Sound field separation with sound pressure and particle velocity measurements

International audienceIn conventional near-field acoustic holography (NAH) it is not possible to distinguish between sound from the two sides of the array, thus, it is a requirement that all the sources are confined to only one side and radiate into a free field. When this requirement cannot be fulfilled, sound field separation techniques make it possible to distinguish between outgoing and incoming waves from the two sides, and thus NAH can be applied. In this paper, a separation method based on the measurement of the particle velocity in two layers and another method based on the measurement of the pressure and the velocity in a single layer are proposed. The two methods use an equivalent source formulation with separate transfer matrices for the outgoing and incoming waves, so that the sound from the two sides of the array can be modeled independently. A weighting scheme is proposed to account for the distance between the equivalent sources and measurement surfaces and for the difference in magnitude between pressure and velocity. Experimental and numerical studies have been conducted to examine the methods. The double layer velocity method seems to be more robust to noise and flanking sound than the combined pressure-velocity method, although it requires an additional measurement surface. On the whole, the separation methods can be useful when the disturbance of the incoming field is significant. Otherwise the direct reconstruction is more accurate and straightforward

Modèle monocouche équivalent de plaque multicouche orthotrope

La caractérisation de matériaux complexes comme les multicouches a déjà fait preuve de nombreux travaux. Différentes approches existent, et en particulier, celles basées sur la recherche d'une plaque équivalente homogène (Equivalent Single Layer Model). Ces dernières comparent le multicouche à une plaque mince dont les paramètres simulent le comportement dynamique du multicouche à une fréquence donnée. La caractérisation du multicouche se fait donc par l'obtention de ces paramètres « équivalents ». En particulier, le modèle développé par J.L. Guyader [Internoise 2007] est de type plaque mince, se limitant à la caractérisation d'un multicouche isotrope, indépendant du nombre de couche et permettant d'obtenir comme paramètres équivalents, un module d'Young et un amortissement dynamique. A une fréquence donnée, la plaque équivalente présente le même nombre d'onde naturel que le multicouche. En reprenant une méthodologie similaire, nous proposons d'étendre le modèle de Guyader au cas des multicouches orthotropes, par le calcul des différentes rigidités de flexion D1, D2, D3 et D4 solutions de l'équation de dispersion de la plaque mince équivalente orthotrope. Cette méthode permet d'obtenir une représentation des caractéristiques du multicouche sur le plan d'onde kx ? ky. Des comparaisons expérimentales (vibrométrie laser) / analytiques seront présentées entre 2 et 8 kHz pour différents cas d'orthotropie sur des plaques en fibre de carbone afin d'illustrer les performances de la méthode

Direct formulation of the supersonic acoustic intensity in space domain

International audienceThis paper proposes and examines a direct formulation in space domain of the so-called supersonic acoustic intensity. This quantity differs from the usual (active) intensity by excluding the circulating energy in the near-field of the source, providing a map of the acoustic energy that is radiated into the far field. To date, its calculation has been formulated in the wave number domain, filtering out the evanescent waves outside the radiation circle and reconstructing the acoustic field with only the propagating waves. In this study, the supersonic intensity is calculated directly in space domain by means of a two-dimensional convolution between the acoustic field and a spatial filter mask that corresponds to the space domain representation of the radiation circle. Therefore, the acoustic field that propagates effectively to the far field is calculated via direct filtering in space domain. This paper presents the theory, as well as a numerical example to illustrate some fundamental principles. An experimental study on planar radiators was conducted to verify the validity of the technique. The experimental results are presented, and serve to illustrate the usefulness of the analysis, its strengths and limitations

Multi-harmonic phase demodulation method for instantaneous angular speed estimation using harmonic weighting

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Assessment of the airborne sound insulation from mobility vibration measurements; a hybrid experimental numerical approach

