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Présenté par Jean-François Minster RésuméCette note présente les résultats technologiques et les premières mesures issus du développement d'une méthode de reconnaissance sismique marine haute résolution 3D à destination de la communauté scientifique. Une attention particulière a été portée à la réalisation d'un système opérationnel en adéquation avec les objectifs visés en termes de mise en oeuvre et de traitement. Le dispositif a été transféré durant l'année 2003 dans le parc d'équipements communs. Pour citer cet article : Y.

In musical instrument making and restoration domains, the variability of the materials and the irreversibility of the changes are issues for the experimental study of the impact of design changes and restorations on musical instruments. In addition, the analytical methods based on simplified geometries and models are not sufficiently detailed for the study of complex structures and phenomena. The virtual prototyping, and its different capabilities, can be a powerful method for instrument makers and museum curators as a decision support tool. Nevertheless, the accuracy of the model is an important matter to assess good predictions. In the case of antique and unique instruments, it is sometimes hard to obtain exhaustive geometrical properties. Similarly, it is also difficult to evaluate the material properties of full instruments, and this uncertainty may have a strong impact on the output features of the numerical models. In this study, a numerical model of cello is developed using finite element method. It is used to evaluate the impact of a modification of a geometrical property on dynamical features. It is shown that the lack of knowledge on the arching height of the top and back plates of a cello has a strong impact on the computed dynamical properties of the cello. Secondly, the model is considered with and without repair wedges and defects like galleries excavated by wood-boring insects. It is observed that the bridge admittance exhibits discrepancies above 220 Hz which is in the low frequencies domain of the model and quantify the impact of repairs. This model capability is a starting point for further simulations accounting for material and geometrical uncertainties and to assess the confidence level of a model for restoration issues.

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In this study, the acoustic dissipation is investigated experimentally in wooden pipes of different species commonly used in woodwind instrument making: maple (Acer Pseudoplatanus), pear wood (Pyrus Communis L.), boxwood (Buxus Sempervirens) and African Blackwood (Dalbergia Melanoxylon). The pipes are parallel to the grain, except one which forms an angle of 60° with the fiber direction. An experimental method, involving input impedance measurements with several lengths of air column, is introduced to estimate the characteristic impedance and the attenuation factor in the pipes. Their comparison reveals significant differences of acoustic dissipation among the species considered. The attenuation factors are ranked in the following order from largest to smallest: maple, boxwood, pear wood, and African Blackwood. This order is the same before and after polishing the bore, which is an essential step in the making process of wind instrument. For maple, changing the pipe direction of 60° considerably increases the attenuation factor, compared to those of the other pipes, parallel to the grain. Further, polishing tends to reduce the acoustic dissipation in the wooden pipes, especially for the most porous species. As a result, the influence of polishing in the making procedure depends on the selected wood species.