Acoustic liners are an essential part of noise reduction technologies commonly applied in aircraft turbofan engines. Fan noise suppression can be achieved by selecting an appropriate liner design with optimal acoustic impedance at the blade passing frequency. Great efforts have been made not only to improve experimental characterization and numerical methods for acoustic liners, but also to understand noise generation mechanisms, which ultimately impacts on the liner design itself. To gain confidence in the liner design process, a liner barrel was developed and fabricated for the Fan Noise Test Rig located at the University of São Paulo. To this end, analytical methods were used to determine the optimal acoustic impedance for the Fan Noise Test Rig, and a flat test sample was fabricated for experimental characterization with flow using both in-situ and impedance eduction techniques at the Federal University of Santa Catarina. A liner barrel of same nominal geometry was fabricated and placed at the Fan Noise Test Rig, and a modal decomposition indicated that the Tyler-Sofrin mode has been successfully suppressed at the first blade passing frequency. Numerical predictions of liner transmission loss considering the flat sample impedance showed good agreement with experimental results.
Compilado e revisita de descobertas da pesquisa de mesmo nome, este artigo se divide em três pilares: no primeiro, é realizado um exercício livremente inspirado na arqueologia de interface, com foco na customização na história da computação. Investigamos como as opções de customização se consolidam em sistemas operacionais desktop para Macintosh. O segundo pilar é dedicado à definição e exploração da figura do hacker, seu surgimento, atuação, grupos, ética e classes. Por fim, exploramos as técnicas do jailbreak, na qual hackers aplicam técnicas e ferramentas que buscam modificar a estrutura do sistema operacional iOS e as customizações de interface desbloqueadas por essa prática.
The interest in modeling and prototyping the so-called Vibration Energy Harvesters (VEHs) has increased significantly in the last decades, given the growing demand for energy sources that can capture energy from the vibration of a machine, for example, to power small sensors and vibration monitoring devices. In this work, the design and optimization of a commercial Electromagnetic Vibration Energy Harvester (EMVEH) are presented. Such a device contains in its interior a resonant-type electromagnetic transducer, the latter composed basically by a seismic mass, a mechanical spring and a multi-turn coil. The complete set weighs about 90 g and occupies a total volume of approximately 50.97 cm3, being able to generate up 45mW at its resonance frequency of 60 Hz, with a bandwidth of 2.5 Hz. Furthermore, the linear generator presented in this paper reaches a maximum Normalized Power Density (NPD) of 1.8018mW/(cm3g2) at an acceleration amplitude of 0.7 g (∼ 6.67m/s2). To proceed with electromechanical modeling and further optimization, a numerical model was developed via commercial software COMSOL Multiphysics, from which it was possible to optimize its geometry in order to maximize its NPD and power output. A Surrogate optimization algorithm was then implemented in MATLAB, in which both volume and mechanical stress were considered as project constraints.
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