In this paper, the implementation, characterization, calibration, and testing of a biaxial optical fiber accelerometer for vibration monitoring in three-phase induction motors is presented. The optical sensor uses fiber Bragg gratings to measure the displacement of an inertial mass relatively to a support base. The sensor characterization was measured through the impact hammer, allowing the determination of the natural frequencies in both sensitive directions, the values of 747.5 Hz and 757.5 Hz were estimated for the x-axis and the y-axis, respectively. For calibration, an electromagnetic exciter was used to introduce a controlled harmonic excitation at different frequencies, with this analysis, a high SNR was observed, on average over 30 dB for both sensitive directions, and a sensitivity of 100 pm × g ^-1 was obtained, up to one third of the natural frequency, in each direction. The tests were developed with the main aim of the analysis in induction motors based in vibration monitoring, the analysis can help to prevent wear in motors, increasing its efficiency, and lowering maintenance costs. The optical accelerometer measurements were compared with the ones from a capacitive sensor, during regular operation and with a broken rotor bar operating with 75% and 100% load. The performed tests with the optical sensor allowed to successfully analyze the frequency components, and its changes, for the regular and damage operation.

The mechanical behavior of viscoelastic materials is influenced, among other factors, by parameters like time and temperature. The present paper proposes a methodology for a thermorheologically and piezorheologically simple characterization of viscoelastic materials in the time domain based on experimental data using Prony Series and a mixed optimization technique based on Genetic Algorithms and Nonlinear Programming. The text discusses the influence of pressure and temperature on the mechanical behavior of those materials. The results are compared to experimental data in order to validate the methodology. The final results are very promising and the methodology proves to be effective in the identification of viscoelastic materials.

So-called vibration absorbers, which might more appropriately be called vibration neutralizers, are mechanical devices designed to be attached to another mechanical system, or structure, called the primary system, for the purpose of controlling, or reducing, the vibration (and consequent sound production) of machines, structural surfaces and panels. The cheapest and easiest way to construct a vibration absorber is by incorporating a viscoelastic material, functioning as both the resilient and the energy dissipating component. The viscoelastic material acts as a damped spring. This article sets out to describe how to design an optimal system of viscoelastic absorbers for a known material, through a model using four fractional parameters. A real example, of the design of a system of six viscoelastic vibration absorbers for mitigation of the response to fluid-structure instability in a hydroelectric generator system, is presented and discussed.

This paper presents a new methodology for measuring vibration and temperature using fiber Bragg grating (FBG) sensors embedded in carbon fiber polymer attached directly on the iron core of a power transformer. The device has a quick-coupling clip design and is fabricated from a carbon fiber reinforced composite (CFRP) for robustness and flexibility. Temperature and vibration FBG sensors are embedded in the carbon fiber clip, which is easily and quickly coupled directly to the transformer iron core. In the low frequency ranges, from 0 to 500 Hz, vibrations are mainly generated in the core. Rigidity is controlled by clip thickness and geometry, since the system is designed to have a wide operating frequency range. The embedded strain FBG sensor sensitivity has been improved due to its spring-shaped design static and dynamic simulations applying the Finite Element Method (FEM) were performed to determine the optimal dimensions and structure of the part. The clip’s frequency response function (FRF) was assessed and tested by using three techniques: FEM harmonic analysis, mechanical impact testing, and optical FBG sensing. The results demonstrate a 3.94 % differential among the methods. A comparison was made of the power transformer’s FRF when fitted with a glued free FBG sensor and an embedded FBG sensor. In both cases, the transformer was subjected to varying electrical load conditions (no-load, linear, and nonlinear load). The results showed a 19 % average sensitivity improvement when the embedded sensor was compared to the free sensor.