Browsing by Author "Jongens, A W D"

Now showing 1 - 7 of 7
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    Adaptive noise cancelling applied to machine condition monitoring
    (1990) Bremer, Paul Graham; Jongens, A W D
    The objective of this thesis is to determine whether Adaptive Noise Cancelling can be used successfully in determining the state of machine elements. In addition, this thesis was used to gain experience in real-time computing. This was done by designing and building a real-time machine monitoring package using an IBM PC and a TMS 320C25 digital signal-processing chip manufactured by Texas Instruments. To determine which adaptive algorithm should be used in the package, experiments were carried out on a computer with different types of adaptive noise cancelling algorithms, the two main ones being the Least-Mean-Squares (LMS) and Recursive-Least-Squares (RLS) algorithms.
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    Application of cepstral techniques to the automated determination of the sound power absorption coefficient
    (2012) Jenkin, Lance; Jongens, A W D
    This thesis builds on research by Bolton and Gold, who developed the theory of using cepstral analysis to determine the absorption coefficient of elastic porous materials. Jongens, in his Masters thesis, applied this technique to determine the absorption coefficient of asphalt samples mounted in a sample holder at the end of a tube. Jongens and others identified numerous factors that introduced uncertainties into the measurement. These uncertainties fall into two main categories. The first deals with the influences that the links of the measurement chain have on the ability to separate the incident and reflected signal. The second deals with the influence of the air leakage between the tube and the surface under measurement in-situ. This thesis deals with the first category. The objectives of this project are to continue the work of Jongens, to produce an apparatus that can rapidly determine the sound power absorption coefficient by a non-skilled operator in a noisy environment. The results should correlate closely with the standardised impedance tube method, within 0.05 over the range 200 Hz to 2000 Hz. The constraint that the apparatus be usable by a non-skilled operator means that little or no calibration should be required, nor should the microphone need to be handled. This thesis presents a survey of related methods used to determine the sound power absorption coefficient. Theory of the cepstral technique is discussed, along with methods that could be used to improve the accuracy of the technique. Excitation signals that could be used with the cepstral method are put forward. The Inverse Repeat Sequence (IRS) was used to excite the system. It was chosen for its high noise immunity, as well as its complete odd-order non-linearity immunity. Sources of uncertainties from the links of the measurement chain are considered and methods to overcome them are presented. Issues that arise from liftering - cepstral equivalent of windowing - are then highlighted. The apparatus for the cepstral technique and method of standing wave ratios used to determine the absorption coefficient is given. The results obtained using the cepstral technique are correlated with the impedance tube results. It was found that the cepstral method correlates closely with the impedance tube over the range of 200 Hz to 2000 Hz for a wide variety of samples. The apparatus was developed to be used by a non-skilled operator, only requiring the press of a button to perform the measurement. With the high noise immunity of the IRS signal, the measurement could be carried out in a noisy environment.
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    The development of a rule based expert system to automate the digital analysis of condition monitoring parameters captured on rolling element bearings subjected to simulated failure
    (1991) Leggat, Brad; Noyes, R B; Jongens, A W D
    This synopsis provides a brief summary of the development of a rule based expert system to diagnose bearing failure. Firstly it covers the proposal of a generic, expert system based industrial condition monitoring system. It then discusses in more detail the development of a specific aspect ofthe system, viz. the analysis of rolling element bearing condition. The bearing test rig and data capture system are described, followed by primary research to define the bearing analysis solution space. This includes the use of vibration parameters, measured and derived operating conditions and the bearing running condition. It then explains the development of rulebases for the three analysis tasks of detection, diagnosis and prognosis. Included is a discussion on techniques used to normalise and adjust the vibration parameters to allow analysis under any operating conditions. Finally the synopsis is concluded with a discussion on the performance of the system and contributions made to the developing field of condition monitoring using expert systems.
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    Development of a system to measure marine turbulence
    (1989) Main, Ian Cameron; Jongens, A W D
    Various transducers have been developed turbulent shear in the ocean. The airfoil probe with it's piezoceramic beam encapsulated in a rubber airfoil has the simplest electronic processing system. However, the beam is very fragile and displays unpredictable thermal effects. An airfoil probe with semiconductor strain gauges on an aluminium cantilever beam has been developed as an alternative to the piezoceramic beam. The probe was calibrated by exciting it with a known shear generated by the water flow from an oscillating nozzle. During the calibration the thermal sensitivity of the probe was established to be -1.7 % °C-1• The probe, along with it's high gain, low noise processing system, is fitted to a tethered free-fall vehicle. A solid state data logger situated in the vehicle is used to record the data generated by the turbulence probe and a pressure transducer. Field trials at St.Helena Bay and Hout Bay showed that the sensitivity of the system is 20 dB lower than that of similar systems using piezoceramic beams. The system is able to resolve turbulent dissipation levels above 10-8 W kg-1, making it useful in regions characterised by a typical mixed layer (dissipation level of 10-W kg-1); however, it's sensitivity is not adequate for deep sea measurements where dissipation levels may be as low as 10-10 W kg-1.
