Parameterised time-frequency analysis methods and their engineering applications: A review of recent advances

Multiwire cables are widely used in engineering structures, even though there is a growing concern about the presence of environmental degradation, random overloads, and corrosion affecting their structural integrity. In this work, propagation of guided waves in a multiwire aluminium conductor steel reinforced cable (ACSR) for structural damage detection is studied using time-frequency analysis based on short time Fourier transform (STFT). Identification of propagation vibrational modes and measurements of mode energy amplitude are used to correlate the spectral energy change to the extension of an artificial damage introduced to the cable sample by a notch transversal to the pulse propagation. The results showed that mechanical contact among the wires generates mode conversion of longitudinal to flexural modes.

Study of wave propagation in a multiwire cable to determine structural damage

Damage Detection in the Cable Structures of a Bridge Using the Virtual Distortion Method

The broken strand of overhead ground wire (OGW), which is mainly caused by lightning strikes or the vibration of OGW, can lead to serious damage to the power grid system. Power-line maintenance work is generally carried out by specialized workers under extra-high voltage live-line conditions which involve great risks and high labor intensity. In this paper, we present a broken strand detection method which can be practically applied by maintenance robots. This method is mainly implemented in three steps. First, we obtain the region of interest (ROI) from the image acquired by the robot. Second, a histogram of an oriented gradients descriptor vector is calculated to obtain the image gradient feature in ROI. In the third step, we apply a multiclassifier which consists of two support vector machines to classify the wires into normal wire, broken strand malfunction, and obstacles on OGW. Experiment results successfully demonstrate the effectiveness of the proposed method.

A Vision-Based Broken Strand Detection Method for a Power-Line Maintenance Robot

Influence of attenuation on acoustic emission signals in carbon fiber reinforced polymer panels

The research field of structural health monitoring (SHM) in the realm of civil engineering has emerged rapidly. SHM concepts are based on integrated sensors and actuators to evaluate the structural state. Beside common structural response methods and other nondestructive testing techniques, wave-based ultrasonic techniques are widely used especially because of their flexibility. Monitoring cable structures such as overhead transmission lines or stay cables in suspension bridges is one objective of those wave-based methods. These structures are subject to aging, corrosion and other static and dynamic loads (e.g., wind, temperature). The cylindrical structures act as waveguides whereby monitoring of large distances with a single ultrasonic transducer is possible. However, the wave propagation is multimodal and dispersive, which complicates analysis of the wave motion and development of monitoring applications. This work addresses several aspects of the propagation of guided waves in cylinders, especially the analysis of reflection and transmission at discontinuities using finite element and boundary element methods.

Structural health monitoring of cylindrical structures using guided ultrasonic waves

In this study, the feasibility of continuous, online monitoring of power lines using ultrasonic waves is considered. Local and global wave-based approaches for wire break detection in overhead transmission lines are presented. Both methods use a sending/receiving transducer to generate an ultrasonic, longitudinal, elastic wave in the cable. Defects in the cable cause a portion of the incident ultrasonic wave to be reflected back to the transducer, which when received, can be used to identify the presence of the defect. Although the transducers can only be attached to the surface of the cable, subsurface wires can also be interrogated since elastic energy spreads to these wires through friction contact. This study also explores how the elastic energy of a propagating wave becomes distributed among contacting rods via friction contact. This work focuses specifically on a two-rod system in which the wave energy from an excited “active” rod is transmitted to a neighboring “passive” rod through friction contact. An energy-based model is used to approximate the time average elastic wave power in the two rods as a function of propagation distance. Power predictions from the energy-based model compare well with experimental measurements and finite element simulations.

Wave-based defect detection and interwire friction modeling for overhead transmission lines

Guided Lamb waves are commonly used in nondestructive evaluation to monitor plate-like structures or to characterize properties of composite or layered materials. However, the dispersive propagation and multimode excitability of Lamb waves complicate their analysis. Advanced signal processing techniques are therefore required to resolve both the time and frequency content of the time-domain wave signals. The chirplet transform (CT) has been introduced as a generalized time-frequency representation (TFR) incorporating more flexibility to adjust the window function to the group delay of the signal when compared to the more classical short-time Fourier transform (STFT). Exploiting this additional degree of freedom, this paper applies an adaptive algorithm based on the CT to calculate mode displacement ratios and attenuation of Lamb waves in elastic plate structures. The CT-based algorithm has a clear performance advantage when calculating mode displacement ratios and attenuation for numerically-simulated Lamb wave signals. For experimental data, the CT retains an advantage over the STFT although measurement noise and parameter uncertainties lead to larger overall deviations from the theoretically expected solutions.

https://link.springer.com/content/pdf/10.1155%2F2010%2F375171.pdf

Helge Sprenger

Papers

Structural health monitoring of cylindrical structures using guided ultrasonic waves

Wave-based defect detection and interwire friction modeling for overhead transmission lines

Attenuation analysis of lamb waves using the chirplet transform

Numerical and experimental investigation of wave propagation in rod-systems with cracks