Application of very-high-frequency (VHF) method to ceramic insulators

A VHF method (30-300 MHz) is applied to identify faults and defects in ceramic insulators. Insulators which exhibit internal cracks and fractures are used as test samples. Different artificial conditions are introduced to the test samples according to the IEC 507 standard under wet and dry conditions. Using a cascading signal processing technique and analysis methods such as FFT and fractal analysis, VHF signals acquired by digital scope are processed and analyzed. This study indicates that the fractal dimension can be used as an effective tool to isolate the common faulty conditions found on the ceramic insulators. The results from this study strongly support the prospect of using a VHF method to monitor the physical condition of ceramic insulators.

Seventy-year-old habitual volleyball players have larger tibial cross-sectional area and may be differentiated from their age-matched peers by the osteogenic index in dynamic performance

The osteogenicity of a given exercise may be estimated by calculating an osteogenic index (OI) consisting of magnitude and rate of strain. Volleyball involves repetitive jumping and requires high power output and thus may be expected to be beneficial to bone and performance. The purpose of the present study was to examine if habitual volleyball playing is reflected in OI. Ten elderly habitual volleyball players [age 69.9 (SD 4.4) years] and ten matched controls volunteered [age 69.7 (4.2) years] as subjects. Distal tibia (d), tibial mid-shaft (50) and femoral neck (F) bone characteristics were measured using pQCT and DXA. To estimate skeletal rigidity, cross-sectional area (ToA50), and compressive (BSId) and bending strength indices (SSImax50) were calculated. Maximal performance was assessed with eccentric ankle plantar flexion, isometric leg press and countermovement jump (CMJ). A fast Fourier transform (FFT) was calculated from the acceleration of the center of mass during the CMJ. Maximal acceleration (MAG) and mean magnitude frequency (MMF) were selected to represent the constituents of OI. OI was calculated as the sum of the products of magnitudes and corresponding frequencies. Volleyball players had 7% larger ToA50 and 37% higher power in CMJ, 15% higher MAG and 36% higher OI (P B 0.047) than the matched controls. No difference was observed in leg press, plantar flexion or the MMF (P C 0.646). In conclusion, habitual volleyball players may be differentiated from their matched peers by their dynamic jumping performance, and the differences are reflected in the magnitude but not rate of loading.

Behaviour of stress wave propagation in utility timber pole

Non-destructive testing has been used for many years to evaluate the in situ condition of timber piles. Longitudinal impact is usually applied on the top of piles to induce longitudinal wave to detect faults in piles due to the fact that the longitudinalwave has less dispersive nature at lowfrequency. On the other hand,when it comes to evaluation of poles in situ, it is different as poles are partly embedded in soil and it is more practical to produce bending waves, as the top of the pole is not easily accessible. However, bending wave is known for its highly dispersive nature; especially in the low frequency range which is usually induced in low strain integrity testing. As bending wave can be considered as a hybrid of longitudinal and shear waves, it will be helpful, if it could detect the component of these twowaves separately.To do so, components of displacements or accelerations along radial and longitudinal directions need to be determined. By applying Fast Fourier Transform (FFT) on the signals, the dominant frequencies can be obtained. It has been found that, the longitudinal component decreases along radial direction which indicates the presence of bending wave component and this finding allows to the application of ContinuousWavelet Transform (CWT) on the longitudinal component of wave signals in order to obtain phase velocity. Phase velocities at different frequencies are then determined to draw the dispersive curve and compare with analytical phase velocity curve. The dispersion curve matched well with the analytical curve. © 2013 Taylor & Francis Group.

Acoustic and device feature fusion for load recognition

Appliance-specific Load Monitoring (LM) provides a possible solution to the problem of energy conservation which is becoming increasingly challenging, due to growing energy demands within offices and residential spaces. It is essential to perform automatic appliance recognition and monitoring for optimal resource utilization. In this paper, we study the use of non-intrusive LM methods that rely on steady-state appliance signatures for classifying most commonly used office appliances, while demonstrating their limitation in terms of accurately discerning the low-power devices due to overlapping load signatures. We propose a multi-layer decision architecture that makes use of audio features derived from device sounds and fuse it with load signatures acquired from energy meter. For the recognition of device sounds, we perform feature set selection by evaluating the combination of time-domain and FFT-based audio features on the state of the art machine learning algorithms. Further, we demonstrate that our proposed feature set which is a concatenation of device audio feature and load signature significantly improves the device recognition accuracy in comparison to the use of steady-state load signatures only.

Determinations of stress wave velocity in a timber pole using wavelet transform

This paper presents an application of Wavelet Transfonn (WT) for determination of stress wave velocity for Non-destructive Testing of timber utility poles in service. For surface Non-destructive Testing (NDT), the hammer impact, which produces generally broadband frequency excitation, is used to generate stress wave. Moreover, due to practicality the impact location for field testing of a utility pole is on the side of the pole and 1.5 m above ground level. And the geometry of utility pole could not guarantee non-dispersive longitudinal wave. All of these issues have resulted in lack of accuracy and reliability of results from surface NDT in field testing. In recognition of such problem, this research explores methods to reliably calculate desired wave velocity by isolating wave mode and studying dispersive nature of utility pole. Fast Fourier Transfonn (FFT) is firstly conducted to determine the suitable frequency from a stress wave data. Then WT is applied on the wave data mentioned to perfonn time-frequency analysis. Velocity can be detennined by time history data of desired frequency from WT results which will be compared with the available analytical solution for longitudinal wave velocity. The results of the investigation showed that wavelet transfonn analysis can be a reliable signal processing tool for non-destructive testing in tenns of velocity detennination, which in tum also helps to detennine the embedded length of the timber pole.

On the fast Lanczos method for computation of eigenvalues of Hankel matrices using multiprecision arithmetics

The use of the fast Fourier transform (FFT) accelerates Lanczos tridiagonalisation method for Hankel and Toeplitz matrices by reducing the complexity of matrix-vector multiplication. In multiprecision arithmetics, the FFT has overheads that make it less competitive compared with alternative methods when the accuracy is over 10000 decimal places. We studied two alternative Hankel matrix-vector multiplication methods based on multiprecision number decomposition and recursive Karatsuba-like multiplication, respectively. The first method was uncompetitive because of huge precision losses, while the second turned out to be five to 14 times faster than FFT in the ranges of matrix sizes up to n = 8192 and working precision of b = 32768 bits we were interested in. We successfully applied our approach to eigenvalues calculations to studies of spectra of matrices that arise in research on Riemann zeta function. The recursive matrix-vector multiplication significantly outperformed both the FFT and the traditional multiplication in these studies.