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    Particle ejection system : target particle recovery using a transient water jet
    (1991) Mortimer, Bruce John Peter; Jongens, A W D
    Industry often requires the sorting of one material from another. Although the detection of desired (or undesired) elements is well advanced, the mechanical ejection or removal of particles is fairly underdeveloped. Agriculture and mining applications have used air jets and water jets to eject particles ranging in weight from a few grams to several hundred. With the current trends in mechanization leading towards higher processing speeds, these traditional methods have been found to be unsuitable: they have slow turn-on and turn-off response times, leading to a high volume of material being ejected with the target. Higher processing speeds will lead to even greater amounts of waste material being ejected thus producing even lower yield concentrations. Thus the need for a quick response time, repetitive, impulse ejection mechanism in the sorting industry is apparent. A kinematic analysis of the required ejection mechanism blast strength shows that the required force depends on the target mass, the required deflection angle the force application angle and the force duration. Acoustical techniques in air are unsuitable as ejection force mechanisms. A water jet is proposed to meets these requirements. This water jet is caused by an electrical discharge in a liquid cavity. This produces a weak shock wave which is focused by the cavity to a nozzle where a slug of water is emitted. The cavity is an elliptical cavity of height h, with the electrodes mounted end on at the first focus and a reflecting cone and nozzle at the second focus. The propagation of weak shock waves in the elliptical cavity is studied theoretically and numerically - using a finite difference simulation program. The reflected converging wave is shown to depend on the cavity eccentricity and the wall admittance. The resulting converging shock wave has an asymmetrical pressure distribution. This analysis is used in the design of a prototype water jet generator. The electrical discharge circuit used for the production of shock waves in the cavity is analysed and the physical discharge process of electrical to shock energy conversion reviewed. Conditions for the maximisation of this transfer correspond to large water gap resistances, high voltages and low circuit inductances. Experiments on the prototype generator show that the transient water jet slug energy is relatively low. High speed photographic techniques reveal that the jet velocity is of the order of 30 m/s. Published results show much higher jets speeds are possible. The operation of the electrical discharge circuit is found to critically influence the water jet performance - electrical measurements show that the circuit is a sub-optimum, underdamped RLC circuit. The cone / nozzle operation is also shown to have a marked effect on performance. The nozzle in particular requires optimisation. The prototype in its present form is not suitable for use in an ejection system. Although the pulse length, rise time and channel spread of the device are suitable, the blast strength is not sufficient for deflection of the heaviest range of particles. Optimisation of the electrical circuit and increased energies will increase the blast strength.
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    A review of vibration signal processing techniques for use in a real time condition monitoring system
    (1994) Birch, David; Jongens, A W D
    The analysis of the vibrations produced by roller bearings is one of the most widely used techniques in condition determination of rolling element bearings. This project forms part of an overall plan to gain experience in condition monitoring and produce a computer aided vibration monitoring system that would initially be applied to rolling element bearings, and then later to other machine components. The particular goal of this project is to study signal processing techniques that will be of use in this system. The general signal processing problems are as follows. The vibration of an undamaged bearing is characterised by a Gaussian distribution and a white power spectral density. Once a bearing is damaged the nature of the vibration changes often with spikes or impulses present in the vibration signal. By detecting these impulses a measure of the condition of the bearing may be obtained. The primary goal in machine condition determination then becomes the detection of these impulses in the presence of noise and contaminating. signals and to discriminate between those caused by the component in question and those from other sources. A wide range of signal processing techniques were reviewed and some of these tested on vibrations recorded on the Mechanical engineering departments bearing test rig. It was found that the time domain statistics (RMS, kurtosis, crest factor) were the simplest to use, but could be unreliable. On the other hand, frequency domain analysis techniques, such as the power spectrum were more reliable, but more difficult to apply. By making use of a variety of these techniques and applying them in a systematic manner, it is possible to make an assessment of bearing condition under a wide variety of operating conditions. A small number of the signal processing techniques were programmed for a DSP processor. It was found that all of the techniques, with the exception of the bispectrum could be programmed for the DSP chip. It was found however that the available DSP card did not have sufficient memory to allow analysis and preprocessing routines to be combined. In addition to this the analogue to digital conversion system would benefit from a buffered IO system. The project should continue, with the DSP card being upgraded and all the necessary signal processing routines programmed. The project can then move to the next phase which would be inclusion of display and interface software and Artificial Intelligence analysis aids.
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    Room acoustics : an investigation into the computer simulation of room acoustics, with special reference to Jameson Hall
    (2000) Priede, Gareth; Jongens, A W D
    This thesis consists of essentially two parts. The first deals with the theory and measurement of room acoustics while the second examines the room acoustic prediction methods.