https://ri.ufs.br/jspui/handle/riufs/2150 2026-08-30T18:06:56Z https://ri.ufs.br/jspui/handle/riufs/25888 Título: Modelagem por equivalente elétrico para dispositivos a onda acústica de superfície Autor(es): Nogueira, Paulo Gabriel Barreto Abstract: Surface Acoustic Wave (SAW) devices find extensive application in telecommunications as delay lines and highly selective filters, and they also operate as high-sensitivity sensors. This versatility arises from their ability to convert electrical signals into acoustic waves through interdigital transducers and from the strong interaction between these waves and physical or chemical perturbations in the propagation medium. Engineers typically characterize these devices using vector network analyzers, which restrict field applications and complicate integration with systems and wireless sensor networks. These limitations motivate the implementation of approaches based on open- and closed-loop electronic oscillators. However, the development of such systems faces constraints related to the acquisition of SAW devices and to their direct use in circuit simulators. As a result, researchers employ equivalent electrical models, particularly those based on resonator crystals. An extensive literature review reveals that currently available models, although simple and physically implementable, diverge in their representation of the electrical coupling between SAW ports. This aspect plays a critical role in the performance and stability of closed-loop oscillators, especially under uncontrolled environmental conditions. In this context, this work proposes the development of an equivalent electrical circuit model for SAW devices based on a resonator crystal with adjustable parameters. The proposed model more accurately represents the coupling between ports and supports applications in the calibration of SAW-based systems, integration with electronic oscillators, and laboratory testing. This approach reduces dependence on real devices and increases the feasibility of field measurements. The study derives the model from an adapted resonator crystal representation and incorporates dedicated blocks to adjust input and output impedances as well as transmission magnitude. 2026-03-06T00:00:00Z https://ri.ufs.br/jspui/handle/riufs/25886 Título: Características de fluidização de misturas binárias contendo casca residual de mandioca e areia Autor(es): Rocha, Raquel Estevez Abstract: The better management of natural resources has become a global agenda and in recent years there is a global trend towards an increase in the use of renewable energy sources. In this context, the conversion of biomass into energy has grown in importance, in order to replace the demand for fossil fuels, as well as to diversify energy sources. Cassava (Manihot esculenta Crantz) is one of the most prominent temporary crops in Brazil, with more than 18.1 million tons produced in 2021. All this productivity generates waste that most often does not have proper disposal. Among solid residues, the cassava peel represents a valuable source of biomass for the production of bioenergy due to its lignocellulosic characteristics. Fluidized bed technology appears as a potential alternative, both for drying as biomass pre-treatment, in order to reduce its high moisture content, and for thermochemical conversion processes. This technology, by promoting an intense mixing between the particles and the fluid, intensifies the rates of heat and mass transfer, and of conversion. To assist in the fluidization of different biomasses, inert particles have been commonly used. Therefore, given the scarcity of information in the literature on the application of the fluidized bed technique for the processing of residual cassava husk, the objective of this work was to investigate the fluid dynamic behavior of single components and binary mixtures containing biomass particles from cassava peel and sand particles in fluidized bed. The fluid dynamic tests were carried out in a typical fluidized bed with air at room temperature, binary mixtures of 1.29 mm biomass with sand of 1.29 mm and 0.93 mm, following a 33 factorial design, in order to evaluate the effects of the bed aspect ratio L/D (1, 1.5 and 2), of the volumetric fraction (25%, 50% and 75%) and of the moisture content of the biomass (10%, 42.5% and 75% b.u.), in addition to influence of the inert particle diameter on the fluidization parameters. Pressure drop and velocity data were measured using an U-tube differential manometer and an anemometer, respectively. The results for the binary mixtures showed that the bed aspect ratio influenced the behavior of the incipient and complete fluidization velocities. The moisture of the particles significantly affected all velocities, including the minimum fluidization, mainly as the volumetric proportion of biomass and the bed aspect ratio increased. The proportion of biomass affected moist and dried biomass in different ways and the velocities generally increased for the larger diameter inert. The slugging phenomenon seen for pure biomass beds did not occur with the binary mixtures, indicating an improvement in the fluidization quality of the mixture with the use of sand as inert, in line with the angle of repose data obtained. Based on the fluid dynamic analysis carried out, the most suitable operating conditions to obtain greater fluidization quality and stability, both for drying the wet cassava peel (75% b.u.) and for the thermochemical conversion processes of the dehydrated biomass (10% b.u.), were those using the binary mixture with the sand having the smallest particle diameter (0.93 mm), with 75% volumetric fraction of biomass and L/D ratio of 1.5. For perspectives of studies resulting from this line of research, there is the definition of the optimal operating conditions to increase the thermal efficiency of a fluidized bed dryer, having as reference the fluid dynamic data determined here, in addition to the application of cassava peel and quartz sand in a fluidized bed reactor. 