https://repositorio.unifei.edu.br/jspui/handle/123456789/87 2026-09-21T19:34:59Z https://repositorio.unifei.edu.br/jspui/handle/123456789/3173 Aquisição e validação de sinal de ruído eletroquímico Corrosion is a global problem, which implies costs in industrialized countries of up to 4.5% of GDP, with either economic, but also social and environmental impacts. In the case of Brazil, the waste of water supply networks due to leaks loss is quite significant and much of it is caused by network degradation, indicating that corrosion control should be promoted whenever possible. This study proposes a corrosion monitoring system, in system subject to the use of inhibitor, with the approach of passive technique for monitoring corrosion by electrochemical noise (EN), in which the classification of events in a corrosion sensor by EN is part of methodological study for structural integrity (or “health”) monitoring system (SHM). Due to very dynamic and stochastic nature of the signal, this study and analysis of EN measurements (ENM) considers numerical and graphic characteristics of two corrosion systems both in saline aqueous solution: carbon steel and stainless steel. These experiments are repeated for accumulating data, which allow the generation of several graphs in time and frequency domains, from which at least one characteristic is extracted, which has a good correlation with data from corrosion processes. Then, based on a supervised machine learning system, the training data allows the model to be calibrated. From the test data, the correctness rate of the model above 50% is verified. Dissertação 2022-02-17T00:00:00Z https://repositorio.unifei.edu.br/jspui/handle/123456789/4471 Estudo numérico de vibrações induzidas por interferência de esteira e efeito de rugosidade no arranjo de dois cilindros alinhados A purely Lagrangian Discrete Vortex Method (DVM) with a roughness model is employed to numerically simulate the two-dimensional, incompressible, unsteady flow around two tandem circular cylinders of equal diameter immersed in an incident flow. The downstream cylinder is located in the wake interference region of the upstream one for streamwise center-to-center distance between two cylinders of L=5D (D is the cylinder diameter). The streamwise spacing ratio L/D=5 is greater than the critical spacing L/D=4, the latter characterizes the known bistable flow for two immovable cylinders, where two values of drag coefficient are identified for two different flow patterns; namely, reattachment-flow and jump-flow regimes for the downstream cylinder. In this work, the downstream cylinder is forced to vibrate transversely in the wake of another fixed tandem cylinder aiming to investigate a regime of Wake-Induced Vibration (WIV) at Re=6.5 x 104. The literature has reported that WIV is a phenomenon resulting from the interaction between the incoming wake and the downstream flexible structure, in which the downstream cylinder vibrates significantly over a wide range of reduced velocities and, additionally, the cross-flow fluid force is not in phase with the body’s motion. The non-dimensionalized vibration amplitude is fixed at A/D=0.15 and the reduced velocity is adopted as VR=5. The phenomenon of WIV appears combined with a resonant regime, in which the downstream cylinder vibrates at the resonant velocity similar to the Vortex-Induced Vibration (VIV) of a single cylinder. For the streamwise spacing ratio of L/D=5, the individual resonant regime is captured for both smooth surfaces. The main contribution of the present research is to show that the variation of downstream cylinder roughness desynchronizes the VIV and WIV regimes, and also promotes transition between them. Dissertação 2026-07-06T00:00:00Z https://repositorio.unifei.edu.br/jspui/handle/123456789/4469 Avaliação de parâmetros associados ao envelhecimento de para-raios submetidos a descargas de corrente Surge arresters are protective devices installed throughout power systems to limit overvoltages caused by lightning impulses, switching operations, and network faults. However, these devices are subject to degradation processes that may compromise their performance, lead to failure, and affect system reliability. In this context, it is essential to investigate the mechanisms associated with surge arrester aging and to identify the most sensitive parameters for monitoring their operational condition. For this purpose, an aging procedure based on current impulse stresses was applied to three groups of surge arresters from different manufacturers, each group consisting of three 15 kV samples. Throughout the aging process, the devices were evaluated through leakage current and partial discharge measurements. At the end of the aging procedure, microstructural analyses were performed on both new and aged samples to investigate the effects of degradation. The results indicated that leakage current-derived parameters exhibited the highest sensitivity for monitoring surge arrester aging, with dissipated power and third-order harmonics standing out as the most representative indicators. Partial discharge activity was detected only in a subset of the samples and during the final stages of the degradation process. Furthermore, samples exhibiting partial discharge activity also showed changes in the final leakage current measurements. Microstructural analyses confirmed the degradation evidence observed in the electrical tests. Therefore, it was concluded that the combined application of the employed techniques was effective for assessing the aging of distribution surge arresters, with leakage current-derived parameters emerging as the most promising indicators for monitoring the degradation of these devices. Dissertação 2026-06-29T00:00:00Z https://repositorio.unifei.edu.br/jspui/handle/123456789/4468 Electric motor fault detection under nonstationary operation using koopman operator spectral analysis. Accurate motor fault detection and flow rate estimation in industrial centrifugal pumps is essential for diagnostics, performance monitoring, and process optimization, yet traditional frequency-domain techniques such as Motor Current Signature Analysis (MCSA) often rely on fixed spectral bands and assume stationarity, making them less effective under variable-speed operation, changing loading conditions, and multiphase flow environments. This work introduces a Koopman-theoretic framework for motor fault and flow-rate classification based on Hankel-embedded Higher-Order Dynamic Mode Decomposition (HODMD), enabling extraction of physically interpretable spectral-dynamical features from multichannel current, voltage, and vibration measurements. The proposed pipeline computes Koopman eigenvalues, modal energies, growth rates, temporal coherence, and spectral entropy to construct a compact descriptor of pump electromechanical behaviour, which is subsequently evaluated through supervised and unsupervised learning pipelines incorporating SMOTE balancing, nonlinear UMAP projection, and extensive hyperparameter optimization via TPESearchCV. Using 2 laboratory datasets, the first consisting of 106 signals describing 4 motor faulty operation states with different input frequencies, its results were as high as 96.8% cross validation accuracy and 80.7% balanced test accuracy. The second dataset consists of 1304 signals spanning multiple rotational speeds, heterogeneous fluid compositions, and 11 unbalanced flow-rate range classes, the system achieves up to 97.8% cross-validation balanced accuracy and up to 92.6% balanced test accuracy while revealing coherent manifold structure aligned with physical flow-rate regimes. Although overlapping operating states and speed-dependent spectral shifts introduce classification challenges, the results demonstrate that Koopman spectral feature captures the essential dynamic structure of the pump more effectively than traditional Fourier-based approaches, highlighting their potential for robust, reliable, and generalizable monitoring and diagnostics of industrial pumping systems. Dissertação 2026-07-08T00:00:00Z