https://repositorio.unifei.edu.br/jspui/handle/123456789/87 2026-10-02T14:09:57Z 2026-10-02T14:09:57Z https://repositorio.unifei.edu.br/jspui/handle/123456789/3173 2024-02-05T10:36:02Z 2022-02-17T00:00:00Z

Título: Aquisição e validação de sinal de ruído eletroquímico Abstract: 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. Tipo: Dissertação

2022-02-17T00:00:00Z https://repositorio.unifei.edu.br/jspui/handle/123456789/4474 2026-10-01T19:06:40Z 2026-07-10T00:00:00Z

Título: Study on multi-modal dynamic vibration absorbers applied to helicopters Abstract: Vibration control is a critical challenge in helicopter engineering, where high-amplitude structural vibrations accelerate component wear and fatigue while degrading crew performance and comfort. Conventional Dynamic Vibration Absorbers (DVA) are widely used in helicopters, as an evolution of the DVA, there is the Multi-Modal Vibration Absorber (MMDVA), which can suppress several rotor harmonics simultaneously with a single device. This study implements a finite element method (FEM) based design methodology for MMDVAs tailored to the main and tail rotor frequencies of a Brazilian Navy Lynx helicopter, utilizing carbon fiber leaf springs integrated with steel inertial masses. Experimental vibration analysis using flight test accelerometer data informed target frequency selection, revealing that while the dominant excitation frequencies are governed by main rotor and tail rotor harmonics, their relative amplitude distribution varies significantly between pilot and co-pilot locations and across flight conditions. From this analysis, four target frequencies were selected for each MMDVA to attenuate. A two-stage optimization routine based on a genetic algorithm was implemented: the first stage aligns the isolated natural frequencies of the MMDVAs with the target frequencies using modal analysis, and the second stage refines its geometry through coupled harmonic analysis to account for damping and interaction with the host structure. Two candidate geometries were proposed, taking advantage of multiple vibration mode shapes like flexion and torsion. The first geometry comprises two mass blocks, each contributing with two vibration modes, generating two antiresonances per block. The second geometry comprises three mass blocks, whose combined motion contributes to four vibration modes of the structure, generating four antiresonances. By generating multiple antiresonances with a single device, the proposed MMDVAs achieve broader vibration suppression than conventional single-mode absorbers, making more efficient use of absorber weight compared to adding multiple independent devices to the structure. Tipo: Dissertação

2026-07-10T00:00:00Z https://repositorio.unifei.edu.br/jspui/handle/123456789/4472 2026-09-29T19:42:45Z 2026-07-01T00:00:00Z

Título: Design, optimization, and real-time structural health monitoring using embedded 3d-printed piezoresistive sensors in composite structures Abstract: Structural Health Monitoring (SHM) is an essential strategy for ensuring the safety and longevity of critical infrastructure and advanced composite structures. While embedded sensors offer a transformative approach to real-time monitoring by enabling in-situ damage detection, their widespread adoption is hindered by challenges at the sensor-material interface, unoptimized geometric designs, and a critical lack of system-level validation in complex load-bearing components. This thesis presents a comprehensive ”Experiment- Model-Optimize-Validate” framework for the development, optimization, and system-level integration of additively manufactured piezoresistive strain sensors. Through a systematic review of the state-of-the-art, the predominance of carbon-based piezoresistive sensors manufactured via Fused Deposition Modeling (FDM) was established, alongside the critical need to balance sensor sensitivity with the mechanical integrity of the host structure. To address this inherent trade-off, a rigorous computational and experimental methodology was developed. A Design of Experiments (DoE) evaluated the influence of geometric parameters (trace width, inter-trace distance, thickness, and end-loops) on sensor performance. Utilizing Gaussian Process Regression (GPR) and a Multi-Objective Particle Swarm Optimization (MOPSO) algorithm, optimal geometries were identified. Experimental validation demonstrated that fully embedded configurations achieved exceptional piezoresistive sensitivity (Gauge Factor ≈ 59), while a geometrically scaled variant successfully restored the host structure’s stiffness to near-native levels (≈ 2.18 GPa) without significant loss of sensitivity. To bridge the gap between laboratory-scale coupon testing and field-ready deployment, the optimized sensing architectures were integrated into a geometrically complex aerospace pylon structure using multi-material FDM. Sensor placement was strategically guided by Finite Element Analysis (FEA) to target critical strain hotspots, and a redundant sensing network was implemented to ensure fault tolerance. System-level testing, validated by full-field Digital Image Correlation (DIC), proved that the embedded sensors exhibited high-fidelity temporal synchronization with mechanical deformation, capturing transient structural events with negligible viscoelastic lag. Furthermore, the redundant architecture successfully maintained monitoring capabilities and diagnosed asymmetrical loading anomalies. Ultimately, this research provides a highly scalable and robust methodology for transitioning 3D-printed embedded sensors from isolated component optimization to integrated, self-sensing structural systems, advancing the technological readiness of real-time SHM in aerospace and civil engineering applications. Tipo: Dissertação

2026-07-01T00:00:00Z https://repositorio.unifei.edu.br/jspui/handle/123456789/4471 2026-09-10T13:03:25Z 2026-07-06T00:00:00Z

Título: Estudo numérico de vibrações induzidas por interferência de esteira e efeito de rugosidade no arranjo de dois cilindros alinhados Abstract: 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. Tipo: Dissertação

2026-07-06T00:00:00Z