties by using a linear time-varying approximation of the actual system dynamics and representing the structural response in the joint time-frequency domain.

Abstract: The steam turbine is the principal mover in the field of electric power generation. It is very important and necessary to monitor and evaluate the running conditions and diagnose the faults of the steam turbine for the safe and normal running of the electric power plant. Fault diagnosis of the steam turbine is a complicated process and requires high level of the expertise. In order to significantly reduce the cost consumed in the fault diagnosis, increase the consistency of diagnosing decision-making, and better utilize the turbine’s management information resource, in this paper, an integrated Web-based expert system of the fault diagnosis for general purpose has been developed for the steam turbine of a power station. Moreover, it can be regarded as an advisory tool to those field engineers having much technical experience and as a training tool to less-experienced personnel who need guidance and advice. This paper describes a research project aiming to develop a web-based intelligent diagnostic system for the steam turbine, and discusses the process of the fault diagnosis and the issues involved in developing the system. The paper also includes several practical issues related to the architectures of the intelligent web-based applications. The system is built on a three-tier architecture, including the following components: knowledge base, inference engine, knowledge administration interface, user interface, knowledge administration, and integrated database. The diagnostic system employs heuristic rules to diagnose the steam turbine faults.

Abstract: The instantaneous speed signals of diesel contain lots of information about machine states, which is useful for fault diagnosis of diesel engine. Mixed fault diagnosis method of diesel engine based on the instantaneous speed has been proposed, which combines with the lower order angular vibration amplitude and SOM neural network to diagnose the cylinder pressure fault, then extracts three feature parameters of instantaneous speed to locate the fault cylinder. The method can detect the cylinder pressure fault accurately in diesel engine and locate the fault cylinder. The experimental confirmation shows that it has good effect on fault diagnosis of diesel engine.

Abstract: The fluid-solid coupling analysis of the nonlinear rotor-bearing system with labyrinth seal was presented. The dynamic equations of rotor-bearing system were built up by combining d’Alemdert principle with Rize way, then the nonlinear oil film forces based on steady short bearing model, unbalanced excitation forces and gas excitation forces calculated by FLUENT could be coupled to system. Such nonlinear equations were numerically solved by Newmark integration method. The dynamics and the representation characteristics were investigated through a lot of numerical calculations, then the occurrence and development mechanism of the different coupling faults revealed based on the results of numerical calculation. The severity and mutation of some faults were also studied.