http://hdl.handle.net/10204/925 2013-05-23T16:12:43Z http://hdl.handle.net/10204/6649 Title: Multi-level infrastructure of interconnected testbeds of large-scale wireless sensor networks (MI2T-WSN) Authors: Abu-Mahfouz, AM; Steyn, LP; Isaac, SJ; Hancke, GP Abstract: Wireless sensor networks (WSNs) have been used in different types of applications and deployed within various environments. Simulation tools are essential for studying WSNs, especially for exploring large-scale networks. However, WSN testbeds are still required for further testing before the real implementation. In this paper we propose a multi-level infrastructure of interconnected testbeds of large- scale WSNs. This testbed consists of 1000 sensor motes that will be distributed into four different testbeds. The variations of these testbeds will allow for implementing and testing algorithms and protocols that could be used for various applications and within several types of environment. Description: 2012 International Conference on Wireless Networks (ICWN'12) and 2012 World Congress in Computer Science Computer Engineering and Applied Computing, Monte Carlo Resort, Las Vegas, Nevada, USA, July 2012 2012-06-01T00:00:00Z http://hdl.handle.net/10204/6605 Title: Combining discrepancy analysis with sensorless signal resampling for condition monitoring of rotating machines under fluctuating operations Authors: Heyns, T; Heyns, PS; Zimroz, R Abstract: This paper proposes a novel framework for monitoring the condition of a rotating machine (for example a gearbox or a bearing) that may be subject to load and speed fluctuations. The methodology is especially relevant in situations where no (or only noisy) shaft angular position measurements are available. Shaft angular position reference measurements are often not available due to physical constraints that render it difficult to install tachometers or encoders on the shaft of interest. The proposed methodology aims to simplify the task of monitoring a time-varying vibration signal by using a neural network to filter out the normal vibration components that generally tend to dominate the signal. The neural network may be optimised without the need for extensive datasets that are representative of different machine fault conditions. The envelope of the filtered signal is referred to as a discrepancy transform, since the discrepancy signal indicates the presence of fault-induced signal distortions. The discrepancy signal tends to be significantly simpler (smoother) than the original vibration waveform and may thus be resampled using a less accurate reference signal than would be required to resample the original waveform. A numerical gear model is used to illustrate the diagnostic potential of the proposed methodology. Description: Copyright: 2012 The British Institute of Non-Destructive Testing. Published in The International Journal of Condition Monitoring, vol. 2(2), pp 52-58(7) 2012-12-01T00:00:00Z http://hdl.handle.net/10204/6549 Title: Effects of slant angle and illumination angle on MTF estimations Authors: Vhengani, LM; Griffith, D; Lysko, M Abstract: Modulation Transfer Function (MTF) is a measure of the spatial resolution of an optical imaging system. For Earth Observation (EO) imaging systems in space, continuous MTF assessment is crucial for data quality. Several techniques of measuring MTF exist and some are still in development. MTF assessment techniques include the use of slanted knife-edge targets, point source techniques that make use of convex mirrors or xenon lamps and pulse methods that use linear features such as bridges. All these techniques have been successfully used to assess the MTF of imaging systems aboard the Ikonos, Landsat and QuickBird satellites. Laboratory experiments were conducted to evaluate the effect of slant angle of the knife-edge target and the effect of light illumination angle on the MTF result. MTF results were computed using a standard method according to ISO 12233. This paper will report the results of these laboratory experiments. Description: The 57th Annual Conference of the SA Institute of Physics (SAIP), University of Pretoria, Pretoria, 9-13 July 2012 2012-07-01T00:00:00Z http://hdl.handle.net/10204/6493 Title: Scanning laser vibrometer measurement of guided waves in rails Authors: Loveday, PW; Long, CS Abstract: Guided wave based inspection and monitoring systems for railway tracks operate at frequencies where as many as 40 modes of propagation may exist. During the development of such systems it is advantageous to be able to measure the amplitude of the individual modes of propagation. The availability of scanning laser vibrometer systems has made it possible to measure the displacement or velocity at a large number of points on the rail surface. The contribution of each mode of propagation may be estimated from the measured frequency responses by using a pseudo-inverse technique and mode shape information computed from a semi-analytical finite element model. Scanning laser measurements were performed in the field at distances of 10m and 500m from a transducer used to transmit the guided waves. A scan of 430 measurement points was used to measure 25 modes at 40kHz. Description: 18th World Conference on Non-Destructive Testing, Durban, South Africa, 16-20 April 2012 2012-04-01T00:00:00Z