39 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
Mapping Britain's underworld. BBC Radio 4, May 25th 2012
No full textFour million holes are dug every year in the UK. Five billion pounds are lost through the economic effects of disruption and traffic hold ups, while hitting a utility pipe or cable can prove fatal for those working on the road. Adam Hart-Davis reports on a major research project which is trying to solve the problems.He takes us underground from his ancient ice house at the bottom of his Devon garden to report on Mapping the Underworld, the £3.5m programme involving universities throughout Britain. The aim is to improve how we locate the increasingly confusing and complex array of pipes, cables and sewers beneath our streets, and assess their condition - as well as ultimately providing a better map of what is beneath our cities to improve planning both above and below ground.At the moment it's often difficult to know where such utilities are - an estimated one in four of all holes are dug in the wrong place. Maps may not be accurate because original records of where the pipes and cables are located often use reference points on the surface which have long since gone.Existing sensors may have problems finding what is underground because of soil or weather conditions, while modern materials such as plastic or fibre optics pose a challenge to existing technologies.Adam Hart-Davis tries out the prototype of a multi-sensor cart where four different sensors operate together to produce an all-in-one solution, so if one technology doesn't work well in certain conditions and with particular materials, another one will. It is not an easy undertaking for the research teams or, as it turns out, for Adam testing the multi-sensor cart
Error analysis of intervertebral kinematic parameters automatically extracted from a videofluoroscopic sequence.
No full textAxisymmetric semi-analytical finite elements for modelling waves in buried/submerged fluid-filled waveguides
No full textEfficient and accurate predictions of wave propagation are a vital component of wave-based non-destructive interrogation techniques. Although a variety of models are available in the literature, most of them are suited to a particular wave type or a specific frequency regime. In this paper we present a multi-wave model for wave propagation in axisymmetric fluid-filled waveguides, either buried or submerged in a fluid, based on the semi-analytical finite elements. The cross-section is discretised with high-order spectral elements to achieve high efficiency, and the singularities resulting from adopting a Lobatto scheme at the axis of symmetry are handled appropriately. The surrounding medium is modelled with a perfectly matched layer, and a practical rule of choice of its parameters, based only on the material properties and the geometry of the waveguide, is derived. To represent the fluid and the solid-fluid coupling, an acoustic SAFE element and appropriate coupling relationships are formulated. The model is validated against both numerical results from the literature and experiments, and the comparisons show very good agreement. Finally, an implementation of the method in Python is made available with this publication
Tree root detection from ground surface vibration measurements
No full textRapid development of urban infrastructure in past decades together with a relatively recent growth of awareness of its impact on the natural environment result in an increased interest in non-destructive ground interrogation methods. Tree root damage is a very well known issue in civil engineering and can emerge as road surface fracture, building foundations disintegration or pipe penetration, among others. In this paper we investigate the feasibility of using a vibroacoustic method for tree root mapping. The core of the idea is that the mechanical waves induced by an excitation mechanism acting on the tree trunk propagate to the roots and then radiate into the surrounding soil. Owing to that, the response measured at the ground surface contains the contribution of waves radiating from roots and can be used for mapping their extent. In this paper, we report a set of field experiments on a 'purpose-built' root-trunk model buried underground. These preliminary results both demonstrate the technique and shed light on related challenges and limitations.</p
Improving acoustic methods of pipeline leak location with distributed sensing
No full textLeaks in water distribution mains are a big problem, with around 20% of supplied potable water lost to leaks during transport. Correlation-based acoustic techniques have provided an accurate and non-invasive way of detecting and locating these leaks for a few decades. These methods have almost exclusively been using two sensors, and so this paper presents work aiming to explore leak detection and location with multiple sensors distributed along a pipe. Beamforming is a well-established method for using arrays of sensors to locate sources, among other purposes. With this premise, the present work adopts an array processing algorithm (MUSIC) in the context of water leak detection, intending to develop a framework for detecting multiple leaks using a sensor array. The concept, processing and implementation details are first supported with numerical simulations using existing acoustic models of water pipes. Then, experiments are presented on a short section of water-filled pipe with leak-like disturbances. These are captured with an array of accelerometers and processed using an implementation of the algorithm, testing the impact of real-world effects studied in simulations. The study considers several aspects of practical interest: (i) the effect of noise, both correlated and uncorrelated; (ii) the effect of reflections from discontinuities, such as pipe fittings and connections; (iii) the number and the distribution of sensors; as well as (iv) the presence of multiple leaks. The results pave the way for implementing this algorithm on practical installation designs, including the rod method developed during a wider research project associated with this study
Wavelet-based and data-adaptive methods for time delay estimation in acoustic leak detection
No full textLeakages in water distribution networks are a common issue encountered in the water industry. The acoustic cross-correlation method is generally employed for detecting and locating leaks in water pipes. One important factor that determines the effectiveness of this method is the accuracy of the time delay estimate which is usually obtained from the cross-correlation function (CCF) of two signals measured on the pipe. However, in some practical situations, accurate time delay estimate cannot be obtained using existing correlation-based time delay estimation (TDE) methods without first filtering the signals prior to calculating the CCF. Incorrect choice of filter cut-off frequencies limits the effectiveness of these methods. To deal with this issue, this paper proposes a scheme based on multi-resolution decomposition for accurately estimating time delays between leak signals. The proposed scheme first decomposes the signals at different scales using a shift-invariant wavelet transform or data-adaptive decomposition and then determines the time delay from the decomposed signals. Simulation and experimental results demonstrate the higher effectiveness of the proposed method compared to the commonly used basic and generalised cross-correlation TDE methods
Limits for leak noise detection in gas pipes using cross correlation
No full textThe cross correlation method is widely used in leak detection and location for pipes. The model of the cross correlation function of the leak noise for water pipes has been established in an earlier study, while there is no such model for gas pipes. In this study, a model of the correlation function of the leak noise in gas pipes is developed. The characteristics of wave propagation in gas pipes, combined with the leak noise spectrum, are incorporated into the model to consider the effects of physical parameters, i.e., turbulence parameters, pipe parameters and flow parameters, on the cross correlation function. This model is capable of describing the main features of the correlation results in gas pipes. Moreover, the model gives an estimation of the detection limits of the leak noise in the absence of noise, which is crucial to the deployment of sensors in real gas pipelines. The findings of this study provide theoretical insight and experimental evidence for optimizing the cross correlation method when conducting leak detection and location in gas pipes
Acoustic leak localisation based on multipath identification
No full textThis paper proposes a method for estimating wave speed and locating leaks in water pipes using multipath identification techniques. The wave speed and leak location are determined simultaneously from the relative arrival times of reflections in acoustic leak signals. Two multipath identification techniques based on the autocorrelation function and power cepstrum are derived and analysed for identifying reflections. Results show that the power cepstral technique is more robust and accurate than the autocorrelation technique. Analysis of simulation and experimental data acquired on a leakage test rig demonstrates that the proposed method is effective for locating leaks, outperforming the commonly used cross-correlation method in some cases. A practical advantage of the proposed method is capability to locate leaks without a priori knowledge of the wave speed
