In this paper, an analytical model of the air-conducted sound propagation in an earplug equipped with a film filter is proposed to explain and predict its acoustic attenuation. The model is developed using the transfer matrix (TM) method under the plane wave assumption, with the elastic film modeled as a prestressed circular plate based on the Kirchhoff-Love theory. This film is coupled with multiple interconnected air cavities to form the TM model of the earplug. The validity and limitations of the model are assessed through comparisons with numerical simulations using the finite element (FE) method. The predicted resonant frequencies deviate by less than 2% within the audible frequency band. The TM model is therefore considered useful to conduct parametric studies in order to provide a physical understanding of the predicted sound attenuation of film filters, as well as their optimization. The influence of the film parameters, such as mass, surface tension, and cavity geometrical parameters on the earplugs' sound attenuation is analyzed both qualitatively and quantitatively, with a focus on amplitude and characteristic frequencies.

Centrifugal double pendulum vibration absorbers (CDPVAs) can be used to reduce torsional vibrations of rotating machines. These passive devices are made of several double pendulums oscillating relatively to a rotor. This study extends former works on CDPVAs by accounting for the rotational inertia of the pendulums and providing detailed linear and nonlinear analyses of CDPVA dynamics. First, the eigenmodes are computed and an efficient design procedure based on the linear response is proposed. Then, the nonlinear behaviour is assessed using an analytical perturbation method. Of particular interest is the nonlinear antiresonance detuning of the double pendulums, which strongly influences vibration reduction. Moreover, CDPVAs are subjected to nonlinear energy localisation. This causes the double pendulums to oscillate differently, thus affecting the proper operation of the system. The analytical results led to new design guidelines that minimise the antiresonance detuning while avoiding instabilities leading to localised responses. These results are validated through a comparison with a numerical resolution of the system's dynamics. They are then visualised in the design space to help identify easily the optimal CDPVA designs.

Rotating machines are often subjected to fluctuating torques, which causes rotor vibrations, early wear and noise pollution. These vibrations can be reduced using centrifugal pendulum vibration absorbers (CPVAs), which are passive devices made of several bodies (pendulums) oscillating along a given path and rotating relatively to a rotor. Previous studies showed that the dynamics of these devices is subjected to instabilities leading to a localisation of the motion of the pendulums. In this paper, the localised behaviour of a CPVA made of two pendulums allowed to rotate about their centre of mass is investigated. To this aim, a dynamical model based on an analytic perturbation method is established. The aim of this model is to highlight some special features of the localised response, such as the appearance of quasi -periodic regimes. The case studies showed that in some special cases, localisation can improve the filtering efficiency as compared to a unison motion. The validity of the model was confirmed through a comparison with numerical resolutions of the system's dynamics.

Centrifugal double pendulum vibration absorbers (CDPVAs) can be used to reduce torsional vibrations of rotating machines. These passive devices are made of several double pendulums oscillating relatively to a rotor. In this work, an original CDPVA architecture made of cylindrical-shape pendulums is proposed. Measurements on a CDPVA made of six double pendulums are performed around the first rotor antiresonance. To the authors' knowledge, this is the first observation of an antiresonance of the rotor and the first comparison of an analytical CDPVA model with experimental results. The first rotor antiresonance is observed where expected and its nonlinear detuning as the forcing amplitude increases is well predicted by the model. Discrepancies between the experimental and analytical results are also observed, mostly regarding the rotor's amplitude after the antiresonance. These are likely due to the slipping of the pendulums and a limitation of the test-bed used for the experiments.

When developing a flying robot on the insect scale, all process must be developed from scratch as usual macroscale solutions for the design and fabrication would not satisfy the extreme mass and power limitations. In this context, the aims of this work are to outline the proposed bioinspired approach and to present the different original concepts deployed to tackle such an issue, before analyzing carefully the simulated and experimental results. More precisely, the presented nano air vehicle is inspired from the diptera order and consists of two pairs of wings micromachined using MicroElectroMechanical Systems technologies and an electromagnetic actuator added to the thorax to control the kinematics of the wings. The prototypes weigh as little as 22 mg with a 25 mm wingspan and 15 mm length and demonstrate a lift force equivalent to their weight.

