I am a retired academic still active in research as an emeritus professor. Before joining UNSW Sydney in 1988, I spent 17 years developing Brüel & Kjær (Denmark)’s condition monitoring systems, after 10 years in the rubber and chemical industries in Australia. Canada and Sweden. My academic positions at UNSW include Senior Lecturer (1988), Associate Professor (1996), Professor (2001), retiring in 2008, after which I was made a Visiting Emeritus professor. Since 1988, I have further developed my research in machine diagnostics, signal processing and vibration analysis, culminating with the publication of my Wiley book Vibration-based Condition Monitoring (1st Ed., 2011, 2nd Ed. 2021), with other contributions in operational modal analysis and noise control.
This paper provides an inspection maintenance model for a production system which is subjected to... more This paper provides an inspection maintenance model for a production system which is subjected to deterioration and random failures. A Markov model for preventive maintenance of such a continuously operating device whose condition deteriorates with time in service has been proposed by Sim and Endrenyi (1993). This model incorporates deterioration and so-called Poisson failures, minimal repair, periodic minimal maintenances, and
In this paper, the nonlinear process of amplitude modulation is modelled as the multiplication of... more In this paper, the nonlinear process of amplitude modulation is modelled as the multiplication of a real positive enveloping function (the modulating function) with another function (the modulated function) which is assumed to be a linear combination of all the resonances excited by mechanical faults (if any) in a particular system under consideration. These resonances appear as multiple carriers in the modulation process. Rectifying the multiplied signal is shown to decompose it into two additive functions. The first of these is the scaled modulating function alone and the second is a complicated function involving the modulating function, sum and difference frequencies of the original multiple carriers (and additive frequency components such as background noise) and higher order terms of the sum and difference frequencies. Because the modulating function is scaled up and at low frequencies while the second, complicated function is at higher frequencies, the characteristic frequenc...
... Received 30 May 2001; accepted 17 December 2001. Available online 28 October 2002. Abstract. ... more ... Received 30 May 2001; accepted 17 December 2001. Available online 28 October 2002. Abstract. This part addresses the feasibility of reconstructing the pressure trace in IC engine from non-intrusive structural vibration measurements by means of an optimal inverse filter. ...
Journal bearings used in IC engines are prone to premature failures and are likely to fail earlie... more Journal bearings used in IC engines are prone to premature failures and are likely to fail earlier than the rated life due to highly impulsive and unstable operating conditions and frequent starts/stops. Vibration signature extraction and wear debris analysis techniques are prevalent in industry for condition monitoring of rotary machinery. However, both techniques involve a great deal of technical expertise, time, and cost. Limited literature is available on the application of these techniques for fault detection in reciprocating machinery, due to the complex nature of impact forces that confounds the extraction of fault signals for vibration-based analysis and wear prediction. In present study, a simulation model was developed to investigate the bearing wear behaviour, resulting because of different operating conditions, to complement the vibration analysis. In current simulation, the dynamics of the engine was established first, based on which the hydrodynamic journal bearing for...
This paper presents the findings of an investigation into the structural properties of a double d... more This paper presents the findings of an investigation into the structural properties of a double deck passenger railcar. The objective of the investigation was to develop an in-service dynamic model about an operational point where the car was travelling at 80km/h over track used in everyday service. A detailed grid of response measurements, providing a spatial definition of the car, were recorded consisting of nearly three hundred accelerometer records in three axes distributed over the structure in more than forty measurement batches while the car was running down the track. Using these measurements, an in-service modal model was constructed by operational modal analysis using the enhanced frequency domain decomposition technique. Of particular interest to this investigation were the primary vertical and lateral bending modes which were found to be coincident, with the lateral mode dominating. The application of whole body vibration weightings however, produced an equivalence of th...
