Browsing by Author "Gelman, Len"
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Item Open Access Advances in test and measurement of the interface adhesion and bond strengths in coating-substrate systems, emphasising blister and bulk techniques(Elsevier, 2019-03-11) Chen, Xiaomei; Shaw, Christopher; Gelman, Len; Grattan, Kenneth T. V.In this paper, recent advances in the minimum-destructive testing of the adhesion of coating-substrate systems are reviewed, focusing on key techniques such as micro- and nano-scale levels of indentation, scratching, laser-induced wave shock, as well as the blister and buckle approach. Along with adhesion failure tests, the latest and most extensive applications of the adhesion test methods in nano-, micro- and bulk-coating technology and the associated techniques to determine the minimum damage defects left on the coatings are discussed and their use reviewed.Item Open Access Novel adaptation of the spectral kurtosis for vibration diagnosis of gearboxes in non-stationary conditions(British Institute of Non-destructive Testing, 2017-08-01) Gelman, Len; Kolbe, Stuart; Shaw, B; Vaidhianathasamy, MIn this paper, the adaptation of spectral kurtosis technology is proposed, demonstrated and experimentally validated. Raw data signals were collected from a single-stage gearbox run in different combinations of speed and load, after which time synchronous averaging was used to leave the classical residual signal once meshing harmonics were removed. Each data file is split into many individual realisations based on the time taken for the time synchronous average to converge on stable values, after which the short-time Fourier transform is used to calculate the spectral kurtosis for each realisation. The effects of adapting spectral kurtosis technology parameters such as the resolution and threshold used in creating a Wiener filter are evaluated, showing the effects on the consistent frequency bands identified throughout the realisations. Taking a baseline set of processing parameters, the probability of correct diagnosis was calculated using a three-stage decision-making technique incorporating the k-nearest neighbour and cluster analysis methods. Adaptation of the spectral kurtosis technology is then shown to dramatically improve the probability of correct diagnosis, highlighting that each speed and load case requires different resolution and threshold values to return the optimal resultsItem Open Access Novel health monitoring technology for in‐service diagnostics of intake separation in aircraft engines(Wiley, 2020-02-24) Gelman, Len; Petrunin, Ivan; Parrish, Colin; Walters, MarkDiagnostics and elimination of airflow separation effects draw essential attention of researchers in the areas of energy generation, civil engineering, and aerospace due to unwanted and harmful interaction of separated airflow with different structures. In aviation, distortion of the intake airflows of an aircraft engine, known as intake separation, not only reduces the efficiency of the engine due to decrease in air intake but also interacts with engine structural components, for example, blades, significantly increasing their vibration. This leads to fatigue and subsequent accelerated failure of these components. Therefore, health monitoring and diagnostics of the intake separation effects using structural health monitoring (SHM) framework are of high importance for ensuring both optimal engine performance and its safe operation. In the present paper, a novel health monitoring technology based on advanced signal processing, the integrated higher order spectral technique, is applied for the first time in worldwide terms for in‐service intake separation diagnostics in aircraft engine using casing vibration data.Item Open Access Novel in-service combustion instability detection using the chirp fourier higher order spectra(Prognostics and Health Management Society, 2017-03-06) Gelman, Len; Parrish, Colin; Petrunin, Ivan; Walters, MarkCombustion instabilities, known as “rumble” and “screech” are the self-excited aerodynamic instabilities in the gas turbine combustor. They cause the premature failures of the gas turbine components, and, consequently, the failure of the gas turbine as a whole. Because of the complex physical effects underlying the rumble and the screech phenomena, it is difficult to eliminate them completely at the design stage. Therefore, special attention should be paid to the detection of the combustion instabilities in the gas turbine in order to prevent its prolonged operation in this mode. There are known techniques, which are able to detect the rumble and the screech in gas turbines. Most of them do not consider the combustion instabilities as non-linear and non-stationary events and, therefore, have lower detection efficiency. Novel technique for in-service combustion instability detection is implemented in this paper. This technique overcomes the limitations of the existing solutions.