Centrifugal pendulum vibration absorbers (CPVAs) are often used by the automotive industry to reduce vibrations of the drivetrain. These passive devices consist of several masses oscillating along a given path relative to a rotor. Recent CPVA systems make use of rocking pendulums, meaning that the pendulums rotate about their centre of mass during their motion along their path. In this work, measurements on a new CPVA architecture made of ball-type rocking pendulums are performed in classical and subharmonic operations. To the authors' knowledge, they lead to the first comparisons between experimental and analytical results regarding the nonlinear detuning of the rotor's antiresonance and the saturation of the rotor's response. It is also the first time this saturation phenomenon is observed experimentally. The CPVA investigated is shown to have a high filtering efficiency but its pendulums are subjected to slipping, which limits the operating range of the system. Experimental and analytical investigations of the slipping are carried-out to estimate the limit of adherence of the system.

The automotive industry uses centrifugal pendulum vibration absorbers (CPVAs) to reduce vibrations of the transmission system. These passive devices are made of several masses oscillating along a given path relative to a rotor. This work addresses a recent design of CPVA, in which the pendulums are allowed to rotate relatively to the rotor. The dynamic stability of this CPVA and the shifting of its operating point are investigated in this paper. These two aspects, crucial for an optimal vibration reduction, are assessed using an analytic dynamical model based on a perturbation method. The results obtained allow to propose new design guidelines. The validity of the model is confirmed through a comparison with a numerical resolution of the system's dynamics.

One way to face the needs for water quality measurement at large scale, all over the world, is obviously through satellite remote sensing applications. From the first satellites up to now, the progress in sensors technology has highly improved the quality of remote data. The applications for sea and natural water quality are numerous and particularly adapted for large countries such as China or Africa. The parameters measured by remote sensors (mainly turbidity, chlorophyll-, and colored dissolved organic matter), the principle of which being often based on optical techniques, are relevant for water quality monitoring. However, ground monitoring is always necessary for the measurement of other parameters and for calibration of the models. The knowledge of water quality parameters at a local scale is an essential complement to monitoring network or spatial observation particularly for high-frequency (time interval) or high-resolution (space interval) measurements.

Closed-form formulations are difficult to find when the material behavior law is nonlinear. A linear approximation, on the other hand, has a very narrow range of validity. In this communication, the normal form (NF) method is used to solve a 1-D nonlinear magnetodynamic problem. The discrete model is formulated in a state-space form suitable for NF applications. The resulting system is then expanded on a linear mode basis to cubic order. Analytical solutions are obtained using the NF technique and compared with traditional solutions. The results show that the cubic polynomial adequately approximates the problem, and the NF solution is valid for some range of magnetic field intensity.

A rapid bibliographical overview shows that the last decade has given rise to numerous scientific and technical works dealing on water quality (WQ) monitoring. During this period, many methods were developed, from complementary ones to standard procedures for improving WQ monitoring. Complementary approaches (online, in situ, remote) aim at giving more rapid and simple ways for WQ data acquisition. They can allow novel solutions to address temporal and spatial variations and lack of WQ data when monitoring is difficult to carry out in poor countries, for example. Finally, this chapter highlights the importance of considering optical characteristics of waters and soils and thus optical methods for WQ measurement.

Summary . The aim of this contribution is to review and compare three different methods that have been proposed in order to derive reduced-order models for geometrically nonlinear structures

This paper proposes a new system-level application for monitoring out-of-step (OOS) events in power systems. As already known, amplitude-dependent frequency shift is a nonlinear phenomenon of electromechanical oscillations under large disturbances. The frequency shift indicates the system's nearness to instability. This new tool utilizes the Normal Form method to identify the named phenomenon, leading to accelerated OOS detection. The proposed strategy is illustrated and compared to the equal-area criterion method in a single-machine-infinite-bus power system. Extensive tests on IEEE 3- and IEEE 50-machine power systems prove the efficacy and potential of the proposed method for online warnings of instability and ranking of vulnerable system modes.