This work aims at monitoring large diesel engines by analyzing the crankshaft angular speed varia... more This work aims at monitoring large diesel engines by analyzing the crankshaft angular speed variations. It focuses on a powerful 20-cylinder diesel engine with crankshaft natural frequencies within the operating speed range. First, the angular speed variations are modeled at the crankshaft free end. This includes modeling both the crankshaft dynamical behavior and the excitation torques. As the engine is
Australian Journal of Mechanical Engineering, 2011
Abstract Lumped parameter models (LPMs) are widely utilised to predict the dynamic behaviour of m... more Abstract Lumped parameter models (LPMs) are widely utilised to predict the dynamic behaviour of mechanical systems such as gearboxes. LPM gives reasonable representation of the dynamics of the system if masses can be lumped at certain locations, such as gears, shafts, bearings, etc. LPM have the advantage of simulating the structure using a limited number of degrees-of-freedom (DOF), which facilitates studying the behaviour of gears and bearings in the presence of nonlinearities and geometrical faults. However, it is difficult to account for the casing flexibility in the LPM models which is an important consideration in the lightweight structures such as in aircraft applications and this results in poor spectral matching over a wide frequency range. In the case of continuous systems, where masses are distributed equally over the structure (gearbox casing), other methods, such as finite element analysis, are often used to study the behaviour of the structure. The use of finite element model (FEM) results in a large number of DOF, which in turn complicates simulating the whole system’s response to the presence of nonlinearities and to gears and bearing faults. This in turn limits the validity of the simulated results and restricts their later usage in the diagnostics and prognostics of the gears and bearings. This paper describes the use of dynamic reduction technique to reduce the FEM of a gearbox casing into manageable and well representative DOF of the casing. The reduced model of the casing is embedded with the LPM of the internals (shafts, gears and bearings), which was previously developed with the aid of Simulink and has the capability of capturing stiffness nonlinearities arising from gears and bearings and has also the capability of simulating geometrical faults (spalls) for both gears and bearings. This paper mainly deals with the simulation of localised and extended inner race bearing faults. The results show the improvements obtained through combining the reduced model of the casing with the LPM model and a much better correspondence with measured signals.
International Journal of Condition Monitoring, 2013
ABSTRACT The dynamic behaviour of a gearbox system was previously analysed using a lumped paramet... more ABSTRACT The dynamic behaviour of a gearbox system was previously analysed using a lumped parameter model (LPM), a reduced nite element model (FEM) and a combined LPM and FEM model of the gearbox casing, and the results were presented at last year's conference. Further investigations into the simulation model indicated the presence of aliasing components in the response spectra. The simulation model has since been updated by using a revised FE model of the casing and addressing the errors detected in the previous model, including aliasing. The FE model reduction was based on the Craig-Bampton method of component mode synthesis (CMS), which has the ability to include the modal properties of the gearbox casing and internals up to a much higher frequency. The reduced mass and stiffness matrices extracted om the FE model were imported into the dynamic model of the gearbox developed in Matlab/Simulink®, which has the capability of simulating time-varying stiffness non-linearities and geometric faults in the gears and bearings. The results of the updated simulation models are compared with a new set of measurements in the presence of extended inner and outer race faults in the bearings. This paper highlights the application of fault simulation techniques in machine condition monitoring (MCM) and in the training of neural networks, by being able to generate a large amount of vibration data without the need to conduct a large number of costly and time-consuming experiments.
This paper provides an inspection maintenance model for a production system which is subjected to... more This paper provides an inspection maintenance model for a production system which is subjected to deterioration and random failures. A Markov model for preventive maintenance of such a continuously operating device whose condition deteriorates with time in service has been proposed by Sim and Endrenyi (1993). This model incorporates deterioration and so-called Poisson failures, minimal repair, periodic minimal maintenances, and
In this paper, the nonlinear process of amplitude modulation is modelled as the multiplication of... more In this paper, the nonlinear process of amplitude modulation is modelled as the multiplication of a real positive enveloping function (the modulating function) with another function (the modulated function) which is assumed to be a linear combination of all the resonances excited by mechanical faults (if any) in a particular system under consideration. These resonances appear as multiple carriers in the modulation process. Rectifying the multiplied signal is shown to decompose it into two additive functions. The first of these is the scaled modulating function alone and the second is a complicated function involving the modulating function, sum and difference frequencies of the original multiple carriers (and additive frequency components such as background noise) and higher order terms of the sum and difference frequencies. Because the modulating function is scaled up and at low frequencies while the second, complicated function is at higher frequencies, the characteristic frequenc...
... Received 30 May 2001; accepted 17 December 2001. Available online 28 October 2002. Abstract. ... more ... Received 30 May 2001; accepted 17 December 2001. Available online 28 October 2002. Abstract. This part addresses the feasibility of reconstructing the pressure trace in IC engine from non-intrusive structural vibration measurements by means of an optimal inverse filter. ...
Journal bearings used in IC engines are prone to premature failures and are likely to fail earlie... more Journal bearings used in IC engines are prone to premature failures and are likely to fail earlier than the rated life due to highly impulsive and unstable operating conditions and frequent starts/stops. Vibration signature extraction and wear debris analysis techniques are prevalent in industry for condition monitoring of rotary machinery. However, both techniques involve a great deal of technical expertise, time, and cost. Limited literature is available on the application of these techniques for fault detection in reciprocating machinery, due to the complex nature of impact forces that confounds the extraction of fault signals for vibration-based analysis and wear prediction. In present study, a simulation model was developed to investigate the bearing wear behaviour, resulting because of different operating conditions, to complement the vibration analysis. In current simulation, the dynamics of the engine was established first, based on which the hydrodynamic journal bearing for...
