This paper presents an exploratory study of aircraft engine fault indicators obtained from sound and vibration recordings. Observing time sequence and frequency spectra of the recordings, a simple yet cost-effective method of detecting engine fault is achieved. A detailed discussion of the study performed, ranging from the hardware and software selection, initial tests, and discoveries made in the time domain and subsequently in the frequency domain will be presented.

This study focuses on creating a spectral matching algorithm that modifies the real strong ground motions in the time domain by adding wavelets adjustment to the acceleration time series. The spectral matching procedure is at its core a nonlinear problem, thus a nonlinear solving method was employed in the proposed algorithm. The Broyden updating method was selected as the nonlinear solving method because it does not require a differentiation analysis. The Broyden updating also makes use the information of spectral misfit and wavelet magnitudes vector to approximate the Jacobian matrix which expected to give an efficient calculation. A parametric study was numerically conducted to obtain a set of gain factors that reduce the computational time and minimize the spectra misfit. The study was conducted using ten different ground motions, taken from FEMA P-695 (FEMA, 2009), which represent far field, near field-pulse and near field-no pulse earthquake ground motions. A study of compatible wavelet functions was carried out to determine the appropriate wavelet function for the proposed method. The study include the baseline drift, the frequency and time resolution, and the cross correlation between wavelet adjustments during the spectra matching procedure. Based on this study, the corrected tapered cosine wavelet was selected to be used in the proposed algorithm. The proposed algorithm has been tested and compared with other methods that are commonly used in spectral matching; the RSPMatch method and the frequency domain method. The comparing parameters were the computational time, the average misfit, the maximum misfit and error, the PGA, PGV, PGD, the Arias Intensity and the frequency content for both acceleration and displacement time histories. The result showed that the proposed method is able to match the target while preserving the energy development and the frequency content of the original time histories. / Master of Science

The effect of coatings on the interfacial strength of a hollow glass microsphere/polyester composite and their capacity to endure thermal stresses were studied by mechanical testing and an active Acoustic Emission (AE) method. AE was postulated to provide more local information at or near the glass/polyester interface due to the sensitivity of elastic waves to the rigidity of polymer chains at the glass sphere/polyester interface compared to mechanical testing. Three frequency ranges identified by multivariate statistics yet consolidated for the initial analysis into a band of 140-240 kHz, were found to be changing with the different coated glass filler for different glass content and heating state. Considering the acoustic behavior of the composites containing different levels of glass sphere content (1-10 vol%), a lower concentration (aminoethylamino)-propyl-trimethoxy silane coated glass (AS6), demonstrated the lowest attenuation after heating (associated with higher interfacial strength). As anticipated, the highest attenuation after heating was observed for uncoated glass (16K) due to expectedly weaker associations. Mechanical testing results after heating were consistent with the AE response for AS6 and 16K for this frequency range. Trends in amplitude for the three narrower, frequency ranges of 130-160 kHz, 180-220 kHz and 230-260 kHz were compared against that of 140-240 kHz and very small differences were observed. It was found that the frequency range of 130-60 kHz was more descriptive of the changes of interfacial strength in composites (at 10 vol%), being consistent with the mechanical test results. Considering the AE response at 130-160 kHz and mechanical data, higher concentration (aminoethylamino)-propyl-trimethoxy silane (AS12), better endured thermal stresses compared to other coatings. A smaller trial looked at the effect of moisture aging and subsequent thermal cycling on the glass/polymer interface strength as another method to perturb the interface. Attenuation for the band of 180-260 kHz was studied for aged versus non-aged composites. The commercial coating, L21 demonstrated a better moisture resistance before and after thermal cycling compared to uncoated glass spheres. An improved evaluation of interfacial strength in glass/polyester was expected using AE technique versus mechanical testing due to its higher sensitivity to changes in internal structure, however; no significant improvement compared to mechanical testing was observed, at least based on the analysis technique currently being used. / Thesis / Master of Applied Science (MASc) / Sheet molded compound (SMC) is a polymer material reinforced by fibers providing a combination of light weight and high mechanical properties and is used in automotive industry. Light weight fillers (hollow glass microspheres) are used to obtain further weight reduction; however, addition of these fillers leads to reduced mechanical properties and further problems during painting process known as ‘paint popping’. The former is due to uncertain interfacial state between polymer and fillers and the latter results from different thermal expansion behavior of the polymer and filler materials while the material is exposed to high temperatures for painting process. This research aims to devise a highly sensitive technique and evaluate its suitability compared to mechanical testing for investigation of the origin of aforementioned problems. Acoustic Emission (AE) is a method with high sensitivity to changes in internal structure of the material which is postulated to provide a better insight on material microstructure compared to more commonly used method i.e. mechanical testing. Use of interfacial controlling agents was examined to reduce the problems as a result of introduction of fillers. The effect of using surface modified fillers and the effect of thermal stresses on material was investigated using AE technique. Application of AE method in this study provided a good insight about the changes in material internal structure; however, it did not demonstrate a significant improvement in detecting the origins of studied problems compared to mechanical testing at least based on the analysis technique used in this study.

