35 research outputs found
An experimental approach for the determination of axial and flexural wavenumbers in circular exponentially tapered bars.
No full textData and code (as Jupyter notebook) allowing for generating results presented in figures in Michał K. Kalkowski, Jen M. Muggleton, Emiliano Rustighi, An experimental approach for the determination of axial and flexural wavenumbers in circular exponentially tapered bars, Journal of Sound and Vibration, Volume 390, 3 March 2017, Pages 67-85, ISSN 0022-460X, http://dx.doi.org/10.1016/j.jsv.2016.10.018
Work was funded by EPSRC, Assessing the Underworld (EP/K021699/1) </span
Spinal fusion for lumbar instability: does it have a scientific basis?
No full textSummary: The validity of spinal fusion for lumbar instability is considered. Some difficulty lies in the interpretation of the term instability. The differing interpretations in the clinical, radiologic, and biomechanical contexts are discussed. These interpretations may only be reconciled if the confusion between hypermobility and instability is removed and some recourse is made to soft tissue integrity. Fusion is considered in the context of the functioning spine as a whole. Although the aim of the surgery is usually to produce a solid arthrodesis, some studies show that this can compromise the functioning of the rest of the spine. Furthermore, there is some evidence that pseudarthrosis itself may not be detrimental. Dynamic imaging offers the potential for improved diagnosis and assessment, but further work is needed to pave the way for better selection criteria and treatment strategies
Assessing the quality of the time delay estimate in acoustic leak localisation
No full textThe problem considered in this paper is assessing the quality of the time delay estimate between leak signals measured on water pipes. This is practically important, as a quantitative assessment of the accuracy of time delay estimation (TDE) results makes it possible to infer the reliability of acoustic leak localisation results in a given situation. Three quality assessment approaches are developed by considering the statistical properties of the cross-correlation function (CCF): information-criterion, processing gain, and statistical approaches. In the information-criterion approach, the Bayes factor (BF) is employed to decide the most likely probability distribution of observed CCF peak values. The processing gain approach determines the quality of the time delay estimate using indices that indicate detectability of the CCF peak, namely, the peak-to-side lobe ratio (PSR) and the peak-to-mean ratio (PMR). In the statistical approach, an index termed inconsistency score (ICS) is used to describe the quality of TDE results based on root-mean square of deviations of time delay estimates from their statistical mode. Experimental results show that the proposed approaches provide effective means of assessing the accuracy of the time delay estimate in acoustic leak detection applications. Also, the proposed indices can be employed as figures of merit for selecting best parameters for TDE, for example, filter cut-off frequencies
Cross-spectral phase method for time delay estimation in acoustic leak detection
No full textThis paper introduces a method for estimating time delays in acoustic/vibration leak signals within water distribution systems, using linear segmentation of the cross-spectral phase. The method applies linear regression to undistorted regions of the phase, automatically identified by a simple algorithm, to calculate the time delay. Simulation and experimental results demonstrate that the method accurately estimates time delays without the need for pre-filtering, even in the presence of multiplicative noise that distorts the cross-spectral phase—offering a significant improvement over correlation-based techniques. Furthermore, the method provides a confidence interval that quantifies the uncertainty in the estimated leak location, thereby enhancing the reliability of leak localisation
Vibration of an exponentially tapered rod embedded in an elastic solid - A piecewise uniform approach
No full textExponentially tapered rods can serve as a simplified physical model for tree roots. Based on an analytical solution for axial waves in a uniform embedded rod, we present a piecewise uniform formulation for modelling the dynamics of a tapered embedded rod. First, we revisit the uniform rod solution and discuss its characteristics. The piecewise uniform approach, in which the tapered rod is approximated as a multi-step structure composed of a number of uniform components, is presented next. The dynamics of the built-up waveguide are written in terms of propagating waves that scatter at the junctions. The assumption is made that the surrounding elastic medium has no effect on the scattering. We conduct a numerical convergence study and verify the accuracy of our model against an axisymmetric finite element (FE) simulation with perfectly absorbing boundaries. Both predictions are in very good agreement except for the low frequency range, where an assumption regarding the boundary contidions is expected to play a role. Finally, some basic observations are given in the context of the dynamics of a free tapered rod.</p
Superimposed imaging of acoustic wave reflections for the detection of underground nonmetallic pipelines
No full textDue to the non-conductive and non-magnetic properties, nonmetallic pipelines are difficult to be detected by traditional pipe location technologies. This paper presents a superimposed imaging method of acoustic wave reflections for pipe location, which operates on the propagation of elastic waves. The propagation and attenuation model of elastic waves in soil are constructed according to the geometric relationship between the acoustic source, geophone array and pipelines. The two-dimensional and three-dimensional acoustic field diagrams of underground pipeline are generated by superimposed imaging of the cross-correlation coefficients between the signals from the sound source and geophone array, with the attenuation caused by hysteretic damping and geometric dissipation considered in the imaging process. In order to suppress clutter interference on the imaging results, the strategy of ‘multi-point transmit, multi-point receive and cross-correlation coefficient superposition’ is adopted. In the simulation, comparison is made to demonstrate the influences of different excitation sources on the detection imaging results, including the single frequency signal, multi-frequency signal, Gaussian pulse signal and sweep signal. It is found that the excitation signals with rich frequency components are more conducive to improving the resolution of detection images. The effectiveness of the proposed imaging method is further verified in the experimental work, which may be beneficial for the visualization and determination of the location, depth and orientation of underground non-metallic pipelines
Supplementary material to 'An experimental approach for the determination of axial and flexural wavenumbers in circular exponentially tapered bars' : First release
No full text<p>Supplementary material to 'An experimental approach for the determination of axial and flexural wavenumbers in circular exponentially tapered bars' by Michał K. Kalkowski, Jen M. Muggleton, Emiliano Rustighi, Journal of Sound and Vibration, Volume 390, 3 March 2017, Pages 67-85, ISSN 0022-460X, http://dx.doi.org/10.1016/j.jsv.2016.10.018</p>
Supplementary Material To 'An Experimental Approach For The Determination Of Axial And Flexural Wavenumbers In Circular Exponentially Tapered Bars' : First Release
No full textSupplementary material to 'An experimental approach for the determination of axial and flexural wavenumbers in circular exponentially tapered bars' by Michał K. Kalkowski, Jen M. Muggleton, Emiliano Rustighi, Journal of Sound and Vibration, Volume 390, 3 March 2017, Pages 67-85, ISSN 0022-460X, http://dx.doi.org/10.1016/j.jsv.2016.10.018</span
On the mechanisms of leak noise generation in water-filled pipes
No full textThis thesis investigates the generation and characterisation of leak noise in water pipes, with the aim of understanding its source and behaviour. Knowledge of leak noise generation and characterisation could help in making informed decisions about detecting leaks and prioritising repair operations, which save time and money. Numerical simulation of leaks on water pipes were carried out in 3-D, using Ansys-Fluent CFD software package and turbulent kinetic energy peaks, found around the edges of the leaks, were demonstrated to be largely responsible for leak noise in the pipes. Flow data obtained from the leak holes of different shapes were incorporated into a derived semi-analytical model to predict leak noise spectra in the pipes. The spectra were then characterised based on different shapes, leak sizes, line pressures, source strengths and leak mean flow velocities, to reveal distinct relationships between the leaks and their spectra