A new measurement procedure is proposed to assess the airborne sound insulation of a partition under diffuse sound field excitation using mobility measurements combined with a numerical procedure. The advantage of this hybrid approach is that the diffuse acoustic field does not need to be physically created, thus avoiding problems related to the generation of such fields at low frequencies. Furthermore, the acoustic properties of both the source and receiving rooms will not affect the determination of the sound reduction index R. The proposed method is especially suited for frequencies below the so called Schroeder frequency of the room, and is complementary to the standardized measurement approaches as described in ISO 10140-2:2010. The measurement part of the proposed procedure involves the measurement of the mobility by forcing the partition along a grid of excitation points (e.g. by means of a shaker) and measuring its response along a grid of response points (e.g. by means of a scanning laser Doppler vibrometer). Using the resulting matrix of mobility transfer functions, the vibrational response of the partition excited by a diffuse acoustic field is numerically calculated, from which the radiated sound power is computed using the Rayleigh integral. Thus the reliance on source and receiving rooms used in standard sound insulation testing is removed entirely. The proposed method provides an estimate that only depends on the properties of the partition. The method was tested in an acoustic laboratory on a single layer glass plate of 1.35 x 1.54 m2, as well as on a funicular shell structure with dimensions of 3 x 3 m2. Comparisons with analytical models and standardized ISO10140-2:2010 measurements confirm the validity of the results.status: publishe

Key research challenges to supporting farm transitions to agroecology in advanced economies. A review

International audienceIn response to the sustainability issues that agriculture faces in advanced economies, agroecology has gained increasing relevance in scientific, political, and social debates. This has promoted discussion about transitions to agroecology, which represents a significant advancement. Accordingly, it has become a growing field of research. We reviewed the literature on and in support of farm transitions to agroecology in advanced economies in order to identify key research challenges and suggest innovative research paths. Our findings can be summarized as follows: (1) Research that supports exploration and definition of desired futures, whether based on future-oriented modeling or expert-based foresight approaches, should more explicitly include the farm level. It should stimulate the creativity and design ability of farmers and other stakeholders, and also address issues of representation and power among them. (2) Research that creates awareness and assesses farms before, during or after transition requires more holistic and dynamic assessment frameworks. These frameworks need to be more flexible to adapt to the diversity of global and local challenges. Their assessment should explicitly include uncertainty due to the feedback loops and emergent properties of transitions. (3) Research that analyzes and supports farms during transition should focus more on the dynamics of change processes by valuing what happens on the farms. Research should especially give more credence to on-farm experiments conducted by farmers and develop new tools and methods (e.g., for strategic monitoring) to support these transitions. This is the first review of scientific studies of farm transitions to agroecology. Overall, the review indicates that these transitions challenge the system boundaries, temporal horizons, and sustainability dimensions that agricultural researchers usually consider. In this context, farm transitions to agroecology require changes in the current organization and funding of research in order to encourage longer term and more adaptive configurations. Keywords Transformation • Sustainable agriculture • Farm • Coupled innovations • Assessment • Design • Foresight Contents Lorène Prost and Guillaume Martin contributed equally

Key research challenges to supporting farm transitions to agroecology in advanced economies. A review

International audienceIn response to the sustainability issues that agriculture faces in advanced economies, agroecology has gained increasing relevance in scientific, political, and social debates. This has promoted discussion about transitions to agroecology, which represents a significant advancement. Accordingly, it has become a growing field of research. We reviewed the literature on and in support of farm transitions to agroecology in advanced economies in order to identify key research challenges and suggest innovative research paths. Our findings can be summarized as follows: (1) Research that supports exploration and definition of desired futures, whether based on future-oriented modeling or expert-based foresight approaches, should more explicitly include the farm level. It should stimulate the creativity and design ability of farmers and other stakeholders, and also address issues of representation and power among them. (2) Research that creates awareness and assesses farms before, during or after transition requires more holistic and dynamic assessment frameworks. These frameworks need to be more flexible to adapt to the diversity of global and local challenges. Their assessment should explicitly include uncertainty due to the feedback loops and emergent properties of transitions. (3) Research that analyzes and supports farms during transition should focus more on the dynamics of change processes by valuing what happens on the farms. Research should especially give more credence to on-farm experiments conducted by farmers and develop new tools and methods (e.g., for strategic monitoring) to support these transitions. This is the first review of scientific studies of farm transitions to agroecology. Overall, the review indicates that these transitions challenge the system boundaries, temporal horizons, and sustainability dimensions that agricultural researchers usually consider. In this context, farm transitions to agroecology require changes in the current organization and funding of research in order to encourage longer term and more adaptive configurations. Keywords Transformation • Sustainable agriculture • Farm • Coupled innovations • Assessment • Design • Foresight Contents Lorène Prost and Guillaume Martin contributed equally