Dans ce mémoire nous allons présenter une méthode de diffusion d’erreur originale qui peut reconstruire des images en demi-ton qui plaisent à l’œil. Cette méthode préserve des détails fins et des structures visuellement identifiables présentes dans l’image originale. Nous allons tout d’abord présenter et analyser quelques travaux précédents afin de montrer certains problèmes principaux du rendu en demi-ton, et nous allons expliquer pourquoi nous avons décidé d’utiliser un algorithme de diffusion d’erreur pour résoudre ces problèmes. Puis nous allons présenter la méthode proposée qui est conceptuellement simple et efficace. L’image originale est analysée, et son contenu fréquentiel est détecté. Les composantes principales du contenu fréquentiel (la fréquence, l’orientation et le contraste) sont utilisées comme des indices dans un tableau de recherche afin de modifier la méthode de diffusion d’erreur standard. Le tableau de recherche est établi dans un étape de pré-calcul et la modification est composée par la modulation de seuil et la variation des coefficients de diffusion. Ensuite le système en entier est calibré de façon à ce que ces images reconstruites soient visuellement proches d’images originales (des aplats d’intensité constante, des aplats contenant des ondes sinusoïdales avec des fréquences, des orientations et des constrastes différents). Finalement nous allons comparer et analyser des résultats obtenus par la méthode proposée et des travaux précédents, et démontrer que la méthode proposée est capable de reconstruire des images en demi-ton de haute qualité (qui préservent des structures) avec un traitement de temps très faible. / In this work we present an original error-diffusion method which produces visually pleasant halftone images while preserving fine details and visually identifiable structures present in original images. We first present and analyze the previous work to show the major problems in halftoning, and explain why we decided to use an error diffusion algorithm to solve the problems. Then we present our method which is conceptually simple and computationally efficient. The source image is analyzed, and its local frequency content is detected. The main components of the frequency content (main frequency, orientation, and contrast) serve as lookup table indices in a pre-computed database of modifications to a standard error diffusion. The modifications comprise threshold modulation and variation of error-diffusion coefficients. The whole system is calibrated in such a way that the produced halftone images are visually close to original images (patches of constant intensity, patches containing sinu- soidal waves of different frequencies/orientations/contrasts, as well as natural images of different origins). Finally, we compare and analyze the results obtained by our method and previous work, and show that our method can produre high-quality halftone image (which is struc- ture aware) within very short time.

Dans ce mémoire nous allons présenter une méthode de diffusion d’erreur originale qui peut reconstruire des images en demi-ton qui plaisent à l’œil. Cette méthode préserve des détails fins et des structures visuellement identifiables présentes dans l’image originale. Nous allons tout d’abord présenter et analyser quelques travaux précédents afin de montrer certains problèmes principaux du rendu en demi-ton, et nous allons expliquer pourquoi nous avons décidé d’utiliser un algorithme de diffusion d’erreur pour résoudre ces problèmes. Puis nous allons présenter la méthode proposée qui est conceptuellement simple et efficace. L’image originale est analysée, et son contenu fréquentiel est détecté. Les composantes principales du contenu fréquentiel (la fréquence, l’orientation et le contraste) sont utilisées comme des indices dans un tableau de recherche afin de modifier la méthode de diffusion d’erreur standard. Le tableau de recherche est établi dans un étape de pré-calcul et la modification est composée par la modulation de seuil et la variation des coefficients de diffusion. Ensuite le système en entier est calibré de façon à ce que ces images reconstruites soient visuellement proches d’images originales (des aplats d’intensité constante, des aplats contenant des ondes sinusoïdales avec des fréquences, des orientations et des constrastes différents). Finalement nous allons comparer et analyser des résultats obtenus par la méthode proposée et des travaux précédents, et démontrer que la méthode proposée est capable de reconstruire des images en demi-ton de haute qualité (qui préservent des structures) avec un traitement de temps très faible. / In this work we present an original error-diffusion method which produces visually pleasant halftone images while preserving fine details and visually identifiable structures present in original images. We first present and analyze the previous work to show the major problems in halftoning, and explain why we decided to use an error diffusion algorithm to solve the problems. Then we present our method which is conceptually simple and computationally efficient. The source image is analyzed, and its local frequency content is detected. The main components of the frequency content (main frequency, orientation, and contrast) serve as lookup table indices in a pre-computed database of modifications to a standard error diffusion. The modifications comprise threshold modulation and variation of error-diffusion coefficients. The whole system is calibrated in such a way that the produced halftone images are visually close to original images (patches of constant intensity, patches containing sinu- soidal waves of different frequencies/orientations/contrasts, as well as natural images of different origins). Finally, we compare and analyze the results obtained by our method and previous work, and show that our method can produre high-quality halftone image (which is struc- ture aware) within very short time.