This paper presents the findings of an investigation into the structural properties of a double d... more This paper presents the findings of an investigation into the structural properties of a double deck passenger railcar. The objective of the investigation was to develop an in-service dynamic model about an operational point where the car was travelling at 80km/h over track used in everyday service. A detailed grid of response measurements, providing a spatial definition of the car, were recorded consisting of nearly three hundred accelerometer records in three axes distributed over the structure in more than forty measurement batches while the car was running down the track. Using these measurements, an in-service modal model was constructed by operational modal analysis using the enhanced frequency domain decomposition technique. Of particular interest to this investigation were the primary vertical and lateral bending modes which were found to be coincident, with the lateral mode dominating. The application of whole body vibration weightings however, produced an equivalence of th...
This work aims at monitoring large diesel engines by analyzing the crankshaft angular speed varia... more This work aims at monitoring large diesel engines by analyzing the crankshaft angular speed variations. It focuses on a powerful 20-cylinder diesel engine with crankshaft natural frequencies within the operating speed range. First, the angular speed variations are modeled at the crankshaft free end. This includes modeling both the crankshaft dynamical behavior and the excitation torques. As the engine is
Australian Journal of Mechanical Engineering, 2011
Abstract Lumped parameter models (LPMs) are widely utilised to predict the dynamic behaviour of m... more Abstract Lumped parameter models (LPMs) are widely utilised to predict the dynamic behaviour of mechanical systems such as gearboxes. LPM gives reasonable representation of the dynamics of the system if masses can be lumped at certain locations, such as gears, shafts, bearings, etc. LPM have the advantage of simulating the structure using a limited number of degrees-of-freedom (DOF), which facilitates studying the behaviour of gears and bearings in the presence of nonlinearities and geometrical faults. However, it is difficult to account for the casing flexibility in the LPM models which is an important consideration in the lightweight structures such as in aircraft applications and this results in poor spectral matching over a wide frequency range. In the case of continuous systems, where masses are distributed equally over the structure (gearbox casing), other methods, such as finite element analysis, are often used to study the behaviour of the structure. The use of finite element model (FEM) results in a large number of DOF, which in turn complicates simulating the whole system’s response to the presence of nonlinearities and to gears and bearing faults. This in turn limits the validity of the simulated results and restricts their later usage in the diagnostics and prognostics of the gears and bearings. This paper describes the use of dynamic reduction technique to reduce the FEM of a gearbox casing into manageable and well representative DOF of the casing. The reduced model of the casing is embedded with the LPM of the internals (shafts, gears and bearings), which was previously developed with the aid of Simulink and has the capability of capturing stiffness nonlinearities arising from gears and bearings and has also the capability of simulating geometrical faults (spalls) for both gears and bearings. This paper mainly deals with the simulation of localised and extended inner race bearing faults. The results show the improvements obtained through combining the reduced model of the casing with the LPM model and a much better correspondence with measured signals.
International Journal of Condition Monitoring, 2013
ABSTRACT The dynamic behaviour of a gearbox system was previously analysed using a lumped paramet... more ABSTRACT The dynamic behaviour of a gearbox system was previously analysed using a lumped parameter model (LPM), a reduced nite element model (FEM) and a combined LPM and FEM model of the gearbox casing, and the results were presented at last year's conference. Further investigations into the simulation model indicated the presence of aliasing components in the response spectra. The simulation model has since been updated by using a revised FE model of the casing and addressing the errors detected in the previous model, including aliasing. The FE model reduction was based on the Craig-Bampton method of component mode synthesis (CMS), which has the ability to include the modal properties of the gearbox casing and internals up to a much higher frequency. The reduced mass and stiffness matrices extracted om the FE model were imported into the dynamic model of the gearbox developed in Matlab/Simulink®, which has the capability of simulating time-varying stiffness non-linearities and geometric faults in the gears and bearings. The results of the updated simulation models are compared with a new set of measurements in the presence of extended inner and outer race faults in the bearings. This paper highlights the application of fault simulation techniques in machine condition monitoring (MCM) and in the training of neural networks, by being able to generate a large amount of vibration data without the need to conduct a large number of costly and time-consuming experiments.
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