Pierre-Olivier Mattei

Enhancing the dynamic range of targeted energy transfer in acoustics using several nonlinear membrane absorbers

Abstract In order to enhance the robustness and the energy range of efficiency of targeted energy transfer (TET) phenomena in acoustics, we discuss in this paper about the use of multiple nonlinear membrane absorbers (called nonlinear energy sinks or NES) placed in parallel. We show this way, mainly thanks to an experimental set-up with two membranes, that the different absorbers have additional effects that extend the efficiency and the possibilities of observation of TET. More precisely, we present the different behavior of the system under sinusoidal forcing and free oscillations, characterizing the phenomena for all input energies. The frequency responses are also presented, showing successive clipping of the original resonance peak of the system, and strongly modulated regimes (SMR). A model is finally used to generalize these results to more than two NES and to simulate the case of several very similar membranes in parallel which shows how to extend the existence zone of TET.

Experimental study of the influence of low frequency flow modulation on the whistling behavior of a corrugated pipe

It is well known that airflow in a corrugated pipe can excite whistling at the frequencies of the pipes longitudinal acoustic modes. This short contribution reports on the results of experiments where a low frequency, oscillating flow with velocity magnitudes of the same order as the airflow has been added. Depending on the oscillation strength, it has been found that this flow may silence the pipe or move the whistling to higher harmonics. It is also shown that the low frequency oscillation itself may excite higher frequency whistling sounds in the pipe.

Synthesis of Noise of Operating Vehicles: Development within SILENCE of a Tool with Listening Features

The European Integrated project SILENCE is dedicated to the reduction of railway and road noise in urban areas. Within this context, SNCF and LMA collaborate in the sub-project B in order to develop a pass-by sound simulation software. This global modelling tool will support parametric studies on the reduction of the noise of a train or a car pass-by, by providing standard indicators (time signature, sound pressure level) and sound samples. It will be used to determine the best combination of optimised sources, developed by manufacturers, in order to reduce the global pass-by noise. In the software, each simulation is based upon the definition of the acoustic sources and the pass-by scenario. Each physical acoustic source on the vehicle is represented by one or several point sources. These point sources radiate either pure tones or broadband noise. A dedicated algorithm is used to simulate each type in an efficient way to reduce the computation time. The characteristics of the sources are obtained either from numerical models, or from standstill and pass-by antenna measurements (carried out in the SILENCE project). As a large source such as a cooling system can not be modelled by several point sources located at close positions, a radiation pattern is allocated to the point source. Dedicated studies are in progress to measure the radiation pattern of classical sources on a train (two series of measurements on a 1:14 scale-model and on a train).

Experimental Study of Energy Pumping in Acoustics

This paper presents an experimental vibro-acoustic set-up that aims to reproduce the energy pumping phenomenon between an acoustic medium and an essentially nonlinear oscillator. It shows a one-way irreversible transfer of energy between the first acoustic mode in a tube and a thin visco-elastic membrane. Various observed aspects of energy pumping are presented: behaviors under sinusoidal forcing, pumping threshold, resonance capture and transient response.Copyright

Vibration control with a bistale nonlinear absorber

The goal of our research is to develop a nonlinear absorber that will be effective at low frequencies and low amplitudes of vibration, notably in the domain of vibroacoustics. From this perspective, the usual Nonlinear Energy Sinks (NESs) based on the idea of the internal resonance have certain limitations due to the relatively high activation threshold. In order to decrease this threshold we developed the idea of a bistable absorber. The bistability provides a chaotic regime in the absorber dynamics that leads to effective dissipation by the NES. While this energy transfer is completely different from the well-known energy pumping, the two types share the main features such as the activation threshold and the functioning region. The bistable NES that we propose consists of a clamped-clamped buckled beam and an attached mass. The experimental and numerical tests performed for our particular realization of a bistable absorber have shown its high efficiency and robustness.The goal of our research is to develop a nonlinear absorber that will be effective at low frequencies and low amplitudes of vibration, notably in the domain of vibroacoustics. From this perspective, the usual Nonlinear Energy Sinks (NESs) based on the idea of the internal resonance have certain limitations due to the relatively high activation threshold. In order to decrease this threshold we developed the idea of a bistable absorber. The bistability provides a chaotic regime in the absorber dynamics that leads to effective dissipation by the NES. While this energy transfer is completely different from the well-known energy pumping, the two types share the main features such as the activation threshold and the functioning region. The bistable NES that we propose consists of a clamped-clamped buckled beam and an attached mass. The experimental and numerical tests performed for our particular realization of a bistable absorber have shown its high efficiency and robustness.

Controlling the Acoustic Resonance in a Corrugated Flow Pipe

A new experimental study, aimed at investigating the coupling between the flow in a corrugated pipe, the acoustically generated flow oscillations, and the emitted resulting noise is carried out. Hot-wire anemometry, Particle Image Velocimetry, and microphone measurements are associated to characterize the flow. The flow response to the corrugation is shown to fit to the sixth to ninth acoustic modes of the pipe according to the flow rate. When low frequency acoustically generated oscillations interfere with this, one checks that they either significantly reduce the noise level or modify the peak frequencies. In addition, theoretical/numerical works are also performed, in order to provide an analytical framework describing the acoustical properties of such corrugated pipe flows.

Acoustic radiation of wind instruments resonators

Optimization of the acoustic radiation of wind instruments resonators may be based on the study of finite length circular ducts radiating in unbounded medium, as this is a model realistic enough, but which allows advanced analytics developments. Our approach is based on the calculation of resonance frequencies of such a simplified wind instrument. These are the complex frequency singularities of the operator describing the global resonator/external fluid system. A Newtons method is used to search for the singularities of the multimodal Greens function of the duct. This is obtained by the product of impedance matrices which relate pressure and velocity between two abscissae inside the duct. A variable coupling factor is introduced with external acoustic radiation, described by a multimodal radiation impedance based on the Zorumski formulation. Examples of variation of the resonance frequencies with this coupling factor will be given. Surprisingly, regular variations of the coupling lead to non regular ev...

Energy pumping in acoustics

Energy pumping corresponds to a particular vibratory regime of a non‐linear system coupled to a linear primary structure. Its non‐linear behaviour allows to reduce vibrations of the primary structure, and is thus a new passive vibration control technique. This phenomenon has mainly been studied in mechanical engineering, so we transposed its principle to noise control in an acoustic medium. The presentation will focus on results about acoustic energy pumping that we observed both experimentally and numerically, in the time and frequency domains. These results highlight two main points: physically, energy pumping corresponds to an irreversible transfer of energy from the primary system to the non‐linear absorber, and practically, its effects are a noise level limitation in the acoustic medium in permanent regime and a much faster sound extinction in transient regime.

Sound transmission through a thin baffled plate: Comparison of a light fluid approximation with the numerical solution of the exact equations and with experimental results

A thin elastic rectangular plate, with clamped boundaries, extended by an infinite perfectly rigid plane baffle is considered. Both half‐spaces are occupied by a gas. A sound source is located on one side of the plate. One is interested by the sound field transmitted through the plate. The boundary value problem governing the system is solved by two methods: A boundary element method, which gives a numerical solution of the exact equations; and a series representation of the solution in terms of the fluid‐loaded plate resonance modes, an analytical approximation which is obtained by a perturbation technique (the ratio of the gas density to the surface mass of the plate being the small parameter). The discrepency between the two methods does exceed 1 dB or so: This shows that the perturbation method, which is much less time consuming than the BEM, is a very powerful prediction tool. The Laboratoire de Mecanique et d’Acoustique in Marseille has two anechoic rooms, which are connected by an aperture. A steel...