Forward acoustic scattering of an immersed solid LINE (cylinder bounded by hemispherical endcaps) in water is investigated in our study. The object is made of stainless steel and its L/2a ratio is equal to 2 (L: Length of the cylinder part and a: the radius is equal to 60 mm). An impulse measurement method is used in the experimentation. Most of results are obtained experimentally, in bistatic configuration. Mobile receiver transducer is located in a distinct position from the emitter. The polar diagram patterns of the scattered pressure shows an important amplitude of pressure in the shadow side of this object. Analysis of this phenomenon is based on theoretical and experimental results obtained for a sphere with the help of elasticity theory. Moreover, this study relies on the grey-level representation of the angular position of the receiver in function of recorded time signals. Thus on forward acoustic time signals, it is possible to identify echoes due to propagation paths of waves on this object.

The vibroacoustic behavior of structures excited by random pressure fields such as turbulent boundary layers or diffuse sound fields is of great interest for industrial applications. Many works have been carried out for periodically stiffened plates. In particular, the influence of Bloch-Floquet waves on the panel radiation has been highlighted. However, few studies have investigated more complex structures under random excitations. The present work studies the influence of internal structures on the vibro-acoustic behavior of submerged cylindrical shells. The geometric complexity is successively increased by including periodic, non-periodic stiffeners and various internal frames. The numerical prediction is based on the combination of two methods developed by the authors. The first one is the wavenumber-point (k,M) reciprocity technique. This method estimates the response of the system at point M from the shell velocity in the wavenumber space under a point excitation at M. The velocity field is estimated with the second method, called the Condensed Transfer Function method. It is a substructuring approach which couples a semi-analytical model of a submerged cylindrical shell with Finite Element models of axisymmetric and non-axisymmetric frames. Numerical results are analyzed to evaluate the influence of the stiffeners and the internal structures on the shell radiation.

L’etude du rayonnement acoustique des coques cylindriques raidies a fait l’objet de nombreux travaux car elles sont d’un grand interet pour les industriels des secteurs naval et aeronautique. Cependant peu d’attention a ete portee aux effets lies a la presence de structures fixees rigidement a l’interieur de la coque, telles que des planchers, des carlingages ou des supports de machines. Recemment, une methode de sous-structuration par fonctions de transfert condensee a ete developpee afin de coupler un modele de coque raidie avec des structures internes non-axisymetriques modelisees par la methode des elements finis. Ces travaux ont montre sur differents cas d’application numeriques que la non-axisymetrie pouvait modifier significativement le comportement vibro-acoustique de la coque excitee par un effort mecanique et conduire a une augmentation de l’efficacite de rayonnement de la coque raidie. Le but de la presente etude est de verifier ces tendances experimentalement par des mesures en laboratoire sur une maquette. Le cylindre raidi est suspendu verticalement et est excite par un pot vibrant. La pression rayonnee est evaluee a partir de mesures en chambre anechoique, avec et sans structure interne. Des cartographies du champ vibratoire de la coque sont egalement etablies a partir de mesures au vibrometre laser. L’analyse de celles-ci dans l’espace des nombres d’onde permet d’apprehender les mecanismes de rayonnement acoustique sous la frequence critique de la coque cylindrique.