2023-02-28T00:00:00Z https://ri.ufs.br/jspui/handle/riufs/25868 Título: Representação e classificação de perfis térmicos de isoladores poliméricos para diagnóstico de poluição superficial Autor(es): Oliveira, Johnny Herbert Paixão de Abstract: Monitoring insulators in electric power systems is essential for reducing the risk of failures associated with surface pollution. In coastal environments, salt deposition and the presence of moisture can intensify surface leakage current and cause localized heating capable of leading the equipment to failure and causing interruptions in the power supply. In this context, infrared thermography is a promising non-invasive technique because it enables the thermal condition of the equipment to be assessed without direct contact or interruption of operation. This dissertation proposes a methodology for classifying the thermal profiles of polymeric insulators, aiming to distinguish between clean and polluted conditions. To this end, one-dimensional thermal profiles are extracted from thermograms, corrected relative to the ambient temperature, segmented into successive windows, and described using features related to thermal level, temperature dispersion, including variance and standard deviation, contrast, distribution shape, including skewness and kurtosis, spatial variation, and spatial dependence. Three forms of representing the information along the profile are evaluated: aggregated, sequential, and symbolic. The aggregated representation summarizes the features obtained from the windows, whereas the sequential and symbolic representations explicitly preserve the spatial order of these windows. For classification, a support vector machine, a random forest, a long short-term memory recurrent neural network, a hidden Markov model with Gaussian mixtures, and a discrete hidden Markov model are evaluated. The dataset comprises 344 thermal profiles distributed across 69 acquisition groups and includes clean insulators as well as insulators subjected to artificial and natural pollution. Feature selection, model tuning, and the initial performance estimation are conducted through nested validation with separation by acquisition groups, thereby preventing samples originating from the same acquisition from being distributed between the training and test sets. The results indicate that all evaluated models are capable of distinguishing between clean and polluted profiles. Subsequently, a robustness analysis is conducted in which the best models for each representation are evaluated over different repetitions of the training–test split, while keeping fixed the selected features, hyperparameters, and structures defined during nested validation. In this analysis, the support vector machine applied to the aggregated representation achieves the best performance, with a balanced x accuracy of 0.923 ± 0.058 and a multicriteria metric of 0.897 ± 0.067. It is concluded that the spatial segmentation of the thermal profile provides relevant information for identifying surface pollution and constitutes a promising approach for the diagnosis of polymeric insulators. 2026-08-05T00:00:00Z https://ri.ufs.br/jspui/handle/riufs/25866 Título: Impacto da evolução do curto-circuito na estabilidade angular do gerador síncrono em sistemas com alta penetração de fontes renováveis Autor(es): Batista, Hugo Carneiro Mute Abstract: Among the various contingencies that affect rotor angle stability in Electric Power Systems, fault evolution stands out due to its potential to compromise secure system operation, leading to generator loss of synchronism, cascading outages, and reduced power supply reliability. Despite its operational significance, this phenomenon remains scarcely addressed in the scientific literature. Furthermore, the increasing penetration of converter-based renewable energy sources has reduced system inertia, making the stability of conventional synchronous generators progressively more vulnerable to disturbances. In this context, investigating the impacts of fault evolution on rotor angle stability is essential to provide a more realistic assessment of power system security and to support the development of strategies that enhance the reliability of modern electric power systems. In this context, this master’s thesis presents studies on the impact of short circuit evolution on the rotor angle stability of a synchronous generator installed in the adapted IEEE 34 bus distribution system with the integration of wind turbines and photovoltaic plants. To this end, the ETAP® software — Electrical Transient Analyzer Program — was used to simulate the IEEE system under short-circuit conditions that evolve spatially. The case studies show that increasing the penetration of renewable power plants reduces the Critical Clearing Time (CCT) and, consequently, indicates, for the analyzed system, a maximum penetration level of 60% relative to the system’s synchronous generation capacity to maintain stability. Additionally, the results demonstrate that short-circuit evolution acts as a limiting factor for rotor angle stability, reducing, for the analyzed system, the allowable penetration level from 60% to 20% in order to preserve the synchronism of the synchronous generator under evolving fault conditions. The transient stability of the system under three-phase faults applied in the vicinity of the synchronous generator was also evaluated, using the CCT as the performance metric. The results demonstrated that increasing the penetration of inverter based renewable energy sources progressively reduces the angular stability margins, as evidenced by the decrease in the CCT values observed across the different scenarios analyzed 2026-07-27T00:00:00Z